| Terahertz wave has many unique and excellent characteristics due to its spectral region between near-infrared and microwave,and is widely used in communication,imaging,computing,and sensing.The use of new mechanisms to design graphene terahertz third harmonic devices is of great significance in the development of terahertz communication.After previous research,it was found that most graphene terahertz third harmonic systems currently have relatively low third harmonic enhancement or high threshold.To address these two issues,this article designed two types of graphene terahertz third harmonic devices:one is a graphene strip grating and the other is a metal coupled cavity graphene grating.A graphene strip grating was designed.Firstly,the spectral characteristics of the distribution of single graphene bands on the substrate layer in the terahertz frequency band were described,followed by the absorption,reflection,and transmission spectra.Then,the resonance characteristics and third harmonic enhancement characteristics of a single graphene strip array were studied.The graphene strip experienced strong resonance,resulting in a significant third harmonic.Finally,the influence of geometric parameter changes on the resonance and third harmonic characteristics of graphene strip gratings was analyzed,and the corresponding third harmonic enhancement was relatively high in the order of 10-5.A double graphene stripe coupled grating is designed.The double graphene stripe has different Fermi energy levels,which excites different order graphene plasmon resonance at about 11THz frequency and produces near field strong coupling,inducing ATS effect.Compared with graphene strip gratings,resonance is significantly enhanced,resulting in stronger third harmonic generation.Then,the influence of geometric parameter changes on the resonance characteristics of graphene strip gratings was analyzed.By extending the graphene strip grating to a double graphene strip coupled grating with near field strong coupling,the near field strong coupling enhances resonance,enhances the third harmonic enhancement,and the corresponding third harmonic enhancement can reach the order of 10 to 4.A metal coupled cavity graphene grating was designed to analyze in detail the distribution of electromagnetic induced transparency（EIT）resonance transparency enhancement during exquisite design,and the distribution of resonance transparency enhancement during splitting.The corresponding third harmonic enhancement is relatively high in the order of 10 to 4.The influence of the width and height of graphene metal coupling cavity and the change of Fermi level on the reflection spectrum is explored,and the distribution of the fundamental frequency electric field and the third harmonic electric field are given.The third harmonic electric field has a similar distribution of echo wall modes.In addition,when the incident terahertz wave is obliquely incident,the signal contrast ratio rapidly decreases,and the electromagnetic induced transparency phenomenon gradually weakens,thereby improving the ability to generate third harmonic conversion efficiency compared to Chapter 2 and Chapter 3.The research results provide new ideas for designing tunable terahertz wave graphene third harmonic devices.It has potential application prospects in fine optical instrument,optical communication equipment,sensors,etc. |
