Design Of Optical Fiber Sensor Research Articles

Highly sensitive curvature fiber sensor based on an enhanced core diameter mismatch.

In this study, a curvature fiber sensor based on an enhanced core diameter mismatch is experimentally proposed and theoretically investigated. The structure is fabricated by splicing two types of step multimode and coreless fibers to excite the high-order cladding modes to improve the curvature sensitivity. Experimental results show that the highest curvature sensitivities of the structure reach -114.74 nm/m-1 in the Dip 1272 nm, -91.08 nm/m-1 in Dip 1408 nm, and -61.10 nm/m-1 in Dip 1644 nm in the measuring range of 0-0.49778 m-1. Meanwhile, the sensor's temperature and strain responses were also tested, which shows little influence on the curvature measurement. Additionally, the proposed fiber sensor exhibits features of easy fabrication, simple structure, and high mechanical strength. This study proposes a device for curvature measurement with potential use in material mechanics and optical fiber sensor design.

Optical Fiber Sensor for PVC Sheet Piles Monitoring

This paper examined the impact of optical fiber sensor design, and its integration to PVC (polyvinyl chloride) sheet piles, on deflection and strain monitoring. Optical fiber sensors based on Brillouin light backscattering (BLS) were prepared, as they can provide accurate strain and deflection measurement results. However, depending on the application of sheet piles systems, high deformation of PVC elements can be observed. Therefore, a fiber sensor design is not trivial. Three types of optical fiber coatings and their integration with PVC sheet piles were investigated. The effect on the value of compressive and tensile strain were analyzed. It has been experimentally proven that PVC sheet piles monitoring, based on BLS method, can be realized using optical fibers with 250 µm, 900 µm, and 3 mm coating diameter. Achieved results are in line with theory. Correction coefficient necessary for 900 µm and 3 mm coatings has been proposed and used to ensure proper strain measurement. It was found that 250 µm coating fiber based sensors can be utilized for PVC strain measurement under low deflection (>1.2 m beam length). On the other hand, sensors based on 3 mm coating fiber, due to a high level of linearity, can be applied to deflection distance measurement under high deformation.

A textile- based optical fiber sensor design for automotive seat occupancy sensing

In our previous publications, the response of perfluorinated (PF) graded index (GI) POFs (62.5/750, 62.5/490 μm) to bending, tensile loading, and cyclic loading was investigated. The results showed that Cytop-1 (62.5/750 μm) was more appropriate to be used as an optical fiber sensor for automotive seat occupancy sensing relative to Cytop-2 (62.5/490 μm). In this study, a textile-based optical fiber sensor was designed and the effect of automotive seat covering including face material and foam backing on a sensor’s performance was analyzed. The pressure interval under which the proposed POF sensor design could perform well was found to be between 0.18 and 0.21 N/cm2, where PF GI POF (62.5/750 μm) was used as the POF material. The responses of the sensor in this interval were observed to be accurate and reproducible. The face fabric structure and the thickness of foam backing were not found to be significant factors to change the sensor response. Artificial neural network (ANN) was used for data analysis, and Qwiknet (version 2.23) software was used to develop ANNs. According to the results of Qwiknet, the prediction performances for training and testing data-sets were 75 and 83.33%, respectively.

Central arterial pulse waveform acquisition with a portable pen-like optical fiber sensor.

Pulse waveform features related to cardiovascular pathologies and arterial stiffness have been extensively studied, and optical fiber sensors have been studied with an aim to simplify the pulse waveform acquisition in the carotid artery. In this paper, a novel optical fiber sensor to record pulse waveform in the carotid artery has been proposed. The pulse waveform optical fiber sensor design, based on fiber Bragg gratings, is presented. The probe was characterized, and its response to controlled waveforms was studied. Finally, tests were performed on human subjects. The developed sensor has a displacement sensitivity of 21.2 pm/μm, with ability to detect the carotid pulse wave in the neck surface, with a resolution of 1.3 mmHg. This study revealed a new technological approach for acquisition of the central pulse waveform.

Morphology and Thermal Stability of Fiber Bragg Gratings for Sensor Applications Written in ${\rm H}_{2}$-Free and ${\rm H}_{2}$-Loaded Fibers by Femtosecond Laser

Bragg gratings written in H2-free and H2-loaded SMF-28 fiber by use of infrared (IR) femtosecond laser radiation with a phase mask have been investigated in terms of their axial and cross-sectional morphology. It was found that Type I-IR and Type II-IR refractive index changes existed simultaneously in a single grating (which is termed a hybrid grating in this paper) written in either H2-free or H2-loaded fiber. The proportion of the two types of refractive index changes is a key factor in determining the thermal stability of the grating and spectral properties such as cladding mode coupling and polarization dependent loss (PDL). High-pressure molecular hydrogen loading (H2 loading) can dramatically enhance the efficiency of grating inscription while preventing the laser-induced damage, due to the enhanced color center formation and the suppressed multiphoton ionization (MPI). The H2 -loaded fiber Bragg gratings thus exhibit spectral properties and annealing behavior which is distinguishable from the H2-free gratings. The findings of this work are of particular importance in the design of optical fiber sensors which can operate at very high temperatures for prolonged periods and thus can have important uses in industry.

Experimental design in fiber optic sensor development

In this paper, experimental design techniques are utilized to understand sources of variation in an optical fiber sensor design and development project in a university research setting. Application of the Taguchi method of robust design assisted fiber optic sensor development in a cost‐effective and timely manner. According to the analysis, compensation of the source of the variation identified in the experimental design results was achieved on a new design concept of a multiplexed optical fiber sensor. The experimental results and conclusions not only are suitable for this sensor structure, but also are useful for other fiber optic sensors based on the technique of Fabry‐Perot interferometry.

Chromatic Modulation for Optical Fibre Sensing Electromagnetic and Speckle Noise Analysis

Abstract Changes in the chromaticity of the transmitted electromagnetic field in an optical fibre are considered. An electromagnetic analysis that predicts the radial dependence of the chromaticity at the exit is presented and coupled to a speckle noise analysis which provides an estimate of the error. Theoretical predictions are compared with experimental results and good agreement between the two is demonstrated. The results can be useful in the design of optical fibre sensors which use the chromatic modulation method.

Complete Phase-Strain Model for Structurally Embedded Interferometric Optical Fiber Sensors

The relation between a three-dimensional state of strain and the optical phase retardation in a single mode optical fiber is formalized by drawing together classical three-dimensional crystal optics and classical waveguide theory. Neumann's strain optic relations are described in a form usable in optical fiber sensor design. These relations are then combined with weakly guiding fiber theory to develop an integral which relates the optical phase shift in a structurally embedded interferometric optical fiber strain sensor to the induced three-dimensional strain field. This process leads to a previously undisclosed, additional waveguide dispersion term which contributes on the same order to the total strain induced phase retardation as does the term derived by Butter and Hocker (1978). Still, however, waveguide dispersion effects are found to be negligibly small, even in three- dimensional loading. Butter and Hocker's equation and the complete phase-strain model developed herein can give very similar results when both are applied to certain embedded sensors. This anomaly can lead to the false conclusion that Butter and Hocker's results are equally valid for any structurally embedded sensor.