Optical components based on multi-refractive-index metamaterials

Abstract

We studied optical components (lenses, prisms, Fabry–Perot-type etalons) comprising a metamaterial-like medium that cannot be described by a single set of refractive-index values, even for a fixed frequency, vacuum wavevector, and polarization. The metastructure that we explored is a periodic stack of dissimilar metal-clad waveguides with a subwavelength width and spacing, which guide light at different phase velocities. From the ray-optics perspective, this multi-refractive-index ‘metamaterial’ (MRIM) can be viewed as a spatial superposition of multiple homogeneous materials, each of which can be engineered independently. Using full-wave simulations, we demonstrate several optical components based on MRIMs, including triangular prisms that deflect light to multiple angles, lenses with multiple focal points, and multi-index Fabry–Perot etalons with an enhanced density of resonant modes. We also analytically derive the Fresnel-like reflection, transmission, and ‘swapping’ coefficients at the interfaces between MRIMs and conventional materials, which enable the design of MRIM-based optical structures.