石墨烯等离激元的光学性质及其应用前景

Optical properties of graphene plasmons and their potential applications

石墨烯等离激元由于其独特的电学可调性、本征低衰减以及局域光场高度增强等特性,引起了广泛的关注并迅速成长为一门新的学科分支——石墨烯表面等离激元光子学.本文介绍了石墨烯等离激元的一些基本性质,包括色散关系、局域的等离激元和传导的等离激元以及石墨烯等离激元对其周边介电环境的敏感性等.在此基础上,进一步介绍了石墨烯等离激元在太赫兹到中红外频段的应用,比如有源光调制器的一些功能器件和增强的红外光谱探测等.

Graphene plasmons have aroused a great deal of research interest in recent years due to their unique features such as electrical tunability, ultra-strong field confinement and relatively low intrinsic damping. In this review paper, we summarize the fundamental optical properties of localized and propagating plasmons supported by graphene, and the experimentaI techniques for excitation and detection of them, with focusing on their dispersion relations and plasmon- phonon coupling mechanism. In general, the dispersion of graphene plasmons is affected by the Fermi level of graphene and the dielectric environment. The graphene plasmons can exist in a broad spectrum range from mid-infrared to terahertz, This has been experimentally verified for both the localized and propagation plasmons in graphene. On the one hand, the excitation frequency and confinement of localized plasmons supported by graphene micro/nano-structures are constrained by the structural geometry. Additionally, influenced from the tunability of the optical conductivity of graphene, the excitation frequency of graphene plasmons can be tuned by electrostatic or chemical doping. On the other hand, propagating plasmons have been launched and detected by using scattering-type scanning near-field optical microscopy. This technique provides the real-space imaging of the electromagnetic fields of plasmons, thereby directly confirming the existence of the graphene plasmons and verifying their properties predicted theoretically. In a similar regime, the launching and controlling of the propagating plasmons have also been demonstrated by using resonant metal antennas. Compared to metal plasmons, graphene plasmons are much more easily affected by the surroundings due to their scattering from impurity charges and coupling with substrate phonons. In particular, graphene plasmons can hybridize strongly with substrate phonons and there are a series of effects on plasmon properties such as resonance frequency, intensity and plasmon lifetime. The designing of the dielectric surrounding can effectively manipulate the graphene plasmons. Finally, we review the emerging applications of graphene plasmon in the mid-infrared and terahertz, such as electro-optical modulators and enhanced mid-infrared spectroscopy.