- Full Control Networks
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1.2. Figure A3 6 Three jumper method optical loss measurement The difference between the refer ence power level and the loss test power level is the power loss in the link under test and the differ ence in the power losses between the reference connection CR1 and connection C1 and between the reference connection CR2 and C2 The actual loss in connections C1 and C2 is not included in the link loss test result NETWORK VISION The IEC 147363 3 document specifies the following formula to calculate the pass or fail outcome of this loss test Link Loss Loss in segment under test Loss C1 CR1 Loss C2 CR2 A3 1 If the loss in CR1 and CR2 were zero this formula would yield the desired results Link Loss Loss in segment under test Loss in C1 Loss in C2 The standard also defines the allowable loss limits for test connectors which we refer to as reference connectors in this document see Table A3 1 Test limit for connectors mated Reference connector limit with a reference connector Singlemode 0 2 dB 0 5 dB Table A3 1 Definition of maximum insertion loss of connections with reference connectors as specified in IEC 14763 3 When we insert the values in table A3 1 for multimode into formula A3 1 above we obtain Link Loss Loss in segment under test 0 3 0 1 0 3 0 1 or Link Loss Loss in segment under test 0 4 In conclusion the stan
3. NETWORK VISION Troubleshooting Instruments Troubleshooting Certification Check for fiber end face Clean contamination contamination or damage Find faults Basic Tier 1 Extended Tier 2 Appendix 2 Test Reference Methods We reviewed the theory of the link loss test for optical fiber links in Process and Equip ment Requirements under the Cabling Certification section of Chapter 3 Testing Theory Performance of Optical Fiber Cabling The loss measurement of an installed optical fiber link is derived from two power measurements The test reference measurement establish es the no loss power level against which the test tool compares the power through the link under test The difference between these two power levels yields the loss of the link under test We have pointed out that it is critically important that the loss measurement is executed with the same source and light launch conditions as used in the reference measurement Many standards recommend the one jumper test reference measurement for premises wiring cabling Relatively short lengths and multiple connections characterize enterprise cabling systems within a building or campus Access or long haul optical fiber links may only have one connector at either end of the link which can be hundreds of times longer than the longer enterprise cabling links It is ve
4. RANGE Auto AVERAGING TIME Auto PULSE WIDTH 1310nm Auto PULSE WIDTH 1550nm Auto Highlight Item Press ENTER Figure 27 4 Set up the OTDR for testing a Choose the fiber type to be tested and or characteristics from setup menu b Set a pass fail limit of 0 3 dB for connectors and 0 1dB for splices c Choose Dual Wavelength Testing from OTDR setup menu d Set launch fiber compensation to simplify your testing by setting the end of your launch fiber as the starting point zero feet meters on the trace e Check to make sure that pulsewidths averaging time distance range are set to Automatic Mode f Set loss threshold to 0 01dB and choose Dual Wavelength Testing 5 Run Channelmap to make sure that the link looks like what you believe you are plugged into OFTM 5612 08 01 2006 2 46 11 p m ChannelMap FIBER LENGTH 207 m End 1 End 2 DATA CENTER BLDG 2 105m Ll a If you cannot see past the end of your launch fiber the problem is that the connec Figure 27a tor is not fully seated in the back of the patch panel b You should see all connectors and cabling segments that you expected to see If not you have a break or an unplugged cable 6 An advanced feature on the OptiFiber OTDR is Faultmap Figure 27b Faultmap uses the event analyzer to determine the quality of each connection without any user setup or programming If Faultma
5. the physical cabling for a transmission Mbps megabits per second OLTS Optical Loss Test Set a baseline Tier 1 certification instrument that measures the loss of a link over its length LSPM Light Source Power Meter basic fiber verification instrument composed of a power meter and a source to measure loss over a link TRC Test Reference Cord a high quality fiber cord between 1 to 3 meters long with high performance connectors ideally with end faces with special scratch resistant hardened surfaces that enable numerous insertions without degradation in loss performance VCSEL Vertical Cavity Surface Emitting Laser commonly used in multimode light sources Verification testing the process of testing the transmission performance of an installed cabling system to ensure that it meets a minimum threshold VFL Visual Fault Locator optical source that transmits a low powered laser to identify breaks in fiber links FLUKI i E networks Appendix 1 Fluke Networks Fiber Test and Verification Verify loss over Check entire link to Check polarity ensure loss budget not exceeded connectivity Specialized Z Fiber D Cleaning PD Supplies l VisiFault VFL FindFiber Remote ID SimpliFiber Pro Optical Loss Mf VA VA Test Kit CertiFiber OLTS FiberInspector Video Microscope DTX Series with Fiber Module DTX Compact OTDR OptiFiber OTDR
6. Schematic representation of setting the reference with duplex TRCs for a link under test ending with LC connectors The ring near the red boot indicates the location of the mandrel for multimode fiber Step C Step D After the tester measures the reference power level it displays these values as shown in Figure 18f If your reference values are acceptable press the F2 soft key to store these values and to proceed with link certification i Acceptable reference with DTX MFM or DTX MFM2 1 20dBm nominal level with LED 62 5 um 2 22 dBm nominal level with LED 50 um ii Acceptable reference with DTX GFM DTX SFM DTX GFM2 or DTX SFM2 1 7dBm nominal level with VCSEL or laser Now disconnect your TRCs at the Input ports only and create the connection that is shown on the screen Figure 18g Disconnect the black boots from the input ports and connect the unused ends with the black boots in the duplex cord set to the adapter on the input port of the unit to which the duplex mate has been con nected Now you have separated the main and remote units so that you can connect a unit at each end of the optical fiber link to be tested Remote End Setup Smart Remote 850 nm 1300nm Input dBm 19 16 19 51 Output dBm 18 54 18 92 Test Method Method B Reference set 05 08 2009 4 48 03 p m Figure 18f Remote End Setup Smart Remote Figure 18g If you need to test a link for which Fluke Networks does
7. 6 less than the critical angle O it travels into the water but changes direction at the boundary between air and water refraction When a light beam strikes the water surface at an angle greater than the critical angle the light reflects on the water surface Each material is characterized by an index of refraction which is represented by the symbol n This index also called refractive index is the ratio of the velocity of light in vacuum c to its velocity in a specific medium v n c v The refractive index in vacuum outer space is 1 v c The refractive index for air n is 1 003 or slightly higher than that of a vacuum while the refractive index for water is 1 333 A higher value of the refractive index n of a material indicates that the light travels slower in that material Light travels faster through the air than in water A Angle of incidence B Critical Angle C Total Reflection 0 lt 0 0 gt 0 Q critical critical EN Figure 2 Principle of total reflection The core of an optical fiber has a higher refractive index than the cladding The light that strikes the boundary between the core and the cladding at an incident angle greater than the critical angle reflects and continues to travel within the core This principle of total reflection is the basis for the operation of optical fiber The critical angle is a function of the refractive index of the two media in this case the glass in the core and the glass
8. Enter and connect the TRCs between main and remote as shown on the screen and press test to make the reference measurement Twisted Pair Coax Fiber Loss Fiber OTDR Network Settings Instrument Settings a Highlight item Y Press ENTER Figure 18a Twisted Pair Coax Fiber Loss Fiber OTDR Network Settings Instrument Settings a Highlight item Y Press ENTER Figure 18b Set Reference View Delete Results Move Copy Internal Results Tone Generator Memory Status Battery Status Self Test Update Software Version Information a Highlight item Y Press ENTER Figure 18c The earlier discussion on setting the reference showed the preferred one jumper method Figure 13 and Figure 14 which is called Method B in the test instrument Note that with the DTX Series in Smart Remote setup we are going to test the Remote End Setup Smart Remote two fibers that make up the transmission link in B i z Connect patch one test Each fiber test module is equipped with cords as shown a light source and light meter In the setup we will use two duplex TRCs One fiber will connect the Output light source at the main unit to Press TEST the Input light meter at the remote unit The second connects the Output at the remote unit to the input at the main unit Figure 18d Special Note The DTX TRCs use the following convention in order to quickly make connections and verify the pol
9. allow the fiber ordering arrangement to be maintained relative to the plug s keying features should be selected Cabling Certification Select the performance standard The standards define a minimum test procedure consisting of 1 Measurement and evaluation of the link loss using an optical loss test set OLTS some standards refer to this test tool as a light source and power meter LSPM OLTS and LSPM tend to be used interchangeably In this document we will choose the terminology OLTS for certification test tools that automatically measure the length of the link under test whereas we will use the term LSPM to designate test sets that do not measure the link length and therefore may require some manual calculations to interpret the measured values The light source is connected to one end of the fiber under test while the power meter is connected at the other end 2 Measurement and evaluation of the link length The length must be known to calculate the loss test limit for many installation standards the maximum loss to be contrib uted by the optical fiber in the link loss limit value The length also plays an important role to certify the link for a specific network ap plication As shown in Table 3 the maximum length of a fiber channel for a given network application depends on the fiber type and bandwidth rating of the fiber NETWORK VISION 3 Verification of link polarity Steps 1 through 3 constitu
10. application of the fiber optics technology NETWORK VISION 2 An Overview of the Principles of Transmission over Optical Fiber Construction Optical fiber cable consists of extremely thin strands of ultra pure glass designed to trans mit light signals Figure 1 depicts the construction of the buffered glass strand that is the basic component in many optical fiber cable constructions The center of the fiber strand is called the core The core actually contains the light signals to be transmitted A glass layer called the cladding surrounds the core The cladding confines the light in the core The outer region of the optical fiber is the coating or buffer The buffer typically a plastic material provides protection and preserves the strength of the glass fiber Core Cladding Coating or Buffer Figure 1 Cross section of an optical fiber A common outer diameter for the cladding is 125 micron um or 0 125 mm The diameter of the core for optical fiber cable commonly used in premises infrastructures is either 62 5 50 or 9 um The larger 62 5 and 50 um diameter defines multimode fiber types singlemode fiber has the smaller diameter with a nominal value of 9 um Reflection and refraction The operation of optical fiber is based on the principle of total internal reflection Figure 2 illustrates this principle when light travels from air into water When light arrives at the water surface at an incident angle
11. connection between the light source and the TRC in any way 2 Connect the light source and TRC at one end of the link under test connector C1 3 Connect a second TRC Added TRC between the other end of the link under test C2 and the power meter This second TRC should exhibit the same quality as the first one used to set the reference It too must be inspected to ensure that both end connections are clean 4 Make a power measurement while the light source transmits the light through the link under test to the power meter 5 The power meter measures the light energy through the link under test and produces a result in dBm Assume that the power measurement through the link under test is 23 4 dBm and the reference power level is 20 dBm By subtracting these two measurement readings we find the loss caused in the link under test In this example the loss is 20 23 4 or 3 4 dB Note that a loss is expressed in dB in contrast with absolute power measurements expressed in dBm An OLTS automatically calculates the difference in power levels the loss of the link under test in dB and compares the result to the limit for the link under test If the measured loss is less than or equal to the limit the test passes Test kr Added reference i TRC cord Figure 14 Connection of Light Source and Power Meter for an optical loss measurement Link segment under test __ _ gt Different methods
12. cross connect is exhibiting excessive Loss 130 m 7m 80 m Sample OTDR trace with high loss connector at 137m NETWORK VISION Event analysis software The latest OTDRs run sophisticated software that automate trace analysis and enable automatic test set up parameters Fluke Networks OTDRs can automatically choose setup parameters not only telling you where events instances of reflectance and loss are on the trace but also telling you what the events are while qualifying each of them Dead zone This is the shortest fiber length an OTDR can detect It can also be de scribed as the distance after a reflective event after which another reflection can be detected All OTDRs have dead zones and should be used with an appropriate launch fiber so that you can measure the first connection on the link Dynamic range Determines the length of fiber that can be tested The higher the dynamic range the longer the fiber under test can be There is a drawback however as the dynamic range increases the wider the OTDR pulse becomes and as a result the deadzone increases Ghosts Not as scary as they might seem ghosting is caused by an echo due to highly reflective events in the link under test Fluke Networks OTDRs identify ghosts on the trace and tell you where the source of the ghost is so that you can eliminate it Gainers Another misunderstood phenomenon on an OTDR trace is called a gainer Simply put a gainer is an apparent
