arXiv subjects

Hailu Luo

Publications and source records attributed to Hailu Luo.

At least 37 records · Page 2Linked to original sources

arXiv2014

Realization of tunable spin-dependent splitting in intrinsic photonic spin Hall effect

We report the realization of tunable spin-dependent splitting in intrinsic photonic spin Hall effect. By breaking the rotational symmetry of a cylindrical vector beam, the intrinsic vortex phases that the two spin components of the vector beam carries, which is similar to the geometric Pancharatnam-Berry phase, is no longer continuous in the azimuthal direction, and leads to observation of spin accumulation at the opposite edge of the beam. Due to the inherent nature of the phase and independency of light-matter interaction, the observed photonic spin Hall effect is intrinsic. Modulating the topological charge of the vector beam, the spin-dependent splitting can be enhanced and the direction of spin accumulation is switchable. Our findings may provide a possible route for generation and manipulation of spin-polarized photons, and enables spin-based photonics applications.

physics.optics↗

arXiv2014

Photonic spin Hall effect for precision metrology

The photonic spin Hall effect (SHE) is generally believed to be a result of an effective spin-orbit coupling, which describes the mutual influence of the spin (polarization) and the trajectory of the light beam. The photonic SHE holds great potential for precision metrology owing to the fact that the spin-dependent splitting in photonic SHE are sensitive to the physical parameter variations of different systems. Remarkably, using the weak measurements, this tiny spin-dependent shifts can be detected with the desirable accuracy so that the corresponding physical parameters can be determined. Here, we will review some of our works on using photonic SHE for precision metrology, such as measuring the thickness of nanometal film, identifying the graphene layers, detecting the strength of axion coupling in topological insulators, and determining the magneto-optical constant of magnetic film.

physics.optics↗

arXiv2014

Photonic spin Hall effect in metasurfaces with rotational symmetry-breaking

Observation of photonic spin Hall effect (SHE) in dielectric-based metasurfaces with rotational symmetry breaking is presented. We find that the spin-dependent splitting is a unique angular splitting in the real position space, and is attributed to the space-variant Pancharatnam-Berry phase (PB). Breaking the rotational symmetry of the PB phase by misalignment of the central axes of the incident beam and the metasurface, the spin-dependent shift is observable. We show that the spin-dependent shift can be enhanced by increasing the rotation rate of the metasurface, so the metasurface provides a great flexibility in the manipulation of photonic SHE.

physics.optics↗

arXiv2014

Generation of cylindrical vector vortex beams by two cascaded metasurfaces

We present a simple and efficient method to generate any cylindrical vector vortex (CVV) beams based on two cascaded metasurfaces. The metasurface works as a space-variant Panchratnam-Berry phase element and can produce any desirable vortex phase and vector polarization. The first metasurface is used to switch the sign of topological charges associated with vortex, and the second metasurface is applied to manipulate the local polarization. This method allows us to simultaneously manipulate polarization and phase of the CVV beams.

physics.optics↗

arXiv2014

Generation of arbitrary cylindrical vector beams on the higher order Poincare sphere

We propose and experimentally demonstrate a novel interferometric approach to generate arbitrary cylindrical vector beams on the higher order Poincare sphere. Our scheme is implemented by collinear superposition of two orthogonal circular polarizations with opposite topological charges. By modifying the amplitude and phase factors of the two beams, respectively, any desired vector beams on the higher order Poincare sphere with high tunability can be acquired. Our research provides a convenient way to evolve the polarization states in any path on the high order Poincare sphere.

physics.optics↗

arXiv2014

Realization of polarization evolution on higher-order Poincare sphere with metasurface

We present a simple and convenient method to yield cylindrical vector (CV) beams and realize its polarization evolution on higher-order Poincare sphere based on inhomogeneous birefringent metasurface. By means of local polarization transformation of the metasurface, it is possible to convert a light beam with homogeneous elliptical polarization into a vector beam with any desired polarization distribution. The Stokes parameters of the output light are measured to verify our scheme, which show well agreement with the theoretical prediction. Our method may provide a convenient way to generate CV beams, which is expected to have potential applications in encoding information and quantum computation.

