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ID Date Author Type Category Subject
2373   Mon Jul 22 20:36:35 2019 KojiElectronics2micronLasersSockets for LaserComponents PDs

We received the TO-66 sockets for LaserComponents PDs (Andon Electronics F425-1009-01-295V-R27-L14 Qty.10). It is made of FRP. It is very nicely made.

Attachment 1: IMG_8793.jpg
Attachment 2: IMG_8792.jpg
Attachment 3: IMG_8791.jpg
2374   Tue Jul 23 21:02:14 2019 Shalika SinghDailyProgress2micronLasersTransfer Function using SR785 spectrum analyzer

The transfer function of the circuit was analyzed.

Attachment 1: The circuit diagramThe usual transimpedance configuration was made using the OP27 IC. There are two TIA as we will be using two PD in our final circuit. The two TIA are connected to Whitening Filter respectively. The Whitening filter has a gain of 10. Apart from that, the output of the two TIA is connected to a differential circuit and whose output is in turn connected to another independent whitening filter.

Attachment 2: The Transfer Function

The transfer function of the transimpedance amplifier, Differential Circuit(at both its input nodes), Whitening Filter was analyzed by using the SR785 spectrum analyzer. A 1V source was applied at the input of the respective circuit under consideration.

**A 1k resistor was kept in series with every node which was given a source of 1V.

The terminology used in the graph:

TIA- Transfer function of the transimpedance amplifier

Differential at node1- TF of Differential circuit by providing source at node1

Differential at node2- TF of Differential circuit by providing source at node2

Whitening Filter- TF of Whitening filter by providing source at node1

TIA and Whitening filter- TF of transimpedance amplifier in series with the Whitening filter, and the source were at node1 of the TIA.

Attachment 1: full_circuit.pdf
Attachment 2: Transfer_Function_of_Circuit.pdf
2375   Wed Jul 24 18:50:27 2019 Shalika SinghDailyProgress2micronLasersCorrection in Transfer Function using SR785 spectrum analyzer

There were some errors in the previously obtained transfer function of the part where TIA was in series with the Whitening Filter. So, below is the updated transfer function plot.

Attachment 1: The circuit diagram

The usual transimpedance configuration was made using the OP27 IC. There are two TIA as we will be using two PD in our final circuit. The two TIA are connected to Whitening Filter respectively. The Whitening filter has a gain of 10. Apart from that, the output of the two TIA is connected to a differential circuit and whose output is in turn connected to another independent whitening filter.

Attachment 2: The Transfer Function

The transfer function of the transimpedance amplifier, Differential Circuit(at both its input nodes), Whitening Filter was analyzed by using the SR785 spectrum analyzer. A 1V source was applied at the input of a 10k resistor which was in turn connected in series with the respective circuit under consideration. The averaging mode is RMS and the input ground node is floating. The input is AC coupled.

The terminology used in the graph:

TIA- Transfer function of the transimpedance amplifier

Differential at node1- TF of Differential circuit by providing source at node1

Differential at node2- TF of Differential circuit by providing source at node2

Whitening Filter- TF of Whitening filter by providing source at node1

TIA and Whitening filter- TF of transimpedance amplifier in series with the Whitening filter, and the source were at node1 of the TIA.

Attachment 1: full_circuit.pdf
Attachment 2: Transfer_Fucntion.pdf
2376   Thu Jul 25 11:15:40 2019 Nathan HollandDailyProgress2micronLasersPhase Noise of Moku.

Attached are the results from measuring the phase noise of the Moku with a SRS DS345, which was the available signal generator in the QIL lab. Attachment 1 is the estimate of the Moku phase noise, with attachement 2 containing the data. Attachment 3 shows the data this was obtained from, and attachment 4 the experimental setup used to measure this. 15.625 kHz is the maximum frequency that the Moku will let you acquire two channels of data, in the phasemeter setup. In this setup I generated a 20 MHz signal on the DS345. This was then split, via a T piece, and sent through cables of length 0.6414 m to inputs 1 and 2 of the Moku. Concurrently the 10 MHz synchronisation signal was sent, also through a 0.6414 m cable, with an additional elbow piece, from the DS345 output to the Moku 10 MHz input. The phase difference between input 1 and input 2, shown in yellow orange in attachment 3, should be sqrt(2) times the phase noise of the Moku.

Attachment 5 shows the same setup, but with the spectrum straight from the Moku, which can be acquired at a maximum speed of 488 Hz. They are relatively consistent in the overlapping frequencies. Attachment 6 shows what happens when the 10 MHz synchronisation is removed. The low frequency performance of individual channels suffers but there is not a substantial change in the difference, yellow orange.

Attachment 8 shows the phase difference performance at 10 MHz, with attachment 7 showing the setup for this measurment. The cable length for this measurment was 0.9993 m for all paths. Again the difference, yellow orange, is comparable to other measurements.

Attachment 1: 20190725__Moku_phase_noise_SRS-DS345.pdf
Attachment 2: Moku_Phase_Noise_Estimate__20190724.csv
Attachment 3: 20190725__Moku_phase_diff_fast_1.pdf
Attachment 4: 20190725__Moku_phase_noise_setup.pdf
Attachment 5: Moku_phasediff_SRSDS345_20MHz_Sync_Screenshot.png
Attachment 6: Moku_phasediff_SRSDS345_20MHz_NoSync_Screenshot.png
Attachment 7: 20190725__Moku_10MHz_phase_diff_setup.pdf
Attachment 8: Moku_phasediff_SRSDS345_10MHz_SyncSig_Screenshot.png
2377   Mon Jul 29 14:46:09 2019 Nathan HollandDailyProgress2micronLasersOptical Phase noise of 2 um Mach Zehnder Interferometer.

Figure 1, attached, shows the phase noise I measure from the 2 um Mach Zehnder interferometer. This phase noise is from the optical path and is affected by:

• Intensity noise.
• Laser frequency noise.
• Differential polarisation shifts through the IFO arms.
• Changes in differential arm length.
• Changes in refractive index.
• Detector noise, in which I am also grouping noise due to the amplifier.

The next step is to determine contributions from each of these sources.

Attachment 2 shows the setup used to measure this noise. Attachment 3 shows the measured phase spectra from both phasemeters of the Moku. Attachment 4 contains the both time series and spectra. The spectra shown here are:

1. Converted to radians, from cycles.
2. Subtracted, in time domain.
3. Converted into power spectra, using Welch's method, 30 averages and Hanning windows.
4. Converted into amplitude spectra, by taking the square root.
Attachment 1: Optical_Phase_Noise_Spectra_2um_Mach_Zehnder__20190729.pdf
Attachment 2: 20190729__Initial_Phase_Noise_Measurement_setup.pdf
Attachment 3: Measured_phase_spectra_2um_Mach_Zehnder__20190729.pdf
Attachment 4: 2um_Mach_Zehnder_data__20190729.hdf5
2378   Mon Jul 29 15:46:50 2019 KojiLaser2micronLasersOptical Phase noise of 2 um Mach Zehnder Interferometer.

