Microsphere resonator integrated inside a microstructured optical fiber

Optics Letters (Impact Factor: 3.29). 04/2013; 38(8):1301-3. DOI: 10.1364/OL.38.001301
Source: PubMed


A compact and robust scheme for broadband excitation of whispering gallery mode (WGM) resonances into a microsphere is demonstrated. A polymer microsphere (10 μm) is encapsulated into the capillary of a microstructured optical fiber, in direct contact with the guiding core. Such a configuration allows efficient and reproducible excitation of the in-MOF-microsphere resonator that is characterized by two launch/collection schemes: core input/scattering output, and sphere input/core output. The latter allows an excitation of the microsphere WGMs externally to the fiber. Numerically calculated WGM spectra are in agreement with experiments. Q factors in the range of 103 are typically measured.

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Available from: Gianluigi Zito, Mar 04, 2015
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    • "Similar measurements were performed with the same microsphere samples in aqueous solution, drastically decreasing the refractive index contrast between the microresonator and its surrounding environment, resulting in higher confinement losses of the propagating modes as the reflectivity at the interface is reduced and a higher portion of the evanescent field leaks out of the resonator. As a consequence, all the higher order modes are quenched and only the first order TE and TM modes can be seen in Figure 4 (A), which shows a typical WGM spectrum of a 10 μm dye doped polystyrene microsphere in water [22] [23] . Figure 4 "
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    ABSTRACT: Whispering-gallery modes have been studied extensively for biosensing applications. Whilst the vast majority of work undertaken has focused on high Q factor resonators, with the main improvement being a reduction of the resonator size to improve sensitivity, we have chosen a different pathway by starting with resonators that exhibit extremely high refractive index sensitivity but low Q factor. A way forward to overcome this limitation is to introduce a gain medium and operate the resonator above its lasing threshold. This has been shown to result on average in a 5 fold increase in the Q factor. With the lasing threshold itself being dependent on the Q factor, amongst other parameters, the Q factor enhancement can be exploited to either reduce the lasing threshold or alternatively enable smaller resonators to be operated above their lasing threshold. As a demonstration we present a 10 μm diameter polystyrene microsphere lasing in aqueous solution for refractive index sensing applications, which to the best of our knowledge is the smallest polystyrene microsphere laser ever demonstrated in these conditions.
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    ABSTRACT: We present a novel form of a Whispering Gallery Mode (WGM) sensor that exploits dye doped polystyrene microspheres, as active resonators, positioned onto the tip of a Microstructured Optical Fiber (MOF) as a means of overcoming the limited Q-factors for small resonators. We show that it is possible to substantially enhance the fluorescence emission of selected WGMs of the microspheres, resulting in an increase of the signal-to-noise ratio of the modes and of the effective Qfactor. This is done by positioning the resonator into one of the holes of a suspended core MOF and matching the resonator diameter with the hole diameter where it sits, effectively breaking the symmetry of the environment surrounding the sphere. Furthermore we demonstrate that using this experimental configuration, the lasing efficiency of the dye doped microspheres is also significantly enhanced, which also contributes to an enhancement in the observed Q-factor.
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