My feeling was that the saturation was caused by the LSC whitening filter which was always on.
Once the LSC whitening filter is controlled from C1LSC, we would be able to remove the attenuator.
- attenuation of RF signal
Since the PDH signal taken by C1LSC's ADC had been saturated somewhat, we introduced a ND filter of 10 on the photo diode to attenuate the RF signal.
As a result the amplitude of the PDH signal on dataviewer became more reasonable. No more saturations.