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1. Equipment Operation Verification Operation Verification CAUTION Interferometric Test This test verifies the existence of two interfering optical paths in the Agilent 11980A Lightwave signal analyzer Agilent 71400C shown or Agilent 83810A Lightwave SOUrCe 1 2 Agilent 83400A Synthesized sweeper Agilent 8340 41 or Agilent 83620 or Agilent 8341B Single mode optical cables See Table 5 1 on page 5 2 RF cable APC 3 5 m eee Agilent 11500E SYNTHESIZED SWEEPER FIBER OPTIC INTERFEROMETER Ro wh O agnma oo 0000 0000 cuo 566 CO 9000 Figure 5 2 Interferometric Test Setup Do not exceed the limitations of the laser s maximum input RF modulation power Refer to the laser s operation manual for information on its maximum input RF modulation power 5 5 Procedure Operation Verification Operation Verification Connect the system as shown in Figure 5 2 Set Agilent 71400C reference level and attenuator to appropriate values Set the Agilent 71400C controls as follows Start Frequency 12 MHz Stop FREQUENCY 2 he nw oo 20 MHz Reference level 0 0 0 0 eres 0 dBm Optical Attenuator 7dB ach eure 5 dB div Resolution Bandwidth Lee ee ee ee eens 302. Specifications Specifications Specifications Table 2 1 lists specifications for the Agilent 11980A An asterisk placed after an entry indicates that it is a supplemental characteristic Characteristics are not specifications they are included as additional information for the user Table 2 1 Agilent 11980A Specifications Optical Insertion Loss lt 8 dB at 1320 nm lt 8 dB at 1550 nm Wavelength Range 1250 nm to 1600 nm Delay Time 3 5 US Delay Time Option 005 25 Us Connectors Single mode optical Maximum Input Power 250 mW as limited by lightwave analyzer Temperature Range Operating 0 C to 55 C Storage 40 to 75 C Weight Net 1 9 kg 4 2 Ib Shipping 3 2 kg 7 b Weight Option 005 Net 2 3 kg 5 Ib Shipping 3 5 kg 7 8 b Maximum Dimensions 105 mm H x 215 mm W x 290 mm L 4 1 in Hx 8 5 in W x 11 4 in L a Unmated condition at temperatures above 55 C connectors will be damaged if mated 2 2 Front Panel Knob 3 2 Connector Care 3 2 Cleaning Connections for Accurate Measurements 3 3 User Precautions CAUTION CAUTION User Precautions Front Panel Knob Front Panel Knob The front panel polarization adjust knob will break if it is turned with too much force Do not continue to turn the knob past its stops Connector Care Do not touch the tips of the front panel input or output connectors The optical interface of the Agilent 11980A is composed
3. straight a line as possible Tipping and inserting at an angle can scrape material off the inside of the connector or even break the inside sleeve of connectors made with ceramic material When inserting a fiber optic connector into a connector make sure that the fi ber end does not touch the outside of the mating connector or adapter e Avoid over tightening connections Unlike common electrical connections tighter is not better The purpose of the connector is to bring two fiber ends together Once they touch tightening only causes a greater force to be applied to the delicate fibers With connec tors that have a convex fiber end the end can be pushed off axis resulting in misalignment and excessive return loss Many measurements are actually improved by backing off the connector pressure Also if a piece of grit does happen to get by the cleaning procedure the tighter connection is more likely to damage the glass Tighten the connectors just until the two fibers touch 3 8 User Precautions Cleaning Connections for Accurate Measurements e Keep connectors covered when not in use e Use fusion splices on the more permanent critical nodes Choose the best con nector possible Replace connecting cables regularly Frequently measure the return loss of the connector to check for degradation and clean every connec tor every time All connectors should be treated like the high quality lens of a good camera The weak link in
4. 0448 ii CAUTION CAUTION CAUTION CAUTION CAUTION CAUTION General Safety Considerations Before switching on this instrument make sure that the line voltage selector switch is set to the line voltage of the power supply and the correct fuse is installed Assure the supply voltage is in the specified range This product is designed for use in Installation Category and Pollution Degree 2 per IEC 1010 and 664 respectively VENTILATION REQUIREMENTS When installing the product in a cabinet the convection into and out of the product must not be restricted The ambient temperature outside the cabinet must be less than the maximum operating temperature of the product by 4 C for every 100 watts dissipated in the cabinet If the total power dissipated in the cabinet is greater than 800 watts then forced convection must be used Always use the three prong ac power cord supplied with this instrument Failure to ensure adequate earth grounding by not using this cord may cause instrument damage Do not connect ac power until you have verified the line voltage is correct Damage to the equipment could result This instrument has autoranging line voltage input Be sure the supply voltage is within the specified range Measurement accuracy it s up to you Fiber optic connectors are easily damaged when connected to dirty or damaged cables and accessories The Agilent 11980A front panel OPTIC
5. Cap for adapter HMS 10 5040 9361 5 Option 012 Adapter FC PC 08154 61702 4 Dust Cap for adapter FC PC 5040 9365 9 Option 013 Adapter DIN 47256 08154 61703 5 Dust Cap for adapter DIN 47256 5040 9364 8 Option 014 Adapter ST 08154 61704 6 Dust Cap for adapter ST 5040 9366 0 Option 015 Adapter Biconic 08154 61705 7 Dust Cap for adapter Biconic N A N A 6 2
