Today more than ever, the application of the Internet has affected human’s life. Therefore, it is essential to increase the capacity of telecommunication in order to transmit large amount of data. Optical modulators in these systems are responsible to convert low frequency data into optical signals for data transmission enhancement. In past years, many materials have been used such as dielectric crystal, organic nonlinear optical materials, semiconductors, graphene and plasmonic effect. When light passes through dielectric crystal like lithium niobate and also is exposed by an electrical field, the light is modulated. Mach-Zehnder structure using lithium niobate have simple fabrication process, high extinction ratio and wide bandwidth that is also commercially attractive. High switching voltage and longer phase shifter length are the main challenges. The purpose of this thesis is to design a lithium niobate modulator that is easier for fabrication in comparison with previous works. Moreover, the bandwidth, switching voltage and extinction ratio are acceptable compared to prior structures. Of the former researches that exhibited high performance is the use of etched lithium niobate waveguide on top of a thin film lithium niobate. Such a waveguide has optical loss due to metal electrodes. For this reason, we can place signal electrode and ground electrode at the shortest distance from each other. As a result, the electrical field which is between the two electrodes, becomes stronger. The modulation on the waveguide that is placed between two electrodes increases, Vswitching:L decreases, switching voltage decreases and in some cases bandwidth increases. However, lithium niobate has a crystallian structure, the fabrication of such a waveguide is more expensive and complicated. Thus, there is a need for a waveguide that has low optical loss due to metal electrodes, simple fabrication and inexpensive material. In this work, silicon is used to solve the above problems. The designed waveguide is a hybrid structure including silicon–thin film lithium niobate–silicon. Based on the aforementioned hybrid waveguide, we designed three modulators that have the lowest optical loss due to metal electrodes and bending loss consequently the lowest Vswitching:L among similar modulators. Furthermore, because of the lowest Vswitching:L, the modulator lunches with very low voltage. Since modulators are designed with a silicon substrate, they are also compatible to CMOS circuits.Key Words: Microwave Photonics, Optical Fiber Communication, Electro-optic Modulators, Optical Waveguide, Mach-Zehnder Structure, Lithium Niobate.