Broad passband multi/demultiplexer for multimode fibers using a diffraction grating and retroreflectors

A broad passband multi/demultiplexer for multimode fibers employing a diffraction grating and retroreflectors is presented. As shown by calculation and experimental results, a passband width proportional to the difference between the retroreflector length and the input fiber core diameter is attainable. Using a standard (
50/125 \mu
m) graded index fiber as the transmission fiber, 1-dB passband widths of 100 nm for the multiplexing channel and 94 nm for the demultiplexing channel with a channel spacing of 125 nm are achieved in a two-channel multi/demultiplexer. The minimum insertion losses for each channel are 2.3 and 2.7 dB, respectively.