A full three-dimensional Finite-Difference Time-Domain (FDTD)-based toolkit is developed to simul... more A full three-dimensional Finite-Difference Time-Domain (FDTD)-based toolkit is developed to simulate the whispering gallery modes of a microsphere in the vicinity of a dipole source, placed on the surface. This provides a guide for experiments that rely on coupling to active microspheres. The resultant spectra are compared to those of analytic models used in the field. In contrast to the analytic models, the FDTD method is able to collect flux from an arbitrary collection region, such as a disk-shaped region, analogous to an optical fibre. The flux collection time may also be altered to access transient phenomena that may not appear at long collection times. The customisability of the technique allows one to consider a variety of mode excitation scenarios, such as refractive index inhomogeneity in the material, and different resonator shapes, such as shells and ellipsoids. The coupling efficiency to specific modes within wavelength regions can thus be optimized, preselecting the desired optical properties prior to fabrication. These features are particularly useful for investigating novel properties of optical resonators, and are valuable in assessing the viability of a resonator for biosensing.
Q-factor limits for far-field detection of whispering gallery modes in active microspheres
Optics Express, 2015
This paper investigates the Q-factor limits imposed on the far-field detection of the whispering ... more This paper investigates the Q-factor limits imposed on the far-field detection of the whispering gallery modes of active microspherical resonators. It is shown that the Q-factor measured for a given active microsphere in the far-field using a microscope is significantly lower than that measured using evanescent field collection through a taper. The discrepancy is attributed to the inevitable small asphericity of microspheres that results in mode-splitting which becomes unresolvable in the far-field. Analytic expressions quantifying the Q-factor limits due to small levels of asphericity are subsequently derived.
Whispering gallery modes (WGMs) within microsphere cavities enable highly sensitive label-free de... more Whispering gallery modes (WGMs) within microsphere cavities enable highly sensitive label-free detection of changes in the surrounding refractive index. This detection modality is of particular interest for biosensing applications. However, the majority of biosensing work utilizing WGMs to date has been conducted with resonators made from either silica or polystyrene, while other materials remain largely uninvestigated. By considering characteristics such as the quality factor and sensitivity of the resonator, the optimal WGM sensor design can be identified for various applications. This work explores the choice of resonator refractive index and size to provide design guidelines for undertaking refractive index biosensing using WGMs.
A full three-dimensional Finite-Difference Time-Domain (FDTD)-based toolkit is developed to simul... more A full three-dimensional Finite-Difference Time-Domain (FDTD)-based toolkit is developed to simulate the whispering gallery modes of a microsphere in the vicinity of a dipole source. This provides a guide for experiments that rely on efficient coupling to the modes of microspheres. The resultant spectra are compared to those of analytic models used in the field. In contrast to the analytic models, the FDTD method is able to collect flux from a variety of possible collection regions, such as a disk-shaped region. The customizability of the technique allows one to consider a variety of mode excitation scenarios, which are particularly useful for investigating novel properties of optical resonators, and are valuable in assessing the viability of a resonator for biosensing.
Laser Resonators, Microresonators, and Beam Control XVII, 2015
The whispering gallery modes (WGMs) of optical resonators have prompted intensive research effort... more The whispering gallery modes (WGMs) of optical resonators have prompted intensive research efforts due to their usefulness in the field of biological sensing, and their employment in nonlinear optics. While much information is available in the literature on numerical modeling of WGMs in microspheres, it remains a challenging task to be able to predict the emitted spectra of spherical microresonators. Here, we establish a customizable Finite-Difference Time-Domain (FDTD)-based approach to investigate the electromagnetic WGM spectrum of microspheres. The simulations are carried out in the vicinity of a dipole source rather than a typical plane-wave beam excitation, thus providing an effective analogue of the fluorescent dye or nanoparticle coatings used in experiment. The analysis of a single dipole source at different positions on the surface or inside a microsphere, serves to assess the relative efficiency of nearby radiating TE and TM modes, characterizing the profile of the spectrum. By varying the number, positions and alignments of the dipole sources, different excitation scenarios can be compared to analytic models, and to experimental results. The energy flux is collected via a nearby disk-shaped region. The resultant spectral profile shows a dependence on the configuration of the dipole sources. The power outcoupling can then be optimized for specific modes and wavelength regions. The development of such a computational tool can aid the preparation of optical sensors prior to fabrication, by preselecting desired the optical properties of the resonator.
