Pancharatnam-Berry Phase Optical Elements Research Articles

Chromatic aberration measurement of liquid crystal Pancharatnam Berry phase lens by a RGB full-Stokes imaging polarimeter

Pancharatnam Berry (PB) phase optical elements can manipulate local polarization state of light in the cross-sectional plane by addressing an additional PB phase relating to the orientation of the optical axis of the waveplate-like structure. However, chromatic aberration including spectrum-dependent retardation and diffraction efficiency limits their applications in the field of visible broadband imaging and display. In this article, the chromatic aberration of a liquid crystal (LC) PB phase lens was measured by a home-built RGB full-Stokes imaging polarimeter. The chirality conversion efficiency and depolarization at RGB wavelengths can be calculated from the measured Stokes vectors. Our experiments show that even the spectrum-dependent retardation exists, the measured PB phase lens has a uniform and high diffraction efficiency in the visible band. Affected by the local LC molecule, the input polarization of RGB light was rotated in varying degrees, but the focusing or defocusing manipulation to the right- or left-hand circular polarization, originated from the PB phase, results in fixed focal lengths for different colors. Our experiments show that the LC-based PB phase lens is suitable for the visible broadband applications.

Scalar vortex beams produced by Pancharatnam-Berry phase optical elements that utilize polarization holography.

We discuss the appearance of the Pancharatnam-Berry phase in polarization holography, and confirm the possibility of generating scalar vortex beams by using the Pancharatnam-Berry phase. The polarization holograms used to generate scalar vortex beams are produced in phenanthrenequinone-doped polymethylmethacrylate (PQ/PMMA), where each radial direction consists of an equivalent half-wave plate hologram with gradually changing directions. The spin angular momentum carried by a circular polarization reading wave is converted into orbital angular momentum in a reconstruction process, resulting in the formation of scalar vortex beams with positive and negative topological charges controlled by the reading polarization.

Widely Tunable Narrow Linewidth Dual-Wavelength Yb-Doped Fiber Laser With Inhomogeneous Polarization Output

We demonstrate a widely tunable narrow linewidth dual-wavelength Yb-doped fiber laser with switchable inhomogeneous polarization output based on the Pancharatnam-Berry phase optical elements and volume Bragg grating experimentally. By rotating the Glan laser polarizer, we can obtain the switchable radially and azimuthally polarized beam with tunable wavelength separation ranging from 0.4 nm to 68.2 nm. The delivered spectrum shows excellent stability and linewidth narrower than 0.08 nm. Moreover, the polarization extinction ratio of the radially and azimuthally polarized beam can reach 94.2% and 93.6%, respectively. This tunable narrow linewidth dual-wavelength laser could enrich the manipulation potential of the fiber laser, and would benefit many applications like THz wave generation.

Optically imprinted polarization gratings with a twisted nematic liquid crystal as a photomask

Liquid crystal Pancharatnam–Berry phase optical elements (LCPBOEs) are becoming increasingly attractive elements to be used to enhance near-eye displays or manipulate light beams, owing to their flatness and circular polarization-dependent behavior. The optical imprinting technique that is one of the commonly used methods for fabricating LCPBOEs is considered to be the most promising technique for mass production at a low cost, but the design of the photomask must be improved. In this work, a photomask that is based on a twisted nematic liquid crystal polarization grating (TNLCPG) cell, acting as a broadband linear polarization rotator, is designed. This TNLCPG cell, with a predefined alignment profile of a polarization grating, can convert linearly polarized light into a light field with spatially varying linear polarization and exhibits broadband operation over the entire visible spectrum. The designed TNLCPG photomask is used to demonstrate a liquid crystal polarization grating (LCPG) film using a white flashlight as a writing source. A high diffraction efficiency of greater than 95% is obtained. With its simple design and fabrication, the proposed TNLC-based photomask can potentially be used in the fabrication of LCPBOEs.

Voltage-controlled liquid crystal Pancharatnam-Berry phase lens with broadband operation and high photo-stability.

