Fabrication and characterization of periodically poled lithium niobate single crystal fibers

The nonlinear frequency conversion approach remains as the dominant approach to generate new laser wavelengths that are hardly achievable via regular lasing techniques relying on population inversion. Increasing either a media's optical nonlinearity or the power density of a fundamental beam or increasing both at the same time is believed to be very effective in order to enhance the nonlinear conversion efficiency. In this research, periodic ferroelectric domain structure was introduced into lithium niobate single crystal fibers by electrical poling, which then allows simultaneous use of efficient quasi-phase matching (QPM) method and strong optical confinement inside an optical fiber guide. The introduced periodic domain structures were revealed using a crossly polarized optical microscope (CPOM) and a confocal scanning optical microscope (CSOM) for quality assurance. Efficient second-harmonic generation (SHG) characterization was also performed using such fibers.