Enhancing Goos-Hänchen shift based on magnetic dipole quasi-bound states in the continuum in all-dielectric metasurfaces

Abstract

Metasurface-mediated bound states in the continuum (BIC) provides a versatile platform for light manipulation at the subwavelength dimension with diverging radiative quality factor and extreme optical localization. In this work, we theoretically propose the magnetic dipole quasi-BIC resonance in asymmetric silicon nanobar metasurfaces to realize giant Goos-Hänchen (GH) shift enhancement by more than three orders of wavelength. In sharp contrast to GH shift based on the Brewster dip or transmission-type resonance, the maximum GH shift here is located at the reflection peak with unity reflectance, which can be conveniently detected in the experiment. By adjusting the asymmetric parameter of metasurfaces, the Q-factor and GH shift can be modulated accordingly. More interestingly, it is found that GH shift exhibits an inverse quadratic dependence on the asymmetric parameter. Furthermore, we theoretically design an ultrasensitive environmental refractive index sensor based on the quasi-BIC enhanced GH shift, with a maximum sensitivity of 1.5×107 μ m/RIU. Our work not only reveals the essential role of BIC in engineering the basic optical phenomena but also suggests the way for pushing the performance limits of optical communication devices, information storage, wavelength division de/multiplexers, and ultrasensitive sensors.

Recent advances in strongly resonant and gradient all-dielectric metasurfaces

“…102 Furthermore, an asymmetric nanobar qBIC metasurface was theoretically proposed as a means to enhance the Goos-Ha ¨nchen (GH) shift, which results from the phase variation over the angle of incidence in metasurfaces illuminated by a lightbeam with sufficient beam waist. 103 By employing a MD-qBIC resonance, the asymmetry factor of the metasurface was translated into the resulting GH shift, demonstrating values above three orders of magnitude of wavelength, easily detectable at the reflection peak.…”

Dual symmetry breaking tunable bound states in the continuum in all dielectric split ring metamaterials

“…Quasi-BICs with finite but high Q-factors, transformed from a real BIC, have been used to achieve resonant metamaterials for applications including biosensors, 17 – 19 lasers, 20 – 22 and nonlinear optics 23 – 25 Currently, quasi-BICs obtained in metamaterials are more through the introduction of geometry asymmetry in the single particle, such as tilted bars, 26 split-ring structures, 27 asymmetric nanobar, 7 , 28 , 29 and dielectric nanodisks with asymmetric holes 30 . In addition, symmetric breaking induced by permittivity asymmetry of single particle in the unit cell has also been used to enhance the interaction between light and matter based on the quasi-BIC 31 , 32 .…”

Double-layer symmetric gratings with bound states in the continuum for dual-band high-Q optical sensing

“…In 1929, von Neumann and Wigner first proposed the BIC theory shortly after the advent of quantum mechanics [20], which was then extended to acoustics, electromagnetism, and other fields [21][22][23][24]. A true BIC has an infinite Q-factor and vanishing resonant linewidth, and this can only exist in an ideal lossless infinite structure or in extreme values of the parameters [25,26].…”