1621 & 1623 User Manual Rev D
Contents
1. Open Frequency and Time Response The nanosecond photodetector circuitry is quite straightforward consisting only of the photodiode battery bias and a selectable load resistor The speed limitation of the circuit is established by the junction capacitance of the photodiode and the load resistance Nanosecond Photodetectors General Features and Principles 11 Figure 4 Typical frequency response for the Model 1623 on the 50 setting value Figures 4 and 5 give typical frequency responses and pulse responses for the Model 162X photodetector Gain 10 dB div 400 500 600 0 100 200 300 Frequency M Hz When performing high speed measurements impedance matching effects between your measurement apparatus and the photo detector must be taken into consideration in order to achieve optimal high speed response Typical laboratory measurement equipment may prevent you from achieving nanosecond response times BNC connectors do not match 50 Q transmission lines well for frequencies above 100 MHz The frequency response is therefore not flat between 100 MHz and 500 MHz Above 500 MHz the situation can be worse with typical BNC connectors and cables proving to be quite lossy Therefore while the time response of the nanosecond detector is quite fast it is not expected to provide flat frequency response in the 100 MHz to 500 MHz regime Selecting the internal 50 Q resistor will usually allow you to achieve a2. 1 040 32 Threaded hole 4 03 102 3 NE 8 32 M 4 Threaded insert Nanosecond Photodetectors Characteristics 17 Photodetector Specifications Model 1621 1623 Wavelength Range 350 1000 nm 800 1700 nm Detector Material Type Silicon PIN InGaAs PIN Detector Diameter 0 8 mm 0 1 mm with 1 5 mm diameter ball lens Typical Max Responsivity 0 55 A W at 800 1 0 A W at 1600 nm nm Maximum Optical Power 50 mW 50 mW Load Resistors 50 9 10 kQ and 500 10 kQ and Open user Open user provided provided Typical Rise Time 1 nanosecond 50 Q 1 nanosecond 50 Q setting setting Typical detector capaci 3 pF 0 8 pF tance Electrical Output Connec BNC BNC tor Power Requirements One 9 volt alkaline battery One 9 volt alkaline battery Typical Battery Lifetime gt 500 hours gt 500 hours 18 Characteristics Customer Service Technical Support Information and advice about the operation of any New Focus product is available from our applications engineers For quickest response ask for Technical Support and know the model and serial number for your product Hours 8 00 5 00 PST Monday through Friday excluding holidays Toll Free 1 866 NUFOCUS 1 866 683 6287 from the USA amp Canada only Phone 408 980 5903 Support is also available by fax and email Fax 408 987 3178 Email techsupport new
3. about 0 25 6 4 mm thick A thicker optic can be held in place using the 6 32 nylon tipped set screw Use a 1 16 or 1 5 mm Allen key or ball driver to adjust the set screw The Model 1281 FC fiber adapter allows you to connect an FC connectorized fiber to the front ofthe photodetector The coupling efficiency of light from an optical fiber to the Model 1623 photodetector is typically 70 or greater The coupling efficiency is less than unity because of the small detector size and small variations in the mechanical position of the detector and the fiber See Figure 6 for drawings of these two accessories A variety of fiber couplers fiber collimators and pigtails are also available from New Focus Nanosecond Photodetectors Using Filters and Optical Fiber 15 Figure 6 Model 1280 1 filter holder and the Model 1281 FC fiber adapter holes for tightening ia Retaining ring 1 04 32 for holding 1 thread or 25 mm optics 6 32 nylon tipped dia 1 30 setscrew for 33 0 holding 1 or 25 mm optics Model 1280 patent pending 1 04 32 thread holes for tightening Model 1281 16 Using Filters and Optical Fiber Characteristics Physical Specifications Figure 7 Mechanical 2 50 69 drawing of the E Model 162X 1 16 0 o casing 29 5 Battery check LED Output BNC Load resistor switch ry Power de S o
4. register on your scope or instrument 5 Align an optical beam onto the detector Be careful to keep the optical power under the maximum optical power of 50 mW to avoid damaging the photodetector 6 Select the load Use the black switch on top of the detector to set the load to 50 Q 10 kQ or Open Select Open if you are providing an external load resistor See Supplying your own load resistor on page 9 7 Turn the detector off When you are finished with the detector return the power switch to the off position Nanosecond Photodetectors Operation 7 Conserving Signal Strength 8 Operation Ifyou have a low power signal 50 Q of trans impedance gain can lead to very small output voltages If you need to conserve signal strength it is important to focus your optical beam onto the photodiode Adjusting the photodiode position for optimal signal is best performed as a two step procedure 1 Set the load resistance to 10 kQ or Open 2 Hook the detector output directly into an oscilloscope or other voltage measurement device with a large input impedance 3 Adjust the photodiode position in both transverse and focus directions for maximum DC voltage For optical signal levels above about 1 mW at 10 kQ the voltage will saturate Remember the output voltage can only rise up to the battery voltage 9 V when the battery is fresh If you use the 1 MQ input impedance of an oscilloscope saturation i
