含石墨烯临界耦合谐振器的吸收特性研究

临界耦合谐振器是一种薄膜结构, 可以吸收几乎所有的入射电磁波而不产生散射. 为了有效的实现和控制临界耦合现象, 本文提出了在临界耦合结构中加入了基于石墨烯的多层薄膜结构来代替原来的吸收薄膜层. 计算表明临界耦合现象出现在近红外波段, 且可以通过调节石墨烯的费米能级来获得不同的临界耦合频率; 另外改变多层薄膜结构中介质的厚度、石墨烯的层数, 实现了临界耦合现象的可调谐性, 同时对于弛豫时间和入射角度对吸收效率的影响也做了相应讨论. 本文理论结果为基于石墨烯的临界耦合器件和光探测器件的设计提供了理论依据.

Study on the absorbing properties of critically coupled resonator with graphene

A critically coupled resonator (CCR) is a thin-film structure that can absorb nearly all of the incident electromagnetic radiation, leading to null scattering. In order to effectively achieve and control the critical coupling (CC) phenomena, we replace the polymer absorbing layer by a graphene-based multi-film structure. FDFD (finite difference frequency domain) method is used to solve the Maxwell equation, and the graphene's surface conductivity is calculated by using the Kubo formula. Our results demonstrate that the CC phenomenon is realized at the near-infrared frequency and the frequency of absorption peak can be engineered by the Fermi energy of the graphene sheets. With increasing Fermi energy the absorption peak moves to the longer wavelength side. The effective permittivity of a multi-film structure has a strong dependence on the thickness of the dielectric and the layer number of the grapheme sheets in the multi-film structure. It is found that the central frequency of the absorption peak shifts towards longer wavelength side with increasing layer number of the graphene sheets M and the thickness of dielectric d₁. Moreover, we also demonstrate that the absorption efficiency is affected by the electron-phonon relaxation time and the incident angle. It is clear that the central frequency of the absorption peak has a slight shift and the absorption is changed with the relaxing time and incident angle. The results offer the theoretical basis to the design of graphene-based critical coupling devices and optical detectors.