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  2071   Thu Nov 10 19:04:28 2016 awadeUpdateScatterometerTesting InGaAs camera

Yesterday we had a meeting with Nick Lechocinski from Axiom Optics about InGaAs cameras.  He went over various products they sell, which pretty much fall in the pixel count/noise/price range of the various other competitors.  They have lent us a logarithmic response InGaAs camera.

I have been trying to get the camera to talk to the software on a windows laptop we have in the lab.  It turns out that the interface HAS to be USB 3.0 or higher, which we don't have on any windows computers I know about (unless there is one at the 40m). I've spent a good chunk of time trying to get USB 3.0 ports on my Macbook pro to forward to an instance of Windows 7 on VirtualBox. It frustrating as USB 3 was supposed to be backward AND forward compatible but in this case the camera is not working for whatever reason.  

Having tried various things with VirtualBox (including installing all the extra windows Guest Additions), I'm not sure its worth pushing on with that option. Mike and Christian don't have any PC laptops with USB 3.0 spare.  I may repartition a spare MacMini of mine tomorrow to see if that works and maybe ask around more for a laptop. 

Pictures of camera attached.

 

Attachment 1: 2016-11-09_18.05.48.jpg
2016-11-09_18.05.48.jpg
Attachment 2: 2016-11-09_18.05.55.jpg
2016-11-09_18.05.55.jpg
  2119   Fri Jun 9 16:58:35 2017 DhruvaUpdateWOPOWOPO Experiment Stuff

Today, Eric and I unboxed and inventoried the WOPO experiment components that Andrew had ordered. 

Attached, is a pdf with pictures of the components with the packaging lists. 

Attachment 1: ATF_WOPO_inventory.pdf
ATF_WOPO_inventory.pdf ATF_WOPO_inventory.pdf ATF_WOPO_inventory.pdf ATF_WOPO_inventory.pdf ATF_WOPO_inventory.pdf ATF_WOPO_inventory.pdf ATF_WOPO_inventory.pdf ATF_WOPO_inventory.pdf
  2122   Fri Jun 16 18:55:40 2017 DhruvaUpdateWOPOMode Matching the 1064nm Beam into fibre

In order to collimate the 1064nm beam from the laser into the fibre, we are using the Thorlabs F240-APC-1064 fixed focus collimation package. The required beam diameter for this is 1.76mm. I used ABCD Propagation to try and come up with an optimal 3 lens solution to obtain a collimated beam of this size. The solution is as follows - 

f1 = 30cm at z = 105cm ( z = 0 being the location of the Diabolo waist)

f2 = 20cm at z = 122.5cm

f3 =12.5cm at z = 146cm

I profiled the beam after the first and second lenses in order to correct my estimation of initial beam waist and location. 

I have positioned the third lens in such a way that the spot size 43.5cm (waist location in ABCD prop) from the lens is around 880 microns as required by the collimator 

I have also placed the collimator at the above mentioned location and have connected it to the 1064 single mode fibre. At the other end of the fibre, I have placed a photodiode and am attempting to get a signal from it in order to maximize coupling efficiency. 

 

 

Note: The 400mW beam has been attentuated to 4mW by an HWP and PBS.

 

Attachment 1: 3_lens_solution.pdf
3_lens_solution.pdf
Attachment 2: 1064_f1_profile.pdf
1064_f1_profile.pdf
Attachment 3: 1064_f2_profile.pdf
1064_f2_profile.pdf
Attachment 4: Mode_Matching_Lenses.jpg
Mode_Matching_Lenses.jpg
  2124   Mon Jun 26 10:55:02 2017 DhruvaUpdateWOPOTemperature Control of the PPKTP Waveguide

For the temperature control of the non linear waveguide, we will be using the Newport 3040 Temperature Controller. The phase matching temperature of the crystal is 62.3 C. The TEC will be run with the following settings - 

Lower Lim Temp = 20 C

Upper Lim = 70 C

Max Current = 0.65A

Gain Mode = 10 Fast 

C1 = 1.0445e-3

C2 = 2.5075e-4

C3 = 0 

 

The waveguide has been mounted on a ThorLabs LM14S2 Universal Butterfly Pin Mount. The TEC Driver is a 9 pin input while the TEC output from the controller is a 15 pin output so I made an adapter for the two different configurations.

Upon testing the Temperature Control of the Waveguide, we found that the equilibrium temperature always falls about 1.1 C below the set temperature.

 

 

TO-DO

Plot phase matching curves of SHG in the crystal. 

 

 

 

 

Attachment 1: image2.JPG
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Attachment 10: IMG_20170621_155640512.jpg
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  2125   Tue Jun 27 11:34:00 2017 DhruvaUpdateWOPOMode Matching Woes - Fibre issues

The WOPO experiment has been quite stagnant for the last two weeks because ineffective coupling of the 1064 light into the fibre (max 10%). Beam profiling says that the ABCD simulation results were correct, and there is no problem with the fibre collimation package. Yesterday, Andrew and I found a possible culprit. On examining the fibre with a microscope we found that the core of one of the ends is fine while the other has been damaged. I am attaching pictures of both the ends. 

We will attempt to clean the fibre. If that doesn't work out, then we will order a new one. 

 

Attachment 1: image2.JPG
image2.JPG
Attachment 2: image4.JPG
image4.JPG
  2126   Wed Jun 28 13:24:35 2017 awadeUpdateWOPOPDs for homodyne detector

I asked Koji if he had any hight QE photodiodes to use in a ballenced homodyne detector.  None of the Ad LIGO ones can be used for this but Zach had a small stockpile in the ATF lab.

Pictures attached of the boxes (two in total).  I need to track down the PO or part numbers to work out what they are.  They look like they are ~1.5 mm^2 area, all with windows still on.

 

 

Attachment 1: 2017-06-28_13.21.32.jpg
2017-06-28_13.21.32.jpg
Attachment 2: 2017-06-28_13.17.32.jpg
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Attachment 3: 2017-06-28_13.17.00.jpg
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Attachment 4: 2017-06-28_13.16.51.jpg
2017-06-28_13.16.51.jpg
  2127   Wed Jun 28 20:05:02 2017 KojiUpdateWOPOPDs for homodyne detector

I beieve that they are Exelitas C30642.
FYI: There also is one on the former-gyro optical table. This one doesn't have the cap.

  2128   Thu Jun 29 22:42:28 2017 awadeUpdateWOPOMode Matching Woes - Fibre issues

I've reordered fiber that was damaged.  

Need to profile the beam actually going into the fiber after the third lens.  If the slit profiler isn't large enough for the 1760 µm beam then maybe try the WinCamD CCD profiler.  You might need to ask around to find which lab its in. 

Quote:

The WOPO experiment has been quite stagnant for the last two weeks because ineffective coupling of the 1064 light into the fibre (max 10%). Beam profiling says that the ABCD simulation results were correct, and there is no problem with the fibre collimation package. Yesterday, Andrew and I found a possible culprit. On examining the fibre with a microscope we found that the core of one of the ends is fine while the other has been damaged. I am attaching pictures of both the ends. 

We will attempt to clean the fibre. If that doesn't work out, then we will order a new one. 

 

 

  2129   Fri Jun 30 12:17:07 2017 KojiUpdateWOPOMode Matching Woes - Fibre issues

Measure the profile of the back propagation beam by injecting a beam from the other side.
This gives you how the input mode should be.

  2130   Sun Jul 2 19:47:35 2017 awadeUpdateWOPOMode Matching Woes - Fibre issues

Do you recall if there are any fiber coupled 1064 nm lasers anywhere in the 40m or other bridge west labs?

Quote:

Measure the profile of the back propagation beam by injecting a beam from the other side.
This gives you how the input mode should be.

