Efficient Thermo-Optic Switching and Modulating in\nNonlocal Metasurfaces

High-<i>Q</i> optical resonances\nin nonlocal metasurfaces,\nbenefiting from significantly enhanced light/matter interactions,\nfeature strong responses even under a weak external stimulus. In this\nwork, we leverage the high-<i>Q</i> resonances of quasi-guided\nmodes (QGMs) supported by a photonic crystal slab (PCS) structure\nto achieve efficient optical switching/modulation. The QGMs with\nan experimentally measured <i>Q</i>-factor of ∼2200\nare realized by shifting every second column of air holes in a rectangular\nlattice within a silicon slab. At a weak illumination intensity of\nless than 4.0 W/cm<sup>2</sup> from a 532 nm continuous-wave pump\nlaser, the QGM resonance around 1550 nm experiences a pronounced spectral\nshift, with modulation depth exceeding 55%. This is attributed to\nthe thermo-optic response caused by photothermal heating of the metasurface\ntriggered by the absorption of the pump laser in silicon, which is\nfurther verified by the electrical heating approach. Our reported\nresults showcase a simple yet effective way of tailoring light propagation\nin nonlocal metasurfaces.