15-GHz & 25-GHz Photodetectors Models 1480-S & 1481-S

Transcription

1 1480-S FC Det revb.fm Page 1 Monday, January 14, :38 AM USER S GUIDE 15-GHz & 25-GHz Photodetectors Models 1480-S & 1481-S Includes Model S These photodetectors are sensitive to electrostatic discharges and could be permanently damaged if 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 3635 Peterson Way Santa Clara, CA USA phone: (408) fax: (408) techsupport@newfocus.com

2 1480-S FC Det revb.fm Page 2 Monday, January 14, :38 AM 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, , Newport Corporation. All rights reserved. The New Focus logo and symbol are registered trademarks of Newport Corporation Document Number Rev. B

3 1480-S FC Det revb.fm Page 3 Monday, January 14, :38 AM Contents Operation 5 Introduction Handling Precautions Quick Start Connecting the Power Supply Making the Microwave Connection Connecting the Detector to the Optical Input Characteristics 11 Photodetector Characteristics Bias-Monitor Characteristics Responsivity Troubleshooting 13 Testing the Photodiode Checking the DC-Offset Voltage & Power Supply...13 Basic Optical Test Cleaning the Fiber Connector Customer Service 17 Technical Support Service Appendix: Microwave Connectors GHz & 25-GHz Photodetectors Contents 3

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5 Model 14XX XX-GHz Photodetector Made in USA 1480-S FC Det revb.fm Page 5 Monday, January 14, :38 AM Operation Introduction High-speed measurements are easy with the Models 1480-S and 1481-S photodetector modules. These modules convert your optical signals to electronic signals, in effect giving every high-speed/high-frequency instrument in your lab an optical input. Figure 1: Models 1480-S & 1481-S photodetector modules Battery-check button press to apply the photodiode bias voltage to the bias-monitor port. Power switch Off On Batt Chk Optical Input Bias Monitor Bias-monitor port output is equal to photodiode current times 1000 Ω, for 1 mv/μa. Output K-connector 2.25 (57.1) 2.00 (50.8) 2.00 (50.8) FC/PC connector for fiber-optic input 3.14 (79.8) Each module connects directly to the test instrument or amplifier, eliminating the need for coaxial cables, which could seriously distort picosecond pulses and attenuate microwave signals. The optical signal is delivered to the photodiode in the module through multimode (Models 1480-S and S) or singlemode (Model 1481-S) optical fiber. Moreover, the photodiode bias circuit eliminates the need for external bias networks and reduces the possibility of photodiode damage due to overvoltage. 15-GHz & 25-GHz Photodetectors Operation 5

6 1480-S FC Det revb.fm Page 6 Monday, January 14, :38 AM The photodetectors use GaAs PIN photodiodes designed for high responsivity in the nm wavelength range. The high-speed circuitry produces a clean impulse response, making them ideal for digital communication measurements. A 50-Ω terminating resistor minimizes electrical reflections, which reduces ringing when used with amplifiers which may not have perfect 50-Ω inputs. The Model 1480-S has an internal 62.5-µm multimode fiber which delivers the input light to the 65-µm-diameter photodiode, permitting the use of delivery fibers with core diameters of 62.5 µm or smaller, including single-mode fibers. The internal fiber is angle polished for low back reflection. The Model 1481-S has an internal single-mode fiber, which is angle polished to reduce back reflections. The Model S has an internal 50-µm multimode fiber and uses a GRIN lens to image the fiber output onto the 25-µm photodiode used in these models. The optical elements are anti-reflection coated for low back reflection at 850 nm. Handling Precautions Whenever handling the photoreceiver, make sure to follow these precautions: Prior to handling the detector or making connections, be sure to ground yourself adequately even small electrostatic discharges could permanently damaged the detector. A ground strap provides the most effective grounding and minimizes the likelihood of electrostatic damage. Do not over-torque the microwave K-connector. Excessive torque can damage connectors. Make sure the optical connector is clean and undamaged before connecting it to the detector module. 6 Operation

7 1480-S FC Det revb.fm Page 7 Monday, January 14, :38 AM Quick Start Use the Models 1480-S and 1481-S (including the S) high-speed GaAs photodetector modules for detecting light in the wavelength range from 400 to 870 nm. Each module is 50-¾ terminated and requires a ±15-V power supply. To operate the module, follow these quick-start instructions or consult the other sections of this manual for more detail. 1. Take proper precautions to avoid electrostatic damage to the photodiode. (See Handling Precautions on page 6.) 2. Connect the module to a ±15-V power supply using the supplied cable. 3. Turn on power using the Off/On switch. 4. If you are using the detector for the first time, or you wish to check the DC offset, connect a voltmeter to the Bias Monitor SMA connector. Without an optical input, the voltage should be less than 5 mv. 5. Connect the photodetector module to your measurement instrument, being careful not to overtorque the K-connector. The instrument must have a 50-Ω input impedance. 6. Check that the optical power emerging from your fiber is below the cw saturation power, as appropriate, to ensure detector linearity and to avoid detector damage. (See Characteristics on page 11.) 7. Connect your optical fiber to the connector on the detector module. If any of these steps present problems or you would like more information, please consult the remainder of this manual. 15-GHz & 25-GHz Photodetectors Operation 7

