Vectorial Optical Field Generator Research Articles

Physical conversion and superposition of optical skyrmion topologies

Optical skyrmions are quasiparticles with nontrivial topological textures that have significant potential in optical information processing, transmission, and storage. Here, we theoretically and experimentally achieve the conversion of optical skyrmions among Néel, Bloch, intermediate skyrmions, and bimerons by polarization devices, where the fusion and annihilation of optical skyrmions are demonstrated accordingly. By analyzing the polarization pattern in Poincaré beams, we reveal the skyrmion topology dependence on the device, which provides a pathway for the study of skyrmion interactions. A vectorial optical field generator is implemented to realize the conversion and superposition experimentally, and the results are in good agreement with the theoretical predictions. These results enhance our comprehension of optical topological quasiparticles, which could have a significant impact on the transfer, storage, and communication of optical information.

Compact vectorial optical field generator using a single phase-only spatial light modulator.

In this study, we demonstrate a compact vectorial optical field generator for any coherent light, including femtosecond laser beams. The apparatus utilizes a single Köster prism for both beam splitting and recombining. A phase-only spatial light modulator is used as a diffractive optical element to encode the two complex fields that recombine after being converted to orthogonal polarizations, generating an arbitrary vectorial optical field. We apply this setup to shape focused femtosecond pulses in producing patterned structures.

Compact vectorial optical field generator based on a 10-megapixel resolution liquid crystal spatial light modulator

Vectorial optical fields have attracted great attention with potential applications such as optical micromachining, optical nano-fabrication, surface plasmon excitation, optical micro-manipulation, optical imaging and so on. In this study, a compact vectorial optical field generator that can generate arbitrary complex beam with greatly reduced space and optical elements is designed, constructed and tested. Based on a reflective liquid crystal spatial light modulator with 10-megapixel resolution, the generator can control the four degrees of freedom in the spatial distributions of an optical field including phase, amplitude, polarization ratio and retardation on pixel by pixel level. Several typical complex vectorial optical fields are experimentally generated and quantitatively characterized by the Stokes parameter measurement to demonstrate the feasibility and versatility of the compact generator.

Efficient generation of complex vectorial optical fields with metasurfaces

Vectorial optical fields (VOFs) exhibiting arbitrarily designed wavefronts and polarization distributions are highly desired in photonics. However, current methods to generate them either require complicated setups or exhibit limited functionalities, which is unfavorable for integration-optics applications. Here, we propose a generic approach to efficiently generate arbitrary VOFs based on metasurfaces exhibiting full-matrix yet inhomogeneous Jones-matrix distributions. We illustrate our strategy with analytical calculations on a model system and an experimental demonstration of a meta-device that can simultaneously deflect light and manipulate its polarization. Based on these benchmark results, we next experimentally demonstrate the generation of a far-field VOF exhibiting both a vortex wavefront and an inhomogeneous polarization distribution. Finally, we design/fabricate a meta-device and experimentally demonstrate that it can generate a complex near-field VOF—a cylindrically polarized surface plasmon wave possessing orbital angular momentum—with an efficiency of ~34%. Our results establish an efficient and ultracompact platform for generating arbitrary predesigned VOFs in both the near- and far-fields, which may find many applications in optical manipulation and communications.

Enantioselective optical trapping of chiral nanoparticles using a transverse optical needle field with a transverse spin

Since the fundamental building blocks of life are built of chiral amino acids and chiral sugar, enantiomer separation is of great interest in plenty of chemical syntheses. Light-chiral material interaction leads to a unique chiral optical force, which possesses opposite directions for specimens with different handedness. However, usually the enantioselective sorting is challenging in optical tweezers due to the dominating achiral force. In this work, we propose an optical technique to sort chiral specimens by use of a transverse optical needle field with a transverse spin (TONFTS), which is constructed through reversing the radiation patterns from an array of paired orthogonal electric dipoles located in the focal plane of a 4Pi microscopy and experimentally generated with a home-built vectorial optical field generator. It is demonstrated that the transverse component of the photonic spin gives rise to the chiral optical force perpendicular to the direction of the light's propagation, while the transverse achiral gradient force would be dramatically diminished by the uniform intensity profile of the optical needle field. Consequently, chiral nanoparticles with different handedness would be laterally sorted by the TONFTS and trapped at different locations along the optical needle field, providing a feasible route toward all-optical enantiopure chemical syntheses and enantiomer separations in pharmaceuticals.

