The Research Of Graphene-based Electro-absorption Modulator

Electro-optic modulator is a critical device in optical fiber communication systems, whose performance will directly affect the performance of network transmission. With the development of optical fiber communication technology, electro-optic modulator develops towards the direction of small size, wide bandwidth and low loss. Traditional modulator devices tend to have disadvantages of large volume, difficulty in integration, high modulation voltage, high production cost and so on. Graphene has excellent electrical, optical properties, such as zero-bandgap, high carrier mobility, high light transmittance, which make it attract more and more attention. Therefore, the electro-optic modulators based on graphene have been widely studied in recent years.The thesis firstly describes the advantages and disadvantages of the traditional modulators, including LiNbO3 modulator, silicon-based light modulator and organic polymer light modulator, and introduces the energy band structure, unique optical and electrical properties of graphene. Because of these excellent properties, the interaction between graphene and light is very strong. Therefore, the electro-absorption modulator based on graphene has the advantages of small size, wide bandwidth, high modulation speed, compatible with CMOS and good thermal stability.Next the thesis introduces the operating principle of electro-absorption modulator based on graphene and analyzes the variation of graphene’s chemical potential as a function of the applied voltage. The thesis also shows how the electrical conductivity, the dielectric constant, the refractive index and other parameters of graphene change with its chemical potential. Then the simulation analysis of waveguide with different structures is carried on, and the impact of graphene position in the waveguide, material and thickness of isolation medium and graphene layers on the refractive index of the waveguide is understood. The impact also reflects the ability of light absorption. By comparison, the thesis puts graphene layers under the ridge waveguide and adjusts the height of ridge waveguide and silicon layer, then the graphene layers locate in the strongest light field. And the use of small thickness, low dielectric constant isolation medium makes the modulator performance optimized.Finally, on the basis of the above analysis, the thesis continues to optimize the waveguide structure and proppses an electro-absorption modulator with four graphene layers. The two layers are below the waveguide, the other two layers are in the waveguide. The distance between the two parts of grapheme is adjusted and the mode power attenuation of different structures are analyzed, then the thesis gets the optimal distance. The calculation shows that the electro-absorption modulator with four graphene layers has the advantages of small volume, large extinction ratio, large modulation bandwidth, low insertion loss and low energy consumption.