The large scale fiber grating array sensing system has found lots of applications in fields distributed in underwater, land, sky and space, which is often configured using TDM/WDM multiplexing schemes. In recent years, the integrated fabrication method without any fiber splicing points plays important roles in providing the largest system high reliability and robust detection performance. However, in such fiber grating array, the synthesis of fiber grating array without bringing any damage becomes a difficult problem. The existing reconstruction algorithms are only used for single fiber bragg grating.This paper will start with the fiber grating array which is formed by two low reflectivity FBGs and regarded as a special chirp fiber grating, then a proposal of synthesis the fiber grating array in time domain is presented, which can also suppress the multi-reflections induced signal crosstalk. The research results will provide a solution to the synthesis of the integrated fiber grating array and a new signal processing method to suppress the array signal crosstalk.
A sensor system based on fiber Bragg grating (FBG) is presented which is to estimate the deflection of a lightweight flexible beam, including the tip position and the tip rotation angle. In this paper, the classical problem of the deflection of a lightweight flexible beam of linear elastic material is analysed. We present the differential equation governing the behavior of a physical system and show that this equation although straightforward in appearance, is in fact rather difficult to solve due to the presence of a non-linear term. We used epoxy glue to attach the FBG sensors to specific locations upper and lower surface of the beam in order to measure local strain measurements. A quasi-distributed FBG static strain sensor network is designed and established. The estimation results from FBG sensors are also compared to reference displacements from the ANSYS simulation results and the experimental results obtained in the laboratory in the static case. The errors of the estimation by FBG sensors are analysed for further error-correction and option-design. When the load weight is 20g, the precision is the highest, the position errors ex and ex are 0.19%, 0.14% respectively, the rotation error eθ, is 1.23%.
To realize the miniature of fiber laser accelerometers, a metal-shell-packaged single-cylinder mandrel-structured distributed feedback (DFB) fiber laser accelerometer was proposed, whose key sensing component is the DFB fiber laser with a cavity length of 16mm. Simulation results show that when the weight of the mass is 400g, the radius of the thin shell cylinder is 0.5cm, we will find that the resonance frequency of the sensor is 900Hz and its sensitivity reaches 18.1pm/g. It is also shown that its sensitivity achieved 42.8dB.re.rad/g while demodulated by an unbalanced Michelson optical fiber interferometer with 1m path difference. In addition, the effects of its structure and material parameters on the acceleration sensitivity are also studied.
A novel interferometric fiber optic geophone is introduced in this paper. This geophone is mainly used for geo-acoustic signal detection. The geophone use one of the three orthogonal components of mandrel type push-pull structure in mechanically and single-mode fiber optic Michelson interferometer structure with Faraday Rotation Mirror (FRM) elements in optically. The resonance frequency of the geophone is larger than 1000Hz. The acceleration sensitivity is as high as 56.6 dB (0dB re 1rad/g) with a slight sensitivity fluctuation of ±0. 2dB within the frequency band from 20Hz to 200Hz. The geo-acoustic signals generated by underwater blasting are detected successfully. All the channels show good uniformity in the detected wave shape and the amplitudes exhibit very slight differences. The geo-acoustic signal excitated by the engine of surface vehicles was also detected successfully.
An integrated polarization maintaining fiber polarized Bragg grating is proposed, which achieves reflecting and polarizing functions simultaneously. This integrated polarized grating was designed to replace the traditional fiber polarizer and Bragg grating by a single fiber device, which may induce enormous performance promotion to optical fiber systems incorporating the two devices, such as fiber ring laser, some fiber sensing networks, etc. An integrated fiber polarized grating was fabricated, and the polarization states of both the reflection and transmission were measured. The temperature and strain responses were also tested which indicated sufficient stability. The integrated fiber polarized grating was then applied to the fiber ring laser, and results indicated that a robust single-longitudinal and single-polarization mode laser can be realized by utilizing this design type of integrated polarized grating.
Fiber Bragg grating sensors have been attracted more attention due to its excellent advantages, such as small size, light
weight, low cost, immunity to electromagnetic interference, multiplexing and so on, which offer a widely application in
optical sensing and communication field. Following the appearance of micro/nano-fiber (MNF), it is imperative to
develop the manufactured technology of MNF devices, MNF Bragg gratings are the important passive device among
these. In this paper, we simulate the effective refractive index in fiber core using two-layer model. Meanwhile, we
present a new method to fabricate a 6μm diameter fiber Bragg grating through successive improvement of
manufactured technology. The small cladding diameter fiber was obtained by immersing an optical photosensitive fiber
in different concentrations of hydrofluoric acid solutions. Then a MNF is fabricated from the small cladding diameter
fiber by drawing. Finally a 6μm-diameter fiber Bragg grating was written using phase mask technology with a higher
reflection. The testing results of this grating showed a good agreement with the simulation.
