Light coupling in single-track guiding structures obtained by femtosecond laser writing in lithium niobate

In this Letter we present a study of light coupling into a pair of Type II waveguides made of lithium niobate crystals by using femtosecond laser writing. Simulations based on the beam propagation method and optical fiber coupling experiments with the guiding structures showed good agreement. The presented results can be a suitable tool for designing high-performance optical circuits using femtosecond laser writing techniques for different technological requirements.