Geometric Phase Elements Research Articles

Advanced Transparent Glass‐Ceramics via Laser Anisotropic Nanocrystallization

AbstractTransparent glass‐ceramics, merging the attributes of both glass and ceramics, have diverse applications in ballistic protection, armor materials, dentistry, light‐emitting diode, and optical domains. A limitation of conventional methods for glass‐ceramic fabrication is their inadequacy in precisely controlling the morphology of crystallization, consequently constraining their prospective advancements in diverse areas. Here, a method that facilitates precise control over the formation and growth of polarization‐dependent nonperiodic anisotropic nanocrystals, with a short axis ranging from 15 to 280 nm, in Li2O‐Al2O3‐SiO2 (LAS) glass is proposed. The method utilizes the principles of near‐field anisotropy between light and matter, building upon the classical nucleation‐growth model of glass crystallization. Notably, the glass‐ceramics possessing laser‐induced nanocrystals within the Rayleigh size regime showcase an impressive 99.7% transmittance in the visible and near‐infrared wavelengths. Additionally, the glass‐ceramics with non‐periodic anisotropic nanocrystals macroscopically exhibit form‐birefringence properties, thus enabling transparent optical applications, such as polarization elements, geometric phase elements, and multi‐dimensional optical data storage. This work opens up new avenues for morphological manipulation of nanocrystallization, with potential applications in optics, nanophotonics, functional glass‐ceramics, and high mechanical performance devices.

Development and Application of Liquid Crystal Geometric Phase Elements for Display Systems

Development and Application of Liquid Crystal Geometric Phase Elements for Display Systems

Large aperture and defect-free liquid crystal planar optics enabled by high-throughput pulsed polarization patterning.

The liquid crystal (LC) geometrical phase optics, which is realized by the high-resolution control of the optical axis orientation in transparent micrometer-thin polymer films, is emerging as a next generation of planar optics. It features pronounced optical properties and stimuli-responsive behaviors, which could introduce appealing and new possibilities for photonic purposes. The development of fabrication techniques producing elements with large aperture sizes and arbitrarily varying molecular orientation is of significance in terms of practical utility. Here, we propose the pulsed polarization patterning technique to create large-aperture and defect-free LC geometrical phase elements. We investigated the capability of the azo photo-alignment material responding to nanosecond laser pulses and the corresponding anchoring behaviors to LCs. The threshold was reduced to one fourth of that under the continuous wave recording. The patterning resolution was found to be enhanced to around 0.71 µm, due to the ultra-fast interaction nature of the photo-alignment material with the polarized light field. We proposed the flying exposure mode to deliver high frequency modulated polarized laser pulses (8 kHz), with the precision stage moving in a uniform velocity for light-field stitching and the servo auto-focusing in the sample normal, enabling the stable and reliable polarization patterning for large aperture sizes. We further report on representative fabrication of LC polarization gratings with an aperture of 4 inch and 99.2% average diffraction efficiency.

Generation of Vector Vortex Beams Based on the Optical Integration of Dynamic Phase and Geometric Phase

The phase and polarization of electromagnetic waves can be conveniently manipulated by the dynamic phase and geometric phase elements. Here, we propose a compact optical integration of dynamic phase and geometric phase to generate arbitrary vector vortex beams on a hybrid-order Poincaré sphere. Two different technologies have been applied to integrate dynamic and geometric phase elements into a single glass plate to modulate the phase and polarization of light simultaneously. A spiral phase structure is made on one side of a glass substrate with optical lithography and a geometric phase metasurface structure is designed on the other side by femtosecond laser writing. The vector polarization is realized by the metasurface structure, while the vortex phase is generated by the spiral phase plate. Therefore, any desirable vector vortex beams on the hybrid-order Poincaré sphere can be generated. We believe that our scheme may have potential applications in future integrated optical devices for the generation of vector vortex beams due to its the high transmission efficiency and conversion efficiency.

Electromagnetic radiation focusing lens based on phase transition all-dielectric microstructure

Metasurface can adjust the polarization, amplitude, phase, polarization mode, and propagation mode of electromagnetic waves flexibly and efficiently. Based on Pancharatnam–Berry phase theory, an all-medium geometric phase element structure was proposed to construct a transmission-coded metasurface metalens. In the mid-infrared band, a phase change material (GST) is used to regulate the unit structure in order to achieve the tunability of lens focus. In order to prove that the designed hyperlens has a good focusing effect, we numerically simulate the focusing electromagnetic field distribution characteristics, and the results show that the designed geometric phase hyperlens has a good focusing effect. Using the crystal and amorphous states of phase change materials, we can dynamically control the focus of the superlens.

