Switchable waveguide mode converter based on phase change material

Reconfigurable devices play an important role in photonic circuits. Phase change materials (PCMs) have considerable potential as candidates for the reprogrammable optical platform. Here, we report a switchable on-chip mode converter by coating an active metasurface made from a PCM on a silicon nitride (Si₃N₄) waveguide. Utilizing Ge₂Se₂Te₅ PCM, the dynamic device can convert fundamental TE mode to higher order TM₁₀, TE₁₀ mode or switch to cut-off state depending on the phase of the PCM. The proposed mode converters show high mode purity (>90%) with peak transmission of the converted modes of 37% and 36% in the communication band. Our small-footprint device provides dynamic modulation of guided wave polarization and paves the way for applications of large-scale photonic integrated circuits and optical communications.