Polarization and mutual coupling effects in aluminum nanoantenna arrays

Abstract

General rightsThis document is made available in accordance with publisher policies. Please cite only the published version using the reference above. Full terms of use are available: http://www.bristol.ac.uk/pure/about/ebr-terms Abstract: This paper uses Finite Difference Time Domain (FDTD) modelling to study impact of varying the polarisation of the point source(s) on both the single aluminium dipole nanoantenna and a 2 x 2 array. Starting with the single dipole nanoantenna, this paper demonstrates the strong dependence of the Power Enhancement and resonance on the polarisation of the source by alternating between orthogonal polarisation states. With each element of the array excited by a single point source, the resonance, Power Enhancement and far field radiation patterns are observed as the polarisation of each source is rotated, in varying combinations. The results demonstrate that a unique far field radiation pattern is produced for each polarisation combination, which may lead to applications in sub-diffraction limit imaging and quantum optics. IntroductionThe antenna concept has existed for well over a century [1][2][3] and nanoantennas have now extended the technology into the optics regime; combining classical antenna theory with plasmonics to dramatically enhance the emission and absorption of light [4]. Nanoantennas are nanoscale devices which couple freely propagating light to localised surface plasmons and vice-versa. Applications of the technology range from imaging to photonic circuits and sensors [5][6][7][8][9]. When an optical emitter such as a quantum dot or fluorophore is brought into close proximity to a nanoantenna, Purcell enhanced emission can occur [4,10,11]. Alongside this, the nanoantenna shape will produce a particular pattern in the far field, termed the radiation pattern in classical antenna theory. If the antenna is part of a larger periodic array, the array element spacing can give rise to both radiation pattern shaping effects and surface wave propagation on the array; both of which have been widely studied in the RF literature[12] and the latter is termed Surface Lattice Resonances in the optics field [6,13]. An important and well-known effect in RF antenna arrays is that of mutual coupling. This is where interaction between neighbouring elements in the array modifies the characteristics of the individual antennas. The simplest manifestation of this is detuning of the antenna resonance, thus one cannot simply use the design of a single element to evaluate the resonance of an array. Mutual coupling will also depend strongly on the orientation of emitter near each antenna. This paper will explore these effects through Finite Difference Time Domain (FDTD) modelling [14] and will show how the array far field pattern and resonant wavelength can be used to determine the orientation of emitters [15,16] with respect to the nanoantenna arrays elements; this could find applications in single molecule fluorescence and quantum optics.

Fluorescent emission enhancement by aluminium nanoantenna arrays in the near UV

“…It is also worth noting that, in practice, the dye molecules will be randomly oriented and distributed over the sample surface. Different emission pattern modes may appear based on the relative position and orientation of the dye molecules and antennas, which could significantly impact the observed radiation pattern and enhancement generated from the nanoantennas [5]. Fig 8 shows a comparison of the enhancement for arrays A1-A5 calculated from the model and from the measured results.…”

“…Aluminium based plasmonics has extended existing research interests, to include resonant enhancement of UV fluorescence [4,8,17], enhanced photoluminescence from AlGaN quantum well UV LEDs [18], and structural colour [19]. In [5], we studied a 2 x 2 aluminium dipole nanoantenna array, demonstrating that unique radiation patterns and enhancement can be produced for varying combinations of emitter polarisations, which could be useful for sub-diffraction limit imaging and quantum optics. As in our earlier work, here, we use a higher order resonant mode of the antenna in order to achieve resonance in the UV spectral region, which is of a particular relevance for resonant enhancement of fluorescence.…”

“…Aluminium plasmonics in the ultraviolet (UV) spectral region is the subject of much recent research activity [1][2][3][4][5][6][7][8][9][10]. Aluminium has a relatively high density of free electrons which results in a very short plasma wavelength ( ) l = 84.2 nm p [1] and by extension, the ability to support surface plasmons in the UV.…”