 

  2131   Sun Jul 2 21:21:39 2017 KojiUpdateWOPOMode Matching Woes - Fibre issues

Jenne's laser at the 40m PD testing table is a fiber coupled 1064nm DL.

But you just can couple 5~10% of the beam from the other side of the fiber to know the mode at the input side.
It does not require too much effort if you have the fiber testing illuminator to align the beam.

  2132   Wed Jul 5 16:44:34 2017 KojiUpdateWOPOPDs for homodyne detector

Correction: If the diode is 3mm x 3mm, it is Excelitas C30665.

  2133   Thu Jul 6 15:03:07 2017 DhruvaUpdateWOPOHomodyne Design

I am attaching a schematic of the proposed design for the Homodyne detector. The damping capacitance in the two photodetectors has to be decided based on what we estimate the capacitance of the photodiode to be. 

Please let me know if there's anything I can do to make this better suited for homodyne detection.

 

Attachment 1: Homodyne.pdf
Homodyne.pdf
  2135   Mon Jul 10 12:12:26 2017 DhruvaUpdateWOPOEfficient Fibre Coupling and Phase Matching Plot

Using the 632nm laser provided by Gautam to back couple the 1064nm light into the fibre, I managed to finally get efficient mode matching. For 25.4mW of light going into the collimator, the fibre outputs 19.3mW (~76%).  Now that efficient mode matching has been achieved, I finally managed to plot the SHG Phase matching curve for the PPKTP Waveguide (a plot of output power (532nm) against the temperature). I fit the data obtained to the function 

P_0sinc((T-T_0)/a)^2

Here, the normalised sinc(x) fiunction is given by 

\frac{sin(\pi x)}{\pi x}

The optimised values are 

P_0 = 65.3 \mu W Maximum SHG Power

T_0 = 60.99  Optimum Phase Matching Temperature.

a = 2.609  

That gives the FWHM as 2.32 C.

The maximum output is much lower than expected as that is because of loss at the fibre coupling at the waveguide. This loss is visible and I am attaching a couple of pictures. 

Attachment 1: Phase_Matching.pdf
Phase_Matching.pdf
Attachment 2: Green_Loss_1.jpg
Green_Loss_1.jpg
Attachment 3: Green_Loss_2.jpg
Green_Loss_2.jpg
  2141   Tue Jul 18 22:09:14 2017 DhruvaUpdateWOPOPhotodetector Dark Noise

These are the plots of the dark noise of the Thorlabs photodetectors lying in the ATF lab using the FFT network analyser. For higher frequency ranges, I have to configure the other network analyser. 

These are the settings that the analyser was running on - 

Measure Group: FFT
Measurement: FFT 1
Num of extracted Points: 401
FFT Lines:  400 
Window: Hanning
Averaging Mode: RMS
Averaging Type: Exp. / Cont.
Overload reject: On

Edit : I've added a stiched plot of all the collected data. The noise from 10-100KHz is around the order of 40nV. We're hoping to see if we can do better by designing our own photodetectors. We also see a lot of peaks that correspond to the harmonics of the 60Hz mains. 

 

Edit 2: The Photodetector is the Thorlabs PDA55 detector.  We CANNOT use this detector as it is silicon and has a terrible quantum efficiency at 1064nm. 

Attachment 1: 20170714-pda55noise.pdf
20170714-pda55noise.pdf
  2142   Thu Jul 20 18:16:33 2017 ranaUpdateWOPOPhotodetector Dark Noise

Ugh - I deleted those 1000 bad plots. Just give us 1 trace per PD, all on one plot. Each trace should also include the model # of the PD. Just 'stuff we have laying around' is not useful.

Also, what are the requirements on the PD? Describe how these are computed.

  2144   Sat Jul 22 14:25:55 2017 DhruvaUpdateWOPOTable Noise Issues

Yesterday, with a lot of help from Koji, we built the transimpedance circuit (Gain = 10k) for the photodetectors of the homodyne circuit.

While doing so, we encountered a most bizzare issue. The circuit shows a significantly larger amount of noise (especially in the 10-100kHz band) when it is on the table as opposed to when it is suspended in air. I'm attaching pictures if the setup as well as a comparative plot. We still cannot ascertain the reason behind this extra noise.

Attachment 1: 20170721-_table_noise.pdf
20170721-_table_noise.pdf
Attachment 2: 20170721_Circuit_in_Air.jpg
20170721_Circuit_in_Air.jpg
Attachment 3: 20170721_Circuit_on_Table.jpg
20170721_Circuit_on_Table.jpg
  2145   Sat Jul 22 14:41:07 2017 DhruvaUpdateWOPOPhotodetector Dark Noise

 

Quote:

Yesterday, with a lot of help from Koji, we built the transimpedance circuit (Gain = 10k) for the photodetectors of the homodyne circuit.a

I connected the Excelitas C30665 photodiode to the above transimpedance circuit and measured the dark noise while suspended in air (please refer previous elog on table noise). 

For a mW of light and a quantum efficiency of about 87%, we expect to see about 0.68mA of current. This gives the shot noise to be 14.7pA/sqrt(Hz) which corresponfs to about 147nV/sqrt(Hz) for a 10k gain which is significantly higher than the noise floor of the circuit between 10 and 100KHz.

Attachment 1: 20170721-dark_noise.pdf
20170721-dark_noise.pdf
  2146   Sat Jul 22 14:43:16 2017 DhruvaUpdateWOPOSubtractor Circuit Noise

I also made a op-amp subtractor circuit for the homodyne detector and measured the noise. It is significantly lower than the shot noise.

Attachment 1: 20170721-subnoise.pdf
20170721-subnoise.pdf
  2198   Sat May 5 06:08:35 2018 EricUpdate LabJack U3 New Setup

Changed the setup for LabJack testing so that we can better isolate problems with the DAC and ADC (if they exist). The previous setup consisted of passing two signals through the LabJack and comparing their outputs using the Rayleigh statistic. Since there are problems activating two DACs and two ADCs on the LabJack at once, we needed a different design that would only use one of these at a time. The new design (Figure 1) inputs a digital signal which is stored as a control signal to compare against. Next, the digital signal is passed through the DAC and comes out as an Analog signal through terminal DAC0. Since only the DAC or the ADC can run at one time, the DAC is then paused until the ADC converts the signal back to digital, at which point the ADC is paused and the DAC resumes functioning. Theoretically, this conversion should be happening at 100 Hz, and in practice, this number will be very close to 100 Hz. With this setup, problems occur after running the LabJack where either the DAC or the ADC stops passing through data. This doesn’t happen immediately but will happen seconds to minutes after the test begins. This seems to occur because the DAC and ADC are being turned on and off too quickly. However, if we run the DAC and ADC at too low of a rate then we lose resolution on the test wave and it becomes harder to run statistics on the data set. I believe I can get this setup to work by tuning the sampling frequency of the DAC and ADC so we're in a spot that allows the LabJack to both pass through data but also allows us to have a high enough resolution to run other tests on the data set.

I will attempt to get the first setup to work. However, if I can’t resolve the issues with the DAC or ADC not passing through data, we could also attempt a different setup that moves the Analog to Digital conversion out of the LabJack so that the DAC doesn’t need to be switched on and off (Figure 2). With this setup, we would need to purchase an ADC that can be soldered onto a Raspberry Pi (MCP3008).

Attachment 1: Figure1.JPG
Figure1.JPG
Attachment 2: Figure2.JPG
Figure2.JPG
  2258   Tue Oct 30 10:17:44 2018 RahulUpdate SHI Cryocooler

We have received the SHI cryocooler CH-104 (figure attached), which has been moved to the QIL. I have inspected all the components after unboxing it. Cold head test report supplied by SHI is attached below.

The cryocooler comes with a HC-4A Zephyr air cooled helium compressor. This compressor is a single stage, air cooled and designed to deliver high pressure helium gas to the cryocooler.

