Three-dimensional modulations on the states of polarization of light fields

Light fields with spatially structured states of polarization（SoPs） are gathering increasing attention because of their potential applications from optical imaging and micromanipulation to classical and quantum communications. Meanwhile,the concepts within structured light fields have been extended and applied to acoustic, electron, and matter waves. In this article, we review recent developments of the SoP modulation of light fields, especially focusing on three-dimensional（3 D） modulations on the SoPs of light fields. The recent progress and novel implementations based on 3 D spin-dependent separation are discussed. Following the discussions to this physical phenomenon, we then describe recent developments on the vector fields with 3 D structured SoP and intensity distributions, namely, 3 D vector fields. The discussed phenomena inspire us to explore other structured light fields for the expansion of applications in biomedical, information science,quantum optics, and so on.

Hybrid vector beams with non-uniform orbital angular momentum density induced by designed azimuthal polarization gradient

Based on angular amplitude modulation of orthogonal base vectors in common-path interference method, we propose an interesting type of hybrid vector beams with unprecedented azimuthal polarization gradient and demonstrate in experiment. Geometrically, the configured azimuthal polarization gradient is indicated by intriguing mapping tracks of angular polarization states on Poincaré sphere, more than just conventional circles for previously reported vector beams. Moreover, via tailoring relevant parameters, more special polarization mapping tracks can be handily achieved. More noteworthily, the designed azimuthal polarization gradients are found to be able to induce azimuthally non-uniform orbital angular momentum density, while generally uniform for circle-track cases, immersing in homogenous intensity background whatever base states are. These peculiar features may open alternative routes for new optical effects and applications.

Highly efficient generation of arbitrary vector beams with tunable polarization, phase, and amplitude

We propose an efficient and robust method to generate tunable vector beams by employing a single phasetype spatial light modulator(SLM). With this method, a linearly polarized Gaussian beam can be converted into a vector beam with arbitrarily controllable polarization state, phase, and amplitude. The energy loss during the conversion is greatly reduced and depends mainly on the reflectivity of the SLM. We experimentally demonstrate that conversion efficiency of about 47% is achieved by using an SLM with reflectivity of 62%.Several typical vector beams, including cylindrical vector beams, vector beams on higher order Poincaré spheres,and arbitrary vector beams attached with phases and with tunable amplitude, are generated and verified experimentally. This method is also expected to create high-power vector beams and play important roles in optical fabrication and light trapping.

Polarization oscillating beams constructed by copropagating optical frozen waves

Polarization oscillating beams, namely, polarization standing waves, commonly formed by a pair of coherent counterpropagating light waves with orthogonal polarizations, oscillate their states of polarization periodically within a wavelength interval, offering conceptual and practical interests in light-matter interactions such as the nonreciprocal magnetoelectric effect, and impressive applications in optical imaging, sensing, and chirality detection. Here, we propose a new class of polarization oscillating beams that longitudinally vary states of polarization with spatial intervals within centimeters via the superposition of two copropagating optical frozen waves with preshaped longitudinal intensity profiles and transverse phase structures. The flexibility and manipulability are demonstrated by creating several polarization oscillating beams with different polarization structures. This work paves a new way to manipulate other waves and may be useful for applications of optical standing waves in optical manipulation, light guiding of atoms, polarization-sensitive sensing, etc.

Controllable oscillated spin Hall effect of Bessel beam realized by liquid crystal Pancharatnam-Berry phase elements

Pancharatnam–Berry (PB) phase has become an effective tool to realize the photonic spin Hall effect (PSHE) in recent years, due to its capacity of enhancing the spin-orbit interaction. Various forms of PSHEs have been proposed by tailoring the PB phase of light, however, the propagation trajectory control of the separated spin states has not been reported. In this paper, we realize the oscillated spin-dependent separation by using the well-designed PB phase optical elements based on the transverse-to-longitudinal mapping of Bessel beams. Two typical oscillated PSHEs, i.e., the spin states are circulated and reversed periodically, are experimentally demonstrated with two PB phase elements fabricated with liquid crystal. The displacements and periods of these oscillations can be controlled by changing the transverse vector of the input Bessel beam. The proposed method offers a new degree of freedom to manipulate the spin-dependent separation, and provides technical supports for the application in spin photonics.

Dynamically measuring the holo-information of light fields in three-dimensional space using a periodic polarization-structured light

Spatially structured light field has attracted great attention due to its novel properties and application potential in numerous fields.Among them,the most striking one is the polarization-structured light,known as the vector beam.Here,using a periodic polarization-structured light,we propose a method to dynamically measure the holo-information of light fields,including the amplitude,phase,and polarization distributions,in three-dimensional(3D)space.The measurement system is composed of a Mach-Zender interferometer involving a liquid crystal polarized grating in the reference arm,which is simple,stable,and easy to operate.Featuring the single-shot measurement,this method supports observing the dynamic variation of object light fields.The accuracy,3D polarimetry,and dynamic observation of this method are validated by measuring a calibrated quarter-wave plate,a vector vortex beam,a Poincarébeam,and a stressed polymethyl methacrylate sample.

Modulation of orbital angular momentum on the propagation dynamics of light fields

Optical vortices carrying orbital angular momentum(OAM)have attracted extensive attention in recent decades because of their interesting applications in optical trapping,optical machining,optical communication,quantum information,and optical microscopy.Intriguing effects induced by OAMs,such as angular momentum conversion,spin Hall effect of light(SHEL),and spin– orbital interaction,have also gained increasing interest.In this article,we provide an overview of the modulations of OAMs on the propagation dynamics of scalar and vector fields in free space.First,we introduce the evolution of canonical and noncanonical optical vortices and analyze the modulations by means of local spatial frequency.Second,we review the Pancharatnam–Berry(PB)phases arising from spin–orbital interaction and reveal the control of beam evolution referring to novel behavior such as spindependent splitting and polarization singularity conversion.Finally,we discuss the propagation and focusing properties of azimuthally broken vector vortex beams.

Visible frequency broadband dielectric metahologram by random Fourier phase-only encoding

In recent years,metasurfaces that enable the flexible wavefront modulation at sub-wavelength scale have been widely used into holographic display,due to its prominent advantages in polarization degrees of freedom,viewing angle,and achromaticity in comparison with traditional holographic devices.In holography,the computational complexity of hologram,imaging sharpness,energy utilization,reproduction rate,and system indirection are all determined by the encoding method.Here,we propose a visible frequency broadband dielectric metahologram based on the random Fourier phase-only encoding method.Using this simple and convenient method,we design and fabricate a transmission-type geometric phase all-dielectric metahologram,which can realize holographic display with high quality in the visible frequency range.This method encodes the amplitude information into the phase function only once,eliminating the cumbersome iterations,which greatly simplifies the calculation process,and may facilitate the preparation of large area nanoprint-holograms.