Monolithic Integration of Silicon-, Germanium-, and Silica-Based Optical Devices for Telecommunications Applications

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Abstract
This paper presents our recent progress with the integration of silicon (Si) photonic devices for optical telecommunications. To integrate Si wire waveguides, germanium (Ge) photodetectors (PDs) and silica waveguides, we have developed processes for the selective epitaxial growth of Ge on a Si waveguide core and for the low-temperature deposition of silica waveguide film and introduced spot size converters (SSCs) for coupling Si-wire and silica waveguide with low loss. Using these processes and SSCs, we have managed to monolithically integrate Si variable optical attenuators (VOAs) and Ge PDs, and Si VOAs and a silica arrayed waveguide grating (AWG). In the integrated VOA-PD, the Ge PD accurately detects the attenuation of light power in the Si VOA. The 3-dB cutoff frequency in VOA-PD synchronous operation is around 100 MHz, which is limited by the VOA. The integrated VOA-AWG provides high-speed power-level adjustment independently in every channel of the AWG with a response time of 15 ns. These integrated Si photonics devices exhibit sufficient performance for application to future telecommunications systems that combine WDM and burst-mode packets.