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Single-mode-no-core-single-mode (SNS) optical fiber structures have valuable potential to encapsulate as high-precision temperature sensors, due to their great sensitivity. This paper is to improve the temperature sensitivity of SNS fibers by studying the parameters of fiber length, diameter, and refractive index of the seal liquid. Transmission spectra of the fibers are given in both aspects of experiment and numerical simulation. We find that using a slim no-core fiber section sealed with liquid of high refractive index can effectively improve the sensitivity, while the choice of fiber length mainly affects the width of transmission peak. The results may contribute to the development of high-sensitivity optic temperature sensor. [ABSTRACT FROM AUTHOR]

In the process of fiber optic tweezer manipulating cells, an adjustable and long working distance is very important for cell capture. To address this issue, a graded-index fiber (GIF) optical tweezer based on a UV glue cavity is proposed in this paper, and its ability to capture yeast cells was characterized. The initial air cavity between the single-mode fiber (SMF) and the GIF cone is filled with ultraviolet glue. By adjusting the length of the ultraviolet glue cavity and the laser power, the manipulation distance of the cells can be controlled. The light field distribution of the UV glue cavity is numerically investigated, which is compared with that of the GIF optical tweezers based on conventional air cavity. The contrastive result proved that the UV glue filled between the SMF and the GIF has a longer working distance than the original air cavity. The experimental results indicate that the fiber optical tweezer has a good capture distance controllability. The fiber optical tweezer also has the advantages of simple structure and convenient operation. [ABSTRACT FROM AUTHOR]

Abstract: Characteristics of cladding index modulated fiber gratings for ambient refractive index sensing is studied in this paper. The modes propagation properties and coupling properties in cladding index modulated FBG are studied based on the classical coupling mode theory while considering interactions among multiple modes and developed on a three-layer step-index fiber geometry. Evolution of cladding mode resonance spectra of cladding index modulated FBG with the decreasing of fiber diameter is simulated and compared with the core grating. Sensing characteristics of cladding modes resonance of cladding index modulated FBG to the variation of ambient refractive index is detailed and emphasized for cladding modes resonances has a much narrower bandwidth. Results show that cladding index modulated fiber grating has better spectrum for ambient refractive index sensing applications under the same sensitivity with core index modulated fiber grating and may be applied to many field including biochemical sensing and environmental monitoring. [Copyright &y& Elsevier]

There is a growing need to measure respiratory rate (RR) in a variety of applications, including in clinical and occupational settings, as well as during physical exercises. Fiber optic sensors (FOSs) is an attractive solution for wearable RR monitoring because of their small size, multiplexing capability, chemical inertness, and immunity to electromagnetic fields. Here, we review recent advances in FOSs for breath monitoring. We presented the sensing mechanisms of state-of-the-art sensors and analyze their advantages and disadvantages. We classified recently reported FOSs based on sensing principles and then critically analyze the strengths and weaknesses of representative recent works. Finally, we summarized the challenges and future prospects of breath FOSs, with the aim of applying them to real applications. [ABSTRACT FROM AUTHOR]