다초점 기능을 갖는 그래핀 전극 기반 적외선 프레넬 렌즈
A Graphene-electrode-based Infrared Fresnel Lens with Multifocal Function
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초록
그래핀 전극 아래에 놓인 다층 그래핀 존 플레이트로 구성된 적외선 프레넬 렌즈의 초점 성능을 전산모사를 통해 조사한다. 여기서 패턴된 다층 그래핀의 페르미 에너지 준위(E F )는 그 위에 놓인 그래핀 전극에 의해 조절된다. 4 μm에서 30 μm까지의 광대역 파장에서 유리 기판 위에 놓인 8층 그래핀 존 플레이트와 그래핀 전극의 반사도 대비비에 따른 프레넬 렌즈 효과를 분석하였다. 반사도와 반사도 대비비를 고려한 최적 파장인 8 μm 입사파가 초점거리 240 μm인 프레넬 렌즈에 입사 시, 다층 그래핀의 E F 가 0.4 eV에서 1.6 eV로 증가함에 따라 초점 세기가 4.3배, 그래핀 층수가 2층에서 8층으로 증가함에 따라 5.8배 강화되었다. 이를 통해 인가된 E F 에 따라서 다중 초점(240 μm 및 360 μm) 성능을 보이는 그래핀만으로 구성된 IR 프레넬 렌즈 구조를 초박형 렌즈 플랫폼으로 제안한다.
Abstract
We study through computational simulation the focal performance of an infrared (IR) Fresnel lens, composed of a multilayer-graphene zone plate formed under a graphene electrode. Here the Fermi level E F of the patterned multilayer graphene is adjusted by the overlying graphene electrode. The Fresnel lens effect, with respect to the reflectance contrast between the graphene electrode and the 8-layer graphene zone plate placed on a glass substrate, has been analyzed over a broad wavelength range from 4 to 30 μm. As the optimal wavelength of 8 μm (considering the reflectance and the reflectance-contrast ratio) is incident upon the Fresnel lens with a focal length of 240 μm, the focal intensity is enhanced by a factor of 4.3 as the E F of multilayer graphene increases from 0.4 eV to 1.6 eV, and is improved by a factor of 5.8 as the number of graphene layers increases from two to eight. As a result, an all-graphene-based IR Fresnel zone-plate lens, exhibiting multifocal function (240 μm and 360 μm) according to the selected E F , is proposed as an ultrathin lens platform.
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