Optical vortex | EPFL Graph Search

An optical vortex (also known as a photonic quantum vortex, screw dislocation or phase singularity) is a zero of an optical field; a point of zero intensity. The term is also used to describe a beam of light that has such a zero in it. The study of these phenomena is known as singular optics. Explanation In an optical vortex, light is twisted like a corkscrew around its axis of travel. Because of the twisting, the light waves at the axis itself cancel each other out. When projected onto a flat surface, an optical vortex looks like a ring of light, with a dark hole in the center. The vortex is given a number, called the topological charge, according to how many twists the light does in one wavelength. The number is always an integer, and can be positive or negative, depending on the direction of the twist. The higher the number of the twist, the faster the light is spinning around the axis. This spinning carries orbital angular momentum with the wave train, and will induce t

Spin-to-orbital angular momentum conversion in semiconductor microcavities

Roland Cerna, Benoît Marie Joseph Deveaud, Konstantinos Lagoudakis, Timothy Chi Hin Liew, Francesco Manni, François Morier-Genoud, Taofiq Paraïso

We experimentally demonstrate a technique for the generation of optical beams carrying orbital angular momentum using a planar semiconductor microcavity. Despite being isotropic systems with no structural gyrotropy, semiconductor microcavities, because of the transverse-electric–transverse-magnetic polarization splitting that they feature, allow for the conversion of the circular polarization of an incoming laser beam into the orbital angular momentum of the transmitted light field. The process implies the formation of topological entities, a pair of optical vortices, in the intracavity field.

2011

Brillouin scattering in gas-filled hollow-core fibres

Flavien Gyger

Edward E. Hagenlocker and William G. Rado demonstrated Brillouin interaction in gas for the first time in 1965, right after the very first demonstrations of stimulated Brillouin scattering in solid materials. In their experiment, they used a megawatt pulsed ruby laser that they focused in a gas cell. Such a high optical power was required due to the weak efficiency of the interaction, as a result of the impossibility of confining a high optical intensity for a sufficiently long distance in free space. Thanks to the invention of the hollow-core photonic crystal fibres by Philip St.J. Russell in 1991, it is nowadays possible to tightly confine beams of light over distances of several kilometres. In such fibres, light beams are confined over an area of a few tens of square micrometres and propagate with small optical losses, that might reach those of standard optical fibres in the near future. The Brillouin gain being proportional to the light intensity and to the interaction length of the beams, its value is increased by many orders of magnitude in a hollow-core fibre, as compared with free-space experiments. As a consequence, the Brillouin interaction in a hollow-core fibre only requires optical power of a few tens of milliwatts. Additionally, the Brillouin gain shows a quadratic dependence on pressure. Hence, by pressurising the gas inside the hollow-core fibre, it is possible to further drastically increase the Brillouin gain, that can exceed the values of solid media (e.g. silica). It has to be noted that hollow-core optical fibres are ideal candidates for these kind of experiments since their hollow internal volume is extremely small and they seem able to sustain pressures of several thousand times the atmospheric pressure. The main objectives of this thesis are the demonstration of the quadratic dependence of the Brillouin gain on pressure, both theoretically and experimentally, and the use of this strong Brillouin interaction for practical applications. The first three chapters introduce a theoretical background, explaining light propagation in gases, acoustic waves and their interaction with light waves. The last three chapters give some experimental results to confirm the theoretical part as well as four applications of Brillouin scattering in gas-filled hollow-core fibres: amplification of an optical signal, slow light, gas Brillouin lasing and a novel, intrinsically strain-insensitive, distributed temperature sensor.

EPFL2020

Topological stability of the half-vortices in spinor exciton-polariton condensates

Hugo Pierre Alexandre Flayac

Half-vortices have been recently shown to be the elementary topological defects supported by a spinor cavity exciton-polariton condensates with spin-anisotropic interactions [Y. G. Rubo, Phys. Rev. Lett. 99, 106401 (2007)]. A half-vortex is composed by an integer vortex for one circular component of the condensate, whereas the other component remains static. We analyze theoretically the effect of the splitting between TE and TM polarized eigen modes on the structure of the vortices in this system. For TE and TM modes, the polarization states depend on the direction of propagation of particles and impose some well-defined phase relation between the two circular components. As a result elementary topogical defects in this system are no more half-vortices but integer vortices for both circular components of the condensate. The intrinsic lifetime of half-vortices is given and the texture of a few vortex states is analyzed.

2010

Brillouin scattering in gas-filled hollow-core fibres

Flavien Gyger

EPFL2020