Christian R. Rosberg

Observation of Surface Gap Solitons in Semi-Infinite Waveguide Arrays

We report on the observation of surface gap solitons found to exist at the interface between uniform and periodic dielectric media with defocusing nonlinearity. We demonstrate strong self-trapping at the edge of a LiNbO3 waveguide array and the formation of staggered surface solitons with propagation constant inside the first photonic band gap. We study the crossover between linear repulsion and nonlinear attraction at the surface, revealing the mechanism of nonlinearity-mediated stabilization of the surface gap modes.

Tunable diffraction and self-defocusing in liquid-filled photonic crystal fibers.

We suggest and demonstrate a novel platform for the study of tunable nonlinear light propagation in two-dimensional discrete systems, based on photonic crystal fibers filled with high index nonlinear liquids. Using the infiltrated cladding region of a photonic crystal fiber as a nonlinear waveguide array, we experimentally demonstrate highly tunable beam diffraction and thermal self-defocusing, and realize a compact all-optical power limiter based on a tunable nonlinear response.

Crossover from self-defocusing to discrete trapping in nonlinear waveguide arrays.

We predict a sharp crossover from nonlinear self-defocusing to discrete self-trapping of a narrow Gaussian beam with the increase of the refractive index contrast in a periodic photonic lattice. We demonstrate experimentally nonlinear discrete localization of light with defocusing nonlinearity by single site excitation in LiNbO(3) waveguide arrays.

Observation of two-dimensional nonlocal gap solitons

We demonstrate, both theoretically and experimentally, the existence of nonlocal gap solitons in two-dimensional periodic photonic structures with defocusing thermal nonlinearity. We employ liquid-infiltrated photonic crystal fibers and show how the system geometry can modify the effective response of a nonlocal medium and the properties of two-dimensional gap solitons.

Observation of nonlinear self-trapping in triangular photonic lattices

We experimentally study light self-trapping in triangular photonic lattices induced optically in nonlinear photorefractive crystals. We observe the formation of two-dimensional discrete and gap spatial solitons originating from the first and second bands of the linear transmission spectrum.

Demonstration of all-optical beam steering in modulated photonic lattices

We demonstrate experimentally all-optical beam steering in modulated photonic lattices induced optically by three-beam interference in a biased photorefractive crystal. We identify and characterize the key physical parameters governing the beam steering and show that the spatial resolution can be enhanced by the additional effect of nonlinear beam self-localization.

Tunable positive and negative refraction in optically-induced photonic lattices

We study tunable refraction of light in one-dimensional periodic lattices induced optically in a photorefractive crystal. We observe experimentally both positive and negative refraction of beams that selectively excite the first or second spectral bands of the periodic lattice, and we demonstrate tunability of the output beam position by dynamically adjusting the lattice depth. At higher laser intensities, beam broadening due to diffraction can be suppressed through nonlinear self-focusing while preserving the general steering properties.

Observation of surface gap solitons

We predict, in the framework of a nonlinear discrete model, and demonstrate experimentally in defocusing waveguide arrays, that self-localization near the edge of a photonic lattice can result in the formation of surface gap solitons.

Discrete interband mutual focusing in nonlinear photonic lattices

We study nonlinear coupling of mutually incoherent beams associated with different Floquet-Bloch waves in a one-dimensional optically-induced photonic lattice. We demonstrate experimentally how such interactions lead to asymmetric mutual focusing and, for waves with opposite diffraction properties, to simultaneous focusing and defocusing as well as discreteness-induced beam localization and reshaping effects.

Nonlinear Tamm states in periodic photonic structures

B ack in 1932, the famous Russian scientist Igor E. Tamm predicted that a truncated crystalline lattice could support special types of electronic states that are bound at the very edge of the semi-infinite periodic potential. 1 These states, known in many fields as Tamm states, represent a special class of spatially localized surface waves, which, in general, may appear at interfaces between different physical media. An optical analog of linear Tamm states has been described theoretically and demonstrated experimentally for an interface separating periodic and homogeneous dielectric materials. 2 Despite the fact that many theoretical concepts have been successfully introduced in the physics of surface waves, nonlinear Tamm states have never been experimentally observed. In a recent paper, we experimentally demonstrated self-action of a narrow laser beam propagating near the edge of a lithium niobate (LiNbO 3) waveguide array with defocusing nonlinearity and a semi-infinite periodic refractive index modulation in the transverse direc-lies within the photonic bandgap. This essential feature enables one to draw a direct analogy to the electronic Tamm states and extend this concept to the nonlinear regime, so that the surface gap solitons can be termed nonlinear Tamm states. They possess a unique combination of properties related to both electronic and optical surface waves and gap solitons. Part (c) of the figure depicts a three-dimensional representation of the spatial beam intensity distribution of a nonlinear Tamm state observed in experiment. 3 The nonlinear mode was excited by injecting a narrow probe beam into the surface waveguide at the edge of the periodic structure. Part (d) shows the corresponding interference pattern created when superimposing an inclined plane reference wave in order to reveal the phase structure of the output beam. A half-period vertical shift of the interference fringes, corresponding to an exact p phase jump in the horizontal beam direction, is clearly observed between each lattice site, as predicted by theory. 4 The ability to generate these types of optical surface modes could lead to novel and effective experimental tools for the study of nonlinear effects near surfaces. t tion, 3 as shown schematically in part (b) of the figure. For the first time to our knowledge, we observed the formation of surface gap solitons or nonlinear Tamm states. While linear surface modes do not exist in this kind of system, light self-trapping is observed in the nonlinear regime above a certain threshold power when the propagation …