Theoretical Research On Graphene-Based Electro-Absorption Modulation

Electro-optic modulator is one of the key components of an optical fiber communication network, its performance can directly determine the performance of the system. In future applications, electro-optic modulator requires high modulation speed, small footprint and easy integration. Graphene, as its unique electronic and optical properties, including ultra-high electron mobility, zero band-gap, linear absorption, has attracted great attention, and many graphene-based integrated optical device has been reported recently. Because of graphene’s unique light absorption characteristics, and the absorption rate can be modified by the gate-voltage, electro-absorption modulator based on graphene has been studied heavily recently.In this paper, a “sandwich” like modulator structure that sandwiched the double layer graphene between the ridge waveguide and an additional layer of high refractive index is studied. Theoretically study on the performance of the graphene-based electro-absorption, including theoretical analysis and simulation using COMSOL and MATLAB software is shown. The main work of this paper including:Firstly, a brief introduction to the optical fiber communication systems and different types of electro-optic modulator is shown. Then the research background and the research status of graphene-based modulators is introduced.Secondly, an introduction of the electronic and optical characteristics of graphene including energy level structure, electronic, band characteristics, optical absorption characteristics is given. Then the production method of graphene and how a graphene-based modulator works is simply described.Thirdly, as the absorption of graphene can be modulated by the gate-voltage, a discussion of the dependence of the Fermi level on gate-voltage, dependence of graphene’s complex refractive index and dielectric constant on Fremi level of grapheme is shown. Then simulation and analysis on the characteristics of the graphene-based waveguide using different waveguide structure and parameters through COMSOL software is given.At last, the performance of the modulator base on several key performance indicators is discussed. Calculation on each indicator respectively through MATLAB software with the help of the works before is shown. Then a discussion and comparison of each indicator under different waveguide parameter is given. At the end of this paper, as each modulators’ performance with different parameter are compared and analyzed, the optimize structure of the modulator is given.At present, as research on the grapheme based electro-optic modulator is not too much in China, our theoretical work in this paper might be helpful to those who will do some further theoretical and experimental studies of graphene-based electro-absorption modulator in the future.