Intensity-modulated abrupt tapered Fiber Mach-Zehnder Interferometer for the simultaneous sensing of temperature and curvature

A High Sensitivity Temperature Sensing Probe Based on Microfiber Fabry-Perot Interference

“…As can be seen from Table 1, the temperature sensitivity of FBGs is low, and the encapsulation technology and demodulation optical path are complex [16]. The dual-arms system of Mach-Zehnder interferometers are commonly built using special optical fibers (for example PCF [6,20] or microfibers [18,19,30]) or by splicing different optical fibers [18,21], where the sensitive liquid or polymer were introduced to create a temperature-sensitive probe [6,20,21]. In contrast, the Fabry-Perot fiber interferometer can be easily fabricated on a single fiber.…”

“…In addition to the above complex optical fiber structures, single polymer optical fibers have been demonstrated with a temperature sensitivity of ~10 −3 °C [27], where the temperature performance were revealed by the transmission power and the effect of relative and twist have been experimentally obtained [28,29]. Furthermore, their packaging size is hard to reduce further depending on the bending loss of the optical fiber [30], which will seriously limit their application in a narrow space; the latter ones are carried out as reflective structures, where the temperature sensitive cavity was constructed at the end of the optical fiber by laser or ion beam processing, chemical etching or film forming and special fiber splicing technologies [31,32,33,34,35,36,37]. Among them, femtosecond laser processing can machine a refractive index turning point with good repeatability in the optical fiber, which was used as a Fabry-Perot cavity and can work at high temperatures up to 1000 °C [31]; focused ion beams can etch an air cavity at the tip of an optical fiber, based which a Fabry-Perot temperature sensor with a sensitivity of −654 pm/°C has been experimentally demonstrated [32].…”

High Strain Sensitivity Temperature Sensor Based on a Secondary Modulated Tapered Long Period Fiber Grating

“…As simultaneous measurement is considered an effective way to solve the cross-sensitivity problem, it is of great importance in fiber grating devices. 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]; microtapered fiber grating [22]; asymmetrical fiber Mach-Zehnder interferometer [23]; and others [24], [25].…”

All-Fiber Laser Curvature Sensor Using an In-Fiber Modal Interferometer Based on a Double Clad Fiber and a Multimode Fiber Structure

“…Specially, they have been attracted wide attention in fiber sensing because their many advantages such as high sensitivity, immunity to electromagnetic field, small size, low-cost, low maintenance required, and long term operation. Different approaches of fiber sensors designed with in-fiber structures used as wavelength filter as well as sensing element has been reported to measure refractive index (RI) [ 1 , 2 , 3 ], curvature [ 4 , 5 , 6 , 7 ], temperature [ 8 ], displacement/strain [ 9 , 10 ], and simultaneous or different physical parameters with the same configuration [ 11 , 12 , 13 , 14 ]. In particular, in-fiber curvature sensors have been of increasing interest for applications such as monitoring of smart and composite engineering structures, robotics, prosthetics design, medical treatment, and industrial metrology, among others.…”

“…An in-fiber structure based on modal interference used as sensing device requires a fiber element to recombine the excited coupled modes from cladding with the core modes producing an interference effect leading to a modulated transmission of the input signal. The produced interference effect can be caused by tapered fibers [ 5 , 11 , 15 ], core-offset splices and core diameter mismatch [ 4 , 8 , 13 , 16 ], multimode interference (MMI) [ 2 , 6 , 7 , 10 ], and multipath by micro-structured fibers [ 9 , 14 , 17 ], among others. All of the proposed techniques exhibit their own disadvantages.…”