Radial Polarization Converter Research Articles

Broadband devices for a polarization converter based on optical metasurfaces.

Devices employed for optical polarization conversion are widely used in the areas of optical focusing, optical imaging, and microscopy. To circumvent the problems of traditional optical polarization conversion devices, such as a narrow bandwidth, bulky size, and integration difficulties, a linear-radial polarization converter (LRPC) method based on optical metasurfaces is proposed. For a visible wavelength, i.e., λ=632.8nm, an all-dielectric half-wave plate and a LRPC with a size of 40λ (25.312 µm) are designed. The simulated results demonstrate that the LRPC creates a radially polarized wave from a linearly polarized wave in the wavelength range of 620-680 nm. In addition, a cylindrical vectorial wave with different polarizations can be generated via an adjustment of the polarization direction of the incident wave. These types of polarization converters have the important advantage of high transmittance, while also being ultra-thin and easy to integrate. They are expected to be suitable for miniaturized and integrated optical devices.

Super cosh-Gauss nonuniformly correlated radially polarized beam and its propagation characteristics.

In this paper, a new kind of partially coherent vector beam termed as super cosh-Gauss nonuniformly correlated radially polarized (SCNRP) beam is introduced. Such beam source exhibits almost perfect coherence between two points that are within the beam center region or located on a ring concentric with the beam center. However, the coherence drops or even vanishes when the two points leave the central region and are located on the concentric rings with different radii. The second-order statistical properties, such as the spectral density, the state of polarization (SOP), and the degree of polarization (DOP) of such beam upon free-space propagation are studied through numerical examples. Our results reveal that the beam displays a self-focusing property during propagation. The focusing ability can be enhanced with increasing the beam index and decreasing the beam's spatial coherence width, whereas the DOP and SOP remain unchanged on propagation. Meanwhile, we establish an experimental system with the use of a radial polarization converter and a digital micro-mirror device to synthesize the SCNRP beam with controllable beam index and spatial coherence width. The spectral density and polarization properties of the synthesized beam during propagation are measured and analyzed in the experiment. The experimental results agree well with our theoretical predictions.

Creation of cylindrical vector beams through highly anisotropic scattering media with a single scalar transmission matrix calibration

Cylindrical vector (CV) beams have attracted increasing interest due to their particular properties and their applications in optical imaging, optical manipulation, and light–matter interactions. However, it is challenging to construct CV beams through highly anisotropic scattering media (HASM), such as thick biological tissue, posing a barrier to the applications of CV beams that involve HASM. Here, we present a scheme to construct CV beams beyond high scattering that only requires a single scalar transmission matrix (TM) calibration and manipulation of the spatial degrees of freedom of the scalar input field. Assisted by a radial polarization converter (S-waveplate) and a polarizer, the scheme enables one to obtain the correct incident wavefront for the creation of CV beams through HASM with only one single scalar TM calibration. Compared to the existing method, this user-friendly approach is fast and simple in terms of the optical implements and computations. Both radially and azimuthally polarized beams are experimentally constructed through a ZnO scattering layer to demonstrate the viability of the method. Arbitrarily generalized CV beams and arrays of CV beams are also created through the HASM to further prove the flexibility of the method. We believe this work may pave the way for applications of CV beams that involve a highly anisotropic scattering environment.

Design and Fabrication of a Holographic Radial Polarization Converter

Radial polarization converters can convert an incident light into a radially polarized light, which is beneficial in a variety of applications. In this paper, a new design of holographic radial polarization converter is proposed which consists of eight space-variant polarization-selective volume hologram gratings. According to the coupled wave theory, a feasible design of the polarization-selective volume hologram gratings was described. The prism-hologram-prism sandwiched recording method was adopted for the recording. The s- and p-polarization diffraction efficiencies of the fabricated polarization-selective volume hologram gratings at 443.29 nm are 90.83% and 22.09%, respectively. The operation bandwidth is about 4.42 nm. A prototype of holographic radial polarization converter was successfully assembled and tested. Due to the introduction of volume hologram gratings, this design should have the advantages of high diffraction efficiency, narrow band, compactness, and planar configuration, meaning it is especially suitable for low-cost mass production and has high application potential in related fields.

