Design and fabrication of dual-channel symmetric optical 90-degree hybrid based on 8×8 multi-mode interferometer

We propose and demonstrate a dual-channel symmetric optical 90-degree hybrid on a 220 nm silicon-on-insulator (SOI) platform. The device integrates both coherent hybrid and signal splitting functions in a compact footprint based on an 8 × 8 multimode interference (MMI) structure, which helps reduce insertion loss and layout complexity. Simulations predict low phase error and high common-mode rejection ratio (CMRR). Experimental characterization confirms the functionality of the fabricated device. The hybrid formed by Output 1-4 exhibits CMRRs of over 10.6 dB in the 1520-1580 nm range, with a phase error of less than 9.5° in the 1520-1564 nm range. The Output 5-8 hybrid achieves CMRRs exceeding 15 dB in the 1520-1580 nm range, with a phase error remaining below 8.7° in the 1520-1564 nm range. These results validate the design and indicate the potential for further optimization in future fabrication iterations, highlighting the multifunctional integration advantage of the proposed device over conventional designs.