An asymmetric twin-waveguide high-bandwidth photodiode using a lateral taper coupler

We describe a high-bandwidth high-responsivity low-polarization sensitivity p-i-n photodiode based on an integratable asymmetric twin-waveguide structure. Incident light is collected by a diluted large-fiber guide followed by transfer to a thin-coupling waveguide using a low-loss lateral-taper coupler. The light is finally absorbed by the uppermost In/sub 0.53/Ga/sub 0.47/As layer. The device has a responsivity of (0.75/spl plusmn/0.03) ampere per watt and a polarization sensitivity of /spl les/0.4 dB. The measured electrical 3 dB bandwidth is /spl ges/40 GHz. The responsivity is comparable with the best 40-GHz waveguide p-type-intrinsic-n-type photodiodes, while the twin-waveguide design provides a single-epitaxial growth step and a simple means of fabrication with possibility for monolithic integration of the photodiodes with other optical components, such as semiconductor optical amplifiers and in-plane waveguide filters.