Abstract
In this work, we introduced fabrication and interrogation of simple and highly sensitive fiber-optic refractive index (RI) sensors based on ball resonators built on the tip of single-mode fibers. The probes have been fabricated through a CO2 fiber splicer, with a fast (~600 s) and repeatable method. The ball resonator acted as a weak interferometer with a return loss below −50 dB and was interrogated with an optical backscatter reflectometer measuring the reflection spectrum. The ball resonators behaved as weak interferometers with a shallow fringe and a spectrum that appeared close to a random signal, and RI sensitivity could be measured either through wavelength shift or amplitude change. In this work, we reported four samples having sensitivity ranges 48.9–403.3 nm/RIU and 256.0–566.2 dB/RIU (RIU = refractive index unit). Ball resonators appeared as a sensitive and robust platform for RI sensing in liquid and can be further functionalized for biosensing.
Highlights
Optical fiber refractive index (RI) sensors are an emerging technology with significant potential for biomedical applications [1]
We proposed a ball resonator structure for RI sensing, solving many of the problems that gratings and interferometers present in terms of fabrication ease and robustness
The spectra of the four ball resonators described in the previous section, as a function of RI
Summary
Optical fiber refractive index (RI) sensors are an emerging technology with significant potential for biomedical applications [1]. We proposed a ball resonator structure for RI sensing, solving many of the problems that gratings and interferometers present in terms of fabrication ease and robustness. In the early 2000 s, a research group studied the sensing of bovine serum albumin in a phosphate buffer with a microsphere device [23] They identified this system, consisting of a microsphere structure coupled to a tapered fiber, as a microsphere resonator. The reflection spectrum of the ball resonators appeared similar to a random signal due to the weak fringes of the interferometric structure; spectra have a sensitivity that can be measured either weak fringes of the interferometric structure; spectra have a sensitivity that can be measured either as a wavelength shift or as an intensity change. Interrogation of ball resonators, discussing the results on different samples of sensors
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