Great! Can you convert this into the laser frequency noise Hz/rtHz? I believe this [rad/rtHz] was still the measured phase noise and was neither the laser phase noise nor frequency noise yet.

2379   Mon Jul 29 17:52:33 2019 Shalika SinghDailyProgress2micronLasersNoise Analysis of Circuit using SR785 Spectrum Analyser and Zero Simulation

Attachment 1: The Circuit Diagram,

>>  the TIA with a gain of 5.1k

>>  Differential Circuit with a gain of 100.

Attachment 2: Noise across TIA

The input-referred current noise across the trans-impedance amplifier was measured using SR785 and was compared against the incoherent sum of input-referred current noise graph obtained from ZERO simulation.

Attachment 3: Noise across Differential circuit

The input-referred current noise across the Differential circuit was measured using SR785 and was compared against the graph obtained from ZERO simulation.

During measurement of transfer function using SR785, a source of 1V was given to a 10k resistor which was connected in series with the circuit taken into consideration. The channels of SR785 were set to AC coupling and input was set to Ground. Apart from that Hanning window function was used for measurements from SR785.

Attachment 1: full_circuit.pdf
Attachment 2: Noise_across_TIA.pdf
Attachment 3: Noise_across_Differential_Circuit.pdf
2380   Tue Jul 30 20:42:06 2019 ranaDailyProgress2micronLasersNoise Analysis of Circuit using SR785 Spectrum Analyser and Zero Simulation

Oh no! We've lost all of the low frequency data (which is the whole point of this experiment) and all of the contributing noise sources to the circuit!

2381   Thu Aug 1 11:25:27 2019 Shalika SinghDailyProgress2micronLasersNoise Analysis of Circuit using SR785 Spectrum Analyser and Zero Simulation

Input Referred noise to be calculated for trans-impedance.

Attachment 1: The Setup,

The setup was made on a breadboard, as per the circuit diagram.

Attachment 2: The Circuit Diagram on paper,

>>  the TIA with a gain of 5.1k

Attachment 3: Noise across TIA on SR785 screen

This is the noise as seen on the screen of the SR785

Attachment 4: Noise across TIA captured using the SR785 template file

The input-referred current noise across the TIA was measured using SR785 and was compared against the graph obtained from ZERO simulation.

** There is a difficulty in capturing the exact form of data as displayed on the SR785. Previously, I had captured the full span by keeping the start frequency as 1Hz. This gave only two points between 1Hz and 100Hz, all the rest of 798 points out of 800 were plotted at a higher frequency. This gave a straight line of higher magnitudes at low frequency(1Hz to 100Hz) since there were only 2 points. But the plot on the SR785 screen looks different.

** This time, I divided the measurements into 3 parts, 1Hz to 100 Hz, 100Hz to 10kHz and 10kHz to 100kHz. This left me with a graph which looks clumsier than the previous ones. I guess if there is a way that the template files of SR785 can be modified then it can give a graph which will align properly to the simulated results. For the time being, I can try again to take measurements in 3 sections but this time with fewer(300 instead of 800) points.

** It's difficult to avoid 60Hz harmonics with a circuit kept in open as this one. Lots of its effects are visible in the plot.

Attachment 1: Circuit.pdf
Attachment 2: full_circuit.pdf
Attachment 3: SR785_display_screen.pdf
Attachment 4: Noise_across_TIA.pdf
2382   Thu Aug 1 13:01:15 2019 ranaDailyProgress2micronLasersNoise Analysis of Circuit using SR785 Spectrum Analyser and Zero Simulation

always keep the start frequency at 0 Hz no matter what the span, as I was showing you yesterday in the lab. Otherwise, the bin centers end up in weird places.

2383   Fri Aug 2 16:15:01 2019 Nathan HollandDailyProgress2micronLasersFrequency Noise Measured by 2um Mach Zehnder.

Here I follow, essentially, the same setup as in attachment 2 of elog 2377. The difference is that I measured the LO path and IFO paths sequentially, not concurrently. This allowed me to measure at 125 kilosamples per second. Note that there is an error in the pymoku conversion tool when recording on channel 2 only. To circumvent this record both paths with channel 1.

Shown in attachment 1 is the frequency noise of the 2um Mach Zehnder interferometer. Attachment 2 shows the measured phase noises of the individual paths. Attachment 3 contains the plotted frequency spectra, and phase to frequency conversion factor. The conversion factor from phase, in radians, to frequency is:

$\frac{c}{2 \, \pi \, n \, { \Delta L }_{\text{IFO}} }$

The table below gives the values necessary to calculate this. It is 2.73 x 106 Hz rad-1.

 Parameter Value Notes LO arm length 2.103 m Delay line arm length 14.6 m Approximation. Awaiting exact value from Aidan. Refractive Index 1.4 Assuming SiO2. From refractiveindex.info Awaiting manufacturer response for precise value.

The smoothed spectra below were generated by this code. The full time series data is too large to upload here, at 272 MB when doubly compressed. Low frequency data is difficult to obtain due to the length of time that there is sufficient SNR for the phasemeter to lock onto the 80 MHz signal. Locking the Mach Zehnder could resolve this problem.

Attachment 1: Measured_Mach_Zehnder_frequency_noise_SmoothMedian__20190805.pdf
Attachment 2: Measured_phase_spectra_2um_Mach_Zehnder_BB_SmoothMedian__20190805.pdf
Attachment 3: 2um_MachZehnder_frequency_noise__20190805.hdf5
2384   Thu Aug 8 17:19:12 2019 Shalika SinghNoise Budget2micronLasersNoise Analysis of TIA using SR785 Spectrum Analyser and Zero Simulation

Input Referred noise to be calculated for trans-impedance.

Attachment 1: The Circuit Diagram on paper,

>>  the TIA with a gain of 5.1k

Attachment 2: Noise across TIA

The input-referred current noise across the TIA was measured using SR785 and was compared against the graph obtained from ZERO simulation.

** This time, I divided the measurements into 7 parts, 0-800, 800-2.4k, 2.4k-5.6k, 5.6k-12k, 12k-24.8k, 24.8k-50.4k, 50.4k-101.6k. The number of points for each was 800. Hanning Window function was used in the template file and the Input channels were grounded.

Attachment 3: Noise across TIA

The input-referred current noise across the TIA was measured using SR785 and was compared against the graph obtained from ZERO simulation.