physics.optics↗

arXiv2014

Geometric Photonic Spin Hall Effect with Metapolarization

We develop a geometric photonic spin Hall effect (PSHE) which manifests as spin-dependent shift in momentum space. It originates from an effective space-variant Pancharatnam-Berry (PB) phase created by artificially engineering the polarization distribution of the incident light. Unlikely the previously reported PSHE involving the light-matter interaction, the resulting spin-dependent splitting in the geometric PSHE is purely geometrically depend upon the polarization distribution of light which can be tailored by assembling its circular polarization basis with suitably magnitude and phase. This metapolarization idea enables us to manipulate the geometric PSHE by suitably tailoring the polarization geometry of light. Our scheme provides great flexibility in the design of various polarization geometry and polarization-dependent application, and can be extrapolated to other physical system, such as electron beam or atom beam, with the similar spin-orbit coupling underlying.

physics.optics↗

arXiv2014

Realization of Tunable Photonic Spin Hall Effect by Tailoring the Pancharatnam-Berry Phase

Recent developments in the field of photonic spin Hall effect (SHE) offer new opportunities for advantageous measurement of the optical parameters (refractive index, thickness, etc.) of nanostructures and enable spin-based photonics applications in the future. However, it remains a challenge to develop a tunable photonic SHE with any desired spin-dependent splitting for generation and manipulation of spin-polarized photons. Here, we demonstrate experimentally a scheme to realize the photonic SHE tunably by tailoring the space-variant Pancharatnam-Berry phase (PBP). It is shown that light beams whose polarization with a tunable spatial inhomogeneity can contribute to steering the space-variant PBP which creates a spin-dependent geometric phase gradient, thereby possibly realizing a tunable photonic SHE with any desired spin-dependent splitting. Our scheme provides a convenient method to manipulate the spin photon. The results can be extrapolated to other physical system with similar topological origins.

physics.optics↗

arXiv2014

Optimal preselection and postselection in weak measurements for observing photonic spin Hall effect

Photonic spin Hall effect (SHE) holds great potential applications in precision metrology. How to obtain a high measurement precision is an important issue to detect the photonic SHE. In this letter, we propose using optimal preselection and postselection in weak measurements to enhance the measurement precision. We find that the maximum weak value and pointer shift can be obtained with an optimal overlap of preselection and postselection states. These findings offer the possibility for improving the precision of weak measurements and thereby have possible applications for accurately characterizing the parameters of nanostructures.

physics.optics↗

arXiv2013

Photonic spin Hall effect in topological insulators

In this paper we theoretically investigate the photonic spin Hall effect (SHE) of a Gaussian beam reflected from the interface between air and topological insulators (TIs). The photonic SHE is attributed to spin-orbit coupling and manifests itself as in-plane and transverse spin-dependent splitting. We reveal that the spin-orbit coupling effect in TIs can be routed by adjusting the axion angle variations. Unlike the transverse spin-dependent splitting, we find that the in-plane one is sensitive to the axion angle. It is shown that the polarization structure in magneto-optical Kerr effect is significantly altered due to the spin-dependent splitting in photonic SHE. We theoretically propose a weak measurement method to determine the strength of axion coupling by probing the in-plane splitting of photonic SHE.

physics.optics↗

arXiv2012

Identifying graphene layers via spin Hall effect of light

The spin Hall effect (SHE) of light is a useful metrological tool for characterizing the structure parameters variations of nanostructure. In this letter we propose using the SHE of light to identify the graphene layers. This technique is based on the mechanism that the transverse displacements in SHE of light are sensitive to the variations of graphene layer numbers.

physics.optics↗

arXiv2012

Steering far-field spin-dependent splitting of light by inhomogeneous anisotropic media

An inhomogeneous anisotropic medium with specific structure geometry can apply the tunable spin-dependent geometrical phase to the light passing through the medium, and thus can be used to steer the spin-dependent splitting (SDS) of light. In this paper, we exemplify this inference by the q plate, an inhomogeneous anisotropic medium. It is demonstrated that when a linearly polarized light beam normally passes through a q plate, k-space SDS first occurs, and then the real-space SDS in the far-field focal plane of a converging lens is distinguishable. Interestingly, the SDS, described by the normalized Stokes parameter S3 shows a multilobe and rotatable splitting pattern with rotational symmetry. Further, by tailoring the structure geometry of the q plate and/or the incident polarization angle of light, the lobe number and the rotation angle both are tunable. Our result suggests that the q plate can serve as a potential device for manipulating the photon spin states and enable applications such as in nano-optics and quantum information.

physics.optics↗

arXiv2012

Metamaterial-based polarization control plate for producing incoherent laser irradiation

