Abstract
A Mach-Zehnder interferometer (MZI) based fiberoptic refractive index (RI) sensor is constructed by uniformly tapering standard single mode fiber (SMF) for RI measurement. A custom flame-based tapering machine is used to fabricate microfiber MZI sensors directly from SMFs. The fabricated MZI device does not require any splicing of fibers and shows excellent RI sensitivity. The sensor with a cladding diameter of 35.5 µm and length of 20 mm exhibits RI sensitivity of 415 nm/RIU for RI range of 1.332 to 1.384, 1103 nm/RIU for RI range of 1.384 to 1.4204 and 4234 nm/RIU for RI range of 1.4204 to 1.4408, respectively. The sensor reveals a temperature sensitivity of 0.0097 nm/°C, which is relatively low in comparison to its ultra-high RI sensitivity. The proposed inexpensive and highly sensitive optical fiber RI sensors have numerous applications in chemical and biochemical sensing fields.
Highlights
Fiber optic refractive index (RI) sensors have attracted considerable attention for chemical and biochemical monitoring applications over the past few years [1,2] because of their useful characteristics, such as small size, high-resolution detection, excellent aging characteristics, ability to operate in chemically hazardous environments, and immunity to electromagnetic noise
The combination of interferometers and gratings has been reported in the literature; for instance, Mach-Zehnder interferometer (MZI) has been constructed based on a pair of long period gratings (LPGs) to further increase RI sensitivity [14,15]
We present an ultra-high sensitivity, easy to fabricate, inexpensive, and mechanically robust in-line MZI based RI sensor constructed by tapering an single mode fiber (SMF)
Summary
Fiber optic refractive index (RI) sensors have attracted considerable attention for chemical and biochemical monitoring applications over the past few years [1,2] because of their useful characteristics, such as small size, high-resolution detection, excellent aging characteristics, ability to operate in chemically hazardous environments, and immunity to electromagnetic noise. Concatenation of core-offset section and SMF abrupt taper is suggested to form an MZI [31] This sensor revealed a relatively low RI sensitivity of 28.2 nm/RIU for a sensor length of 30 mm and its fabrication involved complex steps. The fabrication process was simple and cost-effective, the reported RI sensitivity was relatively low Another MZI sensor for RI measurement based on sandwiching and core-mismatched splicing of an SMF between two short sections of thin-core fibers was proposed by. The MZI sensor was fabricated by splicing a stub of PCF between two SMFs followed by PCF tapering Such MZI configurations may not be feasible for many monitoring applications due to their weak mechanical strength and the use of expensive fiber. 4234 nm/RIU was attained in the RI range of 1.4204 to 1.4408 for TWD 35.5 μm and taper waist length of 19.8 mm
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