Promising results of various coupling experiments between laser diodes and single-mode fibers to determine the optimum coupling method are reported. The cylindrical lens method is shown to be most efficient, with a coupling loss of 1.8 dB under optimum alignment conditions. More than −2 dB coupling efficiency is attained with a cylindrical lens whose radius is less than 8 μm. The laser to fiber coupling characteristics are estimated by Gaussian beam approximation. The optimum radius of a cylindrical lens, which gives maximum coupling efficiency, is derived by theoretical calculation, using the ray matrix method. The cylindrical lens alignment tolerance is also shown theoretically and experimentally.
© 1979 Optical Society of America
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