Abstract

Monolithic waveguide/photodetector coupling is essential for optoelectronic integration using waveguide optical signal processing. Previous coupling approaches have restricted applicability because of poor detector bandwidth for thick waveguide layers,¹ difficult fabrication (multiple material-growth cycles on nonplanar surfaces),^2-4 or strongly wavelength-dependent coupling.³,⁴ Here we describe two alternatives suitable for thick waveguides; they exhibit low input coupling loss from optical fibers (< 1 dB) at 1.5 μm wavelength. Our approaches are variants of conventional butt-coupling² or vertical-coupling¹ schemes and achieve efficient absorption with minimal detector area for high-bandwidth detection. Our butt-coupling variant uses integrated mirrors to couple guides on one wafer surface to detectors on the opposite surface, as was first suggested by Trommer.⁵ In contrast to Trommer's system, however, our large waveguide size minimizes diffraction in the substrate. This reduces the detector area (50 × 80μm²) and capacitance (0.25 pF) and maintains low optical insertion loss (~1 dB). Our vertical-coupling variant uses impedance-matching for coupling enhancement, resulting in a low input coupling loss (0.8 dB), a guide/diode coupling of 70–99%, and bandwidths of 5.5-11 GHz.

© 1990 Optical Society of America