5. single 9 volt alkaline battery The photoreceiver s slim casing shown below makes it easy to position it in a set up between closely spaced optics The switches and BNC output connector are located on top of the receiver for easy access Figure 2 Power switch Battery check LED Model 162X Load resistor switch casin g DD a Output BNC Photodetector Ho N 4 ountin threads A full mechanical diagram of the Model 162X casing is available on page 17 6 Operation Using the Photodetector 1 Check the battery voltage The Model 162X is powered by a single 9 volt alkaline battery To check the battery condition push the red power switch to the BATT CHK position If the green LED lights up the battery is in good condition if the LED does not light the battery needs to be replaced see page 10 2 Mount the photodetector Use the 8 32 thread M4 for metric versions on the bottom of the casing to mount the photoreceiver to a post or pedestal The threading is seated in a non conductive plastic pad to reduce the electrical noise associated with ground loops Be careful not to over tighten when attaching the casing to a post or pedestal or the threaded insert can strip out of the plastic pad CAUTION 3 Connect the detector output Connect your voltmeter oscilloscope or other instrument to the Output BNC connector on top of the detector 4 Turn the power switch to on The output voltage should
6. USER S GUIDE Nanosecond Photodetectors Models 1621 amp 1623 These photodetectors are sensitive to electrostatic discharges and could be permanently damaged if CAUTION subjected even to small discharges Ground your self adequately prior to handling these detectors or making connections A ground strap provides the most effective grounding and minimizes the likelihood of electrostatic damage p New Focus A Newport Corporation Brand 3635 Peterson Way Santa Clara CA 95054 USA phone 408 980 5903 fax 408 987 3178 e mail techsupport newfocus com www newfocus com Warranty Newport Coporation guarantees its products to be free of defects for one year from the date of shipment This is in lieu of all other guarantees expressed or implied and does not cover incidental or consequential loss Information in this document is subject to change without notice Copyright 2012 2001 1998 Newport Corporation All rights reserved The New Focus logo and symbol are registered trademarks of Newport Corporation Document Number 162107 Rev D Contents Operation 5 Introduction ssi iaia eee ere wen URI 5 Using the Phetodetector23 ist foci curar dna nadas 7 Conserving Signal Strength cnr edhe teeta 8 Supplying your own load resistor 9 Checking and Replacing the Battery 10 General Features and Principles 11 Photoreceiver Circuitry curatela 11 Frequency and Time Re
7. as a characteristic impedance of 50 Q This has been chosen for best compatibility with 50 Q impedance equipment If you terminate this transmission line with a non 50 Q load you should expect degraded frequency response When you use 50 Q impedance equipment you should switch the nanosecond photodetector into the Open position If you leave the internal 50 Q resistor switched in the photocurrent will be divided between the two loads cutting your signal in half If you leave the internal 10 kQ resistor switched in it will have little effect as the 50 Q load will draw the majority of the photocurrent DC blocking devices are a potential source of confusion Some sensitive high frequency equipment requires o V at DC input In this case we recommend that you put a high frequency DC blocking load between the nanosecond detector and your equipment If so you must supply a DC path to ground for your photocurrent This is easiest to do by switching in the photodetector s 50 Q internal load resistor If you switch in the 10 kQ load resistor you Nanosecond Photodetectors Operation 9 must be certain that the circuit does not saturate itself on the DC level Checking and Replacing the Battery 10 Operation The Model 162X is powered by a single standard 9 volt battery The battery lifetime depends on the load resistor and on the optical input power to the photodetector Under normal operating conditions the battery lifetime wi
8. focus com We typically respond to faxes and email within one business day Service In the event that your photodetector malfunctions or becomes damaged please contact New Focus for a return authorization number and instructions on shipping the unit back for evaluation and repair Nanosecond Photodetectors Customer Service 19 20 Customer Service
