Single-mode Fiber-optic Sensor Research Articles

Single mode optical fiber sensor based on surface plasmon resonance for the detection of the oil aging for the electrical transformers

Single mode optical fiber sensor based on surface plasmon resonance for the detection of the oil aging for the electrical transformers

Fluidic Flow Measurement Using Single Mode–Multimode–Single Mode Optical Fiber Sensor

The measurement of flow in fluidic channels is an essential task required for the proper operation of devices in many interesting applications. In this work, an optical fiber sensor based on a single mode - multimode - single mode (SMS) fiber structure is used to measure the flow in a millimeter-sized Polydimethylsiloxane (PDMS) fluidic channel. The measurement is based on the phenomena of vortex shedding, where the immersed fiber section acts as an obstructing strut. The sensing principle assumes slight fiber bending with vortex shedding, resulting in intensity variations of the light transmitted through the fiber sensor. To the best of our knowledge, this is the first time modal interference in an SMS fiber structure is explored for flow detection in a microfluidic device. The flow-related shedding frequency was detected through intensity variations of the transmitted light at a suitable laser wavelength. The linearity of the detected frequency with flow rate is confirmed over the investigated flow range with high R <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> values up to 99%. The frequencies detected are compared to the theoretically expected frequencies based on the theory of vortex shedding past a rigid strut. Nevertheless, their relation to the flow velocity is found to deviate in slope from that of the theoretical relation, which could be due to the interaction of the flow with the flexible optical fiber shedding strut. The good linearity of this sensor makes it a promising component for macro and microfluidic flow measurement in many applications.

Sensitivity Comparison of Refractive Index Transducer Optical Fiber Based on Surface Plasmon Resonance Using Ag, Cu, and Bimetallic Ag-Cu Layer.

A single-mode optical fiber sensor uses surface plasmon resonance (SPR) with a bimetallic silver–copper (Ag–Cu) coating compared to a single layer of Ag and Cu itself. Bimetallic Ag–Cu sensors are constructed by simple fabrication on a side-polished optical fiber, followed by an electron beam evaporation of Ag and Cu films. For this investigation, the thickness of the single Ag layer was set to 30 nm and the single Cu layer was set to 30 nm; whereas for the bimetallic combined Ag–Cu layer the thickness of Ag was 7 nm and Cu 23 nm. The sensor performance was analyzed and compared experimentally and numerically using the COMSOL Multiphysics. A white light source was used with a broad optical bandwidth to provide a range of wavelengths to the optical fiber. The characteristics of the thin layers of Ag, Cu, and Ag–Cu as alcohol sensors were evaluated. We found that Cu was the most sensitive metallic layer compared to the Ag and the bimetallic Ag–Cu layers. For a 100% alcohol concentration, Cu showed a sensitivity of 425 nm/RIU followed by the bimetallic Ag–Cu layer with 108.33 nm/RIU, whereas the Ag layer was not detected. Interestingly, sensitivity reached saturation beyond the 20 nm thick layer of Ag. This shows that the Cu and the bimetallic Ag–Cu layers are suitable for an alcohol-based optical sensor.

Study of strain measurement by fiber optic sensors with a sensitive fiber loop ringdown spectrometer

Abstract A sensitive fiber loop ringdown (FLRD) spectrometer without any additional optical component was utilized to obtain strain measurement on a single mode fiber optic sensor. The strain data were obtained by employing the theory of bending loss in single mode fibers. The best sensitivity of the sensors was obtained as 5.99 μe with an 80.0 cm long sensor head when the sensor heads were stretched at the midpoint. The spectrometer system had a baseline-stability of 0.22%. Stretching the sensor head from off-midpoint positions resulted faster decays with higher optical losses. Comparison of the slopes relative to the stress positions showed that it may be utilized to obtain strain location without using any high-cost equipment. This portable, basic, and simpler FLRD spectrometer system offers high sensitivity with great baseline stability without utilization of any additional optical components and/or creating air-gap/air-cavity and encapsulation on the sensor head region. With its very attractive features of such as easy setup, low cost, and simple design, sensitive FLRD sensors may have a high potential for early detection in several applications such as structural health monitoring, biomedical sensing, mining, transportation and rail applications for continuous monitoring in real-time.

Response of Distributed Fiber Optic Temperature Sensors to High-Temperature Step Transients

Experiments were performed to test fiber optic temperature sensors under thermal conditions similar to those that would be experienced in the transient reactor test facility (TREAT) at the Idaho National Laboratory. Specifically, four single-mode optical fiber sensors were dropped into a pre-heated furnace to simulate a step temperature transient, for steps from room temperature to indicated furnace temperatures, ranging from 700 °C to 1100 °C. The four fibers were a standard SMF-28 fiber, a fiber with inscribed type-I fiber Bragg gratings (FBGs), and two fibers with inscribed type-II FBGs. The two type-II FBG fibers were different in the initial backscatter signal of the gratings; one fiber had gratings with greater backscatter reflection than the other. The type-I FBG sensor and standard SMF-28 sensor measured temperature for temperature transients with a final temperature of 700 °C. The low reflection type-II FBG sensor measured temperature transients with final temperatures up to 950 °C. The high-reflection type-II FBG sensor successfully measured temperature for short times with final temperatures up to 1050 °C. For long times at 1050 °C, there was a drift in the temperature sensing. We conclude that the high-reflection type-II FBG sensor would perform acceptably for application in the thermal environment of TREAT, or for other step temperature transients from room temperature to final temperatures up to 1000 °C.

