Geometric Phase Optical Elements Research Articles

Asymmetric phase-split axicon masks for a improved Bessel beam-based glass stealth dicing

The precision glass micromachining technology employing ultrashort laser pulses has reached a state of maturity. This technology enables the precise drilling, cutting, or ablation of various types of glass, achieving accuracy up to a few microns. As laser sources continue to advance in average power and repetition rate, the efficient utilization of laser beam irradiation patterns becomes increasingly crucial. The Bessel beam, known for its ability to create elongated channels in transparent materials because of its invariant focal zone, gains significance in this context. The elongated focal zone of the Bessel beam proves advantageous for expeditious glass cutting, surpassing the efficiency of using a standard Gaussian beam. This study delves into the glass-cutting process by studying asymmetric phase-split diffractive axicon masks to generate such Bessel beams. For this purpose, geometric phase optical elements are created using transparent nanogratings inscribed in the volume of glass. This approach allows high-power asymmetric Bessel-like beams to be generated and experimentally used to investigate beam-shaping performance, ultimately determining the optimal parameter set for applications such as glass stealth dicing.

Hyperspectral optical orbital angular momentum modulation from tunable structured waveplates.

Shaping the orbital angular momentum of optical pulses in the spectral domain is a means of managing light in space and time that offers many possible applications. However, these are limited by the small number of techniques available, whose flexibility does not yet rival that of the continuous regime. We propose here to implement a tunable hyperspectral management of the orbital angular momentum of a polychromatic light field. The main idea is to exploit the dispersive nature of geometric phase optical elements by intentionally choosing to work in a regime of high anisotropic optical retardance. An experimental proof of principle is demonstrated in the visible range using a supercontinuum laser and an optically thick, electrically controllable, liquid crystal structured wave plate.

Active rejection-enhancement of spectrally tunable liquid crystal geometric phase vortex coronagraphs

Geometric phase optical elements made of space-variant anisotropic media customarily find their optimal operating conditions when a half-wave retardance condition is fulfilled, which allows imparting polarization-dependent changes to an incident wavefront. In practice, intrinsic limitations of a man-made manufacturing process or a finite spectrum of a light source lead to a deviation from the ideal behavior. This implies an implementation of strategies to compensate for the associated efficiency losses. Here, we report on how the intrinsic tunable features of self-engineered liquid crystal topological defects can be used to enhance rejection capabilities of spectrally tunable vector vortex coronagraphs. We also discuss the extent of which current models enable to design efficient devices. The simplicity and decent performance of our approach offer the possibility to an amateur astronomy community to consider the use of vortex coronography.

Ultrafast laser nanostructuring in transparent materials for beam shaping and data storage [Invited

We review recent progress in femtosecond laser anisotropic nanostructuring of transparent materials, including silica glass and thin films. With different writing parameters, oblate nanopores, single lamella-like structures and nanoripples are demonstrated, which can be used in geometric phase optical elements, space variant polarization converters and multiplexed optical data storage.

3D Engineering of Orbital Angular Momentum Beams via Liquid‐Crystal Geometric Phase

AbstractOrbital angular momentum (OAM) provides a novel degree of freedom for light, deeply inspiring versatile light‐matter interactions and large‐density multiplexing computing. Recently, multimode and multichannel control of OAM beams have aroused extensive curiosity, whereas their flexible engineering in 3D space still remains challenging. Here, a new type of liquid‐crystal geometric phase optical elements is demonstrated to achieve on‐demand 3D tailoring of OAM beams. Via integrating binary and continuous phase patterns into photo‐aligned liquid crystals, customized 3D lattices of identical or propagation‐variant OAM beams are generated in an electrically tunable broadband manner. By altering the incident spin, these volumetric OAM beams can be switched among different states on the higher‐order Poincaré sphere. This work demonstrates a practical approach toward efficient OAM harnessing with large channel capacity and high spatial mode diversity, holding great potential for 3D optical manipulation, recording, and microscopy.

Quantum walks of two correlated photons in a 2D synthetic lattice

Quantum walks represent paradigmatic quantum evolutions, enabling powerful applications in the context of topological physics and quantum computation. They have been implemented in diverse photonic architectures, but the realization of two-particle dynamics on a multidimensional lattice has hitherto been limited to continuous-time evolutions. To fully exploit the computational capabilities of quantum interference it is crucial to develop platforms handling multiple photons that propagate across multidimensional lattices. Here, we report a discrete-time quantum walk of two correlated photons in a two-dimensional lattice, synthetically engineered by manipulating a set of optical modes carrying quantized amounts of transverse momentum. Mode-couplings are introduced via the polarization-controlled diffractive action of thin geometric-phase optical elements. The entire platform is compact, efficient, scalable, and represents a versatile tool to simulate quantum evolutions on complex lattices. We expect that it will have a strong impact on diverse fields such as quantum state engineering, topological quantum photonics, and Boson Sampling.

