Refractometric sensor based on whispering-gallery modes of thin capillarie.

Whispering-gallery modes resonances of submicron wall thickness capillaries exhibit very large wavelength shifts as a function of the refractive index of the medium that fills the inside. The sensitivity to refractive index changes is larger than in other optical microcavities as microspheres, microdisks and microrings. The outer surface where total internal reflection takes place remains always in air, enabling the measure of refractive index values higher than the refractive index of the capillary material. The fabrication of capillaries with submicron wall thickness has required the development of a specific technique. A refractometer with a response higher than 390 nm per refractive ind…

Interrogation of whispering-gallery modes resonances in cylindrical microcavities by backreflection detection

The excitation of whispering-gallery-mode resonances of cylindrical microcavities, using narrow fiber tapers, produces simultaneously the excitation of spiral modes. The power coupled to the spiral modes leads to a significant broadening of the dips observed in the spectrum of light transmitted through the taper. We demonstrate that whispering-gallery modes resonances of cylindrical microcavities can also be interrogated by measuring the reflection spectrum. Unlike the dips observed in transmission, the peaks in the reflection spectrum are symmetric and narrower than the corresponding transmission dips.

Refractive index sensor based on whispering gallery modes resonances of thin capillaries

Cylindrical optical microcavities: Basic properties and sensor applications

Abstract A detailed theoretical analysis of the basic properties of whispering-gallery modes (WGM) of thin capillaries is presented. The sensitivity of the resonances, as well as the Q factor is analyzed as a function of the structural parameters of the capillary and the refractive index inside the capillary. A practical application where thin capillaries are used for the measurement of glucose concentration in water is presented as a chemical sensor demonstrator. A best sensitivity of 1.24 nm/% of glucose concentration in water is reported, which corresponds to more than 850 nm/RIU. Additionally, different experimental approaches are discussed to improve the sensitivity and the detection l…

Back-scattering of whispering-gallery-modes resonances of cylindrical microcavities: Refractometric applications

Whispering-gallery modes (WGM) resonances of microcapillaries are directly compatible with microfluidic systems and have demonstrated its suitability for refractometric applications [1]. Microcapillaries with a submicrometric wall exhibit very large wavelength shifts as a function of the refractive index of the liquids that fill the inside of the capillary [2]. The spatial separation between the surface where the total internal reflection takes place (the outer surface) and the sensing surface (the inner surface) where the wave interacts with the analyte is a unique property that can be exploited to deal with analytes with a refractive index higher than that of the capillary [2].

Excitation and interrogation of whispering-gallery modes in optical microresonators using a single fused-tapered fiber tip

We show that whispering-gallery modes (WGMs) in optical microresonators can be excited and detected using a fused-tapered fiber tip (FTFT). The fabrication of FTFTs is simple and inexpensive; they are robust and allow the excitation and interrogation of the resonances with a single fiber. Excitation of high-Q WGMs in silica microcylinders and microspheres is demonstrated.