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Structured light, with spatially varying amplitude, phase, and polarization, has attracted widespread attention for its potential application in many fields ranging from optical communications to imaging. However, it remains a challenge to realize reconfigurable manipulation of structured light beams in a compact and convenient method. Here, through mechanical operations on the two cascaded liquid crystal Pancharatnam–Berry phase elements such as rotation and translation, diverse kinds of typical structured light can be experimentally generated in a reconfigurable manner, including Gaussian, Hermitian–Gaussian, vortex, and cylindrical vector beams. Moreover, by rotating a liquid crystal element, tunable photonic spin Hall effect is also achieved in the proposed cascaded‐elements scheme, which allows for tailoring the spin‐dependent shifts in the structured beams. In such a reconfigurable generator, the mechanical operations on the phase element bring new degrees of freedom into the manipulation of structured light field, which may pave the avenue for future optical applications. [ABSTRACT FROM AUTHOR]

The spin Hall effect of light, a phenomenon characterized by the transverse and spin dependent splitting of light at an optical interface, is highly promising for collecting precise quantitative data from interfaces and stands as an appealing option for improving precision metrology. This high level of precision is attributed to the principles of weak measurement. Since its conceptual introduction, the spin Hall effect of light has been empirically observed through weak measurement techniques, adhering closely to the initially proposed experimental configuration. Recently, it has been suggested that the setup can be downsized without compromising precision. Here, the first experimental demonstration of “compact weak measurement” is achieved by observing the spin Hall effect of both reflected and refracted light. Compared to the conventional weak measurement, this compact setup performs the same measurements but requires less free space by replacing the two convex lenses with a set of concave and convex lenses. The compact weak measurement demonstrates excellent agreement with theoretical predictions and experimental findings from traditional setups across both isotropic–isotropic and isotropic–anisotropic interfaces. The experimental validation of the compact configuration paves the way for the practical application of the spin Hall effect of light in devices with a smaller form factor.

The refractive index (RI) of biological tissues is a fundamental material parameter that characterizes how light interacts with tissues, making accurate measurement of RI crucial for biomedical diagnostics and environmental monitoring. A Janus sensor (JBS) is designed in this paper, and the photonic spin Hall effect (PSHE) is used to detect subtle changes in RI in biological tissues. The asymmetric arrangement of the dielectric layers breaks spatial parity symmetry, resulting in significantly different PSHE displacements during the forward and backward propagation of electromagnetic waves, thereby realizing the Janus effect. The designed JBS can detect the RI range of 1.3~1.55 RIU when electromagnetic waves are incident along the +z-axis, with a sensitivity of 96.29°/refractive index unit (RIU). In the reverse direction, blood glucose concentrations are identified by the JBS, achieving a sensitivity of 18.30°/RIU. Detecting different RI range from forward and backward scales not only overcomes the limitation that single-scale sensors can only detect a single RI range, but also provides new insights and applications for optical biological detection through high-sensitivity, label-free and non-contact detection. [ABSTRACT FROM AUTHOR]

Graphene is of particular interest in optoelectronics due to its remarkable transport properties. We analyze the photonic spin Hall effect (PSHE) of a light beam reflected from a layered structure of graphene in its current-carrying state. The relativistic effects arising due to the motion of massless Dirac electrons in graphene greatly influence the transverse displacements of light induced by PSHE. The mentioned effect is studied with different drifting speeds of the charged particles in graphene as well as different thicknesses of the graphene sheet. The substrate on which the graphene is deposited is also shown to play a vital role in manipulating this relativistic PSHE. This study provides a platform for efficient light-matter interaction in which the medium is a current-carrying graphene channel.

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Multidimensional manipulation of photonic spin Hall effect (PSHE) has attracted considerable interest due to its potential in a wide variety of spin-based applications. Plenty of research efforts have been devoted to transverse or longitudinal spin-dependent splitting; however, the splitting pattern that can self-rotate in a three-dimensional (3-D) space appears to be missing in literature. In this paper, we introduce a novel 3-D rotational PSHE, which can be realized and tuned using well-designed Pancharatnam–Berry phase metasurfaces. To demonstrate this phenomenon, we first show that when a single dielectric metasurface is used, the lobe-structured spin-splitting patterns on the transverse planes rotate and evolve along the propagation path. Then, we present that under two cascaded metasurfaces, the rotation angle of the splitting patterns are tunable by adjusting the relative rotation angle between the two metasurfaces. Finally, we manifest that the lobe number of the two spin-dependent splitting patterns can be independently controlled once we introduce a dynamic phase, which produces an asymmetrical rotational PSHE. The demonstrated phenomena can be used to achieve active manipulation of spin photons in multiple dimensions, and the developed device might find potential applications in various areas, e.g., optical microscopy.

The spin Hall effect of light (SHEL), a microscopic and transverse splitting of linearly polarized light into circularly polarized components during refraction and reflection, can be measured at subnanometer scales using weak measurements and has emerged as a powerful candidate for precision measurements. However, despite the strong demand for compact and miniaturized sensors and precision metrology, no efforts have downsized the weak measurements. Here I demonstrate that the location of the interface where the SHEL occurs does not impact the results of weak measurements and building on this observation, propose a modified setup called the compact weak measurement to reduce the form factor by replacing one convex lens with a concave one. The concept is theoretically validated and numerically confirmed across various setup parameters and interfaces. The compact weak measurement effectively reduces the required free space distance by twice the focal length and will facilitate the implementation of SHEL-based precision measurements in practical applications.

