Fiber Inclinometer Research Articles

Comprehensive Error Equation for Fiber Optic Inclinometer

Optical fiber inclinometer technology has been gradually used in various projects. However, the error analysis of this method is decisive for its subsequent development and application. In this study, through three tests, the monitoring length, layout plane, and boundary conditions that may lead to measurement errors are studied in detail and the contribution of different factors to measurement errors is explored. The research results reveal that the measurement errors caused by monitoring length and layout plane have an empirical function relationship with the monitoring length <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> and the angle θ between the layout plane and the inclined direction. Any changes in the boundary conditions will result in an overall deviation in the calculated deflection curve. After analyzing the characteristics of each error, a comprehensive error equation is proposed. This equation has guiding significance for error correction and technical improvement in optical fiber inclinometer.

Optical fiber inclinometer with dynamically controllable excitation length of quantum dots liquid-core waveguide based on a photo-controlled bubble.

An ultracompact fiber inclinometer based on a bubble controlled by Marangoni force is proposed in this Letter. By coupling a 980-nm laser, the bubble can suspend in a quantum dots (QDs) liquid-core waveguide (LCW) due to the Marangoni effect. Under the excitation of a 405-nm laser, QDs LCW exhibit green emissions centered at 523 nm. When the tilt angle changes, the position of the bubble changes as well, which causes the variation of the 523-nm fluorescence intensity. The experimental results show that the sensitivity based on the peak intensity ratio (PIR) reaches 0.22/° with a linearity of 0.979 from 0° to 35°. Furthermore, the sensor has excellent stability and repeatability.

Fiber optic sensors enabled monitoring of thermal curling of concrete pavement slab: Temperature, strain and inclination

An intellectual system is developed to monitor concrete pavement slab subjected to external temperature fluctuations. Truly distributed fiber-optic temperature and strain sensors and an innovative Fabry-Perot interferometer-based optical fiber inclinometer are installed in the concrete pavement slab so as to monitor and evaluate its thermal curling process. The system is demonstrated to be effective in detecting the thermal curling of slab. The results substantiate that the top surface of the slab has a fast reaction rate to the heating/cooling process. The bottom surface temperature has a time-lag comparing to the top surface, which results in a sharp increase then a slow reduction in the top-vs-bottom temperature difference. In the light of the inclinometer, it is proven that the tilt angle of the curvature of the slab has a high degree of synchronization with the top-vs-bottom temperature difference. The temperature/strain distribution maps are also presented and uneven distributions of temperature and strain are captured. Moreover, taking the advantage of the multiplexing capacity of the distributed fiber-optic sensors, the coefficient of thermal expansion (CTE) of the slab can be easily obtained and used to feed a finite element model. Finally, a three-dimensional finite element model is established to completely understand the curling process measured from the monitoring system. The model and the experimental data agree well with each other. While the sensors output realistic temperature and deformations at certain locations, the validated model is able to reveal more details of the nonlinearity inside the slab.

Research on a novel inclinometer based on distributed optical fiber strain and conjugate beam method

The inclinometer is widely used in the deformation monitoring of civil and hydraulic engineering, but the manual observation required for existing traditional inclinometers is time-consuming, laborious and workload-intensive; an inclinometer with automatic monitoring is expensive, difficult to use for achieving distributed monitoring and shows poor instrument durability. To overcome the shortcomings of traditional inclinometers, a distributed optical fiber inclinometer (DOFI) is developed based on the conjugate beam method and distributed strain measurement technology. Compared to Euler-Benuli beam based converting method, the conjugate beam based method is more flexible and accurate to monitor the deformation of the slope under the heterogeneity geological conditions. Numerical simulation and laboratory tests show that the conjugate beam based inclinometer (DOFI) is effective, feasible and accurate. It can be used to quickly and accurately measure the deformation and direction of rock and soil mass, such as slope, and can realize long-term on-line monitoring.

A macrobending-based optical fiber inclinometer to measure the ground tilt in the depth which forms a positive and negative angle to the gravity axis

This paper discusses an optical fiber inclinometer to measure ground tilt in soil depth, which forms an angle between vertical axis to the gravity axis. The macrobending based-inclinometer consists of a laser source system, fiber cable, geotechnical cylinder; rolling wheels and pressing levers each sitting on top and bottom support; stainless steel rope, cylinder loads, light detection and output data. The stabilized laser was split into four by an optical coupler into ports of sensor fiber 1, sensor fiber 2, reference fiber and one backup port, then entering into a geotechnical cylinder housed in a standard geotechnical pipe. If there is instability of the soil condition resulting in a tilting of the soil surface, the geotechnical cylinder changes its position to form an angle to the gravity axis, furthermore the active pressure lever will suppress the optical fiber sensor. At this stage, the optical fiber will undergo a macro bending resulting in a change of its output. This intensity change output will correspond to the change of the angle for each tilting direction (left and right). The fiber inclinometer has a measurement range of 10° for both direction with accuracy of 0.5°.

