Micro-spectroscopy investigation on femtosecond laser writing of LiNbO3 crystal

Abstract LiNbO3 is a widely used material for photonics. In this work, we have used femtosecond laser writing to inscribe both Type I and II structures in a same LiNbO3 crystal for direct comparison. The guiding properties of the laser-written waveguides are obtained, which indicates that only guidance along the extraordinary index polarization for both geometries. The micro-spectroscopy (i.e., photoluminescence and Raman) investigation reveals the difference on the crystal properties and lattice structural changes of two types of modifications. We have found that, the laser-induced modifications reveal the different structural changes of the LiNbO3 network for the Type I and II configurations, which reflects on the spectral properties of the spectra. The refractive index changes are correlated to the crystal defects and the stress field induced by the femtosecond laser pulses.