Centre of Expertise in Photonics (CoEP)
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Founded in early 2005, the Centre of Expertise in Photonics (CoEP) is a research initiative within the School of Chemistry & Physics at the University of Adelaide focusing on the design, fabrication and application of soft glass optical fibres.
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Browsing Centre of Expertise in Photonics (CoEP) by Author "Afshar Vahid, S."
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Item Open Access A full vectorial model for pulse propagation in emerging waveguides with subwavelength structures part I: Kerr nonlinearity(Optical Soc Amer, 2009) Afshar Vahid, S.; Monro, T.The propagation of pulses through waveguides with sub-wavelength features, inhomogeneous transverse structure, and high index contrast cannot be described accurately using existing models in the presence of nonlinear effects. Here we report the development of a generalised full vectorial model of nonlinear pulse propagation and demonstrate that, unlike the standard pulse propagation formulation, the z-component of guided modes plays a key role for these new structures, and results in generalised definitions of the nonlinear coefficient gamma, Aeff , and mode orthognality. While new definitions reduce to standard definitions in some limits, significant differences are predicted, including a factor of approximately 2 higher value for gamma, for emerging waveguides and microstructured fibers.Item Metadata only A novel approach to Bragg fibre bandgap analysis: Stratified planar anti-resonant reflecting optical waveguides(IEEE, 2008) Rowland, K.; Afshar Vahid, S.; Monro, T.; Australian Conference on Optical Fibre Technology (ACOFT) (2008 : Sydney, Australia)We present a generalisation of the ARROW model, describing the topology and positions of novel features in Bragg stack bandgap spectra. Applications to Bragg bandgap fibres, including single-material hollow-core Bragg fibres, are discussed.Item Open Access Bandgaps and antiresonances in integrated-ARROWs and Bragg fibers; a simple model(Optical Soc Amer, 2008) Rowland, K.; Afshar Vahid, S.; Monro, T.We consider the spectral properties of dielectric waveguides with low refractive index cores and binary layered claddings, such as Bragg fibers and integrated-ARROWs. We show that the full, nontrivial, 2-D spectrum of Bloch bands (hence bandgaps) of such claddings correspond, in structure and topology, to the dispersion properties of both constituent layer types; quantitatively demonstrating an intimate relationship between the bandgap and antiresonance guidance mechanisms. The dispersion functions of these layers, and the interactions thereof, thus form what we coin the Stratified Planar Anti-Resonant Reflecting OpticalWaveguide (SPARROW) model, capable of quantitative, analytic, descriptions of many nontrivial bandgap and antiresonance properties. The SPARROW model is useful for the spectral analysis and design of Bragg fibers and integrated-ARROWs with cores of arbitrary refractive index (equal to or less than the lowest cladding index). Both waveguide types are of interest for sensing and microfluidic applications due to their natural ability to guide light within low-index cores, permitting low-loss guidance within a large range of gases and liquids. A liquid-core Bragg fiber is discussed as an example, demonstrating the applicability of the SPARROW model to realistic and important waveguide designs.Item Metadata only Emerging nonlinear optical fibers: fabrication and access to new properties(IEEE, 2009) Monro, T.; Ebendorff-Heidepriem, H.; Zhang, W.; Afshar Vahid, S.; IEEE/LEOS Winter Topicals Meeting (2nd : 2009 : Innsbruck, Austria)We review the properties and limitations of conventional and emerging nonlinear fibers. We describe advances in soft glass microstructured fibers, including fabrication, the demonstration of extreme nonlinearity and a generalisation of the underpinning nonlinear theory.Item Metadata only Emerging Nonlinear Optical Fibers: Revised Fundamentals, Fabrication and Access to Extreme Nonlinearity(IEEE-Inst Electrical Electronics Engineers Inc, 2009) Monro, T.; Ebendorff-Heidepriem, H.; Zhang, W.; Afshar Vahid, S.We review the properties of conventional and emerging nonlinear fibers. More specifically, we describe advances in soft glass microstructured fibers, including fabrication, the demonstration of extreme nonlinearity and a generalisation of the underpinning nonlinear theory.Item Metadata only Emerging waveguides with subwavelength and high index features: extensions of standard models and new applications(2008) Monro, T.; Afshar Vahid, S.; International Commission for Optics (ICO-21) (2008 : Sydney, Australia)Item Open Access Enhanced fluorescence sensing using microstructured optical fibers: a comparison of forward and backward collection modes(Optical Soc Amer, 2008) Afshar Vahid, S.; Ruan, Y.; Warren-Smith, S.; Monro, T.A general model of excitation and fluorescence recapturing by the forward and backward modes of filled microstructured optical fibers (MOFs) is presented. We also present experimental results for both backward and forward fluorescence recapturing within a MOF as a function of fiber length and demonstrate a good qualitative agreement between the numerical model and experimental results. We demonstrate higher efficiency of fluorescence recapturing into backward modes in comparison with that of forward modes.Item Open