Bending Vector Sensor Based on a Sector-Shaped Long-Period Grating
TL;DR: In this paper, a novel optical fiber grating vector bending sensor head is proposed, which is embedded in the sensor head by tilting the grating planes at increasing angles, as moving away from the center grid of the structure.
Abstract: A novel optical fiber grating vector bending sensor head is proposed. The asymmetric characteristics are embedded in the sensor head by tilting the grating planes at increasing angles, as moving away from the center grid of the structure. A high-frequency-CO2-laser is used to fabricate the sensor head. Due to the characteristics of the asymmetric structure, the bending sensitivity for the curvature range from −2 to 0 $\text{m}^{\mathrm { {-1}}}$ reaches 8.53 nm/ $\text{m}^{\mathrm {{-1}}}$ , and for the curvature range from 0 to 2 $\text{m}^{\mathrm { {-1}}}$ reaches 2.82 nm/ $\text{m}^{\mathrm {{-1}}}$ , respectively.
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TL;DR: The fabrication of long period fiber gratings written in two-mode fiber as mode converter to realize the mode conversion between LP01 mode and LP11 mode with an efficiency of up to 99.9% is demonstrated.
Abstract: We demonstrate the fabrication of long-period fiber gratings (LPFGs) written in the two-mode fiber (TMF) by CO2 laser. Both uniform and tilted LPFGs were fabricated to provide the light coupling between LP01 mode and LP11 mode with a coupling efficiency of more than 99%. The writing efficiency and the bandwidth of the LPFG mode converter can be adjusted by changing the tilt angle of the tilted TMF-LPFGs. The torsion sensitivity of conventional and tilted LPFG mode converters were measured to be 0.37 nm/(rad/m) and 0.50 nm/(rad/m), respectively. Two orthogonal vector modes (the HEeven 21and HEodd 21 modes) and corresponding orbital angular momentum state were successfully obtained at the resonance wavelength. The proposed LPFG mode converter could be used as not only a high efficiency wavelength tunable mode converter in the mode division multiplexing system but also a high sensitive torsion sensor in the field of optical sensing.
147 citations
TL;DR: The authors' MCF bending sensor was found to be highly sensitive (4094 pm/deg) to small bending angles and it is capable of distinguishing multiple bending orientations.
Abstract: In this Letter, we demonstrate a compellingly simple directional bending sensor based on multicore optical fibers (MCF). The device operates in reflection mode and consists of a short segment of a three-core MCF that is fusion spliced at the distal end of a standard single mode optical fiber. The asymmetry of our MCF along with the high sensitivity of the supermodes of the MCF make the small bending on the MCF induce drastic changes in the supermodes, their excitation, and, consequently, on the reflected spectrum. Our MCF bending sensor was found to be highly sensitive (4094 pm/deg) to small bending angles. Moreover, it is capable of distinguishing multiple bending orientations.
113 citations
TL;DR: A review of optical fiber bending sensors is presented in this article, where the authors mainly focus on the measurement methods of the structure bending and the existing problems of the bending measurement methods and the future prospects of different bending sensors.
88 citations
TL;DR: In this article, the use of long period gratings (LPGs) for the implementation of a directional curvature sensor has been studied and a set of three different LPGs were inscribed in a seven core optical fiber using a selective inscription technique.
Abstract: Multicore optical fibers are especially attractive for the fabrication of curvature and shape sensors due to the spatial distribution of the different cores. Fiber Bragg gratings have been used in the past for the implementation of these sensors, however, despite their inherent properties, they have a very limited sensitivity. In this paper, we study the use of long period gratings (LPGs) for the implementation of a directional curvature sensor. We inscribed a set of three different LPGs in a seven core optical fiber using a selective inscription technique. We inscribed a single LPG in the external cores and an array of three LPGs in the central core. We have characterized the proposed sensor for strain, torsion, and curvature magnitude and direction. The proposed sensor shows a linear response for curvature magnitudes from 0 to 1.77 m–1 with a maximum curvature sensitivity of –4.85 nm/m–1 and shows a near sinusoidal behavior in all the cores with curvature directions from 0° to 360°. The sensor shows a good insensitivity to strain. The torsion in the multicore optical fibers can be detected and measured using the maximum attenuation of the LPGs in the external cores.
79 citations
Cites background from "Bending Vector Sensor Based on a Se..."
...2764951 interferometers have been proposed for the implementation of curvature sensors [1], [2]....
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TL;DR: Off-axis fiber Bragg gratings are inscribed by ultraviolet irradiation limited to expose only a portion of the fiber core cross section and the coupling to cladding modes is significantly increased, and the amplitude of the cladding mode resonances becomes sensitive to bending in magnitude and direction.
Abstract: Off-axis fiber Bragg gratings are inscribed by ultraviolet irradiation limited to expose only a portion of the fiber core cross section. The coupling to cladding modes is significantly increased, and the amplitude of the cladding mode resonances becomes sensitive to bending in magnitude and direction. Sensitivities ranging from +1.17 dB/m(-1) to -1.25 dB/m(-1) were obtained for bending in different directions relative to the offset direction of the grating, for curvatures from 0 to 1.1 m(-1), a range ideal for the shape sensing of large structures. The bending sensor response is also shown to be independent of temperature and the surrounding refractive index.