Dynamical generation of multiple focal spot pairs with controllable position and polarization

We report a flexible method to dynamically generate multiple sub-wavelength focal spot pairs with adjustable polarization, position and number at the focal plane of a high numerical aperture (NA) objective lens. The desired incident field on the pupil plane can be analytically derived by employing the time-reversed method combined with the dipole antenna radiation theory. The numerical simulations of the corresponding tightly focused field are conducted using the Richards-Wolf vectorial diffraction theory. The validity of the presented method is demonstrated through experimental generation of several designed pupil fields with a versatile vectorial optical field generator and characterization of the produced focused fields with Stokes parameter measurements.

Complete Control of Multichannel, Angle‐Multiplexed, and Arbitrary Spatially Varying Polarization Fields

AbstractIn recent years, much effort is dedicated to the generation of vectorial optical fields with an arbitrary spatially varying polarization distribution by means of metasurfaces. However, simultaneous and independent control of the amplitude, phase, and polarization is still challenging, especially for the multichannel generation of a vectorial optical field with an angle‐multiplexed functionality. Here, a facile route, called coherent pixel polarization metaholography, is proposed to realize multichannel, angle‐multiplexed, and arbitrary spatially varying polarization fields and demonstrate how to enable a fully independent realization of full Poincaré beams (lemon, start, spider, and web beams), dual‐way switching print images, vectorial print images, and optical polarization knot profiles. Importantly, the demonstrated angle‐multiplexed metasurfaces have an independently controllable handedness and azimuth and can possess up to four channels. Such angle‐multiplexed multichannel arbitrary spatial polarization fields may enable various applications, including optical dynamic displays, information communication, optical encryption, and quantum experiments.

Nonlinear frequency conversion of vectorial optical fields with a Mach-Zehnder interferometer

Vectorial optical fields with inhomogeneous polarization states have attracted great interest for their unique properties in both quantum and classical physics. In this paper, we propose a method to realize such nonlinear frequency conversion of the vectorial optical fields, which is by using a Mach–Zehnder interferometer. The separated arms enable two nonlinear processes to simultaneously proceed in two vertical directions. In our experiment, nonlinear frequency conversion of fundamental frequency vectorial optical fields with topological charge l=3 is studied. To illustrate the flexibility of this method, Taiji and clover patterns with inhomogeneous polarization distribution are also generated at second harmonic wavelengths. This research proposes a more flexible method to realize nonlinear frequency conversion of the vectorial optical fields and may have potential applications in the generation of ultrafast vectorial optical fields.

Effective iterative method for accurate amplitude modulation in complex optical field generation

We experimentally demonstrate an iterative method for a vectorial optical field generator (VOF-Gen) to achieve accurate amplitude modulation in creating arbitrary complex beams. The method could converge rapidly in several steps and is effective to optimize the patterns applied to the liquid crystal spatial light modulators on a pixel-by-pixel basis to obtain arbitrary desired amplitude distribution. Meanwhile, this method could also mitigate the speckles caused by the defects of the optical components used in the VOF-Gen system and calibrate the wavefront related to the amplitude distribution. Several kinds of optical fields with different intensity distributions are successfully generated to verify the capability and versatility of the presented technique. This effective method may find many important applications in optical tweezers, microscopy, and unidirectional coupling.

Focus shaping and optical manipulation using highly focused second-order full Poincaré beam.

Generation of vectorial optical fields with arbitrary polarization distribution is of great interest in plenty of applications. In this work, we propose and experimentally demonstrate the generation of a second-order full Poincaré (FP) beam and its application in two-dimensional (2D) flattop beam shaping with spatially variant polarization under a high numerical aperture focusing condition. In addition, the force mechanism of the focal field with 2D flattop beam profile is numerically studied, demonstrating the feasibility to trap a dielectric Rayleigh particle in three-dimensional space. The results show that the additional degree of freedom provided by the FP beam allows one to control the spatial structure of polarization, to engineer the focusing field, and to tailor the optical force exerted on a dielectric Rayleigh particle. The findings reported in the work may find useful applications in laser micromachining, optical trapping, and optical assembly.

