The Key Technologies Research For High Speed Electro-optic Modulators Based On Lithium Niobate Waveguide

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.Because the traditional Finite Difference Beam Propagation Method (FD-BPM) based on Crank-Nicholson scheme has the weakness of low accuracy and low efficiency, Generalized Douglas scheme with non-uniform grid is introduced to simulate two dimensions Mach-Zehnder optical waveguide. The optimal parameters of waveguide are acquired. In order to overcome the boundary truncation error, the author has developed BPM based on Series Expansion method (SEM) to calculate three dimensions M-Z waveguide. According to the results from analysis Y branch shape, the Y branch with cosine profile is better than that with rising- negative-sine profile. And the analytical results are identical to those of SEM-BPM, which shows the method is accurate.Another key technology in design optical modulator is how to design electrodes structure. Based on a free SC tool from University of Delaware, the author writes much programme to simulate electrodes structure of modulators in detail. The results show that the structures with high electrode, ridge waveguide, low refractive index buffer layer and slot in substrate 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. The results also show that the x-cut modulator has better performance than that of z-cut modulator in single drive.Besides velocity mismatch, the transmission loss will decrease bandwidth of modulators. In order to increase the bandwidth of modulators, the improved Finite Difference of Time Domain, namely C-FDTD, is used to analyses the relations 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.During high modulation frequency, the effect of chirp parameter on bandwidth is very obvious. The factors impact on chirp parameter are analyzed in this thesis. It shows that asymmetric Y branch, asymmetric modulation signal, the relative locations between electrodes and integral factor will have effect on chirp parameter. And the adjustable or negative chirp parameter can decrease bit error rate of transmission system through reducing dispersion penalty.Combined with the theories of electrooptic modulation and transmission line, the author has quantitatively analyzed the effect of velocity mismatch and transmission loss on output optical pulse. The results show that velocity mismatch will decrease the pulse peak, broaden the pulse width. While transmission loss only decreases the pulse peak,but not broaden the pulse width. On the other hand the results from frequency response show that the transmission loss and length of electrodes have large impact on frequency response. Because of many factor's effect, the relationships between the parameters of modulators and bandwidth and largest driving power are not simply decreasing or increasing.Our research results show that ridge waveguide has good effect on performance of modulators. The experiment researches on how to fabrication ridge op...