Today I removed the “Fiber Noise  box 2” in the Atrium  used for the phase noise suppression loop. The goal would be to bring it to Padova to upgrade it. In particular, the idea is to actively -stabilize the plate that houses the fibers and, if needed, shorten the fibers using the  fiber splicing.

Activity on detLab:

First I  connected the output of the fiber going to the squeezer directly to the SQZ main PLL. This way, the retroreflector is excluded; otherwise, it would have reflected about 50% of the power back toward the injection (see Fig1).

In this configuration the power reaching the PLL from the injection is doubled . This is evident from the DC value of the PLL photodiodes (see Fig2)

Activity on EE-Room

I turned off the RF amplifier that powered the AOM in the fiber noise  box 2 . The amplifier was then removed and will be taken to Padova along with the box.

Activity in the Atrium

After disconnecting the cables and the optical fibers from the  Fiber noise Box 2 , I removed the  box. The optical fiber that powered the box is now directly connected to the fiber that carries the signal to detection. This connection was made by inserting a 10 dB Thorlabs  fiber attenuator to keep the power reaching the squeezer approximately the same (figure 1). After this operation, the DC value of the photodiodes slightly increased to above 0.30  V (figure 3).

The disconnected cables in the atrium  are labelled as

“Fiber Box” RF amplifiers power supply

“Fiber Box LO Sin” RF output of the first amplifier in the box

“FiberBox LO Des” RF output of the second amplifier in the box

“Fiber Box LO AOM” RF power to the AOM in the box