Demonstration of a vectorial optical field generator with adaptive close loop control.

We experimentally demonstrate a vectorial optical field generator (VOF-Gen) with an adaptive close loop control. The close loop control capability is illustrated with the calibration of polarization modulation of the system. To calibrate the polarization ratio modulation, we generate 45° linearly polarized beam and make it propagate through a linear analyzer whose transmission axis is orthogonal to the incident beam. For the retardation calibration, circularly polarized beam is employed and a circular polarization analyzer with the opposite chirality is placed in front of the CCD as the detector. In both cases, the close loop control automatically changes the value of the corresponding calibration parameters in the pre-set ranges to generate the phase patterns applied to the spatial light modulators and records the intensity distribution of the output beam by the CCD camera. The optimized calibration parameters are determined corresponding to the minimum total intensity in each case. Several typical kinds of vectorial optical beams are created with and without the obtained calibration parameters, and the full Stokes parameter measurements are carried out to quantitatively analyze the polarization distribution of the generated beams. The comparisons among these results clearly show that the obtained calibration parameters could remarkably improve the accuracy of the polarization modulation of the VOF-Gen, especially for generating elliptically polarized beam with large ellipticity, indicating the significance of the presented close loop in enhancing the performance of the VOF-Gen.

Tightly focused optical field with controllable photonic spin orientation.

The spin angular momentum of photons offers a robust, scalable and high-bandwidth toolbox for many promising applications based upon spin-controlled manipulations of light. In this work, we develop a method to achieve controllable photonic spin orientation within a diffraction limited optical focal spot produced by a high numerical aperture objective lens. The required pupil field is found analytically through reversing the radiation patterns from two electric dipoles located at the focal point of the lens with orthogonal oscillation directions and quadrature phase. The calculated pupil fields are experimentally generated with a vectorial optical field generator. The produced photonic spin orientations are quantitatively evaluated by their spin densities according to the tightly focused electric fields calculated by Richard-Wolf vectorial diffraction theory to demonstrate the validity and capability of the proposed technique.

Experimental generation of complex optical fields for diffraction limited optical focus with purely transverse spin angular momentum.

We demonstrate a method to generate complex optical fields at the pupil plane of a high numerical aperture (NA) objective lens for the creation of diffraction limited optical focus with purely transverse spin angular momentum. The complex optical fields are analytically deduced through reversing the radiated patterns from two electric dipoles, which are located at the focal point of the high NA lens and oscillate respectively in x- and z- directions with phase difference of π/2. The derived fields can be experimentally created with a vectorial optical field generator. Using the Richard-Wolf vectorial diffraction theory, the electric fields within the focal region are calculated to evaluate the intensities and polarization distributions of the tightly focused beams corresponding to both the theoretical and experimentally generated pupil fields and the results clearly demonstrate the validity of the proposed technique.

Precise transverse alignment of spatial light modulator sections for complex optical field generation.

Based on the properties of the dove prism and the Fourier optics approach, the coordinate relationships among four spatial light modulator (SLM) sections in a vectorial optical field generator are derived and experimentally verified. Taking the coordinate system of the first SLM section as a reference, the coordinate displacements between the first section and subsequent sections are determined via employing specially designed four-quadrant patterns, which enable the visualization of the degree of freedom controlled by each SLM section. A complex optical field could be accurately generated through combining the derived coordinate relationships and pre-compensation of the measured coordinate displacements. Several typical complex optical fields are experimentally generated to demonstrate the validity of the proposed transverse alignment method.

Engineering of cylindrical vector fields with a twisted nematic spatial light modulator

We demonstrate a technique for the generation of vectorial optical fields based on a single pass of light onto a reflective twisted nematic spatial light modulator (TN-SLM). Using a beam splitter and a quarter-wave plate, a polarization rotator is implemented. A curve of the behavior of this polarization rotator with the twisted nematic modulator in use proves a modulation up to 177 deg, making this setup suitable for engineering of cylindrical vector fields. A mathematical justification and an experimental demonstration of the generation of these beams and their quality are presented. The experimental results show that despite the presence of a small component of elliptical polarization, a twisted nematic modulator can be used to achieve local polarization control. A series of vector fields with variations of the parameters of topological charge, phase offset, and quadratic phase are engineered, analyzed with a linear polarizer, and captured. The proposed setup represents a simple approach for polarization manipulation using a TN-SLM and few optical elements, achieving polarization purity greater than 94%.

