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 struct ure. Incident light is collected by a diluted large-fiber guide followed by transfer to a thin-coupling waveguide using a low-loss lateral-taper coupl er. The light is finally absorbed by the uppermost In-0.53 Ga0.47As layer. The device has a responsivity of (0.75 +/-0.03) ampere per watt and a polar ization sensitivity of less than or equal to0.4 dB, The measured electrical 3 dB bandwidth is greater than or equal to 40 GHz, The responsivity is com parable with the best 40-GHz waveguide p-type-intrinsic-n-type photodiodes, while the twin-waveguide design provides a single-epitaxial growth step an d a simple means of fabrication with possibility for monolithic integration of the photodiodes with other optical components, such as semiconductor op tical amplifiers and in-plane waveguide filters.