Pancharatnam-Berry phase optical elements (PBOEs) have received much attention due to their ability to generate complex structured light or to manipulate the shape of a light beam. This work demonstrates a tunable liquid crystal (LC) Pancharatnam-Berry (LCPB) lens using a simple and cost-effective PB phase hologram optical setup and thermal polymerization to form an irreversible photo-patterning alignment layer. The LCPB lens with high photo-stability supports ultra-broadband operation and provides a diffraction efficiency of ∼90% throughout the visible spectral range, achieved by applying the appropriate voltages. The LCPB lens functions as a convex or a concave lens, depending on the handedness of the circularly polarized incident light, so its image reduction and magnification functions are demonstrated, and its photo-stability is characterized. The fabrication of the proposed LC PBOEs is simpler and more cost-effective than previous methods, and the irreversible photo-patterning alignment layer that is formed by thermal polymerization allows larger operational bandwidths, supporting new applications.

Photo-Aligned Ferroelectric Liquid Crystal Devices with Novel Electro-Optic Characteristics

This paper examines different applications of ferroelectric liquid crystal devices based on photo-alignment. Successful application of the photo-alignment technique is considered to be a critical breakthrough. A variety of display and photonic devices with azo dye aligned ferroelectric liquid crystals is presented: smart glasses, liquid crystal Pancharatnam–Berry phase optical elements, 2D/3D switchable lenses, and laser therapy devices. Comparison of electro-optical behavior of ferroelectric liquid crystals is described considering the performance of devices. This paper facilitates the optimization of device design, and broadens the possible applications in the display and photonic area.

Cylindrical vector beam generator using a two-element interferometer

We realize a robust and compact cylindrical vector beam generator that consists of a simple two-element interferometer composed of a beam displacer and a cube beamsplitter. The interferometer operates on the higher-order Poincaré sphere transforming a homogeneously polarized vortex into a cylindrical vector (CV) beam. We experimentally demonstrate the transformation of a single vortex beam into all the well-known CV beams and show the operations on the higher-order Poincaré sphere according to the control parameters. Our method offers an alternative to the Pancharatnam-Berry phase optical elements and has the potential to be implemented as a monolithic device.

Fast-response Pancharatnam-Berry phase optical elements based on polymer-stabilized liquid crystal.

In this paper we demonstrate fast-response Pancharatnam-Berry (PB) phase optical elements (PBOEs) based on polymer-stabilized liquid crystal (PSLC). First, a non-interferometric photo-alignment technique is employed to generate PB patterns in a dye-doped liquid crystal by green laser light. Then the samples are exposed to UV light to form polymer networks. Due to the greatly increased elastic constant in PSLC, all PBOEs can achieve submillisecond response time, while maintaining high diffraction efficiency (>90%). Furthermore, a varifocus PB lens (PBL) is implemented based on two identical PB lens elements and its application in fatigue free augmented-reality (AR) displays is verified. The fast response PBOEs based on PSLC hold great potential for various display and photonics applications.

49‐2: Distinguished Student Paper: High‐Efficiency Switchable Optical Elements for Advanced Head‐up Displays

The Pancharatnam‐Berry phase optical elements (PBOEs) are utilized to enhance the performance of head‐up displays (HUDs). The PB lenses provide varifocal functionality, while the PB deflectors can function as optical combiners and waveguide couplers. Rigorous coupled wave analysis based on scattering matrix is also developed and applied for structure optimization.

Pancharatnam–Berry optical elements for head-up and near-eye displays [Invited

Liquid-crystal-based Pancharatnam–Berry phase optical elements (PBOEs), also known as diffractive wave plates (DWPs), geometric phase optics (GPO), or geometric phase holograms (GPHs), are functional planar structures with patterned orientation of anisotropy axis. Several scientifically interesting yet practically useful electro-optical effects, such as focusing, beam splitting, waveguide coupling, and wavelength filtering, have been realized with PBOEs. Because of the high degree of optical tunability, polarization selectivity, nearly 100% diffraction efficiency, and simple fabrication process, PBOEs have found widespread applications in emerging display systems, particularly virtual/augmented/mixed reality displays and head-up displays. In this review, we will describe the basic operation principles, present device fabrication procedures, discuss numerical modeling methods, and address applications of PBOEs in emerging display systems.