** This time, I divided the measurements into 1 part, 10-6.4k. The number of points for each was 800. Hanning Window function was used in the template file and the Input channels were grounded.

** To measure the noise the output was measured at the pin6 of the OpAmp.

** A source of 1V was applied to the circuit by keeping a 10k in series with the input of the circuit when Transfer Function was being measured.

** It's difficult to avoid 60Hz harmonics with a circuit kept in open as this one. Lots of its effects are visible in the plot.

Attachment 4: Noise of the power supply used

The power supply was observed to be used to be noisy.

Attachment 1: TIA.pdf
Attachment 2: Noise_across_TIA.pdf
Attachment 3: Noise_across_TIA.pdf
Attachment 4: powersupply.pdf
2385   Fri Aug 9 21:10:48 2019 Shalika SinghNoise Budget2micronLasersNoise Analysis of Circuit using SR785 Spectrum Analyser and Zero Simulation

Input Referred noise is calculated for the circuit that is to be used for characterization of photodiodes. For the biasing 12V was used from SR560 as it provides cleaner voltage as compared to other voltage supplies.

Attachment 1: The Circuit Diagram TIA

>>  the TIA with a gain of 5.1k

Attachment 2: Input Referred noise of TIA

The input-referred current noise across the TIA was measured using SR785 and was compared against the graph obtained from ZERO simulation.

Attachment 3: Differential Circuit

>> gain of 100

Attachment 4: Input Referred noise of Differential Circuit

The input-referred voltage noise measured using SR785 and was compared against the graph obtained from ZERO simulation.

Attachment 5: Whitening Filter Circuit

>> gain of 10

Attachment 6: Input Referred noise of Whitening Filter Circuit

The input-referred voltage noise was measured using SR785 and was compared against the graph obtained from ZERO simulation.

Some points that were observed:

*** I am observing deviation from simulated results at higher frequencies. Presently, I am unable to understand the cause of this deviation.

*** At low frequencies deviation from simulated results is perhaps caused due to 60Hz harmonics and 1/f noise.

Attachment 1: TIA.png
Attachment 2: Noise_across_TIA.pdf
Attachment 3: Differential_Circuit.png
Attachment 4: Noise_across_Differential_Circuit.pdf
Attachment 5: Whitening_Filter.png
Attachment 6: Noise_across_Whitening_Filter.pdf
2386   Sun Aug 11 01:22:04 2019 Shalika SinghNoise Budget2micronLasersNoise Analysis of voltage regulator using SR785 Spectrum Analyser

A comparison between the types of voltage regulators was done in order to know which should be preferred to provide a clean bias supply.

Attachment 1: The Circuit Diagram of the voltage regulator

Tere are 3 types of voltage regulators that were tested.

a. LM317

b. LM7915

c. LM7815

Attachment 2: Output Voltage noise of all 3 voltage regulators

A voltage of 12V(+/-) was provided using SR560 to the respective input of the regulator IC and the output noise across each were measured using the SR785.

LM317 will be a better choice to make a voltage regulator for the circuit mentioned in elog entry 2381.

Attachment 1: regulator.pdf
Attachment 2: Noise_across_Voltage_Regulator_Circuit.pdf
2387   Sun Aug 11 14:35:41 2019 KojiNoise Budget2micronLasersNoise Analysis of voltage regulator using SR785 Spectrum Analyser

Questions:

1) Has the DC output voltages of the regulators checked?

2) What's the target voltages of the regulator circuits? And how the voltages were supplied from the power supply port of the SR560? 7815 is the regulator meant for +15V and 7915 is for -15V. So the input voltages need to have at least 3V larger voltages than the target voltages (like +18V for 7815, -18V for 7915). If the +/-12V are naitvely applied, the regulators don't reach the operating point.
Check "Voltage Drop" descriptions in the data sheets of the regulator chips.

3) What's the purpose of these diodes? I believe they are for the regulator protection against the transient sign flip during power switching etc as well as over voltageprotection. The circuit of the 7915 has the larger potential difference (like -18V) while the output has -15V. This means the diode will always be on. If this is just a typo in the figure, it's not a big deal. If this is the real situation, it is a big problem.

4) Why were there such huge 60Hz lines? Was the SR560 properly operated with its battery?

2388   Sun Aug 11 19:15:32 2019 Shalika SinghNoise Budget2micronLasersNoise Analysis of voltage regulator using SR785 Spectrum Analyser

1. For LM317 I received the output of 11.2V and for LM7915 -10V and for LM7815 at 10.4V

2. I did a mistake with the supply. Next time I won't use SR560 and will use a voltage supply instead.

3. The diode is for protection purpose. How should I use the diode for 7915, should I put it in forward bias or not use it at all?

4. I did check the voltage supply provided by SR560 using a multimeter, they were 12V.

 Quote: Questions: 1) Has the DC output voltages of the regulators checked? 2) What's the target voltages of the regulator circuits? And how the voltages were supplied from the power supply port of the SR560? 7815 is the regulator meant for +15V and 7915 is for -15V. So the input voltages need to have at least 3V larger voltages than the target voltages (like +18V for 7815, -18V for 7915). If the +/-12V are naitvely applied, the regulators don't reach the operating point. Check "Voltage Drop" descriptions in the data sheets of the regulator chips. 3) What's the purpose of these diodes? I believe they are for the regulator protection against the transient sign flip during power switching etc as well as over voltageprotection. The circuit of the 7915 has the larger potential difference (like -18V) while the output has -15V. This means the diode will always be on. If this is just a typo in the figure, it's not a big deal. If this is the real situation, it is a big problem. 4) Why were there such huge 60Hz lines? Was the SR560 properly operated with its battery?

2389   Sun Aug 11 22:34:50 2019 KojiNoise Budget2micronLasersNoise Analysis of voltage regulator using SR785 Spectrum Analyser

3. You need to flip the direction of the diode.

1&2 OK, so the circuits were not fucntioning. Use a dual voltage supply (in a proper cascading setting) and give +/-18V.

4. When you use SR560 as a power supply, you need to disconnect the AC power supply. Otherwise, the AC power, which charges the +/-12V lead battery, contaminates the output voltage with the 60Hz lines.

2390   Mon Aug 12 11:37:36 2019 Shalika SinghNoise Budget2micronLasersNoise Analysis of Circuit using SR785 Spectrum Analyser and Zero Simulation

Referring to elog entry 2385. I did the measurements again because mistakingly I had been using the SR560 with it's AC supply on. This time I used the 12V supply with no connection to the AC supply.

Attachment 1: The Circuit Diagram TIA

>>  the TIA with a gain of 5.1k

Attachment 2: Input Referred noise of TIA

The input-referred current noise across the TIA was measured using SR785 and was compared against the graph obtained from ZERO simulation.

