Development and Characterisation of Plasmonic Devices for Sensing Applications

In recent years, discoveries and advances that utilise nano-scale (10^-9m) structures and associated phenomena have led to a number of entirely new areas of research in the fields of physics, chemistry, biology, and materials science. The photonic field of plasmonics is the study of light interaction with nanometer-scaled metal-dielectric features, which gives rise to a variety of phenomena, including surface plasmon resonance, localised surface plasmon resonance, and metal enhanced fluorescence. The focus of this thesis is on the development and characterisation of nanophotonic devices, which utilise plasmonic phenomena and have potential for sensor applications. During the course of this research a surface plasmon resonance analysis platform was devised, which utilises the gold grating of commercially available compact disks as the sensing substrate. This measurement method offers a high resolution refractive index analysis of gases and surface chemistry and is capable of analysing a large number of samples by scanning over the entire disk surface. The system implements a method of phase-polarisation contrast to improve the sensing performance. It enhances signal detection through redistributing the residual p-polarised waves, which have been strongly absorbed by the surface plasmon resonance substrate/sensor. This effectively lowers the reflected light intensity at the surface plasmon resonance minimum. The scheme results in the deepening of the intensity minimum to below 3.5% reflection and the enhancement of resonance to non-resonance contrast by up to 14 times, and thereby increasing sensitivity. A range of new nanophotonic structures have been modelled, developed, fabricated, and characterised, which we call wavelength and polarisation selective polariton generators (SPGs). These polarisation-sensitive structures combine a tuneable plasmon resonator and a subwavelength aperture to selectively generate and transmit polaritons of a desired wavelength through a central nanohole. Individual SPGs permit modulation of transmission intensity, with calculated enhanced optical transmission (ratio of output to input flux) of up to 10 and up to 4-fold measured amplitude modulation. The paired SPGs gave rise to multiple spectrally discrete transmission peaks which, when modulated, provide a multi-state operation in a single device. The measured amplitude modulation was up to 10-fold. For the linearly continuous SPG, by controlling the polarisation as a tuning variable, it selectively generated and transported polaritons of a desired wavelength. It exhibited a spectral shift of 40 nm over the full range of polarisation angles. The modelled enhanced optical transmission was calculated to be up to 17.2. An instrument was developed for measuring and characterising light transmission through single nanoholes, nanohole arrays, and other complex structures. The operational characteristics of these elements show close agreement between model predictions and experimental data. It also demonstrates new designs of plasmonic structures which utilise selective behaviour based on the polarisation of incident light

Polarization tunable selective polariton generator

A selective polariton generator (SPG) design, based on surface plasmon antennae principles, is demonstrated to provide a selective light transmission peak. The polarization-sensitive structure selectively generates and transports polaritons of a desired wavelength through a circular subwavelength aperture. By varying the SPG structure around a central nanohole, we are able to control the peak optical transmission wavelengths via the polarization state of the incident photons. We find good agreement between simulations and experimental results

Polarisation and wavelength selective transmission through nanohole structures with multiple grating geometry

Excitation and localization of surface plasmon polariton modes in metal-dielectric structures can be utilized to construct nanophotonic materials and devices with tuneable optical dispersion. We present a selective polariton generator (SPG) device that demonstrates switching of light transmission based on surface plasmon antennae principles. This polarization-sensitive structure selectively generates and transports polaritons of a desired wavelength through subwavelength apertures. Two of these SPGs have been combined around a nanohole into a new, single device that allows polarization and wavelength selective switching of transmission. The multi-state operation is confirmed by experiment results

Phase-polarisation contrast for surface plasmon resonance based on low cost grating substrates

This paper presents a new grating configuration that combines the benefits of multi-angle interrogation with the phase-polarisation contrast method. The setup is based on the gold grating of a commercially available recordable compact disk, which allows the excitation of surface plasmons. The compact disks are mass produced by injection-moulding, which results in low cost disposable grating substrates. The measurement method allows high resolution analysis of gases and surface chemistry. Results for this system have been demonstrated using helium, air and carbon dioxide gases