Matteo and Yuhang

To check what is the rotation angle of the Faraday rotator, we removed the HWP after it. We found the 2nd PBS reflected IR power decreased from 458uW to 192uW after removing HWP. This tells us that the rotation is arctan((458-192)/192) = 54 degree.

By adjusting the relative position between magnet and TGG crystal, we achieved reflection 213uW and transmission 226uW. In this case, the rotation is arctan(226/213) = 47 degree.

We put back HWP after optimizing HWP and found a transmission of 6uW from the 2nd PBS. After rotating HWP, we reduced it to 4uW.

In the end, we checked round trip loss of Faraday isolator using a IR HR mirror reflecting back the reflection from dichroic mirror. We found injection of 449uW, 2nd PBS reflection of 438uW, and total reflection of 390uW. The round trip losses from Faraday isolator is 11% now.