Jianfa Zhang

An electromechanically reconfigurable plasmonic metamaterial operating in the near-infrared

Current efforts in metamaterials research focus on attaining dynamic functionalities such as tunability, switching and modulation of electromagnetic waves. To this end, various approaches have emerged, including embedded varactors, phase-change media, the use of liquid crystals, electrical modulation with graphene and superconductors, and carrier injection or depletion in semiconductor substrates. However, tuning, switching and modulating metamaterial properties in the visible and near-infrared range remain major technological challenges: indeed, the existing microelectromechanical solutions used for the sub-terahertz and terahertz regimes cannot be shrunk by two to three orders of magnitude to enter the optical spectral range. Here, we develop a new type of metamaterial operating in the optical part of the spectrum that is three orders of magnitude faster than previously reported electrically reconfigurable metamaterials. The metamaterial is actuated by electrostatic forces arising from the application of only a few volts to its nanoscale building blocks-the plasmonic metamolecules-that are supported by pairs of parallel strings cut from a flexible silicon nitride membrane of nanoscale thickness. These strings, of picogram mass, can be driven synchronously to megahertz frequencies to electromechanically reconfigure the metamolecules and dramatically change the transmission and reflection spectra of the metamaterial. The metamaterials colossal electro-optical response (on the order of 10(-5)-10(-6) m V(-1)) allows for either fast continuous tuning of its optical properties (up to 8% optical signal modulation at up to megahertz rates) or high-contrast irreversible switching in a device only 100 nm thick, without the need for external polarizers and analysers.

An All‐Optical, Non‐volatile, Bidirectional, Phase‐Change Meta‐Switch

Non-volatile, bidirectional, all-optical switching in a phase-change metamaterial delivers high-contrast transmission and reflection modulation at near- to mid-infrared wavelengths in device structures down to ≈1/27 of a wavelength thick.

Nanostructured Plasmonic Medium for Terahertz Bandwidth All-Optical Switching

Periodic nanostructuring can enhance the optical nonlinearity of plasmonic metals by several orders of magnitude. By patterning a gold film, the largest sub-100 femtosecond nonlinearity is achieved, which is suitable for terahertz rate all-optical data processing as well as ultrafast optical limiters and saturable absorbers.

Continuous metal plasmonic frequency selective surfaces

The fabrication of indented (‘intaglio’) or raised (‘bas-relief’) sub-wavelength metamaterial patterns on a metal surface provides a mechanism for changing and controlling the colour of the metal without employing any form of chemical surface modification, thin-film coating or diffraction effects. We show that a broad range of colours can be achieved by varying the structural parameters of metamaterial designs to tune absorption resonances. This novel approach to the ‘structural colouring’ of pure metals offers great versatility and scalability for both aesthetic (e.g. jewellery design) and functional (e.g. sensors, optical modulators) applications. We focus here on visible colour but the concept can equally be applied to the engineering of metallic spectral response in other electromagnetic domains.

Giant Nonlinearity of an Optically Reconfigurable Plasmonic Metamaterial

Metamaterial nanostructures actuated by light give rise to a large optical nonlinearity. Plasmonic metamolecules on a flexible support structure cut from a dielectric membrane of nanoscale thickness are rearranged by optical illumination. This changes the optical properties of the strongly coupled plasmonic structure and therefore results in modulation of light with light.Jun-Yu Ou, Eric Plum, ∗ Jianfa Zhang, 2 and Nikolay I. Zheludev 3, † Optoelectronics Research Centre and Centre for Photonic Metamaterials, University of Southampton, SO17 1BJ, UK College of Optoelectronic Science and Engineering, National University of Defense Technology, Changsha, 410073, China The Photonics Institute and Centre for Disruptive Photonic Technologies, Nanyang Technological University, Singapore 637378, Singapore (Dated: June 22, 2015)

Optical response of plasmonic relief meta-surfaces

Bulk metal surfaces patterned with arrays of sub-wavelength surface features can couple incident light into localized plasmon modes, thereby modifying the intensity and phase of reflected light. Beyond previously reported applications to colour control, we report on the functionality of continuously metallic meta-surfaces for optical magnetic reflection, perfect absorption, and active photonic switching/sensing.

Chalcogenide glass photonics: Non-volatile, bi-directional, all-optical switching in phase-change metamaterials

Non-volatile, bi-directional, all-optical switching in a phase-change metamaterial delivers high-contrast transmission and reflection modulation at visible and infrared wavelengths in device structures only ~1/8 of a wavelength thick.

Controlling Light with Light in a Plasmonic Nanooptomechanical Metamaterial

We demonstrate metamaterial with a cubic optical nonlinearity that is ten orders of magnitude greater than the reference nonlinearity of CS2. The nonlinearity has optomechanical nature and is underpinned by light-induced electromagnetic near-field interactions.

All-optical, non-volatile, chalcogenide phase-change meta-switch

We show experimentally that bistable, optically-induced phase switching in germanium antimony telluride (GST) - a member of the Te-based chalcogenide alloy family upon which all of todays re-writable optical disc and phase-change RAM technologies are based - provides a platform for the engineering of non-volatile metamaterial transmission/reflection modulators (Fig. 1) for near- to mid-infrared wavelengths with thicknesses down to 1/27 of the operating wavelength. These hybrid materials provide a robust and versatile platform for a new generation of optical switching and memory devices.

Metamaterial ‘gecko toe’: Optically-controlled adhesion to any surface

A new optical near-field force between plasmonic metamaterials and dielectric/metallic surfaces is identified. It can exceed Casimir, radiation and gravitational forces to provide an optically-controlled adhesion mechanism mimicking the gecko toe.