A Compact Integrated Receiver Optical Sub-Assembly With High Sensitivity and Low Crosstalk for 100 Gb/s Ethernet Systems

A 25Gb/s guardring-free planar AlInAs avalanche photodiode (APD) and 100-Gb/s APD receiver optical sub-assembly (ROSA) employing a quasi-collimated beam for reducing the optical loss and optical demultiplexer (DEMUX) size are demonstrated for a 40-km optical link. The APD so fabricated achieves a very low dark current of 63 nA at a multiplication factor of 10, with a high gain-bandwidth product of 225 GHz due to the optimum multiplication layer and absorption layer. Additionally, the assembled APD ROSA exhibits a high receiver sensitivity of more than -23 dBm optical modulation amplitude (OMA) (BER = 5.0 × 10
^-5
) at temperatures ranging from -5 to 80 °C for each lane. Investigating the transmission over fibers with dispersions of -119 and +40 ps/nm reveals that a sufficiently low penalty of less than 0.9 dB is obtained for all lanes. Furthermore, it is confirmed that the APD ROSA suffers little crosstalk penalty thanks to the isolation achieved by this design of optical DEMUX.