Mode Coupling Effects In THz Metamaterials And Its Influence To The Sensing Property Of Metamaterial-Based Sensors

Metamaterial as an artificial structural material has become a hot topic in optic research in recent years due to the designable and adjustable resonant modes as well as its fancy physical properties,such as negative refractive index,negative optical pressure.Terahertz wave is the electromagnetic wave located between the infrared region and microwave region.The response of traditional material to terahertz wave is weak,while the terahertz metamaterial can enhance the terahertz response of nature material.Plasmonic modes in metamaterials are analogy to the surface plasmon polaritons in conventional material which is sensitive to the dielectric change of surrounding environment.Consequently,the plasmonic modes are suitable for the interrogation mode for sensing applications.The resonance frequency of plasmonic mode is sensitive to the metamaterial structure,size,dielectric surroundings,and the electromagnetic property of the materials that constitute metamaterials.Thus,the properties of metamaterial can be changed and improved by adjusting plasmonic mode frequency in several ways.Meanwhile,the mode couplings occur when different modes are near in frequency.Mode coupling widely exists in metamaterial and has significant reference value in optical switch,sensing applications and so on.However,the research in mode coupling and sensing applications still in the infancy and needs further investigation.Herein,we focus our study on the coupling effects between metamolecular plasmonic mode and lattice diffraction mode,and the coupling effects between Lorentz phonon mode and plasmonic mode,as well as the influence of coupling effect to the sensitivity of metamaterial-based sensors.The main achievements and contributions are organized as follows:In chapter one,we introduced the concept of metamaterial and its applications in terahertz region firstly.Next,we review the recent progress and applications with the plasmonic modes in metamaterials.Then,we presented several dispersion models for materials and listed their suitable conditions.What is more,we summarize the current research states of mode coupling and its influence in metamaterial absorber and sensing applications.In chapter two,we study the coupling effects between the lattice diffraction mode and plasmonic mode in terahertz region.The result demonstrates that,both in TM and TE incidence,anti-crossing effects between the coupled modes have been observed in the strong coupling region,and blue shifts of plasmonic mode in weak coupling region have also been discovered under short lattice constant.The physical mechanism of metamaterial behind the coupling between plasmonic mode and lattice diffraction mode has been explored.What is more,we analyze the coupling influence to the sensitivity of metamaterial sensor.Finally,we take the full advantage of mode coupling to improve the sensitivity of metamaterial-based sensors.In chapter three,we study the coupling effects between Lorentz phonon mode and plasmonic mode,because many nature materials have the Lorentz dielectric responses due to phonon vibration in materials.The degenerated plasmonic mode split into non-degenerate modes due to the coupling effects between plasmonic mode and phonon mode.The splitted non-degenerate plasmonic modes interact with each other and an anti-crossing effect can be observed.We propose an interaction Hamiltonian to understand the physical mechanisms of the plasmonic splitting.Analog to Stark effects,the splitting frequency difference increases as the increasing of the DC dielectric function,which provides a classical platform for mimicking the optical quantum behaviors.Furthermore,the splitting is convincible for small Lorentz dielectrics such as sugar and amino acid in THz region,which afford a platform for the biomolecular sensing applications.In chapter four,we summarize the research content,innovation and the research significance of our work.The next step of the work is prospected in this chapter.