Fabrication of Pancharatnam-Berry phase optical elements with highly stable polarization holography.

Polarization-dependent diffraction based on Pancharatnam-Berry phase optical elements (PBOEs) offers considerable benefits compared to conventional metasurfaces, such as negligible absorption, nearly 100% diffraction efficiency and an inexpensive fabrication process. Polarization holography is a simple way to fabricate PBOEs, which entails the interference of beams with different polarizations to generate a spatial-varying polarization field. Thus, the quality of recorded PBOEs manifests high sensitivity to the length change and phase shift between polarized beams, usually caused by environmental vibration and air flow. Here, new polarization holography based on modified Sagnac interferometry is developed for fabricating liquid crystal-based PB gratings and lenses, where the pitch of grating and optical power of lens could be easily tuned. This approach offers high tolerance to environmental disturbance during the exposure process. Detailed design parameters are analyzed, and the fabricated PBOEs with high optical quality are also demonstrated.

High numerical aperture multifocal metalens based on Pancharatnam-Berry phase optical elements.

A high numerical aperture multifocal metalens was proposed based on well-designed Pancharatnam-Berry phase optical elements. Both circularly and linearly polarized incident lights could be tightly focused into diffraction-limited focal spots. Right and left circularly polarized focal spots could be realized simultaneously by illuminating a linearly polarized beam. The highest numerical aperture reached to 0.84 with full width at half-maximum of 263nm. Moreover, we also presented a metalens whose optical elements are hybrid arranged and the metalens can realize spin-independent focusing with a numerical aperture of 0.8. The presented metalens has significant potential applications in particles manipulation and high-resolution imaging.

Structured light generation by magnetic metamaterial half-wave plates at visible wavelength

Metamaterial or metasurface unit cells functioning as half-wave plates play an essential role for realizing ideal Pancharatnam–Berry phase optical elements capable of tailoring light phase and polarization as desired. Complex light beam manipulation through these metamaterials or metasurfaces unveils new dimensions of light–matter interactions for many advances in diffraction engineering, beam shaping, structuring light, and holography. However, the realization of metamaterial or metasurface half-wave plates in visible spectrum range is still challenging mainly due to its specific requirements of strong phase anisotropy with amplitude isotropy in subwavelength scale. Here, we propose magnetic metamaterial structures which can simultaneously exploit the electric field and magnetic field of light for achieving the nanoscale half-wave plates at visible wavelength. We design and demonstrate the magnetic metamaterial half-wave plates in linear grating patterns with high polarization conversion purity in a deep subwavelength thickness. Then, we characterize the equivalent magnetic metamaterial half-wave plates in cylindrical coordinate as concentric-ring grating patterns, which act like an azimuthal half-wave plate and accordingly exhibit spatially inhomogeneous polarization and phase manipulations including spin-to-orbital angular momentum conversion and vector beam generation. Our results show potentials for realizing on-chip beam converters, compact holograms, and many other metamaterial devices for structured light beam generation, polarization control, and wavefront manipulation.

Recent progress in Pancharatnam–Berry phase optical elements and the applications for virtual/augmented realities

AbstractIn this review paper,we report recent progress on Pancharatnam-Berry (PB) phase optical elements, such as lens, grating, and deflector. PB lenses exhibit a fast switching time between two or more focal lengths with large diopter change and aperture size, which is particularly attractive for addressing the accommodation mismatch in head-mounted display devices. On the other hand, PB gratings and deflectors offer a large-angle beam deflection with wide acceptance cone and high efficiency, as compared to conventional volume gratings. Such merits provide great advantages for waveguide-coupling augmented reality headsets. Moreover, the thickness of PB optical elements is only a few micrometers, thus they can be conveniently integrated into modern wearable display systems.

Wavelength-locked vectorial fiber laser manipulated by Pancharatnam-Berry phase.