Attachment 3: Differential Circuit

>> gain of 100

Attachment 4: Input Referred noise of Differential Circuit

The input-referred voltage noise measured using SR785 and was compared against the graph obtained from ZERO simulation.

Attachment 5: Whitening Filter Circuit

>> gain of 10

Attachment 6: Input Referred noise of Whitening Filter Circuit

The input-referred voltage noise was measured using SR785 and was compared against the graph obtained from ZERO simulation.

Attachment 7: The Scripts

All the scripts and data used in the measurement.

** I did notice a reduction in 60Hz harmonics but I still see a deviation from simulated results at higher frequencies and at frequencies below 10Hz.

Attachment 1: TIA.png
Attachment 2: Noise_across_TIA.pdf
Attachment 3: Differential_Circuit.png
Attachment 4: Noise_across_Differential_Circuit.pdf
Attachment 5: Whitening_Filter.png
Attachment 6: Noise_across_Whitening_Filter.pdf
Attachment 7: Noise.zip
2391   Mon Aug 12 11:51:38 2019 Shalika SinghNoise Budget2micronLasersNoise Analysis of Voltage Regulator using SR785 Spectrum Analyser

Referring to elog entry QIL:2387. I did the correction with the voltage supply and now provided a supply of 18V(+/-) to LM7815 and LM7915. The position of diodes was also corrected for LM7915. The Electrolytic Capacitors(100uf) I am using are getting heated when using with LM7915 only. I didn't find any tantalum capacitors of 100uf in EE shop. Should they be replaced with some other capacitors?

Attachment 1: The Circuit Diagram Voltage regulator

The component used                   Input Voltage                              Output Voltage

a. LM7915                                    -18 V                                  -15.1 V

b. LM7815                                    18 V                                    14.86 V

c. LM317                                      18 V                                    17 V

Attachment 2: Output Voltage noise of regulator circuit

The noise observed using SR785 at the output of each regulator.

Attachment 1: regulator.pdf
Attachment 2: Noise_across_Voltage_Regulator_Circuit.pdf
2392   Mon Aug 12 12:09:00 2019 Nathan HollandSummary2micronLasersAdjusting the Voltage/Frequency Offset on the Brimrose AOM Driver.

The 80 MHz brimrose AOM driver, which came with the AOM, can actually drive between 75 MHz and 85 MHz. It has an input port, which accepts between 0V and 10V, for altering the frequency.

Previously, before Friday 2019-08-09, I had set the offset to + 5V, using a signal generator because that was what was available in the QIL lab. The signal generator, for some unclear reason, had then moved this offset to +4.4 V, when plugged into the AOM driver. Attachment 1 shows a power spectrum, from the BB PD, One notices a large peak negatively detuned from the 80 MHz signal frequency. Attachement 2 shows a zoom in, around 70 MHz, revealing this peak to be two peaks, one near 78 MHz, and another smaller one near 79 MHz.

I decided to adjust the voltage, input to the frequency port, to minimise the RF sidebands I observed. The results of this adjustment can be seen in attachments 3, and 4. Notice that there no observable sidebands. This was achieved with an offset of 4.52V.

Attachement 5 is the manual for the AOM, and its driver. (Removed by KA)

Attachment 1: 2um_MachZehnder_wide_PowerSpectrum_Screenshot.png
Attachment 2: 2um_MachZehnder_narrow_PowerSpectrum_Screenshot.png
2393   Mon Aug 12 15:17:05 2019 KojiNoise Budget2micronLasersNoise Analysis of Voltage Regulator using SR785 Spectrum Analyser

1. Heat: Check the polarity of the electrolytic or tantalum caps.

2. Add 0.1uF high-K ceramic caps in pararel to these electrolytic or tantalum caps.

3. Why does LM317 have only one volt drop? It requires minimum 3V mergin between the input and output voltages. (See the datasheet)

2394   Tue Aug 13 16:53:57 2019 Nathan HollandElectronics2micronLasersPhase Noise of Brimrose AOM Driver (VCO).

After reviewing the Brimrose AOM driver mnual, yesterday, it turns out I was previously using it incorrectly. It is a VCO with the frequency port accepting a DC voltage, between 0 and 10 V to control the frequency of the AOM - note that the mapping is not intuitive so one should refer to the manual. The modulation port is used for amplitude modulation, not frequency modulation. This port, modulation, has 50 ohm input impedance and accepts signals between DC and 10 MHz - modulating the power output. Table 1 below shows the operating parameters we should use:

Table 1: Recommended, constant, operating procedures for Brimrose AOM driver.
Frequency +9.08 Gives 80 MHz modulation frequency.
Modulation +0.85 Gives 27 dBm of RF output, which is 90% of the maximum linear range of the Brimrose AOM.

Following this I characterised the phase noise of this VCO. Results are shown in attachment 1, for various powers. The setup is shown in figure 2, with the data for M = +0.85 V provided in attachment 3. These results show that this VCO has poor phase performance. A value of M = +0.02 V gives the same RF power as when a 0.5 Vpp signal @ 80 MHz was input into the modulation port - as I was previously doing.

This has a few implications for previous measurements:

• The reason it was hard for the Mach Zehnder to remain locked for a substantial duration was due to the low input power to the AOM. This probably resulted in little signal in the Mach Zehnder LO arm.
• Previously the amplitude modulation would have provided a 80 MHz signal in the Mach Zehnder LO arm

The script used to create the smoothed ASD can be found here.

Attachment 1: 20190813__Brimrose_AOM_Driver_phase_noise.pdf
Attachment 2: 20190813__VCO_phase_noise_setup.pdf
Attachment 3: brimrose_AOM_driver_VCO_phase_noise_spectra.hdf5
2395   Tue Aug 13 17:59:25 2019 Nathan HollandNoise Budget2micronLasersPhase Noise of Mach Zehnder with VCO.

Following up from my previous post I measured the phase noise of the Mach Zehnder setup with the AOM driven properly with its VCO. The setup is shown in attachment 1, and compressed data in attachment 2 (goto here to get the python library to decompress this data). The value of M for this data shown is +0.85 V, though I have data for other voltages - however it should affect the performance. Using the low frequency preview I was able to see that I would need to coherently subtract the phase measurements of both measurements, which restricted me to a maximum sampling frequency of 15 kHz.

The measured data is shown in attachment 3. Already you can see that the phase noise of the VCO limits the measured phase from the IFO. This also tells me that previously, when I was modulating the VCO, the AM was affecting the measured phase. When I convert this difference into frequency noise the result can be seen in attachment 4. One upside of this setup is that the signal from the IFO is much more robust, so the PLL can stay locked for longer. This is a consquency of increased drive, 24 dB more, on the AOM.

