Linear-polarization-independent photonic spin Hall effect in a broad range

Generally, most of the photonic spin Hall effect (SHE) are investigated based on the Gaussian beam, and the research of the photonic SHE in novel beams with non‐Gaussian distribution is relatively rare. The Airy beam is one of the novel beams whose initial field distribution is asymmetric and tunable. Thus, it is necessary to explore the photonic SHE in the Airy beam. Here analytical solutions for the transverse and in‐plane shifts of the Airy beam are derived, and the peculiar photonic SHE of the Airy beam is systematically researched. The theoretical research results show that the transverse shifts of the left‐ and right‐handed circularly polarized beams are asymmetric, and the in‐plane shifts of the left‐ and right‐handed circularly beams are identical. More importantly, the variation rules of the transverse and in‐plane shifts with the incident centroid position are obtained, and the incident centroid position is regulated by the decay factor of the Airy beam. That is, the spin‐dependent transverse and in‐plane shift can be manipulated flexibly and purposefully by adjusting the beam parameter. It is believed these findings will provide more ideas for exploring the application of the photonic SHE based on novel beams.

The photonic spin Hall effect (SHE), featured by a spin-dependent transverse shift of left- and right-handed circularly polarized light, holds great potential for applications in optical sensors, precise metrology and nanophotonic devices. In this paper, we present the significant enhancement of photonic SHE in the terahertz range by considering the InSb-supported long-range surface plasmon resonance (LRSPR) effect. The influences of the InSb/ENZ layer thickness and temperature on the photonic SHE were investigated. With the optimal structural parameters and temperature, the maximal spin shift of the horizontal polarization light can reach up to 2.68 mm. Moreover, the spin shift is very sensitive to the refractive index change of gas, and thus a terahertz gas sensing device with a superior intensity sensitivity of 2.5 × 105 μm/RIU is proposed. These findings provide an effective method to enhance the photonic SHE in the terahertz range and therefore offer the opportunity for developing the terahertz optical sensors based on photonic SHE.

Highly sensitive biosensor with graphene-MoS2 heterostructure based on photonic spin Hall effect

Photonic spin Hall effect: Physics, manipulations, and applications

The photonic spin Hall effect (SHE), featured by a spin-dependent transverse shift of an impinging optical beam driven by its polarization handedness, has many applications including precise metrology and spin-based nanophotonic devices. It is highly desirable to control and enhance the photonic SHE. However, such a goal remains elusive, due to the weak spin-orbit interaction of light, especially for systems with optical loss. Here we reveal a flexible way to modulate the photonic SHE via exceptional points, by exploiting the transverse shift in a parity-time (PT) symmetric system with balanced gain and loss. The underlying physics is associated with the near-zero value and abrupt phase jump of the reflection coefficients at exceptional points. We find that the transverse shift is zero at exceptional points, but it is largely enhanced in their vicinity. In addition, the transverse shift switches its sign across the exceptional point, resulting from spontaneous PT-symmetry breaking. Due to the sensitivity of transverse shift at exceptional points, our work also indicates that the photonic SHE can enable a precise way to probe the location of exceptional point in photonic systems.

The surface plasmon resonance (SPR) with the bimetallic film can achieve minimum reflectivity and higher evanescent field enhancement than the SPR configuration with the single gold film, which makes it to be a much better option for enhancing the photonic Spin Hall Effect (SHE). It is found that the thicknesses of silver and gold films have a major impact on the photonic SHE, and the maximal transverse shift of horizontal polarization state can reach to 5.34 μm near the SPR resonant angle by optimizing the thicknesses of silver and gold films in the bimetallic film. Our results are far greater than the previously reported transverse shifts in the conventional SPR structure. This novel phenomenon is attributed to the higher evanescent field enhancement and the larger refractive index variation gradient of silver/gold bimetallic film. These findings provide us an effective method to manipulate the photonic SHE and therefore establish a strong foundation for developing photonic devices based on photonic SHE.

