A low-loss silicon photonic wire waveguide with low-impedance p-i-n carrier injection structures was developed. The propagation loss of the waveguide was less than 2 dB/cm and the input-impedance was adjustable around a few ten ohms. In a compact variable optical attenuator using this waveguide, the power consumption giving 30-dB attenuation was about 55 mW, and the response time was about 2 ns. A Mach-Zehndar interferometer switch with a sub-nanoseconds response was also developed. Moreover, ultra-fast extraction of photo-induced carriers was observed when reverse bias was applied to the p-i-n structure. Carrier lifetime time in the waveguide was measured to be less than 30 ps. Such a fast carrier extraction would enhance the efficiencies of silicon-based nonlinear optical devices.
We describe our recent progress in Si photonic integration technology focusing on the monolithic integration of a germanium photodetector and a silicon-wire-waveguide variable optical attenuator.
Fast optical power equalisation using a monolithic integrated germanium photodetector and a silicon variable optical attenuator on a compact silicon photonic platform is demonstrated. With an external electronic feedback circuit, the output power of the device is stabilised within a residual deviation of 2.7 dB for 22 dB input power variation. For a surge pulse, a sudden input power increase of over 16 dB can be suppressed within 50 ns for a 3 dB recovery.
