We propose a new type of noncanonical optical vortex, named "power-exponent-phase vortex (PEPV)". The spiral focusing of the autofocusing Airy beams carrying PEPVs are experimentally demonstrated, and the physical mechanism is theoretically analyzed by using the energy flow and far field mapping. In addition, the influences of the parameters of PEPVs on the focal fields and orbital angular momenta are also discussed. It is expected that the proposed PEPVs and the corresponding conclusions can be useful for the extension applications of optical vortices, especially for particle trapping and rotating.
We demonstrate coherent interactions between spatial gap solitons in optically induced photonic lattices. Because of the "staggered" phase structures, two in-phase (out-of-phase) bright gap solitons can repel (attract) each other at close proximity, in contrast to soliton interaction in homogeneous media. A reversal of energy transfer direction and a transition between attractive and repulsive interaction forces can be obtained solely by changing the initial soliton separation relative to the lattice spacing.
We study nonlinear propagation of optical vortices in presence of hybrid nonlinearity as established in a nonconventional biased photorefractive crystal. Our results indicate that under hybrid nonlinearity the breakup of a singly-charged vortex along with the loss of its angular momentum is suppressed considerably as compared with that under conventional self-focusing or self-defocusing nonlinearity. Disintegration of a doubly-charged vortex under hybrid nonlinearity is also presented. Our experimental results are in good agreement with the numerical simulations.
We present a simple method to measure the topological charges of optical vortices with multiple singularities. Using a cylindrical lens, a vortex beam can decay into a light field distribution with multiple separated dark holes, whose number just equals the topological charge of the input beam. This conclusion is then verified via experiments and numerical simulations of the propagation of vortex beams with multiple singularities. This method is also reliable to measure the topological charges of broadband vortex beams with different distributions of singularities, which does not resort to multiple beam interferometric experiments.
Abstract:We study coherent and incoherent interactions between discrete vortex and fundamental solitons in two-dimensional photonic lattices, presenting a new scheme for all-optical routings and topological transformations of vorticities. Due to the multi-lobe intensity and step-phase structure of the discrete vortex soliton, the coherent soliton-interactions allow both solitons to be steered into multiple different possible destination ports depending on the initial phase of the discrete fundamental soliton. We show that charge-flipping of phase singularities and orbital angular momentum transfer can occur during the coherent interactions between the two solitons. For incoherent interactions, by controlling the relative intensities of the two solitons, we reveal that soliton-steering can be realized by either attracting the discrete fundamental soliton to four ports or localizing the four-lobe discrete vortex soliton into a ring soliton.
We demonstrate both experimentally and numerically linear symmetry-breaking diffraction and nonlinear dynamic self-trapping of an optical beam in hexagonal photonic lattices. We show that a stripe multivortex beam undergoes asymmetric linear diffraction, but evolves into a moving self-trapped beam under a self-defocusing nonlinearity. Fine features of symmetry-breaking in diffraction of elliptical multivortex beams are also observed and discussed.
The generation and propagation dynamics of multiple optical vortices hosted in a Gaussian beam are experimentally demonstrated by use of the computer-generated holography. Fluid-like motions of the multi-vortex beam are observed owing to the helical phase structure. The multi-vortex beam with identical topological charge presents rotation, which can be suppressed by changing the sign of the topological charge alternately. In addition, the transverse motion control of the multi-vortex is proved by inserting an additional vortex. Finally, rotary and stationary vortex lattices with different periodic arrays are experimentally constructed. The results exhibit potential applications in inducing twisted or stable waveguide arrays and new types of optical traps.
We study controllable self-shifting Bloch modes in anisotropic hexagonal photonic lattices. The shifting results from a deformed band structure due to deformation of the index distribution in each unit cell. By reconfiguration of the index profile of the unit cell, the direction in which the Bloch modes move can be controlled. Our theoretical predictions are experimentally demonstrated in hexagonal lattices optically induced in an anisotropic nonlinear crystal.
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