There are 2 helium supply/return (although both the hose says supply, which I am not sure why, hence will check it out) hose along with a kit to install it. This is currently charged with helium pressure of 280 psi, however, once it is installed then the helium pressure has to be adjusted (I am currently reading the manual to assemble the system).

The cryoocoler cold head will be finally placed on a bench which we have bought. I plan to use a breadboard to clamp it down. The compressor will be placed a few feet (based on hose length) away from it. Typically the compressors are noisy, hence later on we can get longer hose to keep the compressors further away.

The vacuum chamber (collar) will be moved in the lab and on the optical bench this Thursday (although this was supposed to be moved in last week, however due inadequate communication by the Caltech moving service this couldn't happen).

The top and bottom flange covers for the vacuum chamber (fabricated by Kurt Lesker) has been shipped on 24 Oct and we should be receiving it this week.

Attachment 1: cryocooler.jpg
cryocooler.jpg
Attachment 2: compressor.jpg
compressor.jpg
Attachment 3: supply_hose.jpg
supply_hose.jpg
Attachment 4: Cold_test_report_SHI.jpg
Cold_test_report_SHI.jpg
  2259   Fri Nov 2 08:59:26 2018 RahulUpdate Vacuum chamber

We have our shiny new vacuum chamber (fabricated by Nor-Cal), now sitting on the optical bench.

Attachment 1: IMG_0005.jpg
IMG_0005.jpg
Attachment 2: IMG_0008.jpg
IMG_0008.jpg
Attachment 3: IMG_0007.jpg
IMG_0007.jpg
  2260   Fri Nov 9 14:57:54 2018 RahulUpdate Cryo-vacuum chamber

SHI Cryocooler – Vacuum chamber assembly

The attached picture shows a schematic of the assembly/connection of SHI cryocooler to the vacuum chamber. The cryocooler has warm flange mounting holes. Using a mating flange – hose/bellows will be connected to the cryocooler. The mating flange will have a port for roughing pump and vacuum gauge connection. The hose/bellows will be connected to the flange reducer which will be bolted to the CF (4-5/8 size) flange of the cryostat.

I will upload a CAD model of the mating hose and will also look for an appropriate size hose and flange reducer.

Attachment 1: Picture1.jpg
Picture1.jpg
  2261   Wed Nov 14 16:49:47 2018 RahulUpdateCryo vacuum chamberassembly

The top (seen with several threaded holes along with 16 through holes) and bottom (only 2 threaded holes for lifting and 16 through holes) plate for the vacuum chamber has arrived and I have moved them into the QIL optical bench/table. Using some aluminum struts/bosch, I am making a simple 3’’ tall spacer on top of which the bottom plater will be resting. After wiping them with solvents, I will start assembling the chamber and the plates.

Attachment 1: Bottom_plate.jpg
Bottom_plate.jpg
Attachment 2: top_plate.jpg
top_plate.jpg
  2301   Fri Mar 8 17:05:52 2019 AnjaliUpdate Frequency stabilization of 2 micron source

 

The schematic of the homodyne configuration is shown below.

Following is the component list

Item Quantity Availability Part number Remarks
Laser diode 1 Yes EP 2004-0-DM-B06-FA  
Isolator 1 Yes    
Coupler(50/50) 5 Yes TW2000R5A2A Fiber type : SM2000
Delay fiber   Yes SM2000 Need to check the exact length of the fiber
Photodetector 4 Yes DET10D  
SR560 3 Yes    

 

Attachment 1: Homodyne_setup_2micron.png
Homodyne_setup_2micron.png
  2313   Tue Mar 26 17:13:53 2019 AnjaliUpdate2micronLasersFrequency stabilization of 2 micron source

Experimental plan 

  • The aim is to repeat the homodyne measurement setup with  balanced detection scheme for the frequency stabilisation of 2 micron laser source.
  • Attachment # 1 shows the schematic of the experimental setup.
  • All the components specified in the schematic are available.
  • For the balanced detection, we can initialy use SR560, but we need to design a new circuitry for the same.
Attachment 1: Homodyne_setup_for_2_micron.pdf
Homodyne_setup_for_2_micron.pdf
  2317   Thu Mar 28 18:16:59 2019 JonUpdateComputingCymac assembly started

This afternoon Chris and I installed the ADC and DAC cards in fb4.

  • We connected them to the timing card adapters (left external to the computer chassis for now).
  • We found fb4 to be running Debian 8 so first attempted to upgrade to 9, as that is the version supported by Jamie's cymac binaries.
  • However, we encountered problems during the upgrade, apparently with gdm (the linux GUI). 
  • By switching to consol mode and killing gdm, were able to proceed to the point of updating all the packages.
  • It completed successfully, but then the system failed to reboot, even in recovery mode.
  • During boot, the advligo-rts kernel fails to start, and then boot hangs completely at the point the graphical interface is started.

We may want to start with a fresh install of Debian 9 and just reinstall the LIGO binaries.

  2319   Mon Apr 1 11:03:24 2019 JonUpdateComputingCymac assembly started

I know there is some CTN slow channel data on the disk. Is it at all possible to boot so that can be recovered?

Quote:

This afternoon Chris and I installed the ADC and DAC cards in fb4. We connected them to the timing card adapters (left external to the computer chassis for now).

We found fb4 to be running Debian 8 so first attempted to upgrade to 9, as that is the version supported by Jamie's cymac binaries. However, we encountered problems during the upgrade, apparently with gdm (the linux GUI). By switching to consol mode and killing gdm, were able to proceed to the point of updating all the packages. It completed successfully, but then the system failed to reboot, even in recovery mode. During boot, the advligo-rts kernel fails to start, and then boot hangs completely at the point the graphical interface is started.

We may want to start with a fresh install of Debian 9 and just reinstall the LIGO binaries.

 

  2323   Wed Apr 10 12:17:34 2019 AnjaliUpdate2micronLasersIntensity noise stabilization of 2 micron source

[Aidan, Anjali]

  • Attachment #1 shows the cleaned up setup for  2 micron experiment
  • We also have received the AOM . The initial test is to do the intensity stabilisation of 2 micron laser diode using AOM
  • Today, we started with the laser and AOM characterisation
  • Attachment #2 shows the schematic of the experimental setup for the laser characterisation. Laser output is connected to a Faray isolator and the isolator output is measured using Thorlabs thermal power meter.
  • The current limit on the current controller is set to 95 mA (maximum allowed current to the laser diode is 120 mA) and thermistor is set to 10 kohm (maximum value of thermistor resistance is 10 kohm)
  • Attachment #3 shows the output power as a function of input current to the laser diode.
  • From the data sheet of the laser diode, the threshold current is 20 mA.For a given inut current,  the output power measured is less compared to the value given in the data sheet. This is beacuse of the insertion loss of the isolator in the path.
  • The slope efficieny is calculted to be 0.018 mW/mA. The value given in the data sheet is 0.3 mW/mA. The reduction is because of the insertion loss of the isolator
  • The output of isolator is then connected to the AOM. Attachement #4 shows the schematic of the setup. The zeroth order port of the AOM is connected to the power meter and the output power from the first order port is blocked.
  • We then applied a dc voltage to the modulation input port of the AOM driver. We expect a decrease in the power from the zeroth order port with increase in the input voltage to the  AOM driver as the light is getting deflcted and power is geting coupled to the first order port.
  • Attachmet #5 shows the variation in power from zeroth order port with input voltage to the AOM driver.As expected, the power levels are decreasing with increase in input voltage
  • It is also observed that the output power levels are fluctuating. This could be because of temperature fluctuation and the thermal power meter is sensitive to that. 
Attachment 1: 2_micron_setup.jpg
2_micron_setup.jpg
Attachment 2: Laser_chara_setup.png
Laser_chara_setup.png
Attachment 3: Laser_characteristics.pdf
Laser_characteristics.pdf
Attachment 4: AOM_chara_setup.png
AOM_chara_setup.png
Attachment 5: AOM_characteristics.pdf
AOM_characteristics.pdf
  2325   Wed Apr 10 18:58:48 2019 ranaUpdate2micronLasersIntensity noise stabilization of 2 micron source

OK...but how will the amplitude stabilization be done? How about a diagram showing the feedback loop and electronics?