6. Eus al a erai usi rs nl 1 SPAN GH R8 3 80 HH 3 88 kHz ST 7 334 Figure 4 4 Chirp Under Sinusoidal Modulation Modulation frequency 100 MHz 4 6 Operation Applications Figure 4 5 shows the Bessel function nature of the modulated DFB laser Null ing the first or second Bessel sideband occurring at FM modulation indexes of 2 4 and 3 8 respectively allow full FM characterization of the single line laser Note that the width of each sideband is the linewidth of the laser Thus linewidth can be viewed with laser modulation away from the 0 Hz axis AL 25 ae dBa E T T T usb us i E i ER BENE E Coy je f UNE 28 ee eee eee p uus ws re eas ME NN I Dni STAR RI RB 1 88 MHz UB 3 88 kHz 3 388 sec Figure 4 5 FM Sidebands Shown Low Level Chirp Modulation frequency 500 MHz 4 7 Operation Verification 5 2 Optical Insertion Loss Test 5 3 Interferometric Test 5 5 Operation Verification Test Equipment Operation Verification Operation verification for the Agilent 11980A consists of an optical insertion loss test and an interferometric test These tests verify the Agilent 11980A s optical integrity Interferometers with excessive inser
7. examination and return loss measurements are the best way to ensure good measurements Good cleaning practices can help ensure that optimum connector performance is maintained With glass to glass interfaces any degradation of a ferrule or the end of the fiber any stray particles or finger oil can have a significant effect on connector performance Where many repeat connections are required use of a connector saver or patch cable is recommended Figure 3 4 shows the end of a clean fiber optic cable The dark circle in the center of the micrograph is the fiber s 125 um core and cladding which carries the light The surrounding area is the soft nickel silver ferrule Figure 3 5 shows a dirty fiber end from neglect or perhaps improper cleaning Material is smeared and ground into the end of the fiber causing light scattering and poor reflection Not only is the precision polish lost but this action can grind off the glass face and destroy the connector Figure 3 6 shows physical damage to the glass fiber end caused by either repeated connections made without removing loose particles or using improper cleaning tools When severe the damage of one connector end can be transferred to another good connector endface that comes in contact with the damaged one Periodic checks of fiber ends and replacing connecting cables after many connections is a wise practice The cure for these problems is disciplined connector care as described in the followi
8. kHz Video Bandwidth pee EYE e pa ede 30 kHz Ronee CEG DE Ra bes MAX HOLD Sweep the modulation frequency of the modulation source between 12 MHz and 20 MHz The Agilent 71400C should have a display similar to that shown in Figure 5 3 Reference level and attenuator values can be adjusted to position the trace for the particular laser output power that is being used The nulls represent can cellation effects due to the separate paths available to the optical energy and indicate continuity in both optical paths of the interferometer If the displayed trace does not indicate any nulls then the test has failed 5 6 INNO n Replaceable Parts Replaceable Parts Replaceable Parts Replaceable Parts The Agilent 11980A contains no user serviceable parts Opening the inner sheetmetal cover voids your warranty The label affixed to the inner cover must be left intact in for Agilent Technologies to service your unit if the label is not intact any servicing required will not be covered by warranty The Agilent 11980A has three replaceable parts the optical interface adapter adapter dust cap and the front panel knob The part numbers are shown in Table 6 1 Table 6 1 Agilent 11980A Replaceable Parts Description Agilent Part Number cD Front panel knob 0370 2389 7 Option 011 Adapter HMS 10 08154 61701 3 Dust
9. or lens paper Cotton swabs can be used as long as no cotton fibers remain on the fiber end after cleaning Clean the ferrules and other parts of the connector while avoiding the end of the fiber 3 Apply isopropyl alcohol to a new clean lint free cotton swab or lens paper Clean the fiber end with the swab or lens paper Do not scrub during this initial cleaning because grit can be caught in the swab and become a gouging element Immediately dry the fiber end with a clean dry lint free cotton swab or lens paper Blow across the connector end face from a distance of 6 to 8 inches using filtered dry compressed air Aim the compressed air at a shallow angle to the fiber end face Nitrogen gas or compressed dust remover can also be used CAUTION User Precautions Cleaning Connections for Accurate Measurements Do not shake tip or invert compressed air canisters because this releases particles in the can into the air Refer to instructions provided on the compressed air canister As soon as the connector is dry connect or cover it for later use If the performance after the initial cleaning seems poor try cleaning the con nector again Often a second cleaning will restore proper performance The second cleaning should be more arduous with a scrubbing action To clean an adapter The fiber optic input and output connectors on many Agilent Technologies instruments employ a universal adapter such as those show
10. sometimes as little as 0 1 dB of loss with high performance con nectors Return loss is a measure of reflection the less reflection the better the larger the return loss the smaller the reflection The best physically contacting connectors have return losses better than 50 dB although 30 to 40 dB is more common 3 9 WARNING CAUTION User Precautions Cleaning Connections for Accurate Measurements Visual inspection of fiber ends Visual inspection of fiber ends can be helpful Contamination or imperfections on the cable end face can be detected as well as cracks or chips in the fiber itself Use a microscope 100X to 200X magnification to inspect the entire end face for contamination raised metal or dents in the metal as well as any other imperfections Inspect the fiber for cracks and chips Visible imperfec tions not touching the fiber core may not affect performance unless the imperfections keep the fibers from contacting Always remove both ends of fiber optic cables from any instrument system or device before visually inspecting the fiber ends Disable all optical sources before disconnecting fiber optic cables Failure to do so may result in permanent injury to your eyes Cleaning Connectors The procedures in this section provide the proper steps for cleaning fiber optic cables and Agilent Technologies universal adapters The initial cleaning using the alcohol as a solvent gently removes any grit