The spin Hall effect of light is an appealing toolset for metrology that holds incredible potential for precision measurements due to its high sensitivity to the refractive index and nanostructure physical parameters. Here, we theoretically examine the quantized spin Hall effect of light on the surface of a monolayer graphene–substrate system subjected to an external perpendicular magnetic field. We discuss the impact of Landau levels induced by the external magnetic field B and the photon energy on magneto-optical conductivities and Fresnel reflection coefficients. We find that the spin-dependent splittings in graphene exhibit quantized characteristics due to the Landau levels quantization of the magneto-optical conductivities and Fresnel’s reflection coefficients near the Brewster angle. Moreover, the spin-dependent shifts are quantized and show oscillatory behavior with changes in the magnetic field and the photon energy. Our results manifest that the quantized photonic spin-dependent separations are sensitive to variations in the incidence angle, magnetic field, and incident photonic energies. The quantized spin-dependent splitting opens a promising route to find the quantized Hall conductivity and discrete Landau levels in the monolayer graphene by a direct optical weak measurement.

Optical differential operation is an important scheme for image edge detection due to its advantages of high efficiency, real time and low consumption. In this paper, the actively manipulating optical differential operation is proposed in a quasi-PT-symmetric structure containing graphene, and applied to realize edge imaging with tunable contrast. It is found that there are abrupt changes of the in-plane shift and transverse shift in the photonic spin Hall effect at the Fermi energy of 0.4 eV, where the quasi-exceptional points exist according to the degeneracy analysis of scattering matrix eigenvalues. Based on the photonic spin Hall effect near the quasi-exceptional points, we design the optical differential operation whose spatial transfer function is actively manipulated by changing the external electric field to adjust the Fermi energy of graphene. Finally, the edge imaging with different contrast can also be achieved when the optical differential operation is applied to image processing. The actively manipulating optical differential operation opens up new possibilities in microscopic imaging and smart driving.

This study presents an innovative refractive index (RI) sensor that measures glucose concentration by utilizing the photonic spin Hall effect (SHE) in a resonant optical tunneling effect (ROTE) structure. The ROTE structure consists of three InP layers with the high RI and two analyte layers (with a high‐low‐high‐low‐high RI distribution), in which glucose solution samples with the low RI are injected. By subjecting the InP layers to external bias‐assisted light, the photonic SHE can be flexibly manipulated, enabling the modulation of the sensing performance accordingly. It is found that the transverse shift of photonic SHE presents a large variation in response to the tiny change in glucose concentrations. By optimizing the parameters (i.e., intensity or wavelength) of bias light, the sensitivity of this sensor can reach as high as 735.7 µm RIU−1. Compared to traditional glucose sensors, this original work implements the novel photonic SHE with the superior sensing performance. Therefore, the proposed design shows promising potential for biomedical applications, such as medical diagnoses and drug discovery. [ABSTRACT FROM AUTHOR]

In this work, a transverse spin-dependent shift of the horizontal photonic spin Hall effect at a fixed wavelength (0.6328 μm) is simulated for cancer cell detection based on refractive index, chemical potential, and electrical voltage variations applied to a plasmonic sensor with five layers (Ge20Ga5Sb10S65 chalcogenide prism, silver, gold, grapheme, and cancerous medium). When the conventional weak measurement is applied and when the chemical potential is increased from 0.3 eV to 8 eV, the chemical and voltage resolutions are 3.87 × 10–7 eV, 13.3327 μV for n5 = 1.38 RIU (cancerous skin cell), 5.17 × 10–7 eV, 17.7889 μV for n5 = 1.392 RIU (cancerous cervical cell), 4.95 × 10–7 eV, 17.0249 μV for n5 = 1.390 RIU (cancerous blood cell), and 5.50 × 10–7 eV, 18.9514 μV for n5 = 1.395 RIU (cancerous adrenal gland cell), respectively. The values of the chemical and voltage resolutions (1.90 × 10–7 eV, 6.5560 μV for n5 = 1.36 RIU and normal skin cell) are better than for the case when the spin Hall effect is not applied (0.00513 eV, 0.1766 V). The voltage resolutions calculated with the conventional weak measurement method are comparable or considerably better to the best experimental values which can resolve voltage differences as small as 15 μV. [ABSTRACT FROM AUTHOR]

Surface polaritons are surface electromagnetic waves propagating along the surface of a medium, which play an important role in enhancing the photonic spin Hall effect (SHE). Among them, the successful excitation of surface exciton polaritons (SEPs) often requires cryogenic temperature, which limits their practical applications. In this contribution, a promising mechanism is presented for enhancing the photonic SHE by taking advantage of room‐temperature SEPs in a prism‐glass‐TDBC‐air configuration. By depositing the TDBC layer on plasmon active metal, the hybrid polariton, namely, surface plasmon exciton polariton (SPEP) can be observed, which gives rise to the further enhancement of photonic SHE. Furthermore, a refractive index sensor based on SEP (or SPEP) enhanced photonic SHE is proposed with the superior sensing performance. The results pave the way for the realization of giant photonic SHE in this simple and promising method, and offer the opportunity for developing highly sensitive optical sensors. [ABSTRACT FROM AUTHOR]