8 1480-S FC Det revb.fm Page 8 Monday, January 14, :38 AM Connecting the Power Supply Note 8 Operation 1. Prior to handling the detector, ground yourself with a grounding strap to prevent electrostatic damage to the receiver. 2. Connect the power cable to the power supply. Two power cables were included with the detector; use the appropriate cable for your power supply. Connecting to a New Focus power supply: Use the cable provided to connect to the power supply s 100-mA output. Connecting to another power supply: Use the cable provided to connect to the power supply. Be careful to connect the banana plugs as follows; connect the red plug to a well-regulated, +15-V, 200-mA source; connect the black plug to a -15-V, 200-mA source; connect the green plug to the common ground of the two sources. 3. Connect the bias-monitor port to a voltmeter. 4. Press and hold the Batt Chk button and observe the bias monitor output. The positive voltage (minus 0.6 V) is momentarily applied to the Bias Monitor SMA connector. A reading of 14 V indicates proper connection. 5. Release the Batt Chk button and observe the voltage level on the voltmeter. This voltage is the DC offset plus dark current. This dark voltage should be less than 5 mv. If you are coupling light into a fiber, use the voltmeter to monitor the photocurrent to help optimize the coupling. Making the Microwave Connection 1. Connect the photoreceiver module s microwave connector to a test instrument that has a 50-Ω

9 1480-S FC Det revb.fm Page 9 Monday, January 14, :38 AM input, such as an oscilloscope or spectrum analyzer, or to another 50-Ω load. If necessary, use a high-frequency cable (best performance is achieved without a cable). 2. To avoid connector damage and signal distortion, be sure that the cable and the instrument you intend to connect to the module have compatible connectors. See Appendix: Microwave Connectors on page 19 for a list of compatible connectors. Connecting the Detector to the Optical Input 1. Measure the peak power in the fiber prior to connection to the module to be sure it is within the safe operating range (see Photodetector Characteristics on page 11). 2. Connect the fiber-optic cable to the fiber-optic input on the detector module. If needed, the Bias Monitor may be used to optimize coupling to the fiber. 15-GHz & 25-GHz Photodetectors Operation 9

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11 1480-S FC Det revb.fm Page 11 Monday, January 14, :38 AM Characteristics Photodetector Characteristics The values below are given at 850 nm. Model # 1480-S 1481-S Wavelength Range dB Bandwidth 15 GHz 25 GHz Rise Time 25 ps 15 ps Conversion Gain 10 V/W 10 V/W Responsivity 0.4 A/W 0.4 A/W Output Impedance 50 Ω 50 Ω Minimum NEP 45 pw/ Hz 45 pw/ Hz cw Saturation Power >5 mw >2 mw Detector Material/Type GaAs/PIN GaAs/PIN Detector Diameter 65 m 25 m Input-Fiber Core Diameter -50 version 62.5-μm multimode N/A 9-μm single mode 50-μm multimode Power Requirements ±15 V, 50 ma ±15 V, 50 ma Optical Input Connector FC/PC FC/PC Electrical Output Wiltron K Wiltron K 15-GHz & 25-GHz Photodetectors Characteristics 11

12 1480-S FC Det revb.fm Page 12 Monday, January 14, :38 AM Bias-Monitor Characteristics Model # DC Gain 1 mv/μa 1 mv/μa DC Offset (max.) 5 mv 5 mv Output Impedance 10 k¾ 10 k¾ Bandwidth 1 MHz 1 MHz Responsivity A graph of the typical responsivity of the Models 1480-S and 1481-S is shown below. Figure 2: Responsivity vs. wavelength Responsivity, A/W Wavelength, nm 12 Characteristics

