Technology of three-dimensional femtosecond writing for creating integrated optics elements

A permanent change in the refractive index affected by femtosecond laser pulses at a small depth (2–15 μm) under the surface of a lithium niobate crystal has been studied. Based on the technology of femtosecond writing, solutions for the problems of industrial electro-optical modulators are proposed. For interference schemes obtained by lithographic methods, a correction track with a reduced refractive index (Δn = –3 ∙ 10–3) was writing to reduce the coupling between the channels of the splitter and to increase its temperature stability. Apart from the above, a possibility of a fully femtosecond writing of a depressed cladding waveguide with a core diameter of 12 μm at small depths below the surface of a lithium niobate crystal has been demonstrated to create a noninterference electro-optical modulator based on the effect of electrooptic rotation of polarization.