11. AL OUT connector is no excep tion When you use improper cleaning and handling techniques you risk expensive instrument repairs damaged cables and compromised measurements Before you connect any fiber optic cable to the Agilent 11980A refer to Cleaning Con nections for Accurate Measurements on page 3 3 iv Contents General Information Description 1 2 Options 1 3 Initial Inspection 1 4 Returning the Instrument for Service 1 5 Preparing the instrument for shipping 1 5 Agilent Technologies Service Offices 1 8 Specifications Specifications 2 2 User Precautions Front Panel Knob 3 2 Connector Care 3 2 Cleaning Connections for Accurate Measurements 3 3 Choosing the Right Connector 3 3 Inspecting Connectors 3 6 Cleaning Connectors 3 10 Operation Theory of Operation 4 2 Applications 4 3 Static Linewidth Measurement 4 3 Chirp and FM Measurements 4 5 Operation Verification Operation Verification 5 2 Optical Insertion Loss Test 5 3 Interferometric Test 5 5 Replaceable Parts Replaceable Parts 6 2 Contents 1 Description 1 2 Options 1 3 Initial Inspection 1 4 Returning the Instrument for Service 1 5 Agilent Technologies Service Offices 1 8 General Information General Information Description Description The Agilent 11980A fiber optic interferometer is a Mach Zehnder interferome ter built with a fixed length of single mode optical fiber The Agilent 11980A splits the opt
12. Agilent 11980A Fiber Optic Interferometer Operation and Service Manual s Agilent Technologies Copyright Agilent Technologies 2000 All Rights Reserved Repro duction adaptation or trans lation without prior written permission is prohibited except as allowed under copy right laws Agilent Part No 11980 90012 Printed in USA April 2000 Agilent Technologies Lightwave Division 1400 Fountaingrove Parkway Santa Rosa CA 95403 1799 USA 707 577 1400 Notice The information contained in this document is subject to change without notice Com panies names and data used in examples herein are ficti tious unless otherwise noted Agilent Technologies makes no warranty of any kind with regard to this material includ ing but not limited to the implied warranties of mer chantability and fitness for a particular purpose Agilent Technologies shall not be lia ble for errors contained herein or for incidental or conse quential damages in connec tion with the furnishing performance or use of this material Restricted Rights Legend Use duplication or disclo sure by the U S Government is subject to restrictions as set forth in subparagraph c 1 Gi of the Rights in Technical Data and Computer Software clause at DFARS 252 227 7013 for DOD agencies and sub paragraphs c 1 and c 2 of the Commercial Computer Software Restricted Rights clause at FAR 52 227 19 for other agencies Warra
13. and oil If a caked on layer of material is still present this can happen if the beryllium copper sides of the ferrule retainer get scraped and deposited on the end of the fiber during insertion of the cable a second cleaning should be performed It is not uncommon for a cable or connector to require more than one cleaning Agilent Technologies strongly recommends that index matching compounds not be applied to their instruments and accessories Some compounds such as gels may be difficult to remove and can contain damaging particulates If you think the use of such compounds is necessary refer to the compound manufacturer for information on application and cleaning procedures Table 3 1 Cleaning Accessories Item Agilent Part Number Pure isopropyl alcohol Cotton swabs 8520 0023 Small foam swabs 9300 1223 Compressed dust remover non residue 8500 5262 3 10 CAUTION User Precautions Cleaning Connections for Accurate Measurements Table 3 2 Dust Caps Provided with Lightwave Instruments Item Agilent Part Number Laser shutter cap 08145 64521 FC PC dust cap 08154 44102 Biconic dust cap 08154 44105 DIN dust cap 5040 9364 HMS10 dust cap 5040 9361 ST dust cap 5040 9366 To clean a non lensed connector Do not use any type of foam swab to clean optical fiber ends Foam swabs can leave filmy deposits on fiber ends that can degrade performance Apply pure isopropyl alcohol to a clean lint free cotton swab
14. ard Case Soft center 4 125 um Fiber Centered to abou 0 2 microns Figure 3 3 Cross section of the Diamond HMS 10 connector The nickel silver allows an active centering process that permits the glass fiber to be moved to the desired position This process first stakes the soft nickel silver to fix the fiber in a near center location then uses a post active staking to shift the fiber into the desired position within 0 2 um This process plus the keyed axis allows very precise core to core alignments This connector is found on most Agilent Technologies lightwave instruments 3 5 User Precautions Cleaning Connections for Accurate Measurements The soft core while allowing precise centering is also the chief liability of the connector The soft material is easily damaged Care must be taken to mini mize excessive scratching and wear While minor wear is not a problem if the glass face is not affected scratches or grit can cause the glass fiber to move out of alignment Also if unkeyed connectors are used the nickel silver can be pushed onto the glass surface Scratches fiber movement or glass contamina tion will cause loss of signal and increased reflections resulting in poor return loss Inspecting Connectors Because fiber optic connectors are susceptible to damage that is not immedi ately obvious to the naked eye poor measurements result without the user being aware Microscopic
