User`s Guide for Model 21X7 10-MHz Adjustable Balanced Receivers
Contents
1. 16 Performance Data for Noise cece ee eee eens 18 Common Mode Rejection 0eceeeeeeeene eens 19 Characteristics 21 Physical Specifications cngiennie ki ceecksPiwsda sae 21 Model 2107 Specifications s o oi0 404esne peed vaedeandnage 22 Model 2117 Specifications cg aang indevuins nian nies 23 Customer Service 24 Technical Support scent Sey aw weal ea eae ea 24 SOIVICE se la scctebidsabar eeivareeewe ws oe seas ap iebeacdees 24 Models 2107 amp 2117 Contents 3 4 Contents NEW FOCUS Inc Operation Introduction The Model 21X7 is a general purpose balanced photoreceiver with adjustable gain and bandwidth These receivers can be powered by batteries or by an external 15 V power supply There are two models available each based on a different photodetector Free space FS and fiber coupled FC versions are available for each model Model Wavelength a Active Area 2107 FC 300 1070 nm silicon 0 8 mm2 2107 FS 300 1070 nm silicon 0 8 mm2 2117 FC 900 1700 nm InGaAs 0 0078 mm 2117 FS 900 1700 nm InGaAs 0 08 mm2 Complete specifications begin on page 21 The 10 MHz three stage transimpedance amplifier includes selectable gain and selectable low and high pass filters for easy signal optimization Models 2107 amp 2117 Operation 5 Figure 1 Typical responsivities of the Model 2107 amp 2117 photodiodes Responsivity A W 400 800 122. z 3 xt oOo g 6 E9 3 5 2 12 15 0 01 0 10 100 Frequency MHz Gain Setting 10 Ss 0 Cc oS x1 amp 3 g S 4 E 5 g x3 12 0 01 0 10 100 Frequency MHz 16 Frequency Response and Noise NEW FOCUS Inc Gain Setting 102 xl Normalized Gain dB x3 15 0 01 0 1 0 100 Frequency MHz Gain Setting 10 Normalized Gain dB 0 01 0 1 1 Frequency MHz Gain Setting 10 Normalized Gain dB 0 01 0 1 1 Frequency MHz Models 2107 amp 2117 Frequency Response and Noise 17 Performance Data for Noise Figure 4 shows the typical noise spectrum expressed as photocurrent noise for Model 21X7 photoreceivers on the highest gain setting To derive the receiver s Noise Equivalent Power NEP divide the photocurrent noise by the photodiode responsivity To convert to output voltage noise RMS multiply the photocurrent noise by the gain setting from the 21X7 front label then by 630 V A the scaling factor between the gain setting labels and the actual amplifier transimpedance gain For example the output voltage noise RMS fo
3. is CAUTION often the limiting factor in broadband measurements Summary With the Model 2107 on the highest gain setting the minimum NEP is 0 8 pW Hz and this yields an output noise voltage of 4 mV ms Viewed another way for operation at the peak responsivity wavelength of 900 nm and for the high gain setting you will achieve a signal to noise ratio of unity if the input power is 390 pW For the Model 2117 with an InGaAs photodiode the NEP at peak response wavelength of 1500 nm is 0 4 pW Hz over the 150 kHz bandwidth The full Models 2107 amp 2117 Frequency Response and Noise 15 bandwidth signal to noise ratio of 1 is achieved around 200 pW Note that this assumes operation without any post photoreceiver filtering and with the full photoreceiver bandwidth By using the built in electronic band pass filter or an optical chopper and a lock in amplifier the receiver can detect significantly weaker optical signals Performance Data for Frequency Response Figure 3 Typical frequency response for Model 21X7 at each gain setting The 3 dB frequency bandwidth is defined as the frequency where the photoreceiver s transimpedance gain has decreased by a factor of 2 The typical frequency responses for the Model 2107 and Model 2117 are shown in the following figures Gain Setting 1 3 ao 0
4. response details for each gain setting ea g Specification Typical Performance 1x1 10 MHz 12 MHz 3x1 A 6 MHz 1x10 A 12 MHz 3x10 A 6 MHz 1x10 A 8 MHz 3x10 A 6 MHz 1x103 A 700 kHz 3x103 A 700 kHz 1x104 A 250 kHz 3x104 150 kHz 250 kHz Optical Power and Output Voltage The typical operating range for these receivers is from a few nanowatts up to 2 to 5 mW depending on the model and gain setting Be careful to keep the differential optical power below the maximum optical power difference of 10 mW to avoid damaging the photoreceiver To compute the approximate output voltage for a given input optical power use the relationship Vout P4 P R G 10 General Features amp Principles NEW FOCUS Inc where P and P_are the input optical powers in Watts on the right and left photodiodes respectively R is the photodetector s response factor in V mW and G is the amplifier s gain setting Estimate the value of the response factor by dividing the responsivity shown in Figure 1 by 1 5 For example the Model 2107 on the 1x10 gain setting and with 10 pW of optical power at 900 nm on one photodiode will have an output voltage of approximately 0 01 mW 0 35 V mW 1x102 3 5 V The maximum differential optical power that can be detected by the photoreceiver is determined by the input optical power at which eith
