| Compared with the first presentation of the Internet concept in the second half of the 20 th century,the amount of information transmission and processing in the communication system has increased geometrically in just a few decades,and the optical fiber-based information communication network is facing severe challenges.For the encoding and loading of information,the electrical signal needs to be loaded on the light wave through the optical modulator.Facing the proliferation in information transmission and processing in the communication network,the optical modulator itself has higher demand for the core performance such as information processing speed.The performance of signals such as modulation rate,device integration level,multi-working single width and single-byte energy consumption needs to be broadened and improved.However,traditional electro-optical modulation devices are limited due to objective factors such as materials and crafting limits,and cannot meet the required performance.Intrinsic graphene is a hexagonal honeycomb layered material composed of a single layer of carbon,which has excellent point optical characteristics of ultra-high carrier mobility at room temperature,controllability of material refractive index under external voltage.Furthermore,its processing technology is compatible with standard CMOS technology.The integration of graphene material and traditional electrooptical modulation device structure provides higher possibilities to have great improvements regarding critical features of optical modulators including bandwidth,response rate,size,energy consumption and integration level.The researches about this orientation are rising all over the world.This thesis aims to improve the performance of electro-optic modulators,and uses the electro-optic modulation characteristics of graphene combined with graphene materials to integrate silicon-based conductive optical modulators as the main research object.The paper established a numerical model for the electro-optical properties of graphene materials,combined with the silicon-based waveguide structure,designed several new graphene electrooptical modulation devices with different structures,studied the technological process of the micro-nano machining of the device manufacturing and designed the corresponding photomask membrane structure,mastered the preparation technology of graphene material transfer that is not available in the CMOS process,proposed the protection technology for the coupling port of the device under the abnormal processes,completed the preparation of the electro-optic modulator with the on-chip structure,and performed the electro-optical and all-optical tests with the finding of light-induced loss.The specific research work is as follows:The preparation and characterization of graphene materials as well as several optical waveguide design analysis theories are reviewed.The preparation methods of commonly used graphene materials in common use include mechanical exfoliation,redox and chemical vapor deposition methods.Among them,the method for preparing graphene materials by mechanical exfoliation has been improved;the main characterization methods include optical microscopy,scanning electron microscopy and Raman spectroscopy.Theories used for numerical calculations of optical waveguides include effective refractive index method,beam propagation method,finite difference time domain method and finite element method.The electro-optical response characteristics of graphene were studied and a numerical model was established.The absorption of the light field by graphene is characterized by the imaginary part of its refractive index,and the refractive index is related with the change of the graphene chemical potential(Fermi level).Because the chemical potential of graphene can be applied to external voltage and chemical doping,the imaginary part of the refractive index of the material can be adjusted under the applied electric field.The relationship between the chemical potential of graphene,applied voltage,optical conductivity,and relative permittivity,etc.is studied,and the working principle of graphene used in electro-optic modulators is explained.Four types of graphene combined with on-chip integrated electro-optic modulation device structures are proposed,including double-layer straight waveguide absorption type,thermooptical single-ring single-waveguide wide-spectrum absorption type,phase type and four-ring dual-waveguide multiplexing absorption type.Numerical simulation results show that for the double-layer straight waveguide absorptive modulator,when the dielectric layer is made of silicon oxide and the length of graphene material is 43 8),the modulation rate of the modulator can reach 16.3 GHz;for single-ring single-waveguide modulators,when the length of the graphene is 5.24 8),the modulation depth of the device can reach 31.32 d B.When the silicon oxide is used as the dielectric layer,the modulation rate of the device can reach 134 GHz.When phase modulation is used,when the length of the graphene is 5.13 8),the modulation depth of the device is 7.64 d B,and the modulation rate can reach 137 GHz;for a four-ring dualwaveguide multiplexer device,four groups of different wavelengths can be simultaneously modulated in the device.With a 5.24 8)graphene structure,the modulation rate can reach 125 GHz.The micro-nano machining process of the preparation of graphene electro-optical modulation devices was studied.The corresponding structure mask was drawn using Layout and L-edit software.The manufacturing technology from material transfer to the final package was mastered,and the device coupling end face protection technology was proposed.The problem of light-induced loss caused by the abnormal processes is successfully resolved.The production of integrated electro-optical modulation devices is finally completed.The electrooptical and all-optical performance tests of the devices were carried out.The manufacturing problems in the electro-optical devices were found.Also,two feasible schemes of the leveling process for the waveguide were completed and preliminary process exploration was completed with the finding of the phenomenon of light-induced loss in the all-optical performance test. |
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