2D graphs for robustness of injection and reflection telescopes

I made the codes on Python to compute the 2D graphs in order to study the robustness of the injection (fig 1) and reflection (fig 2) telescopes, taking into account the correlations moving the two lens.

The mismatch is consistent with the results of entry #1311 and there is a region of positions in which the mismatch is under 10% also for the reflection telescope.

Squeezing measurement after engagement of cc noise eater

I measured again the squeezing and anti-squeezing after the engagement of cc noise eater. Also, the measurement is done after the implementation of the s-pol GRMC lock. The measurement result is attached.

We could see that we have 3.30dB of squeezing and 16.47dB of anti-squeezing. This precise number is done by averaging the noise spectrum from 30kHz to 500kHz and then subtracting. In the attached figure, we can see there is still a lot of peaks.

Lock GRMC with s pol again

Since we have enough green power, we decided to use s-pol again. By changing the gain of GRMC and MZ servo, we could lock both of them again. Also, I changed the integrator of MZ.

We could have 50mW of green light going inside OPO as before.

However, I observed a more stable coherent control 1 loop. This is quite beneficial for the future. 

PR pitch local control loop closed

The pitch local control  loop of PR has been closed.

The mechanical TF and the closed loop TF are shown in pic 1 and 2.  The comparison between the open and closed loop spectrum is shown in pic 3.

UGF is crossed two times at 3Hz and 10 Hz. The phase seems above 50 deg.

300kHz noise source of homodyne noise spectrum is figured out

Participant: Yuhang, Matteo, Eleonora, Aritomi

We checked many things and want to figure out why we have a 300kHz peak in the spectrum of homodyne.

We tried to remove green by putting line filter(1064nm), tried to investigate the locking of OPO, tried to see the effect of leaked p-pol to homodyne. Finally, we confirmed the problem comes from the coherent control beam directly.

Then we found the noise eater doesn't give any difference when we switch on/off noise eater. So we suspected that this is because we are using not enough power of cc laser. This guess is mainly from the remind of Chienming. Then we tried to increase the cc power. We found the peak disappeared after going beyond a current value of ~1.2A. So we confirmed that increasing the current value above ~1.2A can engage the noise eater.

Then we set the current value of 1.305 and temperature of 34.37 degrees for cc laser. This is done by compromising available ND filters, desirable value 15mW of IR after filters and the avoid of mode hop. As we know, we lose alignment each time after putting the ND filter. We also recovered alignment. The alignment situation is attached in figure 1. We will keep this setting for the future until we find additional problem.

Phase noise measurement after solving cc PLL loop problem

Participant: Eleonora, Aritomi, Matteo, and Yuhang

Today we found the problem why I can have so large noise of cc-PLL. The reason is fiber PD is broken again. We just swap the PD and we could lock cc PLL very well. After the swap, we measured the beatnote level which is 7dBm now(measured by hp-E4411B, so the real amplitude should be -10dBm). This should be a reference for the future.

Then I measured the phase noise of both loops again. The result is shown in the attached figure 1. As you can see, in this figure, the RMS phase noise of cc PLL is 5mrad. This is 30 times smaller than the previous measurement. (Actually, I made a mistake of estimating the phase noise level of the previous measurement) While the measurement of p-pol PLL shows RMS phase noise of 15mrad, which is 3 times higher than the measurement of Marco.

While I was checking the demodulated beat note of p-pol PLL, I found a very low-frequency oscillation. This is shown in the attached figure 2. We should investigate how to remove this oscillation because it brings us almost 1rad of phase noise, which is a lot.

Next step:

buy new power cable for fiber PD or many batteries.

we should also check the level of p-pol beat note.

