• Re: Multimode Fiber Output Model

    From Himansu Pattanaik@21:1/5 to wadex...@provide.net on Tue Nov 16 13:23:40 2021
    On Saturday, July 7, 2007 at 11:23:46 PM UTC-5, wadex...@provide.net wrote:
    On Jul 7, 11:29 pm, Farsang <youzpal...@netscape.net> wrote:
    Hi Michael:

    This is primarily for image analysis, but would like also to do
    Physical Optics to simulate better the real situation.

    This is the application:

    We'd like to get spot size of dia = 2 Cm - 5 Cm (absolute Max) at a
    minimum distance of 100 feet (ideally 250 feet) from the fiber.
    Fiber output power is 200 W and wavelength = 980 nm.

    I was thinking to get the required spot size using Geometric Image
    Analysis of ZEMAX and then do the physical optics
    for closer simulation.

    Because of the optical invariance it'll be difficult to achieve the
    above spot size using catalog optics.

    Do you have any idea how we could get this spot size, appreciate your suggestions and comments?

    Ideally we'd like to have

    Spot Size = 2 Cm - 3 Cm at 250 feet
    Power in the Spot = 200 W
    Hi Farsang,
    If you are doing imaging analysis, you can model the output of a
    fiber as follows: Go to the Field Data box and click on "Object
    Height". Enter enough field points to represent your fiber, perhaps
    by a point in the center of the fiber, at the .7 zone, and at the
    fiber's edges. Set your wavelength in the wavelength box. In the
    Lens Data Editor, set the distance from your fiber face to the next
    lens or point of interest. Set the fiber's numerical aperture by
    setting <General> <Aperture> <Aperture Type: Object Space NA>,
    <Aperture Value: 0.22>. Make the fiber's output telecentric by
    clicking on "Telecentric Object Space".
    If you are looking for the footprint of the light through all of
    the lens surfaces (and the image plane, if there is one), you'll have
    to go to <Analysis> <Geometric Image Analysis> <Settings>, set the
    Field Size: to 0.500 (if your units are set to millimeters), set the
    File: to CIRCLE.IMA, set the Image Size: to the size of your area of
    interest at a particular surface, then set Surface: to your surface of interest.
    If you are coupling the fiber's light into another fiber, set the
    NA in the <Analysis> <Geometric Image Analysis> <Settings> box to the numerical aperture of the fiber being coupled. That will let you see
    the coupling efficiency.
    If you are doing physical optics propagation, you'll have to wait
    for Michael's reply.
    But from your last post, I think I see what you are doing.
    To model the optical system, if you need a 3 cm spot at 250 feet,
    from a 0.5 mm diameter source, your optical system's focal length
    needs to be about (250/30)* 0.5 (sorry about the mixed units) = 4.16
    feet. At a numerical aperture of 0.22, your system's aperture needs
    to be about 23 inches in diameter. It might be hard to come up with a
    23" diameter f/2.27 diffraction-limited lens. It's not impossible,
    but it would be expensive. Even the military might want to see a
    better solution.
    The problem arises from the size of your source. You'll get a lot
    further if you use the output of the diode directly (whose source is effectively the size of a bacterium), without passing it through a
    fiber, if that is possible.
    Wade Kelman

    Hi Wade,
    I am working on something similar. I can do the geometric image analysis with CIRCLE.IMA. But what you described will give me the beam profile at the image plane for one field. If I have to get superposition of all the field points so that I can have
    the geometric image of the fiber core at the image plane, what do I have to do in Zemax?

    Thanks
    Himansu

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