Fig. 1. Reusable hybrid plasmonic–photonic metasurface supporting both high-Q plasmonic SLRs and BICs. (a) Hybrid structure comprising a rectangular array of gold nanorods and a dielectric cladding. Here l=200  nm, w=80  nm, h=30  nm, Px=500  nm, and Py and t are variable. The incident plane wave is polarized along the x direction (TE excitation). (b) Schematic diagrams of SLRs and BICs. The red (blue) curves indicate the electric field in the x direction of the SLR (BIC). (c) Simulated angle-resolved transmission spectra of a sample (Py=1100  nm, t=940  nm) under TE wave excitation. The dashed white box highlights the SLR and BIC generated by modes coupling. Insets: magnified view (left panel) and radiation polarization state of high-energy branch (right panel). The red (blue) color corresponds to right-handed (left-handed) polarization. (d) Transmission spectra extracted from (c) at incident angles θ=0° and 2°. The red (blue) regions indicate the SLR (q-BIC). Insets: simulated magnitude of electric field |E| for the unit cell of both SLR (θ=0°) and q-BIC (θ=2°). The dashed white lines indicate the cladding layer. (e) Helium-ion microscopic image of one of the fabricated metasurfaces without dielectric cladding (Py=800  nm).

Fig. 2. Multipole expansion. (a)–(c) Multipole expansion at incident angle θ=0°, where (b) and (c) display the dominant components of ED and MD, respectively. (d)–(f) Multipole expansion at incident angle θ=2°, where (e) and (f) show the dominant components of ED and MD, respectively. All the results are shown in logarithmic coordinate, and the highlighted areas correspond to Fig. 1(d). ED, electric dipole; MD, magnetic dipole; TD, toroidal dipole; EQ, electric quadrupole; MQ, magnetic quadrupole.

Fig. 3. Experimentally measured angle-resolved transmission spectra of three typical reusable samples using a fiber with core diameter of 600 μm under the TE wave excitation and extracted Q-factors of BIC bands. (a)–(f) Measured angle-resolved transmission spectra of representative samples A (Py=500  nm), E (Py=800  nm), and I (Py=1100  nm) with the cladding thickness (a)–(c) t=340  nm and (d)–(f) t=940  nm. The dashed white ellipses indicate the BICs. The solid black arrows indicate the upper branch SLRs, and the dashed black arrows indicate the lower branch SLRs. (g)–(i) Extracted Q-factors of BIC bands in (a)–(f). (g) corresponds to (a) and (d), (h) corresponds to (b) and (e), and (i) corresponds to (c) and (f).

Fig. 4. Mode analysis of simulated angle-resolved transmission spectra of sample E (Py=800  nm) with different cladding thicknesses under the TE-wave excitation. (a) Measured and simulated transmission spectra under normal incidence (t=340  nm and 940 nm). (b) Near-field electric field profiles of resonances indicated in (a) for t=940  nm. The dashed white lines indicate the cladding layer. (c)–(e) Full-wave simulated angle-resolved transmission spectra with band fitting results using a coupled oscillator model. The simulated results show excellent agreement with the measured results, and only half k-space of the fitting results is presented to facilitate comparison with the simulation results. The horizontal and diagonal dashed black lines denote the LSPR and RAs with different orders, while the diagonal dashed green curves indicate WGMs with different orders. The solid curves are hybrid modes resulting from mode coupling, with the pink curves highlighting the BIC bands. (f)–(h) Hopfield coefficients of BIC bands corresponding to pink curves in (c)–(e), respectively.

Fig. 5. Impact of core diameter d of the collecting fiber. (a) Schematic diagram illustrating the influence of the core diameter d on the actual resolution of the Fourier plane. (b) Measured Q-factors of BICs of all samples (A–I) by three fibers with different core diameters d=600  μm, 400 μm, and 105 μm at Γ point. Error bars are shown in the curves with d=105  μm. (c)–(f) Measured transmission spectra (solid black curves) and fitting curves (solid red curves) of SLRs (c), (d) and BICs (e), (f) of sample I using two different fibers at Γ point (d=600  μm, top panel; d=400  μm, bottom panel). The Q-factors in (b) indicated by the arrows are obtained from the fitting of the measured transmission spectra in (e) and (f), respectively.

Fig. 6. Comparison of Q-factors between SLRs and BICs using a fiber with core diameter of 400 μm. (a) Measured transmission spectra of sample I under different incident angles, with the highlighted red (blue) regions indicating the evolution trend of SLR (BIC) resonances. (b) Simulated transmission spectra corresponding to (a). (c) Extracted Q-factors from the data in (a) and (b).