Novel Photodetector Chip for Polarization Diverse Detection

A new photodetector chip for polarization diverse detection is presented. The presented chip allows for smaller footprints and design simplifications by utilizing a waveguide-integrated multiple-quantum well photodiode (MQW-PD) serially coupled to a bulk photodiode (PD) in InP technology. The MQW-PDs with their large polarization-dependent responsivities (PDR) detect the transverse electric (TE) polarized light, while the transverse magnetic (TM) polarized light is predominantly absorbed in the succeeding bulk detector with much lower PDR. Especially polarization diverse coherent optical receivers (PD-CRx) will benefit from this monolithic photodetector concept because neither polarization beam splitters nor rotators are needed. The separated detection of TE- and TM-polarized light will improve the fabrication tolerances and will reduce the footprint of a conventional, fully integrated PD-CRx to approximately 25%. The external TE and TM responsivities of the serially connected MQW- and bulk-PDs were measured up to 0.65 A/W and 0.45 A/W, respectively. Detection of 2 × 25 GBaud for dual polarization signals with a bit error rate of 10 ⁻⁶ is demonstrated without any post-compensation algorithms.