65 citations
References
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TL;DR: In this paper, a novel long-period fiber grating (LPFG) fabricated by using a new writing technique that is mainly based on the thermal shock effect of focused high-frequency CO/sub 2/ laser pulses at several kilohertz was reported.
Abstract: In this paper, we report a novel long-period fiber grating (LPFG) fabricated by using a new writing technique that is mainly based on the thermal shock effect of focused high-frequency CO/sub 2/ laser pulses at several kilohertz. A number of unique characteristics of such a LPFG, such as bend, torsion, and transverse load, are observed by experiments, for the first time, to our knowledge. Based on these unique features, a novel bend-insensitive LPFG sensor that could solve the problem of cross-sensitivity between bend and other measurands, a novel torsion sensor that can realize absolute measurement of twist rate, and a load sensor that can achieve simultaneous measurement of transverse load and temperature using a single LPFG element are proposed and demonstrated. These unique features of the LPFGs are mainly due to the asymmetrical distribution of the refractive index on the cross section of the LPFG induced by high-frequency CO/sub 2/ laser pulses.
384 citations
TL;DR: This work describes what is to their knowledge the first use of fiber Bragg gratings written into three separate cores of a multicore fiber for two-axis curvature measurement.
Abstract: We describe what is to our knowledge the first use of fiber Bragg gratings written into three separate cores of a multicore fiber for two-axis curvature measurement. The gratings act as independent, but isothermal, fiber strain gauges for which local curvature determines the difference in strain between cores, permitting temperature-independent bend measurement.
266 citations
"Bending Vector Sensor Based on a Se..." refers background in this paper
...Generally fiber grating based bending vector sensors could only be achieved in specifically designed fibers with asymmetrical core or cladding geometry, such as multicore fibers [1], eccentric core fibers [2], and D-shaped fibers [3]....
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TL;DR: In this article, the authors examined the changes in wavelength and attenuation of long period fiber gratings subjected to bends with curvatures from 0 to 4.4 m/sup -1/.
Abstract: The authors examine the changes in wavelength and attenuation of long period fibre gratings subjected to bends with curvatures from 0 to 4.4 m/sup -1/. The wavelength change with curvature is nonlinear, with a projected minimum detectable curvature change of 2/spl times/10/sup -3/ m/sup -1/. The magnitude of the bend-induced wavelength shift depends on the rotation of the cylindrical fibre relative to the bending plane.
226 citations
"Bending Vector Sensor Based on a Se..." refers background in this paper
...Generally fiber grating based bending vector sensors could only be achieved in specifically designed fibers with asymmetrical core or cladding geometry, such as multicore fibers [1], eccentric core fibers [2], and D-shaped fibers [3]....
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...In recent years, a few bending sensors with directional discrimination based on asymmetric refractive index modulation were reported through writing long-period fiber grating (LPFG) or tilted fiber Bragg grating (TFBG) in SMF or photonic crystal fiber [3]–[9]....
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TL;DR: In this paper, a bend-sensor consisting of one LPFG induced by a UV laser and two LPFGs induced by high-frequency CO/sub 2/ laser pulses is proposed and demonstrated.
Abstract: A novel long period fiber-grating (LPFG) sensor that can not only measure curvature directly, but also determine every bend-direction within the circular range of 0/spl deg/-360/spl deg/, is proposed and demonstrated in this paper. Such a bend-sensor consists of one LPFG induced by a UV laser and two LPFGs induced by high-frequency CO/sub 2/ laser pulses. The curvature is measured by the UV laser-induced LPFG whose bend-sensitivity is independent of the bend-directions, and the bend-direction is determined by the CO/sub 2/ laser-induced LPFGs whose bend-sensitivities depend strongly on the curved directions. In addition, the unique bend-characteristics of LPFGs induced by high-frequency CO/sub 2/ laser pulses are demonstrated.
142 citations
TL;DR: The finite element method (FEM) model was used to investigate the modal behavior in multicore Fiber and to predict the phase-matching curves of the long period grating inscribed into multicore fiber.
Abstract: Long period grating was UV inscribed into a multicore fiber consisting of 120 single mode cores. The multicore fiber that hosts the grating was fusion spliced into a single mode fiber at both ends. The splice creates a taper transition between the two types of fiber that produces a nonadiabatic mode evolution; this results in the illumination of all the modes in the multicore fiber. The spectral characteristics of this fiber device as a function of curvature were investigated. The device yielded a significant spectral sensitivity as high as 1.23 nm/m-1 and 3.57 dB/m-1 to the ultra-low curvature values from 0 to 1 m-1. This fiber device can also distinguish the orientation of curvature experienced by the fiber as the long period grating attenuation bands producing either a blue or red wavelength shift. The finite element method (FEM) model was used to investigate the modal behavior in multicore fiber and to predict the phase-matching curves of the long period grating inscribed into multicore fiber.
100 citations
"Bending Vector Sensor Based on a Se..." refers methods in this paper
...Two segments of tape tags are attached to the two ends of the SLFPG vertically, which are used to ensure that no twist is present in the experiment and recognize the orientation of the SLPFG during bending process [12]....
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...fabricated a vector bending sensor by writing an LPFG in multicore optical fiber [12]....
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