Goos-Hänchen shifts for Airy beams impinging on graphene-substrate surfaces

Enhanced Goos-Hänchen shift in a defective Pell quasiperiodic photonic crystal with monolayer MoS2

Monolayer M o S 2 has attracted wide attention because of its finite bandgap, and it has become a potential candidate for the investigation of the Goos-Hänchen (GH) shift. However, the magnitude of the GH shift in free-standing monolayer M o S 2 is small, which greatly hinders its possible applications in the photoelectric sensors and detectors. We have theoretically designed a defective quasiperiodic photonic crystal and investigated its GH shift, where monolayer M o S 2 is sandwiched between two quasiperiodic photonic crystals arranged by the Pell sequence. By optimizing the thicknesses of all the components and the period number of the Pell quasiperiodic photonic crystal, we find that the GH shift of the designed structure is significantly enhanced at the specific working wavelength. In addition, we discuss the influence of the thicknesses of the dielectric components on the GH shift. Our work confirms that the quasiperiodic photonic crystal structure has the ability to enhance the GH shift of monolayer transition metal dichalcogenides, which provides a new platform for the GH investigations and greatly promotes the applications of this defective structure in optoelectric devices.

Non-reciprocal spatial and quasi-reciprocal angular Goos-Hänchen shifts around double CPA-LPs in PT-symmetric Thue-Morse photonic crystals

We theoretically investigate the Goos-Hänchen (GH) shifts of reflected light beams in Thue-Morse photonic crystals. The systems are constituted by two Thue-Morse dielectrics multilayers and satisfy parity-time (PT) symmetry. Double coherent perfect absorption laser points (CPA-LPs) are achieved in the parameter space composed of the incident angle and the gain-loss factor. Dramatic changes in the phase of reflection coefficient induce giant positive and negative spatial GH shifts at the CPA-LPs, while great angular GH shifts exist around the exceptional points (EPs). The spatial GH shifts present non-reciprocity for the forward and backward incident light waves near the double CPA-LPs, while the angular GH shifts are quasi-reciprocal. Increasing the Thue-Morse sequence number, these characteristics are approved around multiple CPA-LPs as well. Our work could pave the way to explore high-accuracy optical sensors.

Optical Goos-Hänchen effect in uniaxially strained graphene

We prove the existence of relatively large Goos-Hänchen (GH) shifts for graphene in the presence of an applied strain in different crystallographic directions for p and s polarized beams. It is shown that GH shifts are smoothly increased by stretching the graphene's lattice. Moreover, we investigate the GH effect for strained graphene as a function of Fermi energy, which can be controlled by external factors such as gate voltage. We show that applied strain along zigzag and armchair orientations gives different results for GH shifts, which could provide a proper tool for the detection of strain in graphene.

Enhancing the nonreciprocal Goos-Hänchen shift by the Fano resonance of coupled gyromagnetic chains at normal incidence

We report a resonance-enhanced nonreciprocal Goos-Hänchen (GH) shift for the wave reflected from the coupled gyromagnetic chains. We demonstrate that the Fano resonance enhances the GH shift with high reflectivity at normal incidence, and the resonance results from the interference between the leaky guided modes of the coupled chains. Furthermore, we show that the GH shift can be controlled by the number of stacked chains. The Fano resonance-enhanced GH shift offers a new efficiently way to enhance and control the GH shift for reflected wave beam. Such coupled gyromagnetic chains provide an extremely compact way for the devices such as unidirectional couplers and other integration photonic components, paving the way for the applications of nonreciprocal GH shift.

Strong resonance response with ultrahigh quality factor in grating-multilayer systems based on quasi-bound states in the continuum

Optical bound states in the continuum (BICs) exist in many photonic crystals and periodic structures with a strong resonance and ultrahigh Q factor. Such phenomena can be used in the designs of narrowband transmission filters, lasers, and sensors. In this paper, we consider the energy bands of a complex structure consisting of a grating and a multilayer substructure to obtain the position of the BIC in the structure. Hence, the higher Q factor can be obtained in the grating-multilayer structure than can be realized in the simple grating geometry. We analyze the wave propagation process in the complex structure and the change in the Q value via the use of transmission matrix theory. In addition, the reflectance spectrum is found to exhibit a series of asymmetric line-shapes with different values of the asymmetry parameter, δ, due to the interference between the two channels. One of these channels is the broadband channel, induced by the Fabry-Perot resonance, and the other channel is the narrowband channel, induced by guided mode resonance. Quasi-BICs are seen to transform into BICs as the value of δ is decreased gradually to zero. Therefore, a large Goos-Hänchen shift can be achieved as a result of the high Q factor and quasi-BIC. This work designs a complex structure with ultrahigh Q factor and strong resonance properties, which has significant implications for exploring the phenomenon of BICs.

