Abstract

Monolithic integration of optical waveguides with sources or detectors is of current interest for enhancing the functionality of optoelectronic circuits with on-chip optical signal processing. A major drawback to this approach has been the large size, typically many millimeters, required for optical routing structures such as directional couplers. Large chip size is incompatible with the high cost of the III-V materials needed for sources and detectors in fiber optic applications. This paper describes recent demonstrations of compact (< 1 mm long), easily integrable low-loss couplers. We show that self-imaging in over-moded couplers achieves compact lithographically defined devices, and that vertical coupling can provide extremely small (< 100 μm) devices with no critical lithographic tolerances. Both approaches result in couplers that are insensitive to the operating optical wavelength. Vertical impedance matching is shown to provide simple integration of these devices with high performance photodetectors, without epitaxial regrowth.

© 1991 Optical Society of America