Non-volatile 2 × 2 optical switch using multimode interference in an Sb₂Se₃-loaded waveguide

We propose a non-volatile 2 × 2 photonic switch based on multimode interference in an Sb₂Se₃-loaded waveguide. The different modal symmetries of the TE₀ and TE₁ modes supported in the multimode region change their propagation constants distinctly upon the Sb₂Se₃ phase transition. Through careful optical design and FDTD optimization of the multimode waveguide dimensions, efficient switching is achieved despite the modest index contrast of Sb₂Se₃ relative to Ge₂Sb₂Te₅. The fabricated optical switch demonstrates favorable characteristics, including low insertion loss of ∼1 dB, a compact length of ∼27 µm, and small cross talk below -15 dB across a 35 nm bandwidth. Such non-volatile and broadband components will be critical for future high-density programmable photonic-integrated circuits for optical communications and signal processing.