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Attenuation spectra of the aFMZIs under different axial strains. (a) P þ J type, (b) J þ P type, and (c) the dependences of the shifts in the attenuation peak wavelengths of the two types of aFMZI on axial strain at different interference orders at 20 C.
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An asymmetrical fiber Mach-Zehnder interferometer (aFMZI) consisting of a fiber taper and a lateral-shifted junction is proposed and demonstrated to realize simultaneous measurement of axial strain and temperature. The interferometer exhibits different environmental sensitivities for different device architectures. If the taper and the lateral-shif...
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Context 1
... sensitivities within the linear range from 20 C to 100 C. It is noted that the lower interference order m 2 shows a larger shift in the peak wavelength than that of the higher order m 1 . When an appropriate axial strain is applied on the two types of aFMZI kept at a constant temperature of 20 C, the shifts in the attenuation spectra are shown in Fig. 7(a) and (b), as the axial strain is increased from 0 to 2000 ". In the first test during the increasing strain, two interference orders m 1 and m 2 for the P þ J type aFMZI have the attenuation peak wavelengths m1;PþJ of 1531.52 nm and m2;PþJ of 1564.64 nm at 0 ", respectively, and the two interference orders m 1 and m 2 of the J þ P type ...
Context 2
... For the J þ P type aFMZI, the strain sensitivities at the order m 1 and m 2 are À1.51 and À2:76 pm=" (blueshift), respectively. In the second test during the increasing strain, the axial strain sensitivities at the order m 1 and m 2 are À1.46 and À2:7 pm=" for the P þ J type aFMZI and À1.5 and À2:74 pm=" for the J þ P type, respectively. Fig. 7(c) shows the average dependences of the shifts in the peak wavelengths of the two types of aFMZI at different interference orders on the change in the axial strain. Compared with the attenuation peak wavelength of the higher interference order, the peak wavelength of the lower interference order exhibits larger axial strain sensitivity. ...
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... In silica tapers, the red shift of the m-th interference dip is generally explained in terms of the positive variation of Δ and of the length , which is small due to the low thermal expansion coefficient [2], [18], [19], [28]. ...
... Fig. 3 shows the effective refractive index difference between the LP 01 mode and the LP 02 mode versus the wavelength for different temperature variations . The effective refractive index difference between the LP 01 mode and the LP 02 mode increases with In silica tapers, the red shift of the m-th interference dip is generally explained in terms of the positive variation of ∆n eff and of the length L, which is small due to the low thermal expansion coefficient α [2,18,19,28]. ...
This work illustrates, to the best of our knowledge, the first non-adiabatic tapered single-mode zirconium fluoride optical fiber sensor in the mid-infrared spectral range. It is designed and fabricated via pulling and heating technique. A waist diameter d w = 25 µm with no visible crystallization is achieved, overcoming the typical fluoride glass challenges associated with crystallization, narrow temperature fabrication window, and low glass transition temperature. The performance of the non-adiabatic tapered optical fiber is theoretically and experimentally investigated, demonstrating its high potential for a wide range of sensing applications in the mid-infrared spectral range.
... Optical fiber strain sensor has been widely used in civil engineering, aerospace, structural monitoring, military, and medical fields due to their advantages of small size, light weight, convenient installation, anti-electromagnetic interference, and high signalto-noise ratio. [1][2][3] At present, people have developed fiber-optic strain sensors with various structures, such as fiber Bragg grating (FBG), 4-6 long-period fiber grating (LPFG), 7,8 whispering gallery mode, 9 Sagnac interferometer (SI), 10 Michelson interferometer (MI), 11 Mach-Zehnder interferometer (MZI), [12][13][14][15][16] and Fabry-Perot interferometer (FPI). [17][18][19] Different sensor structures can meet the requirements of specific strain applications. ...