Effective-medium theory pertains to the theoretical modelling of homogenization, which aims to replace an inhomogeneous structure of subwavelength-scale constituents with a homogeneous effective medium. The effective-medium theory is fundamental to various realms, including electromagnetics and material science, since it can largely decrease the complexity in the exploration of light-matter interactions by providing simple acceptable approximation. Generally, the effective-medium theory is thought to be applicable to any all-dielectric system with deep-subwavelength constituents, under the condition that the effective medium does not have a critical angle, at which the total internal reflection occurs. Here we reveal a fundamental breakdown of the effective-medium theory that can be applied in very general conditions: showing it for deep-subwavelength all-dielectric multilayers even without a critical angle. Our finding relies on an exotic photonic spin Hall effect, which is shown to be ultrasensitive to the stacking order of deep-subwavelength dielectric layers, since the spin-orbit interaction of light is dependent on slight phase accumulations during the wave propagation. Our results indicate that the photonic spin Hall effect could provide a promising and powerful tool for measuring structural defects for all-dielectric systems even in the extreme nanometer scale. [ABSTRACT FROM AUTHOR]

Beam splitters are widely used in various optical systems, but traditional beam splitters are bulky and heavy, which are not conducive to the integrated utilization of optical devices. Metamaterials have attracted extensive attention as a kind of miniature artificial materials, and there have been many works on the design of metasurface beam splitters. Using metasurfaces, multiple functions of traditional beam splitters can be achieved. Meanwhile, metasurface beam splitters have the advantages of small size, easy integration, flexible design of beam-splitting performance, and tunable functions. This review surveys the current work on metasurface beam splitters and provides a classification and introduction to metasurface beam splitters. Metasurface beam splitters are expected to play a huge role in interferometers, multiplexing, multi-beam communications, and more.

Metasurface-based research with phase-change materials has been a prominent and rapidly developing research field that has drawn considerable attention in recent years. In this paper, we proposed a kind of tunable metasurface based on the simplest metal–insulator–metal structure, which can be realized by the mutual transformation of insulating and metallic states of vanadium dioxide (VO2) and can realize the functional switching of photonic spin Hall effect (PSHE), absorption and beam deflection at the same terahertz frequency. When VO2 is insulating, combined with the geometric phase, the metasurface can realize PSHE. A normal incident linear polarized wave will be split into two spin-polarized reflection beams traveling in two off-normal directions. When VO2 is in the metal state, the designed metasurface can be used as a wave absorber and a deflector, which will completely absorb LCP waves, while the reflected amplitude of RCP waves is 0.828 and deflects. Our design only consists of one layer of artificial structure with two materials and is easy to realize in the experiment compared with the metasurface of a multi-layer structure, which can provide new ideas for the research of tunable multifunctional metasurface. [ABSTRACT FROM AUTHOR]

In this paper, a Janus metastructure sensor (JMS) based on the photonic spin Hall effect (PSHE), which can detect multiple physical quantities, is proposed. The Janus property is derived from the fact that the asymmetric arrangement of different dielectrics breaks the structure parity. Hence, the metastructure is endowed with different detection performances for physical quantities on multiple scales, broadening the range and improving the accuracy of the detection. When electromagnetic waves (EWs) are incident from the forward scale of the JMS, the refractive index, thickness, and incidence angle can be detected by locking the angle corresponding to the PSHE displacement peak that is enhanced by the graphene. The relevant detection ranges are 2~2.4, 2~2.35 μm, and 27°~47°, with sensitivities (S) of 81.35°/RIU, 64.84°/μm, and 0.02238 THz/°, respectively. Under the condition that EWs incident into the JMS from the backward direction, the JMS can also detect the same physical quantities with different sensing properties, such as S of 99.3°/RIU, 70.07°/μm, and 0.02348 THz/° in corresponding detection ranges of 2~2.09, 1.85~2.02 μm, and 20°~40°. This novel multifunctional JMS is a supplement to the traditional single-function sensor and has a certain prospect in the field of multiscenario applications. [ABSTRACT FROM AUTHOR]

In this paper, we discuss the photonic spin Hall effect (PSHE) in the combined structure of periodic dielectric waveguides (PDWs) and photonic crystal waveguide (PCW). By controlling the polarization of the dipole source, we have successfully achieved the arbitrary manipulation of PSHE for the PDW guided mode in our structure. The advantage of PDW is that it can be designed to different shapes without the geometric constraints, and still maintains a relatively high transmission rate. Therefore, by further changing the structure, including the adjustment of the intersection angle between PDW and PCW, and the alteration of the straight PDW to the bending or bifurcated shapes, we find that the output of highly unidirectional PSHE is mainly determined by the intersection angle between PDW and PCW and almost independent of the detailed shape of PDW. [ABSTRACT FROM AUTHOR]

Photonic spin Hall effect (SHE) refers to the transverse separation of spin photons in refraction and reflection phenomena. The photonic SHE has been investigated in various optical systems including air–glass interfaces, interfaces containing 2D materials, random media, etc. Here, the spin–orbit coupling (SOC) in nonlinear uniaxial crystals is investigated, and the SHE of second‐harmonic photons is demonstrated theoretically and experimentally. The generation and evolution processes of nonlinear spin photons within the crystal are visualized by the derived four wave coupling equations and wavevector‐varying Berry phases. For a focused fundamental beam, two cascaded SOCs occurring in the fundamental and second‐harmonic fields are connected by the nonlinear wave mixing near the focal position. Thus the SHE of nonlinear photons depends on the focal position, different strongly from linear photons whose SHE is independent of the focal position. Similar to the focal‐position‐dependent SHE, the focal‐position‐dependent optical vortex generations are also demonstrated for the nonlinear fields. Finally, a high‐speed modulation scheme for the SHE is proposed based on an electro‐optical polarization controller, which routes nonlinear spin photons into different destinations. These findings deepen the understanding of spin–orbit coupling in nonlinear systems and facilitate the development of spin multiplexed electrooptic devices. [ABSTRACT FROM AUTHOR]

