Generation and active steering of optical beams based on nanometallic structures

Abstract

Generation and active control of highly collimated and non-diffractive beams based on nanometallic structures are rapidly gaining popularity in applications that require exquisite control over light concentration and emission processes. Although much effort has been devoted to developing nanoscale structure for active control of optical beams, no practical active device architecture has been established yet. Research on active control of optical beams even at the single-pixel level on the microscale or nanoscale has been rare. In this dissertation, various optical beams (e.g. Airy beams, caustic beam, cosine-gaussian beams and plasmonic beams) are generated and steered based on nanometallic structures. Three noble methods are introduced: mechanical actuation , oblique incidence of light, and changing wavelength. First, a novel mechanism for active directional beaming by mechanical actuation of double-sided plasmonic surface gratings is proposed. It is shown that the asymmetric mechanical actuation of optimally designed plasmonic surface gratings surrounding a subwavelength metal slit can produce a steerable off-axis beaming effect. The controllability of the beam direction provides an opportunity to develop novel active plasmonic devices and systems. Second, plasmonic complex fields are generated with double-lined distributed nanoslit segments. As a unit cell, two facing nanoslits are used for tuning both the amplitude and the phase of excited SPPs as a function of their tilted angles. For verification of the proposed design rule, experimental demonstration of some plasmonic caustic curves and Airy plasmons is presented. Finally, a new method to launch the finite power Airy beams based on the metasurface is presented. By tailoring the amplitude and phase of the transmitted fields from the metallic C-aperture array, the launching of Airy beams has been achieved in free space. This structure has multi-frequency characteristic which facilitates Airy beam steering because the trajectory of Airy beams is dependent on the wavelength. Experimental demonstration shows that the Airy beams can be steered by tuning wavelength very easily. These findings facilitate the realization of a new class of active optical beam shaping for use in new optical sources and a wide range of nanoscale optical spectroscopy applications.