We consider a comparative study of radiation effects (γ and electron) on fibre Bragg gratings (FBGs) that were inscribed using a femtosecond laser in single mode silica optical fibre. The FBGs were inscribed using the point-by-point and the plane-by-plane inscription methods. The FBGs were exposed to a total accumulated radiation dose of 15 kGy in both γ and electron cases. The gratings’ spectra were measured and analysed before and after the exposure to the radiation, while complementary characterisation was undertaken using Raman and Fourier transform infrared spectroscopy. In addition, the changes of the temperature coefficient of the FBGs were analysed comparatively prior to the irradiation to explain how material changes responded to the particular types of radiation. Finally, we consider which of the two inscription methods proves more robust in such harsh environments.
Water and oil detection as well as oil (or water) in water (or oil) estimation play important roles in the oil processing industry due to advantages such as reduction of the residence time of oil in oil-water separation units (or three-phase oil separators), increasing of the oil purity and avoiding environmental issues regarding the disposal of water contaminated with oil. In addition, it also enables the detection of water contamination in fuels with important impacts on the environment and oil quality. Advantages such as lightweight, multiplexing capabilities, water affinity and electromagnetic fields immunity make polymer optical fibers (POFs) an interesting option for detecting water and oil contamination. This paper presents the development of a POF sensor for oil, water and oil in water detection using chirped fiber Bragg gratings (CFBGs). The grating structure was inscribed in cyclic transparent optical polymer (CYTOP) fibers through the plane-by-plane method using a femtosecond laser. The CFBG is submerged in the liquids (water, mineral oil and their mixture) in order to verify the ability of such sensor of performing temperature independent measurements, which is accomplished by analyzing not only the central reflected wavelength, but also the full width half-maximum. The results indicate the capability of the proposed sensing approach of detecting oil and water. Furthermore, oil contamination as low as 0.1% (in volume) in water was detected using the CFBGs inscribed in CYTOP fibers. Therefore, the results depicted in this work can result in reliable systems for oil or water quality monitoring, which finds important application in oilfields and process industry.
We report on the inscription of a long period grating (LPG) in a multimode cyclic transparent optical polymer (CYTOP) fibre using the plane-by-plane femtosecond laser inscription method. The LPG was inscribed in the centre of the fibre core and tailored for operation at C-band wavelength range. The CYTOP-LPG sensitivity was characterised in transmission for relative humidity and temperature. The humidity measurements performed are the first for a POF-LPG, whereas the temperature sensitivity is significantly higher than reported in other works. In addition, dynamic mechanical measurements were performed comparing the mechanical characteristics of the laser exposed sections of the polymer fibre, where the LPG was inscribed, with the unexposed regions.
FBG in polymer optical fibers (POFs) is a promising technology for a wide range of sensing applications due to a lower Young’s modulus and a large range of applying strain. Furthermore, POFs have several properties which make them attractive for biosensing applications such as nonbrittle nature, flexibility in bending and biocompatibility. Chirped Fiber Bragg gratings (CFBGs), which are characterized by a nonuniform modulation of the refractive index show a broad reflection spectrum, enabling shortlength distributed sensing. The combining benefits of POF and CFBGs is attractive for biomedical applications. Here, we present a novel method to obtain CFBG in POF with a postprocess uniform POF FBG by using resin.
This paper presents an optical fiber embedded intelligent carpet for gait analysis, where the system is able of measuring the ground reaction force and the foot position on the carpet (which can be used on the gait spatiotemporal parameters assessment). The system comprises of fiber Bragg gratings (FBGs) inscribed in silica fibers to detect the foot positioning and intensity variation-based sensors on polymer optical fibers (POFs) to estimate the ground reaction forces. The proposed system was characterized as function of foot impact positioning as well as applied forces and a high correlation between the sensors responses and the applied parameters was obtained on each case. Then, a proof-of-concept test was performed, where a volunteer placed his foot in different positions on the carpet, which show the feasibility of the system in the proposed application.
This paper presents a technique for temperature cross-sensitivity compensation in liquid level sensor based on an in-fiber Mach-Zehnder interferometer. By using a commercial splicing machine and three different fibers, it is possible to construct a liquid level sensor with range of 120 mm and submillimeter resolution (0.88 mm). The sensor arrange is anchorage into a glass pipette, where the liquid level can be easily supervised. A broadband source is used to illuminate the sensor and the transmitted spectrum is monitored with an optical spectrum analyzer with 30 pm resolution. The interference pattern, created by the interferometer, is analyzed with either the traditional method of tracking peaks and dips or the overall spectrum envelope. These interferometers are sensitive to temperature variations, leading measurements errors on the liquid level estimation. Thus, an analysis of the temperature effect in the sensor response is performed. The result shows that the proposed technique reduces the sensor temperature cross-sensitivity by more than an order of magnitude. With traditional method (using peaks and dips), the value achieved was ~9.595 mm/°C, whereas the proposed approach based on the spectrum envelope leads to a temperature cross-sensitivity of about 0.562 mm/°C. The proposed sensor arrange is suitable for industrial applications such as chemical processing, fuel storage and transportation systems, oil tanks/reservoirs, and treatment plants, where there is simultaneous variations of temperature and level.
This work consists on the design and implementation of a compact and accurate biaxial optical fiber sensor (OFS) based on two in-line fiber Bragg gratings (FBGs) for the simultaneous measurement of shear and vertical forces. The two FBGs were inscribed in the same optical fiber and placed individually in two adjacent cavities. In the calibration and performance tests, the response from the optical fiber cells was compared with the values given by a three-axial electronic force sensor. Sensitivity values obtained for the FBG1 are K1V= (14.15±0.10) pm/N (vertical force) and K1S= (-26.02±0.08) pm/N (shear force) and for the FBG2 are K2V= (7.35±0.02) pm/N and K2S= (-24.29±0.08) pm/N. The conversion of the Bragg wavelength shift, given by the optical fiber sensors, into the shear and vertical force values is also presented along with its comparison to the values retrieved by an electronic sensor, yielding to low RMSE values, which shows the high accuracy of the algorithm applied. This work stands out from the others with optical fiber by the simplicity of its structure. The proposed solution represents a compact and reliable device for simultaneous measurement of shear and vertical forces, useful in several areas, such as: incorporation into insoles for plantar pressure and shear force measurement; electronic skin technologies; smart rehabilitation robotic exoskeletons; or even biomimetic prosthesis.
Polymer optical fibers (POF) have higher strain limits, fracture toughness and flexibility in bend if compared to glass optical fibers. These characteristics enable the application of POFs as curvature sensors. However, the polymer is a viscoelastic material, which does not have a constant response with stress or strain. For this reason, a curvature sensor based on POF may present high hysteresis. This paper proposes a dynamic compensation technique based on the angular velocity of the sensor. Results show a hysteresis up to 10 times lower. Furthermore, it results on a simple calibration equation, which can be applied in real-time measurements.
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