The spin Hall effect of light, i.e., the microscopic and spin-dependent transverse splitting of linearly polarized light into circular polarizations at an optical interface, has been considered as a promising candidate for high-precision measurement when combined with a weak measurement technique. However, in those previous demonstrations, the precision is determined by the interface of interest, hindering its versatility. Here, by leveraging the direct correlation of precision with the spin Hall shift, we propose nanophotonic-assisted approaches to increase the precision of the weak measurement by controlling the spin Hall effect of light at the target interface. The refractive index sensing of an isotropic medium is demonstrated as a proof of concept, in which the precision can be increased, in principle, to infinity by placing an index-below-unity slab in the vicinity of the target interface. Furthermore, a single-layer metasurface comprising two-dimensional subwavelength patterns is introduced as an experimentally favorable platform. This study lays the foundation for nondestructive and high-precision investigation of unknown parameters of interfaces and will find wide sensing applications in material science, medical engineering, and other interdisciplinary fields.

Chiral perovskites have attracted considerable attention as excellent spin-emitting materials for applications in spintronics, quantum optics, and biological. Especially in drug development of biological, weak chirality molecules are frequently selected to reduce the side effects of toxics, and there is a common defect for accurately detecting the weak chirality with common methods at room temperature. In this study, formamidine lead bromide perovskite nanocrystals (FAPbBr3 NCs) were coated with chiral ligands, whose chirality was too weak to be observed in the visible region at room temperature. Thus, by characterizing the transverse shift of photonic spin Hall effect (SHE), the accurate discrimination of weak chirality in the visible region was achieved successfully. By measuring the shift value and light spot splitting of photonic SHE at the same concentration, NEA-coated FAPbBr3 NCs can effectively enhance the chirality of naphthalene ethylamine (NEA) ligands when under the mutually reinforcement of chiral molecular and inorganic parts. In addition, we furtherly clearly distinguished the tiny chiral distinction of NEA-coated FAPbBr3 NCs with different particle sizes, which revealed that the chirality decreases with the increase of particle size. These findings could provide effective solutions for the detection and application of weak chirality in hybrid perovskite nanocrystals in universal environment.

The photonic spin Hall effect (SHE) refers to the transverse spin separation of photons with opposite spin angular momentum, after the beam passes through an optical interface or inhomogeneous medium, manifested as the spin-dependent splitting. It can be considered as an analogue of the SHE in electronic systems: the light’s right-circularly polarized and left-circularly polarized components play the role of the spin-up and spin-down electrons, and the refractive index gradient replaces the electronic potential gradient. Remarkably, the photonic SHE originates from the spin-orbit interaction of the photons and is mainly attributed to two different geometric phases, i.e., the spin-redirection Rytov-Vlasimirskii-Berry in momentum space and the Pancharatnam-Berry phase in Stokes parameter space. The unique properties of the photonic SHE and its powerful ability to manipulate the photon spin, gradually, make it a useful tool in precision metrology, analog optical computing and quantum imaging, etc. In this review, we provide a brief framework to describe the fundamentals and advances of photonic SHE, and give an overview on the emergent applications of this phenomenon in different scenes.

The photonic spin Hall effect (PSHE), featured by a spin-dependent shift driven by its polarization handedness, is proposed to facilitate the applications in precision metrology and quantum information processing. Here, due to the magnetoelectric coupling of the chirality, the PSHE is accompanied with Goos–Hänchen and Imbert–Fedorov effects. Taking advantage of this superiority, the transverse shift (TS) and longitudinal shift (LS) can be applied simultaneously. Rearranging the PT-symmetric scattering matrix, the responsive PSHE near the exceptional points and their basic physical mechanisms are discussed in detail in the case of complex chirality κ. Re[κ] and Im[κ] regulated the rich (at multi-angle), gaint (reach upper limit) and tunable (magnitude and direction) TS and LS, respectively. Based on the chirality-modulated PSHE, the novel applications in binary code conversion and barcode encryption are proposed systematically. By incorporating the quantum weak measurement technology, our applications provide new mechanisms to realize optoelectronic communication.

With the recent discovery of three dimensional Dirac semimetals, their integrations with the optoelectronic devices allow the novel optical effects and functionalities. Here, we theoretically report the photonic spin Hall effect in a periodic structure, where three dimensional Dirac semimetals and the dielectric materials are assembled into the stack. The incident angle and frequency dependent spin shift spectrum reveals that the spin shifts of the transmitted wave in this structure emerge the obvious peaks and valleys for the horizontal polarized wave and their magnitudes and positions display a distinct dependence on the incident angle around the specific frequency. These observations originate from its zero value of the effective perpendicular permittivity and its greatly reduced transmission in the multilayered structure, whose mechanism is different from those in the previous works. Moreover, both the peaks and valleys of the transmitted spin shift are significantly sensitive to the Fermi energy of three dimensional Dirac semimetals, whose magnitudes and positions can be tuned by varying it. Our results highlight the vital role of three dimensional Dirac semimetals in their applications of the spin photonic devices and pave the way to explore the tunable photonic spin Hall effect by engineering their Fermi energies. [ABSTRACT FROM AUTHOR]

