Quadratic Array Spatial Solitons: New Phenomena in Nonlinear and Soliton Science

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0098647StegemanSpatial solitons are non-diffracting beams which can be self-trapped in Kerr, saturable Kerr, photorefractive and quadratically nonlinear media (near phase-matching for parametric mixing). Quadratic solitons are based on the second order nonlinearity X (2) and in the simplest case consist of a fundamental and a harmonic field which are mutually self-trapped as the y propagate. Previous experiments have dealt with solitons guided in homogeneous media, either in bulk or in waveguides. Recently Falk Lederer's group at Frederich Schiller University in Jena predicted that quadratic solitons can also be guided by arrays of closely spaced, parallel channel waveguides in Quasi-Phase-Matched (QPM) LiNbO3 at power levels of a few watts. These array solitons are guided by virtue of strongcoupling both between fundamental and harmonic fields, and between adjacent channels in the array. Their first observation, characterization and interactions between them are the thrust of the program proposed here. This research is expected to lead to the first bservations of novel solitons, position dependent soliton interactions and new guiding phenomena in array structures. This should also lead to new knowledge that can be generalized to the field of nonlinear discrete systems, an area not readily accessible by experiment to date.The PI is an integral and formal part of a European Community (EC) program to study novel applications of QPM LiNbO3. The European collaborators include Falk Lederer, as well as Wolfgang Sohler whose group (Un. Paderborn) has fabricated QPM LiNbO3 waveguides, phase-matched over 8 cms. In such samples for 20 um wide array spatial solitons, typically 1 cm is required for a soliton control operation or collision. Thus for the first time these waveguides offer the prospect of exciting such solitons and investigating multiple sequential soliton interactions. Furthermore, these samples allow soliton excitation at watt peak power levels, a reduction of orders of magnitude over previous cases.In collaboration with the Jena and Paderborn groups, the PI proposes to generate such array spatial solitons in QPM LiNbO3 slab waveguides, investigate their properties, including collisions and electro-optic and all-optical steering control. The PI's European partners are already funded by ROSA, an EC program which unfortunately does not allow funding of the US part. Here the PI requests funding for the component of the program.Although this program will be focused on basic science, the potential for applications will also be assessed. The extra degrees of freedom introduced by the array lead to a large variety of new stable soliton modes, many without analogs in homogenous quadratic media, and some which do not exist in any currently known nonlinear system. Their properties are in their early theoretical stages and will be investigated experimentally at 1550 nm wavelengths. Preliminary calculations have revealed a rich spectrum of interactions, including position-dependent outcomes, and they will be investigated experimentally. Soliton phenomena associated with gain (already demonstrated in erbium implanted QPM LiNbO3 at Paderborn) will also be investigated including focusing, deflection etc. Furthermore, scanning of the soliton across the array by changing its power, the channel separation, or the refractive index electro-optically will be studied.