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Thread: Nichia NDB7875 collimation Math help

  1. #1
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    Unhappy Nichia NDB7875 collimation Math help

    can someone help shed "light" on this tutorial..

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    Last edited by b52productions; 08-08-2015 at 20:22.

  2. #2
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    Can I just ask from what text or book does your image come from? I think it looks like something which would be worthwhile reading?

    Cheers

    Steve

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  4. #4
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    i suppose this is the actual question.. solve for f using the example post 1

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  5. #5
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    if i understand your question right.. it is 3.22mm

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    so next..

    With this information known, it is now time to choose the appropriate collimating lens. Thorlabs offers a large selection of aspheric lenses to choose from. For this application the ideal lens is a -B AR-coated molded glass aspheric lens with focal length near 5.6 mm. "3.22 in our case" The C171TMD-B (mounted) or 354171-B (unmounted) aspheric lenses have a focal length of 6.20 mm, which will result in a collimated beam diameter (major axis) of 3.3 mm.

    Q... it is safe to say then our "ideal" lens if should be placed at 3.22mm from diode for a 3mm dia beam.. or is this all junked because of wide stripe..

    and if so... couldnt we use a small grin lens and then use the aspherical lens ? good info here.. http://www.edmundoptics.com/optics/o...145/?print=Pdf

    i did just find this...

    https://books.google.com/books?id=Vg...stripe&f=false
    Last edited by b52productions; 08-08-2015 at 22:04.

  7. #7
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    i guess since this is a multi transverse diode this would be a better illustration.

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  8. #8
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    has anyone tested a Gradient Index (GRIN) Rod Lenses with these diodes? im just looking for a better way
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  9. #9
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    These are some good questions and I have a few initial thoughts, however I'm going to have to look at this in more detail.

    The NA issue is simpler. The Thorlabs paper points out that it is the large divergence axis that drives the NA and this makes sense because for any given diode to lens distance this will be the larger dimension at the plane of the lens. The lens to diode spacing is determined by the FL of the lens and this distance will be very close to the the actual FL of the lens. At this position, the larger the NA or in other words the diameter, the greater the capture of the outlying rays and this will contribute to reducing the diffraction related divergence. Once the diameter of this lens drops below the NA of the diode then diffraction will skyrocket. I suspect that the collimators we use have a greater NA than the diode (because if it were less the power would drop rapidly as well), but they might improve if they had a larger diameter. However, there is a problem with trying to gather a wider field and that is the near field beam diameter will increase even though it may contain little obvious light. The optics that combine and manipulate this light will have to allow for this. It might actually be more productive to simply increase the FL of the collimator and place it appropriately farther from the diode. The necessary NA for the larger lens can be smaller and maybe more available commercially and the errors associated with lens alignment reduce by the FL^2.

    The highly asymmetric divergence of the fast and slow axises means that incorporating a cylinder pair as well as the radially symmetric collimator gives us another degree of freedom to manipulate and this also helps.

  10. #10
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    have not seen suitable GRIN.. but seen some with ar coating in visible spectrum..

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