We propose and demonstrate the wave front correction of a vortex laser beam by using dual phase only liquid crystal spatial light modulators (LC-SLMs) and a stochastic parallel gradient descent (SPGD) algorithm. One phase only LC-SLM is used to generate vortex laser beam by loading spiral phase screen onto the wave front of input quasi-Gaussian beam. The other phase only LC-SLM under SPGD controller based on the subzone control method adaptively compensates the wave front of vortex laser beam. Numerical simulation and experimental results show that after correction, vortex doughnut like beam is focused into a beam with airy disk pattern distribution in the far field. The adaptive corrections of vortex laser beam with different optical topological charges are studied. The results show that the optical topological charge has little influence on adaptive correction. The powers in the main lobe of far field intensity distributions of vortex laser beams with different optical topological charges are all greatly improved by adaptive correction. The technique proposed in this paper can be used in optical communication, relay mirror and atmospheric turbulence correction. 相似文献
I attempted to produce a laser beam with no light in the central line of the beam, by Fresnel diffraction of the Gaussian beam by a spiral zone plate (SZP). The study imparts an arbitrary-order phase singularity on the light field. The experimental results show that the optical vortex radius depends on the singularity’s integer order n (also termed topological charge, or order of the dislocation). Also, the radius of maximum intensity is shown to depend on the singularity number. Anomalous behavior of the spectra at phase singularity produced by various zone plates near the focus of a converging Gaussian beam is also studied using a simple experimental technique. It is found that the spectrum of the beam on the SZP (spiral zone plate) consisting of a single spectral profile shows almost vanishing intensity at all frequencies with a tendency of splitting into two peaks at the on-axis point and shows redshift and blueshift around the phase singularity. A comparative study of the anomalous behavior of the spectra at phase singularity produced by various SZPs, with varying phase singularity order n, near the focus of a converging Gaussian laser beam is studied. 相似文献
Diffraction of uniformly polarized laser beams with vortex phase singularity is theoretically analyzed using the plane wave expansion. It is shown that for a high numerical aperture, an intense longitudinal electric field component is formed on the optical axis in this case. It is numerically demonstrated that an analogous effect is ensured for diffraction of a conventional Gaussian beam from asymmetric binary axicons. The field intensity on the optical axis can be varied either by rotating the optical element or by changing the direction of polarization of radiation. 相似文献
Experimental and numerical techniques allowed us to predict and verify the existence of a robust phase singularity in the spatial coherence function when a vortex is present. Though observed in the optical domain, this phenomenon may occur in any partially coherent vortex wave. 相似文献
We performed three-dimensional finite elements simulations of the optical response of holey plasmonic vortex lenses, i.e., spiral grooves milled on a thin gold film with a hole at the center. We focus in particular on the properties of the wave transmitted in the underlying half-space, which is shown to be a relevant part of the transmitted field. We find out that the angular momentum selection rule for this part of the field is different from the one for the transmitted plasmonic vortex, although closely related to the plasmonic interaction of the impinging wave with the chiral geometry. 相似文献
Optical dark traps such as Laguerre-Gaussian beams, modulated optical vortices, and high-order Bessel beams have been used in the micromanipulation of microparticles. Such optical traps are highly versatile, as they are able to trap both high- and low-index microparticles as well as to set them into rotation by use of the orbital angular momentum of light. Holography has been widely used to modulate the shape of an optical vortex for new optical traps. We show that, by designing the shape of a spiral phase plate and using electron-beam lithography for fabrication, one can modulate the amplitude and the phase of an optical vortex with respect to the specific shape of the spiral phase plate as required. Furthermore, to the best of our knowledge this is the first report of transferring orbital angular momentum from a spiral phase plate to an absorptive microparticle in an experiment. Hence, with this technique, optical dark traps can easily be designed and fabricated. 相似文献
A spiral wave front source produces an acoustic field that has a phase that is proportional to the azimuthal angle about the source. The concept of a spiral wave front beacon is developed by combining this source with a reference source that has a phase that is constant with the angle. The phase difference between these sources contains information about the receiver's azimuthal angle relative to the beacon and can be used for underwater navigation. To produce the spiral wave front, two sources are considered: a "physical-spiral" source, which produces the appropriate phase by physically deforming the active element of the source into a spiral, and a "phased-spiral" source, which uses an array of active elements, each driven with the appropriate phase, to produce the spiral wave front. Using finite element techniques, the fields produced by these sources are examined in the context of the spiral wave front beacon, and the advantages of each source are discussed. 相似文献
In recent years, optical vortex beams possessing orbital angular momentum have received much attention due to their potential for high‐capacity optical communications. This capability arises from the unbounded topological charges of orbital angular momentum (OAM) that provide infinite freedoms for encoding information. The two most common approaches for generating vortex beams are through fork diffraction gratings and spiral phase plates. While realization of conventional spiral phase plate requires complicated 3D fabrication, the emerging field of metasurfaces has provided a planar and facile solution for generating vortex beams of arbitrary orbit angular momentum. Among various types of metasurfaces, the geometric phase metasurface has shown great potential for robust control of light‐ and spin‐controlled wave propagation. Here, we realize a novel type of geometric metasurface fork grating that seamlessly combine the functionality of a metasurface phase plate for vortex‐beam generation, and that of a linear phase gradient metasurface for controlling the wave‐propagation direction. The metasurface fork grating is therefore capable of simultaneously controlling both the spin and the orbital angular momentum of light.
The far-field diffraction pattern of an elliptical vortex beam by a slit hexagon aperture is investigated theoretically and experimentally. It is found that the number of the dark spots or stripes in the Fraunhofer diffraction intensity distribution is just equal to the topological charge value of the measured optical vortex, and that the centre of each dark spot or stripe is just a phase singularity point. Based on this property, it provides us a simple way to detect the orbital angular momentum (OAM) of an optical vortex beam. 相似文献
A chiral arrangement of molecular nanoemitters is shown to support delocalised exciton states whose spontaneous decay can generate optical vortex radiation. In contrast to techniques in which phase modification is imposed upon conventional optical beams, this exciton method enables radiation with a helical wave‐front to be produced directly. To achieve this end, a number of important polarisation and symmetry‐based criteria need to be satisfied. It emerges that the phase structure of the optical field produced by degenerate excitons in a propeller‐shaped array can exhibit precisely the sought character of an optical vortex – one with unit topological charge. Practical considerations for the further development of this technique are discussed, and potential new applications are identified. 相似文献
The diffraction of an optical vortex through an iris diaphragm which is a close approximation to a circular aperture has been investigated. The results are compared with those obtained from the diffraction of a Gaussian beam through the same aperture. In our findings the diffraction of an optical vortex and a Gaussian beam produce ball bearing sort of structure of darkness and brightness. The singularity of the vortex beam is found to be consistent even after the diffraction through the aperture. The presence of singularity at the centre of diffraction pattern of an optical vortex has been confirmed by interferometry. There is a good agreement between the experimental and numerical results. We propose that these results may find various applications in optical trapping experiments. 相似文献
We present here controlled generation of asymmetric optical vector-vortex beams using a two-mode optical fiber and study the dynamic evolution of the transverse energy flow (TEF) when focused through a spherical lens. The dependence of the TEF on various factors such as the vortex charge, vortex anisotropy and polarization structure around the vortex core is explored. It is found that the TEF is directly proportional to the phase gradient and its direction is governed by the vortex charge. The presence of C-point polarization singularity in the beam and the polarization structure around it results in vibrational phase gradient which is the major factor deciding the TEF in vector-vortex beams. 相似文献