13. in the cladding The refractive index for the core typically is around 1 47 while the refractive index for the cladding is approximately 1 45 Because of this principle we can describe an imaginary cone with an angle a which is related to the critical angle see Figure 3 If the light is launched into the fiber end from within this cone it is subject to total reflection and travels in the core The notion of this cone is related to the term numerical aperture the light gathering ability of the fiber Light launched into the fiber end outside of this cone will refract into the cladding when it meets the core cladding boundary it does not stay within the core Core index of refraction n1 1 47 Cladding index of refraction n2 1 45 Figure 3 Numerical aperture and total reflection Light that enters the fiber within an angle a travels in the core Signaling Local area networks like Ethernet and Fibre Channel transmit pulses that represent digital information The bit short for binary digit is the basic unit of digital information This unit can only take one of two values 0 or 1 Numeric data is transformed into a digital number Other data such as characters are coded in a string of bits An On or an Off NETWORK VISION state electronically represents the value of a bit Similarly a serial string of light pulses represents the digital information transmitted over an optical fiber link The On state repre
14. launch condition Recall that the higher order modes modes traveling through the outer range of the core refract out of the core when the fiber is bent The five well defined wraps control the modes that will enter the link under test to measure the loss The TRC connected to the light source must be attached to the mandrel as shown in Figure 16 and remain attached for all testing Place top wrap in groove under 47 retainer Wrap 5 times in grooves Right no bends at retainer Wrong bends at retainer ET Figure 16 How to wrap the optical fiber test reference cord correctly around a mandrel The mandrel also improves the accuracy of the measurements by establishing a realistic test reference value When we examine the setup in Figure 13 the overfilled launch condi tion excites the highest order modes in the TRC and may also launch some light into the cladding of the TRC The higher order modes in the core and the light in the cladding will not travel very far but may travel the short distance of the TRC if the TRC is not subjected to any bends The wide angle input to the power meter captures the light energy in the cladding This light will however not survive in the link under test unless it would be a very short and straight fiber run Without a mandrel the power meter measures light ener gy during the reference setting that will not travel through the link under test The power level establ
15. negative loss at an event where there is a change in the optical performance This is usually due to a mismatch between the index of refrac tion of two spliced fibers or connection of a 50um multimode fiber into a 62 5um fiber This type of event will often exhibit excessive loss in the other direction Patch panel Receive fiber if used OTDR Certification Set up Setting up for OTDR Certification Testing Setup Turn the rotary switch to Setup and choose Settings from menus in five setup screens 1 First select which port you want to test from multimode or singlemode what test limit you want to use the fiber type and desired wavelength e It is possible to create multiple sets of OTDR test limits and select one for a particular job Each OTDR test passes Figure 21 or fails Figure 22 based on a comparison against the selected set of test limits 2 On the second setup screen you may then set launch fiber compensation designate which end you are testing from and notate what you want to call each end of the fiber Using Launch Fiber Compensation LFC Launch fiber compensation is used to simplify testing HBL LIMIT Ses eee tac Multimode 50 and remove the launch and receive fibers losses and Dual 850 1300 nm lengths from measurements End 1 DATA CENTER e It shows you where your launch and or receive z F eid A Length 55 9 M fiber is on the trace and eliminates it from the ed 0 19 dB certifi
16. result data Test cords should make polarity easy for you Fluke Networks cords feature red boots on the end at which light enters and black boots on the end at which light exits Cords should be kept clean and replaced when they show signs of wear Choose test limits that are appropriate to both generic cabling standards and application standards NETWORKS RVISION 8 How to Troubleshoot Common Faults with an OTDR OTDRs are the most powerful troubleshooting tool for fiber optic cabling Smart use of an OTDR can eliminate time consuming trial and error troubleshooting Benefits of troubleshooting with an OTDR include e Single ended testing no need place test equipment at both ends of a fiber optic link making it easier for one technician to efficiently troubleshoot e Precise location of faults OTDRs can see the location of breaks too tight bends dirty connectors e Qualification of known events such connectors and splices with their locations infer their associated loss and reflectance Finding faults with an OTDR 1 Make sure that opto electronics are not live on fiber links 2 Turn the OTDR on and plug a good quality clean launch fiber at least 100m into OTDR port 3 Plug the launch fiber into one end of the channel don t forget to clean the end face before connecting to tester SETUP TEST LIMIT General Fiber WAVELENGTH Dual 1310 1550 nm LAUNCH COMPENSATION Enabled _OTDR PLOT GRID Disabled
17. to use requiring manual calculations and subjective interpretation by an experienced technician However newer instruments have eliminated time consuming loss calculations by automating the process of comparing power measurements versus set references Figure 17 Conducting an LSPM test While convenient basic verification of end to end loss using an LSPM set does not specify where the trouble areas are making failures difficult to locate Even in instances where the loss is within a specified threshold the LSPM set does not provide any warning or indication of where a defect or problem may be located In other words although an entire link may pass it is possible that individual splices or connections within it may fail industry specifications creating a potential problem in the future during adds moves or changes where multiple dirty connectors can potentially be grouped together to result in a failure An OTDR is the proper test tool to pinpoint locations connections displaying a high loss or reflectance 5 How to Certify Fiber Optic Cabling with OLTS and LSPM Industry standards require testing with an LSPM or OLTS to certify that the loss of each link meets performance standards As mentioned previously this is referred to as basic or Tier 1 Certification It is a double ended test which produces an absolute loss measurement which is then compared with installation cabling standards and or channel application s
18. we discussed above Bandwidth can be defined and measured in a variety of ways The three standardized bandwidth specifications and applicable measurements are Overfilled Bandwidth Restricted Modal Bandwidth and Laser Bandwidth or Effective Modal Bandwidth EMB The reason for these different methods stems from the differences in the characteristics of the light sources used to transmit information The traditional light source for 10 Mbps and 100 Mbps Ethernet has been the Light Emit ting Diode LED an excellent option for applications operating up to speeds of 622 Mbps LEDs produce a uniform light output that fills the entire core of the optical fiber and excites all of its modes To best predict the bandwidth of conventional multimode fibers when used with LED light sources the industry uses a method called Overfilled Bandwidth OFL As mentioned above LEDs cannot be modulated fast enough to transmit the one billion or more pulses per second required for Gbps data rates A common light source to support the gigabit transmission speeds in premises network applications is the VCSEL Vertical Cavity Surface Emitting Laser at 850 um wavelength Unlike an LED the light output of a VCSEL is not uniform It changes from VCSEL to VCSEL across the end face of the optical fiber As a result lasers do not excite all the modes in multimode fiber but rather a restricted set of modes And what may be more important each laser fills a different set
19. 2 PASS a y Endface Image End2 PASS meets generic cabling standards or eaaa an ent i nw sann Module OFTM 5612 system designer s requirements Qualifies workmanship for cabling installation Identifies problems for immediate ChannelMap troubleshooting with OTDR Da Te 4200200 cc EP ME bris Fiber Length 152 m i e Secondly perform basic tier 1 test for BATACENTER pennen QUAD a 100m 2m 50m the channel against the application eons Project EVERETT UNIVERSITY standard Certifies channel length and ACME EVT UN loss and calculates margin based on Figure 25 Sample LinkWare Results Management the standard Software printout e If bidirectional testing is not required measure channel loss at the wavelength of the application NETWORKSUPERVISION 7 Common Faults Insufficient power or signal disturbances result ing from common faults cause failures in optical transmission Fiber optic connections involve the transmis sion of light from one fiber core into another Fiber cores are smaller than the diameter of a human hair To minimize loss of signal power this requires good mating of two fiber end Figure 26 Example of a common cause of a fiber failure faces e Contaminated fiber connections Leading cause of fiber failures results from poor connector hygiene Dust fingerprints and other oily contamination cause excessive loss and permanent damage to connector end faces e Too many conne
20. I a a networks NETWORKSUPERVISION Optical Fiber Cabling for Data Communication Test and Troubleshooting Handbook NETWORK VISION Table of Contents 1 INTODUCHON sivsssesesscescossstecscccdsccscsvesseosscesieevesaveisesesoascdeesssesesvessesieansiassosasys 2 2 An Overview of the Principles of Transmission over Optical Fiber 3 CONStUCHON ioc rec easter onda shadamdeadeaeuienere EEE CEEE ET ks 3 Reflection and refraction 0 c eee eedt EEEa EEEE E EE 3 S Signding sura 4 e Requirements for reliable transmission 0 0 00 0c cee eee e eee ee 5 3 Testing Theory Performance of Optical Fiber Cabling 12 e Industry performance standards 0 c eee c eect eee e es 12 Cabling certifications eirate ais anes seas eWeek Pan tap emnte a Fences 16 4 Fiber Verification Testing 0 unaenea rererere nents 25 5 How to Certify Fiber Optic Cabling with OLTS and LSPM 26 6 How to Certify Fiber Optic Cabling with an OTDR 32 e Cable certification test strategy 0 cece cee cette teen eee 36 72 gt Common Faults seersant pokoendedsreaeedasaeacaeeararsaaededs 37 8 How to Troubleshoot Common Faults with an OTDR 39 e Finding faults with an OTDR 2 eee cence nce eee ees 39 9 End Face Inspection and Cleaning 00 cece eee eens 44 InSpech
21. ON includes the requirement of documentation of the test results this documentation provides the information that demonstrates the acceptability of the cabling system or support of specific networking technologies The link attenuation allowance calculation Link Attenuation Allowance dB Cable Attenuation Allowance dB Connector Insertion Loss Allowance dB Splice Insertion Loss Allowance dB Where Cable Attenuation Allowance dB Maximum Cable Attenuation Coefficient dB km x Length km Connector Insertion Loss Allowance dB Number of Connector Pairs x Connector Loss Allowance dB Splice Insertion Loss Allowance dB Number of Splices x Splice Loss Allowance dB Table 1 lists the cable attenuation coefficient by cable type this coefficient is 3 5 dB km for all multimode optical fiber types recommended for premises cabling systems Indoor rated singlemode fiber has an attenuation coefficient of 1 5 dB km while outdoor rated singlemode fiber has a coefficient of 1 dB km or lower The standards also specify the maximum connector loss allowance as 0 75 dB and the maximum splice loss allowance as 0 3 dB Well executed cabling installations should generally deliver connections that exhibit significantly lower connection losses The same statement applies to splice losses Note that the length of the fiber link must be known or must be measured by the test tool to determine the loss limit Table 2 shows an example applicat
22. Some light in the higher order mode groups is no longer reflected and guided within the core The length of the fiber and the wavelength of the light traveling through the fiber primar ily determine the amount of attenuation The loss in an installed optical fiber link consists of the loss in the fiber plus the loss in connections and splices The losses in connections and splices represent the majority of the losses in shorter fiber optical links typical in the premises network application A troubleshooting tool like an Optical Time Domain Reflec tometer OTDR will allow you to gauge and inspect the loss at each connection or splice Dispersion Dispersion describes the spreading of the light pulses as they travel along the optical fiber Dispersion limits the bandwidth of the fiber thereby reducing the amount of data the fiber can transmit We will limit the discussion of dispersion to modal dispersion in multimode fiber The term multimode refers to the fact that numerous modes of light rays propagate simul taneously through the core Figure 8 shows how the principle of total internal reflection applies to multimode step index optical fiber The term step index refers to the fact that the refractive index of the core is a step above the index of the cladding When the light enters the fiber it separates in different paths known as modes The principle of total in ternal reflection described above and shown in Fi
