[Miyoki, Enomoto, Sugimoto]

=What we did=

1.Locked the interferometer for fiber noise cancelation, and measured control signal with compressor and most of KOACH, FFUs OFF state.

However we didn't see significant change from ON state (fig1).

2.Currently, we had put a mirror just after fiber coupleer and reflect back 100% of the beam. 

So we removed this mirror and recoverd the original configuration, where retro reflectin mirror is put behind the 10% picoff mirror.

Then, we locked the loop again, and confirmed that the control signal was not different much from the previous configuration (fig2).

OLTF shown in the third figure.

It requires a somewhat precise adjustment of the gain due to the resonance exist around 3.5 kHz and 10 kHz.

The phase margin is about 25 deg.

3.Measured dark noise of DCPD (fig4 , Red plot is PD noise and black plot is ADC noise).

(In this figure the noise amplified 100 times by SR560.)

There is some large peak around 2kHz.

=Note=

The lock tended to lose at several minutes intervals due to the drift.

We plan to compensate this drift by introducing temperature control to the coiled fiber.