Photonic Spin Research Articles

Signature of the photonic spin Hall effect in monolayer MoS2 via weak measurement

We report the direct experimental evidence of the photonic spin Hall shift (PSHS) in monolayer M o S 2 for a fundamental Gaussian beam via a weak measurement scheme involving definite preselection and postselection spin states. We find that the PSHS is largely dependent on the angle of incidence, postselection angles, and polarization states along with specific ways of interaction of the light with the M o S 2 surface. Our findings reveal a unique signature linking angular positions at which the spin Hall shifts (SHS) (zero crossing) with the discontinuity in the phase difference ( ϕ P − ϕ S ) of the reflection coefficients further establishing the connection of the PSHS to the geometric phases of the light. An effective theoretical model is applied to confirm the experimental measurements. This paper, thus, deepens our understanding of the tiny spin-dependent splitting in monolayer M o S 2 , opening a new, to the best of our knowledge, avenue for the practical applications of the PSHSs.

Photonic spin Hall effect in a one-dimensional photonic crystal with a graphene defect film

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.

Complete analysis of beam analyzing powers in at near threshold energies

Focusing attention on the photon spin in at near threshold energies of interest to Big Bang Nucleosynthesis, a complete analysis of beam analyzing powers in reaction is carried out. A complete analysis of the reaction needs not only measurements using one state of linear polarization of photon but also measurements using another state of linear polarization inclined to the first at π/4 and the two states of circular polarization of the photon. A discussion on the complete characterization of the states of photon polarization is presented. The beam analyzing powers with respect to photon polarization are discussed theoretically, using model independent irreducible tensor formalism.

Photonic Bandgaps of One-Dimensional Photonic Crystals Containing Anisotropic Chiral Metamaterials

Conventional photonic bandgaps (PBGs) for linear polarization waves strongly depend on the incident angle. Usually, PBGs will shift toward short wavelengths (i.e., blue-shifted gaps) as the incident angle increases, which limits their applications. In some practices, the manipulation of PBGs for circular polarization waves is also important. Here, the manipulation of PBGs for circular polarization waves is theoretically investigated. We propose one-dimensional photonic crystals (1DPCs) containing anisotropic chiral metamaterials which exhibit hyperbolic dispersion for left circular polarization (LCP) wave and elliptical dispersion for right circular polarization (RCP) wave. Based on the phase variation compensation effect between anisotropic chiral metamaterials and dielectrics, we can design arbitrary PBGs including zero-shifted and red-shifted PBGs for LCP wave. However, the PBGs remain blue-shifted for RCP wave. Therefore, we can design a high-efficiency wide-angle polarization selector based on the chiral PBGs. Our work extends the manipulation of PBGs for circular polarization waves, which has a broad range of potential applications, including omnidirectional reflection, splitting wave and enhancing photonic spin Hall effect.

Higher-order topological states in two-dimensional Stampfli-Triangle photonic crystals.

In this Letter, the higher-order topological state (HOTS) and its mechanism in two-dimensional Stampfli-Triangle (2D S-T) photonic crystals (PhCs) is explored. The topological corner states (TCSs) in 2D S-T PhCs are based on two physical mechanisms: one is caused by the photonic quantum spin Hall effect (PQSHE), and the other is caused by the topological interface state. While the former leads to the spin-direction locked effect which can change the distribution of the TCSs, the latter is conducive to the emergence of multiband TCSs in the same structure due to the characteristics of plentiful photonic bandgap (PBG) and broadband in 2D S-T PhCs. These findings allow new, to the best of our knowledge, insight into the HOTS, and are significant to the future design of photonic microcavities, high-quality factor lasers, and other related integrated multiband photonic devices.

Asymmetrical photonic spin Hall effect based on dielectric metasurfaces

The photonic spin Hall effect has attracted considerable research interest due to its potential applications in spin-controlled nanophotonic devices. However, realization of the asymmetrical photonic spin Hall effect with a single optical element is still a challenge due to the conjugation of the Pancharatnam–Berry phase, which reduces the flexibility in various applications. Here, we demonstrate an asymmetrical spin-dependent beam splitter based on a single-layer dielectric metasurface exhibiting strong and controllable optical response. The metasurface consists of an array of dielectric nanofins, where both varying rotation angles and feature sizes of the unit cells are utilized to create high-efficiency dielectric metasurfaces, which enables to break the conjugated characteristic of phase gradient. Thanks to the superiority of the phase modulation ability, when the fabricated metasurface is under normal incidence with a wavelength of 1550 nm, the left-handed circular polarization (LCP) light exhibits an anomalous refraction angle of 28.9°, while the right-handed circular polarization (RCP) light transmits directly. The method we proposed can be used for the flexible manipulation of spin photons and has potentials in high efficiency metasurfaces with versatile functionalities, especially with metasurfaces in a compact space.

