The study of surface SHG and polygonal microcavity design for nonlinear applications on LiNbO3

Sono, Tleyane J. (2009) The study of surface SHG and polygonal microcavity design for nonlinear applications on LiNbO₃. University of Southampton, Optoelectronic Research Centre, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

A z-cut congruent lithium niobate crystal (LiNbO₃) has been used in this thesis, as a platform for the surface second harmonic generation (SHG) studies and for the designs of polygonal microcavities for nonlinear applications.

Reflection second harmonic generation (RSHG) experiments were performed on LiNbO₃ to reveal the interfacial layer symmetry as the crystal is rotated around the z axis. RSHG was also used, unsuccessfully as a non-destructive tool to map the domain-inverted area in the poled LiNbO₃ crystals. But nevertheless, the polarity of the direction of the y-axis of the crystal was determined from RSHG data and the data shows that this direction also inverts, during domain inversion. RSHG was used unsuccessfully to monitor the relaxation of the internal field within the domain inverted area of the poled LiNbO₃.

A general operational principle of optical microcavities was discussed, in which a detailed theory governing the operational modes of a resonating hexagonal microcavity, made from bulk LiNbO₃ crystal was reviewed for nonlinear device applications. A model for a total internal reflection (TIR) technique for the QPM method in a double-resonating hexagonal microcavity was formulated. The TIR-QPM model was based on finding a suitable hexagonal dimension in which, both the fundamental and SHG signal resonate simultaneously while at the same time allowing QPM to occur via TIR. The TIR-QPM model and the FDTD simulation were used to demonstrate the potential capability of the double-resonating hexagonal microcavity for efficient SHG. The model to achieve a nonlinear microcavity by periodically poling ring/disk resonator Ti:LiNbO₃ ridge waveguide was introduced.