5. 00 1600 Wavelength nm To obtain the value of the response factor in V mW divide the photodiode responsivity by 1 5 For more information on frequency response and noise see page 13 6 Operation NEW FOCUS Inc Using the Photoreceiver 1 Models 2107 amp 2117 Mount the photoreceiver Use the 8 32 thread M4 for metric versions on the bottom of the cas ing to mount the photoreceiver to a post or pedes tal Supply power Power the Model 21X7 using either two 9 volt alkaline batteries or a 15 V low noise linear power supply such as the New Focus Model 0901 Connect the receiver output Connect your voltmeter oscilloscope or other instrument to the Output SMA connector on the receiver If you wish to connect to a BNC cable you can purchase a BNC to SMA adapter such as the New Focus Model 1225 Turn on the photoreceiver power For external power use 15 VDC ON for battery use Batt Mode ON Align optical beams onto the detectors The photodiodes are not very large so take care when aligning each beam Adjust the gain Use the knob and rocker switch on the receiver to set the gain The bandwidths vary with the gain setting see table on page 10 Adjust the filters Select low pass and high pass corner frequencies using the knobs on the receiver Balance the optical input levels Alternately block each diode and observe the signal strength When they are approximately equal and opposite
6. 00 nm Max Differential Power 10 mW 1600 nm Max Power per Photodiode 10 mW 1600 nm damage threshold Detector Material Type InGaAs PIN Detector Active Area 0 3 mm diam FS 0 1 mm diam FO Optical Input FC or Free Space Electrical Output SMA Power Requirements 15 VDC lt 150 mA External Power Supply or Two 9 V Batteries Models 2107 amp 2117 Characteristics 23 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 numbers 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 408 919 1500 Support is also available by fax and email Fax 408 980 8883 Email techsupport newfocus com We typically respond to faxes and email within one business day Service In the event that your photoreceiver malfunctions or becomes damaged please contact New Focus for a return authorization number and instructions on shipping the unit back for evaluation and repair 24 Customer Service NEW FOCUS Inc
7. O a switch q T E 131 2 external SMA power 2 50 ty HLL oat 635 15VDC i 8 32 M4 THD 3 a gt 1 24 a 2 31 58 6 31 5 Models 2107 amp 2117 Characteristics 21 Model 2107 Specifications Wavelength Range Model 2107 300 1070 nm 3 dB Bandwidth 10 MHz 5 MHz 150 kHz Typical Common Mode Rejection 25 dB Rise Time 80 ns Peak Conversion Gain 9 4 x 10 V W Typical Max Responsivity 0 5 A W Max Transimpedance Gain 18 8 x 10 V A Output Impedance 16Q Minimum NEP 0 8 pW Hz CW Saturation Power 20 mW 850 nm Max Differential Power 20 mW 850 nm Max Power per Photodiode if balanced damage threshold 20 mW 850 nm Detector Material Type Si PIN Detector Active Area 1 0 mm x 0 8 mm Optical Input Electrical Output FC or Free Space SMA Power Requirements 15 VDC lt 150 mA External Power Supply or Two 9 V Batteries 22 Characteristics NEW FOCUS Inc Model 2117 Specifications Model 2117 Wavelength Range 900 1700 nm 3 dB Bandwidth 10 MHz 5 MHz 150 kHz Typical Common Mode Rejection 25 dB Rise Time 80 ns Peak Conversion Gain 18 8 x 10 V W Typical Max Responsivity 1 A W Max Transimpedance Gain 18 8 x 10 V A Output Impedance 160 Minimum NEP 0 4 pW JHz CW Saturation Power 10 mW 16
8. USER S GUIDE 10 MHz Adjustable Balanced Photoreceivers Models 2107 amp 2117 O New Focus j4 A Division of Bookham 2584 Junction Avenue San Jose CA 95134 1902 USA phone 408 919 1500 e mail contact newfocus com www newfocus com Warranty New Focus Inc 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 2004 New Focus Inc a division of Bookham Technology plc All rights reserved The pret Fecus logo and NEW FOCUS Inc are trademarks or registered trademarks of Bookham Technology plc in the U S A or other countries Products described in this document may be covered by one or more patents in the U S A and abroad Document Number 200331 Rev A Contents Operation 5 Introductions gasetan rire Fe Seek E hae 5 Using the Photoreceiver iio vies eins 304s 35 AEs We Sena none 7 Checking the Battery on hea 5 28 oe See at ener 8 General Features amp Principles 9 Photoreceiver Circuitry 2 3245455 5755 s2acadseadasmdesanes 9 Optical Power and Output Voltage 2 eee 10 Frequency Response and Noise 13 Measuring Band widthijndst dada xeaexanieseeeaan eevee 13 M as ring IN OSE n iss ed esc aiend ca ah ast eater ae peg anaes 13 Performance Data for Frequency Response
