title: Wavelength dependence of focusing properties of two-dimensional photonic quasicrystal flat lens.
abstract: We investigated the wavelength dependence of the focusing properties of a germanium-cylinder-based two-dimensional (2D) decagonal Penrose-type photonic quasicrystal (PQC) flat lens for the first time, to the best of our knowledge. We found that near the second bandgap and in the high-frequency side (between the bandgap boundary and the first light intensity peak) of the pass band, the flat lens can exhibit a focusing effect for a point light source and that the focusing wavelengths can directly be drawn from the photonic band structure. For all the focusing wavelengths, the summation of the object distance and the image distance is less than the thickness of the flat lens when the object distance is half the thickness of the flat lens. As the wavelength increases, the image distance, the image quality, and the effective refractive index of the flat lens increase, whereas the image power of the point light source decreases. The effective refractive index of the flat lens is less than -1.
authors.affiliation: School of Astronautics, Harbin Institute of Technology, Harbin, China. liujjhit@163.com
authors.forename: Jianjun
authors.initials: J
authors.lastname: Liu
authors.forename: Zhigang
authors.initials: Z
authors.lastname: Fan
authors.forename: Haili
authors.initials: H
authors.lastname: Hu
authors.forename: Maohua
authors.initials: M
authors.lastname: Yang
authors.forename: Chunying
authors.initials: C
authors.lastname: Guan
authors.forename: Libo
authors.initials: L
authors.lastname: Yuan
authors.forename: Hao
authors.initials: H
authors.lastname: Guo
authors.forename: Xiong
authors.initials: X
authors.lastname: Zhang