We have investigated the problem of coupling light emitting diodes to contemporary low-loss multimode optical fibers (NA ~ 0.14) for optical communications. We have calculated the maximum coupled light power and the coupling efficiencies for a disk geometry and a strip geometry with and without a lens. In our calculations, we assumed that the homostructure LED has a radiance of 30 W/sr cm2 and requires an electrical power input JV or 2 × 104 W/cm2. In the disk geometry without a lens, the maximum coupled light power of 36 μW can be achieved. With a lens the LED junction area can be reduced so that the coupled light power of 31 μW which is 0.1% of the input electric power, is possible. In the strip geometry with a lens a coupled light power of 260 μW is achievable.
© 1975 Optical Society of America
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