Electro-optic Tuning Of Lithium Niobate Waveguide Grating For A Long Period Of Time

With the rapid development of optical networks, wavelength routing and switchingdevices are becoming more and more important in the optical network, especially thegrating, which has a structure of the refractive index of cyclical changes and is veryimportant in the field of optical fiber communications and sensing application due to thenature of its optical transmission spectra changing along with the light wavelength.After years of development, various tunable grating devices, such as tunable opticalfilter, optical couplers, and light attenuator have been realized. In this dissertation, thecharacteristics of electro-optic tunable long-period waveguide grating （LPWG） onLiNbO₃were studied. The main work is provided as follows:Ⅰ. Principle of the LPWG systemFirstly, the electro-optic effect of lithium niobate （LiNbO₃） is introduced. Then, therefractive index distribution features of annealed proton exchange （APE） LiNbO₃optical waveguide was described and the single-mode LiNbO₃optical waveguides wasdesigned. Subsequently, the working principle of the LPWG is introduced. Theband-stop function is realized based on the coupling between the core mode andcladding mode at a particular wavelength. so, the important characteristics of LPWGwere investigated theoretically, such as the transmission spectral features, the resonantwavelength, period and bandwidth. All of these researches provide a theoretical basisfor designing and analyzing LPWG.Ⅱ. Design of the LPWG systemThe waveguide and electrode structure of LPWG utilizing a x-cut LiNbO₃waferwas designed. A two-step annealed proton exchange （APE） process was carried out tofabricate a cladding layer and channel waveguide on the x-cut LiNbO₃substrate. Theimportant parameters of the effective depth and width of the waveguide wereinvestigated and obtained. Then, the electrode structure was designed. Where, themaximum EO modulation can be obtained by putting the tunable electrodes on the sidesof the waveguide core, and with such an electrodes structure, large stop-band rejectioncan be realized by small drive voltage. Finally, the temperature characteristics of the device was investigated, and we found that the characteristics of the resonantwavelength moves to the short wavelength with increasing of the temperature, whichwill expand the application of the device.Ⅲ. Experiment and testAt last, in order to realize the four-layer LiNbO₃optical waveguide required byLPWG, a lot of APE experiments and precision optical tests were carried out and a largenumber of experimental data were obtained. Finally, by analyzing these data, someimportant parameters for realization of the four-layer LiNbO₃optical waveguiderequired by LPWG, such as the first and the second exchanging time, the first and thesecond annealed time was obtained, which is advantageous to the fabrication of thedevice.