基于石墨烯超材料的可調電磁誘導透明的研究
發(fā)布時間：2018-10-26 19:59
【摘要】：近年來,THz技術得到了巨大的發(fā)展。由于在電磁波譜中的特殊位置,THz波在醫(yī)療診斷、環(huán)境監(jiān)測、移動通訊和軍用雷達等方面具有非常廣闊的應用前景。然而,有效材料的缺乏限制了 THz技術的深入發(fā)展和實際應用。石墨烯作為新興的二維半導體材料,具有超高的載流子遷移率和優(yōu)異的光電性能,在THz器件的研制中具有獨特的優(yōu)勢。本文主要針對基于石墨烯超材料結構的可調電磁導透明進行了研究。本文的主要研究內容及結論概括如下:1.基于石墨烯電導率的可調性,研究了 T型石墨烯納米結構。通過研究我們發(fā)現(xiàn),當亮模式與暗模式互相靠近時,可以產生電磁誘導透明(EIT)現(xiàn)象。討論了不同幾何尺寸情況下,EIT效應隨頻率的變化情況。結果表明當兩個石墨烯條中心距離由Onm增加到20nm時,透明窗口由3THz變?yōu)?.5THz,且窗口的右側出現(xiàn)了第二個透明窗口。當入射偏振角由垂直入射變?yōu)樾?0度入射時,透射由0.7變?yōu)?.85,耦合強度大大減弱。討論了費米能級對EIT效應的影響,證實了改變石墨烯費米能級可以調節(jié)窗口頻率大小,并實現(xiàn)光速減慢。2.研究了具有非對稱性的級聯(lián)兀型石墨烯納米結構,模型中豎直放置的石墨烯條作為暗模式,水平石墨烯條作為亮模式。在入射光的激勵下,亮模式和暗模式發(fā)生耦合,實現(xiàn)了 EIT效應。討論了模型尺寸參數對EIT的影響并得出結論。在該模型的基礎上研究了更為緊湊的超材料結構,以實現(xiàn)將電場集中在更小的模式體積上。討論了石墨烯費米能級的變化對EIT及慢光效應的影響,為慢光效應的按需調節(jié)提供了另一種思路。3.基于兩個亮模式之間的弱雜化,研究了一種新型平面石墨烯超材料結構,可以在THz波段實現(xiàn)EIT效應。該結構由一個石墨烯圓環(huán)和一個石墨烯長條組成,結構的透射強度很高,可以從5%調節(jié)到95%。由于圓環(huán)和長條都可以被外電場單獨激發(fā),因此二者都視為亮模式。兩模式之間的弱雜化和頻率失諧產生了 EIT現(xiàn)象,出現(xiàn)了透明窗口。改變石墨烯的費米能級,可實現(xiàn)對EIT效應的動態(tài)調諧。透明窗口附近可觀察到較大的群速率延遲,窗口處達到0.5ps。
[Abstract]:In recent years, THz technology has been greatly developed. Because of its special position in electromagnetic spectrum, THz wave has a very broad application prospect in medical diagnosis, environmental monitoring, mobile communication and military radar. However, the lack of effective materials limits the further development and practical application of THz technology. As a new two-dimensional semiconductor material, graphene has a unique advantage in the development of THz devices because of its ultra-high carrier mobility and excellent optoelectronic properties. In this paper, the adjustable electromagnetic conductivity transparency based on graphene supermaterial structure is studied. The main contents and conclusions of this paper are summarized as follows: 1. Based on the adjustable conductivity of graphene, T-type graphene nanostructures were studied. It is found that electromagnetically induced transparent (EIT) can occur when the bright and dark modes approach each other. The variation of EIT effect with frequency under different geometric dimensions is discussed. The results show that when the central distance of two graphene strips increases from Onm to 20nm, the transparent window changes from 3THz to 1.5THZ, and a second transparent window appears on the right side of the window. When the incident polarization angle changes from vertical incidence to oblique 60 degree incident, the transmission is changed from 0.7 to 0.85, and the coupling strength is greatly weakened. The effect of Fermi level on EIT effect is discussed. It is proved that the window frequency can be adjusted by changing the Fermi level of graphene, and the speed of light can be slowed down. The cascaded unsymmetrical graphene nanostructures with vertical graphene strips as dark mode and horizontal graphene strips as bright modes are studied. The EIT effect is realized by coupling the bright mode with the dark mode under the excitation of the incident light. The influence of model size parameters on EIT is discussed and the conclusion is drawn. On the basis of this model, a more compact structure of metamaterials is studied in order to concentrate the electric field on a smaller mode volume. The effect of the change of Fermi level of graphene on EIT and slow light effect is discussed, which provides another way of thinking for the adjustment of slow light effect on demand. 3. Based on the weak hybrid between two bright modes, a novel planar graphene supermaterial structure is studied, which can realize the EIT effect in THz band. The structure consists of a graphene ring and a graphene strip. The transmission intensity of the structure is very high and can be adjusted from 5% to 95%. Since both the ring and the strip can be excited by the external electric field, both are considered as bright modes. The weak hybrid and frequency detuning between the two modes lead to EIT phenomenon and transparent window. The EIT effect can be dynamically tuned by changing the Fermi level of graphene. A large group rate delay can be observed near the transparent window, which reaches 0.5 ps.