23. TRC1 attached moves to one end of the link segment under test and the power meter with TRC2 attached moves to the opposite end of the link segment under test The optical loss reference measurement captures the loss in the connection of Test Refer ence Cord 1 TRC1 and the Light Source the loss in TRC1 TRC2 TRC3 the loss of the reference connections CR1 CR2 and the loss in the connection between TRC2 and the Power Meter CR1 CR2 mn Light source Power meter 1 1 Figure A3 5 Three jumper reference method The optical loss reference measurement captures the loss in the connection of Test Reference Cord 1 TRC1 and the Light Source the loss in TRC1 TRC2 TRC3 the loss of the reference connections CR1 CR2 and the loss in the connection between TRC2 and the Power Meter The analysis of the losses for the link measurement shown in Figure A3 6 shows that the losses in the link under test are fully included but that we are measuring the difference in the loss between CR1 and C1 and the difference between C2 and CR2 rather than the full losses in C1 and C2 The loss inside the link segment under test consists of the sum of the loss in fiber internal connections and splices if present The full loss in neither of the end connections of the link under test is included in the measurement results VEL gg ane TRC2 Light source 1 et 1 Power meter se EEE H Link segment under test l
24. acterize the modal dispersion in multimode optical fibers Loss Loss or attenuation has been a well established performance parameter in the cabling and network application standards The signal must arrive at the end of the fiber optic link the input to the detector at the receiving device with sufficient strength to be properly detected and decoded If the detector cannot clearly see the signal transmis sion certainly has failed Attenuation or signal loss in optical fiber is caused by several intrinsic and extrinsic factors Two intrinsic factors are scattering and absorption The most common form of scattering called Rayleigh Scattering is caused by microscopic non uniformities in the optical fiber These non uniformities cause rays of light to partially scatter as they travel along the fiber core and thus some light energy is lost Rayleigh scattering is responsible for roughly 90 of the intrinsic loss in modern optical fibers It has a greater influence when the size of the impurities in the glass is comparable to the wavelength of the light Longer wavelengths are therefore less affected than shorter wavelengths and longer wave lengths are subject to less loss than the shorter wavelengths Extrinsic causes of attenuation include cabling manufacturing stresses and bends in the fiber Bends can be distinguished in two categories microbending and macrobending Microbending is caused by microscopic imperfections in the geome
25. added TRC and the difference of the loss between connections CR1 and CR2 The loss in the one meter TRC3 is small with 850 nm light this loss is 0 0035 dB The difference between the two reference con nections is less that 0 05 dB half of the total loss specification for reference cords The error observed or measurement uncertainty of the two jumper method has approximately been reduced to 1 10th using the modified one jumper method a sea RU Ga bee ska TRC3 TROD Light source Ko ts Soest Power meter Link segment under test 1 1 Figure A3 4 The Modified One jumper method optical loss measurement The difference be tween the reference power level and the loss test power level is the power loss in the link under test connections C1 and C2 the added TRC3 and the difference between the loss in CR1 and in CR2 two reference connections The three jumper method ISO IEC standard 147363 3 emphasizes the three jumper method as a generic method that can be applied regardless of the type of connectors used at the ends of the link under test or in the test equipment Figure A3 5 shows the reference connection As the name of this method implies you use three TRCs to make the connection for the reference measure ment Then you remove the middle TRC TRC3 in Figure A3 5 and replace this TRC with the link under test as shown in Figure A3 6 Replace means that the light source with
26. ally accomplished with an LSPM test set Fiber verification test tools are typically less expensive tools they can also ef fectively be used to troubleshoot troublesome links A quick inspection of the end to end link loss may provide the indication whether or not the optical fiber cable is suspect or whether other network functions are the cause of the detected malfunction An LSPM determines the total light loss along a fiber link by using a known light source at one end of the fiber and a power meter at the other But before the test can be done as described earlier a reference power level from the source is measured and recorded to set a baseline for the power loss calculation After this reference is established the meter and source are plugged into the opposite sides of the fiber link to be tested The source emits a continuous wave at the selected wavelength On the distant end the power meter measures the level of optical power it is receiving and compares it to the reference power level to calculate the total amount of light loss Figure 17 If this total loss is within the specified parameters for the link under test the test passes A loss budget should be well established and used as a benchmark during cabling installa tion If this type of verification testing is performed during installation it can be expected that yield will increase and certification testing will go smoother LSPM test sets have historically been more difficult
27. annot detect the full impact of the misalignment It reports a lower loss value optimistic loss value than a test executed with an overfilled light source Controlling launch conditions Over the years better methods have been devised to control these overfilled launch condition into a narrow range with the goal to produce re peatable and accurate loss test results The standards established two independent metrics to characterize and control the launch conditions They are the Modal Power Distribution and the Coupled Power Ratio The Modal Power Distribution measures the relative power level in the different modes transferred between the light source and the TRC This metric must be satisfied by the design of the equipment such as the selection of the LED diode and the coupling inside the light source instrument between the LED and the internal fiber connection All fiber optic test modules designed and manufactured by Fluke Networks after 2002 satisfy the MPD requirements Coupled Power Ratio CPR is a measure of the amount of modal filling in a multimode fiber test reference cord It became popular because it could be measured in the field Both the light source and the TRC can be rated with a CPR index A CPR value is measured as the loss between a multimode TRC coupled into a singlemode TRC When the light in the multimode fiber contains significant energy in the high order modes the loss in this coupling will be greater than when the m
28. arity of the link un der test The light enters the cord at the red boot the light leaves the TRC at the black boot So one end of a TRC has a red boot and at the other end of that same cord is a black boot The light travels from red to black The DTX screen display shows the boot color Figure 18d Figure 18e shows a schematic representation of this reference setup This figure uses a different color for the two duplex cords These colors do not relate to the real cords but were chosen to add clarity to the figure The yellow cord connects the Output light source of the main unit s fiber module to the Input light meter of the remote unit One of the yellow cords is not connected in the reference setting One of the darker colored cords makes the connection in the opposite direction Figure 18e also shows the location of the mandrel near the end with the red boot that is to be connected to the light source The duplex cords have one longer leg with the red boot After this leg has been wrapped around the mandrel the lengths of both cords in the duplex arrange ment are equal The DTX fiber modules Output ports are always SC connectors The removable adapters for the Input ports are chosen to match the end connectors of the link under test The example in Figure 18e depicts the example in which the link under test is equipped with LC connectors NETWORK VISION Main to Remote Maine LC Adapters Remote Unit Figure 18e
29. ation Certification Process and equipment requirements Table 3 illustrates that the channel loss limits for high throughput network applications are relatively small In order to make the Pass Fail decisions with confidence the test pro cedure must be executed with precision and with accurate OLTS or LSPM equipment When the loss limit value is 2 6 dB 10GBASE S a measurement error of even 0 25 dB consti tutes an error approaching 10 of the limit value This section will review the procedural steps and equipment requirements to achieve accurate and repeatable measurements Two issues have proven to make a critical contribution to the topic of measurement accuracy 1 The reference for the loss measurement 2 The launch condition of the light source into the link under test Measurement units The dB or decibel expresses a ratio of power levels using a logarithmic function If we rep resent the input power into a black box as P and the output power as P we calculate out the amplification or attenuation of the signal processed through the black box in dB using the following function 10 x log10 P P Note that when P out is greater than P the black box has amplified the signal and the mathematical formula above yields a positive number If on the other hand P is lower than the P in the signal has been attenuated and the formula produces a negative number Since the latter is always the case
30. ations The standards do not designate Pass Fail limits for this test It is recommended that generic cabling require ments for components and design criteria for the specific job be considered An OTDR can be used bi directionally as a single ended tester for or with a receive fiber for certification testing What you need to know about OTDRs OTDRs were once laboratory equipment that were difficult to operate and impractical for field use They were big heavy and complicated for inexperienced technicians to set up for a test and operate accurately Once a test was performed it was difficult to understand test results This led to a stigma of fear and confusion However many new OTDRs today many new OTDRs are small light and easy to use An ordinary technician can now perform troubleshooting like an expert but a basic understanding of how an OTDR works is still helpful e Basic operation An OTDR infers loss reflectance and location of events It sends pulses of light into a fiber and uses a sensitive photo detector to see the reflections and plot them graphically over time In order to accurately test the optical characteris tics of the fiber must be determined and set prior to running the test e OTDR trace The OTDR plots the reflectance and loss over time in a graphical trace of the fiber Experienced technicians can read a trace and explain it For example on the below trace an experienced eye can spot that one side of a
31. cation test results If you are a contractor Largest Event 0 04 dB your customers want to know where an event is in their fiber plant not where it is on your test setup When you enable LFC a connector that is 50m from the patch panel will show up at 50m not 150m on the trace Just turn the Figure 21 Pass Screen on the rotary switch to Setup go to the 2nd tab and pry Compact OTDR enable Launch Fiber Compensation Then turn it again to Special Functions and choose Set Launch Fiber Compensation Choose Launch only if you are just using a launch fiber or HL Other Options if you are also using a receive Multimode 50 N Dual 850 1300 nm fiber End 1 DATA CENTER 3 Third designate the fiber characteristics or allow Length 312 0m Overall Loss 1 98 dB default to the selected fiber in the first step or choose User Defined and select Numerical X Largest Event 0 78 dB Aperture and Back scatter coefficient for the fiber under test Figure 22 Fail Screen on the DTX Compact OTDR NETWORK VISION 4 Now choose from a menu to set Distance Range Averaging Time 5 Finally choose from the menu to set Pulse Widths and Loss Threshold i 2024m With the DTX Compact OTDR many settings such ee Benes as Distance Range Averaging Time Pulse 0 23 dB Widths and Loss Threshold can be aut
32. ce Contaminated fiber end face Figure 30 Comparison between a clean and dirty fiber end face The same problem occurs when using shirt sleeves or clean cloths to wipe connectors in fact the trace amounts of lint and dust attracting static from using such materials will likely add to the contamination rather than reduce it Even isopropyl alcohol IPA which has historically been viewed as an acceptable solvent is proving to be inferior to specially formulated solutions IPA s inability to dissolve non ionic compounds such as pulling lube and buffer gel and its residue leaving evaporation process make engineered solvents the superior choice When using these solvents the proper cleaning order is wet to dry using clean lint free wipes Figure 31 Figure 31 Wet to dry cleaning methodology Apply a small spot of solvent to the starting edge of a wipe Holding the end face connector perpendicularly swipe the end face from the wet spot to the dry zone The types of cleaning resources vary in complexity and price ranging from simple wipes to devices that incorporate ultrasound with water Which tool you use will be dependent upon need and budget but for the majority of the cabling jobs and projects the pairing of lint free wipes and swabs with engineered solvents now found in fiber inspection certi fication and cleaning kits will be sufficient 10 Conclusion Cabling installation is a multi step p
