Abstract
A fiber inline Mach-Zehnder interferometer (MZI) consisting of ultra-abrupt fiber tapers was fabricated through a new fusion-splicing method. By fusion-splicing, the taper diameter-length ratio is around 1:1, which is much greater than those (1:10) made by stretching. The proposed fabrication method is very low cost, 1/20–1/50 of those of LPFG pair MZI sensors. The fabricated MZIs are applied to measure refractive index, temperature and rotation angle changes. The temperature sensitivity of the MZI at a length of 30 mm is 0.061 nm/°C from 30–350 °C. The proposed MZI is also used to measure rotation angles ranging from 0° to 0.55°; the sensitivity is 54.98 nm/°. The refractive index sensitivity is improved by 3–5 fold by fabricating an inline micro–trench on the fiber cladding using a femtosecond laser. Acetone vapor of 50 ppm in N2 is tested by the MZI sensor coated with MFI–type zeolite thin film. The proposed MZI sensors are capable of in situ detection in many areas of interest such as environmental management, industrial process control, and public health.
Highlights
Optical fiber sensors have attracted tremendous research interest in recent years [1,2,3,4]
High-order cladding modes are excited in fiber Mach-Zehnder interferometers (MZI), which are guided by the cladding-ambient interface and directly exposed to the environment
This study proposes an MZI consisting of two ultra-abrupt fiber tapers fabricated by a fusion splicer using ordinary single mode fibers
Summary
Optical fiber sensors have attracted tremendous research interest in recent years [1,2,3,4]. By fusion-splicing, the taper diameter-length ratio is 1:1, which is much greater than those (1:10) made by stretching reported in the previous works [5,6]. When it is used as a RI sensor, the sensitivity is comparable to LPFG pair MZI sensors [10] and the taper-based MZI sensors fabricated by stretching method [5,6]. The refractive index sensitivity is improved by 3–5 fold through imbedding an inline side-ablated micro-trench on the fiber cladding using a femtosecond laser. Temperature and rotation angle tests are conducted
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