High-Speed Avalanche Photodiode and High-Sensitivity Receiver Optical Subassembly for 100-Gb/s Ethernet

This paper reviews a 25-Gb/s avalanche photodiode (APD) with an inverted p-down structure and its application to a 100-GbE receiver optical subassembly (ROSA). The APD exhibits high responsivity (0.9 A/W), large bandwidth (18 GHz at
$M = 10$
), and a large gain-bandwidth product (235 GHz) by optimum design of the absorption layer (1.0 μm) and InAlAs avalanche layer (0.1 μm). Stable
I–V
characteristics without edge breakdown were observed owing to a strong confinement of a high electric field in the avalanche layer by two field-control layers and a triple-mesa structure. We also describe a 100-Gb/s (4 × 25-Gb/s) ROSA using a monolithic four-channel APD array and an ultrasmall planar-lightwave-circuit demultiplexer. The performance indicates a record minimum receiver sensitivity of –20 dBm and 50-km error-free transmission without an optical amplifier.