E-beam lithography fabricated optical 90-degree hybrid on InP platform

Integrated optical 90-degree hybrid has the advantages of compact structure and stable performance, which has been implemented on different integrated platforms, including silicon-on-insulator, silicon nitride, InP, and so on. InP is a promising platform for photonic integrated circuits (PIC) with both passive and active devices. Here, we simulated, fabricated, and demonstrated an InP optical 90-degree hybrid using a 4×4 multimode interference coupler. The designed device exhibits a phase error within ±5° in a spectral range from 1540 nm to 1565 nm, a common mode rejection ratio better than 19.6 dB, and an imbalance less than 0.91 dB in a spectral range from 1545 nm to 1560 nm experimentally. Performance improvement is on the way by optimizing the fabrication process.