The enhanced photonic spin Hall effect (SHE) based on the D-shaped fiber with Ag-Ni alloy/silicon layers is proposed and theoretically investigated under excitation of surface plasmon resonance (SPR). In order to achieve the maximum transverse spin-dependent displacements for practical photonic devices, parameters such as the thickness of the Ag-Ni alloy and silicon layers in the D-shaped fiber are optimized. Theoretical modeling and numerical simulation demonstrate that the multilayer structure can effectively enhance the photonic SHE. The maximum transverse shift of 420 μm obtained with optimized parameters is larger than those in the literature. In addition, a maximum angular sensitivity of 114.6°/RIU is achieved by the wavelength interrogation method. Our concept and theoretical assessment suggest a novel and effective means to enhance the photonic SHE, bring us one step closer to the possibility to characterize parameters of dielectric layers by weak measurements, and accelerate the development of optical fibers based on the photonic SHE.

Photonic structures offer unique opportunities for controlling light‐matter interaction, including the photonic spin Hall effect associated with the transverse spin‐dependent displacement of a light beam that propagates in specially designed optical media. However, due to small spin‐orbit coupling, the photonic spin Hall effect is usually weak at the nanoscale. Here we suggest theoretically and demonstrate experimentally, in both optics and microwave experiments, the photonic spin Hall effect enhanced by topologically protected edge states in subwavelength arrays of resonant dielectric particles. Based on direct near‐field measurements, we observe the selective excitation of the topological edge states controlled by the handedness of the incident light. Additionally, we reveal the main requirements to the symmetry of photonic structures to achieve the topology‐enhanced spin Hall effect, and also analyse the robustness of the photonic edge states against the long‐range coupling. image

Time-reversal symmetry-breaking Weyl semimetals (WSMs) exhibit an interesting optical response in the mid-infrared band, offering what we believe to be a novel approach to study the manipulation of the photonic spin Hall effect (PSHE). This article theoretically investigates the PSHE phenomenon in a prism-coupled structure composed of the WSMs. It is found that the excitation of surface plasmon polaritons (SPPs) and the nonreciprocity inherent in WSMs have a positive effect on enhancing the PSHE phenomenon of the reflected light. Especially, the PSHE can also be manipulated by varying the separation distance and twist angle between the Weyl nodes. Through parameter optimization, we obtained a lateral displacement of 12.14 μm. The effects of the separation distance between Weyl nodes, the twist angle, and the incident light angle on the PSHE were further elucidated. We believe the tunable PSHE with WSMs can provide promising avenues for developing spintronic devices, as well as other photonic applications.

The intrinsic connection between the transverse photonic spin Hall effect (PSHE) and the Imbert–Fedorov shift has been well characterized. However, physical insights into the longitudinal photonic spin splitting associated with the Goos-Hänchen (GH) shift remain elusive. This paper aims to expand the theory of the PSHE generation mechanism from the transverse to the longitudinal case by examining the reflection of each spin component from an arbitrarily linearly polarized incident Gaussian beam on the air-dielectric interface. Unlike the transverse case, both spin-maintained and spin-flipped modes exhibit non-zero longitudinal displacements, with the latter being affected by the second-order expansion term of the Fresnel reflection coefficient with respect to the in-plane wave-vector component. Meanwhile, the polarization angle plays a crucial role in determining the longitudinal PSHE since each reflected total spin component is a coherent superposition of these two corresponding modes. Remarkably, the imaginary part of the relative permittivity of the dielectric significantly affects the symmetry of the longitudinal PSHE. Furthermore, the GH shift results from a superposition of individual spin states’ longitudinal displacements, taking into account their energy weights. By incorporating the corresponding extrinsic orbital angular momentum, we explore the generation mechanism of the symmetric/asymmetric longitudinal PSHE. The unified physical framework elucidating the longitudinal photonic spin splitting and GH shift provides a comprehensive understanding of the fundamental origin of the PSHE and beam shifts, paving the way for potential applications in spin-controlled nanophotonics.

The photonic spin Hall effect can engender transverse spatial and angular displacements in both transmission and reflection, with significant applications in optical imaging, edge detection, and the development of spin-based nanophotonic devices. While previous research has focused on enhancing the photonic spin Hall effect, suppression can be beneficial for photonic spin-switching, offering advantages such as increased speed and sensitivity in nanophotonic devices. In this study, we establish a quantitative correlation between the reflection coefficient and the transverse spatial and angular displacements of reflected light, as induced by the photonic spin Hall effect, grounded in electromagnetic theory. We find that the transverse spatial displacement of reflected light can be eliminated under the condition r pp = -r ss , where r denotes the reflection coefficient, and the first (second) superscript denotes the polarization of the reflected (incident) light. This condition applies to light with arbitrary polarization states, at arbitrary incident angles, and is independent of wavelength and beam waist. A similar outcome is obtained for the transverse angular displacement of the reflected light. Such distinctive displacements are attainable through the use of an electromagnetic interface that satisfies the reflected condition r pp = -r ss . Additionally, we provide a succinct overview of the methodologies for constructing reflective spin switches.

