Experimental Study On Tunable Filter Based On Lithium Niobate Long Period Waveguide Grating

With the development of optical fiber communication and fiber-to-the-home and the advent of digital and information society,higher requirements have been placed on optoelectronic devices,such as tunable filters,tunable dispersion compensators,and controllable optical arbitrary waveforms,and so on.The key technology of these devices is the ability to dynamically tune their spectral response.Researching low-cost and miniaturized devices with dynamically tunable spectral response plays a key role in the future development of optical communications in the direction of high speed,large capacity,and intelligence.As a commonly used optical filter,the grating's spectral characteristics are determined by its own material properties and refractive index distribution.In theory,the spectral response of different filter characteristics(square top,steep side,low side lobes,flat dispersion)can be produced by varying the amplitude,period and phase distribution of the refractive index modulation of the grating.Waveguide gratings made of lithium niobate crystals have been widely studied and applied due to their large electro-optic coefficient,fast tuning speed,good thermal stability and low cost.Therefore,the exploration and research of tunable optical filters based on lithium niobate waveguide gratings will have important theoretical and practical value.The main work of this paper is as follows:1.A method for fabricating long-period waveguide gratings is proposed.The method uses a patterned long-period grating amplitude mask,combined with a photolithography and annealed proton exchange waveguide fabrication process,to fabricate a long-period waveguide grating in a x-cut lithium niobate substrate.The influence of the grating length,waveguide width difference and the period of the long-period waveguide grating on its spectral characteristics are analyzed by simulation.The amplitude mask of long-period waveguide grating is designed,and the fabrication process is described.The experimental waveguide and long-period waveguide grating were fabricated and the spectrum of waveguide and waveguide grating was measured.2.Based on the uniform phase-shifted long-period grating,the voltage-tuned waveguide grating filter is designed and fabricated by the electro-optical effect of lithium niobate crystal.The gold electrode is sputtered on both sides of the long-period waveguide grating on the sample fabricated by the APE process.The tunability of the filter for wavelength,amplitude,and transmittance is achieved by varying the magnitude of the applied electric field.3.The spectral characteristics of cascaded long-period waveguide gratings are analyzed.A tunable comb filter is proposed by using the electro-optical effect of lithium niobate crystal.According to the photorefractive effect of lithium niobate crystal,a long period waveguide grating was fabricated by lithography on a titanium diffusion lithium niobate waveguide using an amplitude mask and the preliminary experimental results were obtained.