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Thread: fiber beam splitter

  1. #1
    Join Date
    Jul 2006

    Default fiber beam splitter

    When browsing through the new arrivals at I noticed this one:

    Probably based on something like:

    Could this be used in reverse to combine single mode diodes?
    Last edited by jeejeedr; 11-25-2014 at 04:45. Reason: typo's
    Trying to create a good diode mount....

  2. #2
    mixedgas's Avatar
    mixedgas is online now Creaky Old Award Winning Bastard Technologist
    Infinitus Excellentia Ion Laser Dominatus
    Join Date
    May 2007
    A lab with some dripping water on the floor.


    We've looked at these before a few years ago, when someone was selling them cut for red.
    It was not a winning idea.

    As for the listed advert Their specs don't add up.

    9 dB of insertion loss per channel, for example, 3 dB is half your power gone, 9 dB means nearly 1/10th transmission.

    While the directivity is excellent, the loss is huge.

    If that is truly 900 u fiber, your looking at ~ 20-30 mm collimated beam diameter. Plus 8 expensive launch optical trains. Planter's spatial filtered red beats that.

    I can get 8 to 12 single mode red diodes into a 200 uM or smaller fiber using free space optics at better then 90% coupling. I just need the better part of half a square meter of bench space and one custom curved mirror to do it.

    Last edited by mixedgas; 11-25-2014 at 05:33.
    Qui habet Christos, habet Vitam!
    I should have rented the space under my name for advertising.
    When I still could have...

  3. #3
    Join Date
    May 2009


    It is interesting to see such things on dealextreme, but there are a few reasons that wont help you laser show applications.

    1. That device is designed for telecom wavelengths in the infrared, it wont work in the visible (the fiber will go multimode and the coupling ratio will be incorrect).
    2. The fiber size spot on that spec page is the outer diameter of the fiber, the actual piece of glass inside is common 10um core 125um cladding fiber used in telecom applications. You could couple singlemode diodes into it, but it will be almost impossible to couple into the fundamental mode that the coupler is designed to use.
    3. The concept of using a fiber splitter to combine beams is fundamentally flawed in the same way that you cannot use a bunch of beamsplitters (not dichroic mirrors or knife edges, just normal partially reflective beam splitters) to combine beams. At best you get the same power on the output port as 1 diode (in practice it will be less than even a single diode worth of power) and all of the power leaks out of the unused ports of the splitters.

    You can get devices that look like that which are made with fiber designed for visible applications, where each port is designed for a different wavelength, which act like dichroic mirrors, an it may be possible to custom order one with a very tight wavelength spacing so that you could combine something like 639+640+641 but it will be quite costly and not really practical for laser show applications.

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