Access Enhancement of fluorescence-based sensing using microstructured optical fibres(Optical Soc Amer, 2007) Afshar Vahid, S.; Warren-Smith, S.; Monro, T.We develop a generic model of excitation and fluorescence recapturing within filled microstructured optical fibres (MOFs) with arbitrary structure and demonstrate that the light-matter overlap alone does not determine the optimal fibre choice. Fibre designs with sub-wavelength features and high-index glasses exhibit localised regions of high intensity, and we show that these regions can lead to approximately two orders of magnitude enhancement of fluorescence recapturing. Here we show how this regime can be exploited for sensing and demonstrate experimentally in-fibre excitation and fluorescence recapturing within a filled, solid-core MOF.Item Metadata only Generalised model of Raman gain in microstructured fibres(2008) Turner, M.; Monro, T.; Afshar Vahid, S.; International Commission for Optics (ICO-21) (2008 : Sydney, Australia)Item Metadata only Highly efficient fluorescence sensing using microstructured optical fibres: general model and experiment(SPIE, 2008) Afshar Vahid, S.; Monro, T.; Ebendorff-Heidepriem, H.; Ruan, Y.; Warren-Smith, S.; International Conference on Optical Fibre Sensors (19th : 2008 : Perth, W.Aust.); Sampson, D.; Collins, S.; Oh, K.; Yamauchi, R.A general model of excitation and fluorescence recapturing by the forward and backward modes of filled microstructured optical fibres (MOFs) is developed for fluorecence-based fibre optic sensors. It is demonstrated that the light-matter overlap alone does not determine the optimal fibre choice for maximum sensing efficiency. Fibre designs with sub-wavelength features and high-index glasses exhibit localised regions of high intensity, and we show that these regions can lead to approximately two orders of magnitude enhancement of fluorescence recapturing. We demonstrate higher efficiency of fluorescence recapturing into backward modes in comparison with that of forward modes. We present experimental results for both backward and forward flourescence recapturing and demostrate a good qualitative agreement between the numerical model and experimental results.Item Metadata only Highly-efficient fluorescence sensing using microstructured optical fibres; side-access and thin-layer configurations(S P I E - International Society for Optical Engineering, 2008) Warren-Smith, S.; Afshar Vahid, S.; Monro, T.; International Conference on Optical Fibre Sensors (19th : 2008 : Perth, W.Aust.); Sampson, D.; Collins, S.; Oh, K.; Yamauchi, R.A model is presented for calculating the performance of fluorescence-based optical-fibre sensors that considers the full vectorial nature of optical-fibre electromagnetic-field solutions making it suitable for modeling microstructured optical fibres with wavelength and sub-wavelength-scale features. By applying the model to a specific fibre geometry it is shown that high-index, small core (subwavelength) fibres allow for enhanced fluorescence capturing due to the formation of a thin, high-intensity layer at the core-cladding boundary. The model is evaluated in this regime for two sensing configurations of particular interest for future sensing systems, a side-access sensor for liquid-based sensing and a thin-layer (surface) sensor. Both configurations can offer improvements for fluorescence-based sensing.Item Metadata only Kerr nonlinearity in small core optical fibres and nanowires: a generalised model, and application to microstructured fibres(IEEE, 2008) Afshar Vahid, S.; Monro, T.; Australian Conference on Optical Fibre Technology (ACOFT) (2008 : Sydney, Australia)We develop a generalized relation for effective nonlinear coefficients of waveguides with arbitrary refractive index profiles. Significant differences between the new definition and usual one are demonstrated in the regime of strong guidance or waveguides with sub-wavelength inclusions.Item Metadata only Low loss, low dispersion and highly birefringent terahertz porous fibers(Elsevier Science BV, 2009) Atakaramians, S.; Afshar Vahid, S.; Fischer, B.; Abbott, D.; Monro, T.We demonstrate that porous fibers in addition to low loss and high confinement, have near zero dispersion for 0.5–1 THz resulting in reduced terahertz signal degradation compared to microwires. We also show for the first time that these new fibers can be designed, introducing asymmetrical sub-wavelength airholes within the core, to achieve high birefringence ≈0.026. This opens up the potential for realization of novel polarization preserving fibers in the terahertz regime.Item Metadata only Low loss, low dispersion T-ray transmission in Microwires(IEEE, 2007) Afshar Vahid, S.; Atakaramians, S.; Fischer, B.; Ebendorff-Heidepriem, H.; Monro, T.; Abbott, D.; Conference on Lasers and Electro Optics (CLEO/QELS) (29th : 2007 : Baltimore, U.S.A.)We present low loss, < 0.01 1/cm, and dispersion, < 10 ps/(km.nm), properties of microwires for terahertz transmission. These wires have diameters smaller than the operating wavelength, resulting in the propagation of enhanced evanescent fields. © 2007 Optical Society of America.Item Open Access Microwire fibers for low-loss THz transmission(SPIE, 2007) Atakaramians, S.; Afshar Vahid, S.; Fischer, B.; Ebendorff-Heidepriem, H.; Monro, T.; Abbott, D.; Smart Structures, Devices, and Systems (3rd : 2006 : Adelaide, Australia); Al-Sarawi, S.F.In this paper, we will investigate microwire fibers for low-loss terahertz