【學位授予單位】：山東科技大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：O613.71;O441
本文編號：2296796
[Abstract]:In recent years, THz technology has been greatly developed. Because of its special position in electromagnetic spectrum, THz wave has a very broad application prospect in medical diagnosis, environmental monitoring, mobile communication and military radar. However, the lack of effective materials limits the further development and practical application of THz technology. As a new two-dimensional semiconductor material, graphene has a unique advantage in the development of THz devices because of its ultra-high carrier mobility and excellent optoelectronic properties. In this paper, the adjustable electromagnetic conductivity transparency based on graphene supermaterial structure is studied. The main contents and conclusions of this paper are summarized as follows: 1. Based on the adjustable conductivity of graphene, T-type graphene nanostructures were studied. It is found that electromagnetically induced transparent (EIT) can occur when the bright and dark modes approach each other. The variation of EIT effect with frequency under different geometric dimensions is discussed. The results show that when the central distance of two graphene strips increases from Onm to 20nm, the transparent window changes from 3THz to 1.5THZ, and a second transparent window appears on the right side of the window. When the incident polarization angle changes from vertical incidence to oblique 60 degree incident, the transmission is changed from 0.7 to 0.85, and the coupling strength is greatly weakened. The effect of Fermi level on EIT effect is discussed. It is proved that the window frequency can be adjusted by changing the Fermi level of graphene, and the speed of light can be slowed down. The cascaded unsymmetrical graphene nanostructures with vertical graphene strips as dark mode and horizontal graphene strips as bright modes are studied. The EIT effect is realized by coupling the bright mode with the dark mode under the excitation of the incident light. The influence of model size parameters on EIT is discussed and the conclusion is drawn. On the basis of this model, a more compact structure of metamaterials is studied in order to concentrate the electric field on a smaller mode volume. The effect of the change of Fermi level of graphene on EIT and slow light effect is discussed, which provides another way of thinking for the adjustment of slow light effect on demand. 3. Based on the weak hybrid between two bright modes, a novel planar graphene supermaterial structure is studied, which can realize the EIT effect in THz band. The structure consists of a graphene ring and a graphene strip. The transmission intensity of the structure is very high and can be adjusted from 5% to 95%. Since both the ring and the strip can be excited by the external electric field, both are considered as bright modes. The weak hybrid and frequency detuning between the two modes lead to EIT phenomenon and transparent window. The EIT effect can be dynamically tuned by changing the Fermi level of graphene. A large group rate delay can be observed near the transparent window, which reaches 0.5 ps.
【學位授予單位】：山東科技大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：O613.71;O441
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