The photonic spin Hall effect provides a quantitative way to characterize the spin–orbit interaction of light and enables many applications, such as the precise metrology, since this effect is featured with a spin‐dependent transverse shift of the light beam. This transverse shift is generally nonzero during the reflection/transmission process, and it is sensitive to the polarization and the incident angle of the light beam. By contrast, here it is revealed that for the transmitted light, the transverse shift can be always zero and polarization‐independent, irrespective of the incident angle. The underlying mechanism is that the conversion between the spin and orbit angular momenta of light is fully suppressed during the transmission process. Such an exotic photonic spin Hall effect occurs, if tpp=tss${t^{{\rm{pp}}}} = {t^{{\rm{ss}}}}$, tps=−tsp${t^{{\rm{ps}}}} = - {t^{{\rm{sp}}}}$, and θt=θi${\theta _t} = {\theta _i}$, where t stands for the transmission coefficient and its first (second) superscript represents the polarization of the transmitted (incident) light, and θt${\theta _t}$ (θi${\theta _i}$) is the transmitted (incident) angle. These transmission conditions are achievable, e.g., by exploiting an interface only with a chiral surface conductivity. Similarly, a polarization‐independent photonic spin Hall effect is revealed for the reflected light. [ABSTRACT FROM AUTHOR]

In this work, we analyze the design of a graphene- and germanium-based plasmonic sensor with photonic spin Hall effect (PSHE) for detection of refractive index (RI) of a gas medium and magnetic field (B) applied to the graphene monolayer in THz frequency region. The PSHE phenomenon is studied in both conventional as well as modified weak measurements. The effect of gaseous medium thickness (d4), transverse magnetic (TM) mode's order, and amplified angle parameter (Δ) is studied on the sensor's performance. Parameters such as sensitivity, resolution, and figure of merit have been considered for sensor's performance evaluation. The results indicate that in the conventional weak measurements, for a TM1 mode (with d4 = 20 µm, B = 0, and Δ = 0.1°), an RI resolution of 2.32 × 10−12 RIU is achievable for gas medium in the range 1–1.1 RIU. In the modified weak measurements, for a TM3 mode (with d4 = 100 µm, B = 0, and Δ = 0.1°), the RI resolution close to 1.39 × 10−10 RIU is achievable for gas sensing. The same sensor design was also studied for magnetic field sensing while keeping the value of gaseous medium RI (n4) as 1. The results indicate that for a TM1 mode (with d4 = 20 µm and Δ = 0.1°), in the conventional weak measurements, a magnetic field resolution of 5.31 × 10−4 µT (i.e., 0.53 nT) is achievable for a range 0–1 T of B. Further, it is found that in contrast with the conventional case, the resolutions in the modified weak measurements are improved for large values of the Δ. Some of the results emerge better or comparable with the resolutions of RI and magnetic field measurement (5 × 10−9 RIU and 0.7 µT or 1.22 × 10−11 RIU and 1.46 × 10−2 µT) existing in the literature. [ABSTRACT FROM AUTHOR]

The manipulating of photonic spin Hall effect (SHE) plays a crucial role for development of spin‐dependent nanodevices and systems. Since the photonic SHE is generally enhanced near the Brewster angle, the choice of incident angle usually has low flexibility with natural materials due to their dielectric constants. Herein, an efficient method to flexibly enhance the photonic SHE by utilizing selective Brewster angle in an anisotropic metamaterial is proposed. Through adjusting the thickness ratio of two media in metamaterial, the Brewster angle can be flexibly adjusted in a broad range (nearly 0–90°). With the selective Brewster angle, the spin‐dependent transverse shift can be enhanced at nearly arbitrary incident angles. Furthermore, based on this structure, a binary encoding system is demonstrated, realizing information conversion around incident angles. This research work provides more possibilities for applications in manipulating photonic SHE. [ABSTRACT FROM AUTHOR]

The spin Hall effect of light (SHEL) is the microscopic splitting of light into two circular polarizations at the optical interface along the perpendicular direction. With the advent of metamaterials/metasurfaces and their fast‐developing applications, the SHEL has been garnering significant scientific interest. Here, the principle and recent developments in SHEL research is reviewed. A theoretical description of the SHEL is provided, including the formalism and general techniques. Also, recent studies on and applications of the SHEL are extensively reviewed, including the enhancement of the spin Hall shift and efficiency, implementation of dynamic tunability, elimination of polarization dependence, and precision measurements. The review is concluded with a discussion on the future direction and prospects of the SHEL. [ABSTRACT FROM AUTHOR]

The spin Hall effect of light, referring to the spin-dependent and transverse splitting of light at an optical interface, is an interface-dependent phenomenon. In contrast to this commonly accepted statement, it has been recently reported that the spin Hall effect under circularly polarized light is interface-independent. Despite this interface-independence, however, the reflection of the spin Hall shifted beam is mostly suppressed under near-normal incidence, where the spin Hall shift is large because of the handedness reversal that occurs during the reflection. Here we present a single-layered dielectric metasurface to realize the interface-independent and strengthened spin Hall effect of light. Numerical simulation results confirmed that the anisotropic geometry of the metasurface induced phase-reversed reflection for one linear polarization and phase-preserved reflection for the other, thereby strongly strengthening the reflection of the spin-Hall-shifted beam. Our work will pave a route toward the precise displacement of the beam at the nanoscale without perturbing its polarization state. [ABSTRACT FROM AUTHOR]

Metal nanocrystals synthesized in achiral environments usually exhibit no chiroptical effects. However, by placing nominally achiral nanocrystals 1.3 nm above gold films, we find giant chiroptical effects, reaching anisotropy factors as high as g ≈ 0.9 for single nanodecahedra placed on a gold mirror (NDoM). We show that this is a general phenomenon depending on the geometry, demonstrating it for various nanocrystal shapes. Theoretical modeling reveals that tiny chiral imperfections are strongly enhanced by edge modes in the gap, which coherently superpose with in-plane dipoles to generate strong chiroptical signatures. This phenomenon results in photonic spin Hall effects and distinctive chiral scattering patterns.

