Darren Freeman

Microfluidic photonic crystal double heterostructures

The support of the Australian Research Council through its Federation Fellow, Centres of Excellence, Denison Foundation, and Discovery Grant programs is gratefully acknowledged.

Efficient coupling to chalcogenide glass photonic crystal waveguides via silica optical fiber nanowires

We demonstrate highly efficient evanescent coupling between a highly nonlinear chalcogenide glass two dimensional photonic crystal waveguide and a silica fiber nanowire. We achieve 98% insertion efficiency to the fundamental photonic crystal waveguide mode with a 3dB coupling bandwidth of 12nm, in good agreement with theory. This scheme provides a promising platform to realize low power nanocavity based all-optical switching and logic functions.

Photosensitive post tuning of chalcogenide photonic crystal waveguides.

We present experimental results on photosensitive post-tuning the dispersion of a two-dimensional photonic crystal waveguide made from chalcogenide glass. A 5 nm shift of the resonant wavelength is reported.

Characterization and modeling of Fano resonances in chalcogenide photonic crystal membranes

We demonstrate resonant guiding in a chalcogenide glass photonic crystal membrane. We observe strong resonances in the optical transmission spectra at normal incidence, associated with Fano coupling between free space and guided modes. We obtain good agreement with modeling results based on three-dimensional finite-difference time-domain simulations, and identify the guided modes near the centre of the first Brillouin zone responsible for the main spectral features.

Bragg gratings in silicon-on-insulator waveguides by focused ion beam milling

We report Bragg grating structures fabricated by focused ion beam milling in optical waveguides, and demonstrate that they can be used as a powerful diagnostic of optical modes in very high index waveguides. We show that higher-order lossy modes, which can be present in large numbers even in single-moded silicon-on-insulator waveguides, can dramatically affect the optical transmission spectra of Bragg gratings in these waveguides, even though these modes are normally not observable. Our results not only illuminate challenges to realize practical gratings in high index waveguides, but raise the possibility of devices based on mode conversion to extremely high order modes.

Dual resonance mechanisms facilitating enhanced optical transmission in coaxial waveguide arrays

We experimentally and computationally demonstrate high transmission through arrays of coaxial apertures with different geometries and arrangements in silver films. By studying both periodic and random arrangements of apertures, we were able to isolate transmission enhancement phenomena owing to surface plasmon effects from those owing to the excitation of cylindrical surface plasmons within the apertures themselves.

Extraordinary optical transmission with coaxial apertures

This work was partially supported by the Office of Naval Research. Computations were carried out under the Department of Defense High Performance Computation Modernization Project. The support of the Australian Research Council through its Centers of Excellence, Federation Fellow and Discovery programs is gratefully acknowledged.

Higher order mode conversion via focused ion beam milled Bragg gratings in Silicon-on-Insulator waveguides

We report the first Bragg gratings fabricated by Focused Ion Beam milling in optical waveguides. We observe striking features in the optical transmission spectra of surface relief gratings in silicon-on-insulator waveguides and achieve good agreement with theoretical results obtained using a novel adaptation of the beam propagation method and coupled mode theory. We demonstrate that leaky Higher Order Modes (HOM), often present in large numbers (although normally not observed) even in nominally single mode rib waveguides, can dramatically affect the Bragg grating optical transmission spectra. We investigate the dependence of the grating spectrum on grating dimensions and etch depth, and show that our results have significant implications for designing narrow spectral width gratings in high index waveguides, either for minimizing HOM effects for conventional WDM filters, or potentially for designing devices to capitalize on very efficient HOM conversion.

Nanoscale Annular Array Metamaterials

The paper presents computational and experimental studies investigating the optical properties of nanoscale annular array metamaterials fabricated by ion beam milling. Both experimental results and simulations demonstrate high transmission efficiencies in the near infra-red regime for these devices. Implications for imaging such structures using near-field microscopy are also discussed.

Efficient coupling to chalcogenide glass photonic crystal waveguides via tapered optical fiber nanowires

We achieve > 98% coupling efficiency (18 dB) to a highly nonlinear chalcogenide glass photonic crystal membrane waveguide via evanescent coupling from a silica fibre nanowire.