Polarization induced non-reciprocal phase controlled all-fiber loop mirror based inclinometer

An optical fiber inclinometer based on non-reciprocal phase change effect in a single-mode fiber loop mirror (FLM) is proposed. The phase of light waves in FLM is controlled by two-phase shifters (PSs). The relationship between the inclination angles and phase differences of the two-PSs, and transmitted light power was derived by Jones calculus. The signature of the birefringence obtained through simulation on the output light has been confirmed by experimentation. From the results, it was found that when the birefringence of the two-PSs are different, two measurement sensitivities (17.07 × 10−3 deg−1 and 21.37 × 10−3 deg−1) can be realized with one angle measurement system. We also report a method for changing measurable ranges, and measurement sensitivity. Since the angle can be directly measured from the transmitted light power, the results of this work contribute to the realization of simple and low-loss inclinometers using standard single-mode fiber.

Terahertz-range interrogated grating-based two-axis optical fiber inclinometer

We report a two-axis fiber inclinometer fabricated using an ultraweak terahertz-range fiber Bragg grating. Three sensing grating structures were inscribed along a single-mode optical fiber using a femtosecond laser, bound together into a sensing array using thermoformed plastic, and fixed to a two-axis rotational stage. Inclination tests were performed in which the fiber was deflected from 0 to 1.7 deg. These tests were repeated at eight azimuthal angles in increments of 45 deg (from 0 to 315 deg). The standard deviation of the largest incli- nation angle error was 0.048 deg and the stability of the inclination angle was 0.030 deg.©2016 SocietyofPhoto-Optical

Temperature Independent Tapered Fiber Bragg Grating-Based Inclinometer

A new concept for an optical fiber inclinometer based on tapered fiber Bragg grating (TFBG) is presented. The sensor was characterized by the experimental measurement of the dependence of inclination angle on the spectral response in fluctuating temperature conditions. The research showed that the TFBG made it possible to simultaneously measure both the inclination angle and temperature, and to operate as a temperature insensitive 0°–90° tilt sensor, in a different interrogation regime. Inscription of the FBG in the tapered optical fiber section offered not only sensor miniaturization, but also the possibility of temperature sensing by the fiber section adjacent to the inclination area. Moreover, due to the reflective mode of the TFBG, the sensor offers excellent sensitivity due to the double-loss operation.

Optical Fiber Inclinometer Based on a Fiber Taper Cascading a Peanut-Shape Structure

An optical fiber inclinometer applying modal interference based on an abrupt tapering cascading a peanut-shape configuration is proposed. The abrupt taper splits part of the core mode into cladding modes and the interference occurs when the peanut-shape recombines the cladding modes and core mode together. Four inclinometers with different lengths have been fabricated and characterized, and the high sensitivities of -1.76 and -4.49 nm/° are obtained in the angle range of 0°-3° and 3°-6.66°, respectively.

Optical inclinometer based on a tilted fiber Bragg grating with a fused taper

An optical fiber inclinometer based on a tapered-tilted fiber Bragg grating (TFBG) was proposed. The sensor head is formed by tapering a 22mm-long TFBG with a 10° tilt angle. The reflection spectra of the cladding modes and the core mode revealed the information of the bending angle. Experimental results showed that the inclinometer provided a relatively large measuring range from 0° to 25° with a sensitivity of 4.16dB/deg.

Temperature-independent fiber inclinometer based on orthogonally polarized modes coupling using a polarization-maintaining fiber bragg grating.

A reflection fiber inclinometer is proposed and experimentally demonstrated based on two linearly polarized (LP) modes coupling. The configuration consists of a section of polarization-maintaining fiber (PMF) containing a fiber Bragg grating (FBG) splicing with single mode fiber (SMF). Bending the PMF in the upstream of FBG can induce an additional birefringence of PMF, which results in the intensity changes of two LP modes owing to orthogonal polarization coupling. The experimental results represent that the device shows different bending responses at the angle range from 0° to 40°and from 64° to 88°, respectively. Moreover, the temperature change just shifts the wavelengths of LP modes reflected and does not influence their intensities, which effectively avoid the temperature cross-sensitivity and make it a good candidate for measuring inclinometer and temperature simultaneously.

Direction-independent fiber inclinometer based on simplified hollow core photonic crystal fiber

A fiber optical inclinometer based on modal interferometer is demonstrated for bend angle sensing. The device consists of a piece of simplified hollow core photonic crystal fiber sandwiched between single mode fibers with lateral offset. The measurement of bend angles up to 45° is demonstrated, and the spectrum exhibits a blueshift of over 50 nm. The sensitivity is found to increase with the applied bend angles and reaches 2.4 nm/deg at 45°, and the response is independent of the direction of bending. A low temperature sensitivity of 0.5 pm/°C is observed between room temperature and 1000°C. Due to its capacity for withstanding high temperature, the device can work as a direction-independent inclinometer in high-temperature environments.