Bandwidth Enhancement of 2x4-MMI-Coupler-Based Optical 90° Hybrid on Silicon-on-Insulator

We demonstrate the bandwidth enhancement of optical 90° hybrid based on
$2\times 4$
MMI coupler for the silicon-on-insulator platform, without adding any fabrication complexity. By optimizing the width of the conventional
$2\times 4$
MMI coupler, our design achieves an operating bandwidth of 72 nm.