Yuzhen Liang
Xiamen University of Technology, China
Title: Reducing radiation loss of near zero-index metamaterials
Biography
Biography: Yuzhen Liang
Abstract
Optical metamaterials can achieve an unconventional eff ective index of refraction by engineering the geometry of the building blocks. In extreme cases, the eff ective index can approach zero, resulting in infi nite phase velocity and spatial wavelength. However, because of the zero index corresponds to an electric monopole mode and two magnetic dipole modes degenerating at the center of the Brillouin zone, which is innately above the light line, opening a loss channel to the direction perpendicular to the substrate, i.e. the guided wave propagating within the zero-index metamaterial can couple to a planewave radiating in the out-of-plane direction (the direction perpendicular to the substrate). Here we eliminate this out-of-plane radiation loss via the destructive interference between the plane waves radiating upward and downward, forming a bound state in the continuum. A zero-index metamaterial design with a refl ector that reduces radiation loss through the destructive interference of multiple lossy channels, resulting inbound states in the continuum. Th e design includes a silicon pillar array and a planar reflector. By adjusting the distance between the refl ector and the pillars, out-of-plane radiation can be eliminated completely. However, for near zero-index metamaterials (ZIMs), there is no similar design and method to reduce the out-ofplane radiation losses. We design a low-loss near zero-index metamaterial composing of an array of silicon pillars without a reflector. Under an in-plane TM excitation, the pillars support two Bloch modes at the center of the Brillouin zone: an axial electric monopole mode, and a transverse magnetic dipole mode. By adjusting the radius and pitch of the pillar array, we can achieve the degeneracy of these modes at the center of the Brillouin zone and a given operating wavelength, in our case 1525nm.