Timothy D. James

Tunable optical antennas enabled by the phase transition in vanadium dioxide

Optical antennas, subwavelength metallic structures resonating at visible frequencies, are a relatively new branch of antenna technology being applied in science, technology and medicine. Dynamically tuning the resonances of these antennas would increase their range of application and offer potential increases in plasmonic device efficiencies. Silver nanoantenna arrays were fabricated on a thin film of the phase change material vanadium dioxide (VO(2)) and the resonant wavelength of these arrays was modulated by increasing the temperature of the substrate above the critical temperature (approximately 68 °C). Depending on the array, wavelength modulation of up to 110 nm was observed.

Filling schemes at submicron scale: development of submicron sized plasmonic colour filters.

The pixel size imposes a fundamental limit on the amount of information that can be displayed or recorded on a sensor. Thus, there is strong motivation to reduce the pixel size down to the nanometre scale. Nanometre colour pixels cannot be fabricated by simply downscaling current pixels due to colour cross talk and diffraction caused by dyes or pigments used as colour filters. Colour filters based on plasmonic effects can overcome these difficulties. Although different plasmonic colour filters have been demonstrated at the micron scale, there have been no attempts so far to reduce the filter size to the submicron scale. Here, we present for the first time a submicron plasmonic colour filter design together with a new challenge - pixel boundary errors at the submicron scale. We present simple but powerful filling schemes to produce submicron colour filters, which are free from pixel boundary errors and colour cross- talk, are polarization independent and angle insensitive, and based on LCD compatible aluminium technology. These results lay the basis for the development of submicron pixels in displays, RGB-spatial light modulators, liquid crystal over silicon, Google glasses and pico-projectors.

Experimental demonstration of a wave plate utilizing localized plasmonic resonances in nanoapertures

Here we demonstrate the fabrication and characterization of a plasmonic wave plate. The device uses detuned, orthogonal nanometric apertures that support localized surface plasmon resonances on their interior walls. A device was fabricated in a thin silver film using focused ion beam milling and standard polarization tomography used to determine its Mueller matrix. We demonstrate a device that can convert linearly polarized light to light with an overall degree of polarization of 88% and a degree of circular polarization of 86% at a particular wavelength of 702 nm.

The plasmonic J-pole antenna

The plasmonic J-pole antenna is the nanoscale version of a radio frequency design, consisting of a half wavelength arm connected to a quarter wavelength feed pair. Here, we report on an optical J-pole antenna that displays both a dipole (1015 nm) and quadrupole resonance (653 nm). The excitation of the quadrupole resonance is optimum at an angle of incidence directly related to the geometry of the antenna, demonstrating the flexibility of the design. The J-pole antenna shows great promise for enhancing and shaping the angular emission pattern of quantum emitters.

Optical investigation of the J-pole and Vee antenna families.

The J-pole and Vee RF antenna design families are investigated for their suitability as optical antennas. The modal and spectral properties are experimentally examined to select the most suitable resonant optical plasmonic mode, which is used to inform the optimal positioning of a quantum emitter in relation to the antennas.

A Chiral Plasmonic Metasurface Circular Polarization Filter

Here, we demonstrate a proof of principle circular polarization filter based on a far-field interference effect using an array of pairs of simple nanoapertures. We demonstrate computationally and experimentally device performance which show good agreement and close to a 10% difference in transmission through the structure for left- and right-circularly polarized light. This ultracompact device could prove useful for remote sensing and advanced telecommunication applications.

Switchable polarization rotation of visible light using a plasmonic metasurface

A metasurface comprising an array of silver nanorods supported by a thin film of the phase change material vanadium dioxide is used to rotate the primary polarization axis of visible light at a pre-determined wavelength. The dimensions of the rods were selected such that, across the two phases of vanadium dioxide, the two lateral localized plasmon resonances (in the plane of the metasurface) occur at the same wavelength. Illumination with linearly polarized light at 45° to the principal axes of the rod metasurface enables excitation of both of these resonances. Modulating the phase of the underlying substrate, we show that it is possible to reversibly switch which axis of the metasurface is resonant at the operating wavelength. Analysis of the resulting Stokes parameters indicates that the orientation of the principal linear polarization axis of the reflected signal is rotated by 90° around these wavelengths. Dynamic metasurfaces such as these have the potential to form the basis of an ultra-compact, low-...

Modified stripe waveguide design for plasmonic input port structures

Abstract. We present a modified asymmetric stripe plasmonic waveguide design for plasmonic integrated input port structures. Such a waveguide shape can significantly increase the surface plasmon polariton (SPP) propagation length. A computational investigation of the waveguide mode analysis, excitation, and guiding is presented as well as SPP propagation length improvement strategies. The proposed structure has the potential to be CMOS compatible and could be used in highly integrated optoelectric circuits.

Vanadium dioxide thickness effects on tunable optical antennas

Vanadium Dioxide is an optically dense phase change material that has been applied to modulating the resonances of plasmonic structures resonant in the THz, infrared and optical ranges. It has been shown previously that fabrication of optical antennas on thin films of Vanadium Dioxide can result in a resonance shift of more than 10% across the phase change. This post-fabrication, dynamic tuning mechanism has the potential to significantly increase the possible applications of plasmonic devices. Here, we show that optical antenna arrays fabricated on differing thicknesses of Vanadium Dioxide supported by a silicon substrate show a dependence of their resonant wavelengths on this thickness. Along with the geometry of the antennas in the arrays this constitutes an additional degree of freedom in the design of the tuning range of these devices, offering further potential for optimisation of this mechanism. The potential extra blue-shift provided by optimising this thickness may be used, for example, in lieu of reducing antenna dimensions to avoid increasing antenna absorption and the additional plasmonic heating that can result.

Directed Chemical Assembly of Single and Clustered Nanoparticles with Silanized Templates

The assembly of nanoscale materials into arbitrary, organized structures remains a major challenge in nanotechnology. Herein, we report a general method for creating 2D structures by combining top-down lithography with bottom-up chemical assembly. Under optimal conditions, the assembly of gold nanoparticles was achieved in less than 30 min. Single gold nanoparticles, from 10 to 100 nm, can be placed in predetermined patterns with high fidelity, and higher-order structures can be generated consisting of dimers or trimers. It is shown that the nanoparticle arrays can be transferred to, and embedded within, polymer films. This provides a new method for the large-scale fabrication of nanoparticle arrays onto diverse substrates using wet chemistry.