M-z-loss Characteristics Of The Lithium Niobate Modulator

High speed electro-optic modulators have been key devices for large capacity optical fiber transmission network and high speed information process in opto-electronic system. Because China masters few core technologies about the devices, developing of high speed electro-optic modulators with China's intellectual property is in favor of the long–term development for Chinese opto-electronic industry.In this thesis, the emphases are placed on the key technologies in the design and fabrication of Lithium Niobate (LiNbO3) electro-optic modulators based on the introduction of the devices'development and application in the world. Finite Difference Beam Propagation Method (FD-BPM) is introduced to simulate the loss of Mach-Zehnder optical waveguide. The optimal parameters of waveguide are acquired.The analysis concentrates on those performances of a modulator: the loss from Y branch, conductor loss, dielectric loss, radiation loss and transmission loss. The Y branch loss as the main element is analyzed by FD-BPM. The thesis gives a simulation result of bend loss and transmission loss of Y branch. According to the results from analysis Y branch shape, the Y branch with cosine profile is better than that with rising- negative-sine profile.Another key technology in design optical modulator is how to design electrodes structure. The author simulates electrodes structure of modulators in detail. The results show that the structures with high electrode, ridge waveguide and low refractive index buffer layer can improve the performance of modulators in different degree. But these parameters have different effect on bandwidth, characteristic impedance and conductor loss; compromising structure must be adopted in practical design to gain perfect modulation performance. Besides velocity mismatch, the transmission loss is another important parameter of modulators. Between conductor loss, dielectric loss, radiation loss and modulation frequency with different electrode's parameters. It can be seen that modulation frequency is higher, dielectric loss and radiation loss have larger impact on bandwidth, even larger than that of conductor loss. The bandwidth can become larger through improve electrodes structure, because all structure parameters have effect on different loss.The experiment researches on proton exchange LiNbO3 optical waveguide have been done.