The measurement setup for the transmission measurement has been made at the output of the fiber.
- First, we looked at the fiber output with a PBS. It wasn't P-pol so we rotated the ourput coupler.
What we found was that it wasn't actually linearly polarized.
So the input coupler was rotated to correct it. This terribly misaligned the input coupling.
After some iteration of rotating and aligning the input/output couplers, we obtained reasonable
extiction ratio like 10mW vs 100uW (100:1) with 11mW incidence. (Where is the rest 0.9mW!?)
- The P-pol (transmission) out of PBS goes into the mirror. Here we tested mirror A1.
The mirror is mounted on the prism mount supported by a rotational stage for precise angle adjustment
We limited the input power down to 5mW so that we can remove the attenuator on the power meter.
The reading of the power meter was fluctuating, indeed depending on MY position.
So we decided to turn off the lighting of the room. This made the reading very stable.
The offset of the power meter was -0.58uW
The transmitted power for the normal incidence was 39.7uW with the incident 4.84mW.
[39.7-(-0.58)] / [4.84*1000-(-0.58)] *10^6 = 8320 ppm
The transmitted power for the 4deg incidence was 38.0uW with the incident 4.87mW.
[38.0-(-0.58)] / [4.87*1000-(-0.58)] *10^6 = 7980 ppm
cf. The specification is 7931ppm