arXiv subjects

Etienne Brasselet

Publications and source records attributed to Etienne Brasselet.

At least 19 recordsLinked to original sources

arXiv2026

Topological robustness of optical skyrmions through a real-world free-space link

Structured light offers a promising solution for the increasing data demands of modern optical networks, opening up new degrees of freedom that can be leveraged for greater channel capacity and more bits per photon. However, its implementation is hindered by real-world distortions, for example, atmospheric turbulence in free-space, with severe and rapidly evolving phase perturbations that alter the amplitude, phase and vectorial polarization structure of the beam. Here, we demonstrate that optical topologies in the form of skyrmions are highly resilient to the effects of real-world atmospheric turbulence. We create and transmit these particle-like topologies of light through a 270~m free-space optical link, revealing their robustness across a wide variety of conditions and turbulence strengths. While we observe severe distortion in the states' underlying degrees of freedom, we show that the topological numbers are preserved in all cases. We account for fast changes to the medium, where the channel produces statistically averaged outcomes, by probing the state's decoherence, showing that while the degree of polarisation consequently decays, the topology remains intact. Using topology, we show information can be transmitted through the channel with almost perfect fidelity (>98%) in most cases, only decreasing to 86% in the most severe conditions tested. Our work is the first to demonstrate the potential for optical topologies as reliable and robust information carriers in a real-world environment and points to the potential for other complex channels too, offering attractive features for classical and quantum communication alike.

physics.optics↗

arXiv2025

Universal nondiffractive topological spin textures in vortex cores of light and sound

We report universal skyrmionic spin textures in the cores of optical and acoustic vortex beams, described within the framework of Laguerre-Gaussian modes. We analytically demonstrate nondiffractive propagating spin merons, independent of whether the field is transverse or longitudinal, with their sign controlled by the wavefront helicity. Experimental confirmation is provided in acoustics through full three-dimensional measurements of the velocity vector field. Although these phenomena are intrinsic to vortex cores, we also show that the claimed universality breaks down for higher-order topological charges, depending on the carrier mode, here exemplified using the Bessel framework.

physics.optics↗

arXiv2025

Dual-wavelength quantum skyrmions from liquid crystal topological defect

We propose a spin-orbit strategy for generating dual-wavelength quantum skyrmions, realized either as entangled photon pairs at dual wavelengths or as heralded single-photon states at a given wavelength -- regimes neither previously conceptualized nor demonstrated. By coupling a two-photon entangled state to an electrically tunable liquid crystal topological defect, we engineer both nonlocal and local skyrmionic topologies in a reconfigurable platform. We highlight with examples how this approach may open new directions for engineered topological quantum states that exploit the topological richness of liquid crystals.

quant-ph↗

arXiv2025

Wavelength-adaptive spin-orbit orbital angular momentum management in three-wave mixing

Here we propose the use of an adjustable liquid crystal spin-orbit device to shape bi-colour structured light to create bimodal states. We demonstrate the proof-of-principle for two individual wavelengths in a nonlinear optics framework. The spin-orbit device has an inhomogeneous optical axis orientation and birefringence, allowing it to modulate two wavelengths of light with pre-selected transmission functions by simply tuning a voltage. We combine this bi-colour functionality in a nonlinear optical experiment by employing three-wave mixing in a periodically poled crystal to show how the combined effect of linear spin-orbit transformation rules and nonlinear selection rules gives rise to novel approaches for light to modulate light, and light to unravel light. We show that the roles of the nonlinear crystal and spin-orbit device can be switched to either characterise the device with known light, or unravel unknown light with the device. This synergy between spin-orbit and nonlinear optics offers a novel paradigm where light manipulates and reveals its own structure across spectral domains.

physics.optics↗

arXiv2025

Complementary Speckle STED Microscopy

Stimulated Emission Depletion (STED) microscopy has emerged as a powerful technique providing visualization of biological structures at the molecular level in living samples. In this technique, the diffraction limit is broken by selectively depleting the fluorophore's excited state by stimulated emission, typically using a donut-shaped optical vortex beam. STED microscopy performs unrivalably well in degraded optical conditions such as living tissues. Nevertheless, photo-bleaching and acquisition time are among the main challenges for imaging large volumetric field of views. In this regard, random light beams like speckle patterns have proved to be especially promising for three-dimensional imaging in compressed sensing schemes. Taking advantage of the high spatial density of intrisic optical vortices in speckles -- the most commonly used beam spatial structure used in STED microscopy -- we propose here a novel scheme consisting in performing STED microscopy using speckles. Two speckle patterns are generated at the excitation and the depletion wavelengths, respectively, exhibiting inverted intensity contrasts. We illustrate spatial resolution enhancement using complementary speckles as excitation and depletion beam on both fluorescent beads and biological samples. Our results establish a robust method for super-resolved three-dimensional imaging with promising perspectives in terms of temporal resolution and photobleaching.