Asymmetric spin splitting of Laguerre-Gaussian beams in chiral PT-symmetric metamaterials

We systematically study the spin Hall effect of light (SHEL) in chiral PT-symmetric metamaterials when Laguerre Gaussian beams (LG beams) are incident and discover that cross-polarization (r_{s p}, r_{p s}) and intrinsic orbital angular momentum (IOAM) result in an asymmetric splitting of left-spin circularly polarized (LCP) light and right-spin circularly polarized (RCP) light. Additionally, there are spin Hall shift peaks near |r_pp | ≪ |r_ss | (r_{s s} and r_{p p} are Fresnel reflection coefficients). Altering the topological charge number ℓ, the chiral parameter κ, the dimensionless frequency M, and the incident angle θ may also influence the asymmetric spin splitting and displacement peak. We believe that this research will provide new ways to manipulate and enhance the asymmetric spin splitting of light and provide new applications for spin photonic devices.

Generation of finite energy Airyprime beams by Airy transformation

In this paper, the lone generation of a new kind of beam named finite energy Airyprime (FEA) beam through the Airy transformation of the coherent superposition of four different elegant Hermite-Gaussian modes is reported for the first time. Analytical expressions of the centroid, the r.m.s beam width, the divergence angle, and the beam propagation factor of the FEA beam are derived in the output plane of Airy transformation, respectively. The effects of the Airy control parameters on the intensity distribution, the centroid, the r.m.s beam width, and the beam propagation factor are examined in detail through numerical examples. Unlike the Airy beam, the FEA beam upon free space propagation will be associated with an additional Airy mode, and the beam pattern of the FEA beams propagating in free space will evolve into a solid beam spot with two tails along two transverse directions, as well as the the intensity of main lobe of the FEA beam decays much slowly during free space propagation. Further, an experiment setup is established to generate the FEA beam via Airy transformation of four mixed elegant Hermite-Gaussian modes. The propagation characteristics such as the intensity distribution, the r.m.s beam width and the beam propagation factor are measured. The experimental results agree well with the theoretical predictions. Our study affords an effective and novel approach to generate the FEA beam, and is beneficial to expand the potential application of the FEA beam.

Controllable photonic spin hall effect of bilayer graphene

Bilayer graphene, composed of two layers of monolayer graphene in AB stacking order, has emerged as an alternative platform for atomically thin plasmonic and optoelectronic devices. However, its behavior of photonic spin hall effect remains largely unexplored. In this work, we have theoretically observed that bilayer graphene has two obvious discontinuities but monolayer graphene only has a single step in the spectra of the spin shifts as a function of wavelength at the Brewster angle over the midinfrared frequency range, which enables a possible route of distinguishing monolayer graphene and bilayer graphene. Additionally, the magnitudes and positions of the peak and valley values in the spectrum of spin shifts of bilayer graphene can be tuned by its Fermi energy. We also achieved the enhanced out-of-pane spin shift of the glass-AB stacking bilayer graphene-air structure at both the Brewster angle (33.55°) and the critical angle (41.31°) with the aid of the high order of Laguerre-Gaussian beam. The realization of large and controlled spin shift in bilayer graphene indicates its promising applications in precision measurements and refractive index sensors at the midinfrared frequency region.

Giant and controllable Goos-Hänchen shift of monolayer graphene strips enabled by a multilayer dielectric grating structure

The discovery of monolayer graphene allows the unprecedented chance for exploring its Goos-Hänchen (GH) shift. However, most of the pronounced GH shifts are achieved in various structures with two-dimensional continuous monolayer graphene. Here, we report on the giant GH shift of reflected wave in monolayer graphene strips by constructing the multilayer dielectric grating structure under them. The observed GH shift here is as high as 7000 times that of the incident wave at the near-infrared frequency region, whose magnification is significantly larger than that of the monolayer graphene ribbon array. We further elucidate that the enhanced GH shift originates from the guided mode resonance of the dielectric grating structure and its magnitude and sign can be manipulated by chemical potential of the monolayer graphene strip. Our work enables a promising route for enhancing and controlling the GH shifts of reflected wave in monolayer graphene strips, which might contribute to their applications in biosensors and detectors.

Goos-Hänchen and Imbert-Fedorov shifts of off-axis Airy vortex beams

Based on the angular spectrum of high order off-axis Airy vortex beams (AiVBs), Goos-Hänchen (GH) shifts and Imbert-Fedorov (IF) shifts near the Brewster angle are numerically calculated. It is found that both GH and IF shifts increase with the increase of the vortex's topological charge of AiVBs. The influences of the vortex's positions on GH and IF shifts are studied for the case of the topological charge m = 1. The studies of the off-axis vortex show that the influences of the vortex's position on shifts are inversely proportional to the distance between the vortex's position and the origin point.