33. ctions in a channel Simple but it is important to consider the total allowable loss per intended application standard and typical loss for connector type during the design process Even if the connectors are properly terminated if there are too many in a channel the loss may exceed specifications e Misalignment The best way to achieve good fiber alignment is to fuse the two fibers together with a precision splicing machine But for several practical reasons connection of fibers is often done mechanically with fiber optic connectors There are many com mercially available connector types that all have their advantages and disadvantages Typical loss specifications are a good proxy for how good they are able to align fibers Any such specifications used for data communications should be compliant with FOCIS standards Poor quality connectors or faulty termination Good quality connectors have very tight tolerances in order to maintain precise alignment End face geometry Performance of fiber optic connectors is largely a function of the geometry of the end face This geometry can be measured in a laboratory with preci sion interferometry equipment In the field the following parameters are inferred in loss and reflectance measurements e Roughness Scratches pits and chips produce excess loss and reflectance e Radius of curvature The convex surface of the connector should nicely mate up with another connector e Apex offset The core
34. dard uses a correction factor of 0 4 dB to account for the fact that the actual losses in the end connections of the link under test are not measured by the three jumper method The quality of the TRC cords is critical e Testing with cords that are worse provide a more lenient limit e Testing with cords that are better provide a tougher limit e This is counter intuitive but creates a real problem DTX customers can measure the patch cord loss but this additional step represents a huge inconvenience for the contractor and we are guessing that this additional step will not be done in the field Now you probably understand why Fluke Networks does not recommend this method if the job can be performed using a method with less uncertainty which equals more accuracy and advocates the one jumper method FLUKE networks Your authorized Fluke Networks distributor NETWORKSUPERVISION Fluke Networks Inc P 0 Box 777 Everett WA USA 98206 0777 800 283 5853 Fax 425 446 5043 Western Europe 00800 632 632 00 44 1923 281 300 Fax 00800 225 536 38 44 1923 281 301 Email info eu flukenetworks com Canada 800 363 5853 Fax 905 890 6866 EEMEA 31 0 40 267 5119 Fax 31 0 40 267 5180 Other countries call 425 446 4519 Fax 425 446 5043 E mail fluke assist flukenetworks com Web access http www flukenetworks com 2009 Fluke Corporation All rights reserved Printed in U S A 5 2009 3473059 Rev A
35. de as standard equipment the SC connector with optional adapters and test reference cords available to test ST LC or FC connector systems with the preferred one jumper test method NETWORK VISION 2 All TRCs are manufactured to the same exacting specifications with end faces that have been hardened using a patented method to provide scratch resistant and du rable cords with an optimum geometry for light coupling The overall loss limits for these TRCs is 0 1 dB In the case of the DTX Series fiber test modules the TRCs are implemented as duplex cords The added TRC is therefore attached and is of equal quality and performance as the cord used to set the reference The fact that the added TRC is attached assures that a high quality cord is readily available to the test technicians in the field Of course there are connector systems for which the one jumper test reference method cannot be adopted The most prevalent example is the MT RJ connector type We will first explain the two jumper method and follow that section with an adaptation of the two jumper method which we will call the modified one jumper method because it meets the requirement to properly and accurately account for the losses in the end connections of the link segment under test The two jumper method Figure A3 1 demonstrates the connections for the two jumper reference measurement The power meter is connected to the test reference cord TRC1 while the power met
36. difference accurately represents the loss in the link segment under test The difference fully covers the link segment under test and connection C2 but not C1 The reference measurement includes the loss of the connector CR1 During the link measurement we measure the difference between the reference con nection CR1 and connection C1 This difference does not equal the loss in connection C1 This difference cannot be known or predicted The two jumper loss measurement method does not fully evaluate the link segment and both of the connections at its ends If you are testing against an application standard the result is likely low with 0 5 dB more or less This is not acceptable when loss limits are in the 2 6 to 3 5 dB range A 0 5 dB error represents an error of 25 or 14 If you had selected an installation test standard this method can somewhat be adjusted by ensuring that you exclude the C1 connection from the count of connections in the link The test limit calculation then excludes the loss allocated to one connection We said somewhat because the advantage of the LSPM loss measurement rests on the fact that the contribution of each element is accurately counted The modified one jumper method We can adjust for the error in the two jumper method by adding a TRC when measuring the link loss as shown by TRC 3 in Figure A3 4 The reference measurement for this method is identical to the method for the two jumper method we just r
37. elpful advice on relevant structured cabling topics e Unsurpassed technical assistance from the highly trained Fluke Networks Technical Assistance Center TAC e Certified Test Technician Training CCTT classes available around the world e Gold Support program comprehensive maintenance and support including priority repair with loaner annual e calibration and priority TAC support with after hours and weekend coverage NETWORK VISION 11 Glossary Certification testing the process of testing the transmission performance of an installed cabling system to a specified standard requires an OLTS for Tier 1 certification and an OTDR for Tier 2 certification Channel end to end transmission medium between a transmitter and receiver dB logarithmic unit of measurement used to express magnitude of power relative to a specific or implied reference level usually associated with loss dBm power level expressed as the logarithm of the ratio relative to one milliwatt FiberInspector Fluke Networks popular line of handheld fiber end face and bulkhead port inspection instruments ranging from tube to video microscopes Gbps gigabits per second Launch cord fiber length of fiber placed between the link segment under test and the OTDR to improve the OTDR s ability to grade the near end connector and any abnor malities n the first connection LED Light Emitting Diode a relatively low intensity light source Link
38. er is connected to a similar test reference cord TRC2 For the reference measurement the two TRCs are connected with the appropriate reference adapter CR1 We recommend to use adapters manufactured for singlemode applications since these adapters are manufactured to more exacting mechanical specifications that ensure better and more repeatable align ment of the fiber cores CR1 TRC1 TRC2 Light source Power meter I Figure A3 1 Two jumper reference method The optical loss reference measurement captures the loss in the connection of Test Reference Cord 1 TRC1 and the Light Source the loss in TRC1 the loss of the reference connection CR1 the loss in TRC2 and the loss in the connection between TRC2 and the power meter We will repeat the analysis of the reference power measurement as we did in our analysis of the one jumper reference measurement illustrated in Figure 13 It is worthwhile to emphasize once more the importance of the launch conditions from the light source into TRC1 We have not shown the mandrel but the installation and use of the proper mandrel is mandatory to obtain reliable and repeatable test results Our analysis follows the light path from the light source to the power meter The coupling of light energy from the light source into TRC1 will be affected by the status of the connection between the test instrument and TRC1 This does not need to be perfect and its condition does not have to be known in d
39. etail as long as it remains stable for the duration of the test Therefore do not modify in any way the connection between TRC1 and the light source A minor loss occurs in each of the short TRCs recall that the typical loss for the 850 nm wavelength is about 0 0035 dB per meter For the 1300 nm wave length this loss is 0 0015 dB Assuming we will not abuse the TRCs the loss in the fiber do not change while we test the links in the network A loss occurs in the adapter CR1 between the two test reference cords We will discuss its influence in a moment There is also some loss in the coupling of TRC2 into the power meter Using this method we will not have to touch this coupling as we connect to the link segment under test Look ahead at Figure A 2 which shows the test connections for the link segment loss test TL Sr v TRE Light source 7 Power meter E a E i Link segment under test i V pp Figure A3 2 Two jumper method optical loss measurement The difference between the reference power level and the loss test power level is the power loss in the link under test loss in connection C2 and the difference in the loss between CR1 reference connection and C1 This difference can vary the total loss in connection C1 is not included in the link loss test result We will now examine the difference in the light loss between the reference measurement and the link measurement to ensure that this
40. eviewed as is shown in Figure A3 3 NETWORK VISION We have colored the connections in Figure A3 3 and A3 4 to show that the connectors in the test tools and those at the end of the link under test do not need to be the same type Fluke Networks recommends this method for a connector type like the MT RJ for which the true one jumper method cannot be used These TRCs are hybrid cords which means that they are terminated with different connectors at either end TRC3 for the MT RJ applica tion must have alignment pins installed to properly mate with the two standard connec tions An MT RJ TRC kit is available from Fluke Networks Recall that removable adapters at the power meter offer the preferred method to use the true one jumper method when this alternative is available CR1 TRC1 TRC2 Light source Power meter I Figure A3 3 The modified one jumper reference method uses the exact same reference method as the two jumper reference method Note that the TRCs are hybrid cords terminated at one end with a connector matching the test equipment and at the other end with a connector that matches the link under test The figure highlights the different connector types by using different colors The analysis of the losses through the configuration shown in Figure A 4 shows that the loss in connection C1 is fully accounted for as well as the loss in the link under test and in connection C2 We also measure the loss in TRC3 the
41. filled bandwidth rating below 200 MHzekm are not included in this table and are no longer recommended in the design of any new installations The OM3 designation describes the high bandwidth laser optimized multimode optical fiber cable Among the different fiber optic based transmission stan dards for 10 Gbps Ethernet 10GBASE SR the serial transmission of 10 Gigabits per second using the short wavelength VCSEL 850nm is the most economical implementation of this high speed network application in the premises local area network the datacenter or the storage area network And for this application OM3 is the preferred fiber optic cable type Manufacturers of optical fiber have developed laser optimized multimode fiber with modal bandwidth characteristics that are better than the OM3 type specifications This may lead to the adoption of an OM4 rating with a proposed effective laser bandwidth in the range from 3 500 to 4 700 MHzekm 052 is commonly referred to as low water peak singlemode fiber and is characterized by having a low attenuation coefficient near 1383 nm 2 Telecommunications Industry Association TIA TIA represents the telecommunication industry in association with the Electronic Industries Association TIA is accredited by the American National Standards Institute ANSI as a major contributor to voluntary standards Standard ANSI EIA TIA 568 Commercial Building Telecommunications Cabling Standard is the primary standard
42. gure 3 guides each path or mode through the fiber core One mode travels straight down the center of the fiber Other modes travel at different angles and bounce back and forth due to the internal reflection The modes bouncing the most are called the higher order modes The modes bouncing very little are the lower order modes The shortest path is the straight line All other paths taken by the light modes are longer than the straight line path the steeper the angle the more bounces taken and the longer the path traveled As the path length varies so varies the travel time to reach the end of the fiber link The disparity between arrival times of the different light rays also known as differential mode delay DMD is the reason for disper sion or spreading of the light pulse as it travels along the fiber link Core index of refraction n1 1 47 Cladding index of refraction n2 1 45 Figure 8 The optical fiber gathers all the light that enters within the angle determined by the Numerical Aperture The light reflects at the boundary between the core and the cladding and travels along different paths A path is also called a mode Multimode optical fiber guides the light along multiple paths or modes The light that enters at the wider angle takes more bounces and travels a longer way It represents the higher order modes The effect of dispersion increases with the length of the optical fiber link As pulses travel farther t
43. he difference in the path length increases therefore the difference in arrival times increases and the spreading of the pulses continues to grow The effect is that the light pulses arriving at the end of the longer fiber link run into each other and that the receiver can no longer distinguish them let alone decode their state value Higher data rates are achieved by sending shorter pulses at rapid succession Dispersion limits the rate at which pulses can be transmitted In other words dispersion limits the bandwidth of the cabling Figure 9 The net effect of dispersion causes the transmitted pulses to run together and overlap at the end of the link input to the detector The detector can no longer recognize and decode the state of individual pulses NETWORK VISION To compensate for the dispersion inherent in multimode step index fiber multimode graded index fiber was developed Graded index refers to the fact that the refractive index of the core gradually decreases farther away from the center of the core The glass in the center of the core has the highest refractive index which causes the light in the center of the core to travel at the slowest speed The light that takes the shorter path through the fiber is traveling at a slower speed This core construction allows all the light rays to reach the receiving end in approximately the same time reducing the modal dispersion in the fiber As Figure 10 depicts the light i
