I measured the TF of ckt in Fig 1 with EOM. 

The TF obtained using Moku is in Fig 2 and Fig 3. I will need to use a tunable capacitor to match the resonant frequency to the desirable one. 

In any case, the circuit looks good now. The measurement has been taken with HV probe with attenuation factor of 10. Also the range on moku was 50Vp-p, which implies that there was 5x attenuation inside moku as well. (Attenuation using cable (10x = 20dB) + attenuation using Moku(5x = 13.9dB))

Fig 4 and Fig 5 is how circuit looks now. 

Things left to change in the circuit

Use ceramic capacitor for RF part.

Use electrolytic for power line. 

Use high imepdance cable to measure the TF with EOM (not the normal cable)

I will be using an Opamp to match impedance the input impedance of my circuit with Moku output. 

Previously I was using a resistor of 1Mohm. This caused an issue where the circuit gain was depleted at high frequency, because it overrid the imepdance of Opamp (the opamp impedance is in 1M ohm range, so using a 1M ohm resistor affects the opamp TF). This issue could be seen in elog 3860.

Also, just to be sure, I am using a newly purchased Opamp. 

The voltage regulators, LM7815, 7915 are being used to take input of 18V and give opamp supply of 15V. (self reminder- I need to change the capacitor here to electrolytic ones)

I changed the Opamp circuit as shown in Fig 2.

The opamp part is good now. The TF can be seen in Fig 3. There is a uniform gain of factor 5 ish (1000/220 for inverting opamp). Hence around 12dB. 

I have borrowed 1.5um laser and the related optics that were stored by Rishabh in the dessicator. I have taken permission from Aso sensei about this. They will be in tama now. 

I recovered squeezing and saw that the noise floor was completely stable with no glitches. The noise floor level is not so good, only -5 dB, and there is some excess noise in the spectrum from probably mode cleaner motion. Also the green path is still behaving strangely. Still, I saw ~ 5dB squeezing for about 10 minutes continuously with only stationary noise, which is a small relief to close out the year at least. The two main problems now are green lock stability and IRMC power level noise.

Piece by piece details

Second harmonic generator

SHG electronics have some weird behaviour. For a while the appropriate lock threshold has been about 10x what the transmission spectrum on the oscilloscope would suggest. Actually right now it's at the maximum of the range. I guess there is a gain in there somewhere that needs to be turned down. Also the SHG servo gain has some very annoying behaviour - it seems the ideal gain is about 1.5 to 2, however, sometimes on lock it will have a weird 250 Hz oscillation. This is a separate issue from the usual high gain oscillation of a generic control loop, which happens at gain ~ 2.5-3. The 250 Hz oscillation can sometimes be made to disappear by turning the gain a little bit up or down, but sometimes it also just loses lock. This also sometimes causes unlock of the SHG.

Green mode cleaner and Mach Zender

As mentioned a few times before, the green mode cleaner will arbitarily switch demodulation phase from I to Q and unlock the green path. This is now the main issue preventing long term measurement of squeezing. Specifically, I optimized the demod phase to I-phase and then proceeded with squeezing. The GRMC outputs TEM00 at 25 mW as usual, and from the CC error signal it produces the nominal level of nonlinear gain. But then after some time it unlocks, and looking at the error signal immediately after shows that it has gone completely to Q-phase. After some time it drifts a bit and 10 minutes later it's at I guess halfway between I and Q phase. I don't really know whether it's optical or electronic. I tried turning the green phase shifter PZT offset all the way up to 150 V (usually sits at 75 V), which is about enough to switch it from "halfway between" to "almost I-phase" . But in retrospect I don't think it has anything to do with the CC loop actuation of the GRPS since this happens even without the CC engaged. I think I really need to clean up my understanding of the green path and electronics.

Phase locked loops

No major issues. Seems completely fixed.

Infrared mode cleaner

As I noticed in my last post, the IRMC error signal had a large DC offset. I don't know where it came from, but it seems to be a recent issue. I used the "offset" knob on the servo to center the error signal at the appropriate level. The IRMC remained locked for > 1 hour using ND1 on the reflection PD with 424 mV error signal. However, the error signal peak size seems to be fluctuating quite a lot, and the IRMC reflected power also is not very stable. Qualitatively I didn't the see the same behaviour as much when looking at the transmitted power with the power meter, though I just lazily held the power meter and didn't mount it (the ring sensor doesn't have a clamping base and there weren't any left in FC cleanroom). I suspect that the sideband power is fluctuating a lot for some reason, a bit more compared to the carrier. However, the SHG error signal, which uses the same sidebands, is quite stable.