The influence of coherence collapse due to Rayleigh backscattering on the scale of DFB fiber laser sensor array is
investigated. The largest scales of a two-element sensor array and a three-element sensor array are measured to be 160 m
and 250 m. Results indicate that coherence collapse due to Rayleigh backscattering does not limit the multiplexing
capability of DFB fiber laser sensor array when the multiplexing capacity remains to be several tens, which is significant
for the scale extension of DFB fiber laser sensor array.
Optical fiber polarizer and grating are two widely used fiber components and in this paper we proposed an integrated
polarizing grating fabricated in polarization-holding fiber, which achieves reflecting and polarizing functions
simultaneously. A D-shaped multilayer grating waveguide model was established and the linearly polarizing principles
in both reflection and transmission ports were presented. An integrated polarization-holding fiber polarizing grating was
fabricated and the laser polarization states of incidence, reflection and transmission were all measured, showing that this
integrated fiber device can achieve reflecting and polarizing functions simultaneously. The discrimination between the
reflection and transmission was also investigated.
This paper presents comprehensive research on fused-tapered Bragg reflection integrative FGC where high-quality and
easy-fabricating are two main considerations. The technical procedure of FGC fabrication is fixed after a series of
experiments. The possible factors that may determine the device performance were carefully analyzed. The
fused-tapered FGC was successfully fabricated and a novel testing system was established. The adding and dropping
functions of FGC were investigated experimentally.
The finite element method was used to analyze the interior stress distributions and the birefringence of the side hole fiber. The paper has analyzed the dependence of the birefringence of the side hole fiber on the side holes' physical dimensions. The calculation result shows that the fast axis of the fiber is along the line which links the two holes' centers, the geometrical birefringence can be neglected, and the birefringence can be improved through increasing the radius of the side holes or reducing the distance between the core and the side hole centers.
A reflective displacement sensor utilizing three fibers, one transmitting and two receiving with different core diameters, is described in this paper. On the basis of optical field distribution of multimode fiber, the intensity compensation mechanism of this sensor is analyzed in great detail, at the same time the displacement modulating functions and corresponding simulating carves are presented. Results show that this sensor can effectively compensate for variations in the source intensity, for losses in the optical fibers, and for variations in the reflectivity of the reflector surface.
Although there are lots of research papers on the intensity modulated fiber sensors, a very important problem is always neglected, which is the effect on the intensity modulation caused by perpendicularity between the axes of fiber pair and the reflector. Though several papers gave some literal description that the axes of fiber pair should be perpendicular to the reflector, few of them put forward a precise model and quantitative analysis. Just thinking about this, the mathematical model on this effect is established. The simulation curves with different obliquity of the reflector are computed and plotted. Results show that the obliquity of reflector has great influence on modulation function. So advice is presented that the axes of fiber pair should be perpendicular to the reflector.
Based on the math-model of coordinate measurement of the two-CCDs vision sensor, which is established in this paper, the relationships among the coordinate measuring precision, the effective viewing field, the structural parameters of this sensor and the parameters of CCD itself are analyzed. In the meantime, the optimal structure layout is performed by means of computer simulation. And the simulation results show that the optimal layout of the two-CCDs vision sensor is symmetric structure.
A new kind of distributed fiber optic sensor is described in the paper. On the basis of mode coupling between two orthogonal fundamental modes of HiBi polarization- maintaining fiber, a new method is developed to locate the mode coupling point caused by external pressure applied on the fiber.
In the paper, two general theoretical models of a cylinder edge-checkout with white light scanning and laser scanning are established. The simulation for the models is performed by means of a computer and their simulating curves are obtained respectively. The factors that affect the sensitivity of the cylinder edge-checkout are also analyzed. Besides, the correctness of the two models is inspected with three kinds of edge-checkout methods.
In order to obtain high measuring accuracy, a method of optimization-design is established. Then the computer simulation for the model is introduced. Finally, as results, the optimum structure parameters corresponding to two kinds of target-planes with different size are tabled. In addition, a group of 3D figures of the error distribution are given.
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