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Compact High-Responsivity Receiver Optical Subassembly With a Multimode-Output-Arrayed Waveguide Grating for 100-Gb/s Ethernet

We developed a compact receiver optical subassembly (ROSA) for 100-Gigabit Ethernet (100 GbE) using multimode-output-arrayed waveguide grating (MM-AWG) and arrayed photodiodes (PDs). The four-channel silica-based MM-AWG has low insertion loss of less than 1 dB. The back-side-illumined PD with maximized-induced current structure provides high responsivity of 0.95 A/W. To avoid the distortion of the responsivity spectrum due to poor coupling between the multimode beam and PD, we employ a racetrack shape for the active region of the PD. The optical coupling between the MM-AWG and lens-coupled PD is optimized in terms of the flattening ratio of the racetrack shape. The fabricated ROSA has high responsivity of over 0.7 A/W with a flat-top spectrum and obtains high environmental stability thank to its large assembly tolerance of over ± 4 μm. For 4 × 25-Gb/s signals after 10-km transmission, the minimum receiver sensitivity of the ROSA has a margin of 4.8 dB for the Ethernet standard. The transmission performance with a 100-GbE transmitter optical subassembly was also confirmed.