Ultra-Broadband and Ultra-Compact Optical 90° Hybrid Based on 2×4 MMI Coupler with Subwavelength Gratings on Silicon-on-Insulator

We propose an ultra-broadband and ultra-compact optical 90° hybrid based on a subwavelength gratings dispersion-engineered 2×4 MMI coupler on silicon-on-insulator. Our device is only 41.3 μm in length, with an operating bandwidth over 150 nm.