Focusing reflector and lens with non-periodic phase-matched subwavelength high contrast grating

In this paper, we propose novel planar subwavelength non-periodic high contrast gratings (HCGs) with excellent focusing abilities due to their phase-matched structures. Rigorous coupled-wave analysis (RCWA) method and finite-element method (FEM) are performed to investigate the non-periodic HCG structures for either focusing reflector or lens at the wavelength of 1.55 mu m. The structure with focusing ability is optimized to simultaneously meet the phase-matched conditions of the reflectors and lenses. When the grating bars material is silicon, the HCG serves as focusing reflector, and the HCG with the grating bars of GaN has transmission focusing ability. Both reflector and lens have large numerical aperture (NA), high diffraction efficiency and excellent focusing ability. These HCG structures are promising for designing and fabricating photonic devices that require focusing components, especially for silicon and III-nitride integrated photonic devices.