9. ll typically be greater than 500 hours To check the condition of the battery push the red switch to the BATT CHK position Ifthe green LED lights up the battery is in good condition When the battery voltage falls below about 6 5 volts the green LED will not light up and the battery should be replaced Replacing the Battery 1 Turn the red power switch to off to prevent damage to the receiver 2 Removethe screw on the back of the photodetector casing and remove the back cover Unplug the old battery Install a new 9 volt alkaline battery RY Reinstall the back cover Ne Test the new battery s status by pushing the power switch to the BATT CHK position General Features and Principles Photoreceiver Circuitry Figure 3 Functional schematic of the Model 162X circuitry The circuitry inside the Model 162X consists of a reverse biased photodetector and a load resistor with three settings 50 Q 10 kQ and Open The 50 Q setting has 50 V A sensitivity and can be used to achieve the 1 nanosecond response time The 10 kQ setting has a reduced time response but gives a higher sensitivity 10 000 V A and can be used for alignment purposes and for detecting low power pulses The Open setting allows you to hook up your own external load resistor and choose the best gain bandwidth combination for your application WwW Batt ON q o LED a OFF Battery Check Circuit Output 10 kQ
10. response speed which is limited by your detection equipment Typical laboratory oscilloscopes for instance have only 10 MHz to 100 MHz bandwidth When you select the 10 kQ 12 General Features and Principles resistor the speed is RC limited and the response speed will typically be 50 ns Figure 5 Typical pulse response for the a Model 1621 and b Model 1623 photodetectors a M odel 1621 4 Time ns og TT 0 2 4 6 8 10 Time ns A 0 15 ps pulse at 1 06 um was used to test the photodetectors and the output was measured using a 12 GHz oscilloscope Nanosecond Photodetectors General Features and Principles 13 14 General Features and Principles Using Filters and Optical Fiber New Focus offers accessories sold separately to attach a 1 diameter filter or an optical fiber to the detector Both accessories attach to the casing using the 1 04 32 threads located in the casing around the detector Note that the accessories are also compatible with two other New Focus products the Model 203X large area photoreceiver and the Model 215X femtowatt photoreceiver The Model 1280 1 filter holder allows you to mount a 1 diameter optic in front ofthe photodetector For instance you can mount a colored glass filter to remove unwanted wavelengths or a neutral density filter to attenuate the optical power incident on the photodetector The Model 1280 has a plastic ring for mounting a filter that is up to
11. s even easier to reach 4 Select the 50 Q resistor or supply your own small load resistance suitable to your gain and frequency response requirements Make fine adjustments to the photodiode position until the maximum signal is achieved To compute the approximate output voltage for a given input optical power use the relationship Vout Pin RG where Pin is the input optical power in watts R is the photodetector s responsivity in A W see page 6 for typical responsivities and G is the load resistance V A For example with 10 mW of optical power a responsivity of 0 5 A W and with the load set to 50 Q the photodetector will produce an output voltage of approximately 10 mW 0 5 A W 50 V A 0 25 V Supplying your own load resistor At high frequencies typical resistors begin to exhibit parasitic inductance and capacitance For instance if you want to operate on the Open setting and supply your own 100 Q resistor you might be tempted to use a standard carbon film resistor soldered across the terminals of a BNC tee The problem with this approach is that the parasitic inductance of such a home made resistor will cause a significant change in the impedance at high frequencies So for best results you may need to buy a precision load resistor that is optimized for high frequency use You must also watch out for impedance mismatch problems The internal transmission line from the photodiode to the BNC output h
12. sponse ss aereas 11 Using Filters and Optical Fiber 15 Characteristics 17 PhiysiclSpedhicafionsa i crasso italia 17 Photodetector Specifications eee ees 18 Customer Service 19 Technical Support ssi iaia 19 Service gt ct fo O28 andar dardo hand elena 19 Nanosecond Photodetectors Contents 3 4 Contents Operation Introduction The Model 162X is a general purpose battery powered photodetector for measuring optical signals down to nanosecond time scales There are two versions of the Model 162X detector each based on a different photodetector diode Model Wavelength Type Diam 1621 350 1000 nm silicon PIN 0 8mm 1623 800 1700 nm InGaAs PIN 0 1 mm with a 1 5 mm ball lens Complete specifications for the Model 162X nanosecond photodetectors begin on page 17 This product is ideal for detecting light pulses or monitoring optical signals from DC to several hundred MHz where an electronic amplifier is not required The large diameter detectors and the DC response make alignment and operation of the Model 162X easy Figure 1 shows the typical responsivity curves for the photodetectors used in the Models 1621 and 1623 Nanosecond Photodetectors Operation 5 Figure 1 Typical Model 1623 responsivities of 3 Model 1621 S ana Mode Model 1621 1623 200 400 600 800 1000 1200 1400 1600 1800 2000 Wavelength nm Each Model 162X photodetector runs off a
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