Inverse design of deformed Sb₂Se₃ stripes in silicon waveguide for reconfigurable mode converters

Abstract

Reconfigurable photonic devices integrated with silicon waveguides are important building blocks for future on-chip photonic circuits. In this paper, we focus on the mode order conversion in silicon waveguides with non-volatile reconfigurable capability. Deformed phase change material Sb2Se3 (antimony triselenide) stripes are introduced at the edges of the functional region to provide the refractive index difference required by mode conversions. The shapes of stripes are inversely designed by a gradient-based iterative optimization strategy with 57 (19) iterations for TE0-to-TE1 (TE0-to-TE2) mode converter. The footprint of the functional region is as compact as square center wavelength. In the crystalline phase, TE0-to-TE1 and TE0-to-TE2 mode conversions are realized with conversion efficiencies of 98.5% and 96.3% at a center wavelength of 1550 nm, respectively. While in the amorphous phase, the input TE0 mode directly passes through the functional region with efficiencies of 93.0% and 92.4%, respectively. The output mode can be reconfigured by changing the phase of Sb2Se3 stripes. Moreover, after introducing ±10 nm geometrical deviations to the perfect Sb2Se3 stripe design, corresponding red and blue shifts of conversion efficiency spectra can be observed, and the simulation results reflect the reasonable robustness of the proposed mode converters.