http://hdl.handle.net/10468/220 2013-05-02T23:44:22Z http://hdl.handle.net/10468/325 Thermo-optical tuning of whispering-gallery modes in Er:Yb co-doped phosphate glass microspheres Ward, Jonathan M.; Nic Chormaic, Síle We demonstrate an all-optical, thermally assisted technique for broad-range tuning of whispering gallery modes in microsphere resonators fabricated from an Er:Yb co-doped phosphate glass (IOG-2). The microspheres are pumped at 978 nm and the heat generated by absorption of the pump expands the cavity, thereby altering the cavity size and refractive index. We demonstrate a significant nonlinear tuning range of greater than 700 GHz of both C- and L-band cavity emissions via pumping through a tapered optical fibre. Finally, we show that large linear tuning up to ∼488 GHz is achievable if the microsphere is alternatively heated by coupling laser light into its support stem. 2010-08-07T00:00:00Z http://hdl.handle.net/10468/219 Short vertical tube furnace for the fabrication of doped glass microsphere lasers Ward, Jonathan M.; Wu, Yuqiang; Khalfi, Krimo; Nic Chormaic, Síle We report on the design of an electric tube furnace that can be used for the fabrication of doped glass microsphere lasers. The tube furnace has a short hot zone of length 133 mm and is based on a quartz tube design. Doped laser glass particles, specifically Er:Yb phosphate glass (IOG-2), of ∼ 1 μm diameter are blown into the furnace using a 60 ml syringe and microspheres ranging in size from 10 to 400 μm are collected at the output of the tube furnace in a Petri dish. The furnace operates at a wall temperature of ∼ 900 °C and is capable of making microspheres from glasses with glass transition temperatures of at least 375 °C. High quality (Q ∼ 10^5) whispering gallery modes have been excited within the microspheres by optically pumping at 978 nm via a tapered optical fiber. 2010-07-01T00:00:00Z http://hdl.handle.net/10468/226 Ultralow threshold green lasing and optical bistability in ZBNA (ZrF4–BaF2–NaF–AlF3) microspheres Wu, Yuqiang; Ward, Jonathan M.; Nic Chormaic, Síle Upconversion lasing and fluorescence from active microspheres fabricated from a novel fluorozirconate, Er3+ doped glass, ZBNA (ZrF4-BaF2-NaF-AlF3), when pumped at 978 nm via a tapered optical fiber is demonstrated. An ultralow, green lasing threshold of similar to 3 mu W for 550 nm emissions is measured. This is one order of magnitude lower than that previously reported for ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF) microspheres. Optical bistability effects in ZBNA microspheres are reported and the bistable mechanism is discussed and attributed to shifts of the whispering gallery modes due to thermal expansion of the sphere, where heating is achieved by optical pumping around 978 nm. The effect of the bistability on the upconversion lasing is examined and we report multiple bistability loops within the microspheres. 2010-02-01T00:00:00Z http://hdl.handle.net/10468/330 Manifestation of the van der Waals surface interaction in the spontaneous emission of atoms into an optical nanofiber Minogin, V. G. (Vladimir Georgievich), 1950-; Nic Chormaic, Síle We study the spontaneous emission of atoms near an optical nanofiber and analyze the coupling efficiency of the spontaneous emission into a nanofiber. We also investigate the influence of the van der Waals interaction of atoms with the surface of the optical nanofiber on the spectrum of coupled light. Using, as an example, Rb-85 atoms we show that the van der Waals interaction may considerably extend the red wing of the spontaneous emission line and, accordingly, produce a well-defined asymmetry of the spontaneous emission spectrum coupled into an optical nanofiber. 2010-01-01T00:00:00Z