44. his copper cabling can support network connectivity to a distance of 100 meters 328 feet Optical fiber cabling is the preferred medium for distances beyond 100 meter such as riser cables in the building This booklet reviews best practices for test and troubleshooting methods as well as the test tools to ensure that installed Optical Fiber cabling provides the transmission capability to reliably support LAN or enterprise network applications Certification or the process of testing the transmission performance of an installed cabling system to a specified standard ensures a quality installation It also provides official documentation and proof that the requirements set by various standards committees are fully satisfied Fiber optics is a reliable and cost effective transmission medium but due to the need for precise alignment of very small fibers problems ranging from end face contamination to link damage can occur Regardless narrowing down the source s of failure is often a time con suming and resource intensive task For this reason Fluke Networks has created an enterprise focused fiber troubleshooting guide to assist in ensuring 1 proper assessment of cable installation quality and 2 efficient troubleshooting to reduce the time spent identifying the root cause of a problem before tak ing corrective action to fix it Note that this guide does not address issues that are especially germane to the long haul telecommunications
45. ion of the loss limit calculations The calculation is performed for a 300 m OM3 fiber link segment with just two end connectors and no splices that is used with an 850 nm light source Max loss per unit length or per item Length number Calculated loss dB Max loss in fiber 3 5 dB km 0 3 1 05 Max loss in connections 0 75 dB 2 1 5 Max loss in splices 0 3 dB 0 0 0 Link loss limit 2 55 Table 2 Loss limit calculation for a 300 m MM link segment with 850 nm light source Wavelength and directional requirements 1 Horizontal cabling or Cabling Subsystem 1 link segments TIA 568 C 0 need to be tested in one direction at one wavelength either 850 nm or 1300 nm for multimode and either 1310 nm or 1550 nm for single mode 2 Backbone riser cabling Cabling Subsystem 2 and Cabling Subsystem 3 link segments shall be tested in at least one direction at both operating wavelengths to account for attenuation differences associated with wavelength Multimode link segments shall be tested at 850 nm and 1300 nm singlemode link segments shall be tested at 1310 nm and 1550 nm Links that use keyed connectors to implement the fiber polarity can only be tested in the direction prescribed by the keying of the connectors Network application standard For certification the network application standards such as the IEEE standard 802 3 for Ethernet or the ANSI standard for FibreChannel FC must also be co
46. ionsaussr der isori tiaaaieredancaccaowenedsn dad E E EENE 44 CLEANING EEE 45 10 CONCLUSION 4 603 one ee eels oh ae Ee pls Se Go ees 46 TIe GlOSSATY ihe cco nana dean E E RE A NE E EEEE 47 12 Appendices su nessssiriskegden ee Dra aieanandecdos r EERE cod EEEE ees 48 1 Introduction s fiber links support higher speed network bandwidths with increasingly stringent require ments it is becoming all the more important to ensure that your backbone links meet tightening loss standards The need for higher data transmission capacity continues to grow as network applications grow and expand These higher transmission speeds demand cabling that delivers higher bandwidth support This testing guide outlines cabling performance requirements field testing certification and troubleshooting techniques and instruments to ensure that the installed optical fiber cabling supports the high data rate applications such as 1 and 10 Gigabit per second Gbps Ethernet Fibre Channel and the anticipated 40 and 100 Gbps Ethernet applications A local area network LAN or an enterprise premises network connects users up to a distance of 2 to 5 km It encompasses the intra building connectivity as well as inter build ing cabling or the campus cabling Optical fiber cabling is primarily used for longer distance higher bandwidth connectivity while twisted pair copper cabling typically provides the connection to the end user or to the edge devices T
47. is a new connection between the Added TRC and the power meter This difference is also very small assuming the end faces of the Added TRC are indeed clean since the meter is equipped with a wide angle lens to capture all the light transmitted by the link under test We judge the measurement error due to the Added TRC to be less than 0 01 dB which also happens to be the resolution of a power meter The one jumper method can only be applied if the connector in the power meter and the end connectors of the link under test are the same type for example SC connectors After setting the reference we disconnect the TRC from the power meter and are only able to connect this TRC to the link under test if the end connector of the link C1 in Figure 14 properly mates with this TRC To be able to use the preferred one jumper method with different connector types many of Fluke Networks power meters to include the SimpliFiber Pro are equipped with a removable adapter A set of hybrid TRCs assures proper measurement connections while taking full advantage of the accuracy of the one jumper method The applicable standards listed in Table 5 make provisions for three different methods to set the reference for an optical fiber loss test The names of these methods in the different standards documents can be confusing We will use the following names in this document one jumper method the two jumper method and the three jumper method The
48. ished during the reference test is higher than it should be which will overstate the loss In the example discussed above we assumed that the power meter measured 20 dBm for the reference setting When we do not use a mandrel wrap the power level may actually be as high as 18 dBm with the same power source The loss calculation now yields 18 23 4 dB or 5 4 dB rather than 3 4 dB In essence we overstated the loss by 2 dB This a huge error since the highest order modes and the light entering the cladding cannot travel very far in the link under test NETWORK VISION Future launch condition control method At the time of this writing standards committees are defining a method that improves on the launch conditions today controlled by MPD CPR and mandrel wraps The proposed method is based on the concept of Encircled Flux EF which fine tunes and controls the modes launched in the link under test This method is currently still under study with the ultimate goal to further improve the accuracy and consistency of power measurements and loss tests in multimode links 4 Fiber Verification Testing Fiber verification testing including end face inspection and cleaning should be practiced continually as standard operating procedure Throughout the cable installation process and prior to certification loss of cabling segments should be measured to ensure the quality of the installation workmanship This type of a test is norm
49. ith one test reference cord TRC A TRC is a high quality fiber cord between 1 to 3 m with high performance connec tors at either end The end faces of the connectors should be treated by the manufacturer to provide scratch resistant hardened surfaces that support a multitude of insertions without degradation in performance It is critically important that the end faces of TRCs are kept very clean and are inspected regularly and cleaned if necessary throughout the day when certifying optical fiber links i Test reference cord Light source Power meter Figure 13 Principle for connections to set the reference for an optical loss measurement The light source in Figure 13 launches the light into the TRC which directs the light into the power meter The power meter measures the light energy level and typically expresses it in dBm Refer to sidebar The reference power reading with LED light sources falls in the range of 18 dBm to 20 dBm The 20 dBm level corresponds to 0 01 mW When test ing a singlemode fiber link with a laser light source the reference power measurement may yield 7 dBm which corresponds to approximately 0 2 mW a power level that is about 20 times stronger than the LED light output Therefore always use caution that you do not look into an active fiber link light used for data communication falls outside the visible spectrum but can cause permanent harm to your eye The reference power measurement compensates fo
50. ment of the channel is called the permanent link The figure shows a generic horizontal link model that contains optional connections such as the CP Consolidation Point Often an optical fiber link is constructed with several segments or sections and the net work equipment is often not installed yet when the cabling installation is certified It is not sufficient to test each segment against the installation standards Ensuring that the installed cabling system will support the intended network application requires that the installed channels end to end fiber links meet the length and loss requirements defined in the application specification as shown in Table 3 You may select one of two methods to assure that the installed channel meets the application requirements before you turn up the network service 1 Calculate the channel loss by adding the data for each link segment in the channel and adding the expected loss contribution of the interconnecting patch cords IEC stan dard 14763 3 makes explicit assumptions about the loss of a TRC connection with a link 0 3 dB see Table A3 1 versus the maximum loss of connections made with commercial patch cords 0 75 dB 2 Measure the channel loss as demonstrated in Figure 12 The end connections of the channel connections made with the network equipment are not included in the chan nel loss limit By replacing the equipment cords with TRCs the loss in the end connections is not part of
51. ming sequence is used The FiberInspector option for OptiFiber also allows end face images to be merged into the same records to prove cleanliness and combined to generate professional reports that combine all the test data into one docu ment These can be easily created and printed out or emailed in PDF form Cable certification test strategy There are several possible ways to perform a complete certification test of fiber optic cabling The standards are clear about defining required and optional tests test limits and test equipment that may be used But they do not suggest how the testing should be per formed for optimum efficiency in the field Based on decades of working with contractors installers technicians Fluke Networks has developed proven best practice procedures to perform a complete fiber certification in the most efficient way e Make sure that design criteria and test limits are established before installation genene I e Confirm proper fiber strand polarity end face conditions and verify loss Cable ID 1A 8A B 05 Test Summary PASS with simple verification tools during reemos tem n End ENGINEERING QUAD Fom Wind So installation OTDR End1 PASS a 1850 nm net 498 Endface Image End PASS e Perform extended tests using the tier iaren ss ETE 2 certification tests OTDR analysis pwn OST N as the first certification step Doing S em 5 so Sss e M Ensures connector performance OTDR End
52. mode fibers using the longer wavelengths retain the fidelity of each light pulse over longer distances since they exhibit no modal dispersion caused by multiple modes Thus more information can 1 Cutoff Wavelength The wavelength below which a singlemode optical fiber ceases to transmit in a singlemode be transmitted per unit of time over longer distances intrinsic loss is less at the higher wavelengths This gives singlemode fibers higher bandwidth compared to multimode fiber Singlemode fiber design has evolved over time as well Other dispersion mechanisms and non linearities exist which we will not cover since they play a much less important role in the optical fiber application in premises networks Singlemode fiber has some disad vantages The smaller core diameter makes coupling light into the core more difficult The tolerances for singlemode connectors and splices are more demanding to achieve good alignment of the smaller core Furthermore the longer wavelength laser light sources are more expensive than the VCSEL operating at 850 nm Bandwidth A key fiber performance characteristic is bandwidth or information carrying capacity of the optical fiber In digital terms bandwidth is expressed in a bit rate at which signals can be sent a given distance without one bit interfering with the bit before it or following it Bandwidth is expressed in the product MHzekm The interference occurs because of the dispersion phenomenon
53. n When the light source in the transmitting device generates a pulse train like the one depicted in Figure 4 the optical fiber link must transmit this pulse train with sufficient signal fidelity so that the detector at the receiving device can detect each pulse with its true value of On or Off Minimally two things are required to ensure reliable reception and transmission Channel insertion loss the maximum signal loss or signal attenuation allowed over the transmission medium from the transmitting device to the receiving device The term channel defines the end to end transmission medium between transmitter and receiver The signal loss consists of the cumulative losses in the optical fiber cabling and in each connection or splice Signal dispersion As we will discuss the light pulses have a tendency to spread out as they are traveling along the fiber optical link due to dispersion The spreading must be limited to prevent the pulses from running together or overlapping at the receiving end Both of these parameters channel loss and signal dispersion play a critical role in es tablishing reliable and error free transmission Dispersion cannot be measured in the field The network standards define a maximum channel length for an optical fiber channel the maximum length is a function of data rate and the bandwidth rating of the optical fiber The bandwidth rating in turn is based on laboratory measurements to char
