Research On The Electromagnetic Properties Of Hybrid Plasmon-Phonon Polaritons In Graphene-Hexagonal Boron Nitride Heterostructures And Their Applications

Polaritons with extremely confined fields are known to promote optical synthesis and highspeed optical signal proccesing.Since the signal isolation and system modularity is highly dependent on operating wavelength when considering optical integration and energy dissipation,the hybrid plasmon-phonon polaritons supported in graphene-hexagonal boron nitride waveguide reduces the operating wavelength from infrared(1550 nm)to ultraviolet(300 nm).Such promising property shall significantly reduce the dimensions of a device,thus the chip size,which can avoid redundant isolators and optimize the space occupation.In the thesis,the author investigated macroscopic electromagnetic responses through the evaluation of 2D free electron gas in hexagonal lattice.The obtained constitutive parameters enable the design of selective coupling from evanescent quasi-particles of dipole sources to hybrid plasmon-phonon polaritons in graphene-h BN heterostructures.Those discoveries are able to benefit the design principles in optoelectronic system integrations.In the meanwhile,they are potentially a great platform in photon momentum characterization,various light-matter interactions and the intrinsity between field and particle.The specific works down are:(1)Graphene conductivity tensor at different chemical potentials.The graphene electrical conductivity tensor is obtained from tight-binding method and self-consistent field theory.From the phonon,electron modes and the graphene's band structure,the author reveals the interconnection between microscopic electron responses and phonon momentum p,electron momentum hk as well as the momentum from external electriomagnetic potential hq.Moerover,the electrical conductivity is evaluated at different graphene chemical potentials.(2)Sommerfeld integral path in hyperbolic materials.The property of shifting and rotating upper Riemann sheets and lower Riemann sheets is demonstrated in uniaxial media.The flipping of both Riemann sheets is shown in hyperbolic materials like h BN.This thesis also investigated the proper Sommerfeld integral path in graphene-h BN heterostructures,ensuring the robust excitation of hybrid plasmon-phonon polaritons and inhibiting the crosstalk from antiparticles.(3)Tunable polariton directionality in single graphene-h BN heterostructure waveguide.In a single graphene-h BN waveguide,hybird plasmon-phonon polaritons are supported in the first restrahlen band of h BN: the hybrid polaritons tailor its behaviour from phonon-like mode to plasmon-like mode with the increasing doping rate of graphene.In other words,phonon-like polaritons can be observed when graphene chemical potential is less then 0.1 e V,which have negative group velocities.Plasmon-like polaritons follow when graphene chemical potential is high enough(e.g.0.4 e V).They have positive group velocities and change the direction of propagation.(4)Polariton direction tunability in miltilayer graphene-h BN heterostructures subject to various polarized dipoles.Circularlc polarized,Huygens,Janus dipoles are involved in the multilayer graphene-h BN heterostructures.According to Wigner's rule,excited polaritons in those waveguides are locked by the spin momentum from the dipole source.Therefore,the hybrid plasmon-phonon polaritons are odd spatial symmetric/even vertical symmetric/even horizontal symmetric subjet to circular/Huygens/Janus dipoles respectively.