13 1480-S FC Det revb.fm Page 13 Monday, January 14, :38 AM Troubleshooting Testing the Photodiode The photodiode can be damaged by electrostatic discharge or excessive optical power, which can lead to an increased dark (or offset) voltage. A damaged photodiode can result in a degraded responsivity and frequency/impulse response. See Checking the DC- Offset Voltage & Power Supply, below. Checking the DC-Offset Voltage & Power Supply 1. With no light on the photodetector, turn the detector on. 2. Use a voltmeter to measure the bias monitor output voltage. This voltage is the DC offset plus dark current. 3. If the output is >5 mv, then the detector is probably damaged and will need to be returned to New Focus. If the output is <5 mv, then perform the Basic Optical Test described below. 4. Press and hold the Batt Chk button and observe the bias-monitor output. The positive supply voltage (minus 0.6 V) is momentarily applied to the Bias Monitor SMA connector. A reading other than 14 V indicates a problem with either the power supply or the cable. 15-GHz & 25-GHz Photodetectors Troubleshooting 13

14 1480-S FC Det revb.fm Page 14 Monday, January 14, :38 AM Basic Optical Test 14 Troubleshooting To quickly test the photodiode in your detector, run this simple DC optical test. 1. Turn the detector on. 2. Using a voltmeter or oscilloscope, measure the output voltage from the Bias Monitor on the front panel of the bias supply. With no light on the detector, the Bias Monitor voltage should be <10 mv. 3. Illuminate the photodetector. 4. With the voltmeter or oscilloscope, you should observe a DC output voltage. If you know the optical power and wavelength, you can calculate the expected output voltage (V out ) using the expression: V out = P in R G, where P in is the input optical power (watts), R is the photodetector s responsivity (A/W), and G is the amplifier s transimpedance gain (V/A). The gain of the bias monitor port is 1000 V/A. If the output voltage is low, then the fiber connector may be dirty (see Cleaning the Fiber Connector, below). If you suspect the unit is damaged, contact New Focus to arrange for a repair (see Customer Service on page 17). Cleaning the Fiber Connector The high-speed photodetectors have an internal fiber connector and a fiber pigtail that brings the input light to the detector. If the fiber connector is dirty, this can block the input light so that light sent into the detector will produce little or no output voltage. Note also that if the fiber types are not compatible (e.g. multimode to single mode), this can also be the cause of a very low output voltage.

15 1480-S FC Det revb.fm Page 15 Monday, January 14, :38 AM To clean the fiber: 1. Turn off the module. 2. Blow filtered air or another inert gas (such as nitrogen) into the input fiber connector. This will help to remove any dust or dirt particles that might be blocking the input light. If more cleaning is needed, proceed with steps Wear a grounding strap. 4. Remove the two screws on the back panel with a Phillips screwdriver. Remove the back panel. 5. Remove the two screws on the bottom of the detector using an Allen key (1/16" or 1.5-mm), and carefully slide the detector housing off. Caution: For steps 6 8, be extremely careful not to pull on the fiber. The fiber is not designed to withstand excessive stress where it connects to the microwave housing. 6. Carefully disconnect the fiber connector from the fiber receptacle attached to the front panel of the detector. 7. The front surface of the fiber can be cleaned using acetone or alcohol and lens tissue. 8. Carefully reconnect the fiber to the front panel receptacle, re-install the detector housing (be careful not to pinch or damage the fiber), and reinstall the back panel. 15-GHz & 25-GHz Photodetectors Troubleshooting 15

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17 1480-S FC Det revb.fm Page 17 Monday, January 14, :38 AM 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: NUFOCUS ( ) (from the USA & Canada only) Phone: (408) Support is also available by fax and Fax: (408) We typically respond to faxes and 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. 15-GHz & 25-GHz Photodetectors Customer Service 17

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19 1480-S FC Det revb.fm Page 19 Monday, January 14, :38 AM Appendix: Microwave Connectors The performance you obtain from the Model 148X photodetector modules depends largely on the instrument you use to measure their microwave outputs and how the connections are made to this instrument. Connect the male connector of the photodetector directly to the female connector of the instrument. If an intervening coaxial cable is used, make sure it has sufficiently low loss in the frequency range of interest Even if you are not using an intervening cable, performance can be degraded if an improper adapter is chosen for mating to the instrument. Common SMA connectors, for example, are intended for use only to 18 GHz. The following table lists a few connectors and the frequency ranges in which they may be used. (For more information, request Application Note 1.) Connector Frequency Range Compatibility BNC DC 2 GHz SMA DC 18 GHz Wiltron K, 3.5 mm 3.5 mm DC 34 GHz SMA, Wiltron K Wiltron K DC 40 GHz SMA, 3.5 mm 2.4 mm DC 55 GHz Wiltron V Wiltron V DC 65 GHz 2.4 mm New Focusalso offersthe following adapters: Model1225 Male-SM A to Fem ale-bn C Model1226 Fem ale-sm A to Male-BN C Model GHz Flex Cable,Fem ale-k to Male-K 15-GHz & 25-GHz Photodetectors Appendix: Microwave Connectors 19

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