The present invention relates to a NxN single-mode optical coupler (10, 26) employing evanescent wave coupling between mutually adjacent optical waveguides (11) sufficiently close to one another to facilitate coupling among all the waveguides. An optical signal of a narrow frequency band, e.g. appreciably less than 100 gigahertz, introduced to an input port (15i) of one of the waveguides is found to be nonuniformly distributed among the output ports (16) of the coupler. A first embodiment uses the nonuniform distributions of narrowband optical signals to the output ports of the coupler to enable the present invention to be used as essentially a selective switching device. A second embodiment introduces one or more predetermined broadband optical signals to one or more input ports of the coupler to produce an appreciably uniform power distribution among the output ports of the coupler. A third embodiment uses electrooptic or magnetooptic waveguides and the application of a high-frequency, continuously changing magnitude, oscillatory electric or magnetic field (17), respectively, throughout the coupling region of the waveguides to produce a substantially uniform power distribution among the output ports of the coupler for a narrowband optical signal applied to an input port of the coupler.