15. ation and to maintain the product safe condition If this instrument is not used as specified the protection provided by the equipment could be impaired This instrument must be used in a normal condition in which all means for protection are intact only No operator serviceable parts inside Refer servicing to qualified personnel To prevent electrical shock do not remove covers To prevent electrical shock disconnect the Agilent 11980A from mains before cleaning Use a dry cloth or one slightly dampened with water to clean the external case parts Do not attempt to clean internally This is a Safety Class 1 product provided with a protective earthing ground incorporated in the power cord The mains plug shall only be inserted in a socket outlet provided with a protective earth contact Any interruption of the protective conductor inside or outside of the product is likely to make the product dangerous Intentional interruption is prohibited For continued protection against fire hazard replace line fuse only with same type and ratings type T 0 315A 250V for 100 120V operation and 0 16A 250V for 220 240V operation The use of other fuses or materials is prohibited Verify that the value of the line voltage fuse is correct For 100 120V operation use an IEC 127 5x20 mm 0 315 A 250 V Agilent part number 2110 0449 For 220 240V operation use an IEC 127 5x20 mm 0 16 A 250 V Agilent Technologies part number 2110
16. chanical assembly that holds the ferrule in position against another identical ferrule Connectors also vary in the polish curve and concentricity of the core within the cladding Mating one style of cable to another requires an adapter Agilent Technologies offers adapters for most instruments to allow testing with many different cables Figure 3 1 on page 3 4 shows the basic components of a typical connectors The system tolerance for reflection and insertion loss must be known when selecting a connector from the wide variety of currently available connectors Some items to consider when selecting a connector are How much insertion loss can be allowed Will the connector need to make multiple connections Some connectors are better than others and some are very poor for making repeated connections What is the reflection tolerance Can the system take reflection degradation Is an instrument grade connector with a precision core alignment required Is repeatability tolerance for reflection and loss important Do your specifica 3 3 User Precautions Cleaning Connections for Accurate Measurements tions take repeatability uncertainty into account e Will a connector degrade the return loss too much or will a fusion splice be re quired For example many lasers cannot operate with reflections from connectors Often as much as 90 dB isolation is needed Connecting Body and Ferrule 2 5 mm Mechanical Retainer Fiber 125 u
17. chnologies specifically dis claims the implied warranties of merchantability and fitness for a particular purpose Exclusive Remedies The remedies provided herein are buyer s sole and exclusive remedies Agilent Technolo gies shall not be liable for any direct indirect special inci dental or consequential dam ages whether based on contract tort or any other legal theory Safety Symbols CAUTION The caution sign denotes a hazard It calls attention to a procedure which if not cor rectly performed or adhered to could result in damage to or destruction of the product Do not proceed beyond a cau tion sign until the indicated conditions are fully under stood and met WARNING The warning sign denotes a hazard It calls attention to a procedure which if not cor rectly performed or adhered to could result in injury or loss of life Do not proceed beyond a warning sign until the indicated conditions are fully understood and met The instruction man A ual symbol The prod uct is marked with this warning symbol when it is necessary for the user to refer to the instructions in the manual The laser radiation symbol This warning symbol is marked on products which have a laser output The AC symbol is used to indicate the required nature of the line module input power The ON symbols are used to mark the posi tions of the instrument power line switch O The OFF symbols are u
18. e length in its 1250 nm to 1600 nm operating range Equipment Lightwave 5 Agilent 83400A Optical average power meter Agilent 8153A shown or Agilent 8152A Single mode optical fiber patch cords and adapters see Table 5 1 on page 5 2 FIBER OPTIC INTERFEROMETER POWER METER LIGHTWAVE SOURCE LASER OUTPUT Figure 5 1 Insertion Loss Test Setup CAUTION Do not touch the tips of the front panel input or output connectors The optical interface on the Agilent 11980A is composed of precision polished single mode connectors that are easily scratched Any damage to the optical interface will increase the insertion loss of the Agilent 11980A and damage the connector interfaces 1 Note that the Agilent 71400C 71401C lightwave signal analyzer has a built in optical power meter 5 3 Procedure Operation Verification Operation Verification Allow the laser and power meter to warm up until sufficiently stabilized any drifts in these instruments will cause measurement errors Set the power meter s wavelength calibration to the appropriate setting Connect the laser to the power meter via a single mode fiber cable Record the optical power Connect the Agilent 11980A as shown in Figure 5 1 Record the optical power 5 Calculate the difference between the two readings This value is the insertion loss which must be less than 8 dB 5 4 Description