Engineering shortcut-based operations on a nitrogen-vacancy spin qubit and microwave photons via optimized drivings

Optimal control of quantum systems is of significance to information processing and state engineering. Here an efficient scheme is proposed for engineering shortcut-based operations on a nitrogen-vacancy spin qubit and microwave photons via simplified drivings. The spin qubit dispersively coupled to a cavity field constitutes a composite system. Within a three-state subspace, we treat an effective interaction between the composite system and two classical drivings. By the technique of invariant-based shortcuts to adiabaticity, a state swap via Rabi pulses with sine- and cosine-typed waveforms and the generation of entangled states using constant Rabi pulses can be constructed, respectively. Moreover, with the accessible rates of qubit decoherence and photon decay, robust operations could be achieved by numerically simulating noise effects. The strategy could offer simple yet versatile avenues to implement the shortcut-based operations on the composite spin–photon system experimentally.

Intrinsic Spin-Momentum Dynamics of Surface Electromagnetic Waves in Dispersive Interfaces.

Intrinsic spin-momentum locking is an inherent property of surface electromagnetic fields and its study has led to the discovery of phenomena such as unidirectional guided waves and photonic spin lattices. Previously, dispersion was ignored in spin-momentum locking, resulting in anomalies contradicting the apparent physical reality. Here, we formulate four dispersive spin-momentum equations, revealing in theory that transverse spin is locked with kinetic momentum. Moreover, in dispersive metal or magnetic materials spin-momentum locking obeys the left-hand screw rule. In addition to dispersion, structural features can affect substantially this locking. Remarkably, an extraordinary spin originating from coupling polarization ellipticities is uncovered that depends on the symmetry of the field modes. We further identify the properties of this spin-momentum locking with diverse photonic topological lattices by engineering their rotational symmetry akin to that in solid-state physics. The concept of spin-momentum locking based on photon flow properties translates easily to other classical wave fields.

Enhanced photonic spin Hall effect of reflected light from a doubly linear gradient-refractive-index material.

The photonic spin Hall effect (SHE), manifesting itself as spin-dependent splitting of light, holds potential applications in nano-photonic devices and precision metrology. However, the photonic SHE is generally weak, and therefore its enhancement is of great significance. In this paper, we propose a simple method for enhancing the photonic SHE of reflected light by taking advantage of the gradient-refractive-index (GRIN) material. The transverse shifts for a normal (homogeneous) layer and linear GRIN structure with three different types (singly increasing, singly decreasing, and doubly linear ones) are theoretically investigated. We found that the doubly linear GRIN materials exhibit the prominent photonic SHE of reflected light, which is mainly due to the Fabry-Perot resonance. By optimizing the thickness and the lower (higher) refractive index of the doubly linear GRIN layer, the transverse shift for a horizontally polarized incident beam can nearly reach its upper limitation (i.e., half of the beam waist). These findings provide us a potential method to enhance the photonic SHE, and therefore establish a strong foundation for developing spin-based photonic devices in the future.

Enhanced spin Hall effect of reflected light due to optical Tamm states with Dirac semimetal at the terahertz range

In this work, the enhanced photonic spin Hall effect (PSHE) of reflected light at terahertz range is achieved by using a multilayer structure consisting of Dirac semimetal, spacer layer, and distributed Bragg reflector structure. This enhanced PSHE phenomenon originates from the excitation of optical Tamm states (OTSs) at the interface between the Dirac semimetal and distributed Bragg reflector structure. The theoretical results show that by optimizing the Fermi energy and the thickness of Dirac semimetal, the reflection coefficient ratio of s-polarization to p-polarization can be increased, thus creating conditions for enhanced PSHE. Moreover, the spin behavior of this composite structure is also proved sensitive to incidence angle and the dispersion characteristics of the spacer layer, thus making this configuration an effective candidate for developing photonic devices based on PSHE at the terahertz range.

Photonic spin Hall effect from quantum kinetic theory in curved spacetime

Based on quantum field theory, we formulate the Wigner function and quantum kinetic theory for polarized photons in curved spacetimes which admit a covariantly constant timelike vector. From this framework, the photonic chiral/zilch vortical effects are reproduced in a rigidly rotating coordinate. In a spatially inhomogeneous coordinate, we derive the spin Hall effect for the photon helicity current and energy current in equilibrium. Our derivation reveals that such photonic Hall effect are related to the photonic vortical effect via the Lorentz invariance and their transport coefficients match each other.

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 () and the critical angle () 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.

Plasmonics-based gas sensor with photonic spin hall effect in broad terahertz frequency range under variable chemical potential of graphene.

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.Supplementary InformationThe online version contains supplementary material available at 10.1007/s11082-022-03626-7.

Magnetically tunable and enhanced spin Hall effect of reflected light in a multilayer structure containing anisotropic graphene.

In this paper, the magnetically tunable and enhanced photonic spin Hall effect (PSHE) of reflected light beam at terahertz frequencies is achieved by using a multilayer structure where anisotropic graphene is inserted. This enhanced PSHE phenomenon results from the excitation of surface plasmon polariton (SPP) at the interface between two dielectric materials. By considering the 4×4 transfer matrix method and the quantum response of graphene, the PSHE of the reflected light can be enhanced by harnessing the anisotropic conductivity of graphene. Besides, the PSHE can be tuned through the external magnetic field and structural parameters. This enhanced and tunable PSHE approach is promising for fabricating anisotropic graphene-based terahertz spin devices and other applications in nanophotonics.

