Multimode fiber coupler.

Two types of multimode fiber couplers made from plastic-clad fibers are described: (1) cross type couplers with coupling efficiencies from 30 dB to 50 dB depending on the crossover angle; and (2) parallel type couplers with low transmission loss and coupling efficiencies from 15 dB to 30 dB depending on the coupling length. These experimental results are in good agreement with theory.