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Coupling Xe Arc Lamp into Fiber Bundle

  1. Apr 17, 2015 #1

    we are trying to couple the light of a 75 W Xe Arc Lamp (Hamamatsu L2194) into a 800um(0,8mm) diameter fiber bundle (7 fibers). Now we have 2 plano convex lenses (25mm diameter, 30mm EFL, edmund serial #45-364), the first for collimating the second for focusing onto the fiber.

    We are trying to move the fiber bundle around the focus, so all the fibers in the bundle receive light, because the fibers close to the edge receive just a small portion of the light

    I would like to improve this. I looked up the arc lamp datasheet and found the radiant flux distribution.

    page 5

    It seems they are radiating in a 100° cone, so I could replace the 25 mm lenses with bigger ones, so it could collect more light.

    Also i thought of replacing the lens material from N-BK7 to fused silica maybe, but from the xe lamp spectrum it may not be a good idea.

    I also thought of using a diffuser, but I do not have any experience with them.

    Maybe replacing the lamp with a bigger one?

    And finally I thought, maybe I could first focus the light into a 800um diameter fiber first, and then couple the light from it into the fiber bundle. I think the fiber would scrample the light distribution this way, am I correct in this?
  2. jcsd
  3. Apr 17, 2015 #2

    Quantum Defect

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    Can you just put the bundle next to the light?

    With a 25mm lens, 30mm focal length as the collector, you will be collecting a very small fraction of the solid angle. PI *12.5^2 /(4 PI 30^2) = 4% of the light. A goodly fraction of this will be lost to reflection on each lens surface.

    Bigger lenses will be more expensive, fast lenses will be quite thick.

    Another strategy would be to use reflective optics. Edmunds sells some ellipsoidal reflectors. If you put the lamp at one of the foci and the fiber bundle at the other, you might get gobs of light into the fiber. I am not sure if they have one big enough for your lamp, but you might be able to find a smaller light that would fit one of their larger reflectors. You could do the same thing with two parabolic reflectors, and if you are on a budget you could probably find something that would work at an auto parts place.
  4. Apr 17, 2015 #3
    Put it all in hollow tin foil ball. Or would this overheat the lamp?
  5. Apr 20, 2015 #4
    The ellipsoid mirror and the tin foil ball is not an option, our Xe lamp is in a temperature controlled box, with a hole in it, where the Xe arc is. But maybe putting a mirror behind the light source, we could salvage some of the light which is radiating in the direction of the box and not out of it.
  6. Apr 20, 2015 #5

    Andy Resnick

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    Is this a 'bare' bulb, or do you have a housing for it? For example, the housing for my (Osram) arc lamps has both reflector optics (to collect some of the light going 'the wrong way') and condenser lenses to focus the light. However, I don't think I can couple that much light into a 800um diameter fiber bundle- the etendue of the housing optics is too low. You may be able to find housings fairly easily.

    What is your application? Why are you using a fiber bundle? Why is the diameter set to 800 um? Typically, I couple into a liquid-filled light pipe, about 3mm in diameter. Liquid-filled light guides may be better for your application, for a variety of reasons.
  7. Apr 20, 2015 #6
    It is a bare bulb, it has a housing but it does not contain any optics, it is for temperature control. We collimate the light with a lens, and then focus it onto the bundle with another lens.

    The application would be a transmission measurement system, from the light bundle we take the fibers and attach it to different parts of the sample, so with a bundle with 7 fibers, we can meassure at 7 points at the same time. I do not know why did they choose this diameter, the guys at the lab have this system and they asked me to couple more light into the fibers. I have no experience in liqued filled light guides, but I do not think it is usable for this method.
  8. Apr 20, 2015 #7
    Sadly the hamamatsu housing for the 75W lamp of Hamamatsu does not contain optics, only the housing of the 150W arc lamp.
    http://goo.gl/X1HYbz page 13
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