19. easurement The presence of the gate function allows for the continuous addition of the laser in its modulated and unmodulated states at the optical detector in a lightwave signal analyzer This results in the display of the homodyne spectrum of the optical electric field Figure 4 4 shows a chirp measurement using this tech nique This DFB laser chirped 10 GHz under the applied 100 MHz sinusoidal modulation Note that with the laser acting as a local oscillator the minimum optical resolution bandwidth of the measurement is limited by the laser line width as shown in Figure 4 5 Lightwave signal analyzer Agilent 71400C shown or Agilent 83810A Synthesized Agilent 8340 41 or Agilent 83620 Function Agilent 3312A 4 5 Operation Applications FIBER OPTIC LASER UNDER TEST INTERFEROMETER ISOLATOR MODULATED LIGRT COUPLED LIGHTWAVE SIGNAL ANALYZER SYNTHESIZED SWEEPER GATED RF MODULAT ON our os 0000 op 0000 locos naso ob OPTICAL INPUT MODULAT I ON INPUT FUNCT1ON GENERATOR 147 kHz or 20 kHz OPT 001 SQUARE WAVE Figure 4 3 Typical Modulated Laser Power Spectrum Test Setup for Chirp Measurement RL 15 B d n MKR 1 FRQ 11 88 GHz
20. ervice Sealed Air Corporation Commerce California 90001 Air Cap looks like a plastic sheet filled with air bubbles Use the pink antistatic Air Cap to reduce static electricity Wrapping the instrument several times in this ma terial will protect the instrument and prevent it from moving in the carton 4 Seal the carton with strong nylon adhesive tape 5 Mark the carton FRAGILE HANDLE WITH CARE 6 Retain copies of all shipping papers 1 7 General Information Agilent Technologies Service Offices Agilent Technologies Service Offices Before returning an instrument for service call the Agilent Technologies Instrument Support Center at 800 403 0801 visit the Test and Measurement Web Sites by Country page at http www tm agilent com tmo country English index html or call one of the numbers listed below Agilent Technologies Service Numbers Austria Belgium Brazil China Denmark Finland France Germany India Italy Ireland Japan Korea Mexico Netherlands Norway Russia Spain Sweden Switzerland United Kingdom United States and Canada 01 25125 7171 32 2 778 37 71 11 7297 8600 86 10 6261 3819 45 99 12 88 358 10 855 2360 01 69 82 66 66 0180 524 6330 080 34 35788 39 02 9212 2701 01 615 8222 81 426 56 7832 82 2 3770 0419 5 258 4826 020 547 6463 227357 59 7 095 797 3930 34 91 631 1213 08 5064 8700 01 735 7200 01 344 366666 800 403 0801 1 8 Specifications
21. ervice on page 1 5 If the shipping container is damaged or the cushioning material shows signs of stress notify the carrier as well as the Agilent Technologies office Refer to Agilent Technologies Service Offices on page 1 8 Keep the shipping materials for the carrier s inspection Agilent Technologies will arrange for repair or replacement without waiting for a claim settlement 1 4 General Information Returning the Instrument for Service Returning the Instrument for Service The instructions in this section show you how to properly return the instru ment for repair or calibration Always call the Agilent Technologies Instrument Support Center first to initiate service before returning your instrument to a service office This ensures that the repair or calibration can be properly tracked and that your instrument will be returned to you as quickly as possi ble Call this number regardless of where you are located Refer to Agilent Technologies Service Offices on page 1 8 for a list of service offices Agilent Technologies Instrument Support Center 800 403 0801 If the instrument is still under warranty or is covered by an Agilent Technolo gies maintenance contract it will be repaired under the terms of the warranty or contract the warranty is at the front of this manual If the instrument is no longer under warranty or is not covered by an Agilent Technologies mainte nance plan Agilent Technol
22. ical energy into two paths delaying one path with respect to the other and recombines them in a second optical coupler A polarization adjust ment helps align the optical fields for maximum interference as shown in Figure 1 1 The Agilent 11980 is a lightwave accessory for use with the Agilent 71400C 71401C and 83810A lightwave signal analyzers The Agilent 11980A allows you to measure linewidth chirp and FM characteristics of single line lasers INPUT gt OUTPUT COUPLER COUPLER POLARIZATION ADJUST Figure 1 1 Agilent 11980A Fiber Optic Interferometer Simplified Schematic 1 2 General Information Options Options Several options are available when ordering the Agilent 11980A Option 005 lengthens the delay line from 760 meters to 5 2 kilometers al lowing measurement of narrower linewidths Options 011 through 015 allow you to order your choice of several optical connector interfaces This makes it simple to interface to your connector standard Table 1 1 lists the available connector interface families Table 1 1 Agilent 11980A Connector Options Option Agilent Part Number Interface Standard 011 810001 HMS 10 012 81000 FC PC 013 810005 DIN 47256 014 81000VI ST 015 81000WI Biconic a Includes dust cap 1 3 General Information Initial Inspection Initial Inspection If the shipment contents are incomplete or damaged refer to Returning the Instrument for S
