Graham Town - Academia.edu (original) (raw)

Papers by Graham Town

Summary An optical continuum was generated in microstructured optical fibre using an incoherent p... more Summary An optical continuum was generated in microstructured optical fibre using an incoherent pump generated by stimulated Raman scattering in a step index fibre with normal dispersion. Accelerated spectral broadening to longer wavelengths was observed.

Integrated Optics: Devices, Materials, and Technologies XIV, 2010

ABSTRACT We describe and analyze the phenomenon of partial image revivals in a multi-channel dire... more ABSTRACT We describe and analyze the phenomenon of partial image revivals in a multi-channel directional-coupler (MCDC) structure. Using supermodes, a MCDC is described as a composite waveguide structure and then analyzed in terms of multi-mode interference and the principle of self-imaging. As we bring the waveguides in the array closer together the supermodes beat to form partial images in between the complete mirror- and self-images. In this case, we have the advantage of the increased coupling and hence shorter image lengths, but with the disadvantage that the images are partial revivals of the input field. Nonetheless, we can take advantage of the partial image revivals that occur near complete mirror- and self-images, as they are almost complete images themselves. To demonstrate the use of this phenomenon we describe the simple design of a compact 1×2 wavelength division multiplexer based on a MCDC. The design highlights a trade-off between device length and isolation ratio, where although we use the partial self-image at 1.55 mum for a more compact device, the trade-off is a reduced isolation ratio when compared to 1.3 mum where a complete mirror-image is present.

Losses in tapered microstructured fibres have been calculated as a function of shape and length u... more Losses in tapered microstructured fibres have been calculated as a function of shape and length using finite-difference time-domain calculations. Minimal losses are incurred even in non-optimally shaped tapers shorter than 100 micron. The results have important implications for splice losses and device applications.

A simplified, cost-effective millimeter-wave radio-over-fiber system is proposed by heterodyning ... more A simplified, cost-effective millimeter-wave radio-over-fiber system is proposed by heterodyning two independent low-cost light-sources and RF homodyning at the receiver that suppresses phase-noise effects. Proposed system avoids phase/frequency locking, high-speed modulators and local oscillators/mixers in CO and BSs.

We describe a novel delta-k electro-optic switch for 1310 nm using a multi-channel directional co... more We describe a novel delta-k electro-optic switch for 1310 nm using a multi-channel directional coupler structure incorporating an organic electro-optic crystal for the cladding layer.

Proceedings of 5th European Quantum Electronics Conference, 1994

ABSTRACT Not Available

We suggest a novel form of polymeric based 3D photonic crystal prisms for THz frequencies which c... more We suggest a novel form of polymeric based 3D photonic crystal prisms for THz frequencies which could be fabricated using a standard fiber drawing technique. The structures are modeled and designed using a finite element analyzing technique. Using this simulation software we theoretically study their performance.

Workshop on Specialty Optical Fibers and their Applications, 2013

ABSTRACT The room temperature deposition of self-assembling silica nanoparticles onto D-shaped op... more ABSTRACT The room temperature deposition of self-assembling silica nanoparticles onto D-shaped optical fibres (“D-fibre”), drawn from milled preforms fabricated by modified chemical vapor deposition, is studied and preliminary results reported here.

24th European Conference on Optical Communication. ECOC '98 (IEEE Cat. No.98TH8398), 1998

ABSTRACT Ultrafast optical pulse-code generation was demonstrated using an optical fibre Bragg gr... more ABSTRACT Ultrafast optical pulse-code generation was demonstrated using an optical fibre Bragg grating. Single 1.8 ps input pulses were converted into a train of output pulses separated by 21.5 ps, each with controlled amplitude, representing a digital codeword

35th Australian Conference on Optical Fibre Technology, 2010

Advanced Photonics & Renewable Energy, 2010

ABSTRACT We describe a 1x2 guided-wave 532/590 nm wavelength division multiplexer for fluorescenc... more ABSTRACT We describe a 1x2 guided-wave 532/590 nm wavelength division multiplexer for fluorescence biosensing using a multi-channel directional coupler structure.

International Conference On Photonics 2010, 2010

ABSTRACT We describe an optical chemical sensor using a multi-channel directional coupler with sl... more ABSTRACT We describe an optical chemical sensor using a multi-channel directional coupler with slot waveguides.

2010 International Conference on Electromagnetics in Advanced Applications, 2010

We describe a delta-k electro-optic modulator for 1310 nm using a multi-channel directional coupl... more We describe a delta-k electro-optic modulator for 1310 nm using a multi-channel directional coupler structure. The device employs a poled electro-optic polymer material for the cladding layer.

ACOFT/AOS 2006 - Australian Conference on Optical Fibre Technology/Australian Optical Society, 2006

ABSTRACT We report the generation of microwave signals by mixing a tunable semiconductor laser wi... more ABSTRACT We report the generation of microwave signals by mixing a tunable semiconductor laser with a short-cavity dual- wavelength distributed Bragg reflector (DBR) fiber laser. The DBR laser generated two continuous-wave longitudinal modes separated by 25GHz.

