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

Photonic jet in terahertz (THz) frequency range (terajet) plays an important role in modern THz scanning systems to achieve a superresolution beyond the diffraction limit. Based on analytical simulations, we introduce a synergetic effect of a mesoscale dielectric sphere and graphene to improve the focusing properties of a particle. We show that a graphene-covered dielectric sphere is able to enhance the field behind it if the 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 the 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 terajet-assisted imaging with semiconductor technology.