9. V batteries with fresh ones Replace the back panel and the two screws Ne a Recheck the battery level as described above NEW FOCUS Inc General Features amp Principles Photoreceiver Circuitry The circuitry inside the Model 21X7 consists of two photodiodes followed by a three stage transimpedance amplifier The gain can be adjusted from 626 V A to 18 8x10 V A in 5 dB steps The low noise amplifier design is optimized to maximize bandwidth at each gain setting At the higher gain settings the bandwidth is limited by amplifier gain bandwidth product The plots of Figure 3 show the typical frequency responses for the different gain settings Figure 2 15 V o 49 V REG Hon 9 V Functional ooi f BaT schematic of M No gV the Model 21X7 i circuitry 15 V o 9V REG ADJUSTABLE GAIN STAGE x104 49V 4493 INDEPENDENTLY ADJUSTABLE GAIN x102 ADJUSTABLE 6 dB OCTAVE STAGE x10 HIGH AND LOW PASS FILTERS 3 x1 x1 A SMA fl fH gt DETECTOR HOUSING IS 3V GROUNDED Models 2107 amp 2117 General Features amp Principles 9 The following table summarizes the bandwidth at each gain setting The bandwidth on the 3x settings is somewhat lower than the 1x settings and significantly decreases at the highest gain settings There is little difference in frequency response between the visible Model 2107 and IR Model 2117 models The plots of Figure 3 show the frequency
10. adjust their relative intensity until the balanced output is zero volts Turn off the photoreceiver power When you are finished with the receiver place the power switch in the 15 VDC ON position and switch off or unplug the external power supply Operation 7 Checking the Batteries 8 Operation The Model 21X7 can be powered by two standard 9 volt alkaline batteries Under normal operating conditions with low light levels and a high impedance load attached to the BNC connector the photoreceiver draws about 20 mA from the batteries and the battery lifetime is approximately 24 hours To check the condition of the battery 1 Turn on the photoreceiver using the power switch 2 Set the Low Frequency adjustment to DC 3 Set the Gain to 3x104 4 Focus at least 1 uW of optical power on the detector or place the detector in front of a desk lamp The output should be greater than 7 V If it is not replace the batteries with fresh ones Replacing the Batteries The Model 21X7 is shipped with two fresh 9 V batteries installed To avoid confusion due to low batteries replace the batteries on a monthly basis when the receiver is in frequent use or use an external linear power supply such as the New Focus Model 0901 1 Turn off the receiver using the power switch 2 Usea Phillips head screwdriver to remove the two screws on the back panel of the photo receiver Remove the back panel Replace the used 9
11. er stage of the transimpedance gain saturates We can calculate the saturation power at 900 nm for the Model 2107 at its maximum output voltage of 7 V with fresh batteries or operating from an external 15 VDC power supply Using the expression 7 V P a R G the Model 2107 has a differential saturation power of 20 mW for the lowest gain setting up to 0 7 pW for the highest gain setting At other wavelengths where the responsivity is lower the saturation power increases inversely with response factor Models 2107 amp 2117 General Features amp Principles 11 12 General Features amp Principles NEW FOCUS Inc Frequency Response and Noise Measuring Bandwidth The frequency response and noise characteristics of the photoreceiver depend on the selected gain The figures beginning on page 16 give the typical frequency response and noise behavior for the photoreceivers at each of the gain settings The frequency response of the transimpedance gain is plotted using the expression 20 log Gain Ff Gain 0 where f is the frequency and Gain 0 is the gain at DC The photoreceiver s bandwidth is defined as the frequency where the gain has decreased by 3 dB ora factor of 2 Measuring Noise The photoreceiver noise is characterized using the noise equivalent power NEP which is a measure of the weakest optical signal that the photoreceiver can detect The NEP is the optical power which will produce a signal to noi
