Optical micro- and nanofibres: Higher mode generation and particle manipulation studies

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dc.contributor.advisor Nic Chormaic, Síle en
dc.contributor.author Frawley, Mary
dc.date.accessioned 2015-08-17T15:39:31Z
dc.date.issued 2014
dc.date.submitted 2014
dc.identifier.citation Frawley, M. 2014. Optical micro- and nanofibres: Higher mode generation and particle manipulation studies. PhD Thesis, University College Cork. en
dc.identifier.uri http://hdl.handle.net/10468/1917
dc.description.abstract This thesis is centred on two experimental fields of optical micro- and nanofibre research; higher mode generation/excitation and evanescent field optical manipulation. Standard, commercial, single-mode silica fibre is used throughout most of the experiments; this generally produces high-quality, single-mode, micro- or nanofibres when tapered in a flame-heated, pulling rig in the laboratory. Single mode fibre can also support higher transverse modes, when transmitting wavelengths below that of their defined single-mode regime cut-off. To investigate this, a first-order Laguerre-Gaussian beam, LG01 of 1064 nm wavelength and doughnut-shaped intensity profile is generated free space via spatial light modulation. This technique facilitates coupling to the LP11 fibre mode in two-mode fibre, and convenient, fast switching to the fundamental mode via computer-generated hologram modulation. Following LP11 mode loss when exponentially tapering 125μm diameter fibre, two mode fibre with a cladding diameter of 80μm is selected fir testing since it is more suitable for satisfying the adiabatic criteria for fibre tapering. Proving a fruitful endeavour, experiments show a transmission of 55% of the original LP11 mode set (comprising TE01, TM01, HE21e,o true modes) in submicron fibres. Furthermore, by observing pulling dynamics and progressive mode-lass behaviour, it is possible to produce a nanofibre which supports only the TE01 and TM01 modes, while suppressing the HE21e,o elements of the LP11 group. This result provides a basis for experimental studies of atom trapping via mode-interference, and offers a new set of evanescent field geometries for sensing and particle manipulation applications. The thesis highlights the experimental results of the research unit’s Cold Atom subgroup, who successfully integrated one such higher-mode nanofibre into a cloud of cold Rubidium atoms. This led to the detection of stronger signals of resonance fluorescence coupling into the nanofibre and for light absorption by the atoms due to the presence of higher guided modes within the fibre. Theoretical work on the impact of the curved nanofibre surface on the atomic-surface van der Waals interaction is also presented, showing a clear deviation of the potential from the commonly-used flat-surface approximation. Optical micro- and nanofibres are also useful tools for evanescent-field mediated optical manipulation – this includes propulsion, defect-induced trapping, mass migration and size-sorting of micron-scale particles in dispersion. Similar early trapping experiments are described in this thesis, and resulting motivations for developing a targeted, site-specific particle induction method are given. The integration of optical nanofibres into an optical tweezers is presented, facilitating individual and group isolation of selected particles, and their controlled positioning and conveyance in the evanescent field. The effects of particle size and nanofibre diameter on pronounced scattering is experimentally investigated in this systems, as are optical binding effects between adjacent particles in the evanescent field. Such inter-particle interactions lead to regulated self-positioning and particle-chain speed enhancements. en
dc.description.sponsorship Science Foundation Ireland (SFI Grant 08/ERA/I1761 through the NanoSci-E Transnational Programme); European Commission (European Co-operation in Science and Technology (COST)) en
dc.format.mimetype application/pdf en
dc.language.iso en en
dc.publisher University College Cork en
dc.rights © 2014, Mary Frawley en
dc.rights.uri http://creativecommons.org/licenses/by-nc-nd/3.0/ en
dc.subject Physics en
dc.subject Optics en
dc.subject Optical nanofibres en
dc.subject Optical tweezers en
dc.subject Higher modes en
dc.title Optical micro- and nanofibres: Higher mode generation and particle manipulation studies en
dc.type Doctoral thesis en
dc.type.qualificationlevel Doctoral en
dc.type.qualificationname PhD (Science) en
dc.internal.availability Full text not available en
dc.check.info Indefinite en
dc.check.date 10000-01-01
dc.description.version Accepted Version
dc.contributor.funder European Commission en
dc.contributor.funder Okinawa Institute of Science and Technology Graduate University, Japan en
dc.contributor.funder Science Foundation Ireland en
dc.description.status Not peer reviewed en
dc.internal.school Physics en
dc.check.type No Embargo Required
dc.check.reason No embargo required en
dc.check.opt-out Yes en
dc.thesis.opt-out true
dc.check.embargoformat Not applicable en
dc.internal.conferring Autumn Conferring 2014

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© 2014, Mary Frawley Except where otherwise noted, this item's license is described as © 2014, Mary Frawley
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