DGS calibration

The DGS input/input output voltage ranges are:

ADC:  ± 20 V

DAC:  ± 5 V

The volts to counts calibration is  2^15/(Vpk):

ADC: 1 V  =  1638 count

DAC: 1 V  =  6544 count 

Measurement of phase noise of coherent control PLL

I followed the Marco method and measured the phase noise of CC PLL. It shows an RMS phase noise of 149mrad. It is almost 50 times higher than p-pol PLL phase noise level.

p-pol PLL servo correction signal

I measured the p-pol PLL fast and slow loop correction signal. We can see from the attached figure. Although at that time fast loop is not stable, it shows very low-frequency drift. But slow loop reads this signal can try to bring the loop back to the original state. Since I calculated the correlation coefficient of these two signal, the slope of these two signal is the same. So the correlation coefficient is -1.

I think this is better than the coherent control loop. It is measured and shown in the entry here.

Coherent control loop realized by Pierre

Yuhang and Pierre

We tune the servo for locking the coherent control loops.

For green coherent control, we use 20dB attenuator and 50Om for error in. The measured open loop transfer function is attached as figure 1. We have unity gain frequency of 85Hz.

For local oscillator coherent control, we use 30dB attenuator and 50Om for error in. The measured open loop transfer function is attached as figure 2. We have unity gain frequency of 51Hz.

IR injection and reflection telescope update

I did another simulation for injection (-400 mm focal is not a common lens) and for the reflection (avoiding to change the already installed injection telescope into the homodyne).

The robustness for the injection telescope is really good, less than 3% moving the first lens in a range of +/- 5mm and less than 10% for the other one.

The robustness for the reflection telescope is not as good, we reach also 20% mismatch for +/- 5mm movement of one lens.

Squeezing and anti-squeezing spectrum

Modification of the CC-2 Servo-filter (IR Phase Coherent Control)

The following settings and modifications were done for the CC-2 (IR Phase Coherent Control) Servo-filter to the original Servo-filter which electronic schematics and bill of material are saved on the wiki.

0- Current configuration:

Notch filter 1, Notch filter 2 ans LP filter are disable.
The Servo-filter must be set only on 1/f integrator.
An attenuator of 30dB with a 50 Ohm load is set on the ERROR IN input.
The gain is set to minimum (position 0).
The unity gain frequency was measured to 50Hz.


1-Setting of switches on the front panel:

* The differentiator shall be disabled on the front panel in setting the switch on "OFF".

* The switch INV/NON INV on the front panel, shall be set on INV.


2-Setting of the 8 straps on the board:

Notch filter 1, notch filter 2 and Low-pass filter are disabled in setting strap on connectors P7, P8 and P9 between pins 2 and 3.

* The transmission signal is ont used.
The strap on connector P4 (3 pins) is set between pin 2 and 3.

* Strap is set on connector P11 (3 pins), between pins 2 and 3, in order to activate the sample-and-hold on the triangular signal, on the locking.
* Strap is set on connector P3 (2 pins) to connect the triangular signal to the output stage.

* Strap is set on connector P2 (3 pins), between pins 1 and 2, for test purpose.
To check notch 1 and notch 2 filters (in scan mode) between TEST IN and TEST OUT. For this test the differentiator, shall be set on "ON" (not intuitive but important). After this test, the differentiator shall be disabled the front panel in setting the switch on "OFF".

* Strap is set on connector P1 (2 pins), in order to be able to tune the offset.


3-Modification of components:

* Integrator 1/f: corner frequency changed to 22 kHz
Capacitor CMS 1206: C38 = 3.3nF

* Integrator 1/f2: unchanged

* Low-pass filter: unchanged

* Notch filter 1: unchanged

* Notch filter 2: unchanged

* Gain adjustment (G): Gmin = 0.0125 / Gtyp = 5

* Input impedance
Resistor CMS 1206 : R145 and R146 removed

Modification of the CC-1 Servo-filter (Green Phase Coherent Control)

The following settings and modifications were done for the CC-1 (Green Phase Coherent Control) Servo-filter to the original Servo-filter which electronic schematics and bill of material are saved on the wiki.

