title: Broadband surface-wave transformation cloak.
abstract: Guiding surface electromagnetic waves around disorder without disturbing the wave amplitude or phase is in great demand for modern photonic and plasmonic devices, but is fundamentally difficult to realize because light momentum must be conserved in a scattering event. A partial realization has been achieved by exploiting topological electromagnetic surface states, but this approach is limited to narrow-band light transmission and subject to phase disturbances in the presence of disorder. Recent advances in transformation optics apply principles of general relativity to curve the space for light, allowing one to match the momentum and phase of light around any disorder as if that disorder were not there. This feature has been exploited in the development of invisibility cloaks. An ideal invisibility cloak, however, would require the phase velocity of light being guided around the cloaked object to exceed the vacuum speed of light--a feat potentially achievable only over an extremely narrow band. In this work, we theoretically and experimentally show that the bottlenecks encountered in previous studies can be overcome. We introduce a class of cloaks capable of remarkable broadband surface electromagnetic waves guidance around ultrasharp corners and bumps with no perceptible changes in amplitude and phase. These cloaks consist of specifically designed nonmagnetic metamaterials and achieve nearly ideal transmission efficiency over a broadband frequency range from 0(+) to 6 GHz. This work provides strong support for the application of transformation optics to plasmonic circuits and could pave the way toward high-performance, large-scale integrated photonic circuits.
authors.affiliation: State Key Laboratory of Modern Optical Instrumentation, Zhejiang University, Hangzhou 310027, China; The Electromagnetics Academy at Zhejiang University, Department of Information Science and Electronic Engineering, Zhejiang University, Hangzhou 310027, China;
authors.forename: Su
authors.initials: S
authors.lastname: Xu
authors.affiliation: Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371; Centre for Disruptive Photonic Technologies, Nanyang Technological University, Singapore 637371;
authors.forename: Hongyi
authors.initials: H
authors.lastname: Xu
authors.affiliation: Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA 02139;
authors.forename: Hanhong
authors.initials: H
authors.lastname: Gao
authors.affiliation: State Key Laboratory of Modern Optical Instrumentation, Zhejiang University, Hangzhou 310027, China; The Electromagnetics Academy at Zhejiang University, Department of Information Science and Electronic Engineering, Zhejiang University, Hangzhou 310027, China;
authors.forename: Yuyu
authors.initials: Y
authors.lastname: Jiang
authors.affiliation: School of Aeronautics and Astronautics, Zhejiang University, Hangzhou 310027, China;
authors.forename: Faxin
authors.initials: F
authors.lastname: Yu
authors.affiliation: Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, MA 02139 joannop@mit.edu hansomchen@zju.edu.cn hdsun@ntu.edu.sg blzhang@ntu.edu.sg.
authors.forename: John D
authors.initials: JD
authors.lastname: Joannopoulos
authors.affiliation: Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, MA 02139.
authors.forename: Marin
authors.initials: M
authors.lastname: Soljačić
authors.affiliation: State Key Laboratory of Modern Optical Instrumentation, Zhejiang University, Hangzhou 310027, China; The Electromagnetics Academy at Zhejiang University, Department of Information Science and Electronic Engineering, Zhejiang University, Hangzhou 310027, China; Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, MA 02139 joannop@mit.edu hansomchen@zju.edu.cn hdsun@ntu.edu.sg blzhang@ntu.edu.sg.
authors.forename: Hongsheng
authors.initials: H
authors.lastname: Chen
authors.affiliation: Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371; Centre for Disruptive Photonic Technologies, Nanyang Technological University, Singapore 637371; joannop@mit.edu hansomchen@zju.edu.cn hdsun@ntu.edu.sg blzhang@ntu.edu.sg.
authors.forename: Handong
authors.initials: H
authors.lastname: Sun
authors.affiliation: Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371; Centre for Disruptive Photonic Technologies, Nanyang Technological University, Singapore 637371; joannop@mit.edu hansomchen@zju.edu.cn hdsun@ntu.edu.sg blzhang@ntu.edu.sg.
authors.forename: Baile
authors.initials: B
authors.lastname: Zhang
keywords: broadband; invisibility cloaks; surface wave; transformation optics