25-Gb/s 1310-nm Optical Receiver Based on a Sub-5-V Waveguide-Coupled Germanium Avalanche Photodiode

We demonstrate low-voltage waveguide-coupled germanium avalanche photodetectors (APDs) with a (wafer-scale mean) gain×bandwidth product of 140 GHz at -5 V by utilizing a 185-nm-thick Ge layer. An optical receiver based on such an APD operating up to 25 Gb/s is demonstrated.