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    Coupling a 125 or 200UM Core-Diameter Fiber Onto a Led Die

    by:
    FIBER & CABLE: Ask FOC Ask FOC
    Published: July 24, 2015

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    QUESTION: I am interested in efficiently coupling a 125 or 200um core-diameter fiber onto an LED die. My understanding is that the coupling efficiency is limited by the NA and core diameter of the fiber in most circumstances. Is it possible to use a tapered fiber, e.g. starting at 1000um core and moving to 125 or 200 um core to increase the irradiance at the small diameter fiber side?

     

    ANSWER:

    Transmission light from the LED die into any fiber is controlled by both the core and NA as well as the NA of the light coming out of the source. Obviously, the larger the fiber NA and core the better the coupling efficiency. We’ve done a lot of work using LED dies in conjunction with 1000um POF fiber which is a perfect match. Due to most application requirements, we’ve been forced to develop methods of coupling to 200um fibers with a .37NA and .48NAs. Inexpensive tapers did not work unless they were very long which are very expensive. Also, tapers had to be manufactured with a gl/gl fiber of .22NA which defeat the purpose of the design criteria. The shorter the taper, the more severe the internal angle thus the coupling efficiency is very poor. This can be easily modeled by performing a ray trace on zemax. Here is what we’d recommend, assuming the power is fairly low, a plastic lens would be the most cost effective as well as having the best coupling efficiency.   There will be other issues that will have to be dealt with here related to the output pattern of the LED die.

    1. Oval or rectangular shape.

    2. Hot spots

    3. Cladding modes of the fiber.

    4. Fiber output, if the length is short will be very strange as well.

    In short, there are quite a few issues to consider and we are more than happy to put you in contact with someone to discuss further.

     

    ADDITIONAL CONTENT & RESOURCES:

     

    SM6AskFOCIcon  Answered by AskFOC Technical Team July 24, 2015

     

     

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    FOC FAQ Fiber Optic Center has a team of technical experts and marketing strategists with decades of years in the field. This team contributes to the fiber, cable and specialty industries coverage through news, alerts, reports and general media information.
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    About Fiber Optic Center, Inc.
    Fiber Optic Center, Inc., (FOC), is an international leader in distributing fiber optic components, equipment and supplies and has been helping customers make the best cable assemblies in the world for over two decades. Several areas of specialization and expertise, in which they are the industry leader, make them the preferred choice for many of the world’s fiber professionals. In these key technology areas, FOC is "at least as technical as the manufacturer" about the products they sell. Striving to "make the business part easy," they offer outstanding and personal customer service, low or no minimum purchase order values, and from-stock delivery on industry-leading products and technology. FOC is the industry connection to the most innovative optical products, technologies and technical experts who integrate their manufacturing knowledge and vast experience into customers' worldwide operations. @FiberOpticCntr

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