Parametric Solitons in Nonlinear Photonic Crystals

Abstract

Abstract:We present theoretical and experimental investigations on the soliton dynamics associated to multiple second harmonic generation resonances in two-dimensional nonlinear photonic crystals, highlighting a wealth of new possibilities for soliton management in such structures.Self-guiding filaments of light or optical spatial solitons, resulting from the balance between nonlinearity and diffraction, hold promise for the development of novel, reconfigurable photonic architectures for switching and routing. They have been predicted and demonstrated in a variety of physical settings [1], including quadratic media. In the latter case, diffractive beam spreading is counteracted by the parametric interplay of three wavelength components, resulting in the mutual trapping and locking of multi-frequency waves (i. e. multicolor solitons). The original predictions on soliton formation via three-wave mixing [2] were confirmed nearly a decade ago by the first experiments carried out in KTP and LiNbO 3 [3][4]. Since then, the development of Quasi-Phase-Matching (QPM) materials such as Periodically Poled LiNbO 3 (PPLN) has opened up new possibilities for quadratic soliton science and engineering [5][6]. QPM has also recently been extended to higher-dimensionalities, to demonstrate 2D PPLN Nonlinear Photonic Crystals (NPC), i.e. 2D lattices in the second-order susceptibility χ (2) , enabling novel and more versatile geometries for parametric interactions [7][8].Here we report the first experimental and theoretical investigations on soliton formation in two-dimensional NPC, using hexagonal lattices in lithium niobate. The studies were performed in a (1+1)D configuration, using buried planar waveguides embedded in the NPC structure for maximum efficiency [9]. The results unveil an excitingly rich scenario for soliton physics and optical processing, arising as a result of multiple spatial -as well as spectralnonlinear resonances in the 2D nonlinear lattice.The 2D NPC used in the experiments is an Hexagonally Poled Lithium Niobate (HexLN) planar waveguide fabricated by reverse-annealed proton-exchange [9], optimised for twin-beam second harmonic generation (TB SHG) from λ ω ∼ 1.55µm (Fig.