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The effect of a waveguide on the formation of optical terahertz solitons

Nowadays the generation of terahertz pulses using the mechanism of optical rectification is intensively studied both theoretically and experimentally. If the group velocity of an optical pulse is equal to the phase velocity in the terahertz range of a medium with quadratic nonlinearity, then a two-component optical-terahertz temporal soliton can be formed. In the present work, we study the possibility of forming an optical-terahertz spatiotemporal soliton (optical-terahertz bullet) in a gradient focusing waveguide. If the duration of the input optical pulse lies in the femtosecond region, then when generating a terahertz signal, the nonlinearity dispersion is important. This also leads to the influence of the phase modulation of the optical pulse on the generation process. We take this circumstance into account when considering the formation of optical-terahertz bullets. The system of related equations for the complex envelope of the optical pulse and the electric field of the THz pulse is solved numerically. The original conservative nonlinear finite-difference scheme is realized with the help of a pseudo-spectral method. We find the conditions under which it is possible to trap an optical terahertz pulse into a focusing waveguide with the formation of optical-terahertz bullets.