  1. what is the feedback circuit?
  2. Can it drive the low impedance of an AOM driver?
  3. What is the photodiode?
  4. It has to be an AC coupled feedback (DC coupled is always terrible).
  5. What is the requirement on the intensity noise as a function of frequency?
Quote:

[Aidan, Anjali]

  • Attachment #1 shows the cleaned up setup for  2 micron experiment
  2328   Wed Apr 24 09:01:49 2019 AnjaliUpdate2micronLasersIntensity noise stabilization of 2 micron source

Attachment #1 shows the schematic of the experimental setup for amplitude stabilization using AOM. The proposed idea is as follows

  • The output power from the  Zeroth order port of the AOM depends on the RF power supplied to the AOM and the  RF power from the RF driver is dependent on the input voltage to the driver. 
  • When amplitude of the laser chnages to due to amplitude noise, the output from photodiode will also changes. The output of one of the photodiodes is connected through a gain element (G) to the RF driver of AOM. So, when PD output changes , the gain of the gain element should be adjusted such that the input voltage to the AOM driver changes and thus the RF power which affect the output power from the AOM. 
  • The gain element could be SR560 (I still have to understand more about it) and the photodiodes that we have are thorlabs DET10D detector which are DC coupled. We also need additional TIA stage after the PD. There were two of them built by the summer student. We tested both and one of them only works fine now.
Quote:

OK...but how will the amplitude stabilization be done? How about a diagram showing the feedback loop and electronics?

  1. what is the feedback circuit?
  2. Can it drive the low impedance of an AOM driver?
  3. What is the photodiode?
  4. It has to be an AC coupled feedback (DC coupled is always terrible).
  5. What is the requirement on the intensity noise as a function of frequency?
Quote:

[Aidan, Anjali]

  • Attachment #1 shows the cleaned up setup for  2 micron experiment

 

Attachment 1: Intensity_stabilisation.png
Intensity_stabilisation.png
  2338   Fri May 10 16:22:45 2019 AnjaliUpdate2micronLasersCharacterization of RF driver and AOM .

Following are the results from RF driver and AOM characterisation.

  • Attachment #1 shows the results from  characterisation of Brimrose RF driver . The RF power and frequency are measured on Agilent spectrum analyser. A 30 dB attenuator was also used in the path from RF driver to spectrum analyser. This attenuation value is taken care in RF power output calculation. The RF driver has two BNC connectors labelled as “Modulation” and “Frequency” , located on the front panel. Varying the modulation input (in the range 0 V to 1 V) changes the RF output power from the RF driver as shown in attachment #1 (a). The maximum RF output power is about 0.6 W and the input RF power to the AOM is limited to this value as exceeding the same might cause damage to the AOM. Varying the frequency input (in the range 0 V to 10 V) changed the RF frequency from the RF driver as shown in attachment #1 (b). The AOM centre frequency is at 80 MHz with a frequency shift range of 8 MHz.

  • Attachment #2 and #3 shows the output power from the zeroth order and first order port of the AOM when the frequency input voltage to the RF driver (thus the RF frequency from the driver) is varied. The output power from the first order port is maximum (output power from zeroth order is minimum) when the frequency is about 78.8 MHz.  As expected, the power in the zeroth order port is completely transferred to the first order port. This happens when the frequency input voltage to the RF driver is about 8.8 V.

  • Attachment #4 and #5 shows the output power from the zeroth order port of the AOM when the Modulation input voltage to the RF driver (thus the RF power from the driver) is varied. The output power from the first order port is maximum (output power from zeroth order is minimum) when the RF power to the AOM is maximum. This happens when the modulation input voltage to the RF driver is 1 V.

  • Attachment #5 shows the diffraction efficiency to the first order port (we use output power from first order port for the heterodyne measurement) as a function of frequency and RF power. The diffraction efficiency is calculated from the ratio of Power in first order port to the input power to the AOM.The power at the input end of AOM is 1.29 mW. So the percentage value calculated includes the insertion loss ( as per data sheet : 3-4 dB for the first order port ) as well . So the conclusion is , inorder to get maximum diffraction efficiency to the first order port of AOM, we should supply RF power of about 0.6 W at 78.8 MHz . If we are using the Brimrose driver, this can be set by giving modulation input voltage of 1 V and frequency input voltage of 8.8 V.

Attachment 1: RF_driver_characterisation.pdf
RF_driver_characterisation.pdf
Attachment 2: AOM_zero_order_output_Vs_Frequency.pdf
AOM_zero_order_output_Vs_Frequency.pdf
Attachment 3: AOM_first_order_output_Vs_frequency.pdf
AOM_first_order_output_Vs_frequency.pdf
Attachment 4: AOM_zeroorder_output_Vs_RF_power.pdf
AOM_zeroorder_output_Vs_RF_power.pdf
Attachment 5: AOM_first_order_output_Vs_RF_power.pdf
AOM_first_order_output_Vs_RF_power.pdf
Attachment 6: Diffraction_efficiency.pdf
Diffraction_efficiency.pdf
  2343   Wed May 15 20:08:01 2019 AnjaliUpdate2micronLasersPLL loop for frequency noise measurement
  • We are trying to setup the phase locked loop (PLL) for the frequency noise measurement of 2 micron laser. We started with a sample experiment in which we were trying to lock an arbitrary function generator (AFG) with the Marconi using PLL. Attachment #1 shows the schematic of the PLL setup. We are using a level 7 mixer (ZFM-3-S+). The RF port is connected to  AFG and LO port to Marconi. Output of mixer is passing through a low pass filter with cut off frequency at 1.9 MHz (SLP-1.9 +). The output of LPF is fed into input A of SR 560. SR560 is set with 1 MHz low pass. Initially, we set a gain value of 10 dB and actuation slope of 100 kHz/V in SR 560 and Marconi respectively. The 50 Ohm output  of SR 560 was connected to Marconi and the 600 Ohm output was connected to an oscilloscope to check the performance of PLL. The carrier frequency from AWG and Marconi were set close to each other (~ 11 MHz). We observed  a dc output at about 60 mV on the oscilloscope. This ensures that PLL is working.
  • We then attempted to measure the band width. To do that, the source output from SR785 was fed into input B of SR560. Part of the source output was fed into channel 1 of SR 785, through T connector, for the transfer function measurement. We also used a T connector at the input A port of SR 560 and one of the ports of this T connector was fed into channel B of SR785. I still must interpret most of the results that we got.

  • Attachment # 2: Closed loop transfer function (a) Magnitude (b) Phase, at different gain values  in SR 560 when the Marconi actuation slope is 10 kHz/V.

  • Attachment # 3: Closed loop transfer function at different actuation slope value in Marconi when the gain is 7 dB.  The increase in noise at lower frequency in phase plot (b) may indicate that the phase/frequency noise of the Marconi increases if the actuation slope value is increased. 

  • Attachment # 4: Closed loop transfer function at different actuation slope value set in Marconi when the gain is 10 dB. The transfer function measured for the case of gain = 10 dB and actuation slope = 100 kHz/V (that is the product of gain and actuation slope is larger) shows significantly different characteristics.