In this paper, a physical model is established to reveal the relationship between polarization phase of incident light and in-plane spin splitting (IPSS) of reflected beam, and the impact of polarization phase on the IPSS is systematically investigated. Three interesting features of the effect of polarization phase on IPSS were discovered. Furthermore, it is found that the IPSS can be effectively enhanced and suppressed by adjusting the polarization phase near ±π/2. The enhanced IPSS shift can almost reach its upper limit (that is, half of the beam waist) and the suppressed IPSS shift can be reduced to zero. In addition, it is also found that the spin cumulative direction of spin components can be reversed adjusting the polarization phase at ±π/2. These findings not only provide a deeper insight into photonic spin Hall effect, but also open a path for the photon manipulation, precision metrology and the manufacture of photonic spin switching devices.

When a paraxial light beam is reflected from/ transmitted through an optical element with rotation symmetry, a tiny small incident angle can arise wave-vector-varying Pancharatnam-Berry (PB) phases, resulting in high-performance photonic spin Hall effect (PSHE). Differently, here we investigate the PSHE in photonic crystal slabs of square lattices constructed with air holes, and demonstrate that the C4v symmetry of the slabs enables giant PSHE in both isotropic and anisotropic band structures with a small incident angle. The guided-mode resonances of the subwavelength-thickness slab enhance the PSHE, allowing the spin separation to exceed the incident beam waist. Via changing the incident angle, wavelength and even the beam waist, the spin separation can be adjusted in a wide range, which makes our proposal more flexible in manipulation of spin photons.

The spin Hall effect of light (SHEL) is the microscopic spin-dependent splitting of light at an optical interface. Whereas the spin Hall shift under linearly polarized light is well-formulated, studies on the SHEL under elliptically or circularly polarized light have primarily relied on numerical computation. In this work, an explicit analytic formula for the spin Hall shift is derived under arbitrarily polarized incidence. Furthermore, from this explicit expression, we demonstrate that the spin Hall shift can be enhanced at any incident angle by using polarization degree of freedom and is independent of the Fresnel coefficients of an interface under circularly polarized light. The analytic formula will help us understand the SHEL under general polarization intuitively and realize unprecedented modulation of the SHEL.

Beam splitters are widely used in various optical systems, but traditional beam splitters are bulky and heavy, which are not conducive to the integrated utilization of optical devices. Metamaterials have attracted extensive attention as a kind of miniature artificial materials, and there have been many works on the design of metasurface beam splitters. Using metasurfaces, multiple functions of traditional beam splitters can be achieved. Meanwhile, metasurface beam splitters have the advantages of small size, easy integration, flexible design of beam-splitting performance, and tunable functions. This review surveys the current work on metasurface beam splitters and provides a classification and introduction to metasurface beam splitters. Metasurface beam splitters are expected to play a huge role in interferometers, multiplexing, multi-beam communications, and more. [ABSTRACT FROM AUTHOR]

The spin-polarized conversion and splitting of beam are highly important for photonic researches and applications. Although the photonic spin Hall effect (PSHE) realized by the Pancharatnamâ€"Berry (PB) metasurface has shown unprecedented capabilities to control spin-polarized light, spin-polarized beam splitting metadevices suffer from the limitations of low-efficiency. Here, we present a highly efficient spin-polarized beam splitter (SPBS) based on PB metasurface comprising silicon nano elliptical cylinder (Si-NEC) arrays. Because of the electromagnetic multipole resonance inside the designed Si-NECs, the PB metasurface can achieve high transmittance and enhanced PSHE. Therefore, the SPBS based on the PB metasurface can achieve a high spin conversion efficiency of nearly 100%, while ensuring a transmittance of 87% at 622 nm wavelength. It can also maintain a good working effect within the bandwidth of 600â€"660 nm. Furthermore, by introducing spatial shift between the two reverse Si-NEC arrays, the SPBS can also be used to realize 45° polarization rotation of an incident linearly polarized light, avoiding the input polarization angle dependence. Our design may have potential applications in high-performance and broadband spin-photonic devices. [ABSTRACT FROM AUTHOR]

In this work, we present a surface plasmon resonance (SPR) structure containing AuAl 2 and a nonlinear Kerr medium. Based on the modulation of the refractive index of the Kerr medium by pumped light, we analyze the effects of the SPR structure and pumped light on the photonic spin Hall effect (PSHE). The numerical results indicate that the thickness of the AuAl 2 exerts a profound impact on the SPR, while the intensity of the pump light (I p) exerts a significant influence on the resonance angle. The transverse shift (TS) is very sensitive to the refractive index (RI) of the sensing layer after increasing through the SPR. Furthermore, it is observed that the sign of the TS of the PSHE can be modulated according to I p within a specific angle of incidence. In light of these findings, we put forth a novel optical signal modulation and RI sensing scheme based on PSHE. Our study provides a new mechanism for practical applications of PSHE in optical communication and precision measurement. • Enhanced photonic spin Hall effect by AuAl 2 -based surface plasmon resonance. • By employing nonlinear modulation, this work achieves transverse shift inversion and coding. • A refractive index sensor with sensitivity 2. 599 × 10 6 μ m /RIU. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) materials have attracted considerable research interest due to their potential optoelectronics applications. Black arsenic (B-As), a cousin of black phosphorus, has exceptionally high anisotropy in physical properties. In this study, we report the photonic spin Hall effect on the surface of two-dimensional B-As, manifesting in both transverse and in-plane beam shifts. By applying the beam propagation model near the surface of anisotropic 2D materials, we demonstrate that B-As exhibits higher or comparable photonic spin Hall shifts due to its extreme anisotropy. Moreover, a substantial spin-dependent beam displacement is observed when the incidence conditions meet the Brewster angle. These findings hold potential for novel scientific research and device applications involving anisotropic two-dimensional atomic crystals. • Developed model for photonic spin Hall effect in anisotropic 2D crystals (B-As), describing transverse and in-plane spin-dependent splitting. • Showed spin-dependent shifts are sensitive to optical axis, doping, and interband transitions, key for optoelectronic control. • Uncovered strong spin-dependent shift in B-As near Brewster angle, surpassing graphene due to anisotropic conductivity. [ABSTRACT FROM AUTHOR]

