Study of Ti: sapphire double line waveguide written by femtosecond laser

Ti: sapphire crystal is one of the most important materials as a laser medium, due to its broad absorption band and widely tunable output band, therefore it has wide application in integrated optics. By femtosecond laser with repetition rate of 1 kHz, central wavelength of 800 nm and pulse width of 120 fs, double line waveguide in Ti:sapphire crystal is transversely written. The impacts of the processing conditions, i.e., inscribing depth, writing speed and the track distance on the waveguide formation are systematically studied, and the waveguide with better guiding mode is achieved when laser pulse energy is 2 μJ, inscribing depth is 175 μm, writing speed is 90 μm/s and the distance between two tacks is 26 μm. And the double line waveguide shows polarization dependent optical guiding. Based on the near-field mode intensity, the refractive index profile of the optical waveguide is reconstructed, and the max positive refractive index change is about 1.9×10^-4. In addition, by using the scattering technique, the propagation loss of the waveguide is 1.82 dB/cm.