Highly efficient excitation and detection of whispering gallery modes in a dye-doped microsphere using a microstructured optical fiber

Abstract

A technique for the excitation of whispering gallery modes (WGMs) has been demonstrated using a dye-doped microsphere positioned onto the tip of a suspended core microstructured optical fiber. With this configuration, we have shown that both the excitation and collection efficiency of the WGMs modulated fluorescence spectra of the dye are greatly improved compared to a more conventional excitation scheme; an overall efficiency increase by a factor of 200 is demonstrated. It is also shown that positioning the resonator onto the fiber tip does not impact its sensitivity, providing a compact and robust architecture for applications such as localized in-vivo/vitro biosensing.

Enhancing the radiation efficiency of dye doped whispering gallery mode microresonators

“…In this architecture, the resonator is located on a circular air hole next to the fiber core, enabling a significant portion of the sphere to overlap with the guided light emerging from the cleaved fiber tip [18]. When the resonator is excited through the suspended core fiber, it exhibits an unusually high radiative efficiency, which was initially attributed simply to the higher excitation efficiency that this architecture enables.…”

“…Polystyrene microspheres with a nominal diameter of 5μm 15μm, 20μm and 25μm were doped with Nile Red (λ abs = 532 nm, λ em = 590 nm) using a liquid two phase system described elsewhere [18] Among the different techniques reported in the literature to either introduce a gain medium within a polymer microsphere [13] or simply coat its surface with either quantum dots or organic dye molecules [20,21], this approach enables high dye content to be attained within the polymer sphere which is critical for reaching the lasing threshold of the WGMs. Once the doping process complete, the sphere were rinsed by centrifugation, the supernatant removed and replace by Millipore water.…”

“…Recently we demonstrated that a dye-doped microresonator positioned onto the tip of a suspended core Microstructured Optical Fiber (MOF) can be used as a dip sensor [18]. In this architecture, the resonator is located on a circular air hole next to the fiber core, enabling a significant portion of the sphere to overlap with the guided light emerging from the cleaved fiber tip [18].…”

Whispering-gallery mode lasers for biosensing: a rationale for reducing the lasing threshold

“…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] . The Q factor of the first order mode is also strongly affected, dropping from 4×10 3 to 2×10 sample in air.…”

Optimization of whispering gallery mode sensor design for applications in biosensing

“…With no consideration of such a limit, the Q would continue to increase exponentially, predicting Q values orders of magnitude grater than what is observed experimentally. Currently in our experimental set-up, detailed elsewhere [18,24], the resolution of the spectrometer is limited to 4 picometers. Once again, the solid black line seen on the figure represents the boundary below which the peaks would not be resolvable above the background fluorescence.…”