23. instrument and system reliability is often the inappropriate use and care of the connector Because current connectors are so easy to use there tends to be reduced vigilance in connector care and cleaning It takes only one missed cleaning for a piece of grit to permanently damage the glass and ruin the connector Measuring insertion loss and return loss Consistent measurements with your lightwave equipment are a good indica tion that you have good connections Since return loss and insertion loss are key factors in determining optical connector performance they can be used to determine connector degradation A smooth polished fiber end should pro duce a good return loss measurement The quality of the polish establishes the difference between the PC physical contact and the Super PC con nectors Most connectors today are physical contact which make glass to glass connections therefore it is critical that the area around the glass core be clean and free of scratches Although the major area of a connector excluding the glass may show scratches and wear if the glass has maintained its polished smoothness the connector can still provide a good low level return loss con nection If you test your cables and accessories for insertion loss and return loss upon receipt and retain the measured data for comparison you will be able to tell in the future if any degradation has occurred Typical values are less than 0 5 dB of loss and
24. l connectors that were originally covered when you first received the instrument Cover electrical connectors to protect sensitive components from electrostatic damage Cover optical connectors to protect them from damage due to physical contact or dust Instrument damage can result from using packaging materials other than the original materials Never use styrene pellets as packaging material They do not adequately cushion the instrument or prevent it from shifting in the carton They may also cause instrument damage by generating static electricity Pack the instrument in the original shipping containers Original materials are available through any Agilent Technologies office Or use the following guidelines Wrap the instrument in antistatic plastic to reduce the possibility of damage caused by electrostatic discharge Forinstruments weighing less than 54 kg 120 Ib use a double walled cor rugated cardboard carton of 159 kg 350 Ib test strength The carton must be large enough to allow approximately 7 cm 3 inches on all sides of the instrument for packing material and strong enough to accom modate the weight of the instrument e Surround the equipment with approximately 7 cm 8 inches of packing ma terial to protect the instrument and prevent it from moving in the carton If packing foam is not available the best alternative is S D 240 Air Cap from 1 6 General Information Returning the Instrument for S
25. m actual fiber s diameter is smaller than a human hair Alignment Key Figure 3 1 Basic components of a connector Over the last few years the FC PC style connector has emerged as the most popular connector for fiber optic applications While not the highest perform ing connector it represents a good compromise between performance reli ability and cost If properly maintained and cleaned this connector can withstand many repeated connections However many instrument specifications require tighter tolerances than most connectors including the FC PC style can deliver These instruments cannot tolerate connectors with the large non concentricities of the fiber common with ceramic style ferrules When tighter alignment is required Agilent Technologies instruments typically use a connector such as the Diamond HMS 10 which has concentric tolerances within a few tenths of a micron Agi lent Technologies then uses a special universal adapter which allows other cable types to mate with this precision connector See Figure 3 2 3 4 User Precautions Cleaning Connections for Accurate Measurements Figure 3 2 Universal adapters to Diamond HMS 10 The HMS 10 encases the fiber within a soft nickel silver Cu Ni Zn center which is surrounded by a tough tungsten carbide casing as shown in Figure 3 3 Staking Groove Fixing oper Secondary Staking Active Centering Tun gsten Carbide Nickel Silver H
26. m analyzer the combined beams are cabled to the out put connector on the Agilent 11980A This signal can then be analyzed by a lightwave signal analyzer 4 2 Operation Applications Applications The Agilent 11980A can enhance the capability of a lightwave signal analyzer such as the Agilent 71400C 71401C or 83810A to allow measurement of laser linewidth and chirp Normally the lightwave signal analyzer by itself is capable of measuring only intensity modulation IM However with the Agilent 11980A accessory it is possible to measure the total spectrum of a modulated single mode laser Two examples are described in this section The static linewidth of a single mode laser is measured using the delayed self homodyne technique Chirp is measured by using the gated delayed self homodyne technique Static Linewidth Measurement Figure 4 1 shows the experimental setup for measurement of the unmodu lated linewidth of a single mode laser In using the delayed self homodyne technique the underlying assumption is that the delay in the interferometer is long enough to display less than 10 error in the linewidth due to the coher ence length of the laser Errors greater than 10 occur when the expression 2nAvt is greater than 5 where Av is the linewidth of the laser under test and t is the delay of the interferometer Thus the standard Agilent 11980A is capable of measuring static laser line widths down to approxima
27. n in the following picture These adapters allow you to connect the instrument to different types of fiber optic cables Figure 3 7 Universal adapters Apply isopropyl alcohol to a clean foam swab Cotton swabs can be used as long as no cotton fibers remain after cleaning The foam swabs listed in this section s introduction are small enough to fit into adapters Although foam swabs can leave filmy deposits these deposits are very thin and the risk of other contamination buildup on the inside of adapters greatly out weighs the risk of contamination by foam swabs Clean the adapter with the foam swab 3 Dry the inside of the adapter with a clean dry foam swab 4 Blow through the adapter using filtered dry compressed air Nitrogen gas or compressed dust remover can also be used Do not shake tip or invert compressed air canisters because this releases particles in the can into the air Refer to instructions provided on the compressed air canister 3 12 Theory of Operation 4 2 Applications 4 3 Static Linewidth Measurement 4 3 Chirp and FM Measurements 4 5 Operation Operation Theory of Operation Theory of Operation The Agilent 11980A has optical couplers and fiber whose wavelength charac teristics allow the Agilent 11980A to be used throughout the 1250 nm to 1600 nm telecommunications band Operation below 1250 nm will cause amplitude loss The input signal is split into a long path and a short
