Hi, I have two small issues while carrying out my experiments: 1) While using Mach Zhender interferometer setup to cause a phase delay, I would need to find out, by how much the fringes have moved. But all the fringes look very similar before and after causing the phase delay. Because of this I have not been able to find out by how much the fringes have moved...Does anybody know how I can go about this??? 2) Causing a phase delay in one of the laser beams is only part of another experiment. The rest of the setup where I look at the interaction of laser beams is all fiber based(i.e lasers are confined to optical fibers).. For causing a phase delay, I thought of again using Mach Zhander interferometer setup.. But the problem is, it is free air based (i.e lasers are reflected around in free air) , so coupling the free air based setup with fiber based setup becomes very difficult... Is there any way, I can cause a phase delay using optical fibers itself...? Do you know of any such equipment being commercially sold, that can enable a phase delay and also has to be fiber based.. Will much appreciate any help with these... THANKS!!