A series of passive fiber-optic devices, which includes a new type multiplexer-demultiplexer for WDM transmission, has been developed. The multiplexer-demultiplexer is composed of a single GRIN-rod lens and interference filters. Small in size, it has low-loss and high-isolation characteristics by means of direct attachment of filters on the fiber and the lens end. Total loss and cross talk for a pair of two-channel multiplexer-demultiplexers for two LEDs are <3.0 dB and less than -30 dB, respectively. By this method, multifunction devices such as multiplexer-demultiplexers with an optical switch can be constructed using a single lens.

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