The platform presented here was devised to address the unmet need for real time label-free in viv... more The platform presented here was devised to address the unmet need for real time label-free in vivo sensing by bringing together a refractive index transduction mechanism based on Whispering Gallery Modes (WGM) in dye doped microspheres and Microstructured Optical Fibers. In addition to providing remote excitation and collection of the WGM signal, the fiber provides significant practical advantages such as an easy manipulation of the microresonator and the use of this sensor in a dip sensing architecture, alleviating the need for a complex microfluidic interface. Here, we present the first demonstration of the use of this approach for biological sensing and evaluate its limitation in a sensing configuration deprived of liquid flow which is most likely to occur in an in vivo setting. We also demonstrate the ability of this sensing platform to be operated above its lasing threshold, enabling enhanced device performance.
International Journal of Applied Glass Science, 2015
ABSTRACT In this review, we examine recent developments in the field of chemical and biological s... more ABSTRACT In this review, we examine recent developments in the field of chemical and biological sensing utilizing suspended-core, exposed-core, and hollow-core microstructured optical fibers. Depending on the intended application, a host of sensing modalities have been utilized including labelled fluorescence techniques, and label-free methods such as surface plasmon resonance , fiber Bragg gratings, and Raman scattering. The use of various functionalization techniques adds specificity to both chemical ions and biological molecules. The results shown here highlight some of the important benefits that arise with the use of microstructured optical fibers compared to traditional techniques, including small sample volumes, high sensitivity, and multiplexing.
A full three-dimensional Finite-Difference Time-Domain (FDTD)-based toolkit is developed to simul... more A full three-dimensional Finite-Difference Time-Domain (FDTD)-based toolkit is developed to simulate the whispering gallery modes of a microsphere in the vicinity of a dipole source, placed on the surface. This provides a guide for experiments that rely on coupling to active microspheres. The resultant spectra are compared to those of analytic models used in the field. In contrast to the analytic models, the FDTD method is able to collect flux from an arbitrary collection region, such as a disk-shaped region, analogous to an optical fibre. The flux collection time may also be altered to access transient phenomena that may not appear at long collection times. The customisability of the technique allows one to consider a variety of mode excitation scenarios, such as refractive index inhomogeneity in the material, and different resonator shapes, such as shells and ellipsoids. The coupling efficiency to specific modes within wavelength regions can thus be optimized, preselecting the desired optical properties prior to fabrication. These features are particularly useful for investigating novel properties of optical resonators, and are valuable in assessing the viability of a resonator for biosensing.
Q-factor limits for far-field detection of whispering gallery modes in active microspheres
Optics Express, 2015
This paper investigates the Q-factor limits imposed on the far-field detection of the whispering ... more This paper investigates the Q-factor limits imposed on the far-field detection of the whispering gallery modes of active microspherical resonators. It is shown that the Q-factor measured for a given active microsphere in the far-field using a microscope is significantly lower than that measured using evanescent field collection through a taper. The discrepancy is attributed to the inevitable small asphericity of microspheres that results in mode-splitting which becomes unresolvable in the far-field. Analytic expressions quantifying the Q-factor limits due to small levels of asphericity are subsequently derived.
