Ultrashort pulse propagation through depressed-cladding channel waveguides in YAG crystal: Spatio-temporal characterization

Abstract

Inscription of optical waveguides by direct femtosecond laser irradiation has become a very versatile tool for the development of integrated photonic devices, such as waveguide lasers, frequency converters or photonic lanterns, among many others. The potential application of such devices for the control and manipulation of ultrashort pulses requires the precise knowledge of the temporal distortions that may be induced in the pulse propagation. Currently, research in this topic is scarce, and to our knowledge there is no previous experimental study on the spatio-temporal characterization at the output of waveguides inscribed inside crystals. Here, we have firstly fabricated depressedcladding waveguides with different modal behavior in YAG crystal by direct femtosecond laser irradiation. Then, we implemented an experimental method based on the fiber coupler assisted spectral interferometry technique, that allows obtaining: 1) the temporal dispersion of a pulse at the output of an inscribed waveguide and, 2) full spatio-spectral and spatio-temporal characterization of the output of single-mode and multi-mode waveguides. Our results suggest that the main contribution to the pulse dispersion is due to the material dispersion. Moreover, we found that multimodal waveguides may induce an appreciable inhomogeneity in the temporal features of the pulses that needs to be taken into account in the design of complex devices.

Femtosecond laser direct writing of flexibly configured waveguide geometries in optical crystals: fabrication and application

“…These laser tracks serve as either beam blockers or confiners that reshape the intensity profile of the propagating guided field over a gradually varied or a multi-element assembled configuration. At the expense of more complicated designs and longer fabrication time, photonic-lattice-like cladding waveguides exhibit a designable feature for beam manipulation in a 3D manner, which paves a way to construct compact optical devices based on a wide range of optical crystals [51][52][53][54][55][56] . Furthermore, it has been found that the amount of the track lattice layers is an important factor for light field restriction: multi-layer track lattice offers better light confinement than a single-layer structure 49 .…”