High common mode rejection ratio InP 90° optical hybrid in ultra-broadband at 60 nm with deep-rigded waveguide based on × 4 MMI coupler**Project supported by the National Key Research and Development Program of China (Grant No. 2016YFB0402404), the Beijing Natural Science Foundation, China (Grant No. 4194093), and the National Natural Science Foundation of China (Grant Nos. 61635010, 61674136, and 61435002).

Abstract

An InP optical 90° hybrid based on a × 4 MMI coupler with a deep ridged waveguide is designed and fabricated. The working principle of the 90° hybrid is systematically introduced. Three-dimensional beam ropagation method (3D BPM) is used to optimize the structure parameters of the 90° hybrid. The designed compact structure is demonatrated to have a low excess loss less than –0.15 dB, a high common mode rejection ratio better than 40 dB, and a low relative phase deviation less than ± 2.5°. The designed hybrid is manufactured on a sandwitched structure deposited on an InP substrate. The measured results show that the common mode rejection ratios are larger than 20 dB in a range from 1520 nm to 1580 nm. The phase deviations are less than ± 5 ° in a range from 1545 nm to 1560 nm and less than ± 7° across the C band. The designed 90° optical hybrid is suitable well for realizing miniaturization, high-properties, and high bandwidth of coherent receiver.