Enhancing light compression in photonic funnels with anomalous reflection

Photonic funnels, conical waveguides with hyperbolic metamaterial (HMM) cores, efficiently focus mid-IR light to spatial areas much smaller than the free space wavelength. These devices were originally conceived as having a perfect electric conductor (PEC) coating to confine light as it propagates to their subwavelength tip, however, recent numerical analysis demonstrates that funnels without a conductive cladding exhibit peak intensities over 1,000 times greater than their clad counterparts while maintaining a confinement scale determined by their tip radius. The funnel's conical surface provides an oblique interface between the highly anisotropic HMM and an isotropic medium. This oblique interface enables anomalous reflections which reshape and redirect the incident beam towards the funnel tip. In this work we analyze how the gold cladding suppresses the field enhancement and demonstrate the importance of the anomalous reflection to the funnel's performance.