High-repetition-rate femtosecond-laser inscription of low-loss thermally stable waveguides in lithium niobate

Abstract

Optical-lattice-like waveguides were fabricated in a z-cut lithium niobate crystal by an 11-MHz-repetition-rate pulsed laser. Two simple approaches based on varying the inscribing pulse energy in accordance with the position of the tracks were implemented to enhance the inscription results. Low propagation losses were observed in the visible and near-infrared parts of the spectrum. The minimum losses of less than (0.4 ± 0.1) dB/cm and (3.5 ± 0.2) dB/cm for transverse electric and transverse magnetic polarized light, respectively, in the fundamental guiding mode at 1550nm were achieved after heat treatment at 350∘C for three hours, and were preserved up to 700∘C.