Investigation For High Frequency Dynamic Characteristics And Electro-Optic Modulators Of BaTiO₃ Crystal Thin Film

With the advents of semiconductor laser and low loss fiber,optical communication networks are being developed rapidly.Meanwhile,the rapid developments of the internet of things,the big data and the artificial intelligence in recent years are promoting the people’s demands for data transmission rate and data capacity of optical communications systems are also increasing.In order to expand the transmission rate and capacity of optical communications systems,numerous efforts have been devoted on the research and development of the related theories and technologies,which has promoted the continuous development and progress of various new optoelectronic devices and transmission systems.In an optical communication system,the electro-optic modulator is a core of the transmitter where it converts the high-frequency electrical signal into high-speed digital pulse optical signal,which is equivalent to the heart of the system.Therefore,the research and development of high-performance electro-optic modulators is one of the key problems in solving the high-speed optical communication networks.BaTiO₃,as a typical ferroelectric crystal,has the advantages of ultra-high electro-optic coefficient,special electro-optic modulation mechanism,compatibility/integrity with silicon photonic technology,so it is one of the best electro-optic materials for the research and development of high-performance electro-optic modulators.Therefore,in the past two decades,researchers have carried out research on domain structure,physical properties,electro-optical effect,modulation theory,device structure and processing technology of BaTiO₃ crystal film,and achieved a lot of important results.In this dissertation,based on the electro-optic characteristics and high-frequency dynamic properties of BaTiO₃ crystal film,the special electro-optic modulation mechanism and high-frequency microwave dynamic physical characteristics of BaTiO₃ crystal film waveguide are studied by using nonlinear electro-optical modulation theory and embedded waveguide electrode device structure to improve the modulation bandwidth.The dynamic interference of light waves in Mach-Zehnder interferometer intensity electro-optic modulator caused by phase-polarization enhanced birefringence electro-optic modulation is studied to reduce the bit energy,and the BaTiO₃ crystal thin-film waveguide intensity electro-optic modulator is constructed.Accordingly,this work lays a theoretical foundation and provides a reference for the further investigations of high performance BaTiO₃ crystal thin film waveguide intensity electro-optic modulators,and shows the very important practical significance and scientific value.The main research contents and results are as follows:（1）Based on the nonlinear electro-optic modulation model of the c-axis BaTiO₃ crystal film,the electro-optic modulation mechanism of the Mach-Zehnder interferometer waveguide structure was investigated,the phase-polarization modulation scheme is proposed,and the theoretical model of interference output is also established on this basis.Compared with the traditional optical phase modulation scheme,the phase-polarization modulation scheme improves the optical phase conversion efficiency of electro-optic modulation process and effectively compresses the peak width of interference output signal,which lays a theoretical foundation for the study of high-performance BaTiO₃ crystal thin film waveguide intensity electro-optic modulators.（2）Based on the theoretical model of phase-polarization modulation interference output,the theoretical model of equivalent half-wave voltage and bit energy of Mach-Zehnder interferometer electro-optic modulators with phase-polarization enhanced modulation is established.Then,with the aid of waveguide-electrode embedded structure and non-linear electro-optic modulation theory,the intensity electro-optic modulator was greatly optimized in the parameters of half-wave voltage,electro-optic modulation figure-of-merit,maximum phase conversion rate,equivalent half-wave voltage,and bit energy,providing a theoretical foundation for high performance intensity of BaTiO₃ crystal thin film waveguide electro-optic modulator research.（3）Starting with the polarization characteristics of BaTiO₃ crystal thin films,analyzed the thermal effect and the polarization ratio of crystal axis on the polarization property,and further electro-optic property of BaTiO₃ crystal thin film,so this work provided a reference base for the BaTiO₃ crystal thin film waveguide intensity electro-optic modulators.（4）Based on the optical bandwidth definition of BaTiO₃ thin film waveguide intensity electro-optic modulator and the high frequency dynamic physical characteristics of BaTiO₃thin film,a theoretical model of microwave bandwidth and a theoretical model of high frequency dynamic optical modulation are established.Further,combining with embedded waveguide electrode structure,for the c-axis intensity of BaTiO₃ crystal thin film waveguide electro-optic modulator,simulated/designed the device configuration,analyzed the modulation performance,demonstrated the feasibility of its implementation 100GHz bandwidth,providing a theoretical base for building the prototype devices of high-performance intensity of BaTiO₃ crystal thin film waveguide electro-optic modulator.（5）Based on the embedded waveguide-electrode structure,a c-axis BaTiO₃ crystal thin film waveguide electro-optic modulator with Mach-Zehnder interferometer construction was designed and fabricated,and its modulation performance was tested experimentally,so the phase-polarization ensemble electro-optic modulation effect of BaTiO₃ crystal thin film waveguide intensity electro-optic modulator was verified.With the experimental results,the performance parameters of the BaTiO₃ crystal thin film waveguide intensity electro-optic modulator are simulated and analyzed,which further illustrates the superiority of the phase-polarization ensemble electro-optic modulation and the feasibility of the high-bandwidth low-bit-energy electro-optic modulators.