Multi-tasking geometric phase element array based self-referenced vortex interferometer for three-dimensional topography.

Interferometry is a basic physical method to record and reconstruct the three-dimensional (3D) topography of a complex object. However, mainstream interferometers using two beams can be unstable in a volatile environment. Here, we present a self-referenced optical vortex interferometer employing multi-tasking geometric phase elements. Compared with conventional devices, the multitasking elements can enable vortex filters while deflecting the interference beams to achieve high mode purity in broadband. We use the proposed system to reconstruct the 3D topography of a sample while determining its surface elevations and depressions accurately and conveniently in one static interference pattern.

Broadband real-time full-stokes polarimetry by multi-tasking geometric phase element array

Polarization is a fundamental physical dimension of electromagnetic waves. However, experimental determination of polarization states of light is inherently challenging and inconvenient due to the loss of phase information in conventional optical characterization. In particular, the Stokes parameters are a critical indicator to fully describe arbitrary polarization state, which, however, require multiple intensity measurements in three orthogonal polarization bases. Here, we design and experimentally demonstrate a multi-tasking geometric phase element array to unveil all Stokes parameters in one shot. Such a method is convenient, broad-band, real-time with compact size to accurately characterize the complex polarization states of coherent light, which may find visionary applications in structured light microscopy, polarizable quantum computation, and communication, etc.

Spatially displaced and superposed Bessel beams for transparent material laser microprocessing

Invariant Bessel–Gauss beams have attracted great interest for transparent material microprocessing applications. The small central peak and elongated focal region of the zeroth-order Bessel–Gauss beam provide advantages in laser micromachining. However, many transparent material processing applications need asymmetric beams to induce directional cracking. Therefore, in this work, we investigate analytically, numerically, and experimentally a beam that was generated by spatially displaced axicon halves, which induces noncylindrical symmetry in the beam phase profile. Analytical solutions were found and verified experimentally. High power and quality beams were generated by writing a needed phase alteration of the beam with a geometric phase element. These beams were able to demonstrate applicability to micromachine processing of transparent material.

Azimuthally modulated axicon vortical beams for laser microprocessing

Non-diffracting beams have contributed greatly to recent developments in high power applications such as laser micromachining. Well known for their elongated focal region (also known as a focal line) are zeroth-order Bessel and Bessel vortical beams which allow achieving high aspect ratio modifications inside transparent materials. A superposition of several optical Bessel vortices of different topological charges allows generating high aspect ratio beams with complexly engineered transverse intensity patterns. Non-diffracting Bessel vortices commonly are created using a conical prism — an axicon. Therefore, they can be referred to as axicon beams. In this work, we have studied the formation of high power and energy axicon vortical beams both numerically and experimentally. We have inscribed sub-wavelength birefringent structures inside fused silica glass to create geometrical phase elements for the azimuthal modulation of the spatial spectra of a zeroth-order axicon (Bessel) beam which allows creating a high power superposition of several Bessel vortices. To prove the concept, we apply azimuthally modulated axicon vortical beams to create modifications inside fused silica glass samples.

33‐5: Fabrication Paths of Liquid‐Crystal Photonics for AR/VR Optical Systems

In this paper, we discuss different photo‐patterning paths for fabricating liquid crystal photonics devices, like geometric phase elements and polarization volume holograms for augmented reality and virtual reality (AR/VR) optical systems. We review the viability of typical photo‐patterning methods for small‐quantity research purposes, with a focus on direct write and interference recording. We present detailed comparisons between direct duplication and projection duplication, with recommendations for cost‐ and time‐efficient manufacturing paths.

Multifunctional metalens generation using bilayer all-dielectric metasurfaces.

