Multiport Programmable Silicon Photonics Using Low-Loss Phase Change Material Sb ₂ Se ₃

Achieving an optimal platform to enable compact, efficient, and scalable reconfigurability is critical for next-generation technologies for large-scale photonic processors. Optical phase-change materials (PCMs) offer a compelling solution, and in particular Sb₂Se₃ stands out for its ultra-low-loss characteristics. Here, we present an experimental platform capable of encoding multiport operations onto the transmission matrix of a compact multimode interferometer architecture on standard 220 nm silicon photonics. The multiport devices are clad with a thin film of Sb₂Se₃, and direct laser writing induces local perturbations to the refractive index. A range of multiport geometries from 2 × 2 up to 5 × 5 couplers are demonstrated, achieving simultaneous control of up to 25 matrix elements with programming accuracy of 90% relative to simulated patterns and consistent optical performance across the C-band. Our work establishes a pathway toward the development of large-scale reconfigurable multiport devices on areas several orders of magnitude smaller than interferometer meshes.