transmission. Microwires, air-clad wire waveguides with diameter smaller than the operating wavelength (a few μm), have an enhanced evanescent field and tight wave confinement resulting in a low loss waveguide structure for the terahertz (T-ray) frequency regime. Based on our experimental data for the bulk material absorption of four glasses (F2, SF6, SF57 and Bismuth) and a polymer (PMMA), we calculate the normalized field distribution, power fraction outside the wire and effective loss. It will be shown that regardless of material, the effective loss of all microwires converges to the same order < 0.01 cm -1.Item Metadata only Nonlinear Material Diagnostics Using Filled Nanostructured Fibres(IEEE, 2006) Rowland, K.; Afshar Vahid, S.; Monro, T.; Australian Conference on Optical Fibre Technology and Meeting of the Australian Optical Society (31st : 2006 : Melbourne, Vic.)A new technique for determining the linear and nonlinear refractive index of liquids by measuring the nonlinearity of filled nanostructured fi bres is proposed.Item Metadata only Nonlinear optics in emerging waveguides: revised fundamentals and implications(Cambridge University Press, 2010) Afshar Vahid, S.; Turner, M.; Monro, T.; Dudley, J.; Taylor, J.Introduction Guided-wave nonlinear optics has attracted significant interest because of the unique environment that waveguides provide for nonlinear interactions, including tight confinement (high intensity), long interaction lengths (especially for fibres), control of propagation constants, and the possibility to incorporate them with integrated circuits (mainly for planar waveguides) [see (Lin et al., 2007; Knight and Skryabin, 2007; Foster et al., 2008; Afshar and Monro, 2009) and references therein]. Recent and rapid progress in design and manufacturing of complex structured microstructured optical fibres and planar waveguides with subwavelength features (including both subwavelength inclusions and voids) has further extended the opportunities to develop nonlinear devices by enabling extreme nonlinearity to combine with tailorable chromatic dispersion (Lin et al., 2007; Knight and Skryabin, 2007; Foster et al., 2008; Koos et al., 2007). The nonlinear optical phenomena that occur in waveguides are determined through two main factors; the linear and nonlinear properties of the constituent bulk materials, and the optical properties of the waveguide. Recent advances in the design and fabrication of complex structured waveguides with high contrast linear refractive indices, inhomogeneous cross-sections, and subwavelength features have provided great potential to accelerate the field of guided-wave nonlinear optics. We define a new class of optical waveguides, “emerging waveguides”, as waveguides with a combination of the following features: High index materials Inhomogeneous and complex structure Subwavelength features such as voids or material inclusions.Item Metadata only Nonlinearity enhancement of filled microstructured fibers operating in the nanowire regime(IEEE, 2006) Rowland, K.; Afshar Vahid, S.; Monro, T.; Conference on Optical Fiber Communication (2006 : Anaheim, California)We predict significant enhancement of the effective nonlinear coefficient of soft glass nanowires and nanostructured fibers by surrounding the cores with a nonlinear liquid. Using bismuth nanostructured fibers, γ as high as 5800 W-1 [superscript minus 1] km-1 [superscript minus 1] is possible.Item Open Access Novel low-loss bandgaps in all-silica Bragg fibers(IEEE-Inst Electrical Electronics Engineers Inc, 2008) Rowland, K.; Afshar Vahid, S.; Monro, T.We demonstrate that higher order bandgaps in all-silica Bragg fibers can have modes with four orders of magnitude lower confinement loss than those using the fundamental bandgap. A scheme for exploiting the higher order gaps for any specific wavelength via a global scaling of the fiber geometry is proposed. This approach provides lower losses than by reducing the confinement loss of the fundamental gap by scaling the core. Using a variety of modeling techniques, we have examined the band structure and guidance of idealized air-core all-silica Bragg fibers. It is demonstrated that the higher order, low loss, bandgaps analyzed here are uniquely accessible to single-material Bragg fibers, and are fundamentally different from the higher order gaps typically associated with depressed-index Bragg fibers such as the ldquoOmniguiderdquo fibers. Further analysis suggests that some of the key features of the guided modes of Bragg fibers can be understood by considering the properties of single hollow-core homogeneous dielectric waveguides (ldquoboreholesrdquo).Item Open Access Porous fibers: a novel approach to low loss THz waveguides(Optical Soc Amer, 2008) Atakaramians, S.; Afshar Vahid, S.; Fischer, B.; Abbott, D.; Monro, T.We propose a novel class of optical fiber with a porous transverse cross-section that is created by arranging sub-wavelength air-holes within the core of the fiber. These fibers can offer a combination of low transmission loss and high mode confinement in the THz regime by exploiting the enhancement of the guided mode field that occurs within these sub-wavelength holes. We evaluate the properties of these porous fibers and quantitatively compare their performance relative to that of a solid core air cladded fiber (microwire). For similar loss values, porous fibers enable improved light confinement and reduced distortion of a broadband pulse compared to microwires.