We report a wavelength-locked cladding-pumped ytterbium-doped fiber laser that can simultaneously emit radially and azimuthally polarized beams based on Pancharatnam-Berry phase optical elements. Multi-wavelength free running operation of the radially and azimuthally polarized laser beams can be switched to a single-wavelength one assisted by volume Bragg grating, with wavelength locked at around 1053.4 nm and spectral linewidth of 0.06 nm (FWHW). By rotating the glan-taylor polarizer, we can obtain switchable radially and azimuthally polarized beams output. The radially and azimuthally polarized beams mode purity can maintain 97.3% and 96.3% at maximum output power, and the polarization extinction ratio (PER) can reach 97.8% and 95.9% for the radially and azimuthally polarized laser, respectively.

Generation of Helical Modes of Light by Spin-to-Orbital Angular Momentum Conversion in Inhomogeneous Liquid Crystals

The helical modes of an electromagnetic wave are characterized by a helical shape of the wavefront. They carry quantized angular momentum of an orbital kind, as opposed to the spin-like angular momentum that can be associated with circularly polarized waves. Here, I review recent results on a novel method for generating helical waves of light by letting a circularly-polarized non-helical wave pass through an azimuthally inhomogeneous birefringent plate made of a suitably patterned liquid crystal, a device dubbed “q-plate”. The q-plate converts the variation of spin angular momentum associated with the switching of light polarization handedness into orbital angular momentum, an optical process that had not been envisioned before. Generalizing this idea, patterned birefringent plates similar to q-plates may be used for shaping the optical wavefront of a circularly polarized beam in any prescribed way. Moreover, these plates allow fast switching between conjugate wavefronts by inverting the handedness of the input polarization. Devices based on this principle have been called Pancharatnam-Berry phase optical elements.

Ladder operators formalism for optical angular momentum transfer and space-variant Pancharatnam-Berry phase

Ladder operators are introduced in SU(2) parameter space to analyze the space-variant Pancharatnam-Berry (PB) phase. The spin and orbital angular momentum transfers to a wave passing through the PB phase optical elements are understood in terms of the PB phase. Space-variant PB phase structures are identified in polarization grating and cholesteric liquid crystal, providing an explanation for the beam propagation direction alteration. A simultaneous occurrence of the wavefront shaping and the beam propagation direction alteration is demonstrated experimentally.

Polychromatic vectorial vortex formed by geometric phase elements

We propose the use of a geometric phase, obtained by spatial polarization state manipulations, for the formation of polychromatic vectorial vortices. Experimental demonstration is obtained by using Pancharatnam-Berry phase optical elements formed by a space-variant subwavelength grating etched on a GaAs wafer. We further demonstrate formation of scalar and unpolarized polychromatic vortices.

Vectorial vortex mode transformation for a hollow waveguide using Pancharatnam-Berry phase optical elements

Transformation and inverse transformation between a free-space linearly polarized beam and the vectorial vortex mode of a circular hollow waveguide by use of Pancharatnam-Berry phase optical elements is proposed. Demonstration was achieved by fabricating GaAs subwavelength gratings and utilizing a 300 microm diameter hollow metallic waveguide for 10.6 microm wavelength CO(2) laser radiation. The mode transformations and the excitation of a single vectorial mode inside the hollow waveguide were verified by full polarization measurements. In addition, the inverse mode transformation of the single vectorial mode excitation in the waveguide enabled us to experimentally obtain a linearly polarized bright spot with a high central lobe.

Propagation-invariant vectorial Bessel beams obtained by use of quantized Pancharatnam-Berry phase optical elements.

Propagation-invariant vectorial Bessel beams with linearly polarized axial symmetry based on quantized Pancharatnam-Berry phase optical elements are described. The geometric phase is formed through the use of discrete computer-generated space-variant subwavelength dielectric gratings. We have verified the polarization properties of our elements for laser radiation at 10.6-microm wavelength and also demonstrated propagation-invariant, controlled rotation of a propeller-shaped intensity pattern through the simple rotation of a polarizer.