Bending Loss Of Optical Fiber Research Articles

Experimental investigation on performance monitoring of the combined optical fiber transducer in landslide

An innovative combined optical fiber transducer (COFT) based on the optical fiber bending loss characteristic has been developed for landslide monitoring. To better understand the working principle and improve the monitoring performance of the transducer, the capability of the COFT for exploring subsurface properties of slopes (sliding direction, magnitude, and rate of slope movement) and the deformation compatibility between the COFT and surrounding geo-materials were explained semi-empirically and semi-theoretically, which was also verified by the laboratory shear experiments of the COFTs constructed with two kinds of host materials (expanded polystyrene and polyvinyl chloride) and three kinds ratios of cement mortars (sand to cement 1:4, 1:5, and 1:6) and the related numerical simulation. In the following, model monitoring tests of an artificial slope and field monitoring application of the proposed COFTs in a field slope were carried out and the progressive slope movements were effectively determined, which validated the performance of the proposed COFT in landslide monitoring.

Experimental research on a novel spring-shaped fiber-optic displacement sensor for settlement monitoring

In this paper an innovative spring-shaped fiber-optic displacement sensor (SSFODS) based on optical time domain reflectometer (OTDR) technology with simple construction and cheap cost was proposed for subgrade settlement monitoring. The sensor incorporated a simple spring-shaped fiber bending modulation that increased its sensitivity in bending, light source and detector. The sensing principle between the measured external displacement and bending loss of optical fiber was theoretically explained and its expression was also derived. Sensor calibration was conducted, which showed that the SSFODS was characterized by a large measurement range of 90 mm, minimum displacement resolution of 0.173 mm, maximum hysteresis error of 2.81% and maximum repeatability error of 8.42%, respectively. A soil drainage model test with the SSFODS was performed to study its performance in determining compression deformation of the soil. At last, a simple field monitoring application with two SSFODSs connected in series was conducted and the progressive compaction behavior of the fill slope was accurately captured by two SSFODSs. Additionally, it is possible to connect these SSFODSs in series on one optical link to realize quasi-distributed sensing monitoring. This capability supports a promising application of the sensor in geotechnical engineering for real-time monitoring of the stability of fill slopes, foundation pits and so on.

A Novel Force Sensor Based on Optical Fibers Used for Semicircular Flexure Beam Unit

In this article, a novel force sensor is designed based on the optical fiber bending loss theory utilizing a structure with periodically corrugated semicircular flexure beam units. The fiber bending loss theory composed of the pure bending loss and the transition loss is related to the curvature radius according to the theoretical analysis. Both the optical working modes and the mechanical properties of the designed sensor are discussed. The output voltage attenuation of different curvature radii is tested and the curvature radius of 6 mm is selected for further experiment. The actual sensing results are acquired using a commercial force sensor. The result shows that the nonlinear errors of the forward and the reverse force applying process are 11.82% and 17.86%, respectively. The sensitivity is 13 mV/N and the precision is 160 mN. The experiment under different temperatures ensures the temperature-insensitive characteristics of the sensor.

Design, sensing principle and testing of a novel fiber optic displacement sensor based on linear macro-bending loss

This paper presents a linear fiber optic displacement sensor for the use over a large range based on the macro-bending loss. The sensor incorporates an extremely simple design, light source and detector. A concentric gear shaft is used to bend the fiber and transfer the displacement. The linear relationship between the measured displacement and the bending loss of optical fiber was proved theoretically and its expression was derived. A series of calibration experiments and performance tests were conducted. The experimental results show that the sensor was characterized by a wide measurement range, a high sensitivity and a minimum displacement resolution of 0–200 mm, 0.1668 dB/mm and 0.06 mm, respectively. The stability and repeatability of the sensor was verified by repetitive testes with a maximum measurement deviation of 0.162 mm. The predicted displacements of the sensor were similar to the actual values, and the difference errors of all samples are basically within 10%. These characteristics demonstrate that the sensor can be used for displacement monitoring for large-scale civil structures and has a promising prospect.

Low-Cost Coil-Shaped Optical Fiber Displacement Sensor for a Twisted and Coiled Polymer Fiber Actuator Unit

This study proposes a low-cost coil-shaped optical fiber (COF) sensor that can be used in the twisted and coiled polymer fiber (TCPF) actuator unit. The TCPF is a thermal-driven artificial muscle with large stroke and large power ratio. To improve its response, several actuator units, which combine the TCPF with a cooling system, were developed. However, the displacement sensors for these units were not established, unlike the encoder for the motor. Although several methods are available to estimate the TCPF displacement, they are based on the resistance of the heating wire and are affected by TCPF actuation and load change. Therefore, to accurately measure displacement, in this study, we focus on the bending loss of optical fiber, which is often used in soft robotics. Because the bending loss of COFs is caused by the change in length of the coil, the displacement can be obtained by measuring the light intensity through the optical fiber. This study experimentally demonstrates that the COF is available, even when driving the TCPF actuator and changing the load.

A High-Speed Distributed Ultra-Weak FBG Sensing System With High Resolution

A high-speed high-resolution distributed sensing system with ultra-weak fiber Bragg grating (FBG) array is presented. The scheme uses a narrow bandwidth filter to translate wavelength shift measurement to a simple intensity measurement. By introducing a reference channel into the system to compensate for the intensity fluctuation from the light source or optical fiber bending loss, we can realize high-resolution and high-speed distributed static and dynamic strain measurement using 342 ultra-weak FBGs with reflectivity of 0.01% and spatial resolution of 2.5 m along 855-m optical fiber. The wavelength variation of all gratings was measured as 0.22 pm at a sampling rate of 100 kHz. Experimental results show that the resolution of strain measurement can achieve 222 $\text{n}\varepsilon $ , and dynamic frequency of 2000 Hz is achieved.

