Research On Long Period And High Order Bragg Waveguide Gratings Based On Lithography

With the application of integrated optical devices represented by waveguide gratings,the studies of waveguide gratings are becoming more and more extensive.Waveguide gratings can be fabricated on LiNb O₃ crystal,polymer,glass and other materials,their design structures are diverse.At present,the common manufacturing processes include: UV lithography,electron beam lithography,focused ion beam etching,double beam interference,etc.The Li Nb O₃ crystal has electro-optic effect,so the waveguide gratings fabricated with LiNbO₃ crystal can be used to realize the electronic tuning.In the paper,X cut LiNbO₃ crystals are used to be the substrate,using lithography and Titanium diffusion processes to fabricate the twice Titanium diffusion long period waveguide grating.The structures of long period waveguide grating and high order Bragg waveguide grating realized by LiNb O₃ waveguide fabrication process only once are proposed.This kind of long period waveguide grating and high order Bragg waveguide grating are fabricated by using lithography and annealed proton exchange.Details are as follows:1.The structure and characteristics of twice Titanium diffusion long period waveguide grating are analyzed.The effects of grating length and grating period on the transmission spectral properties are analyzed in theory.When coupling coefficient remains the same,with the grating length increases,zero bandwidth decreases,and transmissivity decreases first,then increases.The larger the grating period is,the larger the central wavelength is and transmissivity is minimun when the grating is full coupling.The twice Titanium diffusion long period waveguide grating with a period of 420 micrometers is fabricated on the LiNbO₃ single mode waveguide by lithography and Titanium diffusion in experiment and measurement of the grating transmission spectrum is explored.2.The long period waveguide grating structure realized by LiNbO₃ waveguide fabrication process only once is proposed.The effects of waveguide width difference and inclination angle of grating region on the transmission spectrum are analyzed in theory.With waveguide width difference increases,the zero bandwidth decreases and the transmissivity changes periodically.With the inclination angle of grating region decreases,the zero bandwidth decreases more slowly and the changing period of transmissivity become larger.The long period waveguide grating with a period of 100 micrometers order is fabricated only once on the LiNbO₃ by using lithography and annealed proton exchange in experiment and measurement of the grating transmission spectrum is explored.3.The high order tunable Bragg waveguide grating structure realized by LiNbO₃ waveguide fabrication process only once is proposed.The effects of duty cycle,waveguide width difference,inclination angle of grating region and applied voltage on reflectivespectrum of grating are analyzed in theory.With the duty cycle increases,the refractive index modulation changes periodically.When the best duty cycle is chosen,with the waveguide width difference increases,the maximum reflectivity and zero bandwidth increase and the central wavelength shifts to the longer wavelength.With the inclination angle of grating region decreases,the maximum reflectivity and the zero bandwidth increase more slowly and the shift of central wavelength become smaller.With the applied voltage increases,the reflective spectral shapes almost remain the same and central wavelength shifts to the longer wavelength.The high order Bragg waveguide grating with the period of micrometers order is fabricated only once on the Li NbO₃ by lithography and annealed proton exchange in experiment and the spectrum of the grating is measured and analyzed.