54. n graded index multimode fiber no longer travels in straight lines from edge to edge but follows a serpentine path it is gradually reflected back toward the center of the core by the continuously declining refractive index of the glass in the core Figure 10 Graded index multimode fiber The refraction index of the core changes throughout the core It is highest in the center and gradually decreases toward the boundary with the cladding This creates light paths modes that follow a serpentine path as shown in the left panel of this figure The lower modes light center of the core travels slowest while the modes in the outer regions that travel the longer distances travel faster Graded index multimode fiber therefore provides better band width Laser optimized multimode fiber that is to be used for the newer high speed network application data rates in the Gigabit per second range is constructed as graded index multimode fiber This laser optimized multimode fiber also uses the smaller 50 um core diameter The smaller core diameter also decreases the dispersion effect in the fiber by limiting the number of modes Singlemode fiber as the name implies only allows one mode of propagation at wave lengths longer then the cutoff wavelength The 1310 nm wavelength that is used by most premises network application over singlemode fiber 9 um core diameter is well above the cutoff wavelength which is between 1150 nm and 1200 nm Single
55. nk under test that is receiving the light from the other end of the link e When the connections to the link under test are established the instrument will chirp a happy tone to let you know whether polarity has been established Length The tester measures the length as well as the link loss When you select an ap plication standard during the setup it includes the maximum length for the application depending on the bandwidth rating of fiber used in the link under test Table 3 provides an overview of this dependency Make sure that you are using the appropriate fiber test adapter with a connector that matches the fiber patch cord or the patch panel Connect TRCs to the link or channel to be tested repeat the process explained in Figure 18g NETWORK VISION Bidirectional testing If you want to test each fiber in both directions do not forget to select that option in the setup screen see Figure 18b When the tester prompts you to make the connection to test in the second direction remember to switch the TRC at the link end DO NOT remove the TRCs from the tester connections Test Results Be sure to save results before moving onto the next fiber or testing in the other direction Figure 19 shows the detailed measurements of a fiber note that each fiber is tested at both of the wavelengths demanded by the installation standard Applications standards on the other hand only specify performance for the wavelength
56. not or cannot offer adapters such as MT RJ connectors consult Appendix 3 to review alternate methods the set the reference Guidelines for setting a reference e Use high quality TRCs e Clean TRC ends before you set the reference e Let the tester warm up to a steady state internal temperature about 10 min with ambient temp and storage temp difference of lt 20 F e Use preferred one jumper reference method e Plug the SC adapter with red boot plugs into the transmitter OUT connection e Do not unplug red boot on source after setting the reference e After the reference is set do NOT disconnect TRC from light source e For a multimode optical link use the proper mandrel e Reference must be re set after each time the units are powered down e Ensure to maintain precise launch conditions of the reference Run an autotest Select Autotest The test standard you selected for an Autotest determines the test parameters to be measured and the Pass Fail criteria for each test Polarity When you run a successful Autotest using the DTX Fiber Modules you will be able to ensure polarity e Connect the black boot of the TRC to the fiber in the link under test that is transmit ting the light and needs to connect at this end of the link to the transmitter of the network device Light leaves the TRC at the black boot the red boot end of that cord is connected to the Output on the tester e Connect the red boot of the TRC to the fiber in the li
57. nsidered High throughput applications Gbps range and above require more stringent limits on channel length and channel loss that is depending on the type and bandwidth rating of the optical fiber and the light sources used in the network devices Table 3 shows the maximum supported distance and the maximum allowable channel loss for a number of common network applications and for the different fiber types we described earlier in Table 1 The maximum channel length maximum distance supported is a proxy specification for dispersion As long as the channel length does not exceed the maximum stated in the standard dispersion will not cause a communication breakdown Field certification shall verify that fiber optic channel length does not exceed the maximum supported distance the length limit The installation standards discussed above require the measurement of cable length in order to calculate the maximum link attenuation allowance but the installation standards impose a generic maximum length which may far exceed the length specified for the application Table 3 documents that the length is limited and that it decreases for higher data rate applications depending on the bandwidth rating of each fiber type a function of the modal dispersion characteristics of the fiber The maximum channel loss limits decrease becomes more stringent with the higher throughput systems OM1 0M2 0M3 Application Waveleng
58. of modes in the fiber and with differing amounts of power in each mode A superior method of ensuring bandwidth in optical fiber links for the deployment of Giga bit speeds is the measurement of DMD differential mode delay see the prior discussion NETWORK VISION on dispersion This measurement technique is the only bandwidth specification mentioned in the standards for 10 Gbps data rates The Laser Bandwidth or EMB is mathematically derived from the DMD measurements Fiber Types The ISO TEC standard std 11801 defines four types of optical fibers to support various classes of premises network applications The ISO IEC std 11801 or std 24702 defines three multimode optical fiber types 0M1 OM2 and OM3 and two singlemode types 0S1 and 052 These type designations are finding acceptance in the North American market as well and are listed in the TIA 568 C 3 document The following table provides a short overview of the main characteristics of these fiber types Cable attenuation Minimum modal bandwidth coefficient MHzekm dB km Overfilled Laser Wavelength nm 850 1300 850 1300 850 Optical Core fiber type diameter um OM1 50 0r 62 5 BIG LS 200 500 Not specified 0M2 50 or 62 5 3 5 1 5 500 500 Not specified 0M3 50 335 5 1 500 500 2 000 M To be determined ae 30 ae 3 500 4 700 Table 1 Multimode optical fiber types Note that older or legacy multimode fibers with an over
59. of the nee 1300 nM oss applications For example the 10GBASE S standard sl Limit specifies the link requirements at 850 nm The ZN Margin name input fiber or ouput fiber in the test 850 result screen of the tester refers to the port in the NM Loss E S A Limit main unit to which the fiber is connected The Ne D Margin result shown in Figure 19 pertains to the fiber that is connected to the input port at the main tester Press SAVE when done unit The screen title Loss R gt M which means Loss from the Remote unit to the Main unit also indicates the fiber for which the result is displayed Figure 19 Loss test results for the fiber connected to the input port on the Once you have tested all the links and saved each main tester unit The result includes the loss for both multimode wavelengths record results can be downloaded to a PC and man installation test standard aged with LinkWare Results Management software LinkWare allows you to manage and inspect any stored test result on your PC screen You can also print a Summary Test Report for the job as well as a professional report for each link tested LinkWare lets you create or emailed reports in PDF form 6 How to Certify Optical Fiber Cabling with an OTDR TIA TSB 140 amp ISO 14763 3 recommend OTDR testing as a complementary test to ensure that the quality of fiber installations meet component specific
60. of the fiber should be centered near the highest point of the connector e Fiber height A protruding underpolished fiber does not mate well and an undercut overpolished connector will perform poorly due to the presence of an air gap Unseated connectors A connector may be plugged into an adapter bulkhead but may not be seated and connected with its mate Worn or damaged latching mecha nisms on connectors or adapters are sometimes the culprit Poor cable management Strain on a connector may cause misalignment due to becoming partially retracted broken or unplugged e Polarity Perhaps the simplest fiber cabling fault is a reversal of transmit and receive fibers This is usually easy to detect and repair But sometimes connectors are duplexed together and must be broken apart to be reversed Standards designate polarity with a labeling convention that is seldom taken advantage of resulting in confusion Polarity should be designated with A and B labels or colored boots Ais for transmit and B is for receive OR red is for transmit and black is for receive Poor cable management system design or damaged cable also causes faults in fiber cabling systems Fiber has a very high tensile strength but is susceptible to crushing and breaking if abused e Bends Macro and microbending caused by tight cable ties or bend radius violations result in excessive and unexpected loss Breaks Light will no longer propagate past a location
61. omatically 4 gt Cursor 4 Event set Just turn the rotary switch to Autotest and Press ENTER to Set Mark when you push the test button the OTDR will choose the most appropriate setting for the fiber Figure 23 Trace Screenshot on the that you are testing DIX Compact OTDR Running an autotest Now that you are all set up for testing turn the dial to Autotest plug in your launch fiber and press Test If it passes press Save 0 1X 1X name the test and test the next fiber If you want to see a trace just press the f1 softkey The event table and limits are also accessible via softkeys on the main screen m Ou 121 3 pr 0 0m Summary of extended certification Launch Event e OTDR traces characterize the individual compo 0 05 dB PASS nents of a fiber link connectors splices and other 4 gt Cursor Event loss events Extended certification compares the Press ENTER to Set Mark data to specifications for these events to deter mine if they are acceptable e Critical because it identifies faults that may be Figure 24 Pass Trace Screenshot on Soa ana rer the DTX Compact OTDR invisible to basic certification e Evidence that every component in a fiber optic cabling system was properly installed As with the first tier of testing results can be downloaded to a PC and managed with LinkWare Results Management Software It is easy to merge OTDR test results with the other records if the same na
62. ontaminated end faces Tiny foreign debris left on the core can also damage end faces during the mating process as they are connected together Sources of contamination are everywhere whether it be from a touch of a finger or the brush of a clothing fabric much less the omnipresent dust or static charged particles in the air Ports are also subject to the same contamination but are often overlooked Mating a clean connector to a dirty port not only contaminates the previously clean connector but can also cause fiber damage or failure Even the protective coverings or dust caps on straight from the package connectors and assemblies can cause contamination due to the nature of the production process and materials The typical assumption is that a quick visual check of the end faces is sufficient to verify cleanliness As mentioned previously the cores of these fibers are extremely small rang ing from roughly 9 to 62 5um Put into perspective with a diameter of 90um the average human hair is anywhere from 1 5 to 9 times larger With such a tiny core size it is impos sible for any end face defects to be spotted without the aid of a microscope There are two types of fiber inspection microscopes e Optical Figure 28 tube shaped and compact signals transmit ted by the FindFiber sources you to inspect the end faces directly Popular because they are inexpensive however they are not able to view end faces inside equipment or thro
63. p identifies a connector as questionable further analysis is warranted to ensure acceptable connector performance NETWORKS RVISION RESULTS M 5732 FIBER LENGTH 1315 m End 1 End 2 DATA CENTER CLOSET 4 106 m 4 1 0 km 101 m 101 m Figure 27b 7 Now you should change to Autotest and shoot a trace i If the display says that you failed the test look at the trace or event table to identify where the failing event is to locate and identify the failure EVENT TABLE OTDR PORT GHOST SOURCE REFLECTION 102 14 11 1 17 LOSS FAIL 0 19 0 65 REFLECTION PASS 04 4 0 00 0 05 GHOST N A N A END Scroll List Select Field Press EXIT to view SUMMARY View Sort View Trace Field Details Figure 27c Event Table on Fluke Networks OptiFiber OTDR ii If the end of the fiber is much closer that it should be you have a broken fiber at that location iii You may use a visual fault locator or create a macrobend with a real time trace running to physically locate the break or failing event iv Press Next Trace to see the same fiber at a longer wavelength This will often magnify poor events as longer wavelengths are more susceptible to certain types of losses v If you have connectors that fail limits and have long sweeping tailing on the trace you probably have dirty connectors You may use a FiberInspector to physically inspect each connector Make s