28. ng list and in Cleaning Connectors on page 3 10 3 6 User Precautions Cleaning Connections for Accurate Measurements Use the following guidelines to achieve the best possible performance when making measurements on a fiber optic system e Never use metal or sharp objects to clean a connector and never scrape the connector e Avoid matching gel and oils 1 o Figure 3 4 Clean problem free fiber end and ferrule gt gt 5 Lom Ee Figure 3 5 Dirty fiber end and ferrule from poor cleaning 3 7 User Precautions Cleaning Connections for Accurate Measurements it ERES A Figure 3 6 Damage from improper cleaning While these often work well on first insertion they are great dirt magnets The oil or gel grabs and holds grit that is then ground into the end of the fiber Also some early gels were designed for use with the FC non contacting con nectors using small glass spheres When used with contacting connectors these glass balls can scratch and pit the fiber If an index matching gel or oil must be used apply it to a freshly cleaned connector make the measurement and then immediately clean it off Never use a gel for longer term connections and never use it to improve a damaged connector The gel can mask the extent of damage and continued use of a damaged fiber can transfer damage to the instrument When inserting a fiber optic cable into a connector gently insert it in as
29. nty This Agilent Technologies instrument product is war ranted against defects in material and workmanship for a period of one year from date of shipment During the war ranty period Agilent Technol ogies will at its option either repair or replace products which prove to be defective For warranty service or repair this product must be returned to a service facility desig nated by Agilent Technolo gies Buyer shall prepay shipping charges to Agilent Technologies and Agilent Technologies shall pay ship ping charges to return the product to Buyer However Buyer shall pay all shipping charges duties and taxes for products returned to Agilent Technologies from another country Agilent Technologies war rants that its software and firmware designated by Agi lent Technologies for use with an instrument will execute its programming instructions when properly installed on that instrument Agilent Tech nologies does not warrant that the operation of the instru ment or software or firmware will be uninterrupted or error free Limitation of Warranty The foregoing warranty shall not apply to defects resulting from improper or inadequate maintenance by Buyer Buyer supplied software or interfac ing unauthorized modifica tion or misuse operation outside of the environmental specifications for the product or improper site preparation or maintenance No other warranty is expressed or implied Agilent Te
30. of precision polished single mode connectors that are easily scratched Any damage to the optical interface will increase the insertion loss of the Agilent 11980A and damage the connector interfaces The precautions listed below will help prevent fiber damage and help ensure accurate measurements Before any mating of fiber optic tips clean the tips to assure that no dust or other particles adhere to them Refer to Cleaning Connections for Accurate Measurements on page 3 3 for further information e Always replace protective dust caps on any exposed fiber optic tip 3 2 User Precautions Cleaning Connections for Accurate Measurements Cleaning Connections for Accurate Measurements Today advances in measurement capabilities make connectors and connec tion techniques more important than ever Damage to the connectors on cali bration and verification devices test ports cables and other devices can degrade measurement accuracy and damage instruments Replacing a dam aged connector can cost thousands of dollars not to mention lost time This expense can be avoided by observing the simple precautions presented in this book This book also contains a brief list of tips for caring for electrical connec tors Choosing the Right Connector A critical but often overlooked factor in making a good lightwave measure ment is the selection of the fiber optic connector The differences in connec tor types are mainly in the me
31. ogies will notify you of the cost of the repair after examining the unit When an instrument is returned to a Agilent Technologies service office for servicing it must be adequately packaged and have a complete description of the failure symptoms attached When describing the failure please be as spe cific as possible about the nature of the problem Include copies of additional failure information such as the instrument failure settings data related to instrument failure and error messages along with the instrument being returned Preparing the instrument for shipping Write a complete description of the failure and attach it to the instrument Include any specific performance details related to the problem The following 1 5 CAUTION CAUTION General Information Returning the Instrument for Service information should be returned with the instrument e Type of service required e Date instrument was returned for repair Description of the problem Whether problem is constant or intermittent Whether instrument is temperature sensitive Whether instrument is vibration sensitive nstrument settings required to reproduce the problem Performance data Company name and return address Name and phone number of technical contact person Model number of returned instrument Full serial number of returned instrument List of any accessories returned with instrument Cover all front or rear pane
