Fig. 1: Engineering cavity critical coupling in perovskite metasurfaces based on quasi-bound state in the continuum (quasi-BIC).
From: Free space few-photon nonlinearity in critically coupled polaritonic metasurfaces
a Schematic of the perovskite metasurface in a rod-type symmetry-protected quasi-BIC design. Underneath a PMMA superstrate, a periodic array of FAPbBr3 perovskite nano-rods is embedded in the SiO2 substrate. The geometrical unit cell parameters include the lengths of two asymmetric rods L = 252.5 nm and \(L-\triangle L=(1-\alpha )L\), respectively, the width of the rods W = 112.5 nm, the distance between two rods D = 112.5 nm, the PMMA thickness tPMMA = 50 nm, the rod thickness tperovskite = 60 nm, and the period PX = PY = 475 nm. An asymmetry parameter \(\alpha=\triangle L/L\) between 0 and 1 is applied to tune the cavity intrinsic quality factor Qint. A multiplicative scaling factor is applied on the lateral geometrical parameters only (thicknesses unchanged) to tune the resonance wavelength. b Top, Tuning Qint via different \(\alpha\) values to match the material background loss Qbg for the cavity critical coupling. Middle and Bottom, Simulated electric field enhancement inside the perovskite rods as a function of applied asymmetry parameter \(\alpha\) when the non-exciton background loss of perovskite is considered (Middle) and not considered (Bottom). A hypothetical perovskite dielectric function with the exciton resonance turned off is applied (see Supplementary Note 1). Scaling factor = 0.76. c Simulated electric (left) and magnetic (right) field profiles at the quasi-BIC resonance of a perovskite metasurface with \(\alpha\) = 0.30 and scaling factor = 0.76. The arrows show the directions of field vectors. d, e Simulated transmittance spectra of quasi-BIC perovskite metasurfaces under normal incidence as a function of (d) scaling factor and (e) asymmetry parameter \(\alpha\), respectively. The exciton resonance is turned off.