To me this demonstrates that the way forward is to replace the VCO driving the AOM with a RF amplifier, driven by a low noise (or lower noise) signal generator. The Moku is able to drive at 80 MHz. We have a Mini Circuits ZHL-5W-1 (ZHL--5W) amplifier in the laboratory. This has 46.4 dB of gain, and a maximum power output of 37 dBm. The maximum power that can be input into the AOM is 27.8 dBm (0.6 W). Thus with an appropriate setup this miniciruits amplifier should be a viable repalcement for the current VCO.

Attachment 1: 20190813__Phase_Noise_Measurement_VCO_setup.pdf
Attachment 2: MachZehnder_w_AOM_Driver_085_20190813_102449.li
Attachment 3: 20190813__MachZehnder_w_VCO-phase_noise.pdf
Attachment 4: 20190813__MachZehnder_w_VCO-frequency_noise.pdf
2396   Tue Aug 13 19:03:05 2019 Shalika SinghNoise Budget2micronLasersNoise Analysis of Voltage Regulator Circuit using SR785 Spectrum Analyzer

As it was observed that normal voltage supply is noisy and not suitable for our circuit, we plan to use a voltage regulator that will help us provide a clean supply. Referring to previous elog entries the corresponding corrections were made( polarity of electrolytic capacitors, ceramic cap in parallel to electrolytic, 3V difference between input and output of respective regulators).

Attachment 1: The Circuit Diagram of Voltage regulator

The component used                   Input Voltage                              Output Voltage

a. LM7915                                    -18 V                                  -15.1 V

b. LM7815                                    18 V                                    14.86 V

c. LM317                                      18 V                                   14.96 V

Attachment 2: Output Voltage noise of regulator circuit

The noise observed using SR785 at the output of each regulator is shown. It clearly shows that LM317 manifests less noise in comparison to LM7915 and LM7815. It will be therefore a good idea to use this to provide 15V bias in our circuit.

Attachment 3: The Scripts

Find all the scripts and data used in this measurement.

Attachment 1: regulator.pdf
Attachment 2: Noise_across_Voltage_Regulator.pdf
Attachment 3: regulator.zip
2397   Tue Aug 13 19:14:04 2019 JonComputingCymacsNFS server set up

I rebuilt one of our old desktop machines to serve as NFS server for the cymac. It is running Debian 10.0 and assigned IP 10.0.1.169 (hostname qil-nfs). I installed a new 2 TB hard drive dedicated to hosting the LIGO RTS software and frame builder archive, which is shared with all other lab machines via NFS.

I have moved the new machine into the server rack and copied the contents of /opt/rtcds on the cymac into the shared location. Functionality like sitemap and the CDS tools can now be run directly from the QIL workstation (plus any other machine on which we add the NFS mount).

Attachment 1: IMG_3587.jpg
2398   Wed Aug 14 16:07:57 2019 Nathan HollandDailyProgress2micronLasersNew AOM Driver.

After reproting phase noise issues with the VCO, here, I have changed the VCO for a high power RF amplifier - a mini circuits ZHL--5W==sma (ZHL-5W-1). It is being driven by thre Moku to provide the 80 MHz signal. Please note the following:

• This is a high power amplifier so you should follow the correct high power amplifier turn on/off procedure.
• The amplifier can output a maximum of 5W. However the AOM can only tolerate a maximum of 0.6 W. Ensure that an appropriately small signal is input into the amplifier, as to not break the AOM.

The new setup is shown in attachment 1. Attachment 2 show the phase noise of the LO arm. This is now a much more acceptable level, as compared to the previous VCO. I am outputting -19.2 dBm, and measuring 5.3 dBm on input 2. This means I am driving the AOM at 24.8 dBm, or 0.302 W.

With the greater drive on the AOM, as compared to previous incorrect useage of the VCO, the signal from the IFO arm is much more robust. Attachment 3 shows the phase time series of the IFO arm. You will notice the large jumps, which spoil the spectrum, not shown here. In attachment 4 I zoom into the largest of these jumps. You can see it is comprised of several linear transitions, which occur over a short time period.

Aidan has suggested that locking the laser is the best way to avoide these non-stationary noise sources. He suggests that these jumps could be mode hops of the laser.

Attachment 1: 20190814__Phase_Noise_Setup.pdf
Attachment 2: MachZehnder_measured_phase_noise-LO_path__20190814.pdf
Attachment 3: MachZehnder_measured_phase-IFO_path__20190814.pdf
Attachment 4: MachZehnder_measured_phase-IFO_path_zoom__20190814.pdf
2399   Wed Aug 14 19:50:37 2019 Shalika SinghNoise Budget2micronLasersNoise analysis of Sallen Key filter using SR785 and Zero simulation

The photodiode needs a 1V bias so for a clean bias we have decided to use a sallen key low pass filter with a cut off frequency at 1Hz. The quality factor of the designed sallen key filter is 0.707.

Attachment 1: The Circuit Diagram of Sallen Key filter

The gain of the circuit is 1.

Attachment 2: The transfer function of the filter

We can see the cut off frequency at 1Hz

Attachment 3: The Input Referred Noise of filter

The input-referred voltage noise was obtained using SR785 and compared with zero simulation. It deviates a lot from the simulated results by a factor of 100.

Attachment 4: Scripts

Find all the data and scripts used for the measurements.

Attachment 1: sallenkeyfilter.pdf
Attachment 2: Transfer_function_of_sallen_key.pdf
Attachment 3: Noise_across_SallenKey.pdf
Attachment 4: sallenkey.zip
2400   Thu Aug 15 02:30:29 2019 KojiSummary2micronLasersInAsSb PDs accomodated in PD housings / PD cables

InAsSb PDs were housed in the PD cages. The cages were engraved to indicate the batch (Sb3512 or 3513) and the serials (A1, A2, ...).

The PD legs does not have an indicator for the pin1. So, the tab of the PD case is directed "UP". Also the direction of the tab is marked on the cage. The tab of the short plug was also aligned to Pin1. However, the PD case is too thin and the PDs can rotate in the cases.
So the face photo was also taken so that it indicates how Pin 1 looks like from the PD face. (Attachment 4)

Also made the cable for the LaserComponents PD and the InAsSb PD. Pin n shows up as Pin n of DB9 Male connector.

Once we have the PD test is the bias circuit (with a monitor) and some patch panel kind of preparation, we can start working on the PD test.

