【作者】 吴桐；

【导师】 高亚臣；

【作者基本信息】 黑龙江大学 ， 微电子学与固体电子学， 2022， 博士

【摘要】 太赫兹波是频率介于0.1 THz到10 THz的电磁波,它在军事、安全、医疗等领域具有重要应用价值。然而,自然界中缺少与太赫兹波产生强响应的材料,这影响了太赫兹技术的发展与应用。超材料的出现使太赫兹技术得到了发展,通过对超材料的合理设计可以实现对太赫兹波的强响应,进而实现对太赫兹波的有效调控及应用。基于贵金属的传统超材料一旦制备完成,它的电磁特性将无法改变。因此新型可调谐太赫兹超材料引起了人们的广泛关注。本文设计了利用石墨烯、钛酸锶(Strontium titanate,STO)和体狄拉克半金属(Bulk dirac semimetals,BDS)的多种超结构,实现了可调太赫兹宽带吸收和等离子体诱导透明(Plasmon induced transparency,PIT)效应,并研究分析了其特性和物理机制,具体工作如下:1.在太赫兹波段设计了一种基于BDS和钛酸锶的吸收器,利用时域有限差分法(FDTD)研究了该结构在不同BDS费米能和钛酸锶温度下的吸收特性。结果表明,该结构能够实现对太赫兹波的宽带吸收,并且通过调节费米能和温度能够实现吸收带宽及中心频率的调控。利用阻抗匹配理论分析了宽带吸收和调谐机制。并分析了对斜入射条件下超材料的吸收鲁棒性。2.设计了一种基于石墨烯和钛酸锶的太赫兹宽带吸收器。通过FDTD研究了不同石墨烯费米能级和钛酸锶温度下对吸收器的吸收特性的影响。结果表明,通过调节石墨烯费米能级和钛酸锶温度可以实现吸收带宽、中心频率和吸收强度的调控。通过阻抗匹配分析了吸收器宽带吸收和调谐机制。并分析了不同斜入射角度下吸收器稳定性。3.采用金属结构和石墨烯组合设计一种太赫兹可调谐超材料,并利用FDTD算法对其透射特性和慢光特性进行了研究。结果表明,该结构可以实现双PIT效应,并且通过调节石墨烯费米能级可以实现对PIT峰透射率和慢光效应的调控。此外,对双PIT效应超材料的传感特性也进行的研究。在上一研究的基础上,通过添加钛酸锶材料实现对超材料改进,改进后的结构还能通过改变钛酸锶温度还实现频率调控。利用三谐振子模型进行分析了上述两种结构所产生的双PIT效应。通过频率选择表面相关理论分析了改进结构的双PIT效应频率调控机制。4.在太赫兹波段,利用BDS和石墨烯光栅组合设计了一种多功能调控的超材料,利用FDTD研究了其透射特性。结果表明,BDS与石墨烯的耦合实现了单PIT效应。独立或联合调谐BDS费米能和石墨烯费米能级时实现了单PIT窗口的频率调谐,单频光开关和双频光同步开关的功能。此外,通过对原有PIT超材料结构进一步的改进,可以使透射谱从单PIT窗口转变成双PIT窗口。并且通过独立或联合调谐BDS费米能和石墨烯费米能级可以实现双PIT峰频率的调谐、三频同步光开关和四频异步光开关的功能。利用耦合模理论分析了上述两种结构的单PIT和双PIT效应。更多还原

【Abstract】 Terahertz waves are electromagnetic waves with frequencies ranging from 0.1 THz to 10 THz.They have important applications in military,security,medical and other fields.However,there is a lack of materials that strongly respond to terahertz waves in nature,which limits the development and application of terahertz technology.The emergence of metamaterials has enabled the development of terahertz technology.Through the rational design of metamaterials,a strong response to terahertz waves can be achieved,and then effective regulation and application of terahertz waves can be realized.In the early days,once a noble metal-based metamaterial was fabricated,its electromagnetic properties could not be changed.Therefore,tunable terahertz metamaterials based on novel materials have attracted extensive attention.In this paper,using graphene,strontium titanate(STO)and bulk Dirac semimetals(BDS),we design various metamaterials to achieve tunable terahertz broadband absorption and plasma induced transparency(PIT)effects and their properties and physical mechanisms have been studied and analyzed.The specific work is as follows:1.An absorber based on BDS and STO is designed in the terahertz band,and the absorption characteristics of the structure at different BDS Fermi energies and STO temperatures are studied by finite difference time domain method(FDTD).The results show that the structure can achieve broadband absorption of terahertz waves,and the absorption bandwidth and center frequency can be regulated by adjusting the Fermi energy and temperature.The broadband absorption and tuning mechanisms are analyzed using impedance matching theory.The absorption robustness of metamaterials under oblique incidence conditions is also analyzed.2.A terahertz broadband absorber based on graphene and STO is designed.The effects of different graphene Fermi levels and STO temperatures on the absorption properties were investigated by FDTD.The results show that the regulation of the absorption bandwidth,center frequency and absorption intensity can be achieved by adjusting the graphene Fermi level and STO temperature.The broadband absorption and tuning mechanism of the absorber are analyzed by impedance matching.The stability of the absorber under different oblique incidence angles is also analyzed.3.A terahertz tunable metamaterial is designed by combining metal structure and graphene,and its characteristics of transmission and slow light are studied by FDTD algorithm.The results show that the structure can achieve double PIT effect,and the transmission of PIT peak and slow light effect can be regulated by adjusting the Fermi level of graphene.In addition,the sensing properties of double PIT effect metamaterials are also investigated.On the basis of the above research,metamaterials are improved by adding STO materials.The improved structure can also realize frequency regulation by changing STO temperature.The double PIT effect produced by the above two structures is analyzed via three-harmonic oscillator model.The frequency tunable mechanism of the double PIT effect produced by the improved structure was analyzed by frequency selective surface theory.4.In the terahertz band,a multi-tunable metamaterial is designed by combining BDS and graphene grating,and its transmission characteristics are studied by FDTD algorithm.The results show that the single PIT effect is achieved through the coupling of BDS with graphene.When independently or jointly tuning the BDS Fermi energy and graphene Fermi level,frequency selection of single-PIT window,functions of singlefrequency optical switching and dual-frequency optical synchronization switching are realized.In terms of slow-light regulation,metamaterials can realize the frequency selection and switching function.In addition,by further improving the original PIT metamaterial structure,the transmission spectrum is transformed from a single PIT window to a double PIT window.Via independent or joint tuning of BDS Fermi energy and graphene Fermi level,we found that the improved structure realizes the tuning of double PIT peak frequency,three-frequency synchronous and four-frequency asynchronous optical switch.The single-PIT and double-PIT effects achieved by the two metamaterials are analyzed by coupled mode theory.更多还原