A strain sensor formed by a parallel connection of two Fabry–Perot interferometers (FPI) is proposed. The femtosecond laser is used to process a micro groove on the end face of a single-mode fiber (SMF), and then, it is welded with another SMF to form a small air bubble at the fusion point, fabricating an FPI. When the axial strain acts on the air bubble, the transverse length of the air bubble will change, causing the air cavity of the FPI to be easily deformed, and FPI can obtain high strain sensitivity. Three FPIs were manufactured with the air bubble sizes of 63, 78, and 93 µm, respectively, and the strain sensitivities of the three FPIs are 2.9, 2.0, and 1.5 pm/ µε, respectively. The experimental results show that the smaller the air bubble, the higher the strain sensitivity of FPI. Since the free spectral ranges of the three FPIs are relatively similar, we, respectively, paralleled them to form two Vernier effect strain sensors, and their sensitivities are −14.9 and −14.5 pm/ µε, respectively. Their sensitivities are increased by 5.1 times and 7.3 times, respectively. In addition, because three FPIs are composed of air cavities, they have very low temperature sensitivities. When they are connected in parallel, their resonance peak wavelength moves in the same direction with an increase in temperature, forming a reduced Vernier effect, and the temperature sensitivity amplification is very small. Therefore, the temperature cross-sensitivity of the sensor is extremely low and can be ignored.
... Fiber-optic strain sensors are reported in different designs and methodologies, such as fiber Bragg grating (FBG) [5,6], long period grating (LPG) [7,8], Mach-Zehnder Interferometer (MZI) [9][10][11], Michelson Interferometer (MI) [12][13][14], and FPI [15,16]. The FPI Sensors 2022, 22, 7557 2 of 15 in fiber-optic strain sensors is most prominent, which can be realized by creating an airgap/cavity to form two in-line reflective mirrors in an optical fiber. ...
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... Interferometer (MZI) [5][6][7], Michelson Interferometer (MI) [8][9][10], and FPI [11,12]. By exploiting the small-scale difference between the ruler and Vernier scale, the VE was originally used for high-precision length measurements. ...
A highly sensitive strain sensor based on tunable cascaded Fabry-Perot interferometers (FPIs) is proposed and experimentally demonstrated. Cascaded FPIs consist of a sensing FPI and a reference FPI which effectively generate the Vernier Effect (VE). The sensing FPI comprises a hollow core fiber (HCF) segment sandwiched between single-mode fibers (SMFs), and the reference FPI consists of a tunable air reflector, which is constituted by a computer programable fiber holding block to adjust the desired cavity length. Simulation results predict the dispersion characteristics of modes carried by HCF. The sensor’s parameters are designed corresponding to a narrow bandwidth range, i.e., 1530 nm to 1610 nm. Experimental results demonstrate that the proposed sensor exhibits optimum strain sensitivity of 23.9 pm/με in the range of 0 to 3000 με which is 13.73 times higher than the single sensing FPI strain sensitivity of 1.74 pm/με. The strain sensitivity of the sensor can be further enhanced by extending the source bandwidth. The proposed sensor exhibits ultra-low temperature sensitivity of 0.49 pm/°C in the wider temperature range of 25 °C to 135 °C, providing good isolation for eliminating cross-talk between strain and temperature. The sensor is very robust, cost-effective, easy to manufacture, repeatable, and shows a highly linear and stable response in the wider range of axial strain. Based on the sensor’s performance, it may suit plenty of practical applications in the real sensing world
... Refractive index and strain could be measured at the same time by the fiber Bragg grating (FBG) because the period of the grating is sensitive to the axial strain change while the mode effective refractive index is sensitive to the external environment refractive index fluctuation [10]. However, this type of sensor has great cross-sensitivity because the same characteristic of the sensor may not only respond to just one environmental parameter [11][12][13][14][15]. Another way to achieve dual-parameter sensing is to combine different sensing structures. ...
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... To address different requirements in various research fields, sensing characteristics have been selected for simultaneous measurement, such as simultaneous measurement of temperature and strain [3]- [5], temperature and refractive index (RI) [6], temperature and torsion [7], temperature and magnetic field [8], liquid level and RI [9], shape and temperature [10], pressure and temperature [11], and others [12]- [14] Simultaneous measurement of strain and temperature is more widely used in some fields than other dual-parameter measurements, including automobiles, spacecraft, nondestructive evaluation of civil infrastructure, and environmental monitoring. Hence, several structures that can realize simultaneous measurement of strain and temperature have been proposed in recent years, including cascade long period fiber grating (LPFG) [15]; cascade fiber Bragg grating [16]; a fiber grating inscribed on a special optical fiber [17]- [18]; an LPFG induced by electric-arc discharge [19]; an LPFG cascading another fiber structure, as combined with a tapered three-core fiber [20]; hybrid LPFG/MEFPI sensor [21]; micro-tapered fiber grating [22]; asymmetrical fiber Mach-Zehnder interferometer [23]; and others [24]- [25]. It has been confirmed that these proposed structures can solve the problem of temperature interference during strain measurement, but they have a disadvantage of low strain sensitivity. ...
