Femtosecond Laser Writing of Optical Waveguides by Self-Induced Multiple Refocusing in LiTaO3 Crystal

We report on a one-step fabrication method of horizontal dual-line waveguides supporting TE guidance in LiTaO ₃ crystal utilizing multiple refocusing mechanisms of the femtosecond laser. Through the nonlinear process, multiple foci can be formed spontaneously with the interval of a few micrometers along the laser propagation direction. The number and the separation of focal spots, even the entire length of laser-induced tracks, could be modulated by varying the laser parameters. Taking advantage of this spontaneous phenomenon, we further implemented the multi-scan technique to write two parallel damage lines along transverse direction, realizing stress-induced waveguides by horizontal light confinement. Moreover, using this method, one-step two-channel guidance could also be demonstrated by adjusting the pulse energy. The fabrication details and waveguiding performances were studied by both experimental and computational methods. This paper opens the alternative way to construct complex integrated platforms in LiTaO ₃ crystal by using femtosecond laser writing.