Direct observation of Anderson localization in plasmonic terahertz devices

• Published in: Light, science & applications Vol. 6; no. 3; p. e16232
• Main Authors: Pandey, Shashank, Gupta, Barun, Mujumdar, Sushil, Nahata, Ajay
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.03.2017; Springer Nature B.V; Nature Publishing Group
• Subjects: 639/624/399/1015; 639/624/400/561; Anderson localization; Apertures; Applied and Technical Physics; Arrays; Atomic; Classical and Continuum Physics; Devices; Disorders; Gene loci; Lasers; Lattice theory; Molecular; Optical and Plasma Physics; Optical Devices; Optics; Original; original-article; Photonics; Physics; Physics and Astronomy; Plasmonics; Spectrum analysis; Terahertz frequencies; Wave power; Waveguides; terahertz waveguides; Anderson localization; 1D aperiodic lattice; terahertz plasmonics; disordered medium; time domain spectroscopy
• ISSN: 2047-7538; 2095-5545; 2047-7538
• DOI: 10.1038/lsa.2016.232

We present the first experimental observation of Anderson localization in the terahertz frequency range using plasmonic structures. To accomplish this goal, we designed THz waveguides consisting of a one-dimensional array of rectangular apertures that were fabricated in a freestanding metal foil. Disorder is introduced into the waveguide by offsetting the position of each aperture by a random distance within a prescribed range. For example, for a waveguide with apertures spaced by 250 μm in a periodic waveguide, 10% disorder would correspond to the apertures being shifted by a random value between ±25 μm along the waveguide axis. We find that for disorder levels below 25%, there is only an increase in the propagation loss along the device. However, for two specific waveguides with 25% disorder, we observe a spatially localized mode that lies just within the stop band of the device and exhibits a double-sided exponential spatial decay away from the maximum. Terahertz photonics: Anderson localization observed Anderson localization has been experimentally observed in the terahertz region for the first time. The Anderson localization of visible light in disordered media — a phenomenon in which travelling waves become spatially localized due to structural order — has generated great interest in recent years. Shashank Pandey from the University of Utah, USA, and co-workers observed Anderson localization in terahertz waveguides formed from a one-dimensional array of rectangular apertures in a metal foil. The necessary disorder was introduced into the waveguide by slightly offsetting some apertures at various random locations along the device’s length. When the level of disorder was 25%, Anderson localization was observed in two separate waveguides in the terahertz region. At lower levels of disorder, an increase in propagation loss rather than localization was observed.