physics.optics↗

arXiv2022

Numerical simulation of universal morphogenesis of fluid interface deformations driven by radiation pressure

We report on ab initio simulation of fluid interface deformations induced either by acoustic or optical radiation pressure. This is done by solving simultaneously the scalar wave propagation equation and the two-phase flow equations using the boundary element method. Using dimensional analysis, we show that interface deformation morphogenesis is universal, i.e. depends on the same dimensionless parameters in acoustics and electromagnetics. We numerically investigate a few selected phenomena -- in particular the shape of large deformations, the slenderness transition and its hysteresis -- and compare with existing and novel experimental observations. Qualitative agreement between the numerical simulations and experiments is found when the mutual interaction between wave propagation and wave-induced deformations is taken into account. Our results demonstrate the leading role of the radiation pressure in morphogenesis of fluid interface deformations and the importance of the propagation-deformation interplay .

physics.flu-dyn↗

arXiv2018

Tunable high-resolution macroscopic self-engineered geometric phase optical elements

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

physics.optics↗

arXiv2018

Electrically-activated spin-controlled orbital angular momentum multiplexer

We present and test the integration of a static orbital angular momentum mode multiplexer with a dynamical geometric-phase optical element enabling on-demand spin-controlled angular momentum multiplexing. A diffractive optics multiplexer fabricated with 3D high-resolution electron beam lithography performs a conformal mapping for the conversion from linear to azimuthal phase gradients. The latter is functionalized by a dynamic spin-orbit add-on that consists of a self-engineered electrically-activated liquid crystal optical vortex generator having large clear-aperture and high-resolution. By combining several functionalities based on the optical angular momentum of light in a compact manner, the proposed hybrid device could find applications in next-generation high-dimensional mode switchers and routers based on orbital angular momentum.

physics.optics↗

arXiv2018

Macroscopic direct observation of optical spin-dependent lateral forces and left-handed torques

Observing and taming unusual effects arising from non-trivial light-matter interaction has always triggered scientists to better understand Nature and develop technological tools towards implementing novel applications. Recently, several unusual optomechanical effects have been unveiled when subtle spin-orbit interactions come at play to build up optical forces and torques that are hardly seen in everyday life, such as negative optical radiation pressure, transverse optical forces, or left-handed optical torques. To date, there are only a few experimental proposals to reveal these effects despite tremendous conceptual advances. In particular, spin-dependent lateral forces and their angular analog are done either at the expense of direct observations or at the cost of specific instrumental complexity. Here we report on naked-eye identification of light-induced spin-dependent lateral displacements of centimeter-sized objects endowed with structured birefringence. Its angular counterpart is also discussed and the observation of left-handed macroscopic rotational motion is reported. The unveiled effects are ultimately driven by lateral optical force fields that are five orders of magnitude larger than those reported so far. These results allow structured light-matter interaction to move from a scientific curiosity to a new asset for the existing multidisciplinary optical manipulation toolbox across length scales. In addition, this highlights the spin-orbit optomechanics of anisotropic and inhomogeneous media, which is just beginning to be explored.

physics.optics↗

arXiv2017

Ultra-broadband gradient-pitch Bragg-Berry mirrors

The realization of geometric phase optical device operating over a broad spectral range is usually confronted with intrinsic limitations depending of the physical process at play. Here we propose to use chiral nematic liquid crystal slabs with helical ordering that varies in three dimensions. Namely, gradient-pitch cholesterics endowed with in-plane space-variant angular positioning of the supramolecular helix. By doing so, we show that the recently introduced Bragg-Berry mirrors [Opt. Lett. {\bf 41}, 3972-3975 (2016)] can be endowed with ultra-broadband spectral range. Experimental demonstration is made in the case of ultra-broadband optical vortex generation in the visible domain. These results offer practical solution to the polychromatic management of the orbital angular momentum of light combining the circular Bragg reflection of chiral media with the Berry phase.

physics.optics↗

arXiv2017

3D laser printing by ultra-short laser pulses for micro-optical applications: towards telecom wavelengths