64. provides a general overview Volume C 1 Commercial Building Telecommunications Cabling Systems describes the recommended design for commercial buildings and volumes C 2 and C 3 describe the performance specifications for the cabling components C 2 addresses twisted pair balanced cabling and volume C 3 optical fiber cabling These standards address field test specifications for post installation transmission performance which depends on cable characteristics length connecting hardware cords cross connect wiring the total number of connections and the care with which they are installed and maintained For example severe cable bends poorly installed connectors and a very common problem the presence of dust dirt and other contaminants on the end face of fibers in connections negatively influence link attenuation The installation standards specify as a minimum transmission performance that the measured link loss be less than the allowed maximum loss limit which is based on the number of connections splices and the total length of optical fiber cable This certifica tion must be executed with an accurate Optical Loss Test Set OLTS or a Light Source and Power Meter LSPM These test tools will be described in more detail later as well as the Optical Time Domain Reflectometer OTDR An OTDR provides a good indication of total link loss but is not sufficiently accurate for link loss certification testing Certification NETWORK VISI
65. r uncertainties that could translate into measurement errors inaccuracies The exact power output level of the light source is un known and the amount of light coupled into the TRC varies every time we make a connec tion We must accept that there is some loss in the connection between the light source and the TRC Because of the reference measurement we do not need to know exactly how much this coupling loss is as long as it remains unchanged throughout the testing job Therefore the TRC shall not be removed from the light source until we quit or set a new reference The coupling of light from the TRC into the power meter is less variable since the power meter should be equipped with a wide angle input to capture all of the light from the TRC This coupling must be clean and the connectors must be properly seated to ensure that the reference measurement truly establishes the reference Many testers like the fiber loss length modules with the DTX Series CableAnalyzer automatically verify that the measured reference power level is within the acceptable range for the light source This provides some level of assurance that the reference is valid but it does not alleviate the need to make sure you use high quality TRCs that have been inspected to be clean After we have established this reference power level we move to the measurement connections as shown in Figure 14 with the following actions 1 First do NOT tamper with the
66. related to structured cabling systems in North America 3 Testing Theory Performance of Optical Fiber Cabling Certification is the most complete form of field testing As alluded to earlier the certification test procedure ensures that the installed cabling conforms to the transmission performance standards defined in the industry standards such as the applicable Interna tional Organization for Standard International Electrotechnical Commission ISO TEC and TIA standards Industry performance standards Two groups of standards should be considered to obtain a complete specification and ensure that the installed cabling will support the requirements for the intended network applications The goal of certification testing after all is to gain the confidence that the cabling system will not be the source of any network malfunction even before the network equipment is installed The two groups of standards recognize each other s requirements but do not provide a perfect overlap Generic installation standards The generic standards address the general installation rules and performance specifications The applicable standards are the ISO std 11801 2002 and ISO IEC 14763 3 Information Technology Implementation and operation of customer premises cabling Testing of optical fibre cabling and the ANSI TIA 568 C The latter revision C consists of four volumes Volume C 0 Generic Telecommunications Cabling for Customer Premises
67. rocess It is a prudent practice to certify the cabling system after installation to ensure that all installed links meet their expected level of performance Certification will likely identify some failing or marginally passing results In order to deliver a high quality cabling system the defects that cause the failures and marginal passes must be uncovered and corrected Fluke Networks full suite of fiber certification instruments Appendix 2 have a an un paralleled history of providing unique and powerful diagnostics assistance to installation technicians By knowing the nature of typical faults and how the tester s diagnostics report them you can significantly reduce the time to correct an anomaly an installation error or a defective component Personnel responsible for the network s operation can also benefit from the diagnostic capabilities of a certification test tool with the tester s assistance they can limit the duration of network downtime and restore service quickly We highly recommend that you thoroughly familiarize yourself with the capabilities of your test tool it is truly a modest investment that pays for itself many times over In addition to your precision instrument Fluke Networks also provides a wide variety of expert and timely support options Whether you are an installer network owner or contractor the following resources are available e White papers and Knowledge Base articles insightful studies and h
68. ry important that the test of an enterprise cabling system correctly and accurately accounts for the loss contribution of every connections The evaluation of the different methods for setting the test reference evolve in the first instance around the way these methods account for the two end connectors of the link segment under test Each of the test reference methods we will review treat any connec tion or splice between the end connections of the link under test in the same way Table 2 demonstrates that for a simple segment of 300 m with one end connection at either end the loss allowance in these end connections represents 1 5 db out of a budget maximum loss limit of 2 55 dB This is 59 of the link loss budget The one jumper method Refer back to the explanations of Figure 13 and Figure 14 The losses in each of the two end connections of the link under test are completely and accurately included The critique of the one jumper method is two fold a The connectors in the test tool must match the connectors at the end of the link under test b A second test reference cord must be added to connect the power meter to the far end of the link its quality and performance may be unknown Fluke Networks has dealt with this critique in a number of ways 1 The DTX Series fiber test modules as well as other LSPM test tools of recent vintage such as the SimpliFiber Pro offer replaceable adapters for the power meter The tes ters typically inclu
69. sents a bit with value 1 and the Off state represents a bit with value 0 Figure 4 represents such a sample of digital information as transmitted over an optical fiber cable Bit time slot High state ON ie i ER NATTA aa OFF Figure 4 A typical pulse train that represents the digital data The representation of the pulses in Figure 4 is idealized In the real world pulses have limited rise and fall times Figure 5 describes the main characteristics of a pulse Rise time indicates the amount of time required to turn the light to the On state it is typi cally characterized by the time required to transition from 10 to 90 of the amplitude Fall time is the opposite of rise time and represents the duration to turn the light from On to Off Rise time and fall time are critical parameters they determine the upper limit for the rate at which the system can create and transmit pulses lt Width Amplitude Rise time gt lt gt Fall time Figure 5 Analysis of a pulse When transmitting one billion or more bits per second data rate of 1 Gbps or more LED light sources can no longer be used due to the rise and fall time of the LED light sources These higher speed systems only use laser light sources A very common light source in premises networks is the VCSEL Vertical Cavity Surface Emitting Laser that transmits light at the 850 nm wavelength Requirements for reliable transmissio
70. ss for multimode fiber links We discussed how VCSELs have become the light source of choice for all higher throughput network applications using multimode fiber because VCSELs meet the modulation capability to provide short pulses in rapid succession to support the data rate for the 1 and 10 Gbps applications But VCSELs are not well suited for loss testing because each VCSEL may excite a different set of modes with varying energy levels in these modes Furthermore loss testing is performed with a constant light wave rather than a modulated signal LEDs produce a cone of light that is evenly spread over the end face of the fiber even beyond the core LEDs create an overfilled launch condition The degree of overfill how ever produces significant variations in the loss measurement A laser light source includ ing a VCSEL creates an underfilled launch condition These sources shine a narrow cone of light in the center of the core An underfilled launch condition may not properly detect problems in the fiber link and may consequently provide a more optimistic test result Connection a Properly aligned Connection b Improperly aligned Figure 15 Testing the two connections shown with underfilled launch conditions may not detect the misalignment problem in the optical cable NETWORK VISION The misaligned connection in Figure 15 b provides an example in which the loss mea surement with an underfilled launch c
71. tandards Fluke Networks DTX CableAnalyzer and OptiFiber OTDR can be equipped with optional multimode or singlemode fiber test modules that automate most of the test and make basic or Tier 1 certification very easy Note that an OTDR also provides a loss results for the total link but this measurement is based on the reflected light energy The standards demand that the basic certification be executed with an OLTS or LSPM These link loss results provided by using a light source on one end and a light meter at the opposite end are more accurate if properly executed The following steps should be followed to perform a basic loss length certification test e Establish Pass Fail test limits e Choose a test method and set a reference e Run the test and save results e Export to LinkWare to manage and archive the test results LinkWare is Fluke Networks popular and widely used free data management software that lets you create printed or electronics reports 1 Establish Pass Fail limits in accordance to what your certification goals are In this example we will establish limits for the total allowable loss based on an application standard using the Fluke Networks DTX Series tester equipped with the DTX MFM2 fiber loss test modules for multimode If you need to certify singlemode fiber use the DTX SFM2 modules a Once the tester is turned on turn the rotary switch to Setup and select Instrument Settings to input the opera
72. te the minimum certification testing requirement also referred to as Basic Certification or Tier 1 testing Tier 2 testing also known as Extended Certification test is optional and includes the Tier 1 tests plus the addition of an OTDR link analysis with trace and or event table The OTDR analysis can be used to characterize the components within the installed fiber link resulting in an indication of the uniformity of cable attenuation and individual connector insertion loss individual splice insertion loss and other events that may be detected An OTDR analysis provides an overall loss measurement for the link The standards define that the basic certification Tier 1 loss measurement must be executed using OLTS or LSPM equipment which when properly used provides a higher accuracy loss analysis The end user should specify the test standard to be chosen for the optical fiber certifica tion test procedure A test standard defines the tests to be executed and the limits or maximum allowable values for the tests As we have discussed when testing or certifying links that must support high throughput applications data rates in the Gbps range the application standards impose exacting limits for channel length and channel loss When you need to certify the cabling to support such applications it is important that a you select the corresponding application standard in the OLTS setup and b certify the chan nel configur
73. th Dist m Loss dB Dist m Loss dB Dist m Loss dB 10 100BASE SX 850 300 4 0 300 4 0 300 4 0 100BASE FX 1300 2000 11 0 2000 6 0 2000 6 0 1000BASE SX 850 275 2 6 550 3 6 800 4 5 1000BASE LX 1300 550 28 550 23 550 213 10GBASE S 850 33 2 4 82 2 3 300 2 6 FC 100 MX SN I 1062 Mbaud 850 300 3 0 500 809 860 4 6 FC 200 MX SN I 2125 Mbaud 850 150 2 1 300 2 6 500 3 3 FC 400 MX SN I 4250 Mbaud 850 70 1 8 150 Aail 270 206 FC 1200 MX SN I 10 512 Mbaud 850 33 2 4 82 2 2 300 2 6 RDDTEMD 1300 2000 11 0 2000 6 0 2000 6 0 ANSI X3 166 Table 3 Maximum Channel Distance and Loss for multimode optical fiber application by fiber type The channel is the total cabling link including all patch cords or equipment cords that link the active devices Figure 11 depicts the difference between channel and permanent link The permanent link describes the link that is considered a permanent part of the building NETWORK VISION or datacenter infrastructure The network equipment is connected to the permanent link using patch cords or equipment cords Care should be taken to select cords made of the same fiber type as the permanent link optical fiber cabling ea amnel 3 Permanent link Network equipment ae Il cP oe Fixed cabling Equipment Equipment cog Patch cord cord Figure 11 The channel represents the end to end link connecting transmitter and receiver The fixed cabling a subseg
74. the test result The difference in length between the TRCs and the combined length of the equipment cords represents a very small error in loss of 0 0035 dB per meter If we believe that the mated loss between the link under test and the TRCs is lower than the loss with patch cords the test in Figure 12 understates the channel loss somewhat Fluke Networks expects this difference to be much less than the assumptions made in IEC 14763 3 Channel i Test reference cord Patch cord Test reference cord Figure 12 The end connections in Fig 12 are not part of the channel specification By replacing the equipment cords with the Test Reference Cords TRCs for the channel loss and length measurement the error in the loss measurement is represented by the difference in length between one TRC and the sum of the two equipment cords used to complete the channel 1 m of cord represents 0 0035 dB Optical fiber link polarity Local area network installations support bi directional communication by using separate optical fibers in each direction The cabling system shall provide means to maintain correct signal polarity so that the transmitter on one end of the channel will connect to the re ceiver on the other end of the channel Several methods are used to maintain polarity for optical fiber cabling systems Guidelines are described and illustrated in Annex B of TIA 568 C 0 Duplex connector types and array connector systems that
