Direct Laser Writing of LaBGeO5 Crystal-in-Glass Waveguide Enabling Frequency Conversion

We report on a technique of femtosecond laser-induced crystallization of glass, allowing improvement in the homogeneity of continuous crystalline tracks formed in lanthanum borogermanate glass using a focused beam with the elliptical-shaped waist cross section instead of a conventional circular one. Second harmonic generation produced by near-infrared femtosecond laser pulses was demonstrated in the waveguiding mode for the laser written crystalline track. The structure of the fabricated single crystalline waveguides is investigated with high resolution transmission electron microscopy and micro-Raman spectroscopy.