Whispering gallery modes (WGMs) within microsphere cavities enable highly sensitive label-free de... more Whispering gallery modes (WGMs) within microsphere cavities enable highly sensitive label-free detection of changes in the surrounding refractive index. This detection modality is of particular interest for biosensing applications. However, the majority of biosensing work utilizing WGMs to date has been conducted with resonators made from either silica or polystyrene, while other materials remain largely uninvestigated. By considering characteristics such as the quality factor and sensitivity of the resonator, the optimal WGM sensor design can be identified for various applications. This work explores the choice of resonator refractive index and size to provide design guidelines for undertaking refractive index biosensing using WGMs.
A full three-dimensional Finite-Difference Time-Domain (FDTD)-based toolkit is developed to simul... more A full three-dimensional Finite-Difference Time-Domain (FDTD)-based toolkit is developed to simulate the whispering gallery modes of a microsphere in the vicinity of a dipole source. This provides a guide for experiments that rely on efficient coupling to the modes of microspheres. The resultant spectra are compared to those of analytic models used in the field. In contrast to the analytic models, the FDTD method is able to collect flux from a variety of possible collection regions, such as a disk-shaped region. The customizability of the technique allows one to consider a variety of mode excitation scenarios, which are particularly useful for investigating novel properties of optical resonators, and are valuable in assessing the viability of a resonator for biosensing.
Laser Resonators, Microresonators, and Beam Control XVII, 2015
The whispering gallery modes (WGMs) of optical resonators have prompted intensive research effort... more The whispering gallery modes (WGMs) of optical resonators have prompted intensive research efforts due to their usefulness in the field of biological sensing, and their employment in nonlinear optics. While much information is available in the literature on numerical modeling of WGMs in microspheres, it remains a challenging task to be able to predict the emitted spectra of spherical microresonators. Here, we establish a customizable Finite-Difference Time-Domain (FDTD)-based approach to investigate the electromagnetic WGM spectrum of microspheres. The simulations are carried out in the vicinity of a dipole source rather than a typical plane-wave beam excitation, thus providing an effective analogue of the fluorescent dye or nanoparticle coatings used in experiment. The analysis of a single dipole source at different positions on the surface or inside a microsphere, serves to assess the relative efficiency of nearby radiating TE and TM modes, characterizing the profile of the spectrum. By varying the number, positions and alignments of the dipole sources, different excitation scenarios can be compared to analytic models, and to experimental results. The energy flux is collected via a nearby disk-shaped region. The resultant spectral profile shows a dependence on the configuration of the dipole sources. The power outcoupling can then be optimized for specific modes and wavelength regions. The development of such a computational tool can aid the preparation of optical sensors prior to fabrication, by preselecting desired the optical properties of the resonator.
The platform presented here was devised to address the unmet need for real time label-free in viv... more The platform presented here was devised to address the unmet need for real time label-free in vivo sensing by bringing together a refractive index transduction mechanism based on Whispering Gallery Modes (WGM) in dye doped microspheres and Microstructured Optical Fibers. In addition to providing remote excitation and collection of the WGM signal, the fiber provides significant practical advantages such as an easy manipulation of the microresonator and the use of this sensor in a dip sensing architecture, alleviating the need for a complex microfluidic interface. Here, we present the first demonstration of the use of this approach for biological sensing and evaluate its limitation in a sensing configuration deprived of liquid flow which is most likely to occur in an in vivo setting. We also demonstrate the ability of this sensing platform to be operated above its lasing threshold, enabling enhanced device performance.
International Journal of Applied Glass Science, 2015
ABSTRACT In this review, we examine recent developments in the field of chemical and biological s... more ABSTRACT In this review, we examine recent developments in the field of chemical and biological sensing utilizing suspended-core, exposed-core, and hollow-core microstructured optical fibers. Depending on the intended application, a host of sensing modalities have been utilized including labelled fluorescence techniques, and label-free methods such as surface plasmon resonance , fiber Bragg gratings, and Raman scattering. The use of various functionalization techniques adds specificity to both chemical ions and biological molecules. The results shown here highlight some of the important benefits that arise with the use of microstructured optical fibers compared to traditional techniques, including small sample volumes, high sensitivity, and multiplexing.
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Papers by Tess Reynolds