Abstract

Spatial solitary waves propagate in a nonlinear medium by balancing diffraction with a self-focusing nonlinearity. These waves are of fundamental interest, but are also of technological interest if they are stable under propagation. Although a pure Kerr nonlinearity (Δn = n₂I, n₂ > 0) is sufficient to form stable beams diffraction in one transverse dimension (1D), it does not lead to stable self-trapping in two transverse dimensions (2D).¹ Our recent measurements indicate that polydiacetylene para-toluene sulfonate (PTS) has n₂ > 0 and, in addition, n₃ < 0 (Δn = n₂I + n₃l²), which now allows stable solitary wave propagation with low linear loss and negligible nonlinear loss at 1600 nm.^2,3 We now report numerical simulations of beam propagation in PTS, using measured values for n₂ and n₃, and demonstrate stable self-trapping and a new phenomenon in which a Gaussian input beam evolves into an expanding spatial ring and interpret these results in the context of the variational model of nonlinear Gaussian beam propagation. We also show preliminary experimental results suggesting the presence of ring formation.

© 1996 Optical Society of America