title: Nanofocusing beyond the near-field diffraction limit via plasmonic Fano resonance.
abstract: The past decade has witnessed a great deal of optical systems designed for exceeding the Abbe's diffraction limit. Unfortunately, a deep subwavelength spot is obtained at the price of extremely short focal length, which is indeed a near-field diffraction limit that could rarely go beyond in the nanofocusing device. One method to mitigate such a problem is to set up a rapid oscillatory electromagnetic field that converges at the prescribed focus. However, abrupt modulation of phase and amplitude within a small fraction of a wavelength seems to be the main obstacle in the visible regime, aggravated by loss and plasmonic features that come into function. In this paper, we propose a periodically repeated ring-disk complementary structure to break the near-field diffraction limit via plasmonic Fano resonance, originating from the interference between the complex hybrid plasmon resonance and the continuum of propagating waves through the silver film. This plasmonic Fano resonance introduces a π phase jump in the adjacent channels and amplitude modulation to achieve radiationless electromagnetic interference. As a result, deep subwavelength spots as small as 0.0045λ(2) at 36 nm above the silver film have been numerically demonstrated. This plate holds promise for nanolithography, subdiffraction imaging and microscopy.
authors.affiliation: State Key Laboratory of Optical Technologies on Nano-Fabrication and Micro-Engineering, Institute of Optics and Electronics, Chinese Academy of Science, P.O. Box 350, Chengdu 610209, China. lxg@ioe.ac.cn and Key Laboratory of Optoelectronic Technology and System, Ministry of Education, Chongqing University, Chongqing 400044, China. hlyu@cqu.edu.cn.
authors.forename: Maowen
authors.initials: M
authors.lastname: Song
authors.affiliation: State Key Laboratory of Optical Technologies on Nano-Fabrication and Micro-Engineering, Institute of Optics and Electronics, Chinese Academy of Science, P.O. Box 350, Chengdu 610209, China. lxg@ioe.ac.cn.
authors.forename: Changtao
authors.initials: C
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Optical Technologies on Nano-Fabrication and Micro-Engineering, Institute of Optics and Electronics, Chinese Academy of Science, P.O. Box 350, Chengdu 610209, China. lxg@ioe.ac.cn.
authors.forename: Zeyu
authors.initials: Z
authors.lastname: Zhao
authors.affiliation: State Key Laboratory of Optical Technologies on Nano-Fabrication and Micro-Engineering, Institute of Optics and Electronics, Chinese Academy of Science, P.O. Box 350, Chengdu 610209, China. lxg@ioe.ac.cn.
authors.forename: Mingbo
authors.initials: M
authors.lastname: Pu
authors.affiliation: State Key Laboratory of Optical Technologies on Nano-Fabrication and Micro-Engineering, Institute of Optics and Electronics, Chinese Academy of Science, P.O. Box 350, Chengdu 610209, China. lxg@ioe.ac.cn.
authors.forename: Ling
authors.initials: L
authors.lastname: Liu
authors.affiliation: State Key Laboratory of Optical Technologies on Nano-Fabrication and Micro-Engineering, Institute of Optics and Electronics, Chinese Academy of Science, P.O. Box 350, Chengdu 610209, China. lxg@ioe.ac.cn and University of Chinese Academy of Sciences, Beijing 100049, China.
authors.forename: Wei
authors.initials: W
authors.lastname: Zhang
authors.affiliation: Key Laboratory of Optoelectronic Technology and System, Ministry of Education, Chongqing University, Chongqing 400044, China. hlyu@cqu.edu.cn.
authors.forename: Honglin
authors.initials: H
authors.lastname: Yu
authors.affiliation: State Key Laboratory of Optical Technologies on Nano-Fabrication and Micro-Engineering, Institute of Optics and Electronics, Chinese Academy of Science, P.O. Box 350, Chengdu 610209, China. lxg@ioe.ac.cn.
authors.forename: Xiangang
authors.initials: X
authors.lastname: Luo