InP/InGaAsP-Based Integrated 3-dB Trench Couplers for Ultra-Compact Coherent Receivers

We present the design, fabrication, and test results for ultra-compact 3-dB frustrated total internal reflection-based trench couplers in an InP/InGaAsP monolithic integration platform. The trench coupler is integrated with phase modulators and a balanced photodiode (BPD) pair to enable a 180° hybrid ultra-compact coherent receiver. Several trench splitter designs exhibit near 3-dB splitting with a loss of 3 dB. The BPD pair is used to characterize coherent mixing of two input optical signals into the trench splitter, and coherence efficiency of 75% is achieved.