Research Of Graphene Electro-absorption Optical Modulator Based On Organic Polymer Waveguide

Electro-optic modulator is one of the most important devices in photonic integrated chip and optical fiber communication network.It is of great significance to improve the performance of the device.Especially with the rapid development of information technology,such as big data,cloud computing and 5G communication,people put forward higher requirements for the performance of the device.In the past few decades,electro-optic modulators based on different material systems have been widely studied,such as In P modulator,Li Nb O₃modulator,silicon modulator and polarization polymer electro-optic modulator.Among them,the polarization polymer electro-optic modulators have the advantages of simple fabrication process,high electro-optic coefficient,high coupling efficiency with optical fiber and low cost,which has become a research hotspot in recent years.However,the performance of the device depends heavily on the characteristics of electro-optic polymer,which limits its application in photonic integrated chips to a certain extent.Organic polymer has become one of the most promising materials for photonic integrated chips,and various optical devices based on organic polymer materials have been widely studied.Therefore,if we can develop an electro-optic modulation device independent of electro-optic polymer on the passive polymer platform,it will have important research significance and application value.The emergence of graphene provides the possibility for the realization of this device.Graphene is a honeycomb lattice material composed of a single carbon atom unit.It has excellent optical,electrical and mechanical properties,especially its electro-absorption and refraction properties.It can be applied to the study of electro-optic modulation and electro-optic switch.In this paper,we use the electro-absorption characteristics of graphene,and combined with the advantages of simple and flexible processing technology of polymer waveguide,we buried graphene in polymer waveguide,and studied the graphene electro-absorption optical modulator based on organic polymer waveguide.The main contents of this paper are as follows:（1）The electrical and optical properties of graphene materials were studied in detail,and the corresponding numerical simulation model was established,including the relationship between the conductivity and dielectric constant of graphene and its chemical potential.It is proved that graphene can control its Fermi level and carrier concentration by applying bias voltage.The modulation function is realized by adjusting the absorption intensity of graphene layer to the optical signal propagating in the polymer waveguide.（2）In order to enhance the interaction between graphene and the optical signal transmitted in the waveguide,an organic polymer waveguide electro-absorption optical modulator based on buried graphene modulation electrode is proposed in this paper.The best buried position of graphene in the waveguide core is determined by simulation,which improves the modulation efficiency of the device.Meanwhile,the structure of graphene capacitor is optimized to improve the modulation bandwidth of the device.The active region length of the modulator is 800μm,the extinction ratio is29 d B,and the modulation bandwidth of 42 GHz is achieved with the power consumption of 1.55 p J/bit.（3）In order to solve the problem that traditional graphene modulators are sensitive to polarization mode,a polarization insensitive electro-absorption optical modulator based on trapezoidal polymer-graphene waveguide is designed.By optimizing the shape,size and buried position of graphene,graphene electro-absorption optical modulator which can support two polarization modes is realized.The modulation voltage is 1.11 V and the power consumption is 23.6 p J/bit.In C band,the extinction ratio of the modulator in TE and TM polarization modes is higher than 37 d B,and the difference between them is about 0.46 d B.