The High Speed Graphene Electro-optic Modulator Based On D-shape Fiber

With the increasing of communication capacity,we require higher performance of each device in optical communication system.Optical modulator is one of the indispensable devices in optical communication system.It is very important to study the new electro-optic modulator with larger extinction ratio and wider bandwidth.Graphene has many superior characteristics such as saturated absorption,the highest carrier mobility and absorption of broad spectrum.Using graphene as electro-optic material of the modulator is contribute to improve the modulation speed and modulation depth.D-shape fiber has a strong evanescent field on surface,due to the core is near to the fiber surface.When D-shape optical fiber surface coated with electro-optic materials,electro-optic materials can react adequately with light,thus greatly improving the modulation efficiency of the modulator.Compared with the common D-shape graphene electro-optic modulator,the electro-optic modulator parameters of the cascaded structure are flexibly adjustable.In this thesis,combining the advantages of D-shape fiber and graphene,using the evanescent field characteristic of D-shape optical fiber,we proposed a high speed graphene electro-optic modulator of D-shape fiber based on cascaded structure and studied its basic characteristics.The main contents of this thesis are listed as follows:(1)According to KuBo formula,the conductivity,permittivity and refractive index of graphene were deduced,and simulating them under different chemical potentials of graphene,also deduced and studied the driving voltages under different chemical potentials of graphene.(2)We analyzed the single-layer graphene electro-optic modulator based on D-shape fiber.Firstly,we optimized the waveguide structure of the modulator,the research indicates that the remaining cladding thickness of 0.5 ?m,the core radius of 3?m,the index difference between core and cladding of 0.004 will result in better performance of modulator.Secondly,the modulation principle is verified by changing the chemical potential of graphene.Finally,the performance of the modulation is analyzed,the extinction ratio of the single-layer graphene electro-optic modulator is calculated as 6.56 dB,the modulation depth is 0.033 dB/?m.(3)We proposed a graphene electro-optic modulator based on cascaded D-shape fiber.It overcomes the problem of low modulation depth of single-layer graphene electro-optic modulator effectively.Firstly,the structure of the modulator was verified.When D-shape optical fiber is coated with double-layer graphene,the extinction ratio of the device is 18dB,the modulation depth is 0.09dB/?m and the 3dB bandwidth is 18GHz.Secondly,the graphene electro-optic modulator based on cascaded D-shape fiber is analyzed,the basic characteristics of electro-optic modulator for graphene in two sections of optical fiber at different chemical potentials and different layers is studied.We obtained when maximum depth of modulation is about 0.23dB/?m,the maximum required driving voltage is 0.862V,0.942V.