Symmetry-breaking diffraction and dynamic self-trapping in optically induced hexagonal photonic lattices

Abstract

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.

Effect of nonlinearity on dynamic diffraction and interband coupling in two-dimensional hexagonal photonic lattices

“…We consider two-dimensional hexagonal photonic lattices which are optically induced in a photorefractive crystal [34,35]. In order to compensate for the distortion of the induced refractive index pattern due to the photorefractive anisotropy, we use a stretched lattice geometry, with the horizontal and vertical lattice constants resulting in a ratio of η = d y /d x ≈ 2.4, compared to η = √ 3 for the unperturbed hexagonal symmetry [8,[36][37][38]. A simulated intensity distribution of the lattice wave is shown in Fig.…”

Discrete solitons and vortices in anisotropic hexagonal and honeycomb lattices

“…In recent years, the emphasis has somewhat shifted from the consideration of the more customary square lattices to the examination of lattices of hexagonal or honeycomb form. There, a source of emphasis has again been localization and self-trapping in the form of solitonic and vortical structures [7][8][9], but also other aspects have been studied including, e.g., Bloch states [10]. A significant fraction of the focus has been on the emulation by these optical systems of "photonic graphene", leading to numerous remarkable features, including the creation, destruction and experimental observation of topologically protected, so-called, edge states [11,12], and also the emergence of pseudospin and angular momentum [13].…”

Tunable self-shifting Bloch modes in anisotropic hexagonal photonic lattices

“…In a typical photonic lattice, the ability to manipulate light relies on the photonic bandgap design [1,2]. Many interesting phenomena have been observed, such as anomalous diffraction and refraction [3], conical diffraction [4,5], and symmetry-breaking diffraction [6]. According to the Floquet-Bloch theorem, beam propagation in photonic lattices can be analyzed from spatially extended Bloch waves as a complete orthogonal set of allowed eigenmodes of the lattice [2].…”

“…This makes the high-symmetry points always stay at the maximum or minimum points (i.e., the zero-refraction positions) of the diffraction curves, and the corresponding Bloch waves cannot move transversely. Thus, the moving of the Bloch waves is a phenomenon particular to hexagonal lattices and can be considered a type of symmetry-breaking propagation in addition to that in [6].…”