The Research Of Tunable High Order Bragg Grating Based On LiNbO₃ Waveguide

In recent decades,with the rapid development of communication technology,the demands of people for transmission rate and bandwidth of communication systems has been increasing.The all-optical communication system with the characteristics of high speed,long distance and large capacity transmission has attracted more and more attention of researchers.However,the integrated optical devices and systems still restrict the development of all-optical communication system.The devices based on optical fiber are difficult to integrate,so that more and more researchers turn their attention to waveguide devices made of various materials.In all of those,the waveguide devices based on LiNbO₃ crystal has been abroad applicated due to the unique electro-optic performance.The Bragg waveguide grating plays an important role in the integrated optical systems,it is the basic component of many filters and sensors.Fabricating the first-order Bragg grating that the period is only hundreds of nanometers requires high precision equipment like focused ion beam etching?FIB?and electron beam etching?EBL?,which lead to a high production cost.In order to avoid this problem,a high-order Bragg grating that based on LiNbO₃ waveguide is proposed in this dissertation.The period of high-order Bragg gratings can reach to several microns,so that it can be fabricated by UV photolithograph with a low production cost.In this dissertation,the working principle,device design,fabrication and testing results of the proposed high-order Bragg grating based on LiNbO₃ waveguide are studied.The main work is as follows:Firstly,the development history and research status of waveguide grating is introduced,and the research significance of high-order Bragg grating based on LiNbO₃waveguide is discussed.Secondly,the theoretical knowledge of high-order Bragg grating is introduced,including the refractive index distribution and mode analysis of LiNbO₃ waveguide,and the coupled mode theory of high-order Bragg grating.Then,the design idea of high-order Bragg grating based on LiNbO₃ waveguide is introduced.The basic structural parameters of device are determined through computer simulation,including waveguide size,grating period,grating length,etc.After that,the fabrication and testing of the device are studied.It mainly includes the design of the three fabrication schemes,the design of the mask,the fabrication of the devices,the testing results and the optimization of the device parameters.Testing results indicate that the high-order Bragg grating that made by second-exchange method has a good performance,the sample 1 has two stopbands of 8 dB and 10 dB at 1537 nm and1572 nm,and sample 2 has four stopbands of 9 dB,12.5 dB,7 dB and 9 dB at 1538 nm,1557 nm,1576 nm and 1595 nm,and the transmission spectrums can be tuned by electro-optic and annealing.Finally,the experimental results are analyzed,and the optimized scheme are proposed.On this basis,the whole work is summarized and prospected.