Characterization of high index microsphere resonators in fiber-integrated microfluidic platforms

Abstract

We investigate high-Q microsphere resonators with whispering gallery modes using a tapered optical microfiber immersed in a liquid inside a microfluidic platform. The strength of the coupling between the cavity and the microfiber taper is shown to depend on the contact position of the microsphere along the taper and on the refractive index contrast between the microsphere and the liquid environment. We demonstrate that barium titanate glass beads with index around 1.9 are promising candidates for developing sensor and optomechanical applications of such resonator systems.

Whispering-gallery modes excitation in microspheres integrated inside microstructured optical fibers

“…The Q-factor of the peak resolved at 1356 nm reaches the value of 3500, that is, a value more than 2 times higher than in the case of the polystyrene microsphere for the same wavelength region. This value of Q-factor is also greater than the one reported for 5-µm spheres made of BaTiO 3 in [19], where the resonator was excited through a fiber taper of about 1.25 µm in diameter. According to [19], a larger microsphere of a few micrometers would increase the Q-factor by more than a factor of 3.…”

“…This value of Q-factor is also greater than the one reported for 5-µm spheres made of BaTiO 3 in [19], where the resonator was excited through a fiber taper of about 1.25 µm in diameter. According to [19], a larger microsphere of a few micrometers would increase the Q-factor by more than a factor of 3. However, in our in-fiber configuration, using the HNA-5 fiber, a larger microsphere would directly result in different coupling between the core and the microsphere, which should be taken into account; this is imposed by the capillary geometry of the fibre used.…”