0- Current configuration:

Notch filter 1, Notch filter 2 ans LP filter are disable.
The Servo-filter must be set only on 1/f integrator.
The gain is set to minimum (position 0).
An attenuator of 20dB with a 50 Ohm load is set on the ERROR IN input.
The unity gain frequency was measured to 85Hz.


1-Setting of switches on the front panel:

* The differentiator shall be disabled on the front panel in setting the switch on "OFF".

* The switch INV/NON INV on the front panel, shall be set on INV.


2-Setting of the 8 straps on the board:

Notch filter 1, notch filter 2 and Low-pass filter are disabled in setting strap on connectors P7, P8 and P9 between pins 2 and 3.

* The transmission signal is ont used.
The strap on connector P4 (3 pins) is set between pin 2 and 3.

* Strap is set on connector P11 (3 pins), between pins 2 and 3, in order to activate the sample-and-hold on the triangular signal, on the locking.
* Strap is set on connector P3 (2 pins) to connect the triangular signal to the output stage.

* Strap is set on connector P2 (3 pins), between pins 1 and 2, for test purpose.
To check notch 1 and notch 2 filters (in scan mode) between TEST IN and TEST OUT. For this test the differentiator, shall be set on "ON" (not intuitive but important). After this test, the differentiator shall be disabled the front panel in setting the switch on "OFF".

* Strap is set on connector P1 (2 pins), in order to be able to tune the offset.


3-Modification of components:

* Integrator 1/f: corner frequency changed to 22 kHz
Capacitor CMS 1206: C38 = 3.3nF

* Integrator 1/f2: corner frequency changed to 22.5 Hz
Capacitor CMS 1206: C26 = C33 = 2200nF
Capacitor CMS 1206: C25 = C32 = 1000nF

* Low-pass filter: unchanged

* Notch filter 1: notch frequency changed to 11.8 kHz / quality factor changed to 0.9 (measured)
[Capacitor CMS 0805 1% : C49 ; C50 ; C51 ; C53 = unchanged (560 pF)]
Resistor CMS 1206 : R65 ; R66 ; R67 ; R68 = 24k
Resistor CMS 1206 : R73 = 13k

* Notch filter 2: notch frequency changed to 14.2 kHz / quality factor changed to 4.85 (measured)
[Capacitor CMS 0805 1% : C60 ; C61 ; C62 ; C63 = unchanged (560 pF)]
Resistor CMS 1206 : R79 ; R80 ; R81 ; R82 = 16k
Resistor CMS 1206: R89 = 1.3k

* Gain adjustment (G): Gmin = 0.4 / Gmax = 16.5 / Gtyp = 6

* Input impedance
Resistor CMS 1206 : R145 and R146 removed

Re-alignment of ML PLL fiber and homodyne

Comment to IR injection and reflection telescopes new scheme (Click here to view original report: 1305)

-200 lens for reflection telescope is on OPO transmission path and it changes mode matching of OPO transmission. So this configuration is not feasible.

IR injection and reflection telescopes new scheme

I found a new solution, better than the previous one, considering a larger database of lenses.

The robustness is good, moving one lens in a range of 1cm, the total mismatch is lower than 20%.

More boards for GALVO control

I have found (between BS adn NM1 chamber) a rack with 5 more boards for the galvo control. See attached picture.

Maybe some of them are the "new version" Yuefan was talking about?

On two of them there is also a label specifing if the QPD has big or small range. 

PR yaw loop closed with new DGS

After solving the DGS issue with the filter loading, I could test the simulink model on the control of YAW of PR.

The mechanical TF and the closed loop TF are shown in pic 1 and 2.  The comparison between the open and closed loop spectrum is shown in pic 3. The control seems to work fine.

UGF is at ~ 6 Hz and phase margin is ~ 50 deg.  A first, rather basic version of medm screen developped for the control is shown in pic 4.

Error and correction signals are currenty in counts and needs to be calibrated.

200Hz noise from our cleaning room fan

Today we used the sound spectrum analyzer characterized the sound environment. We found a clear frequency from our cleanroom fan. It is 200Hz.