  • Using the SSUserFn option in SR785, we tried to get the open loop transfer function as well from SR 785. The functional form was \frac{x}{1-x}

  • Attachment # 5: Open loop transfer function at different gain values set in SR 560 when the Marconi actuation slope is 10 kHz/V. The unity gain band width are 0.9 kHz, 2.8 kHz and 5.8 kHz respectively when the gain values are 3 dB, 7 dB and 10 dB

  • Attachment # 6 : Closed loop transfer function at different actuation slope value set in Marconi when the gain is 7 dB. The unity gain band width are 3 kHz, 9 kHz and 30 kHz respectively when the actuation slope values are 10 kHz/V, 30 kHz/V, and 100 kHz/V.

  • We also tried to estimate the open loop transfer function from the closed loop transfer function using the equation G_{ol}=\frac{G_{cl}}{1-G_{cl}}

  • Attachment # 7 : Comparison of Open loop transfer function that is measured from SR 785 and that is estimated from the closed loop transfer function using the above expression. These two values are significantly different. Kindly correct me.

Attachment 1: PLL_setup.png
PLL_setup.png
Attachment 2: closed_loop_FM_dvn_10kHz_diff_gain.pdf
closed_loop_FM_dvn_10kHz_diff_gain.pdf
Attachment 3: closed_loop_gain_5_diff_FM_dvn.pdf
closed_loop_gain_5_diff_FM_dvn.pdf
Attachment 4: closed_loop_gain_10_diff_FM_dvn.pdf
closed_loop_gain_10_diff_FM_dvn.pdf
Attachment 5: open_loop_FM_dvn_10kHz_diff_gain.pdf
open_loop_FM_dvn_10kHz_diff_gain.pdf
Attachment 6: open_loop_gain_5_diff_FM_dvn.pdf
open_loop_gain_5_diff_FM_dvn.pdf
Attachment 7: Comparison_measured_estimated_open_loop.pdf
Comparison_measured_estimated_open_loop.pdf
  2344   Thu May 16 13:40:13 2019 anchalUpdate2micronLasersPLL loop for frequency noise measurement

I think you have made some coding error in your attachment 7 plot. Just pick a point in your plot and calculate by hand if your estimate is correct. Otherwise, we need to see your code to pinpoint the error. You can attach your code in a .zip file here.

  2346   Sat May 18 22:25:30 2019 AnjaliUpdate2micronLasersCharacterization of new detector

The new photo detector has arrived (https://www.newport.com/p/818-BB-51F) . We did the DC and AC characterization of the same.

  • Following table shows the results from DC characterisation            
  • Laser diode current (mA) Input power (mW) Output voltage(mV)
    50 0.5 7.2
    70 0.9 13.6
    90 1.3 19.7
  • In this case, the input power was measured after the isolator.The power to voltage conversion is linear. The voltage levels are very low because this is a non-amplified detector. Also, the detector is coupled to a FC/UPC patch cord and we have all FC/APC fiber connectors. So, there could be some coupling loss from FC/APC to FC/UPC. FC/APC to FC/UPC conversion patch cord is ordered. We can check the performance again after it is arrived.

  • We then assembled the Mach-Zehnder interferometer (MZI) for the 2-micron laser source. Attachment #1 shows the schematic of the same. We measured a power level of 0.37 mW when the AOM was not turned on (RF power to AOM off). When AOM is turned ON, the power level measured at the output of MZI is 0.5 mW. Power meter was then replaced with the new photodetector and the beat note was observed on spectrum analyser.

  • Attachment # 2 shows the RF beat note at 78.8 MHz on spectrum analyser. So, the band width of the detector is enough to work at this frequency range. The signal to noise ratio is about 37 dB. There are some small peaks appearing at around 77 MHz and 80 MHz, but they are about  29 dB below the main peak.
  • Attachment # 3 shows the noise floor. There are no other RF interferences at this frequency range.
Attachment 1: setup.png
setup.png
Attachment 2: beat_note.pdf
beat_note.pdf
Attachment 3: Noise_floor.pdf
Noise_floor.pdf
  2347   Sun May 19 22:08:09 2019 AnjaliUpdate2micronLasersPLL loop for frequency noise measurement
  • After the discussion with Prof.Rana, we realised the mistake in our analysis. It was also suggested to make the measurement at the output of SR560. Attachment #1 shows the schematic of the setup for the measurement of closed loop transfer function. The RF power from AFG is 0 dBm and that  from Marconi is 7 dBm.

  • The open loop transfer function is calculated from closed loop transfer function using the expression G_{ol}=\frac{G_{cl}+G_{560}}{G_{cl}} , where G_{560}} is the gain value set in SR560.

  • Attachment #2 : Closed loop and open loop transfer functions at different values of gain in SR 560 when the actuation slope in Marconi is 10 kHz/V. The unity gain frequencies are respectively 1kHz, 3 kHz and 5 kHz when the gain values are 3 dB, 7 dB and 10 dB.

  • Attachment #3 : Closed loop and open loop transfer function at different values of actuation slope in Marconi when the gain in SR 560 is 10 dB.The unity gain frequencies are respectively 5kHz, 16 kHz and 43 kHz when the actuation slope values are 10 kHz/V, 30 kHz/V and 100 kHz/V. It can be seen that the characteristics are significantly different for a larger value for the product of gain and actuation slope (G=10, S=100 kHz/V).

  • The probing signal from SR 785 was then disconnected. In this case, the oscilloscope measure the error signal in time domain and the measurement from SR 785 essentially gives the frequency noise of AFG. The measurement from SR 785 has the unit of V/rt Hz, which is then multiplied with actuation slope to get the frequency noise in Hz/rt Hz. During our measurements, the oscilloscope signal was showing a low level ( mV) DC line , confirming that the PLL is  locked.

  • Attachment # 4 : Frequency noise of AFG at different gain value in SR 560 when the actuation slope in Marconi is 30 kHz/V. In the full span mode, the line width (resolution) is 128 Hz where as the line width is 2 Hz in short span mode. The peak at 60 Hz visible in short span plot corresponds to AC mains. 

  • Attachment # 5 : Frequency noise of AFG at different  actuation slope in Marconi when the gain in SR 560 is 10 dB.  I was thinking, we should measure the same frequency noise irrespective of the setting in the PLL. It can be seen from attachment # 5 that the frequency noise measurement is affected by the value of actuation slope in Marconi. It was earlier observed that the phase noise of Marconi increases with increase in the actuation slope and , from these measurment shown in attachment #5, we are seeing increase in frequency noise value at larger values of actuation slope in Marconi.

Quote:

 

  • We also tried to estimate the open loop transfer function from the closed loop transfer function using the equation G_{ol}=\frac{G_{cl}}{1-G_{cl}}

  • Attachment # 7 : Comparison of Open loop transfer function that is measured from SR 785 and that is estimated from the closed loop transfer function using the above expression. These two values are significantly different. Kindly correct me.

 

Attachment 1: setup_close_loop_transfer_function.png
setup_close_loop_transfer_function.png
Attachment 2: Actuation_slope_10kHzV_diff_gain.pdf
Actuation_slope_10kHzV_diff_gain.pdf
Attachment 3: gain_10_different_actuation_slope.pdf
gain_10_different_actuation_slope.pdf
Attachment 4: FM_noise_AFG_Actuation_30kHzV_diff_gain.pdf
FM_noise_AFG_Actuation_30kHzV_diff_gain.pdf
Attachment 5: FM_noise_AFG_gain_10_different_actuation_slope.pdf
FM_noise_AFG_gain_10_different_actuation_slope.pdf
  2348   Mon May 20 02:23:14 2019 AnjaliUpdate2micronLasersFrequency noise measurement of 2 micron source using PLL
  • Attachment # 1 shows the schematic of the experimental setup for the frequency noise measurement of 2-micron laser source using PLL. Instead of Brimrose driver, another Marconi is used to provide the RF power to the AOM. We know from the characterisation of AOM that we need to give RF power of 28 dBm at 78.8 MHz to achieve maximum diffraction efficiency to the first order port of AOM. The maximum output power from Marconi is 13 dBm. Hence, we used another RF amplifier (ZHL-3-A+) to amplify the RF power from Marconi. We initially tested the RF output from RF amplifier on spectrum analyser (RF power fed into spectrum analyser with proper attenuation in the path) and adjusted the RF frequency and power in Marconi such that we get 28 dBm output power from the RF amplifier at 78.8 MHz. The two marconis are set such that they are share the same time standard.

