Abstract

Monolithic waveguide/photodiode integration is essential for many optoelectronic integrated circuits. Evanescently coupled structures (Fig. 1) offer advantages of single-step epi-growth, ease of diode junction placement, and low diode leakage. Conventional devices (with adjacent waveguide and absorber layers), however, exhibit high capacitance and low bandwidth because of the long diode length L required for appreciable absorption (>1 mm for 3.4-μm-thick guides).^1,2 Use of thin waveguide layers can reduce^2,4 L but also increases fiber-waveguide coupling difficulty. Here we present a novel vertical-impedance matching (VIM) approach that enhances diode absorption by insertion of matching layers between guide and absorber. We demonstrate 500% length reduction over conventional structures without compromising fiber coupling, capacitance, or ease of fabrication.

© 1990 Optical Society of America