title: Super-focusing of center-covered engineered microsphere.
abstract: Engineered microsphere possesses the advantage of strong light manipulation at sub-wavelength scale and emerges as a promising candidate to shrink the focal spot size. Here we demonstrated a center-covered engineered microsphere which can adjust the transverse component of the incident beam and achieve a sharp photonic nanojet. Modification of the beam width and working distance of the photonic nanojet were achieved by tuning the cover ratio of the engineered microsphere, leading to a sharp spot size which exceeded the optical diffraction limit. At a wavelength of 633 nm, a focal spot of 245 nm (0.387 λ) was achieved experimentally under plane wave illumination. Strong localized field with Bessel-like distribution was demonstrated by employing the linearly polarized beam and a center-covered mask being engineered on the microsphere.
authors.affiliation: Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, 117576, Singapore.
authors.forename: Mengxue
authors.initials: M
authors.lastname: Wu
authors.affiliation: Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, 117576, Singapore.
authors.forename: Rui
authors.initials: R
authors.lastname: Chen
authors.affiliation: Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, 117576, Singapore.
authors.forename: Jiahao
authors.initials: J
authors.lastname: Soh
authors.affiliation: Department of Electronic Engineering, Tsinghua University, Beijing, 100084, China.
authors.forename: Yue
authors.initials: Y
authors.lastname: Shen
authors.affiliation: Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, 117576, Singapore.
authors.forename: Lishi
authors.initials: L
authors.lastname: Jiao
authors.affiliation: Department of Physics, National University of Singapore, 2 Sciecne Drive 3, 117542, Singapore.
authors.forename: Jianfeng
authors.initials: J
authors.lastname: Wu
authors.affiliation: Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, 117576, Singapore.
authors.forename: Xudong
authors.initials: X
authors.lastname: Chen
authors.affiliation: Agency for Science, Technology and Research (A*STAR), 2 Fusionopolis way, 138634, Singapore.
authors.forename: Rong
authors.initials: R
authors.lastname: Ji
authors.affiliation: Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, 117576, Singapore.
authors.forename: Minghui
authors.initials: M
authors.lastname: Hong