Synthesis of focused beam with controllable arbitrary homogeneous polarization using engineered vectorial optical fields.

The propagation and focusing properties of light beams continue to remain a research interest owning to their promising applications in physics, chemistry and biological sciences. One of the main challenges to these applications is the control of polarization distribution within the focal volume. In this work, we propose and experimentally demonstrate a method for generating a focused beam with arbitrary homogeneous polarization at any transverse plane. The required input field at the pupil plane of a high numerical aperture objective lens can be found analytically by solving an inverse problem with the Richard-Wolf vectorial diffraction method, and can be experimentally created with a vectorial optical field generator. Focused fields with various polarizations are successfully generated and verified using a Stokes parameter measurement to demonstrate the capability and versatility of proposed technique.

Creation of radially polarized optical fields with multiple controllable parameters using a vectorial optical field generator

A vectorial optical field generator (VOF-Gen) based on two reflective phase-only liquid crystal spatial light modulators enables the creation of an arbitrary optical complex field. In this work, the capabilities of the VOF-Gen in terms of manipulating the spatial distributions of phase, amplitude, and polarization are experimentally demonstrated by generating a radially polarized optical field consisted of five annular rings, the focusing properties of which are also numerically studied with vectorial diffraction theory. By carefully adjusting the relative amplitude and phase between the adjacent rings, an optical needle field with purely longitudinal polarization can be produced in the focal region of a high numerical aperture lens. The versatile method presented in this work can be easily extended to the generation of a vectorial optical field with any desired complex distributions.

Generation of vectorial optical fields with slot-antenna-based metasurface.

A transmission-type metasurface composed of carefully designed rectangular slot antennas for the generation of vectorial optical fields is proposed and demonstrated. Acting as local linear polarizers, these slot antennas enable the spatial modulation of optical fields in amplitude, phase, and polarization for the cross-polarized component of the scattered field. As an illustration, a metasurface capable of forming a radially polarized scattered field with specific vectorial beam patterns with appropriate excitation at normal incidence is designed, fabricated, and tested. The radially polarized scattered field is designed to be further tightly focused by a high numerical aperture objective lens in order to obtain a uniform longitudinally polarized optical needle field along the propagation direction. Characterization experiments demonstrate that its overall extinction ratio satisfies the amplitude modulation requirement, and a corresponding π phase modulation is realized as proposed.

Manipulation of dielectric Rayleigh particles using highly focused elliptically polarized vector fields.

Generation of vectorial optical fields with arbitrary polarization distribution is of great interest in areas where exotic optical fields are desired. In this work, we experimentally demonstrate the versatile generation of linearly polarized vector fields, elliptically polarized vector fields, and circularly polarized vortex beams through introducing attenuators in a common-path interferometer. By means of Richards-Wolf vectorial diffraction method, the characteristics of the highly focused elliptically polarized vector fields are studied. The optical force and torque on a dielectric Rayleigh particle produced by these tightly focused vector fields are calculated and exploited for the stable trapping of dielectric Rayleigh particles. It is shown that the additional degree of freedom provided by the elliptically polarized vector field allows one to control the spatial structure of polarization, to engineer the focusing field, and to tailor the optical force and torque on a dielectric Rayleigh particle.

Design and alignment strategies of 4f systems used in the vectorial optical field generator.

In this paper, the design and alignment strategies of 4f systems used in the vectorial optical field generator are described in detail. Reflection-type 4f systems were adopted due to limited spacing. Alignment patterns are designed and introduced as alignment tools so that the optical property (degree of freedom) controlled by each specific spatial light modulator section can be visualized and alignment of the 4f systems can be performed using the CCD image sharpness as the metric. In particular, blurring due to diffraction effects is minimized when the 4f system is fully aligned.