Graded negative index lens by photonic crystals

Numerical studies on a graded negative index lens made by a slab of graded photonic crystal (PC) are reported. The graded negative index lens is capable of focusing plane waves and can also be made highly insensitive to frequency, enabling broadband negative index imaging. We provide a simple model for the graded PC lens and predict its superior focusing properties such as low chromatic aberrations and broadband operation. Those properties were also confirmed and analyzed by the finite-difference time-domain simulations. We believe the negative index graded PCs will expand the utility of PC lenses and enable new applications in optoelectronic systems.