Birefringent optical retarders from laser 3D-printed dielectric metasurfaces

Structuring light attracts continuous research effort due to its impactful applications in optical information and communications, laser material processing, optical imaging, or optical manipulation of matter. In particular, femtosecond laser direct writing of photoresists is a technology dedicated to the creation of optically isotropic free-form 3D micro-optical elements with size, spatial resolution, and surface quality that qualify to demanding integrated optics needs. Here, we report on the design, production, and characterization of dielectric metasurface birefringent optical retarders made from femtosecond laser 3D printing technology whose polarization conversion efficiency is more than 10 times larger than that previously reported Wang et al., Appl. Phys. Lett. 110, 181101 (2017)]. As the flexibility of the fabrication process allows considering arbitrary orientation of the artificially engineered optical axis, these results open up for 3D printed geometric phase optical elements.

Taming the swirl of self-structured liquid crystal q-plates

Spontaneously formed liquid crystal topological defects under external fields offer a nature-assisted route to the creation of geometric phase optical vortex generators (q-plates). Here we report on the consequences of the unavoidable swirled transverse spatial distribution of the optical axis of such optical elements on the beam shaping and we propose a swirl-compensation scheme based on the arithmetic of geometric phase optical elements.

High-order Laguerre-Gauss polychromatic beams from Bragg-Berry flat optics

We report on the design, fabrication, and experimental characterization of reflective geometric phase optical elements enabling the generation of scalar and vectorial high-order Laguerre-Gauss optical beams over a broad spectral range. This is made possible by combining azimuthal and radial structuring of helix-based liquid-crystal films exhibiting the circular Bragg reflection phenomenon. By extending the previously introduced concept of Bragg-Berry optical elements to the polychromatic shaping of the radial degrees of freedom and showing their combination with azimuthal ones, this work suggests that spectrally broadband spin-orbit processing of optical information over multiple spatial degrees of freedom can be further considered on experimental grounds.

Tunable High-Resolution Macroscopic Self-Engineered Geometric Phase Optical Elements.

Artificially engineered geometric phase optical elements may have tunable photonic functionalities owing to their sensitivity to external fields, as is the case for liquid crystal based devices. However, liquid crystal technology combining high-resolution topological ordering with tunable spectral behavior remains elusive. Here, by using a magnetoelectric external stimulus, we create robust and efficient self-engineered liquid crystal geometric phase vortex masks with a broadly tunable operating wavelength, centimeter-size clear aperture, and high-quality topological ordering.

Babinet-bilayered geometric phase optical elements.

Geometric phase optical elements based on structured anisotropy are widely used for phase shaping via their orientational degree of freedom. To date, amplitude shaping via space-variant retardance is much less investigated, a practical reason being that the spin-orbit interaction of light couples retardance with the dynamic part of the optical phase. Inspired by the complementary diffractive elements associated with Babinet's principle, a bilayered subwavelength grating design is proposed in order to cancel out the spatial modulation of the dynamic phase usually associated with space-variant birefringent phase retardation. This concept is illustrated in the framework of single-mode Laguerre-Gauss beam shaping.

Parallel sorting of orbital and spin angular momenta of light in a record large number of channels.

Parallel sorting of orbital and spin angular momentum components of structured optical beams is demonstrated. Both spin channels are multiplexed within the novel orbital angular momentum (OAM) sorter, reducing the size, weight, and number of elements. The sorted states are linearly spaced over 70 topological charge values. We experimentally and theoretically evaluate the operational range and crosstalk between neighboring channels and find that 30 orbital angular momentum states are available per spin channel for quantum communication or cryptography. This is achieved using an angular momentum sorter that we developed based on geometric phase optical elements. We present two devices consisting of liquid crystal polymer films photoaligned with complex two-dimensional patterns.

Dielectric geometric phase optical elements fabricated by femtosecond direct laser writing in photoresists

We propose to use a femtosecond direct laser writing technique to realize dielectric optical elements from photo-resist materials for the generation of structured light from purely geometrical phase transformations. This is illustrated by the fabrication and characterization of spin-to-orbital optical angular momentum couplers generating optical vortices of topological charge from 1 to 20. In addition, the technique is scalable and allows obtaining microscopic to macroscopic flat optics. These results thus demonstrate that direct 3D photopolymerization technology qualifies for the realization of spin-controlled geometric phase optical elements.

Reflective Spin-Orbit Geometric Phase from Chiral Anisotropic Optical Media.

We report on highly reflective spin-orbit geometric phase optical elements based on a helicity-preserving circular Bragg-reflection phenomenon. First, we present a dynamical geometric phase experiment using a flat chiral Bragg mirror. Then, we show that shaping such a geometric phase allows the efficient spin-orbit tailoring of light fields without the need to fulfill any condition on birefringent phase retardation, in contrast to the case of transmission spin-orbit optical elements. This is illustrated by optical vortex generation from chiral liquid crystal droplets in the Bragg regime that unveils spin-orbit consequences of the droplet's curvature. Our results thus introduce a novel class of geometric phase elements-"Bragg-Berry" optical elements.