Participant: Eleonora, Marco, Matteo and Yuhang

After realize the 7mm collimator is more suitable, we replace the 11mm one. Then we finalize the optical layout of PLL. The main task we did is the new telescope design and fiber alignment.

The new telescope is shown in attached picture. However, the actual case is a little bit different because of the Faraday influence of optical length. But we made sure the beam is very collimated with a size of 2mm in diameter.

For the fiber coupling, we develop a procedure. We assume you have already a coupled fiber.

1. Put the output of this already coupled fiber to collimator. Now, you have both light going in and back through this collimator. Then use the steering mirror to make them overlap. Always make sure the light is a good round shape after you take off the fiber from collimator.

2. Put the multimode fiber to do pre-alignment. If you did very well the first step, you will have a very large coupling directly after you put multimode fiber. Then use steering mirror to align until get 100% coupling. If you cannot, remember to check the shape after collimator is round.

3. Put the single mode fiber. If you did step 2 as we suggest, you will have very good coupling now even for this single mode fiber. Then just use the steering mirror to do standard alignment. You will get a good coupling result.(we got 70 percent)

According to this procedure, we coupled the fiber for the second main laser pick off and AUX 2 laser(p pol). We got 70% coupling for both of them.

The final layout is attached as picture two.