Classical analog of quantum contextuality in spin-orbit laser modes

We experimentally observed the violation of Kujula-Dzhafarov noncontextuality inequalities by non-separable spin-orbit laser modes. Qubits are encoded on polarization and transverse modes of an intense laser beam. A spin-orbit non-separable mode was produced by means of a radial polarization converter (S-plate). The results show that contextuality can be investigated by using spin-orbit modes in a simple way, corroborating recent works stating that such system can emulate single-photon experiments. Additionally, an improvement in the non-separable mode preparation allowed us to observe a greater violation of the Clauser-Horne-Shimony-Holt inequality for such system. The results are in very good agreement with the theoretical predictions of quantum mechanics.

Liquid switchable radial polarization converters made of sculptured thin films

A radial polarization converter is a super-structured optical retarder that converts a conventional linearly polarized light beam into a structured beam with radial or azimuthal polarization. We present a new type of these sophisticated optical elements, which is made of porous nanostructured sculptured single thin films or multilayers prepared by physical vapor deposition at an oblique angle. They are bestowed with an axisymmetric retardation activity (with the fast axis in a radial configuration). In particular, a Bragg microcavity multilayer that exhibits a tunable transmission peak in the visible range with a retardance of up to 0.35 rad has been fabricated using this methodology. Owing to the highly porous structure of this type of thin films and multilayers, their retardance could be switched off by liquid infiltration. These results prove the possibility of developing wavelength dependent (through multilayer optical design) and switchable (through vapor condensation or liquid infiltration within the pore structure) radial polarization converters by means of oblique angle physical vapor deposition.

Radially polarized multi-Gaussian Schell-model beam and its tight focusing properties

In this paper, we introduce a new kind of vector multi-Gaussian Schell-model (MGSM) beam named radially polarized MGSM beam as an extension of recently introduced scalar MGSM beam [Opt. Lett.37, 2970 (2012)], and we obtain the realizability conditions of such beam. The tight focusing properties of a radially polarized MGSM beam passing through a high numerical aperture objective lens are investigated numerically based on the vectorial diffraction theory. It is interesting to find that the intensity distributions of both transverse and longitudinal fields near the focus display flat-top beam profiles due to the special correlation functions of the incident beam. Our results clearly show that engineering the structures of the correlation functions of a radially polarized partially coherent beam provides a novel way for shaping both transverse and longitudinal fields distributions, which have potential applications in particle acceleration and laser machining. Finally, we report experimental generation of a radially polarized MGSM beam with the help of a spatial light modulator and a radial polarization converter.

Converting State of Polarization With a Miniaturized Metasurface Device

We have designed and experimentally demonstrated a radial and azimuthal polarization converter, which is a plasmonic metasurface with a radius of not more than $5~\mu \text{m}$ . The metasurface is composed of an array of metal–insulator–metal gap plasmon resonators, each of which reflects the incident local electric field to a predesignated polarization angle. The simulation results show effective polarization conversion within a broad band from 700 to 930 nm.

Formation of second order optical vortices with a radial polarization converter using the double-pass technique

In this paper we both theoretically and experimentally demonstrate possibility to form double charged optical vortex using only one S-waveplate in double-pass geometry. The experimental results are presented as well as analysis of underlying theoretical principles.

Generation of cylindrically polarized vector vortex beams with digital micromirror device

We propose a novel technique to directly transform a linearly polarized Gaussian beam into vector-vortex beams with various spatial patterns. Full high-quality control of amplitude and phase is implemented via a Digital Micro-mirror Device (DMD) binary holography for generating Laguerre-Gaussian, Bessel-Gaussian, and helical Mathieu–Gaussian modes, while a radial polarization converter (S-waveplate) is employed to effectively convert the optical vortices into cylindrically polarized vortex beams. Additionally, the generated vector-vortex beams maintain their polarization symmetry after arbitrary polarization manipulation. Due to the high frame rates of DMD, rapid switching among a series of vector modes carrying different orbital angular momenta paves the way for optical microscopy, trapping, and communication.

