Simultaneous measurement of temperature and refractive index based on a core-offset Mach-Zehnder interferometer cascaded with a long-period fiber grating

Abstract

An all-fiber sensor based on a cascaded optical fiber device is proposed and demonstrated, and its sensor head is composed of a core-offset Mach-Zehnder interferometer (MZI) and a long-period fiber grating (LPFG). In the experiment, two dips shaped by the intermodulation between the interference fringe of MZI and the resonant wavelength of LPFG are monitored. Experimental results show that temperature sensitivities of two dips are 0.060 7 nm/°C and 0.056 3 pm/°C, and the refractive index (RI) sensitivities are -18.025 nm/RIU and -55.06 nm/RIU, respectively. The simultaneous measurement of the temperature and external RI is demonstrated based on the sensitive matrix. Its low fabrication cost, simple configuration and high sensitivity make this sensor have potential applications in chemical and biological sensing.Fiber sensors are widely used in sensing measurement fields, such as temperature, strain, micro-displacement and refractive index, because of their unique advantages of small size, light weight, immunity to electromagnetic interference, resistance to high pressure and high temperature, corrosion-resistance and so on [1][2][3] .Optical fiber sensors based on interference principle have the advantages of high sensitivity and flexible structure. In recent years, various on-line optical fiber interferometric sensors have been reported, such as single mode-multimode-single mode (SMS) structure [4] , single-mode fiber cascaded with thin-core fiber [5] , tapered fiber or peanut-shape Mach-Zehnder interferometer (MZI) [6] , laser drilling and core-offset splicing [7] . In 2012, Liu et al [8] proposed a single mode-multimode-thin core multimode-single mode (SMTMS) sensor to achieve simultaneous measurement of the temperature and the refractive index (RI). The low-cost structure has high practical value, but the sensitivity needs to be improved. In 2014, Dong et al [9] proposed a highly sensitive micro-displacement sensor based on MZI by a bowknot type taper. The intensity demodulation method is used to avoid the influence of temperature, and a higher sensitivity is obtained experimentally.In addition, some scholars embeded fiber gratings into the above interferometers to achieve a composite parameter sensing by simultaneously monitoring the resonant wavelengths of both fiber grating and interferometer.In 2013, Zhang [10] proposed a cascaded optical fiber device composed of a long-period fiber grating (LPFG) and an S-type fiber taper MZI (SFT-MZI). The crosstalk problem is solved because different resonance peaks of LPFG and MZI possess different RI and temperature sensitivities. In 2014, Meng [11] proposed a new-type sensor which contains a core-offset MZI and a fiber Bragg grating (FBG). The interference fringe of MZI and the Bragg wavelength of FBG would shift with the variation of ambient RI and temperature. The structure has some advantages, such as low fabrication cost and simple configuration, but its sensitivity still needs to be improved. LPFG has been widely used in optical fiber sensing and optical fiber ...

Multiparameter fiber-optic sensors: a review

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Investigation of Relative Humidity Sensing Using Tapered No-Core Fiber Coated With Graphene Oxide Film

“…It can quickly absorb water molecules to form nanoscale molecular films of water [14]. The effective RI of the GO nano-film changes with the humidity of the surrounding environment, which will result in a change in spectral characteristics of an optical fiber interferometric sensor [15], [16], [17]. Several optical sensors based on the interaction between graphene and the evanescent wave of an optical waveguide have been proposed [18], [19].…”

Simultaneous measurement of torsion, strain and temperature using a side-leakage photonic crystal fiber loop mirror

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