An optical wavelength division multiplexer mixer-splitter wherein a precision formed substrate chip is fabricated with a first traversing groove and at least a second intersecting groove. A first input/output optical fiber lies upon one end of the first groove and at least a second input/output fiber lies upon the at least a second groove. An output/input optical fiber is aligned upon the other end of the first traversing groove and terminates at a position adjacent the intersection of the first and second grooves upon the substrate chip. The output/input optical fiber is terminated with an angled end face in optical alignment with the first and at least a second input/output optical fibers. The end face is provided with an integral optical coating whereby the unit may serve as a wavelength division mixer, splitter or optical power tap for two or more optical wavelengths.