Design and optimisation of a cascaded RI-MMI-based 2×4 quadrature phase and power splitter with integrated thermo-optic phase shifters

Abstract

In this study, we present the design and optimisation of a 2 × 4 quadrature phase and power splitter based on cascaded restricted interference-multimode interference (RI-MMI) couplers integrated with thermo-optic phase shifters on a silicon photonic platform. The device operates in the RI regime to achieve a compact, efficient configuration. The proposed circuit consists of two cascaded 2 × 2 RI-MMI couplers with integrated Ti-based heaters enabling precise thermo-optic phase control and switching capability. Numerical simulations using the 3D beam propagation method (BPM) show that the splitter performs effectively across a broad wavelength range of 1.5–1.6 µm, with an excess loss of approximately 0.2 dB at the central wavelength. The four output ports exhibit well-balanced power distribution, with a maximum deviation of about 15 dB, and maintain stable 90° phase differences among the outputs. The device also demonstrates robust thermal stability and tolerance to fabrication errors up to ± 1 nm, ensuring consistent optical performance. These findings highlight the strong potential of the proposed device for advanced optical signal processing applications such as quadrature phase-shift keying (QPSK) modulators, multicarrier phase-coded orthogonal frequency-division multiplexing (OFDM) systems, optical phasors, and multiphase local oscillators, providing a robust, high-precision platform that operates reliably across multiple wavelength bands.