Andrei, Camilla

We aligned the fiber polarization to minimize the H1:SQZ-SHG_GR_DC_POWERMON channel, following the instructions of Report 71761 on rotating the waveplates.

The reduction in monitor power is depicted in the attached screenshot (POWERMON_lesser_timespan.png), showing a decrease from 0.24 [a.u.] to 0.03 [a.u.].

The fiber currently in use (Fiber.png) is SM980-5.8-125 - Single Mode Optical Fiber, 980 - 1550 nm, Ø125 µm Cladding. As it seems from the figure POWERMON_large_timespan.png, power is unstable in the long term. We propose to change the fiber to PS-PM980 - 970 - 1550 nm PM Photosensitive Fiber, 0.12 NA, 6.6 µm MFD and to tightly fixate the optical cable on the optical table to furhter reduce polarization shift.