Adjacent Asymmetric Tilt Grating Structure With Strong Resonance Assisted by Quasi-Bound States in the Continuum

Abstract

In the field of optics, bound state in the continuum (BIC) as a special state to be researched in many photonic crystals and periodic structures, which can produce strong resonance and an ultrahigh Q factor. Some designs of narrowband transmission filters, lasers, and sensors are proposed based on excellent optical properties of quasi-BIC. In this paper, we consider symmetrical rectangular grating structure firstly. Then cut off a corner of rectangular gratings, the Fano line of quasi-BIC can be observed in the spectrum. After that, we change the oblique parameter of the other rectangular grating, which can further decrease the Fano line width. In the momentum space, the change of structure means topological charges split from q=1 into half charges q=1/2. We analyze guided mode resonance (GMR) excitation of the grating structure, and discuss the dispersion relations in the waveguide layer with the position of BIC in energy bands. In addition, the spectrum exhibits asymmetric line-shapes with different values of the asymmetry parameters, M1 and M2. BIC is transformed into quasi-BIC as the symmetry of the structure broken. Thus, a large Goos-Hänchen shift can be achieved as a result of ultrahigh Q factor of quasi-BIC. This work demonstrates a double trapezoid structure with strong resonance properties, which has significant implications for exploring the phenomenon of BIC.

Theoretical Enhancement of the Goos–Hänchen Shift with a Metasurface Based on Bound States in the Continuum

“…However, when n = 1.0001, the GH shift ( θ = 2°) is 37.14 μm (the resonance wavelength λ 0 ( n = 1.0001) = 977.187 nm). The sensor sensitivity, which is defined as S = Δ GH /Δ n , is calculated to be 3.58 × 10 6 μm/RIU, which is much higher than the sensitivity of the BIC resonance-based sensors reported in the literature [ 19 , 43 , 44 , 45 , 46 ], as summarized in Table 1 . Although the metasurface proposed by Zhang et al [ 24 ] can significantly enhance the GH shift and has an ultra-high refractive index sensitivity in the near-infrared waveband, it is suspended in air, which significantly increases the experimental preparation steps and costs; therefore, it is not included in Table 1 .…”

“…As a singularity in the continuous spectrum, an ideal BIC has infinite quality factors and the energy can be perfectly confined within the system. These characteristics greatly enhance the interaction between light and matter and are often used to reduce the laser threshold [ 18 ] and nonlinear harmonic enhancement [ 19 ]. However, due to the finite size of the structure, material absorption, and other external disturbances, the BIC tends to collapse to Fano resonance with a finite Q value, which is called quasi-BIC (QBIC) [ 20 , 21 , 22 ].…”

“…Consequently, BIC is an effective way to enhance the GH shift. At present, many researchers such as Zhiwei Zheng [ 26 ], Feng Wu [ 27 ], and Yuhang Ruan [ 19 ] have achieved GH shift enhancement based on BIC. Zhiwei Zheng et al utilized a silicon nanorod (suspended in air) metasurface to excite reflective BIC, and the maximum GH shift achieved was 1654 times the resonance wavelength.…”

Enhancing the Goos–Hänchen shift based on quasi-bound states in the continuum through material asymmetric dielectric compound gratings

“…The refractive index sensitivity is S = ∆D GH /∆n air = 1.9 × 10 6 µm/RIU, which is significantly higher than those in Refs. [50][51][52][53][54]. However, the sensitivity in Ref.…”

A tunable infrared emitter based on phase-changing material GST for visible-infrared compatible camouflage with thermal management

“…[8][9][10] According to the Stefan-Boltzmann's law, the target detection probability can be reduced only by changing the emissivity or temperature of the target and eliminating the difference in infrared radiation intensity between the target and the background. Based on this idea, some infrared camouflage devices have been successfully developed in recent years by using micro-nano structures and metamaterials, [11][12][13][14][15][16][17][18][19][20] which have also been applied to holographic imaging, 21,22 beam shaping, 23,24 gas sensing, 25 terahertz functional devices 26,27 and chiral optical structures. 28 However, the development of camouflage technology will inevitably promote the progress of detection technology.…”