Quasi-Phase Matching of Third-Order Nonlinear Processes by Direct Laser Writing

Direct laser-writing (DLW) is a well-known approach for creating photonic structures by locally modifying the refractive index of a material [1]. In recent decades, waveguides, splitters, selective filters, and more complex structures have been successfully demonstrated. Experiments on photo-thermo-refractive (PTR) glasses and laser-modified materials have revealed that the modulation of the refractive index is accompanied by a modulation of the third-order nonlinear properties, as demonstrated by various types of non-colinear third-harmonic generation (THG) [2]. This particular property arises from the strong correlation between the linear and non-linear indices [3].