75. to set the reference The implementation of the loss measurement principle shown in Figures 13 and 14 is the one jumper method One jumper or one TRC is used to set the reference This method is preferred for the loss test of all premises wiring cabling These cabling systems are characterized by relatively short fiber lengths but may contain several connections As the example loss calculation in Table 2 demonstrates the maximum loss allowed in a short 300 m link by the two connectors is 1 5 dB out of the total budget of 2 55 dB the connecting hardware loss constitutes 59 This underscores the need to make sure that all connection losses must be properly included in the loss measurement NETWORK VISION When we analyze the reference method shown in Figure 13 the TRC does not introduce a connection between the light source and power meter The TRC connects to each device but does not add any connections Follow the light path between light source and power meter in Figure 14 to realize that the loss in connection C1 the loss in the link under test and the loss in connection C2 are fully accounted for in the measurement The loss measurement also includes the loss of the Added TRC The maximum loss represented in a 2 m TRC is 0 007 dB Table 1 shows that the maximum loss for the fiber types used in premises wiring is 3 5 dB km or 0 0035 dB m Another difference between the refer ence measurement and the link loss measurement
76. tor name job name etc NETWORK VISION b Select Fiber Loss from the Setup screen as shown in Figure 18a Under this setup screen you will choose from a menu of standards to select the correct limits Select the Test limit option as shown in Fig 18b Note that the selected fiber type limits the test limit choices Popular fiber types are also included in the instrument menu As Figure 18b shows the same setup screen allows you to select the Remote End Setup When using the DTX Smart Remote equipped with the fiber test module select Smart Remote as we have done in this example In this mode the tester automatically measures the length of the link under test Lastly this screen provides the option to tell the tester whether you need to test the link under test in both directions If this is the case remem ber never to disconnect the TRC from the test modules always swap the TRC at the connection with the link under test Choose a reference method and set a reference As described earlier setting a reference is a critical aspect of a loss test to obtain accurate test results The power meter and light source are connected together and the power level is measured by the light meter to establish the reference for loss calculations The steps for setting a reference are as follows Step A Turn the rotary switch to Special Functions and choose Set Reference Step B Now press
77. try of the fiber resulting from the manufacturing process such as rotational asymmetry minor changes in the core diameter or rough boundaries between the core and cladding Mechanical stress tension pressure or twisting of the fiber can also cause microbending Figure 6 depicts microbend ing in a fiber and its effect on the light path NETWORK VISION Es Figure 6 A microbend in an optical fiber causes some light to escape the core which adds to the signal loss The primary cause of macrobending is a curvature with a small radius The standards describe the bend radius limits as follows Cables with four or fewer fibers intended for Cabling Subsystem 1 horizontal or centralized cabling shall support a bend radius of 25 mm 1 in when not subject to tensile load Cables with four or fewer fibers intended to be pulled through pathways during installa Figure 7 A macrobend or bend with a tight bending tion shall support a bend radius of radius cause higher order mode light to escape from 50 mm 2 in under a pull load of the multimode core and thus cause signal loss 220 N 50 lbf All other optical fiber cables shall support a bend radius of 10 times the cable outside diameter when not subject to tensile load and 20 times the cable outside diameter when subject to tensile loading up to the cable s rated limit Figure 7 shows the effect of a bend with smaller radius on the path of the light in the fiber
78. two jumper method and the three jumper method are discussed in Appendix 3 IEC IEC Name in this IEC TIA 526 14A TIA 526 7 61280 4 1 61280 4 2 z 5 document 14763 3 multimode singlemode multimode singlemode One jumper One jumper Method 2 Method A1 Method B Method A 1 Two jumper Method 1 Method A2 Method A Method A 2 Three jumper Three jumper Method 3 Method A3 Method C Method A 3 Table 5 Reference to test method names in the installation standards Launch conditions The goal of any certification measurement is to provide Pass Fail indications the end user and the installation contractor can rely on The launch conditions have proven to have a major influence on the accuracy consistency of optical fiber loss measurements We reviewed that the light in graded index multimode fiber propagates in many modes The number of modes that are excited by the launch and the energy level in each mode affects the power measurements If the launch conditions are not controlled from test tool to test tool each tool may provide a different measurement and test results this is a certain indication that none of them are correct or trustworthy The goal is to control the launch conditions such that compliant test tools produce results that fall within a narrow range around the true loss value Factors that influence the launch conditions LEDs are the preferred light sources to test the link lo
79. ugh bulkheads Figure 28 Optical microscope e Video Figure 29 small optical probe is connected to a handheld display The probe size makes them excellent for examining ports that are in hard to reach places large displays enable easy identification of end face de fects They are also safer as they show an image and not the actual end face being observed reducing the risk of exposing one s eye to harmful radiation Within the context of inspecting fiber optics showing the user what the naked eye cannot see the primary desired attribute is detection capability basically the smallest sized object that it can detect Figure 29 Video microscope NETWORK VISION Cleaning Properly cleaned end faces can ractually add up to 1 39 dB onto your loss allowance Figure 30 In other words if you have a fiber plant with an overall loss of 5 0 dB against a specified budget of 4 5 dB cleaning any dirty end faces may help to drop the link loss down to just above 3 6 dB providing a Pass and plenty of head space Conse quently it is important to choose your cleaning tools and methods wisely while avoiding commonly practiced bad habits Perhaps the most typical mistake is using canned air to blast fiber connectors or ports While helpful for displacing large dust particles it is inef fective on oils residues or tiny static charged particles that are equally detrimental in causing failures Clean fiber end fa
80. ultimode fiber carries less energy in the higher order modes The value of this loss measurement defines the desired overfilled condition when an MPD compliant light source is used The standards specify CPR loss values a CPR index of 1 is the desired and recommended rating for the certification measurements of multimode optical fiber links Mandrel Since test equipment with an MPD compliant light source in combination with TRCs with CPR rating 1 may deliver varying loss test results further steps have been designed to limit this variability in results The use of a mandrel for testing multimode optical fiber links is required in order to obtain more accurate loss measurements The proper mandrel limits measurement uncertainties and enhances the accuracy of the loss measurement A mandrel is a small cylinder with a specified diameter that depends on the core size and the construction of the TRC fiber Table 4 shows the mandrel sizes defined in the ANSI TIA 568 C 0 document for several fiber constructions Fiber core clad 900 um buff 2 0 mm jacketed 2 4 mm jacketed 3 0 mm jacketed ding size um ered fiber mm TRC mm TRC mm TRC mm 50 125 25 23 23 22 62 5 125 20 18 18 17 Table 6 Acceptable mandrel diameters for multimode cable types five wraps The multimode TRC is to be wrapped five times around this cylinder to achieve the desired effect of filtering or stripping the higher undesirable modes from the
81. ure to have a good cleaning kit with you b Once you clean and repair any faults retest the link i If it now passes your test limits save the results and export them to LinkWare for record keeping If you have the FiberInspector option you can also save your clean fiber end face images to the same report Summary OTDR End1 ChannelMap Endface Image Endt End1 DATA CENTER NOT GRADED Scale Rings IV 125 um a T 62 5 Fa W 9um v 250x Magnification 400 Magnification Larger Image Figure 27d ii If you would like to do a before and after comparison you can use Trace Overlay to display Note that with some basic testing knowledge efficient first line troubleshooting can also be done with an LSPM kit For example basic polarity verification can be conducted using the SimpliFiber Pro Fiber Test Kit s FindFiber feature This same capability can also greatly simplify the normally time consuming and personnel intensive project of cable identifica tion between patch panels Using FindFiber Remote ID sources a single technician can complete end to end testing by plugging them into the port s to be tested before check ing the ports on the distant end with the SimpliFiber Pro power meter to read the unique identifying signals transmitted by the FindFiber sources NETWORK VISION As an instrument that tests from one end of a fiber plant to the other the LSPM can also be used to narro
82. w down any questionable connections By leaving a light source at one end a technician can systematically disassemble a link by disconnecting each component at the connectors to inspect and clean the fiber end face before testing the plant up until that point If the loss measurement is within expectations you can reconnect after inspecting and cleaning the end face of the link to be mated of course and repeat at the next connection down the line until the problem point is identified and corrected Detecting intermittent power fluctuations is also a common issue where an LSPM can troubleshoot Whether it is a faulty switch or a shoddy connection into the back end of a connector power fluctuations are problematic but difficult to detect and capture because they are so fleeting However the Min Max feature on the SimpliFiber Pro power meter helps you to ensure that transmission is stable over a link by automating the precision tracking of its power level By providing the upper and lower bounds of a wavelength measurement throughout the duration of a testing session you attain better visibility into where any trouble points may be 9 End Face Inspection and Cleaning Inspection Proper inspection helps in detecting two of the most common yet easiest to prevent causes of failure damaged and dirty fiber end faces Damage occurs in the form of chips scratches cracks and pits to the core or cladding and can result from mating c
83. when we measure passive cabling and since the standards use the name Loss the negative sign is omitted in reporting the cabling loss in dB An absolute power level is typically expressed in watt and its multiples like megawatt in the electrical power generation world or fractions of a watt like milliwatt or even microwatt in electronics In the communication field an absolute power level P is often expressed as a ratio to one milliwatt mW using the decibel We apply the formula stated above but replace the reference input power level with the absolute power level of 1 mW 1 dBm 10 x log P mW The m in the symbol dBm indicates a power level referenced to one milliwatt Note the dB scale is not a linear scale as the numbers in the table below demonstrate Power output as a dB loss of the power Input of power lost 1 79 21 2 63 37 3 50 50 1 2 5 32 68 6 25 75 1 4 7 20 80 1 5 10 10 90 1 10 15 3 2 96 8 1 30 20 1 99 1 100 30 0 1 99 9 1 1000 Table 4 Decibel expresses a ratio between two power levels The logarithm of the ratio turns this unit non linear NETWORK VISION Set the reference principle The principle of the loss measurement is based on the difference of two power measure ments Figures 13 and 14 show the principle of the fiber loss measurement of a link In Figure 13 the light source is connected to the power meter w
84. where the glass is crushed or cracked in an optical fiber Intersymbol interference ISI Disturbed Signal is a fault that is usually the result of poor system design A system that is not certified with the application standard in mind is susceptible to ISI Modal dispersion from violation of distance limitations on multimode fibers Reflections from too many highly reflective connectors causing increased bit errors due to excessive return loss Troubleshooting basics e Keep it clean Dirty connections are the worst cause of failing connections and testing challenges Clean fibers each time they are connected You can verify that fibers are clean by using an instrument such as a FiberInspector microscope to examine fiber end faces Dust blocks light transmission Finger oil reduces light transmission Dirt on fiber connectors spreads to other connections Contaminated end faces make testing difficult Remember to inspect equipment ports as these equipment ports routers switches NICs get dirty too Use the correct test setup Test standard per specifications will ensure that you get the most accurate consistent understandable and repeatable results Use recommended fiber mandrels to improve loss measurement accuracy and repeatability High quality TRCs and launch fibers should always be used Use of random questionable quality test cords should always be avoided AIL TRCs for loss testing should come with good test
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