Research On Photonics Crystal Absorber And Electro-optic Modulator Based On Graphene

To meet the needs of high-speed and large-capacity data transmission and the large-scale connection requirement of Internet of Things in the development of wireless communication technology,high performance terahertz and near infrared band optoelectronic devices have turned into an important research direction.Traditional semiconductor optoelectronic devices have complex lattice matching problems in their designing and processing.Their performance will be greatly degraded or even fail in terahertz and infrared wavelengths.In contrast,two-dimensional material graphene can avoid the lattice mismatch problem with simple processing.Since graphene has excellent photoelectric characteristics,photoelectric devices made by graphene have several advantages such like flexible tunability,ultra-wide spectrum absorption,ultra-high working rate and good thermal conductivity.Although the absorptance of single-layer graphene is only 2.3%,and it is difficult to perform and transfer the large-scale and high-quality graphene,those problems can be effectively solved through the structural design of graphene photonic crystal devices and the development of transfer-free graphene optoelectronic devices.Therefore,graphene optoelectronic devices in the terahertz and infrared bands are widely concerned.This thesis focuses on the research of graphene photonic crystal devices and transfer free graphene optoelectronic devices working in the terahertz and infrared bands.Based on the analysis of electrical and optical characteristics of graphene,the characteristics of photonic crystals and the application of the band gap effect of photonic crystals in the design of optical devices,the focus is on the design of graphene photonic crystal absorber and the transfer-free graphene multifunctional optoelectronic devices on sapphire substrates and the fabrication and experimental research of graphene devices on sapphire substrates.The Fabry-Pérot(FP)resonant cavity and Fano resonant grating are used to increase the interaction between the incident wave and graphene,further increasing the light absorbance of graphene in devices.A variety of graphene photonic crystal multi-mode perfect absorbing structures are proposed.In the different resonant cavity structures,more than 96% absorbance of the adjustable multi-mode perfect absorbing modes with abundant line shapes are realized.FP resonant embedded cavities absorber is proposed.Furthermore,dual-wavelength hybrid cavity absorber is proposed.In this absorber,the grating is embedded in the FP resonant cavity to generate mutually coupled FP resonance mode and Fano resonance mode and forma controllable Fano-FP hybrid splitting modes.The absorbances of those resonance modes meet the detection requirements of terahertz light source technology.Meanwhile,a Grating Graphene Photonic(GGP)structure absorption and transmission integrated graphene optoelectronic device is proposed.In the structure,two nearly 100% absorption modes are obtained.One transmission mode is obtained.The amplitude,and the number of the three modes can be flexible changed.The device can be used in the design of terahertz narrowband filter.Next,design theory and analysis method of the capacitive structure graphene electro-optical modulator is elaborated.A series of sapphire substrate graphene electro-optical modulator devices based on processed samples including a transparent grating transfer-free graphene electro-optical detector and two multifunctional graphene optoelectronic devices are proposed.The transparent grating transfer-free graphene electro-optical detector utilizes the Fano resonance provided by the grating structure to enhance the interaction between graphene and light.The transmittance of modulation achieves 50%.It is easy to process and has full transparency and good modulation characteristics.The G-on-P and G-in-P multi-functional graphene photoelectric device are proposed.They can be used as a filter or an absorber.Finally,this thesis carried out research based on high-quality sapphire substrate graphene samples.Atomic Force Microscope(AFM),Raman measurement,terahertz measurement and four-point detection are performed.The surface picture,conductivity distribution and graphene quality of samples are analyzed in detail.The photoelectric characteristic parameters of the graphene samples were obtained.An Electron Beam Lithography(EBL)step-by-step dicing method for efficiently cutting graphene wafers on sapphire substrates is proposed.Raman spectroscopy and AFM imaging are performed on the samples before and after the dicing.The measurement results prove that the good characteristics of graphene can still be maintained after dicing by the method.At the same time,this article carried out the preparation and analysis of the transfer-free graphene electro-optical adjustment device.The processed sample has obvious modulation ability.