We measured the amount of p-pol polarization that enter in HD_IR_PD_MONI photodiode:
dark 0.003 V
LO p-pol 0.016 V over 1.268 V
BAB p-pol 0.09 V 1.254 V
the BAB has about 7% of spurious polarization reaching the fotodiode. This means that, in the calculation of the visibility, we must take into account this contribution.
In order to investigate where this contribution comes from we also measured the p-pol component after the Faraday Isolator and after the mode matching telescope.
Measurements performed with the power meter, placing a PBS along the beam path:
- after the Faraday Isolator
p-pol 0.0023mW over 0.620 mW (0.5uW dark)
- after the MMT
no significant p-pol power measured
Moreover we observed that any spurious polarization was introduced by the homodyne beam splitter.
We have to investigate on the dalay-line mirrors to see if any of them is responsible for this spurious polarization.
NB: all the measurements were done with 0.633 mW of BAB power entering the homodyne detector (0.310 mW towards PD1 and 0.319 mW towards PD2). At the 11:07 we increased the BAB power at its maximum value.