Generation and self-healing of a radially polarized Bessel-Gauss beam

We report experimental generation of a radially polarized Bessel-Gauss (RPBG) beam of order 1 with the help of a spatial light modulator, a spiral phase plate, and a radial polarization converter. Furthermore, we carry out a comparative study of the self-healing properties of a RPBG beam and a linearly polarized Bessel-Gauss (LPBG) beam which are blocked by a sector-shaped opaque obstacle both experimentally and numerically. Our results clearly show that the self-healing ability of a RPBG beam indeed is superior to that of a LPBG beam, and some physical interpretations are given. Our results will be useful for particle trapping and microscopy.

Enhanced Scattered Light Imaging of Nanoparticles by Controlling the Polarization Distribution with Photonic Crystals

An optical microscopy with a high sensitivity and resolution is required for observing semiconductor wafers and biological cells for nanotechnology and biotechnology applications. However, it is difficult to observe samples that are small compared with the optical wavelength since the signal is swamped by background noise such as dark noise and electrical noise and other signals besides that from the sample. Furthermore, light scattered from the sample cannot be focused into a spot in the image plane due to interference of polarized light, resulting in a blurred image that has a low resolution. This study proposes a method for removing the background noise and for improving the image resolution of nanoparticles by controlling the polarization direction. This method can be used to perform optical microscopy with a high sensitivity and resolution. We verify the effectiveness of this method by performing simulations and experiments. Simulations predict that the peak intensity obtained using this method will be 3.4 times higher than that obtained using a conventional microscope and that the resolution of this technique will be 0.43 times smaller than that of conventional microscopy. Experiments show that this method with a photonic crystal utilized as a radial polarization converter is capable of detecting 23-nm-diameter PSLs on a silicon wafer.

Ultrasmall radial polarizer array based on patterned plasmonic nanoslits

We developed an ultrasmall radial or azimuthal polarization converter of size ranged from 10 to 100 μm. The converter consists of a half-wave plate divided into four quadrants, each of which is made of periodic gold nanoslits at different orientations in steps of 45°. The converter and its array were fabricated and followed by an evaluation with the Sénarmont method and the polarization microscopy. Due to the giant birefringence of the gold nanoslits, each slit segment achieved 180° retardation at the wavelength of 633 nm, and the conversion from linear to radial polarization was demonstrated.

Experimental generation of a radially polarized beam with controllable spatial coherence

We have experimentally generated a radially polarized (RP) beam with controllable state of spatial coherence by using a rotating ground-glass plate and a radial polarization converter. Furthermore, experimental and theoretical analysis of the focusing properties of a partially coherent RP beam is carried out. Our results show that we can shape the beam profile of the focused RP beam by varying its initial spatial coherence, which is useful for material thermal processing and particle trapping. The experimental results are in complete agreement with the theoretical predictions.

径向偏振无衍射光束的产生及其传输特性研究

In this paper,we theoretically and experimentally investigate the properties of radially polarized non-diffracting beam.The propagation properties of the radially polarized non-diffracting beam are theoretically simulated.It is shown that the radially polarized non-diffracting beams possess both the radial polarization and non-diffracting characteristics.The radially polarized non-diffracting beam is experimentally generated by a Gaussian beam passing through a radial polarization converter and then focused by an axicon.The dependence of the intensity distribution of radially polarized non-diffracting beam on the polarization angle of the polarizer is experimentally observed,showing good agreement with the theoretical results.The beams with both the radial polarization and non-diffracting properties have many important potential applications.

Microdrilling in steel using ultrashort pulsed laser beams with radial and azimuthal polarization

A linear to radial and/or azimuthal polarization converter (LRAC) has been inserted into the beam delivery of a micromachining station equipped with a picosecond laser system. Percussion drilling and helical drilling in steel have been performed using radially as well as azimuthally polarized infrared radiation at 1030 nm. The presented machining results are discussed on the basis of numerical simulations of the polarization-dependent beam propagation inside the fabricated capillaries.

3-dimensional local field polarization vector mapping of a focused radially polarized beam using gold nanoparticle functionalized tips

We have measured local electric field polarization vectors in 3-dimensional space on the nanoscale. A radial polarized light is generated by using a radial polarization converter and focused by an objective lens. Gold nanoparticle functionalized tips are used to scatter the focused field into the far-field region. Two different methods, rotational analyzer ellipsometry and Stokes parameters, are used in determining the polarization state of the scattered light. Two methods give consistent results with each other. Three dimensional local polarization vectors could be reconstructed by applying back transformation of the fully characterized polarizability tensor of the tip.