Fabrication And Characterization Of Optical-damage-resistant MgO-diffused Near-stoichiometric Ti:PPLN Stripe Waveguide

Recently,quasi-phase matching?QPM?based on periodically poled lithium niobate?PPLN?is one of the research focuses in the field of integrated optics.Furthermore,the absorption of THz wave could be limited to minimum by applying periodically poled lithium niobate on insulator?PP-LNOI?waveguide,which has a great development prospect in research and application of efficient stable source of THz radiation.In this paper,optical-damage-resistant near-stoichimetric Ti:Mg:PPLN stripe waveguide was fabricated to realize second-harmonic generation at 532nm wavelength.Submicron tantalum pentoxide ridge waveguide structure were fabricated on both silicon and LNOI substrate.Finally,a THz generation system was designed based on PPLN optical parametric amplification and PP-LNOI waveguide.This work provides a basis in fabrication of optical-damage-resistant high-power high-efficiency tunable THz radiation source on PPLN.The major work of the dissertation can be summarized as follows:?1?Near-stoichimetric?NS?Ti:Mg:LN stripe waveguide was fabricated by Ti-diffusion,MgO-diffusion and Li-rich vapor transport equilibration?VTE?on+Z face of a Z-cut LN sample.Then,the sample was carried out with an external field poling process and the NS Ti:Mg:PPLN stripe waveguide was obtained.Experiment results showed a conversion efficient of 101%W^-1 in frequency doubling process from1064nm to 532nm wavelength in NS Ti:Mg:PPLN stripe waveguide.The waveguide was observed to be optical-damage-resistant.The main factors that affect the performance of the waveguide were analyzed by the observation of the reversed domain structure in waveguide region and the poling system was improved.?2?Tantalum pentoxide ridge waveguide was fabricated by sputtering tantalum film and following annealing process on silica-on-silicon substrate.End-fire coupling was taken with fiber lens.The results showed that the waveguide was single mode at1.55?m wavelength and the propagation loss was measured to be 1.2dB/cm.The influence factors of waveguide loss were discussed with X-ray diffraction pattern.Tantalum pentoxide ridge structure was also fabricated on the LNOI substrate.?3?According to the QPM theories,we designed the poling periods of optical parametric amplifier to generate 1.5?m tunable output with pump laser at 1064nm wavelength.We also calculated the PPLN poling periods of 2.53THz⁴.47THz tunable terahertz radiation generation using a 1.55?m laser as signal beam.Finally,a THz generation system was designed based on PPLN optical parametric amplification and PP-LNOI waveguide.Innovation points contained in this dissertation includes:1)NS Ti:Mg:PPLN stripe waveguide was fabricated by Ti/MgO diffusion,Li-rich VTE,and external field poling process for the first time.The waveguide was optical-damage-resistant at room temperature.The adverse effects on perimeter reversed domain forming of both Ti-diffusion and MgO-doping was eliminated.2)Ridge waveguide structure was fabricated on LNOI chip.The PP-LNOI composite waveguide structure for THz wave generation was designed,which opening up a new way for the development of the terahertz radiation based on PPLN.