Torsion, Strain, and Temperature Sensor Based on Helical Long-Period Fiber Gratings

Advances on Mode-Coupling Theories, Fabrication Techniques, and Applications of the Helical Long-Period Fiber Gratings: A Review

“…The temperature sensitivity obtained was is estimated to be ~41 pm/°C within a range of 20-150 °C, and the torsion responsivities obtained are ~−1.414 nm/rad/m and ~1.276 nm/rad/m, respectively within a rotation angle of −360°~360° [13]. Furthermore, in 2018, based on the same two-cascaded HLPGs but working at three different cladding modes, the authors' research group proposed and demonstrated a novel method enabling for the simultaneous measurements of the torsion, strain and temperature while the crosstalk effects of these three parameters could be eliminated [72]. However, all the torsion sensors mentioned above rely on the cost-inefficient wavelengthinterrogation method, i.e., in order to precisely measure a wavelength shift, either an optical spectrum analyzer (OSA) with a high wavelength-resolution or an extremely narrow linewidth tunable laser with both a wide tuning region and a high wavelength-scanning speed are desired.…”

“…The temperature sensitivity obtained was is estimated to be~41 pm/ • C within a range of 20-150 • C, and the torsion responsivities obtained are~−1.414 nm/rad/m and~1.276 nm/rad/m, respectively within a rotation angle of −360 •~3 60 • [13]. Furthermore, in 2018, based on the same two-cascaded HLPGs but working at three different cladding modes, the authors' research group proposed and demonstrated a novel method enabling for the simultaneous measurements of the torsion, strain and temperature while the crosstalk effects of these three parameters could be eliminated [72].…”

Recent Progress in Fabrications and Applications of Heating-Induced Long Period Fiber Gratings

“…Results show that the resonant wavelength shift sensitivity and transmission power sensitivity are –1.1 pm/με and 2.2 × 10 –4 dB/με, respectively [58]. In addition, a novel strain sensor based on two successively cascaded HLPFGs exhibits a sensitivity of −0.185 pm/με [59]. A highly sensitive strain sensor with a sensitivity of –61.8 pm/με based on helical structure-assisted Mach–Zehnder interference in an all-solid heterogeneous multi-core fiber was proposed and experimentally demonstrated [60].…”

“…Various heating-induced LPFGs in conventional fiber [12,13,22,28,35,46,47], photonic crystal fiber (PCF) [14,15,16,29,48], and photonic bandgap fiber (PBF) [27,30,31] could then be successfully written. LPFG-based devices have recently attracted great attention and found versatile applications, such as in all-fiber orbital angular momentum (OAM) mode converters [11,13,14,17,49,50,51,52,53,54,55,56], and strain [48,57,58,59,60,61,62,63,64], pressure [16,29,30,65,66], torsion [16,19,38,46] and biochemical sensors [67,68,69,70,71,72,73].…”

Ultrasensitive Temperature Sensor With Cascaded Fiber Optic Fabry–Perot Interferometers Based on Vernier Effect

“…Up to now, a great deal of sensing schemes and structures have been proposed for temperature measurement, such as fiber grating sensors (fiber Bragg gratings (FBGs) [1], [2] and long period fiber gratings (LPFGs) [3], [4]), optical fiber interferometric sensors (OFIS) (in-fiber modal interferometers [5]- [7], Mach-Zehnder interferometers (MZIs) [8], fiber Sagnac interferometers (SIs) [9], [10], extrinsic Fabry-Perot interferences (FPIs) [11]- [13], Silicon-on-insulator (SOI) sensors [14], [15] and surface plasmon resonance (SPR) sensors [16]- [18]. Limited by the small thermal-optical coefficient (TOC) and thermal-expansion coefficient (TEC) of silica, sensitivities of traditional fiber grating sensors and OFI sensors, which employ the fiber itself as the temperature transducer, are usually low (only tens of picometers per degree centigrade).…”