Research On Graphene D-Type Twin Core Fiber Modulator

Optical modulators play a vital role in optical communication and optical sensing systems and have received increasing attention in recent years due to their fixed modulation bandwidth,low loss,and high modulation efficiency.However,the external device will not only complicate the system,but will also has higher insert loss.All-fiber modulators can avoid complex external systems by placing it on fiber directly.Electro-optical phase shift all-fiber modulators have the characteristics of simple structure and low insert loss,but it suffers from low material-light interaction which causes larger footprint and longer modulator length Therefore,graphene has become a new focus in the research of optical modulation systems due to its tunable permittivity,high carrier mobility and other advantages.（1）The research background of the optical modulator is described in detail,and the structural properties,optical properties and electrical properties of graphene are analyzed.The relationship between the conductivity and permittivity of graphene with its chemical potential is deduced by Kubo formula,and the main preparation methods of graphene and the characteristics of various methods are introduced.（2）A compact modulator is proposed to achieve light intensity modulation by adjusting Fermi level of the graphene.The better modulation effect is achieved by placing two-lamellae of graphene embedded in Al₂O₃ and PVB on a side-polished microfiber of M-Z Modulator.The variation range of the effective refractive index of the modulator with the chemical potential of graphene was obtained by finite element analysis software.Extinction ratios of port 1 and port2 can reach 11.54 d B and 11.88 d B in 92μm by substituting the modulator into simulation.While achieving a more compact modulation structure,the insert loss is also controlled below0.0193 d B/μm.The contact width between bilayer graphene and the electrode is increased by placing the electrode at the head and end of the modulator,which leads to 132.427 GHz modulation bandwidth.（3）To further improve the performance of the modulator,a graphene light intensity modulator based on hybrid plasmonic waveguide array is proposed In this paper.The silver-semicircular array is placed on the surface of the transition material as hybrid plasmonic waveguide for the first time in all-fiber modulator.Analyzing by building a 3D model in finite difference time domain software,the hybrid surface plasmon polariton between silver-semicircles significantly enhances the subwavelength confinement and the light-graphene interaction.The modulation range of the real part of effective refractive index(N_eff)can reach to 0.01984 by adjusting the Fermi level of graphene.As a result,a high extinction ratio of39.39d B and 47.77d B can be achieved at both ends of the 45μm modulation structure,and the loss is kept below 0.0159d B/μm through the analysis of the imaginary part of the N_eff.The introduction of plasmonic waveguides also solves the problem of high modulation voltages,and the modulator bandwidth can still reach 59.945 GHz.The application of HPW in graphene optical fiber modulator greatly improves the working efficiency.