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thin film optical filters

Discussion in 'Electronic Design' started by Jon Kirwan, Jun 23, 2009.

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  1. Jon Kirwan

    Jon Kirwan Guest

    I'm dismantling a few old DVD writers for parts and I'm curious about
    the specs on those parts I'm pulling out carefully. One of the pieces
    of glass appears to be a thin film dielectric filter/splitter. It's
    possible it is just a splitter used in the astigmatic/quad detector
    system for focusing... but because this is a writable system I'm
    wondering if it may also double as a bandpass/bandstop filter, as
    well. (A separate wavelength, memory serving, is used to hit a
    differently dyed polymer layer in the disk for writing than for
    erasing.) So I'm wondering if anyone already knows, roughly, the
    details of the thin film dielectric filter/splitter glass used in
    writable DVD units -- what it actually is.

    I've looked around with google and found some things to read -- but
    all of it dated back at 1997 and earlier. Old. And no details on
    these parts that I could find today. (A lot of what I found is
    Japanese and Korean, which is expected, but of far less help to me.)

    I may need to set up a cheap one-off spectrophotometer, callibrated
    with a merc-argon lamp, and do my own work in answering these
    questions. But it would certainly help if someone had some of the
    details in mind about these pieces of glass, before I try and set
    something up here.

    Thanks in advance,
  2. Martin Brown

    Martin Brown Guest

    A shovelware CD with an aluminium coating at grazing incidence is good
    enough in sunlight to resolve the Fraunhofer lines. You should be able
    to see what effect if any your filter has in the visible with some handy
    calibration lines thrown in for free.

    Martin Brown
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