Attachment 1: P_20190814_214159.jpg
Attachment 2: P_20190814_214537.jpg
Attachment 3: P_20190814_215119.jpg
Attachment 4: P_20190814_215158.jpg
Attachment 5: P_20190814_220035.jpg
Attachment 6: P_20190814_220553_003.jpg
Attachment 7: P_20190814_220832.jpg
Attachment 8: P_20190814_220841.jpg
Attachment 9: P_20190814_235137.jpg
2401   Thu Aug 15 08:03:13 2019 ranaNoise Budget2micronLasersNoise Analysis of Voltage Regulator Circuit using SR785 Spectrum Analyzer
I'm glad to see that the voltage regulators can give good noise performance. I wish I understood what the gain peaking features came from - maybe the choice of capacitors?
2402   Thu Aug 15 08:36:29 2019 ShalikaNoise Budget2micronLasersNoise Analysis of Voltage Regulator Circuit using SR785 Spectrum Analyzer

I found only 1uF Tanatalum Capacitors in the EE shop. Maybe a a higher capacitance of tantalum capacitor will help.

Another thing, is it good to compare the input referred noise for the different types of regulators? I did a comparison between the output noise only.

 Quote: I'm glad to see that the voltage regulators can give good noise performance. I wish I understood what the gain peaking features came from - maybe the choice of capacitors?

2403   Thu Aug 15 15:45:30 2019 DuoLab Infrastructure Floor plan around the big cryostat

Chris and I went to the lab and made some plans about how to use the space around the optics table. Attached a drawing of it. A couple notes about the drawing:

1. Green: underneath. The rough pump is under the table. The connection to the coldhead goes on the floor.

2. Rack: electronics rack.

3. Yellow cabinet: the cabinet that has chemicals in it.

4. Turbo/Rough: pumps.

Attachment 1: autodraw_8_15_2019.png
2404   Fri Aug 16 01:28:28 2019 KojiSummary2micronLasersSwitchable breakout bok

DB9 switchable breakout box is ready. We are ready to do some PD test now.

Attachment 1: P_20190815_210355.jpg
Attachment 2: P_20190815_210419.jpg
2405   Sun Aug 18 14:16:59 2019 DuoSummary Measuring the dark current of PD

Koji set up an experiment measuring the dark current of the photodiodes. A bias voltage is given and the current is converted to voltage via a TIA, where it is measured. Also note that in order to provide a high quality bias voltage, we LP the output of the device with a second order sallen key filter cutoff at 1Hz.

Attachment 1: exp.pdf
Attachment 2: IMG_2921.png
2406   Mon Aug 19 13:57:02 2019 ShalikaNoise BudgetPD noiseDark noise of Sb3513_A2

[Koji, Nathan, Duo, Shalika]

The dark noise of the Sb3513_A2 photodiode was observed using an SRS785 spectrum analyzer. Different bias voltages were provided to understand the dependency of dark noise on the bias voltage. It was observed that as the bias voltage deeps on decreasing the dark noise decrease too. A transimpedance amplifier with a gain of 5k was used to convert photocurrent into voltage. A Sallen key low pass filter was used in order to provide a low noise bias.

** Since the gain of the TIA was 5k so the output voltage noise was divided by 5k in order to get dark current noise.

Attachment 1: Dark current noise across Sb3513_A2 500um

Attachment 2: Dark current noise across Sb3513_A2 750um

Attachment 3: Dark current noise across Sb3513_A2 1000um

Attachment 4: Dark Current across Sb3513_A2 500um, 750um, 1000um respectively

Attachment 5: zip file containing all data

[added (Nathan)] Attachment 6: Experiment setup.

Attachment 1: Noise_across_500um.pdf
Attachment 2: Noise_across_750um.pdf
Attachment 3: Noise_across_1000um.pdf
Attachment 4: Dark_current.pdf
Attachment 5: JPL_Sb35313_A2.zip
Attachment 6: PD_test_setup.pdf
2407   Fri Aug 23 12:45:08 2019 Shalika SinghNoise Budget2micronLasersNoise Analysis of Circuit using SR785 Spectrum Analyser and Zero Simulation

The circuit has been soldered(refer entries 2399) and the noise for Sallen Key was analyzed

Attachment 1: Circuit Diagram of Sallen Key low pass filter( cut-off= 1Hz)

Attachment 2: Transfer Function of sallen key.  The Frequency response Measurement was done using the Swept Sine group. The input range was -50dBVpk.

Attachment 3: Noise comparison between zero and SR785 measurements. The noise matches the simulated results to a great extent and also it's less noisy so can successfully be used to bias the photodiodes(1V).

Attachment 4: Zip File

Attachment 1: sallenkeyfilter.pdf
Attachment 2: bodeplot_sallenkey.pdf
Attachment 3: Noise_across_SallenKey.pdf
Attachment 4: sallen.zip
2408   Fri Aug 23 14:15:58 2019 DuoNoise Budget2micronLasersNoise Analysis of Circuit using SR785 Spectrum Analyser and Zero Simulation

I think this is a solid measurement.

 Quote: The circuit has been soldered(refer entries 2399) and the noise for Sallen Key was analyzed Attachment 1: Circuit Diagram of Sallen Key low pass filter( cut-off= 1Hz) Attachment 2: Transfer Function of sallen key0 Attachment 3: Noise comparison between zero and SR785 measurements. The noise matches the simulated results to a great extent and also it's less noisy so can successfully be used to bias the photodiodes(1V) Attachment 4: Zip File

2409   Fri Aug 23 17:35:37 2019 KojiNoise Budget2micronLasersNoise Analysis of Circuit using SR785 Spectrum Analyser and Zero Simulation

The TF looks good. But the noise measurement is obviously limited by the SR785 noise. We need a preamp, which is only for the purpose of the measurement. It has to have the input reffered noise about a factor of a few better than the noise predicted by Zero. At high frequency, probably we will be able to use SR560. With this low noise level, probably we can just use the flat gain of 100 for the SR560 setting. This will give you the input referred noise (of the preamp) of  ~4nV/rtHz at kHz band. Note that the gain needs to be larger than 100 to have low noiseness of SR560.

 Quote: I think this is a solid measurement.

2410   Mon Aug 26 10:45:43 2019 Shalika SinghNoise BudgetPD noise1/f noise analysis and dark current density

The 1/f noise and dark current density were analysed for Sb3513_A2 photodiode.

Attachment 1: Dark current density plot

It was observed that the dark current density has a very less difference for measurements taken across 500um, 750um and 1000um. It means that the leakage current is of low magnitude.

Attachment 2: 1/f noise at 10Hz

The 1/f noise for 500um, 750um and 1000um was plotted and 1/f noise is high for 1000um as the bias is increased. and 1/f noise is high for 500um at low bias voltages.

