Yesterday, we installed a telescope in front of the collimator of fiber. The purpose is to make the output of this telescope have the same beam radius ( roughlty, r=1500um )with the output of fiber.(the simulation of telescope is in Fig.3)
However, during the simulation and installation of this telescope, we found the result doesn't agree with what we found in practise. We measured the beam parameter of AUX1 again.(the parameter of AUX1 is shown in attached Fig.1, we should say that the origin of this measurement is the head of laser box)
Today, We tried to use smaller value of beam radius. I found that this can make coupling better. From 0.1mV to 0.2mV. The input laser is 5mW.
The fiber detector(DET01CFC/M) is 3.5V(5.5mW), that means we have 0.0003mW comes out from fiber now. This is definitly smaller than the case of last week. The coupling is only 0.01% now.
The procedure I did is like this:
1. Without inserting fiber, check the laser is almost going through the center of collimator.
2. Insert the fiber to collamitor, then adjust the x and y of collimator.
3. At the same time, use multi-meter to monitor the fiber detector(without using 50 Om). Until the voltage goes beyond the range of multi-meter, we start to use 50 Om.
4.Now you will 0.1mV on the multi-meter. Usually, this is the time to use two sterring mirrors to maximaze the coupling.
I did this procedure many times, but still the best result is 0.2mV. It seems something maybe wrong.
(By the way, I spoke a wrong thing during today's optics meeting. When we can read 0.1mV on multi-meter, the output of fiber is very weak! I am so sorry that I remember something wrong!)