Si-Ge-Silica Monolithic Integration Platform and Its Application to a 22-Gb/s $\times$ 16-ch WDM Receiver

We describe a Si-Ge-silica monolithic integration platform for telecommunications applications. The monolithic integration process features low-temperature silica film deposition by electron-cyclotron-resonance chemical vapor deposition to prevent thermal damage to Si/Ge active devices. The monolithically integrated Si and SiOx waveguides show propagation losses of 2.8 and 0.9 dB/cm, and the inverse-tapered spot-size converters show a coupling loss of 0.35 dB. We applied the platform to a 22-Gb/s × 16-ch wavelength-division multiplexing receiver, in which a 16-ch SiOx arrayed waveguide grating (AWG) with 1.6-nm channel separation and Ge photodiodes (PDs) are monolithically integrated. The AWG-PD device exhibits fiber-to-PD responsivity of 0.29 A/W and interchannel crosstalk of less than -22 dB and successfully receives 22-Gb/s signal for all 16 channels. In addition, we demonstrate 40-km transmission of 12.5-Gb/s signal and obtain sensitivity of -6.8 dBm at a bit error rate of 10^-9 without transimpedance amplifiers.