Fano-resonant mechanism of terajet formation using graphene-covered high index mesoscale spheres

Photonic jet in terahertz (THz) frequency range (terajet) plays important role in modern THz scanning systems to achieve a superresolution beyond the diffraction limit. Based on analytical simulations, we introduce synergetic effect of a mesoscale dielectric sphere and graphene to improve focusing properties of the particle. We show that a graphene-covered dielectric sphere is able to enhance the field behind it, if refractive index is high. This conflicts with a generally accepted statement that a jet is generated only for low-index dielectrics with n<2. We demonstrate tunability of the terajet characteristics with respect to the graphene Fermi energy and discover a Fano resonance causing the field increase. This design leverages the tuning properties of the graphene allowing dynamic control over the power and size of the generated terajet in real-time. With high-index materials we get the opportunity for integration of the terajet-assisted imaging with semiconductor technology.