Bending Vector Research Articles

Two-axis bending vector sensor based on a long-period fiber grating cascading with a hump-shaped taper

A novel fiber-bending vector sensor based on a Mach–Zehnder interferometer (MZI) is proposed and fabricated. The device consists of a long-period fiber grating (LPFG) written by a high-frequency CO2 laser and a hump-shaped taper (HST) in a segment of single-mode fiber (SMF). The HST is an up-taper with the asymmetry perpendicular to the irradiated direction of the LPFG, which induces asymmetry into the fiber in two-axis directions. In the curvature range of 0.3–1.6 m−1, the device can measure bending curvature as well as distinguish the bending direction with two dips at 1480.45 nm and 1493.20 nm, and the sensitivity can reach −6.592 nm m−1. The response for temperature is also investigated and the temperature sensitivity is about 0.05 nm °C−1 in the range of 25 °C–80 °C. By measuring the separation of the two interference dips, the temperature cross-sensitivity can be almost eliminated.

Bending Vector Sensing Based on Arch-Shaped Long-Period Fiber Grating

A novel arch-shaped long-period fiber grating (ALPFG) is proposed and fabricated by a high-frequency CO2 laser on a single-mode fiber. The ALPFG is composed of a string of arch grids, which can provide stronger refractive index modulation than normal planar grids. The asymmetrical structure induced by arch grid and one-side exposure allows it to sense vector bending in two orthogonal directions. Within the curvature range from 0.5 to 2.2 m−1, its bending sensitivities can reach 22.120 and −18.626 nm/m−1 for the two opposite directions. Its temperature recycle and force characteristics are also provided.

Tunable overlapping long-period fiber grating and its bending vector sensing application

Abstract A novel overlapping long-period fiber grating (OLPFG) is proposed and experimentally demonstrated in this paper. The OLPFG is composed of two partially overlapping long-period fiber gratings (LPFG). Based on the coupled model theory and transfer matrix method, it is found that the phase shift LPFG and LPFGs interference are two special situations of the proposed OLPFG. Moreover, the confirmation experiments verified that the proposed OLPFG has a high bending sensitivity in opposite directions, and the temperature crosstalk can be compensated spontaneously.

Highly Sensitive Two-Dimensional Bending Vector Sensor Using an Elliptic Two-Core PCF

A highly sensitive and simple all-fiber interferometric two-dimensional (2D) bending vector sensor is demonstrated. Fiber interferometer works in reflection mode and formed by manually splicing a small section of elliptic two-core photonic crystal fiber at the end of a single-mode fiber. Due to the birefringence nature of the two cores, the fiber device exhibits orientation-dependent bend sensitivity which is different for different polarization states. A high sensitivity of 6.49 nm/mm is achieved for bending along the x-direction, and the rms deviations for bending in the x- and y-directions are estimated to be 0.015 and 0.098 mm, respectively, by using the matrix method. The device is immune to bend-induced power fluctuation.

Compact assembly-free vector bend sensor based on all-in-fiber-core Mach-Zehnder interferometer.

A novel low-cost, compact, assembly-free and sensitive optical fiber curvature sensor is presented. This device consists of an off-axis positive refractive index modified zone (PRIMZ), induced by a direct femtosecond laser, written in a single-mode fiber (SMF) core. The PRIMZ transforms the original SMF section into a few-mode fiber (FMF). As a result, the whole fiber forms an assembly-free "SMF-FMF-SMF" sandwich Mach-Zehnder interferometer. When the device is bent, a direction-dependent spectral shift of the interference pattern is produced. The sensitivity of the sensor is up to 2.53 and 2.24 nm/m-1 for the 0° and 180° orientations in a wide bend range (from 0 to 4 m-1). In addition, the device is immune to the surrounding refractive index and has a low-temperature crosstalk, which makes it very attractive for practical structural monitoring applications.

Surface reconstruction by means of a flexible sensor array

In recent years, an increasing popularity of flexible sensor systems has been observed, which can largely be attributed to their ability to continuously adapt the shape to deformable bodies with non-planar surfaces without losing functionality. In this paper, we present a self-sensing, ultra-thin and flexible sensor array foil, which allows for determining its actual shape by analyzing signals from 6×6 sensors. Raw sensor signals clearly show the dependence from strength and direction of bending. The local bending vector is determined from signals of sensors oriented in different directions using rules which are already applied for strain gauge rosettes. The algorithm for the surface reconstruction divides the sensor foil into discrete bending segments for which the bending and subsequently new coordinates of segment edges are determined. A sensor diagnostics routine intercepts failure of the complete system due to the failure of single sensors. The functionality of the sensor array and the surface reconstruction is demonstrated for a foil subsequently adapting to a tube in different orientations. The obtained surface reconstruction clearly correlates with the visually observed bending. Such surface reconstruction could provide diagnostic information and potentially be used to detect diseases like pneumothorax. It could not only help to improve medical treatments but also to monitor the structural health of technical constructions.

