Direct Femtosecond Laser Writing of Nonlinear Photonic Crystals

Nonlinear optical processes, which govern the interaction of strong optical signals (e.g., laser beams or pulses) with the media in which these signals propagate, are of great importance for creation of coherent light sources at the frequency bands where the conventional lasers either perform poorly or are unavailable at all [1]. Moreover, the nonlinear processes are of interest because of their potential application in signal processing, mode-locking, pulse compression, etc. [2-4]. The efficiency of a nonlinear parametric process critically depends on relative phase locking of the interacting waves, which is formally expressed by the so-called phase matching condition requiring that phase velocities of all involved waves coincide. In typical optical media this condition cannot be naturally satisfied due to the refractive index dispersion.