  • Now, the output power from the photodetector in MZI (Laser diode operated at input current of 90 mA) is fed into the RF input port of the mixer, instead of AFG. The 600 Ohm output of SR 560 is observed on oscilloscope and SR 785 simultaneously.

  • We observed dc line in the oscilloscope when the gain in SR 560 is set to 13 dB (20 times). Gain value below this ( 10 dB) or above this (17 dB) was showing oscillations in the oscilloscope with frequency varying with the actuation slope in Marconi. Attachment #2 shows the frequency noise measurement from SR 785 (V/rt Hz value from SR 785 multiplied with the actuation slope).  

  • It is observed that, the time domain trace on the oscilloscope was not very stable. In between, we could see the oscillation was popping up. Also, the trace on SR 785 was swinging a lot (attached the video). As we observed in the case of AFG, the FM noise measured increses with the value of actuation slope in Marconi. 

  • In this case, the RF power that is fed into the RF port of the mixer is very small (~ -40 dBm) compared to our previous experiment with AFG. So, I would like to repeat the sample experiment (locking AFG to Marconi) with AFG set to RF power comparable with that from the actual experiment.I should then find out the unity gain frequency of that particular combination of gain and actuation slope,which would help us to find the frequency range upto which the PLL measurment is valid.

  •  I also need to measure the actual delay line length. I will also clean up the fiber connectors again and we can also use the FC/UPC to FC/APC patch cord for the detector after it is arrived. I still must understand the results better.Since we are using Non-PM fibers, the polarisation fluctuation might have also affected the measurement .Kindly give me further suggestions.

Attachment 1: FM_noise_measurement_setup.png
FM_noise_measurement_setup.png
Attachment 2: 2_micron_FM_noise.pdf
2_micron_FM_noise.pdf
Attachment 3: Oscilloscope.mp4
Attachment 4: SR_785.mp4
  2350   Thu May 23 02:53:19 2019 AnjaliUpdate2micronLasersCharacterization of new detector

FC/UPC to FC/APC patch cord has arrived. I repeated the DC characterisation of the photodetector with this patchcord. The couping is improving by about 2 dB (Table below shws the result)

Laser diode current (mA) Input power (mW) Output voltage (mv)
50 0.5 11
70 0.9 20.7
90 1.3 30.3
Quote:

In this case, the input power was measured after the isolator.The power to voltage conversion is linear. The voltage levels are very low because this is a non-amplified detector. Also, the detector is coupled to a FC/UPC patch cord and we have all FC/APC fiber connectors. So, there could be some coupling loss from FC/APC to FC/UPC. FC/APC to FC/UPC conversion patch cord is ordered. We can check the performance again after it is arrived.

  2351   Thu May 23 03:00:24 2019 AnjaliUpdate2micronLasersFrequency noise measurement of 2 micron source using PLL
  • The delay line length is measured to be 15.7 m. 
  • As suggested by Prof.Rana, I used a DC block after the photodetector and the output of it was then fed into a RF amplifier (ZHL-3 A+). Attachment #1 shows the output of the detector (a) MZI output- we see the beat note at 78.8 MHz and SNR is about 37 dB (b) when light is bloked- we see  radiation from RF amplifier with a small amplitude of about -63 dBm at 78.8 MHz  (c) when RF is turned off. 
  • It can be seen that, after the RF amplifier, the noise level is also increased with the signal.
  • The RF level that is now fed into the mixer is about -23 dBm. But the PLL was not getting locked-oscilloscope trace is oscillating. A video is attached, which is captured when the there were no gain in SR 560 (G=1) and actuation slope was 10 kHz/V. Attachment 2 and 3 shows the corresponsing traces from SR 785 in full span mode and short spn mode respectively. It is observed that , the oscillation strength was increasing as I increased the gain value in SR 560. I doubt, this is happening because of the higher noise level at the RF port of the mixer in this case. The trace on SR 785 was more stable and it was not swinging as much as we observed before. 
Attachment 1: Detector_output.pdf
Detector_output.pdf
Attachment 2: FM_noise_full_span.pdf
FM_noise_full_span.pdf
Attachment 3: FM_noise_short_span.pdf
FM_noise_short_span.pdf
Attachment 4: oscilloscope.mp4
  2353   Sun May 26 01:12:33 2019 AnjaliUpdate2micronLasersFrequency noise measurement of 2 micron source using PLL
  • I added one more amplifier stage (ZFL-500 LN) after the detector. Since noise figure of ZFL-500LN (2.9 dB) is lower than that of ZHL-3A (5 dB), ZFL-500LN is the first amplifier stage after the photo detector and it is followed by ZHL-3A.

  • Attachment # 1 shows the beat note spectrum measured from the spectrum analyser. There was a 30 dB attenuator in the path during the measurement. So, the output RF power from the MZI (with two stages of amplification) is now about 3 dBm and the SNR of 37 dB is preserved even after two stages of amplification.

  • So, now the RF power to the RF port of the mixer is 3 dBm. I have attached the video of signal from the PLL loop at different gain (G=1, G=2,G=5) values in SR 560. The time domain trace seems to very noise. I suspect this is because of the inherent large noise in 2-micron laser diode with a broad line width of 2 MHz.

  • I then attempted to do the closed loop transfer function in the present PLL configuration by injecting the signal from SR 785. Attachment 2 shows the closed and open loop transfer functions at different gain values in SR 560 when the actuation slope is 10 kHz/V. Attachment 3 shows the closed and open loop transfer functions at different values of actuation slope when the gain is 5. The magnitude and phase traces are not very smooth as we observed when we did the similar measurement with an arbitrary function generator (AFG) as the RF source. In this case, when MZI output is fed in as the RF source, the RF power is fluctuating.

  • I also tried to do the frequency noise measurement. Attchement # 4 is the FM noise at different gain values when the actuation slope is 10 kHz/V. Attachement 5 is the FM noise at different actuation slope values when the gain is 5. This time, depending on the gain value and the actuation slope value, a short frequency span was considered in SR 785 for the frequency noise measurement. The frequency span is considered based on the value of unity gain frequencies  that are approximated from the open loop transfer functions measured from attachment # 2 and #3

Attachment 1: beat_note.pdf
beat_note.pdf
Attachment 2: Transfer_function_S_10kHzV_different_gain.pdf
Transfer_function_S_10kHzV_different_gain.pdf
Attachment 3: transfer_function_G_5_different_actuation.pdf
transfer_function_G_5_different_actuation.pdf
Attachment 4: FM_noise_diff_gain.pdf
FM_noise_diff_gain.pdf
Attachment 5: FM_noise_G_5_different_actuation_slope.pdf
FM_noise_G_5_different_actuation_slope.pdf
Attachment 6: Gain_1.mp4
Attachment 7: Gain_2.mp4
Attachment 8: Gain_5.mp4
  2355   Wed May 29 08:16:47 2019 AnjaliUpdate2micronLasersFrequency noise measurement of 2 micron source using PLL

Attachment #1 shows the oscilloscope traces at different gain values when the actuation slope is 100 kHz/V. It also shows the base line when there is no input to the oscilloscope. Even in the absence of any signal to the oscilloscope, there is an offset with mean value, RMS value and peak to peak value respectively of 35 mV, 42 mV and 200 mV.

