Light-assisted domain engineering, waveguide fabrication and microstructuring of lithium niobate

Abstract

The thesis is focussing on the interaction of lithium niobate with UV and ultrafast laser radiation to achieve 1) ferroelectric domain inversion, 2) waveguide fabrication, and 3) surface microstructuring. Preferential ferroelectric domain inversion has been demonstrated by 'latent light-assisted poling' and 'inhibition of poling' using ultrafast laser irradiation at 400 nm and CW highly absorbed UV radiation (305..244 nm) respectively. The characteristics of the resultant domains have been experimentally investigated as a function of the fabrication conditions and a theoretical model have been proposed to explain the experimental observations. UV radiation in the 305 nm to 244 nm range have been used for the fabrication of optical waveguides in lithium niobate. The waveguiding characteristics and electro-optic response of the UV written optical channel waveguides have been investigated experimentally. Inhibition of poling and post processing has been used for the fabrication of ridge waveguide structures with enhanced refractive index change. Finally, a method for the fabrication of ultra-smooth lithium niobate single crystal photonic microstructures has been proposed. The method is based on surface tension reshaping of surface microstructures which are produced by preferential poling and subsequent etching. Whispering gallery mode resonators have been fabricated and characterised here