Tailoring Fano Resonance for Flat-Top Broadband Reflectors Based on Single Guided-Mode Resonance

Abstract

We investigated on the interaction between a single guided-mode resonance and Fabry-Perot resonance (FPR) in a high contrast grating (HCG) from a viewpoint of Fano resonance. It has been found that the background reflection due to the FPR in the HCG is useful to implement flat-top broadband reflectors via tailoring the phase polarity of Fano resonance. The novel conceptual approach was elucidated theoretically with the temporal coupledmode theory (TCMT), which was confirmed by the Si HCG broadband reflector design of 380-nm bandwidth for R > 99.9 from 1400 to 1780 nm (a fractional bandwidth of 24.5%). The TCMT model was in good agreement with the rigorous coupled wave analysis calculation. We believe that our approach provides expanded understanding on Fano resonance in a grating, enabling more intuitive and simpler design of a flat-top broadband reflector with grating structures.

Surface wave manipulation by plasmonic metasurface based on mode resonance

“…In this paper, it is revealed that the controlling of surface EM waves can be achieved by simply changing the depth or refractive index of a single deep subwavelength groove in the metal grating, and detailed physical explanation is given. With the increase of the groove depth or refractive index, the surface wave propagation characteristics show obvious periodic changes, which is essentially caused by the mode resonance between the surface modes and the groove cavity modes, similar to the Fano resonance [47][48][49][50] . Moreover, under the mode resonance, the grating surface will form high-intensity local standing waves, which can be applied to deep subwavelength resonators or spasers.…”

Mirror-less unidirectional radiation in an asymmetric single resonator

“…The existence of the partial reflectivity in the channel results in a non-zero mutual coupling coefficient as discussed in Appendix, and = 0 occurs when = (m is an integer.) [4,5]. When = 0 is assumed, from (4) and ( 5), the coupling coefficients of each mode into the respective ports are related as Substituting ( 6) into (3), we obtain…”

“…In addition, the background scattering itself should satisfy the resonant condition ( = 0 or = 1) at the resonant frequency of those two modes. In the design of the structure, we first designed a broadband reflector of ~ 100 % peak reflectivity based on the interaction between a relatively low quality factor (~ 10) GMR mode and the background scattering, where ~ 100 % peak reflectivity verifies the coincidence of the resonance frequencies of the low quality factor GMR mode and the background scattering [5]. Then, the structure is further optimized to make the resonant frequency of another GMR mode of a relatively high quality factor (> ~ 1000) coincide with the peak reflectivity frequency of the broadband reflector.…”

“…One can see that two reflection peak branches intersect near the slab thickness of dSlab = 336nm, where a symmetric broadband reflection spectrum with a peak reflectivity of ~ 100% is achieved as shown in Fig, 3(b). The branch of a broad bandwidth originates from a low quality factor GMR combined with the F-P like background scattering [5]. The electric field (|Ez|) profiles at the reflection peak points for two different slab thicknesses of dSlab = 320nm and 360nm are plotted in the insets of Fig.…”

“…So, conceptually, the proposed approach can be understood as mimicking one-port resonant system due to the internal mirror function. In our previous work, we have shown that a flat-top broadband reflector can be realized by combining a single guided-mode resonance (GMR) and Fabry-Perot (F-P) like background scattering in a slab waveguide grating, and 100% reflection occurs when the GMR coincides with the resonance of the F-P like background scattering ( = 0 or = 1) [5]. If another resonant mode of the same resonance frequency with an optical gain is introduced in this 100% reflector structure, we may get unidirectional emission due to the internal reflection function.…”