Research On High Speed Electro-optic Modulators Based On Silicon-graphene

Microwave photonics is a technology that combines photonic technology and radio frequency technology. It uses photonic method to solve the problems of the generation and processing of ultra high frequency microwave signals. The modulator is a device that converts microwave signals into optical signals, it is the key device for microwave signal generation and processing. Power consumption, size and weight of microwave photonics devices is an momentous index of performance , so integrated microwave photonics has become one of the significant direction of development, and the integrated electro-optic modulator has become an important part of the integrated microwave photonic devices.At present, the materials used in photonic integrated technology has problems such as bad performance in modulation efficiency, difficult in integration and high production costs. Graphene, as a two-dimensional material which widely studied in recent years, has the advantages of high carrier mobility, strong interaction with light and low integration cost. It is an ideal material for integrated microwave photonics. Silicon-graphene based electro-optic modulator enhanced the interaction of graphene and the light by taking advantage of evanescent wave, and increased the interaction range, which can improve the efficiency of microwave photonic modulators. The silicon-graphene based electro-optic modulator provides a new and more efficient integrated solutions for microwave photonics.Aiming at the application of silicon-graphene based electro-optic modulator in integrated microwave photonics, theoretical calculation and simulation analysis of graphene electro-optic modulator parameters was researched, manufacture and corresponding design of the test device was carried out, finally on silicon-graphene based electro-optic modulator was experimentally studied preliminary.This thesis focuses on the application of silicon-graphene based electro-optic mod-ulator in the field of microwave photonics, reviewed the domestic and foreign research.In recent five years, a number of foreign research group has made test devices of silicon-graphene based electro-optic modulator. While there is a little disparity between domestic research and abroad, there are many simulation results in domestic research, and a small number of experimental studies have been reported in recent one year or two .First of all, we carried out the analysis of graphene electro-optic modulator princi-ple theory, focused on the shortage of silicon material, proposed silicon-graphene based composite structure of electro-optic modulator, analyzed the electrical and optical prop-erties of graphene using the energy band structure of graphene, a graphene electro-optic property model was built, put forward the principle scheme of graphene electro-optic modulation. Aiming at the design and optimization of silicon waveguide, waveguide properties of different parameters were simulated by the simulation software, analyzed the transmission and loss characteristics of different waveguide structure, put forward the design scheme of silicon waveguide; For the design and optimization of the modulator,we used multi-software co-simulation, analyzed the influence of different structure and parameters of graphene on the modulator performance. The results show a modulator with 200?m graphene , maximum modulation depth is 22dB, as to the 3dB modulation depth,50?m long graphene is needed; The modulation depth of Mach Zehnder modu-lator with 250?m graphene can reach 35dB, the modulator with 150?m graphene can theoretically reach 8.3dB;Secondly, focused on the fabrication of silicon-graphene based electro-optic modula-tor, combined simulation results with industrial standards, the processing layout design of modulator was carried out. By improving the process, the metal coating and the patterning of graphene has been resolved. The fabrication of Si based electro-optic modulator has been accomplished by electron beam exposure, magnetron sputtering and ion etching.Finally, we built the test platform to test the static performance and dynamic re-sponse of silicon-graphene based electro-optic modulator, the static performance of straight waveguide modulator was experimentally tested, the research is conducted on the transmission efficiency of the waveguide without graphene, transmission efficiency with different modulation wavelength, and the power of the modulated light transmittance and dynamic response of electrical signals, the experimental results show that the system modulation depth is about 2dB.