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Optical Spectrum Analysers

  1. May 9, 2007 #1
    Okay, I'm writing about optical spectrum analysers as part of my AS coursework, but I've been having some problems finding more in depth information on how they work.

    Can anyone explain to me how they work?
    Or link me to a website that can tell me?

  2. jcsd
  3. May 9, 2007 #2


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    Staff: Mentor

  4. May 9, 2007 #3
    Thank's a lot!
    That's just want I needed.

    I'm not sure if there are other ways to make OSAs,
    I've just stated that I was going to use one in my experiment plan (I don't actually have to DO the experiment, I just have to write a plan for it), but my tutor said I needed to give a bit more detail about how they work, and stuff.
    There are a lot of websites out there selling OSAs, but their product descriptions are really vague, so it's been a bit difficult to get the info I wanted.

    Thank's again! :)
    Last edited: May 9, 2007
  5. May 9, 2007 #4


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  6. May 9, 2007 #5
    Lol, I'm still thankful, because I'd been struggling, lol.

    That link's of more use to me than the last, so I should be able to get my work finished in the next few minutes :)
  7. May 10, 2007 #6
    I know two others. The fist one, even from the historical point of view, in to use a prism, and the dispersive power of glass. There have been lots of different designs with prisms.
    But the resolving power is low. That is, it is hard to separate very near wavelengths.
    Grating spectroscopes have a far bigger resolution.
    But the biggest resolution is obtained with FFT spectrometers. FFT stands for Fast Fourier Transform. It is done using a double Michelson and Morley interferometer with a mobile arm. One stage is used for a very precise distance measurement with a known wavelength and the other for the unknown one. The intensity of interferences is measured in function of the arms length and then, with a computer, the Fourier transform is computed. This transform is the spectrum of the unknown light. The precision of this kind on interferometer is equal to the precision of the lenght measure. If you made the measure for a variation of 1 meter of arm length with a precision of 1000 nm, you will obtain a resolution of 10^-6

    By the way, you can make a primitive grating spectroscope, using a CD as grating.
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