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Experimental optics

  1. Oct 23, 2008 #1

    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...

  2. jcsd
  3. Oct 23, 2008 #2


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    1, A video camera? You normally look for small changes in fringe position - if you have many whole fringes of movement you will have to count them as they go past.

    2, You can stretch the fibre to introduce a path difference. Hang the fibre over pulleys and use a weight to stetch it (carefully)
  4. Oct 23, 2008 #3
    Thanks for the reply.

    With regard to the second question... I should be able to control the amount of phase delay it would result in....

  5. Oct 23, 2008 #4


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    With a bit of experimentation you could work out how much weight would stretch it by one wavelength - alternatively there are companies that make peizo based fibre stretchers to modulate the phase delay (can't recomend any in particular)
  6. Oct 23, 2008 #5

    Andy Resnick

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    Can you describe the setup with more detail? For example: I can't tell, but are the two arms of your interferometer different fibers? How is the light combined and split? How is the light coupled into and out of the fiber? How large is the beam at the camera, the mirror, the beamsplitter... etc.

    I can't give advice how to change your setup until I learn what your setup is.
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