Compact thermo-optic switch based on graphene-silicon nitride nanobeam cavity

We propose and experimentally demonstrate a compact optical switch based on a one-dimensional (1D) silicon nitride (Si₃N₄) photonic crystal nanobeam cavity (PCNC) integrated with a graphene microheater. The PCNC exhibits a small optical mode volume of approximately 3.2 μm³, which enhances light-matter interaction and improves thermo-optic (TO) tuning efficiency. Graphene is positioned at the center of the cavity, and heat generation is induced by applying a bias voltage across it. The refractive index of the underlying PCNC is then changed due to the TO effect, thereby enabling resonance wavelength tuning. Additionally, fast thermal response is achieved owing to the high thermal conductivity of graphene. Measurements show a TO tuning efficiency of 0.21 nm/mW and an extinction ratio (ER) of 7 dB at an applied heating power of 5.2 mW. The thermal rise and fall time constants are 4.55 μs and 1.55 μs, respectively. This work achieves a microsecond-level Si₃N₄-based optical switch with a compact device footprint, offering a promising solution for high-density on-chip optical interconnects and routing systems.