Compact 90° optical hybrid on a silicon-on-insulator platform with a wide bandwidth of 130 nm.

In this Letter, we present a compact and broadband 90° optical hybrid on a silicon-on-insulator (SOI) platform. The device achieves equal power splitting through the design of a 2-by-4 star coupler, while the required quadrature 90° phase shift is introduced by tailoring the optical path lengths to the respective output ports. Experimental results show a high common mode rejection ratio exceeding 20 dB and a low phase error of less than 5° across an optical bandwidth of 130 nm. To the best of our knowledge, this is the widest bandwidth ever reported for a passive 90° hybrid on the SOI platform. With a compact footprint of 25 × 20 µm, the proposed optical hybrid is highly suitable for applications requiring both broadband operation and dense arrays of coherent receivers, such as optical imaging and optical computing.