Local oscillator alignment

The LO was a bit misaligned to the homodyne so I rebalanced it. It was also slightly misaligned to the alignment mode cleaner but not so much. I recovered the mode matching to quite a good level. Usually this alignment ends up being the best of the squeezer table (it was 99.99% last time I measured it). The LO seems to be unbalancing quite a lot lately. It might be necessary to carefully re-check the alignment to homodyne.

Squeezing to homodyne alignment

I locked OPO for BAB (ppol 250 MHz) and saw that it was very misaligned at the AMC - TEM00, yaw and pitch HOMs were all about the same level. I realigned to ~95% mode match. That said, the BAB is combining with LO by reflecting at the balancing BS which is used to adjust 50/50 balance of LO to the homodyne, so the misalignment is was probably due to adjusting that BS too much.

Optical parametric oscillator and coherent control

I didn't optimize the green alignment to OPO, temperature or ppol frequency, but by scanning the CC1 (green phase shifter) phase I could see the level of amplification/deamplification in the OPO on the CC1 error signal, and it was the same size as last time I checked so I just moved on. ppol and BAB alignment are fine and lock with no problems. CC1 locked with no issues. CC2 missed a bit at first but that was how I came across the aformentioned sqz/LO misalignment. After sqz to AMC was fixed CC2 locked with no issues. With no CC1 scan, the coherent control error signals are nice and flat compared to the mess they were this time last year.

Squeezing

I observed squeezing to about -137 dB (-5 dB) at high frequency > 30 kHz. The noise floor seemed also ok at about 100 Hz but had a lot of 50 Hz harmonics (spectrum of LO only didn't have much). There is a large bump that looks like a mode cleaner resonance in the range of 5-20 kHz. This might be related to the IRMC power fluctuation mentioned above.

The spectrum noise was completely stationary for about 10 minutes, which is great. Eventually the squeezed state was lost by green unlock. I relocked green again so see how long the squeezing could be maintained, but green lost lock maybe 30 seconds after squeezing was reacquired, and the GRMC error signal had gone back to Q-phase. Therefore, understanding the renewed green lock regime and figuring out the IRMC carrier/sideband noises are the most pressing issues to recover the appropriate squeezing level for the Taiwan tomography project.

Somehow the GRMC/MZ error signal demodulation phase issue was fixed. Actually, part of the problem seemed to be the SHG - for some reason the gain was too low causing the output to have some uncontrolled slow sinusoidal oscillation of output green power as well as poor lock stability. I turned it up to the threshold of oscillation from high gain (separate to the kind of oscillation mentioned in the previous sentence, which is much slower) and then reduced it so that the output stops oscillating - the setting value changes from 0.08 -> 1.6 just by eye. Maybe a little bit change by UGF optimization but I don't know why the optimal gain changed suddenly. Anyway once again the green path seems ok and sends stable 25 mW to OPO.

IRMC still gives me problems. Once again, the system can find the lock threshold but refuses to hold lock very well. Even when it "locks" there are a lot of quite significant bumps and glitches in the reflected power that can be seen on the oscilloscope. I tried switching PZT high voltage drivers with IRPS, GRPS, GRMC but it didn't work. I tried using a variable ND filter at ~ ND0.4 (vs ND1 previously)to bring the base level of the IRMC reflection spectrum to about 9 V, close to the PD saturation. The gain was too high but turning it down, I could see that the IRMC locks... for about 1 minute and then the same problem comes back. I tried a weaker signal with about ND1.5 worth of attenuation but it didn't even find the threshold. The carrier and sideband peaks in the error signal both appear to be fluctuating in power as well - this does not seem to happen for SHG error signal which comes from the same modulator, nor does it happen for IRMC reflection spectrum which uses the same PZT. I might have to try taking the 18 dB RF amplifier in the error signal path. Also when I got home I noticed there was some DC offset on the error signal (fig 1) which I guess I should check out as well.

Katsuki, Shalika

We are measuring new kind of hydrogel. bis-phenyl-1O 1.5 mm sheet.

measurement using 0.5-3.5V with 0.25V step.

C:\Users\atama\Dropbox\Cell Birefringence\Measurement data\hydrogel

the force value is saved in the comment column

input:

Mon, Dec 23, 2024 3-43-55 PM.txt

output:

Mon, Dec 23, 2024 2-57-16 PM.txt

check, before water: -13.23 azi, 21.7 ell . It remains same after adding water to hydrogel during measurement.

Yuheng, Michael

We tried to look at squeezing again to see if our issues went away.