32. path The long path about 760 meters for the standard Agilent 11980A and 5 2 kilometers for Option 005 causes the two signals to lose phase coherency above a certain fre quency This frequency is determined by the delay time in the long length of fiber When these two signals are mixed at the photodetector termed a homo dyne process the phase fluctuations are heterodyned or shifted to a 0 Hz IF and displayed on an electrical spectrum analyzer The short path contains the polarization adjustment The polarization adjust ment operates on the principle of rotating an optical birefringence in the plane of propagation of the entering light energy This birefringence is realized by rotating a looped optical fiber The physical stress in the fiber induces a bire fringence in the refractive index properties of the fiber causing a polarization shift This effect is similar to the quarterwave plate used in bulk optics Rotation of the optical birefringence causes the polarization of the fiber s elec tric field to change state Thus you can more closely match the polarization states of the interfering beams The adjustment will not rotate a given polar ization state to any other desired state It will however change the polariza tion state sufficiently to avoid an interference null due to orthogonal polarization states of the interfering beams After adjusting polarization to achieve maximum signal amplitude as seen on the electrical spectru
33. sed to mark the positions of the instru ment power line switch The CE mark is a reg istered trademark of the European Commu nity The CSA mark is reg istered trademark of the Canadian Stan dards Association The C Tick mark is a registered trademark of the Australian Spec trum Management Agency This text denotes the instrument is an Industrial Scientific and Medical Group 1 Class A product ISM1 A Typographical Conven tions The following conventions are used in this book Key type for keys or text located on the keyboard or instrument Softkey type for key names that are displayed on the instru ment s screen Display type for words or characters displayed on the computer s screen or instru ment s display User type for words or charac ters that you type or enter Emphasis type for words or characters that emphasize some point or that are used as place holders for text that you type il WARNING WARNING WARNING WARNING WARNING General Safety Considerations General Safety Considerations This product has been designed and tested in accordance with IEC Publica tion 61010 1 Safety Requirements for Electrical Equipment for Measurement Control and Laboratory Use and has been supplied in a safe condition The instruction documentation contains information and warnings that must be followed by the user to ensure safe oper
34. tely 250 kHz with its delay of 3 5 us while Agilent 11980A Option 005 with more than 5 km of fiber can measure line widths to 32 kHz Linewidths narrower than these may be measured with larger errors in the displayed linewidth 2 4 will produce between 10 and 20 error Note Interferometric errors are in the direction such that the linewidth appears wider than it actually is 4 3 Equipment Operation Applications Figure 4 2 illustrates the measurement on a distributed feedback DFB laser The marker function of the Agilent 71400C lightwave signal analyzer is set to the 3 dB or half power point of the displayed signal This frequency corre sponds to the 3 dB linewidth of the laser See Agilent Application Note 371 Agilent part number 5954 9137 for further application details Lightwave signal analyzer Agilent 71400C shown or Agilent 83810A Isolatot casein band ere Rey n b EY nud Agilent 81210L1 FIBER OPTIC LASER UNDER TEST INTERFEROMETER I SOLATOR LIGHTWAVE SIGNAL ANALYZER Figure 4 1 Static Linewidth Measurement Test Setup 4 4 Equipment Operation Applications 12 00 dDa 1 FRG 26 4 MHz sapo p sr E 198 khz ET 1 88 kHz ST 14 98 cs je Figure 4 2 DFB Linewidth Measurement with Agilent 71400C Chirp and FM Measurements Figure 4 3 shows the experimental setup for chirp or FM m
35. tion loss may pass the interferometric test They can still make useful measurements but will have worse signal to noise ratios than interferometers with acceptable insertion loss Table 5 1 lists test equipment that is illustrated in the Operation Verification test setups Other equipment may be substituted for these instruments if it meets or exceeds the critical specifications listed in the table The Agilent 11980A contains no internal user accessible adjustments or parts The front panel knob and the optical interface adapters are the only external replaceable parts See Chapter 6 Replaceable Parts for part numbers and ordering information Table 5 1 Recommended Test Equipment Instrument Critical Specifications Recommended Model LD source Wavelength 1250 to 1600 nm Agilent 83400A Externally modulatable to 20 MHz Synthesized sweeper Frequency range 12 to 20 MHz Agilent 8340B Output power 0 dBm Agilent 8341B Residual FM lt 1 kHz Agilent 8360 Lightwave signal analyzer No acceptable substitute Agilent 71400C Agilent 83810A Optical average power Optical power accuracy lt 1 Agilent 8152A meter Agilent 8153A Fiber optic cables Single mode fiber 9 125 with any suitable model appropriate connectors between source and Agilent 11980A Operation Verification Operation Verification Optical Insertion Loss Test Description This test measures the optical insertion loss of the Agilent 11980A at a wav
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