Method of implementing graded index media by symmetry-reduced helical photonic structures

Abstract

We propose a new approach for the realization of a graded index (GRIN) medium using a symmetry reduced unit element in photonic crystals. An index gradient on the order of Delta n = 0.16 is achieved without modifying the filling fraction or cell size dimensions. Various beam manipulation techniques can be implemented with such a GRIN medium. We show that designed GRIN structure may effectively focus an incident beam over wide bandwidth. The arrangement of the photonic crystal (PC) elements within unit cells exhibits structural order which is helical along the transverse to propagation direction. The designed GRIN PC structurally resembles the molecular orientation of cholesteric liquid crystals. (C) 2015 Optical Society of America