We initially tried replacing the ND filter covering the IRMC reflection photodiode. Currently, we have for screw on ND filters, ND 0.3 (too weak), ND 1.0 (too strong), ND2.0. But no ND 0.5 lying around. I purchased a variable ND filter a while ago so we tried putting it between IRMC reflection and the error signal PD. I could adjust it so that the base level of the reflection spectrum is close to saturation (~ 8V) and the PDH error signal is the usual shape with 1.25 Vpk (3 times what it was before). The attentuation was 1.06/2.81 = 0.377 which is ND 0.42. The threshold was adjusted to the good point and the IRMC was locked. The gain had to be turned down from ~ 10 to about 4 to prevent oscillation. However, the homodyne spectrum did not look so good. At first I guessed this was due to the influence of the variable ND filter, so I removed it and put ND1 back (which is what we were using before). But then it turned out that the homodyne was quite misaligned. I rebalanced the homodyne and the spectrum became ok. Anyway, I should purchase some more screw on ND filters since that variable one is not AR coated for 1064.

I could see the CC error signal that indicates that nonlinear gain is present (roughly, nonlinear gain*sin(green phase mismatch)). It seems stable and not causing problems. So the squeezing output seems fine.

I wanted to demonstrate LO/sqz overlap using AMC, but then the IRMC lock became unstable again. I am not entirely sure what is causing the IRMC lock issue. Staring at it for a while, the PDH error signal sometimes becomes much smaller. It seems to go away after we leave and then turn off the high voltage driver and come back some time later. It could be that the high voltage driver is faulty. Switching for an optimal ND filter might be a temporary fix, but it seems we need a new HVD...

Another issue was that the GRMC kept unlocking. It seems the phase of the PDH error signal is randomly changing in a seemingly not continuous manner. Sometimes it is in perfect I-phase and sometimes it goes to almost Q-phase. I don't know what causes it right now but it could have something to do with the 88.3 MHz lock scheme. 

The TF of ckt with EOM was measured using moku. The resonant freq should be around 394kHz, but I don't see any peak at all (even after zooming in at several frequencies). 

Fig 1 - simulation

Fig 2 - moku measurement

I don't know why the circuit doesnt have a narrow rf peak. The gain magnitude doesn't match simulation and there is no peak. 

The RF part and opamp part are currently disconnected. The response of ckt Fig 1 is shown in Fig 2. 

Although the bandwidth of Op27 is 8MHz, it doesn't behave well, after kHz range. Perhaps I should tweak the feedback resistor value. The cables used to measure are very short (<20cm)

C:\Users\atama\Dropbox\LC-Experiment\Measurement Data\Birefringence Measurements\Coating measurement\BB1-E03\20241206\Fri, Dec 6, 2024 2-09-14 PM.txt

The 2nd BS was installed to measure coatings

input calibration

infront of 1st BS with only power meter C:\Users\atama\Dropbox\LC-Experiment\Measurement Data\Polarization states\Wed, Dec 4, 2024 6-39-05 PM.txt

polarization states after 1st BS C:\Users\atama\Dropbox\LC-Experiment\Measurement Data\Polarization states\Thu, Dec 5, 2024 1-10-34 PM.txt

Measurement of the 2nd BS (the BS used to measure coatings)

Front face reflection

C:\Users\atama\Dropbox\LC-Experiment\Measurement Data\Birefringence Measurements\Beam Splitter Calibration\20241205\frontrefl\Fri, Dec 6, 2024 10-55-55 AM.txt

Back face tranmission

C:\Users\atama\Dropbox\LC-Experiment\Measurement Data\Birefringence Measurements\Beam Splitter Calibration\20241205\Backfacetra\Thu, Dec 5, 2024 3-15-50 PM.txt

measurement take again after some time

C:\Users\atama\Dropbox\LC-Experiment\Measurement Data\Birefringence Measurements\Beam Splitter Calibration\20241205\Backfacetra\Thu, Dec 5, 2024 6-35-25 PM.txt

The Back face transmission is the input polarization states

The maximum voltage that can be provided to this circuit should be 0.085V. If the voltage exceeds this, then the OpAmp will be damaged as the current would be more than 20mA. 

So, the safe range for input voltage is from 0-0.085 V. The voltage to crystal will be 0-644V. The half wave voltage is achieved at 0.05V of input.

The PD infront of laser(lightwave 126-1064-100) to just check its stability.

