Abstract
Hyperuniform disordered structures are a class of artificial structures that, despite a
random visual appearance, contain a hidden order that arises from their uniform distribution of geometric features and constrained correlations in the reciprocal space.
Hyperuniform disordered photonic materials have highly tunable scattering characteristics and can exhibit large, isotropic photonic band gaps, which make them attractive to
many areas of research in photonics.
This thesis explores the photonic characteristics of hyperuniform disordered structures
which, combined with the dynamics of active materials, gives rise to complex functionalities in a number of photonic devices. Foremost, we argue that spatial correlations
— in any structure — are central in establishing a fundamental link between geometric
and optical properties. As such, we assemble a toolbox of analytical techniques that
can extract important geometric features from arbitrary structures, such as average
separation of structural features, uniformity, and strength of both long- and short-range
order, which we subsequently deploy in exploring the physics of hyperuniform disordered
photonic materials.
Hyperuniform disordered structures are first employed in the design of a thin solar
cell architecture, where a light trapping technique is devised to attain large absorption
enhancements up 85% over the visible spectrum. This is predicated on understanding
the interplay between two key physical phenomena: the efficient coupling of light to the
guided modes of the absorbing material, and diffraction via a patterned surface layer. By
analysing the absorption spectra of several types of hyperuniform disordered structures,
photonic crystals, and quasicrystals, using finite-difference time-domain computational
simulations, we explore the presence of fundamental correlations not only between the
structures and their optical response, but also between visually contrasting structures
that have similar absorption spectra.
We subsequently probe the transport of electromagnetic waves through a hyperuniform
disordered photonic slab, in which the patterning is two-dimensional but the structure
has a finite vertical thickness. The behaviour of the transmission points towards several
transport regimes that are present in hyperuniform disordered materials: a) complete
suppression in the photonic band gaps, b) Anderson-like localisation in close spectral
proximity to the photonic band gap, c) unimpeded transmission in a “stealthy” region,
where the structure appears transparent to waves below a certain wavevector, and d)
diffusive transport everywhere else. The individual guided resonances that photonic
hyperuniform disordered materials support are also investigated at great depth, particularly those in close spectral proximity to the bandgap. These modes are naturally
localised — the lower frequency band edge modes of the hyperuniform disordered photonic slab exhibit very large quality factors up to 26,000, due to their excellent in-plane
confinement and their localisation within the dielectric material. The spatial extents,
quality factors and robustness of the modes (against a reduction in the expanse of the dielectric structure that surrounds them) are explored using finite-difference time-domain
simulations.
Using this knowledge, we design a laser that utilises a single mode of a hyperuniform
disordered photonic slab to achieve efficient laser action. Employing finite-difference
time-domain simulations, we observe and analyse the lasing dynamics of two lasing
devices: one that utilises hyperuniform disordered structuring and another that uses
periodic structuring.
Our results indicate that hyperuniform disordered materials show a promising future for
implementation in such functionalities, with novel and interesting features that can be
exploited in other applications.