Highly sensitive real-time detection of phase change process based on photonic spin Hall effect

Phase change materials, such as vanadium dioxide (VO2) and Titanium dioxide (Ti2O3) have received extensive attention because of the dramatic changes in their intrinsic properties during phase transitions. However, due to the rapid transition rate and wide dynamics, monitoring of processes is challenging. Previous detection methods are lack of speed and simplicity and require multiple interventions, which largely introduce human factors influencing the results and make it difficult to guarantee the accuracy and visualization. In this paper, the photonic spin Hall effect is used for real-time detection and highly sensitive analysis of the phase transition process of VO2 films. By incorporating with quantum weak measurement, the photonic spin-Hall shift acts as the pointer, and the phase transition process of VO2 is characterized effectively. The high measurement resolution with 63 S/(m μm) is achieved due to weak-value amplification. In our scheme, it does not involve any mechanical adjustment of optical components, thus enabling real-time, visual, non-contact detection of dynamic phase transition processes.

Research on the effect of incident polarization phase on transverse spin splitting of reflected beam

In this work, the theoretical relationship model between the incident polarization phase and transverse spin splitting (TSS) shifts of photonic spin Hall effect (PSHE) is established. Based on the established model, the effect of the incident polarization phase on the TSS is systematically studied, and several characteristic laws are summarized. These findings can help people better understand PSHE. In addition, it is found that, no matter what the incident angle and polarization angle are, the TSS shift at polarization phase equal to ±90° is larger than that at other polarization phases. It can even reach several microns under certain incident angle and polarization angle, and is almost an order of magnitude larger than the usual TSS shift, which is generally tens to hundreds of nanometers. This provides a new way for enhancing PSHE. Furthermore, when the polarization phase is 90° or −90°, under a certain polarization angle, slightly adjust the polarization angle, the TSS shift will change sharply and its direction will be reversed. This interesting finding has great application value in the field of photon manipulation.

Broadband spin-unlocked metasurfaces for bifunctional wavefront manipulations

Recently, Pancharatnam–Berry (PB) metasurfaces have exhibited powerful capabilities to control spin-polarized light. However, the adopted abrupt PB phase, introduced by simply rotating the basic elements, is spin-locked with opposite signs for different spin excitations, greatly limiting their practical applications. Here, we introduce a high-efficiency and broadband spin-unlocked metasurface with two mechanisms of a resonance phase and a geometric phase perfectly combined together. The design strategy is quite simple just through changing one geometric parameter rather than multi parameter optimization. As a proof of concept, the anomalous photonic spin Hall effect based on the spin-unlocked metasurface is demonstrated first, showing high experimental efficiency (over 80%) in a broad frequency range (11.3–16.6 GHz). Furthermore, another spin-unlocked metasurface is built to demonstrate the completely independent wavefront manipulations, i.e., the focusing effect and anomalous reflection. These findings significantly expand the electromagnetic control ability of a metasurface.

Localized States Emerging from Singular and Nonsingular Flat Bands in a Frustrated Fractal‐Like Photonic Lattice (Advanced Optical Materials 9/2022)

In article number 2102523, Haissam Hanafi, Philip Menz, and Cornelia Denz report on the experimental demonstration of localized states that propagate diffractionless in a fractal-like photonic lattice fabricated by femtosecond direct laser writing. These states arise from multiple flat bands of singular and nonsingular nature in the spectrum of the geometrically frustrated lattice. This research reveals fundamental aspects of flat band physics and paves the way for photonic spin liquid ground states.

Broadband and high-efficiency photonic spin-Hall effect with all-metallic metasurfaces.

In this paper, all-metallic reflective metasurfaces comprising S-shape streamline structures are proposed to achieve the photonic spin-Hall effect with average cross-polarization conversion efficiency exceeding ∼84% in the range of 8-14 µm. By comparing with all-metallic nanobricks, it is demonstrated that the electric field coupling could be enhanced by constructing a similar split ring resonator between adjacent unit elements to further improve its efficiency and bandwidth. As a proof of concept, the photonic spin Hall effect and spin-to-orbit angular momentum conversion could be observed by two metadevices with the maximum diffraction efficiency of ∼95.7%. Such an all-metallic configuration may provide a platform for various high-efficiency electromagnetic components, catenary optics, and practical applications.

Screening nearest-neighbor interactions in networks of exciton-polariton condensates through spin-orbit coupling

We study the modification of the spatial coupling parameter between interacting ballistic exciton-polariton condensates in the presence of photonic spin orbit coupling appearing from TE-TM splitting in planar semiconductor microcavities. We propose a strategy to make the coupling strength between next-nearest-neighbours stronger than between nearest-neighbour, which inverts the conventional idea of the spatial coupling hierarchy between sites. Our strategy relies on the dominantly populated high-momentum components in the ballistic condensates which, in the presence of TE-TM splitting, lead to rapid radial precession of the polariton pseudospin. As a consequence, condensate pairs experience distance-periodic screening of their interaction strength, severely modifying their synchronization and condensation threshold solutions.