Jun-Yu Ou

Reconfigurable photonic metamaterials

We demonstrate the first temperature driven mechanically reconfigurable photonic metamaterials (RPMs) providing tunability at optical frequencies.

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.

Multifold Enhancement of Quantum Dot Luminescence in Plasmonic Metamaterials

We report that hybridizing semiconductor quantum dots with plasmonic metamaterial leads to a multifold intensity increase and narrowing of their photoluminescence spectrum. The luminescence enhancement is a clear manifestation of the cavity quantum electrodynamics Purcell effect and can be controlled by the metamaterials design. This observation is an essential step towards understanding loss compensation in plasmonic metamaterials with gain media and for developing metamaterial-enhanced gain media.

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.

Ultrafast all-optical switching via coherent modulation of metamaterial absorption

We report on the demonstration of a femtosecond all-optical modulator providing, without nonlinearity and therefore at arbitrarily low intensity, ultrafast light-by-light control. The device engages the coherent interaction of optical waves on a metamaterial nanostructure only 30 nm thick to efficiently control absorption of near-infrared (750–1040 nm) femtosecond pulses, providing switching contrast ratios approaching 3:1 with a modulation bandwidth in excess of 2 THz. The functional paradigm illustrated here opens the path to a broad family of meta-devices for ultrafast optical data processing in coherent networks.

Electro-optical control in a plasmonic metamaterial hybridised with a liquid-crystal cell

We experimentally demonstrate efficient electro-optical control in an active nano-structured plasmonic metamaterial hybridised with a liquid-crystal cell. The hybridisation was achieved by simultaneously replacing the polarizer, transparent electrode and molecular alignment layer of the liquid-crystal cell with the metamaterial nano-structure. With the control signal of only 7 V we have achieved a fivefold hysteresis-free modulation of metamaterial transmission at the wavelength of 1.55 µm.

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.

A magneto-electro-optical effect in a plasmonic nanowire material

Electro- and magneto-optical phenomena play key roles in photonic technology enabling light modulators, optical data storage, sensors and numerous spectroscopic techniques. Optical effects, linear and quadratic in external electric and magnetic field are widely known and comprehensively studied. However, optical phenomena that depend on the simultaneous application of external electric and magnetic fields in conventional media are barely detectable and technologically insignificant. Here we report that a large reciprocal magneto-electro-optical effect can be observed in metamaterials. In an artificial chevron nanowire structure fabricated on an elastic nano-membrane, the Lorentz force drives reversible transmission changes on application of a fraction of a volt when the structure is placed in a fraction-of-tesla magnetic field. We show that magneto-electro-optical modulation can be driven to hundreds of thousands of cycles per second promising applications in magneto-electro-optical modulators and field sensors at nano-tesla levels.

Ultraviolet and visible range plasmonics in the topological insulator Bi1.5Sb0.5Te1.8Se1.2.

The development of metamaterials, data processing circuits and sensors for the visible and ultraviolet parts of the spectrum is hampered by the lack of low-loss media supporting plasmonic excitations. This has driven the intense search for plasmonic materials beyond noble metals. Here we show that the semiconductor Bi1.5Sb0.5Te1.8Se1.2, also known as a topological insulator, is also a good plasmonic material in the blue-ultraviolet range, in addition to the already-investigated terahertz frequency range. Metamaterials fabricated from Bi1.5Sb0.5Te1.8Se1.2 show plasmonic resonances from 350 to 550 nm, while surface gratings exhibit cathodoluminescent peaks from 230 to 1,050 nm. The observed plasmonic response is attributed to the combination of bulk charge carriers from interband transitions and surface charge carriers of the topological insulator. The importance of our result is in the identification of new mechanisms of negative permittivity in semiconductors where visible range plasmonics can be directly integrated with electronics.

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)