We investigate the photonic spin Hall effect (PSHE) of a Gaussian beam passing through a one-dimensional photonic crystal with a graphene defect film. We show that an epsilon singularity point and an epsilon-near-zero point of graphene emerge by varying its chemical potential. We find that the chemical potential of graphene significantly alters the transverse shifts of PSHE, while the temperature of graphene has a slight impact on the transverse shifts of PSHE. Moreover, we find that the behavior of PSHE near the singularity point considerably differs from that near the epsilon-near-zero point. Additionally, we further explore the different wavelengths of the incident Gaussian beam on the tunability of PSHE. We show that the considerable transverse shifts can be obtained simultaneously depending on the incident wavelength of the Gaussian beam and the chemical potential of graphene. [ABSTRACT FROM AUTHOR]

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 ${6.1} \times {10}^{{5}} \,\,\mu \text{m}$ /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. [ABSTRACT FROM AUTHOR]

Optical analog computing and spatial differentiation have received great attention in many fields. In the field of biology and medicine, it is important to get the high contrast of phase images on a subwavelength scale. Compared with other methods, the optical methods based on the photonic spin Hall effect (PSHE) have the advantages of low costs and detailed detections, but this method also has the disadvantages of lower contrasts. Our work is aimed to improve the contrasts for the edges. In the study, we explore the spin Hall effect of light (SHEL) based on uniaxial crystals and investigate the effects of these crystals on spatial differentiation. It can be seen that in the elliptic–hyperbolic crystal, the PSHE can be enhanced significantly and the spatial differentiation contrasts are consistent with the enhancement of PSHE, which implies that this kind of medium would provide more possibilities in micro imaging.

Arbitrary control and dynamic tuning of circularly polarized (CP) wave are of great significance to photonic research and application. Here, a terahertz switchable metasurface is designed with bifunctional properties based on a mixed structure of graphene and vanadium dioxide (VO2). The design consists of VO2 strips, topas spacer, VO2 film, graphene patch, topas spacer, and metallic film. When VO2 is metal, this metasurface realizes photonic spin Hall effect (PSHE) for CP wave in a wide frequency band of 0.7-1.5 THz. When VO2 is insulator, the design behaves as an absorber. It has a broadband absorption with more than 90% absorptance in the range of 0.48-1.88 THz, and there are two resonant peaks with ∼100% absorptance at 0.92 THz and 1.74 THz. Meanwhile, absorption bandwidth and intensity can be dynamically tuned by changing Fermi energy level of graphene. Besides, broadband absorption is robust against incident angle. Our design may promote the realization of terahertz switchable and multifunctional metasurfaces.

The spin Hall effect of light (SHEL), a spin‐dependent transverse splitting of light at an optical interface, is intrinsically an incident‐polarization‐sensitive phenomenon. Recently, an approach to eliminate the polarization dependence by equalizing the reflection coefficients of two linear polarizations has been proposed, but is only valid when the beam waist is sufficiently larger than the wavelength. Here, it is demonstrated that an interface, at which the reflection coefficients of the two linear polarizations are the same and so are their derivatives with respect to the incident angle, supports the polarization‐independent spin Hall shift, even when the beam waist is comparable to the wavelength. In addition, an isotropic–anisotropic interface that exhibits the polarization‐independent spin Hall shift over the entire range of incident angles is presented. Monte‐Carlo simulations prove that spin Hall shifts are degenerate under any polarization and reach a half of beam waist under unpolarized incidence. An application of the beam‐waist‐scale SHEL as a tunable beam‐splitting device that is responsive to the incident polarization is suggested. The spin Hall shift that is independent of the incident polarization at any incident angle will facilitate a wide range of applications including practical spin‐dependent devices and active beam splitters. [ABSTRACT FROM AUTHOR]

Graphene monolayer of sub-nanometer thickness shows strong metallic and plasmonic behavior in terahertz (THz) frequency range. This plasmonic effect varies considerably when graphene layer is placed under a magnetic field of appropriate strength. The strong adsorption characteristic of graphene layer is another advantage. In this work, a photonic spin Hall effect (PSHE)-based plasmonic sensor consisting of germanium prism, organic dielectric layer, and graphene monolayer is simulated and analyzed in THz aiming at highly sensitive and reliable sensing under variable magnetic field. Modified Otto configuration and magneto-optic effect in graphene are considered. The sensor's performance is examined in terms of sensitivity, limit of detection (LOD), and figure of merit (FOM). The analysis indicates that LOD of the order of 10−5 RIU for gas sensing is achievable, which is finer than recently reported gas sensors based on different techniques. Further, the FOM improves when a larger magnitude of magnetic field is applied. The FOM is even greater for rarer gaseous media, which can make the sensor extremely useful in early detection of airborne viruses such as SARS-Cov-2 (while using appropriate specificity method) and to measure the concentration of a particular gas in a given gaseous mixture. The results further indicate that the same sensor design can be used for magnetic field detection while the FOM of magnetic field detection is significantly greater for rarer gaseous medium (e.g., air), which may enable the probe to be used in early detection of radiation leakage in nuclear reactors. For larger magnitudes of magnetic field, the corresponding LOD becomes finer. [ABSTRACT FROM AUTHOR]