Three dimensional (3D) fast (< 0.5 hour) printing of micro-optical elements down to sub-wavelength resolution over 100 micrometers footprint areas using femtosecond (fs-)laser oscillator is presented. Using sub-1 nJ pulse energies, optical vortex generators made of polymerised grating segments with an azimuthally changing orientation have been fabricated in SZ2080 resist; width of polymerised rods was ~150 nm and period 0.6-1 micrometers. Detailed phase retardance analysis was carried out manually with Berek compensator (under a white light illumination) and using an equivalent principle by an automated Abrio implementation at 546 nm. Direct experimental measurements of retardance was required since the period of the grating was comparable (or larger) than the wavelength of visible light. By gold sputtering, transmission-type optical vortex generators were turned into reflective ones with augmented retardance, n.h defined by the form birefringence, n, and the height h = 2d where d is the thickness of the polymerised structure. Retardance reached 315 nm as measured with Berek compensator at visible wavelengths. Birefringent phase delays of 180 degrees (or half-wavelength) required for high purity vortex generators can be made based on the proposed approach. Optical vortex generators for telecom wavelengths with sub-wavelength patterns of azimuthally oriented gratings are amenable by direct laser polymerisation.

physics.optics↗

arXiv2016

Dielectric geometric phase optical elements from femtosecond direct laser writing

We propose to use 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.

physics.optics↗

arXiv2016

Vortex coronagraphy from self-engineered liquid crystal spin-orbit masks

We report on a soft route towards optical vortex coronagraphy based on self-engineered electrically tunable vortex masks based on liquid crystal topological defects. These results suggest that a nature-assisted technological approach to the fabrication of complex phase masks could be useful in optical imaging whenever optical phase singularities are at play.

physics.optics↗

arXiv2016

Bragg-Berry mirrors: reflective broadband q-plates

We report on the experimental realization of flat mirrors enabling the broadband generation of optical vortices upon reflection. The effect is based on the geometric Berry phase associated with the circular Bragg reflection phenomenon from chiral uniaxial media. We show the reflective optical vortex generation from both diffractive and nondiffractive paraxial light beams using spatially patterned chiral liquid crystal films. The intrinsic spectrally broadband character of spin-orbit generation of optical phase singularities is demonstrated over the full visible domain. Our results do not rely on any birefringent retardation requirement and consequently foster the development of a novel generation of robust optical elements for spin-orbit photonic technologies.

physics.optics↗

arXiv2012

Universal morphologies of fluid interfaces deformed by the radiation pressure of acoustic or electromagnetic waves

We unveil the generation of universal morphologies of fluid interfaces by radiation pressure whatever is the nature of the wave, acoustic or optical. Experimental observations reveal interface deformations endowed with step-like features that are shown to result from the interplay between the wave propagation and the shape of the interface. The results are supported by numerical simulations and a quantitative interpretation based on the waveguiding properties of the field is provided.

cond-mat.soft↗

arXiv2010

Influence of the backward propagating waves on the threshold in planar nematic liquid crystal films

We analyze theoretically the influence of backward propagating waves on the primary threshold when a linearly polarized light impinges at normal incidence on a planarly aligned nematic liquid crystal films. We show, that the primary threshold, as a function of the phase delay induced by the nematic layer, exhibits oscillations. The amplitude of oscillations depends strongly on the drop of the refractivity indices of the nematic and outer media at the boundaries.

cond-mat.soft↗

arXiv2009

Reversible nonreciprocity in photonic structures infiltrated with liquid crystals

We demonstrate how to achieve reversible nonreciprocal optical response in a periodic photonic structure with a pair of defects, one of them being a nonlinear liquid crystal defect layer. The twin defect layers structure is symmetric at low intensity and becomes asymmetric above a power threshold corresponding to the optical reordering of the liquid crystal. We show that nonreciprocal effects can be reversed by changing the wavelength as a consequence of the defect mode dependent light localization inside the structure.

physics.optics↗

arXiv2009

Laser microfluidics: fluid actuation by light

The development of microfluidic devices is still hindered by the lack of robust fundamental building blocks that constitute any fluidic system. An attractive approach is optical actuation because light field interaction is contactless and dynamically reconfigurable, and solutions have been anticipated through the use of optical forces to manipulate microparticles in flows. Following the concept of an 'optical chip' advanced from the optical actuation of suspensions, we propose in this survey new routes to extend this concept to microfluidic two-phase flows. First, we investigate the destabilization of fluid interfaces by the optical radiation pressure and the formation of liquid jets. We analyze the droplet shedding from the jet tip and the continuous transport in laser-sustained liquid channels. In the second part, we investigate a dissipative light-flow interaction mechanism consisting in heating locally two immiscible fluids to produce thermocapillary stresses along their interface. This opto-capillary coupling is implemented in adequate microchannel geometries to manipulate two-phase flows and propose a contactless optical toolbox including valves, droplet sorters and switches, droplet dividers or droplet mergers. Finally, we discuss radiation pressure and opto-capillary effects in the context of the 'optical chip' where flows, channels and operating functions would all be performed optically on the same device.

cond-mat.soft↗