Monolithic MMI-Based 25-Gb/s SOI DPSK Demodulator Integrated With SiGe Photodetector

In this letter, the performance of a 25-Gb/s 1 × 2 multimode interference (MMI) coupler-based monolithic differential phase shift keying (DPSK) receiver integrated with Germanium (Ge) on silicon-on-insulator (SOI) photodetector (PD) is presented. Theoretical analysis suggests that the device exhibits more uniform extinction ratio over the C-band compared with a DPSK demodulator based on 2×2 MMI coupler. Electrical scattering parameters (S-parameters) investigated through component level simulation comparing the fabrication tolerance shows power penalty of 1.2 and 5 dB for unbalanced and balanced detection DPSK receiver, respectively. The SOI 1×2 MMI coupler-based unbalanced DPSK receiver has a sensitivity of 0.41 dBm at a bit error rate of 1×10^-9 without postelectrical amplification. The PD integrated single-end detectionbased receiver has a total footprint area of 0.39 mm².