Attachment 3: Zip file

Attachment 1: Dark_current_density.pdf
Attachment 2: 1_fnoise.pdf
Attachment 3: JPL_Sb35313_A2.zip
2411   Wed Aug 28 21:25:20 2019 Shalika SinghNoise Budget2micronLasersNoise Bump observed at 8kHz during TIA noise analysis

The noise analysis for TIA was done. The circuit was in open but kept away from SR785 (to avoid any noise effect)

Attachment 1 and 2 show how the setup was placed. The wires were kept in a way that there is no tension. The wires that were used for connection from the voltage supply were twisted in order to avoid any inductance issue. The input range was kept at -44BVpk (this was maintained at all points when taking measurements with SR560) while using the SR785. SR560 was used with a flat gain of 100 in order to get above the noise of SR785 and also the AC coupling was used. LM317 and LM337 were used to provide a 15V(+/-) supply to OpAmp. The OpAmp used here is Op27.

Attachment 3 shows the noise analysis across TIA(using Op27). It was observed that the voltage regulators help in noise reduction to a great extent at low frequencies but somehow at around 8kHz, a huge noise bump is being observed. I also checked the noise by using directly the voltage supply at the lab. It does impart high noise at low frequencies but it's clearly visible that noise bump at 8kHz isn't there. The noise bump exists only when the voltage regulators are being used with the OpAmp. I did check if the output of voltage regulators were oscillating due to some reason but they provided a constant output of 15.04V(+/-).  I did check if the OpAmp was broken but it isn't the case because the difference between the voltage at pin 2 and 3 is zero, I have two TIA on my board so I checked the noise for both of them and I observed the same results.

Attachment 4 shows the noise of TIA using LT1792. It was seen that the 8kHz noise bump is evident on even changing the OpAmp.

I am unable to understand how is this issue coming up. I did the measurement quite a few times just to be sure It's not a one-time thing but the noise bump is dominant.

Attachment 5: Zip

Attachment 1: circuit.jpg
Attachment 2: circuit_setup.jpg
Attachment 3: Noise_across_TIA_op27.pdf
Attachment 4: Noise_across_TIA_LT1792.pdf
Attachment 5: TIA.zip
2412   Thu Aug 29 15:36:49 2019 KojiNoise Budget2micronLasersNoise Bump observed at 8kHz during TIA noise analysis

You need to check the voltage noise of the regulator outputs with the opamps connected. Probably you did it. If so, it is a riddle why the 8kHz bump is not observed in the regulator outputs, but is in the opamp outputs...

Does the noise bump happen with the +/-15V supplied by 7815/7915? How about to change the capacitor values for LM317/337 to the ones recommended in the data sheet?

It is great to see the noise peaks were largely reduced by LT1792. This is what I found before although I can't explain why.

2413   Fri Aug 30 05:11:11 2019 ChrisNoise Budget2micronLasersNoise Analysis of Voltage Regulator Circuit using SR785 Spectrum Analyzer

In case we need to seek a further reduction in the voltage regulator noise, Wenzel has kindly published their ideas for a little noise-eating circuit at the regulator output.

 Quote: As it was observed that normal voltage supply is noisy and not suitable for our circuit, we plan to use a voltage regulator that will help us provide a clean supply. Referring to previous elog entries the corresponding corrections were made( polarity of electrolytic capacitors, ceramic cap in parallel to electrolytic, 3V difference between input and output of respective regulators). Attachment 1: The Circuit Diagram of Voltage regulator The component used                   Input Voltage                              Output Voltage a. LM7915                                    -18 V                                  -15.1 V b. LM7815                                    18 V                                    14.86 V c. LM317                                      18 V                                   14.96 V       Attachment 2: Output Voltage noise of regulator circuit The noise observed using SR785 at the output of each regulator is shown. It clearly shows that LM317 manifests less noise in comparison to LM7915 and LM7815. It will be therefore a good idea to use this to provide 15V bias in our circuit. Attachment 3: The Scripts Find all the scripts and data used in this measurement.

2414   Tue Sep 3 16:47:08 2019 DuoLab Infrastructure QIL lab floor plan

We plan to set up the big cryostat in the QIL lab. We make a plan on how to use the space in this area.

We have these items related to this experiment: the chamber, the compressor, the pump and the crane. The crane is used to lift the lid of the chamber when we open it.

The chamber sits on the table, its diameter is about 2'4''. We put it at the corner of the table, giving us more accessible space around it.

The compressor is used to cool the system. It is connected to the chamber via the coldhead so we will need a small table to hold the coldhead at the output of the chamber.

The pump has two parts: rough pump and turbo pump. Rough pump has more noise so we put it under the table. The turbo pump is connected to the chamber and we need a stand for that too.

The current plan for the crane is that we want to screw the crane onto the floor. We do not have space for a big crane base.

Attachment 1: qilfloor.pdf
2415   Wed Sep 4 22:14:12 2019 ranaLab Infrastructure QIL lab floor plan

what about attaching a crane to the ceiling on one of the supporting beams?

2416   Thu Sep 5 11:10:08 2019 Shalika SinghNoise BudgetTIANoise Analysis of transimpedance amplifier

Noise analysis was done using SR785. SR560 was used with a flat gain of 100 to get above the noise floor of SR785. The input range was constantly maintained at -44dBVpk for all measurements. Voltage regulators LM317 and LM337 were used to power the circuit. 200 averages were taken for all the measurements. The TIA was configured with a 5.1k feedback resistor and 100pf feedback capacitor. Please refer elog:2390 for better understanding of the circuit diagram.

** Referring to elog:2411 the 8kHz noise bump went away on its own without changing anything in the circuit. I have no clue how it happened and why it's not happening again.

Attachment 1: Noise analysis using OP27 in transimpedance amplifier. At Frequencies below 100Hz, data was taken in 4 parts, starting from 0Hz with a span of 25Hz but with 10 number of averages(fewer averages were taken only in this case).  At high frequencies(above 100Hz) data was taken with 200 averages. A noise was observed to be 10pA/rtHz was observed at 10Hz and 3pA/rtHz above 300Hz.

Attachment 2: LT1792 was used in this case. It was seen that it is less noisy as compared to OP27. The noise was observed to be 2pA/rtHz above 20Hz.

Attachment 3: LT1012 was used for this measurement. The noise was observed to be 3pA/rtHz above 20Hz.

Attachment 4: AD820 was used for this case. The noise was observed to be 3pA/rtHz above 500Hz.

Attachment 5: OPA140 was used for the TIA during this measurement. The noise was observed to be 2pA/rtHz above 2Hz.

Attachment 6: Noise comparison between all the OpAmps used. It was seen that OP27 isn't able to deliver performance as expected because it is getting affected a lot by the noise(1/f noise). OPA140 performs better than all the others.