Table below summarises the mean value, RMS value and peak to peak value for different combinations of actuation slope and gain.

Actuation slope (kHz/V) Gain Mean value (mV) RMS value (mV) Peak-peak (V)
10  1 -22.5 44 0.3
10 2 -33 74  
10 5 -70 205 1.52
30 1 2.7 33 0.26
30 2 -3.8 71 0.52
30 5 -85 189 1.08
100 1 42 67 0.42
100 2 -32 88 0.6
100 5 -65 207 1.36

The RMS value and the peak to peak value is increasing with increase in gain and the mean value is not showing any trend. I was pressing the Run/stop button before saving the data. I press the same to make the trace alive after saving the data as well. But the mean value read out from the oscilloscope shows different /random values in either case. If I don’t save the data, but only increases the gain, the mean value readout from oscilloscope shows almost the same.

I saw the beat note on the oscilloscope and I was trying to find the change in frequency. The frequency readout from oscilloscope was showing very large fluctuation (60-100 MHz). I feel its not a reliable measurement, but I don’t know whether we have an option to measure the frequency jitter in this oscilloscope (TDS 3032).

Attachment 1: oscilloscope_trace_s_100kHz.zip
  2357   Thu May 30 07:43:21 2019 AnjaliUpdate2micronLasersFrequency noise measurement of 2 micron source using PLL
  • The new 2 micron detector has a 50 ohm termination resistance, which is the transimpedance resistor, and hence the gain is very low 50 Ohms.
  • We observed the output of photodetector (beat note from MZI) on oscilloscope. Initially, we observed a large DC value (20 mV) and a small AC value (peak-peak=5 mV). 20 mV of DC with 50-ohm termination corresponds to a photo current of 0.4 mA.  This corresponds to optical power of 0.42 mW (responsivity = 0.95 A/W). (I'm not sure if its really as good as 0.95 A/W at 2 microns)
  • This ratio of  small AC value to large DC value says that the contrast is poor (25 %). We were then trying to improve the contrast. The RF power and RF frequency to the AOM was already set to have the maximum contrast. Prof. Rana then removed the fiber connection from laser to isolator and redid the connection. Surprisingly, the contrast became very good. We measured a AC peak-peak of 23 mV, which indicates almost 100% contrast.smiley
  • We then added a DC block and an amplifier stage (ZFL-500 LN) after the photodetector. Looking at the RMS value of the sinusoidal signal on oscilloscope, we realised that the RMS value is increasing as the thermistor resistance value set on the temperature controllerfor the laser diode increases. From the oscilloscope readout, we measured RMS value of 80 mV, 89 mV and 105 mV respectively when the thermistor resistance values are 10 kΩ, 11 kΩ and 13 kΩ. But as per the data sheet of the laser, the typical value of thermistor resistance is 10 k kΩ and the maximum value is 10.5 kΩ. Also, as per the data sheet, the thermistor temperature coefficient is -4.4 %/oC. I suppose, from the negative value, the temperature of the laser diode is reducing as the thermistor resistance value increases. Kindly correct me. This laser diode also has a current tuning coefficient of 0.01 nm/mA and temperature tuning coefficient of 0. 1 nm/ oC.
  • Attached the videos of oscilloscope signal when the thermistor resistance is 10 kΩ. From the oscilloscope trace, there is no significant amplitude fluctuation, but the frequency seems to be fluctuating a lot.
  • I have attached another video when the beat note observed on spectrum analyser (this video was captured when we had a dc block and two amplifier stage after the photo detector), but the characteristics are the same, except the power evel is different now. The peak is fluctuating a lot (sometime, the peak is even disappearing). We observed these fluctuations even with a resolution band width of 1 MHz. This indicates that the frequency of the laser diode is fluctuating by a large factor which is even greater than the maximum actuation Marconi can provide. Hence, we will not be able to lock the PLL with this laser having large frequency fluctuationfrown. We need to find another method to measure the frequency noise of the laser. One option is to perform RF herterodyne, but we don’t have a deep memory oscilloscope or ADC with large sampling rate to capture the data. Kindly give further suggestions to perform the frequency noise measurement.

RXA: we have a few options for measuring large frequency fluctuations:

  1. make an electronic delay line frequency discriminator. This is what is used at the 40m lab to track the ALS beat note. This requires the use of a medium power RF amp (ZHL-3A or similar), a splitter, 1 short cable, 1 long cable, and a mixer/LP. Two of these setups to get I & Q.
  2. a VCO with a much larger range than the Marconi - maybe 10 MHz p-p would be enough
  3. Use the heterodyne setup that Anjali mentions: a 90 deg hybrid splitter to get I & Q and then record the two mixer outputs with the Moku
Attachment 1: Oscilloscope.mp4
Attachment 2: Spectrum_analyser.mp4
  2358   Sat Jun 1 09:46:00 2019 AnjaliUpdate2micronLasersFrequency noise measurement of 2 micron source

[Anchal, Anjali]

We tried the Lock in amplifier in Moku lab for the frequency noise measurement. In this case, the output of the photo detector , after dc block and one stage of amplification, is fed into  input 1 of Moku. It gives out the inphase and quadrature component. We have saved the data. I will process the data offline and update later.

  2359   Wed Jun 5 14:16:07 2019 KojiUpdate2micronLasers2um laser / cryo stat: setup inspection and action item updates

[Aidan, Chris, Koji]

We went down to the lab to check the situation of the setups for 2um laser measurement and stabilization and the new cryostat.

[2um laser frequency noise measurement]

  • Looked at the add-on transimpedance amps: Something was wrong with them. The power bypass caps are attached to the "hot" supply lines in parallel (both sides of the caps are soldered to a same line). And some power supply lines have no voltage. This circuit is not necessary to be bipolar. To be fixed (KA)
  • We temporarily connected one of the thorlabs 2um InGaAs biased detectors to an SR560. It showed reasonable output: DC/AC response OK & no nonsense.
  • The AOM was bypassed and the homodyne fringe was checked.
    The fringe visibility was low (~10%) and was dependent on the stress applied to the delayline fiber.
    Suspected polarization rotation somewhere -> ToDo: Check the polarization states of the output beams.
  • ToDo: Check should be done with each component. how much are the output power, output polarization, dependence/fluctuation of the polarization, etc. 
    We might be able to use the 2um Faraday Isolators (as PBSs) for the measuement.
  • Checked the fringing of the fiber delayline Mach Zehnder. We observed one fringe per sec level fluctuation.
  • Laser current actuation was checked and it turned out that it is so strong and sufficient to lock the delayline fringe.

[2um AOM]

  • The fiber coupled AOM gave us a reasonable amount of DC/AC actuation of the laser intensity.
  • The power of the 1st order output has the dependence on the "freq input" of the driver. This is probably because of the matching between the fiber coupling and the deflection angle, which is freq dependent.
  • When the freq input is 8.8V_DC, the 1st order output has the maximum efficiency. The efficiency was 96%@990mV_DC input to the modulation in.
  • The AOM actuation bandwidth was tested to be ~MHz, at least.
  • We are not supposed to give more than 1V to the modulation in while we want to apply 8.8V to the freq input. Incorrect plugging may cause the damage of the modulation input port. The setup needs to be improved with a protection circuits / AOM driver circuit.
  • Our understanding is that the modulation input has a 50Ohm input impedance while the freq input has high-Z
  • The next step towards the intensity stabilization is low noise photodetector circuits and proper interface to the AOM driver.
  • Also we want to set up TECs and other circuits for the LaserComponents PDs.

