[Yokogawa, Sugimoto]

Yeserday, we started preparation for the measurement of fiber noise.

Two parallel fibers (for green) are connected to PSL and POP.
One is used to carry beam from PSL to POP table (fiber A), and the other is spare (fiber B).

Yesterday, we installed an optics to hit light back from POP to PSL using fiber B (in the red frame in the figure below).

Fibers A and B are in bundles and don't separate to near the end, so it was necessary to place two couplers close.

We plan to measure the fiber phase noise by interfering this returning light with light not passing through the fiber.

We aligned to fiber B in the same method as klog#7538.

First, we aligned the beam to a test fiber of 5 m.

Transmittance of the 5m fiber reached about 70%.

And then replaced with fiber B.

We confirmed that the beam is returning at PSL, but it is still weak.

It is necessary to improve the alignment to fiber B, but yesterday it was out of time.