12. iveness of the balanced subtraction Figure 5 shows the CMRR of each model using the following definition CMRR 20 log Voutr Vout Vouti Because the common mode subtraction occurs before the first amplifier stage the only practical bandwidth limitation on common mode rejection is the photodiode bandwidth Thus as seen in the following figures the CMRR for higher gain settings is relatively flat to frequencies well beyond the useful frequency response of the gain setting Models 2107 amp 2117 Frequency Response and Noise 19 Figure 5 Typical CMRR for Model 2107 in each gain setting Figure 6 Typical CMRR for Model 2117 in each gain setting CMRR dB CMRR dB Frequ ency MHz 50 45 40 35 Bx 30 25 4940 20 20 Frequency Response and Noise 0 1 Frequency MHz NEW FOCUS Inc Characteristics Physical Specifications Figure 7 power 178 a L Mechanical joy freq n 45 2 ABE 254 drawing of the comi high freq adjus peu Model 21X7 knob ajust E o o casing O knob photo gain ll l gai detectors 4 knob D multiplier a 517 L
13. n obtained by multiplying the average NEP by BW the square root of the bandwidth The expression BW 2nf 3 gp 4 for a one pole low pass filter is useful for calculating the equivalent noise bandwidth Using the high pass filter set 1 decade below the low pass cutoff reduces noise equivalent bandwidth by approximately 10 For the Model 2107 with a 3 dB bandwidth of 150 kHz the equivalent noise bandwidth is 235 kHz This gives an optical noise equivalent power of about 390 pW so the minimum detectable optical signal at 900 nm with a signal to noise ratio of 1 for the Model 2107 on the highest gain 14 Frequency Response and Noise NEW FOCUS Inc setting is 390 pW when operating at full detector bandwidth You can further improve your signal to noise ratio by using optical modulators or choppers with lock in amplifiers to limit the detection bandwidth Using such techniques you can reduce equivalent bandwidth to 1 Hz or less Calculating Output Voltage Noise The output voltage noise can be calculated from G R NEP BW where Gis the gain V V Ris the photodiode response factor V mW NEP is the average noise equivalent power and BW is the bandwidth This gives an output noise voltage for the Model 2107 on the high gain setting of 3x104 V V 0 35 V mW 0 8x10 mW Hz PE 150 x 10 Hz 4 mV The Johnson noise at the input of a 100 MHz bandwidth oscilloscope with 1 MQ input impedance is 1 6 MV ms This
14. r Model 2117 in the 3x10 setting is approximately 0 4 pA Hz x 3 x 107 x 630 V A 0 75 UV ms a Hz For the 700 kHz of amplifier bandwidth in the 3x10 gain setting the equivalent noise bandwidth is 2x 2 4 x 700 x 102 Hz 1 1 MHz so the predicted output noise voltage is approximately 0 75 UVims JAz X 1 1 x 10 Hz 0 8 MVims Because the NEP is listed at the highest gain setting some additional considerations add to the NEP at lower gain settings First the noise spectrum Figure 4 is not flat rising at frequencies above 100 kHz This contributes an extra 20 to the output noise voltage in the 3 x 10 setting compared to 3 x 104 Also as the output noise voltage approaches 1 MV ms the Johnson noise limit of your measurement instrument will become important Note that the Johnson noise for an oscilloscope with 100 MHz bandwidth assuming perfect roll off and 1 MQ input impedance is 1 2 mVyms 18 Frequency Response and Noise NEW FOCUS Inc Figure 4 21X7 Output Noise Current Typical noise 0 40 spectrum for moet Model 21X7 035 oe ean oie ain 3 x 10 2 0 30 2 025 0 20 0 10 20 30 40 50 60 70 80 90 100 Frequency KHz Common Mode Rejection Using the Model 21X7 balanced photoreceivers with equal signal powers on each photodiode results in an output with reduced common mode signal The common mode rejection ratio or CMRR is a measurement of the effect
15. se ratio of 1 in a 1 Hz bandwidth The minimum detectable optical power can be found using the relationship Minimum Optical Power NEP JBW where BW is the bandwidth Note that NEP is a wavelength dependent quantity that changes with the photodetector s responsivity Models 2107 amp 2117 Frequency Response and Noise 13 Another way to characterize the noise is with the photocurrent noise ln which is related to NEP by R NEP where R is the photodetector s responsivity in A W The photocurrent noise is independent of wavelength because it gives the noise of the photoreceiver with the photodetector s responsivity factored out To characterize the noise of the photoreceiver the output electrical noise spectrum is measured with a spectrum analyzer This voltage noise spectrum is converted to an equivalent optical photocurrent noise by dividing the voltage noise by the transimpedance gain V A The photocurrent noise f has units of pA Hz and is plotted in Figure 3 and Figure 4 using the expression 20 log In f 1 Al Calculating NEP The noise equivalent power NEP can be calculated by dividing the photocurrent noise by R the detector s responsivity see page 6 From DC to 150 kHz the average photocurrent noise for the Model 2107 on the high gain setting is about 0 4 pA Hz corresponding to an average NEP at 900 nm of 0 8 pW Hz The integrated noise equivalent power from DC to 150 kHz is the
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