High-Speed In_0.52Al_0.48As Based Avalanche Photodiode with Top-Illuminated Design for 100 Gb/s ER-4 System

High-speed top-illuminated avalanche photodiodes (APDs) with large diameters (25 μm) are demonstrated for the application of 4-channels 100 Gb/s data rate. They achieve a bandwidth of 17 GHz at low-gain (M_G = 6.2; 3.6 A/W) and large-gain bandwidth (responsivity bandwidth) product (410 GHz (237.8 GHz-A/W); 55% external efficiency at the unit gain) while maintaining invariant high speed (14 GHz) under high power (0.5 mW) and 0.9 V_br operations. By packaging the demonstrated APD with a 25 Gb/s transimpedance amplifier in a 100 Gb/s ROSA package, a good sensitivity of around-20.6 dBm optical modulation amplitude (OMA) at the data rate of 25.78 Gb/s has been successfully demonstrated. The achieved sensitivity not only meets the required receiver sensitivity (-18.5 dBm OMA) in 100 GbE-ER-4 Lite (40 km) system, it is also comparable with that of the high-performance 100 Gb/s ROSA incorporated with the back-side illuminated APD design. Overall, our novel APD structure can eliminate the costly flip-chip bonding package in the 100 Gb/s ROSA without sacrificing its sensitivity performance.