Self-referenced antiresonant reflecting guidance mechanism for directional bending sensing with low temperature and strain crosstalk

A sensitive one-dimensional vector bending fiber-optic sensor based on self-referenced antiresonant reflecting guidance mechanism has been proposed and experimentally demonstrated. Two symmetric air holes in the hollow-core photonic crystal fiber (HCPCF) were infiltrated with refractive index matching liquids with different refractive indices, which formed a self-referenced anti-resonant reflecting optical waveguide. The bending of the HCPCF induces a wavelength shift of lossy dip in the transmission spectrum. Specially, the one-dimensional bending orientation can be detected through the wavelength interval between two lossy dips due to the asymmetric refractive index change of the silica cladding for two resonators. The bending sensitivities are 4.86 and -4.84 nm/m-1 for the curvatures of the 0° and 180° bending orientations in a bending range from 0 to 0.88 m-1, respectively. Moreover, the temperature and strain crosstalk of the proposed sensor can be eliminated through the compensated self-referenced anti-resonant reflecting optical waveguide. The proposed fiber sensor can be used for the monitoring of the structural health of infrastructures.

Two-Dimensional Bending Vector Sensor Based on the Multimode-3-Core-Multimode Fiber Structure

A two-dimensional bending vector sensor based on the multimode-3-core-multimode fiber structure is proposed. The three cores of the 3-core fiber (3CF) distribute in an isosceles triangle. In order to obtain a higher bending sensitivity, two larger diameter external cores are selected in the design of the 3CF. Owing to the asymmetric structure of the 3CF, this sensor can distinguish multiple bending directions. In addition, the linear spectral response for bending and temperature is observed experimentally. The proposed sensor has many advantages. For example, it is compact, inexpensive, and easy to be fabricated. These characteristics of the sensor make it very attractive for two-dimensional bending sensing application.

Temperature insensitive one-dimensional bending vector sensor based on eccentric-core fiber and air cavity Fabry-Perot interferometer

A temperature insensitive directional bending sensor based on an eccentric-core fiber (ECF) cascaded with an air-cavity Fabry–Perot (F-P) interferometer is presented and demonstrated. The ECF-based air cavity F-P interferometer is fabricated by fuse splicing a piece of hollow-core fiber (HCF) in between an ECF and a multi-mode fiber (MMF). The bending sensitivities of the sensor at the two opposite most sensitive directions are 79.5 pm/m−1 and −81.5 pm/m−1, respectively. The temperature sensitivity of the proposed structure is as low as 1 pm °C−1.

Bending Vector Sensor Based on a Pair of Opposite Tilted Long-Period Fiber Gratings

A novel optical fiber grating vector bending sensor head is demonstrated. The sensor head is composed by two cascaded 6° tilted long period fiber gratings, which are separated by a distance d. The asymmetric characteristics of the proposed sensor originate from two tilted long period gratings with angles placed oppositely and asymmetric exposure of the CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> laser pulses. Two selected dips shift toward each other when the sensor head is bent. The interval between the two dips is used for improving the sensitivity of curvature measurement and further decreasing the temperature crosstalk. For the curvature range from 0.5 to 2 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> , the bending sensitivities reach -15.4935 and 15.2852 nm/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> for the opposite bending directions. The temperature sensitivity of the sensor is one third of the normal long period fiber grating.

Skin attachable flexible sensor array for respiratory monitoring

Flexible electronic systems became increasingly popular in recent years. They usually can be bent or even stretched while fully maintaining their functionality opening up a wide field of various new applications. In this paper a novel 6×6 sensor array for curvature sensing in the format of a thin flexible polyimide foil is introduced. The sensor foil is to be used for respiratory monitoring of premature infants by directly attaching it to the skin for measuring the body deformations caused by breathing. Sensor signals shall in future be used not only to trigger the respiration device but also to provide time dependent body surface reconstruction as a diagnostic tool. One single sensor element consists of four gold strain gauges in a Wheatstone bridge configuration. For suppressing sensor response to foil stretching and for increasing bending sensitivity we introduced a double-sided sensor design with strain gauges on both surfaces of the thin foil leading to a 170% higher sensitivity than a one-sided sensor design. The complete sensor array foil of less than 20μm in thickness can be fabricated without flipping the substrate. Single sensor elements can reliably measure in a bending radius range of 1mm ≤r≤380mm and provide a signal of Vout=κ*S with the curvature κ=1/r and a sensitivity of S=49.3mV*mm. The response time of 25ms is currently defined by the signal processing circuitry. Double sided sensor elements with different orientations are arranged in an alternating pattern across the array allowing to fully and unambiguously determine the bending vector utilizing plausibility considerations on basis of signals from neighboring elements. A small initial bending resulting from fabrication induced stresses was observed but could easily be compensated in digital sensor signal analysis. In summary, first tests of this novel sensor array together with the scalability of implemented fabrication processes are very promising. The fundamental criteria to be used as sensor array for respiratory monitoring of infants are met and typical problems associated with existing systems for respiration triggering can be avoided with skin attachable flexible systems.