[Cryostat]

  • Cleaning: there are many components are scattered on the table.
  • Plan:
    • Move the Zack rack to the next of the optical table (or somewhere)
    • Move the yellow chemical cabinet to the place where the rack was. We can pile up some plastic boxes on it.
    • Remove the delicate optics from the steel table.
    • Place heavy cryostat components on the steel table.
    • Connect the cryo cooler to the cryostat. How do we do that? Fisrt rigidly attach for testing and then move to soft attaching?
    • Replace the optical windows to the 2um ones (2"). The current ones are for 1.5um.
    • We need a 2" 50/50 BS at 2um. Lenses and steering mirrors are in hand.
  2360   Fri Jun 7 16:32:59 2019 AnjaliUpdate2micronLasersFrequency noise measurement of 2 micron source

Attachment # 1 show the schematic of the lock in amplifier configuration used in Moku lab. We saved the in phase and quadrature components.

In phase =cos\left ( \right \omega_o\tau+\Delta\phi(t))

quadrature =Sin\left ( \right \omega_o\tau+\Delta\phi(t))

where \omega_0  corresponds to 2 -micron , \tau is the delay time in the delay fiber  and \Delta\phi(t)=\phi(t) - \phi(t-\tau).

 \phi(t) is the phase noise of the laser. 

From the inphase and quadrature component \Delta \phi(t)value is extracted. So, we are actually extrating the combined effect of phase noise of laser as well the phase noise due to fiber length fluctuations due to environmental fluctuations. ASD of this is converted to frequency noise in Hz/rt Hz. Attachment # 2 shows the frequency noise estimated from two sets of measurements. This curve exhibit a 1/f characteristics from about 240 Hz upto 30 kHz

Quote:

[Anchal, Anjali]

We tried the Lock in amplifier in Moku lab for the frequency noise measurement. In this case, the output of the photo detector , after dc block and one stage of amplification, is fed into  input 1 of Moku. It gives out the inphase and quadrature component. We have saved the data. I will process the data offline and update later.

 

Attachment 1: Lock_in_amplifier_moku_lab.jpg
Lock_in_amplifier_moku_lab.jpg
Attachment 2: FM_noise.pdf
FM_noise.pdf
  2362   Thu Jun 13 22:53:25 2019 AnjaliUpdate2micronLasersFrequency noise measurement of 2 micron source

There was a correction in the script I used to estimate the frequency noise from the inphase and quadrature component. Attachment #1 shows the frequency noise estimated after the correction. 

I have also attached the Matlab script ( I am not able to attach the zip file with data files). I remember, while saving the data, we gave the time duration as 70 s. But while processing the data only I realised that the  time domain data is captured only upto 2 s. Even in this case, I would expect the frequency axis to start from 0.5 Hz, but I don't see that in the FM noise plot. Kinldy let me know whther I am doing anything wrong in data proocessing. 

Quote:

Attachment # 1 show the schematic of the lock in amplifier configuration used in Moku lab. We saved the in phase and quadrature components.

In phase =cos\left ( \right \omega_o\tau+\Delta\phi(t))

quadrature =Sin\left ( \right \omega_o\tau+\Delta\phi(t))

where \omega_0  corresponds to 2 -micron , \tau is the delay time in the delay fiber  and \Delta\phi(t)=\phi(t) - \phi(t-\tau).

 \phi(t) is the phase noise of the laser. 

From the inphase and quadrature component \Delta \phi(t)value is extracted. So, we are actually extrating the combined effect of phase noise of laser as well the phase noise due to fiber length fluctuations due to environmental fluctuations. ASD of this is converted to frequency noise in Hz/rt Hz. Attachment # 2 shows the frequency noise estimated from two sets of measurements. This curve exhibit a 1/f characteristics from about 240 Hz upto 30 kHz

Quote:

[Anchal, Anjali]

We tried the Lock in amplifier in Moku lab for the frequency noise measurement. In this case, the output of the photo detector , after dc block and one stage of amplification, is fed into  input 1 of Moku. It gives out the inphase and quadrature component. We have saved the data. I will process the data offline and update later.

 

 

Attachment 1: FM_noise_new_.pdf
FM_noise_new_.pdf
Attachment 2: Mokulab.m
close all
clear all
clc
lam=2e-6;%wavelength
c=3e8;%velocity of light 
n=1.5;%refractive index of fiber
len=15;%length of delay fiber
omeg=2*pi*(c/lam);%optical frequency corresponds to 2-micron
tau=(len*n)/c;%time delay due to delay fier
Fs=500e3;%acquisition rate
... 27 more lines ...
  2424   Mon Sep 23 23:48:12 2019 KojiUpdate2micronLasers2um sensor cards / focusing optics

Fiber Collimator (Thorlabs F028APC-2000+AD11F+LMR1) and MIR sensor cards (Thorlabs VRC6S Qty2) were delivered.

The sensor card is liquid crystal and seems temperature sensitive. It's slow and diffused. But at least we can now see 2um beams in a certain condition.

The fiber collimator seems working fine, but this gave me another issue. Now because the beam is small (w<500um) everywhere, I can't focus it very well. To make a focused beam, one needs a large beam, of course. Previously, the beam was not well focused. Therefore the final focused beam with f=150mm was sufficiently small like w=50um.

It looks like some kind of  telescope is necessary.

Attachment 1: IMG_8936.jpg
IMG_8936.jpg
  2440   Tue Nov 5 20:06:36 2019 RaymondUpdateCryo vacuum chamberCooler to tank connection

Attached is a drawing of the first phase (minimal vibration isolation) cryocooler attachment, where the main tank connects via the blue rimmed feedthrough. Boxed/circled components are those that will require custom fabrication:

  1. Copper adaptor from heat station to thermal strap
  2. 5.25" outer diameter 2-153 o-ring connection to conflat adapter (DN75 (4-5/8" outer diameter, 3" tube OD) pictured, but am comparing this with the DN100 (6" OD, 4" tube diameter))
  3. Conflat to ASA o-ring adapter
  4. a + b: Copper adapter from the flat strap connector to the round copper vacuum feedthrough (closeup shown in second figure)

Currently there are only two connections that require viton o-ring rather than conflat connections (cooler to piece 1, piece 3 to HV feedthrough). 

Attachment 1: CoolerCartoon.pdf
CoolerCartoon.pdf
Attachment 2: Screen_Shot_2019-11-05_at_20.25.54.png
Screen_Shot_2019-11-05_at_20.25.54.png
  2459   Mon Nov 25 15:03:34 2019 KojiUpdatePD QEIn solder and PD mounts are in

The PD mounts were delivered from ProtoLabs. The order was sent on Tue last week and it's here on Monday. Excellent!
And the quality looks pretty good.

The surfaces are sandblasted. Do we want to do any process on the bottom surface to reduce the thermal resistance?

An indium solder string also came in.

Attachment 1: PB259778.JPG
PB259778.JPG
Attachment 2: PB259780.JPG
PB259780.JPG
Attachment 3: PB259781.JPG
PB259781.JPG
  2462   Tue Nov 26 18:49:11 2019 KojiUpdatePD QESocket soldering test piece made

Normal solder (Sn63 Pb37): with flux, wetting o

Pure Indium - In 99.995: no flux, wetting x, low melting temp, like paste

Pb93.5 Sn5 Ag1.5: with flux, wetting o, high melting temp (soldering iron setting 380~430F)

Cryo solder In97 Ag3: no flux, wetting x, low melting temp, like paste

Attachment 1: IMG_9118.jpeg
IMG_9118.jpeg
Attachment 2: IMG_9120.jpeg
IMG_9120.jpeg
Attachment 3: IMG_9121.jpeg
IMG_9121.jpeg
Attachment 4: IMG_9123.jpeg
IMG_9123.jpeg
Attachment 5: IMG_9125.jpeg
IMG_9125.jpeg
Attachment 6: socket.pdf
socket.pdf
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