IEEE Transactions on Terahertz Science and Technology, 2015

ABSTRACT We report two proof-of-principle designs of silicon terahertz (THz) modulators based on ... more ABSTRACT We report two proof-of-principle designs of silicon terahertz (THz) modulators based on guiding structures wherein graphene is introduced to actively control the properties of the waveguides, thus tuning their transmissivity. Using well-established models to characterize the electromagnetic parameters of electrically-doped graphene, we estimate the theoretical performance of the proposed structures, in particular the required switching voltage and the achievable modulation depth. These results predict considerably improved performance with respect to the state-of-the-art of graphene THz modulators, together with reduced size and larger THz bandwidth.

IEEE Transactions on Terahertz Science and Technology, 2012

In this paper, we report on a new form of polymeric 2D photonic crystal filters for THz frequenci... more In this paper, we report on a new form of polymeric 2D photonic crystal filters for THz frequencies fabricated using a standard fiber drawing technique. The band stop filters were modeled and designed using the generalized multipole technique. The frequency and angle-dependent transmission characteristics of the photonic crystal structures were characterized in a THz time-domain spectrometer.

Physical review. E, Statistical, nonlinear, and soft matter physics, 2001

The complex Ginzburg-Landau equation (CGLE) is a standard model for pulse generation in mode-lock... more The complex Ginzburg-Landau equation (CGLE) is a standard model for pulse generation in mode-locked lasers with fast saturable absorbers. We have found complicated pulsating behavior of solitons of the CGLE and regions of their existence in the five-dimensional parameter space. We have found zero-velocity, moving and exploding pulsating localized structures, period doubling (PD) of pulsations and the sequence of PD bifurcations. We have also found chaotic pulsating solitons. We have plotted regions of parameters of the CGLE where pulsating solutions exist. We also demonstrate the coexistence (bi- and multistability) of different types of pulsating solutions in certain regions of the parameter space of the CGLE.

$Research paper thumbnail of <title>Refractive index and thermo-optic coefficient of composite polymers at 1.55 μm</title>$

Photonics: Design, Technology, and Packaging II, 2005

ABSTRACT The refractive index and thermo-optic coefficient of composite polymers of polystyrene a... more ABSTRACT The refractive index and thermo-optic coefficient of composite polymers of polystyrene and polymethylmethacrylate were measured at 1.55mum using an optical fiber refractometer and were found to be 1.483 and 1.570, respectively, at room temperature. The refractive index and thermo-optic coefficient of the copolymers were consistent with the rule of mixtures.

2007 European Conference on Lasers and Electro-Optics and the International Quantum Electronics Conference, 2007

ABSTRACT In recent years, various opto-fluidic devices have emerged as a tool for sensing, imagin... more ABSTRACT In recent years, various opto-fluidic devices have emerged as a tool for sensing, imaging and spectroscopy applications. There has also bee increasing interest in fluidic dye lasers that can act as efficient integrated sources for lab-on-a-chip spectroscopy applications. In this paper, we report microfluidic lasers based on optical fibres, where lasing is achieved without the need of external mirrors, allowing simple, rapid fabrication of compact, visible laser sources. We explore two geometries: capillary tubes of 2 mum core diameter (Polymicro Technologies), and photonic crystal fibres that comprise approximately 50 cores of 3.7 mum diameter. The latter was based on a commercial photonic crystal fibre ESM-12-01 (Crystal Fibre) and demonstrates the potential for multiple laterally integrated fluidic lasers. In both geometries, an advantageous spectral selectivity is observed despite the long cavity lengths.

$Research paper thumbnail of <title>Novel diffractive feedback structures for semiconducting polymer lasers</title>$

Organic Light-Emitting Materials and Devices IX, 2005

ABSTRACT Semiconducting conjugated polymers have recently attracted significant interest as ampli... more ABSTRACT Semiconducting conjugated polymers have recently attracted significant interest as amplifying media for solid-state lasers due to their functional photo-physical properties and simple fabrication. Distributed feedback (DFB) cavities are proving to be the most attractive for polymer lasers, since they can combine the properties of transverse optical pumping, low threshold and practical output beams. To date, in most polymer DFB lasers the feedback is provided by second order diffraction. This has the advantage of surface emission, though it also imposes extensive scattering losses. In this work, we present the use of alternative structures that attempt to reduce the threshold of polymer DFB lasers, and also achieve dual wavelength operation. The former was addressed with cavities formed by alternative symmetries of the Brillouin zone of a square lattice. Using the diagonal GammaM symmetry first order feedback was attained. The threshold energy was thus reduced by almost an order of magnitude as compared with the more commonly used GammaX symmetry of second order square gratings. Finally, we show that two lasing wavelengths may be set independently in a semiconducting polymer laser by using a doubly periodic (i.e. Moiré) DFB grating.