Chandroth P. Jisha

Nonlocal gap solitons in PT -symmetric periodic potentials with defocusing nonlinearity

Existence and stability of

Self-written waveguide in methylene blue sensitized poly(vinyl alcohol)/acrylamide photopolymer material

\mathcal{PT}

Guiding light via geometric phases

-symmetric gap solitons in a periodic structure with defocusing nonlocal nonlinearity are studied both theoretically and numerically. We find that, for any degree of nonlocality, gap solitons are always unstable in the presence of an imaginary potential. The instability manifests itself as a lateral drift of solitons due to an unbalanced particle flux. We also demonstrate that the perturbation growth rate is proportional to the amount of gain (loss), thus predicting the observability of stable gap solitons for small imaginary potentials.

Optical solitons and wave-particle duality.

We report the observation of a self-written waveguide inside a bulk methylene blue sensitized poly/vinyl alcohol)/acrylamide photopolymer material. Light from a low power He-Ne laser is focused into the material, and the evolution of the beam is monitored. The refractive index of the material is modulated in the region of high intensity due to photobleaching and photopolymerization effects occurring in the material. As a result, the beam propagates through the medium without any diffraction effects.

Deflection and trapping of spatial solitons in linear photonic potentials

A mechanism for confining and guiding light that relies on spin–orbit interactions of light is presented.

Stable diffraction managed spatial soliton in bulk cubic-quintic media

We investigate the propagation of optical solitons interacting with linear defects in the medium. We show that solitons exhibit a wave-particle dualism versus power, i.e., depending on the relative size of soliton and defect, responsible for a soliton trajectory dependent on its waist.

Crescent Waves in Optical Cavities

We investigate the dynamics of spatial optical solitons launched in a medium with a finite perturbation of the refractive index. For longitudinally short perturbations of super-Gaussian transverse profile, as the input power varies we observe a transition from a wave-like behavior where solitons break up into multiple fringes to a particle-like behavior where solitons acquire a transverse velocity retaining their shape. For longitudinally long perturbations with an attractive potential solitons get trapped inside the well and propagate with transverse periodic oscillations, resulting in an efficient power-dependent angular steering or deflection. Using the Ehrenfest theorem we derive analytical expressions for soliton trajectory, and achieve excellent agreement between theory and numerical simulations for large powers, that is, narrow solitons.

Phase separation and pattern instability of laser-induced polymerization in liquid-crystal-monomer mixtures

This work analyses the stabilization of a two-dimensional spatial soliton in cubic-quintic media. A diffraction managed model in cubic-quintic media has been formulated and analytical expressions for soliton parameters have been derived using variational analysis. Variational equations and the partial differential equation have been simulated numerically. Analytical and numerical studies have shown that diffraction management stabilizes the two-dimensional spatial soliton against collapse in cubic-quintic media.

Interaction of discrete nonlinear Schr¨ odinger solitons with a linear lattice impurity

We theoretically and experimentally generate stationary crescent surface solitons pinged to the boundary of a microstructured vertical cavity surface emission laser by triggering the intrinsic cavity mode as a background potential. Instead of a direct transition from linear to nonlinear cavity modes, we demonstrate the existence of symmetry-breaking crescent waves without any analogs in the linear limit. Our results provide an alternative and general method to control lasing characteristics as well as to study optical surface waves.

Electromagnetic Confinement via Spin–Orbit Interaction in Anisotropic Dielectrics

Directly written by a ultra-short femto-second laser pulse, we report the phase separation and pattern formation induced by polymerization in a liquid-crystal-monomer mixture. By varying the scanning speed of optical fields along a line, pattern transitions of photon-induced polymer structures are illustrated in shapes of double-humped, single-humped, and broken stripes. The experimental data collected by optical microscopic images are in a good agreement with numerical simulations based on a modified set of coupled 2 + 1 dimensional diffusion equations. The demonstration in this work provides a step for controlling phase separation morphologies as well as transferring patterns in polymer-dispersed liquid crystals.