Fabrication Of Periodically Poled Ti-diffused Near-stoichiometric Lithium Niobate Waveguide(Ti:PPLN)

Periodically poled Ti-diffused near-stoichiometric lithium niobate waveguide(Ti:PPLN) can be used as all-optical wavelength converter, mid-infrared laser lightsource and THz radiation. The dissertation launched a research of anear-stoichiometric Ti: PPLN waveguide, involving improving the high-voltagesquare wave pulse power supply system used in periodically poled process andstudying the impact of Li-rich VTE technology on LiNbO3domain. It makes furtherefforts to introduce the fabrication and characterization of near-stoichiometricTi:PPLN waveguide. The work can be summarized as below:1. Work had been done to improve the purchased high-voltage DC power to besuitable for the periodically poled experiment. A controllable signal generator, anoptical coupler circuit and a power amplifier were added to the system, which couldsupply high-voltage square wave pulse. The liquid electrode polarization device wasdeveloped containing electrode clamps and external polarization circuit. The externalpolarization circuit is equipped with an oscilloscope and a high voltage meter. Theycan detect the process of polarization.2. The relationship between the Li-rich VTE time and poling voltage wasinvestigated by the polarization system. A0.5mm thick Z-cut pure congruent LiNbO3was chosen as sample in the experiment. The result showed that the poling voltagedecreases linearly as Li-rich VTE time increases, when the Li-rich VTE time is lessthan25h. When the VTE treatment time is30h, domain inversion electric field has aminimum of4.0kV/mm. Furthermore, the impact of Li-rich VTE treatment onLiNbO3domain structure was studied. It was found that the Li-rich VTE process caneliminate the domains reversion caused by the heat treatment or Ti-diffused. Thisresearch makes a contribution to further optimize the preparation ofnear-stoichiometric Ti: PPLN waveguide.3. Fabrication and characterization of the near-stoichiometric Ti:PPLN stripwaveguide was developed. To fabricate the waveguide, a0.5mm thick Z-cut purecongruent LiNbO3substrate is prepared, then follow the process photolithography,coating, stripping, Ti-diffused, Li-rich VTE, periodically poled process, anear-stoichiometric Ti:PPLN waveguide was fabricated with7μm width and15mm length initial titanium strip. The poled period of the waveguide is160μm. Thecomponent and guided wave properties were characterized. The results show that: thewaveguide layer component is approximately stoichiometric ratio, besides toincreasing the waveguide loss, the periodically poled process did not significantlyaffect the other waveguide performances. Waveguide loss increased due to imperfectdomain structure. The etching method was applied to display the domain pattern andthe optical microscope was applied to observe the domain pattern.The above investigations are foundation for further research work.