Optical metasurfaces exhibit unprecedented ability in light field control due to their ability to locally change the phase, amplitude, and polarization of transmitted or reflected light. We propose a multifunctional metalens with dual working modes based on bilayer geometric phase elements consisting of low-loss phase change materials (Sb2Se3) and amorphous silicon (a-Si). In transmission mode, by changing the crystalline state of the Sb2Se3 scatterer, a bifocal metalens with an arbitrary intensity ratio at the telecommunication C-band is realized, and the total focusing efficiency of the bifocal metalens is as high as 78%. Also, at the resonance wavelength of the amorphous Sb2Se3 scatterer, the scatterer can be regarded as a half-wave plate in reflection mode. The multifunctional metalens can reversely converge incident light into a focal point with a focusing efficiency of up to 30%. The high focusing efficiency, dynamic reconfigurability, and dual working modes of the multifunctional metalens contribute to polarization state detection, optical imaging, and optical data storage. In addition, the bilayer geometric phase elements can be easily extended to multilayer, which significantly improves the capability of manipulating the incident light field.

Ultrafast laser-inscribed nanogratings in sapphire for geometric phase elements.

We systematically studied femtosecond laser-inscribed self-organized nanogratings and geometric phase elements such as a polarization diffraction focusing lens and Q-plate in sapphire crystal. Besides the void structures observed in the focus, nanogratings with periods of 150~300 nm were observed, depending on a nanoslit that took the role of a seeding effect by localized light field enhancement. The non-polarized refractive index change and birefringence were measured with values around 1∼2×10-3 and 6×10-4, respectively. Based on the laser-inscribed form birefringence, a geometric phase lens and Q-plate were successfully demonstrated in sapphire with high imaging and a focusing effect. We expect that our findings may promote the understanding of laser-induced nanogratings in bulk and potential applications in geometric phase elements.

Switchable Second‐Harmonic Generation of Airy Beam and Airy Vortex Beam

AbstractAiry beam and Airy vortex beam with intriguing characteristics have been extensively studied in linear optics, while their dynamic nonlinear conversion has rarely been explored and remains challenging. Here, through the collaboration of binary mask engineered nonlinear photonic crystal and space‐variant liquid‐crystal geometric phase element, second‐harmonic Airy beam and Airy vortex beam can be generated in a switchable manner. Electrical‐controlled loading of orbital angular momentum (OAM) into fundamental wave unlocks the flexibility of nonlinear process, which is well investigated in theory and further verified by experiment. Wavelength transformation, OAM conversion, and propagation trajectory inflection are realized simultaneously. This offers a convenient and universal strategy for dynamic nonlinear generation and shows great potentials in optical manipulation and information processing.

Generating a 64 × 64 beam lattice by geometric phase modulation from arbitrary incident polarizations.

A laser beam lattice from tailoring spatial dimensions of lights is a kind of structured optical field, which already have found many applications in lots of domains. Here we propose a geometric phase element made from polymerized liquid crystals to transform Gaussian beams into a 64×64 beam lattice with high performance. Different from other geometric phase elements, the proposed element can introduce identical phase modulations for any polarizations, indicating that the beam lattice could be well generated with arbitrary incident homogeneous polarizations but not limited to specific circular polarizations. In the experiment, a 64×64 beam lattice is well generated. It is estimated that the uniformity of the obtained lattice fluctuates about 60% among various incident polarizations, which is very close to the prediction. This work opens a new site for producing high-dimensional beam lattices and will inspire more advanced applications.

Dual‐Polarized Tri‐Channel Encrypted Holography Based on Geometric Phase Metasurface

Metasurface‐based encrypted holography has drawn much attention recently due to its excellent ability in storing/displaying information with good security. To enhance the encryption security of metasurface holograms, multiplexing techniques, for which a large number of parameters need to be scanned to achieve the desired meta‐atoms, are highly demanded. Herein, a metasurface design scheme, which utilizes solely geometric phase elements to manipulate both co‐ and cross‐polarized reflected fields independently, is proposed. Using an improved weighted Gerchberg–Saxton (GSW), a holographic algorithm is proposed for 1‐bit phase, dual‐polarized tri‐channel encrypted metamirrors. Proof‐of‐concept prototypes are fabricated and experimental demonstrations are performed at microwave frequencies. Simulations and measurements are carried out to validate the proposed design, and the results agree well with the theoretical design scheme. Such dual‐polarized and tri‐channel encrypted metamirrors are appealing for applications in polarimetric imaging, information encryption/storage and beam splitting, shaping and steering.

Representing Quantum Information with Digital Coding Metasurfaces.

