表面等离激元传播的调制

Modulation of propagating surface plasmons

光学衍射极限极大地制约了纳米光子器件的发展和应用.基于表面等离激元的纳米器件由于具有突破衍射极限传播和处理光信号的特性而受到广泛关注.通过调控表面等离激元的传播,可以实现纳米尺度上光信号的调制,对片上集成纳米光子回路和光信息处理技术的发展具有重要意义.本文主要介绍了表面等离激元传播调制的基本原理及近年来的研究进展,并分析了不同类型的表面等离激元传播调制的特点.

The diffraction limit of light greatly limits the development of conventional optical devices,which aredifficult to be miniaturized and integrated with high density.Surface plasmons,electromagnetic modes at themetal-dielectric interface,can concentrate light into deep subwavelength dimensions,enabling the manipulationof light at the nanometer scale.Surface plasmons can be used as information carrier to transmit and processoptical signals beyond the diffraction limit.Therefore,nanodevices based on surface plasmons have receivedmuch attention.By modulating surface plasmons,the modulation of optical signals at nanoscale can be realized,which is important for the development of on-chip integrated nanophotonic circuits and optical informationtechnology.In this article,we review the modulations of propagating surface plasmons and their applications innano-optical modulators.The wave vector of propagating surface plasmons is very sensitive to the dielectricfunction of the metal and the environment.By tuning the dielectric function of the metal and/or thesurrounding medium,both the real and imaginary part of the wave vector of surface plasmons can be modified,leading to the modulation of the phase and propagation length of surface plasmons and thereby modulating theintensity of optical signals.We first introduce the basic principles of different types of modulations,includingall-optical modulation,thermal modulation,electrical modulation,and magnetic modulation.The all-opticalmodulation can be achieved by modulating the polarization and phase of input light,pumping optical materials,changing the dielectric function of metal by control light,and manipulating a nanoparticle by optical force tomodulate the scattering of surface plasmons.The modulation based on thermal effect depends on thermo-opticmaterials and phase-change materials,and the temperature change can be triggered by photothermal effect orelectrical heating.For electrically controlled modulation,Pockels electro-optic effect and Kerr electro-opticeffect can be employed.Electrical modulation can also be realized by controlling the carrier concentration ofsemiconductors or graphene,using electrochromatic materials,and nanoelectromechanical control of thewaveguide.The modulation of surface plasmons by magnetic field relies on magneto-optic materials.We reviewrecent research progresses of modulating propagating surface plasmons by these methods,and analyze theperformances of different types of plasmonic modulators,including operation wavelength,modulation depth orextinction ratio,response time or modulation frequency,and insertion loss.Finally,a brief conclusion andoutlook is presented.