Graphene monolayer of sub-nanometer thickness possesses strong metallic and plasmonic behavior in a broad terahertz (THz) frequency range. This plasmonic effect can be considerably manipulated when graphene layer is subjected to a variable chemical potential (Ef) via chemical doping or electrical gating. The strong adsorption characteristics of graphene layer is another important advantage. In this work, a photonic spin Hall effect (PSHE) based plasmonic sensor consisting of germanium prism, organic dielectric layer, and graphene monolayer is simulated and analyzed in THz range aiming at highly sensitive and reliable gas sensing. Modified Otto configuration and Kubo formulation for graphene at room temperature are considered. The sensor's performance is examined in terms of figure of merit (FOM). The analysis indicates that under angular interrogation scheme of sensor operation, the FOM improves for smaller chemical potential (moderate doping) and higher THz frequency. Moreover, the influence of temperature on gas sensor's performance (FOM) is negligible, which suggests that the sensor is capable of providing stable sensing performance against temperature variation. The sensor design is highly flexible in terms of selection of THz frequency as an alternative interrogation scheme (i.e., measuring the variation in spin-dependent shift peak value of PSHE spectrum upon change in gas medium refractive index) can also be implemented. It is found that there is no need to change the moderate doping of graphene monolayer (i.e., Ef remains around its normal value ~ 0.1 eV) as the sensitivity achievable with this alternative method has considerably greater magnitude at smaller THz frequency (e.g., 2 THz). The magnitudes of FOM (with angular interrogation method) and sensitivity (with alternative method) are found to be significantly greater for rarer gaseous media, which might possibly assist in early detection of airborne viruses such as SARS-Cov-2 (while using appropriate specificity method) and to measure the concentration of a particular gas in a given gaseous mixture. [ABSTRACT FROM AUTHOR]

In this work, we propose and analyze a graphene-based plasmonic sensor with four layers (germanium, dielectric, graphene, and gaseous medium) for detection of refractive index (RI) of a gas medium and magnetic field applied to the graphene layer. The main idea is to exploit the strong plasmonic properties of the graphene monolayer in the THz frequency region and their strong dependence on applied magnetic field (B) for achieving high-performance sensor design. The transverse spin-dependent shift (SDS) of the horizontal photonic spin Hall effect (PSHE) at a given frequency (5 THz) is considered. The sensor structure is analyzed for two applications. First, in the conventional weak measurements, for a magnetic field B = 0 T and for an amplified angle ∆ = 0.1°, an extremely fine refractive index resolution of 1.22×10−11 RIU is obtained for gas medium in the range 1-1.1 RIU. The above resolution can be further improved under modified weak measurements, where for an amplified angle ∆ = 5.730° (i.e., 0.1 rad), a refractive index resolution of 6.24×10−17 RIU can be achieved. Second, for magnetic field detection, in the conventional weak measurements and for ∆ = 0.1°, a magnetic field resolution of 0.0146 μT is achievable. Also, in modified weak measurements, for ∆ = 5.730°, the magnetic field resolution of as fine as 3.59×10−6 μT can be achieved with the proposed sensor scheme. Our results are significantly finer than the current stae-of-the-art sensors (5×10−9 RIU and 0.7 μT). Further, the sensing performance for gas detection has the inverse dependence while that of magnetic field sensor has direct dependence on applied magnetic field. The resolution achieved by the proposed sensor design gets finer for smaller THz frequency, where the real and imaginary parts of the graphene RI are large. [ABSTRACT FROM AUTHOR]

Spin-orbital interaction of light attracts much attention in nanophotonics opening new horizons for modern optical systems and devices. The photonic spin Hall effect or Imbert-Fedorov shift takes a special place among the variety of spin-orbital interaction phenomena. It exhibits as a polarization-dependent transverse light shift usually observed in specular scattering of light at interfaces with anisotropic materials. Nevertheless, the effect of the polarization mixing caused by anisotropy on the Imbert-Fedorov shift is commonly underestimated. In this work, we demonstrate that polarization mixing contribution cannot be ignored for a broad range of optical systems. In particular, we show the dominant influence of the mixing term over the standard one for the polarized optical beam incident at a quarter-wave plate within the paraxial approximation. Moreover, our study reveals a novel contribution with extraordinary polarization dependence not observable within the simplified approach. We believe that these results advance the understanding of photonic spin Hall effect and open new opportunities for spin-dependent optical phenomena.

The interactions of photonic spin angular momentum and orbital angular momentum, i.e., the spin-orbit coupling in focused beams, evanescent waves or artificial photonic structures, have attracted intensive investigations for the unusual fundamental phenomena in physics and potential applications in optical and quantum systems. It is of fundamental importance to enhance performance of spin-orbit coupling in optics. Here, we demonstrate a titanium dioxide (TiO2)–based all-dielectric metasurface exhibiting a high efficient control of photonic spin Hall effect (PSHE) in a transmissive configuration. This metasurface can achieve high-efficiency symmetric spin-dependent trajectory propagation due to the spin-dependent Pancharatnam-Berry phase. The as-formed metadevices with high-aspect-ratio TiO2 nanofins are able to realize (86%, measured at 514 nm) and broadband PSHEs in visible regime. Our results provide useful insights on high-efficiency metasurfaces with versatile functionalities in visible regime.

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 Ă— 105 ÎĽm/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. [ABSTRACT FROM AUTHOR]