With the development of science and technology, the way to represent information becomes more powerful and diversified. Recent research on digital coding metasurfaces has built an alternative bridge between wave‐behaviors and information science. Different from the logic information in traditional circuits, the digital bit in coding metasurfaces is based on wave‐structure interaction, which is capable of exploiting multiple degrees of freedom (DoFs). However, to what extent the digital coding metasurface can expand the information representation has not been discussed. In this work, it is shown that classical metasurfaces have the ability to mimic qubit and quantum information. An approach for simulating a two‐level spin system with meta‐atoms is proposed, from which the superposition for two optical spin states is constructed. It is further proposed that using geometric‐phase elements with nonseparable coding states can induce the classical entanglement between polarization and spatial modes, and give the condition to achieve the maximal entanglement. This study expands the information representing range of coding metasurfaces and provides an ultrathin platform to mimic quantum information.

High-Efficiency Fabrication of Geometric Phase Elements by Femtosecond-Laser Direct Writing.

The nanoresolution of geometric phase elements for visible wavelengths calls for a flexible technology with high throughout and free from vacuum. In this article, we propose a high-efficiency and simple manufacturing method for the fabrication of geometric phase elements with femtosecond–laser direct writing (FsLDW) and thermal annealing by combining the advantages of high-efficiency processing and thermal smoothing effect. By using a femtosecond laser at a wavelength of 343 nm and a circular polarization, free-form nanogratings with a period of 300 nm and 170-nm-wide grooves were obtained in 50 s by laser direct ablation at a speed of 5 mm/s in a non-vacuum environment. After fine-tuning through a hot-annealing process, the surface morphology of the geometric phase element was clearly improved. With this technology, we fabricated blazed gratings, metasurface lens, vortex Q-plates and “M” holograms and confirmed the design performance by analyzing their phases at the wavelength of 808 nm. The efficiency and capabilities of our proposed method can pave the possible way to fabricate geometric phase elements with essentially low loss, high-temperature resistance, high phase gradients and novel polarization functionality for potentially wide applications.

Experimental observation of the geometric phase in nonlinear frequency conversion

The geometric phase is a common phenomenon in a variety of physical systems, with significant applications in optics. We report the first experimental demonstration of the adiabatic geometric phase in nonlinear frequency conversion, wherein the coupling between the signal and idler frequencies constitutes the intrinsic two-level dynamics of the system. We observe a variety of effects associated with the geometric phase, including the adiabatic broadening of bandwidth, asymmetric transmission for opposite propagation directions, conjugation of the phase for orthogonal eigenstates, and the nonreciprocity associated with the pump field bias. Our work paves the way towards all-optically controlled geometric phase elements for wavefront shaping, isolation, guiding, and quantum optical applications, harnessing spectral and spatial correlations.

Chirality invertible superstructure mediated active planar optics

Active planar optical devices that can dynamically manipulate light are highly sought after in modern optics and nanophotonics. The geometric phase derived from the photonic spin-orbit interaction provides an integrated strategy. Corresponding elements usually suffer from static functions. Here, we introduce an inhomogeneously self-organized anisotropic medium featured by photo-invertible chiral superstructure to realize geometric phase elements with continuously tunable working spectrum and light-flipped phase profile. Via preprograming the alignment of a cholesteric liquid crystal mixed with a photo-responsive chiral dopant, we demonstrate light-activated deflector, lens, Airy beam and optical vortex generators. Their polychromatic working bands are reversibly tuned in an ultra-broadband over 1000 nm covering green to telecomm region. The chirality inversion triggers facile switching of functionalities, such as beam steering, focusing/defocusing and spin-to-orbital angular momentum conversion. This work offers a platform for advanced adaptive and multifunctional flat optics with merits of high compactness, low loss and broad bandwidth.

P‐208: Late‐News Poster: Single‐exposure fabrication of geometry phase optical elements with arbitrary wavefronts

Geometric phase (GP) elements have become an attractive component candidate in augmented reality (AR) and virtual reality (VR) applications. We propose a method to fabricate GP elements with arbitrary wavefronts through single‐step photo‐alignment. By exposing an azo‐dye doped liquid crystal (LC) by a polarization field controlled by a SLM, arbitrary GP pattern could be realized. The fabricated geometrical phase elements include gratings, q‐plates and a hologram, and they all exhibit good optical properties. This simple fabrication method holds great promise for GP elements in AR&VR systems.