Liquid crystal spatial-mode converters for the orbital angular momentum of light (original) (raw)
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Molecular Crystals and Liquid Crystals, 2012
The angular momentum of light can be split into a spin and an orbital component (SAM and OAM). A few years ago, an optical process involving a conversion of angular momentum from one form to the other was conceived and experimentally demonstrated in a singular patterned liquid crystal cell, also known as "q-plate". In this paper, after reviewing the q-plate concept and technology, we will survey some of the most significant results that have originated from it, with particular attention to the possibility of realizing a physical one-to-one mapping between the polarization Poincaré sphere and an OAM subspace of an optical beam or of a single photon.
Arbitrary optical wavefront shaping via spin-to-orbit coupling
Journal of Optics, 2016
Converting spin angular momentum to orbital angular momentum has been shown to be a practical and efficient method for generating optical beams carrying orbital angular momentum and possessing a space-varying polarized field. Here, we present novel liquid crystal devices for tailoring the wavefront of optical beams through the Pancharatnam-Berry phase concept. We demonstrate the versatility of these devices by generating an extensive range of optical beams such as beams carrying ±200 units of orbital angular momentum along with Bessel, Airy and Ince-Gauss beams. We characterize both the phase and the polarization properties of the generated beams, confirming our devices' performance.
Spin-orbital Conversion of Bessel Light Beams By Liquid Crystal Elements
KnE Energy, 2018
For the first time, the spin-orbital conversion of the linearly polarized Bessel beams in the process of their propagation in the electrically-controlled liquid crystal cell has been realized experimentally. Variations in the polarization, phase, and spatial structure of the beam have been analyzed. It has been shown that, when a Bessel beam is propagating along the liquid crystal director, the generated beam is orthogonally polarized, whereas the topological charge is varied by two unities.
Orbital and Spin Photon Angular Momentum Transfer in Liquid Crystals
Physical Review Letters, 2001
All-optical angular control of the molecular alignment in liquid-crystal films is demonstrated using a laser beam having an elliptically shaped intensity profile. The material birefringence is unimportant, as proven by the fact that good alignment is obtained with unpolarized light. This raises the possibility of achieving optical angular control of transparent isotropic bodies. A general theoretical approach, based on light and matter angular momentum conservation, shows that the optical alignment is due to the internal compensation between the transfer of the orbital and the spin part of angular momentum of the incident photons to the material.
Physical Review A, 2010
We present an easy, efficient, and fast method to generate arbitrary linear combinations of light orbital angular-momentum eigenstates = ±2 starting from a linearly polarized TEM 00 laser beam. The method exploits the spin-to-orbital angular-momentum conversion capability of a liquid-crystal-based q plate and a Dove prism inserted into a Sagnac polarizing interferometer. The nominal generation efficiency is 100%, being limited only by reflection and scattering losses in the optical components. When closed paths are followed on the polarization Poincaré sphere of the input beam, the associated Pancharatnam geometric phase is transferred unchanged to the orbital angular momentum state of the output beam.
Optics Express, 2010
When a left-circularly polarised Gaussian light beam, which has spin angular momentum (SAM) J sp = σħ = 1ħ per photon, is incident along one of the optic axes of a slab of biaxial crystal it undergoes internal conical diffraction and propagates as a hollow cone of light in the crystal. The emergent beam is a superposition of equal amplitude zero and first order Bessel like beams. The zero order beam is left-circularly polarised with zero orbital angular momentum (OAM) J orb = ℓħ = 0, while the first order beam is right-circularly polarized but carries OAM of J orb = 1ħ per photon. Thus, taken together the two beams have zero SAM and J orb = ½ħ per photon. In this paper we examine internal conical diffraction of an elliptically polarised beam, which has fractional SAM, and demonstrate an all-optical process for the generation light beams with fractional OAM up to ± 1ħ
Applied Physics Letters, 2009
We present methods for generating and for sorting specific orbital angular momentum (OAM) eigenmodes of a light beam with high efficiency, using a liquid crystal birefringent plate with unit topological charge, known as "q-plate". The generation efficiency has been optimized by tuning the optical retardation of the q-plate with temperature. The measured OAM m = ±2 eigenmodes generation efficiency from an input TEM00 beam was of 97%. Mode sorting of the two input OAM m = ±2 eigenmodes was achieved with an efficiency of 81% and an extinction-ratio (or cross-talk) larger than 4.5:1.
Generation and decomposition of scalar and vector modes carrying orbital angular momentum: a review
Optical Engineering
Orbital angular momentum (OAM), one of the most recently discovered degrees of freedom of light beam field has fundamentally revolutionized optical physics and its technological capabilities. Optical beams with OAM have enabled a large variety of applications, including super-resolution imaging, optical trapping, classical and quantum optical communication, and quantum computing, to mention a few. To enable these and several other emerging applications, optical beams with OAM have been generated using a variety of methods and technologies, such as a simple astigmatic lens pair, one-/two-dimensional holographic optical elements, threedimensional spiral phase plates, optical fibers, and recent entrants such as metasurfaces. All these techniques achieve spatial light modulation and can be implemented with either passive elements or active devices, such as liquid crystal on silicon and digital micromirror devices. Many of these devices and technologies are not only used for the generation of amplitude phase-polarization structured light beams but are also capable of analyzing them. We have attempted to encompass a wide variety of such technologies as well as a few emerging methodologies, broadly categorized into generation and detection protocols. We address the needs of scientists and engineers who desire to generate/detect OAM modes and are looking for the technique (active or passive) best suited for their application. © The Authors. Published by SPIE under a Creative Commons Attribution 4.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.
Tunable orbital angular momentum mode filter based on optical geometric transformation
Optics Letters, 2014
We present a tunable mode filter for spatially multiplexed laser beams carrying orbital angular momentum (OAM). The filter comprises an optical geometric transformation-based OAM mode sorter and a spatial light modulator (SLM). The programmable SLM can selectively control the passing/blocking of each input OAM beam. We experimentally demonstrate tunable filtering of one or multiple OAM modes from four multiplexed input OAM modes with vortex charge of l −9, −4, 4, and 9. The measured output power suppression ratio of the propagated modes to the blocked modes exceeds 14.5 dB.