Bending vector sensor based on Mach–Zehnder interferometer using S type fibre taper and lateral-offset

A novel, simple and highly sensitive bend vector sensor is proposed and experimentally demonstrated for directional bending measurement. This sensor consists of a lateral-offset and an S fibre taper processed through special fusion splicing method. The asymmetrical fibre structure of S fibre taper and lateral-offset determined a pair of directions along which the bending response to the transmission spectrum is different. Thus, it can be used for bending vector measurement. For a curvature range from −4 to +4 m−1, the bending sensitivities near 1550 nm reach 0.70807 and 0.99695 nm/m−1, respectively.

Ultrasensitive vector bending sensor based on multicore optical fiber.

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.

基于选择填充光子晶体光纤的二维弯曲矢量传感器设计

基于选择填充光子晶体光纤的二维弯曲矢量传感器设计

Bending Vector Sensor Based on the Multimode-2-Core-Multimode Fiber Structure

A novel bending vector sensor formed by splicing 2-core fiber (2CF) between two segments of multimode fibers (MMFs) was proposed and fabricated, in which the MMFs serve as the mode splitting and coupling. Moreover, the 2CF used in the experiment was designed and fabricated in our labs, and the external core with a larger diameter would be provided with a higher bending sensitivity. Besides, the bending responses of the sensor are directionally sensitive due to the asymmetric structure of the 2CF. As a result, along with the implementation of the conformation experiments on the bending and temperature sensor property, and a good agreement has been achieved. The proposed sensor possesses many advantages, such as being inexpensive, compact, and robust.

Simultaneous measurement of one dimensional bending and temperature based on Mach-Zehnder interferometer

A simple and compact optical fiber directional bending vector sensor with simultaneous measurement of temperature based on the Mach-Zehnder interferometer (MZI) is proposed and experimentally demonstrated. The device consists of a piece of photonic crystal fiber (PCF) sandwiched between two single mode fibers (SMFs) with a lateral offset splicing. It shows the capacity for recognizing positive and negative directions. Within a curvature range of -7.13 m-1 to 7.13 m-1, the bending sensitivities of two resonant dips with opposite fiber orientations are obtained to be 0.484 nm/m-1 and 0.246 nm/m-1, respectively. This simple MZI is formed by invoking interference between LP01 and LP21 core modes, which leads to that the sensor is not sensitive to ambient refractive index (ARI). The temperature sensitivity has also been investigated. Two dips have obviously different sensitivities on the temperature and bending, so two parameters of both curvature and temperature can be distinguished and measured simultaneously by constructing a matrix and using one simple model interferometer.

Bending Vector Sensor Based on a Sector-Shaped Long-Period Grating

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.

Two-dimensional bending vector sensor based on Mach-Zehnder interferometer of two orthogonal lateral-offsets

A simple, compact bending vector sensor based on Mach–Zehnder interferometer (MZI) utilizing two orthogonal lateral-offsets is proposed. The two-dimensional bending vector sensing characteristics, including the curvature and four orthogonal directions, could be measured accurately and simultaneously by the MZI using a special data processing method. Besides, the impact of temperature on the MZI can be eliminated through constructing a matrix using the different response of two loss peak to the bending and temperature sensitivities. This research work would be helpful to develop the practicability of fiber bending vector sensors. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:709–713, 2015

Long period grating in multicore optical fiber: an ultra-sensitive vector bending sensor for low curvatures.

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.

A Mach–Zehnder interferometer constructed using lateral offset and a long period fiber grating for two-dimensional bending vector sensing

We report a two-dimensional bending vector sensor based on a Mach–Zehnder interferometer (MZI). The device consists of a strong coupling long period fiber grating (LPFG) and a slight-lateral-offset fusion splicing joint which can generate an interference pattern and keep the resonance dip of the LPFG relatively independent at the same time. The exposure orientation of the LPFG is perpendicular to the lateral-offset orientation, making it capable of identifying two-dimensional bending directions and amplitude simultaneously. Two-dimensional bending vector sensing characteristics, especially in the four orthogonal directions based on the new structured MZI, have been experimentally demonstrated. Temperature cross-sensitivity is eliminated using the different sensitivities of the two resonance dips. The device will have great potential in shape sensing applications due to the advantages of its vector sensing capability, low cost and ease of fabrication.