[Sugioka]

Abstract:

I measured the coupling of PRCL and SRCL into the MICH signal in DRMI 3f (REFL51Q) with various demodulation phases for REFL51.

Background:

As will be reported by Fujimoto-san later, we performed REFL51 phasing by minimizing the peak in REFL51Q while DRMI1f locked and SRCL was excited.
We also set the input matrix to minimize the peak in the MICH signal during PRCL excitation.
We then attempted the DRMI control handover from 1f to 3f; however, the MICH handover failed. 
This indicates that the MICH signal in 3f is not sufficiently decoupled.

Details:

According to Kawakami-kun's simulation (the figure on the right side of the 11th slide in the latter file of JGW-G2617586-v2), there should be an optimal REFL51 demodulation phase that minimizes the PRCL signal. Therefore,minimizing PRCL-to-MICH coupling via phasing and subtracting SRCL using INMTRX is a potential solution for achieving DRMI 3f lock. I measured the coupling of PRCL and SRCL into REFL51Q across various REFL51 demodulation phases.
As Fujimoto-san will post later, SRCL signal was minimized with the demodulation phase of 145 while exciting SRCL.
The three pads in the right side of Figure.1 comfirm this result.
Meanwhile, PRCL signnal was minimized with the demodulation phase of 130 while exciting PRCL, as the three pads in the left side of Figure.1 show.

Since the SRCL/PRCL IN1 is calibrated to nm, the SRCL/PRCL2POP51Q TF gain is also calibrated to dB cnt/nm.

The approximately 15 degree difference between the phases that minimize PRCL and SRCL coupling is consistent with Kawakami-kun's simulation.
However, the measured gain of the PRCL/SRCL2REFL51Q TF appears unreasonable.
PRCL2REFL51Q gain is approximately 4 times larger than that of SRCL2REFL51Q, whereas almost the same value in Kawakami-kun's simulation.

Plans:

There are 3 options for constructiong the MICH signal for 3f control.

1. Minimize the SRCL coupling by phasing and subtract PRCL coupling by INMTRX
With the demodulation phase of 145.
The handover failed using this method previously, but further matrix adjustment may help achieve 3f locking.

2. Minimize the PRCL coupling by phasing and subtract SRCL coupling by INMTRX
With the demodulation phase of 130.

3.Mitigate PRCL and SRCL both by phasing and also adjust INMTRX
With the demodulation phase of 130-140.