Optical Fiber Sensor Experimental Research Based on the Theory of Bending Loss Applied to Monitoring Differential Settlement at the Earth-Rock Junction

Considering the differential settlement in the junction between the structure perpendicular to the dike and the body and foundation of dike (called the earth-rock junction in this paper) during runtime, an experimental investigation of optical fiber sensor monitoring was conducted. Based on the sensing mechanism of single-mode optical fiber bending loss, the experiment focused on the influence of the bending radius of an optical fiber on the bending loss. In view of the characteristics of the differential settlement in the earth-rock junction, we designed a butterfly-type optical fiber sensor and composite optical fiber sensor for monitoring device in monitoring the differential settlement to enlarge the monitoring range and improve the sensibility of optical fiber sensor. Based on the research on the working principle and bending properties of the composite optical fiber monitoring device, we conducted experiments on the bending of the composite optical fiber sensor monitoring device and the use of the device for monitoring the differential settlement. These experiments verified the feasibility of the composite optical fiber sensor monitoring device at monitoring the differential settlement in the earth-rock junction.

Novel Fiber Optic Sensor Probe with a Pair of Highly Reflected Connectors and a Vessel of Water Absorption Material for Water Leak Detection

The use of a fiber optic quasi-distributed sensing technique for detecting the location and severity of water leakage is suggested. A novel fiber optic sensor probe is devised with a vessel of water absorption material called as water combination soil (WCS) located between two highly reflected connectors: one is a reference connector and the other is a sensing connector. In this study, the sensing output is calculated from the reflected light signals of the two connectors. The first reflected light signal is a reference and the second is a sensing signal which is attenuated by the optical fiber bending loss due to the WCS expansion absorbing water. Also, the bending loss of each sensor probe is determined by referring to the total number of sensor probes and the total power budget of an entire system. We have investigated several probe characteristics to show the design feasibility of the novel fiber sensor probe. The effects of vessel sizes of the probes on the water detection sensitivity are studied. The largest vessel probe provides the highest sensitivity of 0.267 dB/mL, while the smallest shows relatively low sensitivity of 0.067 dB/mL, and unstable response. The sensor probe with a high output value provides a high sensitivity with various detection levels while the number of total installable sensor probes decreases.

Distributed fiber-optic bi-directional strain–displacement sensor modulated by fiber bending loss

Abstract The distributed fiber-optic bi-directional strain–displacement sensor is composed of fiber-optic bi-directional strain–displacement chips and optical time domain reflectometer (OTDR). The operational principle is the modulation of fiber loss in OTDR, i.e. the strain and the displacement in monitoring positions are measured by the bending loss of optical fibers bonded on the tension-sensitized and compression-sensitized regions of the fiber-optic strain–displacement chips. Additionally, by inserting the time delay optic fiber, the moving direction of the substrate free ends in the fiber-optic bi-directional strain–displacement sensor can be identified by the trace taken with high spatial resolution in OTDR. The experiments indicate that the fiber-optic bi-directional strain–displacement sensor could measure strain and displacement by adopting the lengths of sensitive region and freely suspended fiber, the chip length, and attachment methods.

Realization of an On-Line Fiber-Optic Bending Loss Measurement System

In this paper, an on-line bending loss measurement system is studied and realized. To avoid complicated calculation of fiber bending loss, we propose a simplified theoretical model for on-line evaluation. A specific fiber adaptor is developed for light signal feeding and picking up through a free space optical fiber coupling technique. Relevant factors, including free space fiber misalignment, are considered. The signal-to-noise ratio of the whole system is improved by optimizing the spatial perturbation length of the fiber and the deformation of the bending fiber. The use of an on-line monitoring technique for measuring the bending loss of optical fibers is presented in this paper. With this technique, manufacturing efficiency can be improved, and the cost of maintaining fiber quality control can be reduced.

A distributed optical fiber bi-directional strain-displacement sensor*

Abstract A distributed optical fiber strain-displacement sensor is developed, which consists of an optical fibergauge of strain-displacement and an optical time domain reflectometer (OTDR). The operational principle is the modulation of fiber loss in OTDR, i. e. the strain and displacement in monitoring position are obtained from the bending loss of optical fiber bonded on the optical fiber gaugeof strain-displacement. After examining the strain and displacement in the cantilever and the microdisplacement rack respectively, the result indicates that the distributed optical fiber gauge of strain-displacement can monitor strains or displacements in different sensitive lengths. The key technique for measuring bi-directional strain-displacement is the pretreatment of bending of the freely suspended optical fibers, which can be identified with OTDR by inserting time delay optical fiber.

Analog data transmission through plastic optical fiber in robot with compensation of errors caused by optical fiber bending loss

A new type of analog data transmission system using a plastic fiber is proposed, where a direct intensity modulation scheme has been employed together with a differential amplifier to compensate for the transmission error caused by the optical fiber bending loss. This system was experimentally applied to transmit analog data of dimensions detected by the displacement sensor attached to the robot arm tip to the robot basement through the plastic optical fiber installed in the robot arm body.