Xinyuan Qi

Asymmetric light propagation in transverse separation modulated photonic lattices

We investigate, both theoretically and numerically, the asymmetric light propagation in transverse separation modulated photonic lattices. The theoretical results show that the transmission contrast η of the structure is determined only by the coupling strengths between the chirped lattice and the two boundary uniform lattice portions. The numerical studies demonstrate that η is independent of the separation modulation function of the chirped lattice, which is in good agreement with the theory.

Polychromatic solitons and symmetry breaking in curved waveguide arrays

We theoretically and experimentally study the nonlinear propagation of polychromatic light in curved waveguide arrays. We show that at moderate light powers the nonlinear self-action breaks the left-right symmetry of the polychromatic beam, resulting in the separation of different spectral components owing to the wavelength-dependent spatial shift. At high light powers a diffraction-managed polychromatic soliton is formed. These results demonstrate new possibilities for tunable demultiplexing and spatial filtering of supercontinuum light.

Observation of nonlinear surface waves in modulated waveguide arrays

We describe theoretically and study experimentally nonlinear surface waves at the edge of a modulated waveguide array with a surface defect and a self-defocusing nonlinearity. We fabricate such structures in a LiNbO(3) crystal and demonstrate the beam switching to different output waveguides with a change of the light intensity due to nonlinear coupling between the linear surface modes supported by the array.

Light controlling in transverse separation modulated photonic lattices.

We numerically study the propagation of Gaussian beams in four different types of transverse separation modulated photonic lattices. We find the modulation obeying hyperbolic secant or rectangular functions can act as optical potentials, and the light waves can be localized or recur in the regions between such two positive potentials, respectively. While the beams decay in the regions between such two negative potentials since these structures could not support localized modes. Our results provide new ways for light controlling and manipulation in photonic lattices.

Gap solitons in optically induced two-dimensional square photonic lattices in LiNbO3:Fe crystals

We fabricated two-dimensional square photonic lattices with a backbone structure in self-defocusing LiNbO3:Fe crystals through optical induction. We systematically observed four kinds of gap solitons and their power spectra in the nonlinear photonic lattices. Our results show that the lightwave is confined more tightly when it is launched into a low-index region at the input face of the crystal than when it is launched into a backbone ridge waveguide.

Linear and nonlinear discrete light propagation in weakly modulated large-area two-dimensional photonic lattice slab in LiNbO3:Fe crystal.

A weakly modulated large-area two-dimensional square photonic lattice slab was fabricated through optical induction technique in a photorefractive photovoltaic LiNbO(3):Fe crystal. Bragg-matched diffraction technique was used to characterize the square photonic lattice slab. Interestingly, linear discrete diffraction typical for waveguide arrays was observed in such a square photonic lattice slab, indicating that the lattice slab can be viewed effectively as a one-dimensional waveguide array. Furthermore, discrete soliton was demonstrated in the photonic lattice slab due to a saturable self-defocusing nonlinearity arising from the bulk photorefractive photovoltaic effect of LiNbO(3):Fe.

Two-dimensional non-reciprocal transmission in dynamically modulated photonic lattices

We propose a method for realizing two-dimensional (2D) non-reciprocal (one-way) transmission of discretized light in a dynamically modulated optical waveguide array. By adjusting the phase of the modulation between the defect site and the most adjacent waveguides, asymmetric transmission in the same layer or between the first and third waveguide layers can be obtained. In particular, when the defect waveguide is lossless, 2D non-reciprocal transmission is realized perfectly.

Nonlinear surface waves in curved waveguide arrays

The features and applications of linear and nonlinear surface waves in periodic photonic structures are attracting increasing attention. It was found that, while strong surface localization is impossible for an array of identical waveguides, Tamm surface waves can exist when the edge waveguide is modified and the introduced detuning exceeds a certain threshold [1]. On the other hand, it was recently predicted theoretically and demonstrated experimentally that arrays of periodically curved waveguide arrays can support a novel type of linear surface modes without any surface defects [2]. In this work, we study, for the first time to our knowledge, the interplay between both types of localized surface modes at the edge of a semi-infinite periodically curved waveguide array with a surface defect. We demonstrate experimentally the signature of such modes, and show that nonlinear beam self-action can provide effective control and switching between different surface states.