A novel sensor structure has been proposed and experimentally investigated for simultaneous strain and temperature measurement. The structure is fabricated by weak power modulation of CO2 laser exposure on tapered long period fiber grating (LPFG). Compared with the transmission spectrum of the tapered LPFG, two peaks appear in the transmission spectrum of the novel structure. These resonance peaks exhibit different sensitivity responses; thus, simultaneous measurement of strain and temperature is realized by monitoring the wavelength shift of the two peaks. Experiment results indicate that strain sensitivities of the two peaks are 1.82 pm/μE and 8.17 pm/μE, and temperature sensitivities are 47.9 pm/°C and 65 pm/°C, respectively.
... Recently, in-line MZI optical fiber sensors are widely utilized in many sensing applications such as strain [1,2], curvature [3][4][5], temperature [6,7], refractive index [8,9], and vibration [10]. Owing to the wide range of sensing parameters, cross-sensitivity issues might affect the reliability of the sensor. ...
... The fundamental mode (HE 11 ) in the fiber core splits into the cladding mode (HE 12 ) at the 1st taper and recouples back into the fiber core at the 2nd taper. As the cladding mode travels within in the cladding from the 1st taper to the 2nd taper, it is highly sensitive to the ambient changes such as bending [19,20], temperature [6,7], vibration [21,22] refractive index [9,8], and torsion at the taper region [23,24]. ...
The Loop integrated Mach-Zehnder Interferometer (LMZI) optical fiber vibrational sensor was proposed to be implemented in pipeline monitoring and leak detection. The vibration sensing is based on power demodulation method using the torsion-sensitive LMZI sensor. In the 40 m steel pipeline field test, the LMZI sensor detected a significant leak-induced peak at ∼100 Hz during leak at 2 bar water pressure, whereas an additional ∼288 Hz peak was detected during leak at 3 bar water pressure. Both of the detected leak-induced frequencies were compared to the commercial accelerometer and showed good agreements with percentage errors of 0.4% and 2.64% at 2 bar and 3 bar respectively. The LMZI sensor is an alternative leak detection method which has great potential in replacing current conventional sensors in the future.
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This article presents a novel study on curvature sensing and crack monitoring in lightweight foamed concrete structural beam using the packaged fibre-based in-line Mach–Zehnder interferometer curvature sensor. The Mach–Zehnder interferometer sensors which consist of two abrupt biconic tapers were fabricated and packaged into polypropylene slabs to protect the sensors under harsh condition of the real sensing environment, as the sensors were embedded into lightweight foamed concrete structural beams for field tests. Pretest characterizations of Mach–Zehnder interferometer sensors based on the packaging thicknesses at different operating wavelengths (1310, 1490 and 1550 nm) were done before the field tests. Three packages with different thicknesses were prepared to justify the effect of the packaging thicknesses on the curvature sensitivity of sensors. Results showed that the Mach–Zehnder interferometer sensor with a thicker bottom slab has the highest sensitivity of up to 3.53 µW m⁻¹ which is capable of detecting a minimum curvature of 0.25 km⁻¹ and a maximum curvature radius of up to 4 km. In the field tests, three Mach–Zehnder interferometer sensors were embedded into the lightweight foamed concrete structural beams with different polypropylene percentages (0.4%, 0.25% and 0%, respectively) to characterize the sensor performance according to the concrete environments with different tensile capacities. Mach–Zehnder interferometer sensor managed to hold up to a maximum loading force of 26 kN in the concrete environment before stopping functioning. Optical powers in response to the loading forces imposed to the beams were mapped to the strains measured by the lead wire alloy foil strain gauges (brand: TML, model: FLK-6-11) with a good correlation value of up to 0.968. Furthermore, the double-sided sensing property of Mach–Zehnder interferometer sensors preponderates over the conventional strain gauges in detecting the internal cracking within the concretes before any earlier sighting of the macrocracks.
