I measured backscattering noise of homodyne in two configurations. The first case is that BHD's signal port opens to filter cavity with the path between filter cavity and OPO blocked. The second case is measuring squeezing case.

The measurement is done with network anylizer with bandwidth of 400Hz, averaage is 100 times. The measurement starting time is put as legend.

The result is attached and we could see that this noise varies between -127 to -120 dBVrms/sqrtHz at 10Hz.