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(a) Setup for fabrication of ultra-high-Q microrod resonators. A fused-quartz rod is mounted on a motorized spindle and a focused CO2 laser beam is used to shape a whispering-gallery mode resonator. The laser focus position can be controlled by a zinc selenide lens mounted on a motorized and computer-controlled translation stage. An additional collinear alignment laser at 633 nm is used for coarse positioning of the laser spot. (b) CO2-laser-machined microrod resonators with diameters ranging from 170 μm up to 8 mm. (c)–(e) Different curvatures of the whispering-gallery side walls between 15 μm and 125 μm. The corresponding major diameters of the resonators are 2 mm in panel (c), 4 mm in (d) and 170 μm in (e).
(a) Mode spectrum of the 8-mm-diameter microrod resonator. The spectrum shows a diode laser sweep across two free spectral ranges of the resonator with approximately 30 different mode families. (b), (c) Finesse and optical quality factors of the resonators shown in Fig. 1(b) . The attained optical quality factors are between 2 × 108 and 1 × 109. (d) 186-kHz-wide mode (Q ∼ 1 × 109) in an 8-mm-diameter microrod resonator. (e) Mode splitting induced by coupling of clockwise and counter-clockwise modes in a smaller resonator (220 μm diameter).
Nonlinear optical effects in microrod resonators. Arrows in the figure show the position of the wavelength of the pump laser. (a) Cascaded four-wave mixing in a 220-μm-diameter resonator (mode spacing ∼ 300 GHz). (b) Cascaded four-wave mixing in an 8-mm-diameter resonator (mode spacing ∼ 8.4 GHz). (c),(d) Cascaded Brillouin scattering in a 6-mm-diameter resonator. The free spectral range of the resonator (∼11 GHz) is close to the maximum of the Brillouin gain bandwidth. The forward direction of the tapered fiber output only shows even orders of Brillouin sidebands, while the backward direction is dominated by the odd orders of sidebands. (e) Raman scattering and four-wave mixing in a 2-mm-diameter resonator.
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