The photonic spin Hall effect [1] or spin Hall effect of light [2] is the photonic analog of the spin Hall effect occurring with charge carriers in solid-state systems. Typically, this phenomenon takes place when a light beam refracts at an air-glass interface, or when it is projected onto an oblique plane, the latter effect being known as the geometric spin Hall effect of light [3]. In general, the photonic spin Hall effect leads to a polarization dependent transverse shift of a light peak intensity [3,4]. An example of the latter effect is the transverse Imbert-Federov beam shift [3], which happens for paraxial beams reflected or refracted at a sharp inhomogeneity of an isotropic optical interface. Potential applications of the photonic spin Hall effect in spin-dependent beam splitters, optical diodes [1], and surface sensors are considered in various fields in photonics, such as nanophotonics, plasmonics, metamaterials, topological optics, and quantum optics [1,2].

The photonic spin Hall effect (SHE), manifesting itself as a spin-dependent splitting of left- and right-handed circularly polarized light, exhibits unique potential for nanophotonic devices, precise metrology and optical sensors. This work presents an original design of refractive index sensor for the cancer detection based on novel photonic SHE. The device consists of BK7 prism, monolayer graphene, glass substrate, and the analyte layer, in which the cell solution is introduced. Three groups of human normal (gastric, liver, epidermal) cells and corresponding cancer cells were chosen for the discrimination. The external optical pumping is applied on monolayer graphene in order to flexibly modulate the photonic SHE, and then the sensing performance can be accordingly tuned. It is found that the proposed sensor can not only discriminate the normal cells and cancer cells, but also distinguish the cancer cells for different concentrations. The superior intensity sensitivity of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${6.1} \times {10}^{{5}} \,\,\mu \text{m}$ </tex-math></inline-formula> /RIU for discriminating the gastric normal and cancer cells can be generated under the optimal pumping power, which is four orders of magnitude greater than previous reported sensors based on the resonant optical tunneling effect. These findings may provide practical applications in medical diagnose, drug discovery and cellular pathological analyse.

The photonic spin Hall effect (PSHE) originates from the spin–orbit interaction (SOI) of light. The literature indicates that the transverse spin-dependent shift, δH− (SDS), from the PSHE is weak (in the nanometer range) and difficult to measure directly. This study utilizes a plasmonic structure to improve the δH− in the PSHE. The obtained results of this study demonstrate that the inclusion of silicon nitride (Si3N4) significantly enhances the δH− relative to its absence; however, plasmonic material is present in both cases. The enhanced shifts exhibit a significant dependence on the resonance angle (θr) and the thickness of layers of the PSHE structure to attain the maximum increase in δH− of 350.82 µm at the plasmonic resonance condition. A systematic analysis of the centroid positions of the reflected beam indicates a distinct and constant separation of opposing spin components. Further, the improved δH− is utilized in cancer cell detection, as changes in the refractive index (RI) of cells facilitate the identification of cancer cells from healthy to cancerous. All examined cell types demonstrate that cancerous cells had a greater δH− than normal cells, owing to their elevated effective RI. These results illustrate that the proposed plasmonic-assisted PSHE structure offers significant enhancement and a high sensitivity of 439.30 µm/RIU for label-free detection of cancer cells.

Photonic spin Hall effect (PSHE) in momentum space can lead to a giant spin-dependent splitting (SDS). However, the SDS in momentum space increases linearly with beam propagation distance, which limits its applications. In this work, a simple method is proposed to transform the PSHE from momentum space to position space. We first theoretically analyze the feasibility of the transformation. The results show that the transformation can be realized when a light wave passes through two identical Pancharatnam–Berry phase metasurfaces. Then an experimental setup is established to verify the theoretical results. Through rational design of the optical path, only one metasurface is needed to complete the transformation of PSHE from momentum space to position space. The experimental results agree well with theoretical calculations. We believe that these results are helpful for the design of photonics devices based on PSHE.