Nishino,

2024.12.04

See

LockAqu/DataLogger.ipynb

Noise2/DataLogger2.ipynb

Fig.1 shows lock acquisition process. IR and GR are phase-locked. First, the main IR is locked to the main cavity. Second, by changing voltage to the piezo on PCM, one finds the optimal position of the PCM which realizes speed meter. Third, by changing the local oscillator frequency for PLL, one makes the fundamental mode of the GR laser resonate in the PCC. Finally, by turning on the loop, the PCC is locked.

Fig.2 shows the IR transmission, which is the interference of the first and second circulation light. This reflects the fluctuation of the PCC length for the IR. Red and blue are the ASD when turning the PCC locking on and off. 

The worst mount is attached. Never buy them, as they have the worst designed actuators and the worst possibly designed tap. They don't have anything good about them!!!!

Please don't buy them if you want to save yourself from facing worst hassle!

I think its from newport.

I checked a bit a day later. The IRMC lock works for about 5 minutes and then goes back to being broken. When unlocked, it seems like the error signal peak voltage is fluctating. I'm not sure if it's the amplitude or demodulation phase. When the lock switch is activated, the servo finds the threshold value but doesn't seem to apply sufficient correction to lock to the good point, and then gives up.

I checked once again the green path. SHG now operates normally, outputting 310 mW green (1.88 V on transmission monitor).

GRMC was a bit misaligned seemingly from PZT hysterisis. I adjusted a bit the steering mirror after the MZ and it went back to good alignment - 1460 mV + (60, 34, 34, 22) -> 90.68% mode matching. GRMC demod phase was changed to 230 degrees, error signal 1.74 mVpp.

GRMC/MZ locks fine and outputs 25 mW stable green (312 mV on the transmission monitor) at the usual 4.2 MZ offset.

OPO error signal was 832 mVpp with good phase. ppol to OPO mode matching was 87.43% which is ok. OPO lock is fine.

I checked how much the CC PLL servo can maximally correct using the fast loop. When the setting is far from resonance (~ 32 MHz) and the fast loop is activated, the CC frequency goes to about 14 MHz. i.e. the fast loop maximum correction is about 18 MHz. This is consistent with what I had read previously in Matteo's thesis. It seems the CC PLL behaves well when the laser starts at a detuning of about 15-20 MHz.

I came across the first hitch which is that I cannot see nonlinear gain on the CC1 error signal and very little on CC2 error signal. Green alignment, ppol frequency and OPO temperature are all optimized. I remember that I was using some old short cables but only remembered after I left and was writing this elog. I should check the LEMO cables monitoring CC EPS and make sure they aren't bad. Considering I saw 6 dB squeezing a couple of weeks ago I don't think CC, BAB or ppol lasers suddenly misaligned. For reference, if the green phase shifter is scanning (nonzero scan amplitude on CC1 servo), you should be able to see about 500 mVpp sine wave from the CC1 unlocked error signal, which indicates that the green phase is being cycled between amplification and deamplification of the CC infrared beam.

Then I ran into a worse problem which is that IRMC servo does not work properly. I saw that the reflected power was extremely unstable (about 20-30% fluctuation in output level), and then got worse in that auto lock didn't work at all. I closed CC and ppol, checked main laser current and temperature, turned main laser noise eater off and on, turned NIM rack off and on, PZT off and on, but it didn't fix the issue. The error signal randomly reduced to about half the amplitude of what it was before (200 mVpp). I checked the demodulation LO - it's fine (4.75 dBm). I put the IRMC near resonance and checked the amplified IRMC REFL RF signal - it seems ok and goes up to about -8 to -9 dBm which is what it was before. The error signal size seems fluctating a bit before the error happened, but it's now stuck at half. When the threshold is at the good value, it seems like the servo is trying to force the PZT to the correct position, but it doesn't reach the lock value. A guess might be the interplay between the PZT scan and threshold. Maybe the correction signal is not strong enough to stop the PZT from scanning? I'm not entirely sure but it's just a guess. But I also tried adjusting the PZT scan amplitude and period and it didn't really fix anything. I have also read previously that the IRMC threshold is a bit strange and usually works best at about 90% of the peak value rather than say 50%.

SHG threshold and Auto Lock magically fixed itself and I don't know how or why. It even returned to the same value I had set (9 V). Output green is 310-320 mW, same as before.

I suspect the circuit break is at the marked location since neither the THRESHOLD OUT nor the SHG lock work correctly when the threshold dial is adjusted over the full range. However, THRESHOLD OUT can detect fast changes in the value, so the power supply connection and potentiometer probably still work.

Unfortunately the suspect point is the connection to screw terminal J14 and resistor R104 which is in a very inconvenient location.