Abstract
Negative curvature hollow core fiber (NCHCF) is a promising candidate for sensing applications; however, research on NCHCF based fiber sensors starts only in the recent two years. In this work, an all-fiber interferometer based on an NCHCF structure is proposed for the first time. The interferometer was fabricated by simple fusion splicing of a short section of an NCHCF between two singlemode fibers (SMFs). Both simulation and experimental results show that multiple modes and modal interferences are excited within the NCHCF structure. Periodic transmission dips with high spectral extinction ratio (up to 30 dB) and wide free spectral range (FSR) are produced, which is mainly introduced by the modes coupling between HE11 and HE12. A small portion of light guiding by means of Anti-resonant reflecting optical waveguide (ARROW) mechanism is also observed. The transmission dips, resulting from multimode interferences (MMI) and ARROW effect have a big difference in sensitivities to strain and temperature, thus making it possible to monitor these two parameters with a single sensor head by using a characteristic matrix approach. In addition, the proposed sensor structure is experimentally proven to have a good reproducibility.
Highlights
Optical fiber interferometric sensors have been widely investigated and employed for monitoring the changes of a wide range of physical and bio-chemical parameters, with their inherent advantages of simpleSensors 2020, 20, 4763; doi:10.3390/s20174763 www.mdpi.com/journal/sensorsSensors 2020, 20, 4763 structure, ease of fabrication, high sensitivity, immunity to electromagnetic interference and ability to work in harsh environments and to operate remotely [1,2]
The Negative curvature hollow core fiber (NCHCF)-based modal interferometer was fabricated by fusion splicing a short section of NCHCF between two singlemode fibers (SMFs) using a Fujikura 62S+ fusion splicer (Fujikura (China) Co., Ltd., Shanghai, China)
Series of periodic transmission dips with large extinction ratios and wide free spectral range (FSR) have been observed for all samples over a wide wavelength range from 1220 nm to 1550 nm
Summary
Optical fiber interferometric sensors have been widely investigated and employed for monitoring the changes of a wide range of physical and bio-chemical parameters, with their inherent advantages of simpleSensors 2020, 20, 4763; doi:10.3390/s20174763 www.mdpi.com/journal/sensorsSensors 2020, 20, 4763 structure, ease of fabrication, high sensitivity, immunity to electromagnetic interference and ability to work in harsh environments and to operate remotely [1,2]. Interferometers based on PCFs suffer from relatively high loss and poor reproducibility, since the small air cores in PCFs are easy to collapse during fusion splicing, and both the splice power and arc duration are found to have significant influence on the final transmission spectrum of the PCF-based structure [2,10]. In 2011, negative curvature hollow core fiber (NCHCF) was first proposed by Pryamikov et al [11]. In less than 10 years since its first appearance, the NCHCF attracted tremendous attention for various applications, such as high power/ultrafast laser delivery and other laser-related applications due to its advantages of large bandwidth, reduced transmission loss, simple structure and easy fabrication [12,13]
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