We present a metamaterial-based random polarization control plate to produce incoherent laser irradiation by exploiting the ability of metamaterial in local polarization manipulation of beam upon transmission via tuning its local geometry. As a proof-of-principle, we exemplify this idea numerically in a simple optical system using a typical L-shaped plasmonic metamaterial with locally varying geometry, from which the desired polarization distribution can be obtained. The calculating results illustrate that this scheme can effectively suppress the speckle contrast and increase irradiation uniformity, which has potential to satisfy the increasing requirements for incoherent laser irradiation.

physics.optics↗

arXiv2012

Weak measurements of a large spin angular splitting of light beam on reflection at Brewster angle

We reveal a large spin angular splitting of light beam on reflection at the Brewster angle both theoretically and experimentally. A simple weak measurements system manifesting itself for the built-in post-selection technique is proposed to explore this angular splitting. Remarkably, the directions of the spin accumulations can be switched by adjusting the initial handedness of polarization.

physics.optics↗

arXiv2012

Method for arbitrary phase transformation by a slab based on transformation optics and the principle of equal optical path

The optical path lengths travelled by rays across a wavefront essentially determine the resulting phase front irrespective of the shape of a medium according to the principle of equal optical path. Thereupon we propose a method for the transformation between two arbitrary wavefronts by a slab, i.e. the profile of the spatial separation between the two wavefronts is taken to be transformed to a plane surface. Interestingly, for the mutual conversion between planar and curved wavefronts, the method reduce to an inverse transformation method in which it is the reversed shape of the desired wavefront that is converted to a planar one. As an application, three kinds of phase transformation are realized and it is found that the transformation on phase is able to realize some important properties such as phase reversal or compensation, focusing, and expanding or compressing beams, which are further confirmed by numerical simulations. The slab can be applied to realizing compact electromagnetic devices for which the values of the refractive index or the permittivity and permeability can be high or low, positive or negative, or near zero, depending on the choice of coordinate transformations.

physics.optics↗

arXiv2012

Generation of optical beams with desirable orbital angular momenta by transformation media

We propose a scheme to controllably convert the wavefront of an arbitrary incident beam into a helical one by compact transformation slabs, thus enabling the output beam to carry desirable orbital angular momentum (OAM). First, based on transformation optics, a three-dimensional (3D) phase transformation between any two wavefronts by °at transformation media is established and then used to mold a wavefront of Gaussian beam into a helical one. Second, 3D FDTD simulations are performed to confirm the spiraling evolutions of the resultant field and phase, clearly demonstrating OAM generated. Further theoretical analyses show that the refractive index exhibiting a helical distribution leads to the oppositely spiral phase front and that it is feasible to produce desirable OAM by generators of unit OAM. The results not only provide an additional way to manipulate phase and photon OAM, but reciprocally shed further light on the phase structure of helical beams, which leads to a new transformation way by a surface.

physics.optics↗

arXiv2012

Goos-Hänchen and Imbert-Fedorov Shifts of Vortex Beams at Air-Left-Handed Material Interfaces

In this paper, we present a systematic study of beam shifts and angular momenta of paraxial vortex beams at air-left-handed material (LHM) interfaces. It is shown that, compared to their counterparts at air-right-handed material (RHM) interfaces, the spatial Goos-Hänchen (GH) and Imbert-Fedorov (IF) shifts remains the same, while the angular GH and IF shifts are reversed, at air-LHM interfaces. The spatial and angular shifts of paraxial vortex beams have their respective origins in transverse angular momenta and transverse linear momenta. The spatial GH and IF shifts remain unreversed as a result of the both reversions of transverse angular momenta and z-component linear momentum, while the angular GH and IF shifts are reversed due to that the z-component linear momentum is reversed and the transverse linear momenta are unreversed, at air-LHM interfaces. In addition, we perform a quantitative analysis on spin-orbit angular momentum conversion and orbit-orbit angular momentum conversion, which further helps us understand the essence of vortex beam shifts at air-LHM interfaces and their fundamental distinctions with those at air-RHM interfaces.

physics.optics↗

arXiv2012

Experimental observation of the spin Hall effect of light on a nano-metal film via weak measurements

We theorize the spin Hall effect of light (SHEL) on a nano-metal film and demonstrate it experimentally via weak measurements. A general propagation model to describe the relationship between the spin-orbit coupling and the thickness of the metal film is established. It is revealed that the spin-orbit coupling in the SHEL can be effectively modulated by adjusting the thickness of the metal film, and the transverse displacement is sensitive to the thickness of metal film in certain range for horizontal polarization light. Importantly, a large negative transverse shift can be observed as a consequence of the combined contribution of the ratio and the phase difference of Fresnel coefficients.

physics.optics↗