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.

I. Introduction

With the rapid growth of Internet services such as big data and cloud computing, data-center networks and mobile backhaul have been employing the high-speed 100−gigabit Ethernet (100 GbE) standardized in IEEE [1]. These networks require not only higher data rates but also compact transceivers that can be mounted in a limited space. C form-factor pluggable (CFP) [2], specified in a multi-source-agreement (MSA) for 100 GbE transceivers, is being replaced with the more compact CFP2 and CFP4. CFP4 can extend total capacity in a line card to 3.2 Tb/s, which is eight times denser than the 400 Gb/s of CPF. The current CFP also consists of many discrete devices, such as laser diodes, photodiodes (PDs), and optical filters. The performance of each device is ensured, although a large footprint is inevitable. A key feature for the compactness of CFP4 is the integration of these optical and electrical devices.