Reconfigurable Photonic Circuit for On-Chip Optical Routing with Engineered Si-ITO Platform

Abstract

Reconfigurable photonic circuits are essential for programmable optical signal processing and high-speed optical interconnects; however, achieving compact and electrically tunable routing elements with low optical loss remains a major challenge in integrated photonics. We propose a 4 × 4 reconfigurable photonic circuit, enabling flexible routing of optical signals between multiple input and output ports based on mesh architecture of an electrically tunable directional coupler. The Si-indium tin oxide (ITO)-based engineered directional coupler serves as an electrically tunable building block for photonic routing architecture. The device integrates a low-loss Si-ITO phase shifter within the coupling region, enabling active modulation of the effective refractive index through carrier accumulation at the Si-ITO interface. The ITO layer is engineered via controlled oxygen partial pressure during radio frequency (RF) sputtering, enabling optimized carrier concentration for enhanced electro-optic modulation with low optical loss. This electrically induced index variation modifies the evanescent coupling between adjacent waveguides, allowing optical power to be dynamically switched between the cross and bar ports. Through systematic device optimization, the influence of waveguide width, coupling gaps, operating wavelength, and applied voltage on the coupling characteristics is investigated. The proposed device demonstrates an insertion loss of ∼5–8 dB, propagation loss of ∼0.02 dB/μm, an extinction ratio of ∼47 dB, and VπL product of approximately 0.308 V·cm. The proposed 2 × 2 device demonstrates stable operation over the 1.5–1.6 μm wavelength range and compatibility with silicon photonic fabrication processes. These results highlight the potential of the proposed architecture as a scalable building block for programmable photonic circuits, optical switching fabrics, and integrated photonic computing systems.