Study On The Bragg-type Guided-wave Acousto-optic Modulator Driven By Surface Acoustic Wave

Bragg-type guided-wave acousto-optic modulator has a good prospect of applicationin the fields such as optical frequency-domain reflectometry, Q-switched fiber laser,and optical communication due to its many advantages, such as small size, low driverpower requirement, high switching speed, excellent design flexibility, and ease ofintegration.In order to design high-efficiency guided-wave acousto-optic devices, acomprehensive theoretical study on guided-wave acousto-optic interaction in LiNbO3and LiTaO3is carried out in this thesis. Experimental studies and theoretical design ofa new-type guided-wave acousto-optic modulator is performed. The main work andinnovations of this thesis are as following:1. The guided-wave acousto-optic interaction in LiNbO3is systematicallyanalyzed for the first time. The influences of crystal cut direction, propagationdirection and frequency of surface acoustic wave (SAW), parameters of opticalwaveguide, wavelength and modes of guided wave on guided-wave acousto-opticinteraction are studied respectively. TM polarized light with a well-concentratedoptical field modulated by200MHz SAW in128°YX-LiNbO3offers the highestefficiency of guided-wave acousto-optic interaction. Therefore,128°YX-LiNbO3isone of the best substrates for guided-wave acousto-optic modulator. Furthermore,XZ-LiNbO3can be used as the substrate of guided-wave acousto-optic deflector forlarge bandwidth of guided-wave acousto-optic interaction and nonsensitive topolarizations of optical wave.2. The guided-wave acousto-optic interaction in AlN/128°YX-LiNbO3isanalyzed theoretically. The AlN film can improve the temperature stability and theswitching speed of guided-wave acousto-optic interaction in128°YX-LiNbO3. For TMpolarized light with a well-scattered optical field, the use of AlN film can also greatlyimprove the efficiency of guided-wave acousto-optic interaction.3. LiTaO3is first proposed as the substrate of high-power guided-waveacousto-optic interaction. The efficiency of guided-wave acousto-optic interaction inLiTaO3is studied theoretically. TE polarized light with a well-concentrated opticalfield in X136°Y-LiTaO3offers the best performance in guided-wave acousto-opticinteraction. 4. Experiments of1.06μm new-type guided-wave acousto-optic modulator arecarried out. The insertion loss of the modulator is6dB, and the diffraction efficiencyis4.3%. In order to improve the performance of the modulator, the design parametersof modulator are optimized theoretically. The theoretical diffraction efficiency ofimproved modulator is82.3%, and the insertion loss is about3dB. The application oftapered waveguides with different transition boundary in modulator is analyzed. Theconvexly exponentially tapered waveguide offers better performance in modulator.5.1.55μm new-type guided-wave acousto-optic modulator with switching speedof tens ns is designed. The theoretical diffraction efficiency of the modulator is80.8%.The case of multiple wavelengths modulated simultaneously in modulator is studied.When using proton-exchange waveguide, the diffraction efficiency of modulator inthe C-, L-and S-bands is in the range of79.5%to80.8%. The thesis also firstproposes the design ideas of grid-type, comb-type and improved comb-type N×Nguided-wave acousto-optic switches.