Compact and ultra-low power Sb 2 Se 3 -LNOI directional coupler switch

We propose a compact and energy-efficient directional coupler (DC) based on a lithium niobate-on-insulator platform. The DC integrates a pair of identical Sb 2 Se 3 waveguides with widths of 391 nm and lengths of 0.69 µm and 2.1 µm for TE 0 and TM 0 modes, respectively. To enable efficient thermal control, a pair of identical graphene heaters is symmetrically positioned on the Sb 2 Se 3 waveguides at the centre of the DC structure. This compact configuration achieves remarkably low power consumption, requiring only 0.236 mW for crystallisation and 0.772 mW for amorphisation in TE 0 mode, and 0.7397 mW and 2.4197 mW, respectively, in TM 0 mode. The device exhibits excellent performance, achieving crosstalk of < −32.4 dB, extinction ratios (ERs) above 32.27 dB, and a loss of