(a) Schematic of the entire device. (b) Cross section of the waveguide supporting the photonic BIC mode. (c, d) Electric field |E| profiles of the TM bound mode (c) and a TE continuous mode (d) supported by the waveguide in (b). The photonic BIC mode refers to the TM bound mode (c) that under certain conditions does not interact with the TE continuous modes (d) and thus experiences zero propagation loss in the waveguide in (b). (e) Simulated and measured intrinsic optical quality factor of the cavity resonance as a function of the waveguide width w. (f) Illustration of an SAW propagating across a BIC waveguide and an etched waveguide. The etched waveguide causes reflection and scattering of the incident SAW, but the BIC waveguide does not.