Attachment 7: Zip file to re-create all data

Attachment 1: Noise_across_TIA_Op27.pdf
Attachment 2: Noise_across_TIA_LT1792.pdf
Attachment 3: Noise_across_TIA_LT1012.pdf
Attachment 5: Noise_across_TIA_OPA140.pdf
Attachment 6: Noise_comparison_across_TIA.pdf
Attachment 7: TIA_4sep.zip
2417   Thu Sep 5 15:40:22 2019 ranaNoise BudgetPD noiseNoise Analysis of transimpedance amplifier

I'm pretty sure that the OP27 data is still not right. You should use the small binwidth and larger # of averages as we talked about earlier this week. In the elog, you should give the PSD parameters.

2418   Sun Sep 8 16:08:04 2019 ranaElectronicsGeneralSolder: what kind of solder to use and why?

This is a summary of some information on types of solder and their usefulness.

Summary: use the 63/37 Sn/Pb solder from Kester. It is eutectic and has a low melting point so that your opamps won't get damaged.

Eutectic:

We want our solders to be "eutectic" so that it goes from the liquid phase directly to solid with no intermediate slurry. This makes a reliable (and nice looking!) solder joint.

The tin-lead solder is a good combo.

1. Basics of solder choice from Hackaday
2.  NASA's Tin Whiskers homepage
3. "Tin Whiskers are Real & Complex" Maxim
2419   Tue Sep 10 17:17:11 2019 Shalika SinghNoise BudgetPD noiseDark Noise measurement of Extended InGaAs

**edited as per suggestions in elog:2420

The dark noise of IG22X2000T9(serial: X8906 and X8905), Extended InGaAs photodiodes was measured. A low pass sallen key filter(using OP27) with a gain of +1 and cut off frequency of 1Hz was used to provide the bias voltage to the photodiode. A transimpedance amplifier(using OPA140, refer elog:2416 for noise spectrum of TIA) with a gain of 5.1k was used to convert the output current of the photodiode to voltage. The input range was maintained at  -50 dBVpk during the measurement.

A bias voltage of 1.017 V was provided and the output voltage across the transimpedance amplifier was observed to be as follows:

X8906:    -0.030V, which implies that the dark current was -5.887uA.

X8905:   -0.097V, which implies that the dark current was -19.01uA.

Attachment 1: Setup representation

Attachment 2: Experimental Setup. It was made sure that the cables are free from any tension. Connections were made using BNC connectors. The transimpedance amplifier and sallen key filter were placed in a box and were not in direct contact with the optical bench. During measurement data was taken with a linewidth of 125mHz(was increased logarithmically for subsequent measurements, since measurement was taken in parts) with 200 averages for each set.

Attachment 3: Dark noise plot. The data was taken for X8906 for 5 different bias voltages. The input range was maintained at  -50 dBVpk during the measurement. It was observed that dark noise decreases with decrease in bias voltage.

Attachment 4: Dark noise plot. The data was taken for X8905 for 4 different bias voltages. The input range was maintained at  -46 dBVpk during the measurement. It was again observed that the dark noise decreases with a decrease in bias voltage.

***** The noise is observed very low for a 0V bias for both the photodiodes below 10kHz. It was observed that noise is high above 10kHz at all the bias voltages for both the series.

Attachment 5: Dark Current plot for both X8905 and X8906 series of photodiodes.

Attachment 6: Dark Current Density for both X8905 and X8906 series.

Although being made of the same material both the photodiodes have some difference in their dark current. It was observed that the photodiodes are very noisy at room temperature. I think they will deliver better performance at low temperatures.

Attachment 7:  The 1/f noise was observed at 10Hz for both the series of photodiodes.

Attachment 8:  Zip file to re-create the data.

Attachment 1: PD_test_setup.pdf
Attachment 2: setup.jpg
Attachment 3: Noise_across_extended_InGaAs_X8906.pdf
Attachment 4: Noise_across_extended_InGaAs_X8905.pdf
Attachment 5: Dark_current_Extended_InGaAs.pdf
Attachment 6: Dark_current_density_Extended_InGaAs.pdf
Attachment 7: 1_fnoise_Extended_InGaAs.pdf
Attachment 8: Extended_InGaAs.zip
2420   Tue Sep 10 18:38:18 2019 KojiNoise BudgetPD noiseDark Noise measurement of Extended InGaAs

- Previously, your TIA was pretty much dominated by the thermal noise current of the 5K transimpedance resistor (=0.129/sqrt(5000) nA/rtHz ~2pA/rtHz).
So, I believe it's impossible to measure 1pA/rtHz. Please check if you had any saturation or anything along the chain.

- Do you need SR560? If you think you are limited by the input noise of SR785 when having no SR560, you can use your whitening filter, which is supposed to be sufficient and better in terms of the output voltage range.

- Please note the serial number of the PD under the test.

- And, try to isolate your box from the optical table.

2421   Tue Sep 17 23:42:41 2019 Shalika SinghLaserPD QEMeasuring Quantum Efficiency of Extended InGaAs Photodiode

[Koji, Shalika]

Further measurements were done after elog:2419 for Quantum Efficiency of Extended InGaAs Photodiodes(X8906). A Laser of wavelength 2um was used with an incident power of 0.80+0.02mW.  The Ophir RM9 power meter was used to check the incident power and also measure the reflectivity.

Attachment 1: The Setup. A Fibre launcher was used to project the laser along with a converging lens of the focal length of 40.0 mm which was further arranged with a subsequent converging lens of  150mm focal length. A mirror was used to reflect the laser light on the photodiode at an angle of 45o. The bias voltage was provided to pin 4 of photodiode using a Sallen Key low pass filter and the output at pin 3 of the photodiode was fed to a transimpedance amplifier (with a gain of 5.1k) which converted the photocurrent to voltage.

Attachment 2: The Quantum Efficiency is plotted with respect to different bias voltages, It was observed that the quantum efficiency increases with an increase in bias voltage. An External Quantum Efficiency of 77.4% was observed at 1V(maximum bias voltage for the photodiode). The Internal Q.E was observed to be 83.8% taking into account Reflectivity of (60.0+1) uW at an angle of 17deg.

Attachment 3: To recreate all data

Attachment 1: IMG_8915.JPG
Attachment 2: QE_X8906.pdf
Attachment 3: Extended_InGaAs.zip
2422   Fri Sep 20 17:31:25 2019 DuoDailyProgressGeneralGeneral update

Basically two things are happening in the lab now.

1) We are assembling a shop list for the lab, buying a couple things to put the stuff together. After the purchase, relevant items will be uploaded under this post.

2) I made the TIA with OP27, trying to measure it noise. But the lab has too much environment noise. I will try measuring it after hours or in the EE shop and see if that gives a better results. Progress on that front will reply to this post later too.

ELOG V3.1.3-