Interfacial delamination in glass-fiber/polymer-foam-core sandwich composites using singlemode–multimode–singlemode optical fiber sensors: Identification based on experimental investigation

Identification of interfacial delamination in the glass fiber/polymer-foam-core sandwich composites is difficult if the delamination does not propagate to the side surface of the specimen. However, these damages may eventually lead to compromising the sandwich composite structural component. A cost-effective novel embedded fiber optic sensor is being proposed in this manuscript, which works on the principle of multimode interference, to perform distributed sensing of interfacial delamination within the sandwich composites while in service. Even though this easy to use methodology has been used to identify interfacial delamination, this methodology can also be used for different other types of interfacial/interlaminar distributed strain sensing of samples under mechanical as well as thermal loads.

A novel technique for acoustic emission monitoring in civil structures with global fiber optic sensors

The application of acoustic emission (AE)-based damage detection is gaining interest in the field of civil structural health monitoring. Damage progress can be detected and located in real time and the recorded AEs hold information on the fracture process which produced them. One of the drawbacks for on-site application in large-scale concrete and masonry structures is the relatively high attenuation of the ultrasonic signal, which limits the detection range of the AE sensors. Consequently, a large number of point sensors are required to cover a certain area. To tackle this issue, a global damage detection system, based on AE detection with a polarization-modulated, single mode fiber optic sensor (FOS), has been developed. The sensing principle, data acquisition and analysis in time and frequency domain are presented. During experimental investigations, this AE-FOS is applied for the first time as a global sensor for the detection of crack-induced AEs in a full-scale concrete beam. Damage progress is monitored during a cyclic four-point bending test and the AE activity, detected with the FOS, is related to the subsequent stages of damage progress in the concrete element. The results obtained with the AE-FOS are successfully linked to the mechanical behavior of the concrete beam and a qualitative correspondence is found with AE data obtained by a commercial system.

Research of Coupling Single-Mode Fiber-Optic Vibration Sensor and Experimental Test

A new kind of coupling single-mode fiber-optic sensor is presented and the working theory is discussed. Vibration tests of the sensor are carried out. The vibration experimental system based on cantilever are setup and explained in detail. Dynamic response of coupling single-mode fiber-optic sensor compared with piezoelectric sensor is investigated and the result is excellent. Experimental results show that the coupling single-mode fiber-optic sensor is suitable for vibration measurement practically.

Real-time monitoring of railway traffic using slope-assisted Brillouin distributed sensors

The application of a Brillouin distributed sensor for the monitoring of railway traffic is presented in this work. The field test is performed on the Italian regional line San Severo-Peschici, operated by Ferrovie del Gargano. A single-mode optical fiber sensor was attached along a rail length of about 60 m. The strain associated with train passage was acquired along the monitored rail length at 31 Hz acquisition rate and 1 m spatial resolution. The data acquired by the sensor demonstrates its capability of retrieving useful information in railway traffic monitoring, such as train identification, axle counting, speed detection, and dynamic load calculation.

Raman Slow Light in Distributed Raman Fiber Sensors

Distributed Raman sensor offers a number of advantages to the implementation of smart grid, which is aimed to improve reliability and energy efficiency as compared with traditional power grid. However, the fantastic properities of slow light are rarely considered in the former studies on the Raman sensor systems. In this paper, the effects of Raman slow-light on room-temperature single-mode optical fiber sensors are examined by extracting the Raman pulse-delay terms from extended nonlinear Schrodinger equation (NLSE). Numerical study shows that pulse parameters such as pulse position, frequency chirp, and envelope distortion may be greatly affected by slow light. Two important points of pump power are show clearly keeping the Raman pulse zero walk-off or chirp free, respectively. We demonstrate a method based on pump power adjustment for compensating the slow light induced impairment. DOI: http://dx.doi.org/10.11591/telkomnika.v11i5.2472

Effect of Raman Slow Light on Distributed Raman Fiber Sensors

The effects of Raman slow-light on room-temperature single-mode optical fiber sensors are examined by extracting the Raman pulse-delay terms from extended nonlinear Schrodinger equation (NLSE). Numerical study shows that pulse parameters such as pulse position, frequency chirp, and envelope distortion may be greatly affected by slow light. We demonstrate a method based on pump power adjustment for compensating the slow light induced impairment.

Detection Method Optimization of Optical Fiber Evanescent-Wave Hydrogen Gas Sensor

As the optical power variation is relatively small before and after the Pt/WO3film was exposed to hydrogen gas, traditional detective method to measure directly the variation of optical power in the fiber core is susceptible to interference. Therefore a new detection method, which is able to improve the relative variation for nearly 9 times by detecting the variation of optical power in the evanescent field, was proposed through mathematical analysis and simulations. The fundamental structure and working principle of step-index single mode optical fiber sensor were introduced.

Experimental Study of Coupling Fiber-Optic Vibration Sensor Based on Variational Theory

According to the character of fiber-optic coupler, its coupling output is sensitive to the variation of coupling region’s length. A new kind of coupling fiber-optic vibration sensor is presented base on this principle. The theory of coupling single-mode fiber-optic sensor is analyzed. A prototype of fiber optic vibration detection system has been successfully built, including a sensor head, a low-cost control unit and a software package for signal processing with high resolution. The response of fiber-optic sensor and piezoelectric sensor to periodic vibration and shock is measured and the results of the coupling fiber-optic vibration sensor are closely in accordance with high precision piezoelectric sensor. The cross-axis anti-disturbance ability of the fiber-optic sensor is discussed in addition. Experimental results indicate that the coupling fiber-optic vibration sensor has favorable vibration detection capability; it can meet the requirement of vibration measurement.

双包层单模光纤传感器及其在温度/湿度传感方面的应用

双包层单模光纤传感器及其在温度/湿度传感方面的应用

Optical Fiber Loop Sensors for Structural Health Monitoring of Composites

AbstractIn the present work a fiber-optic loop-sensor is designed and tested for possible applications in structural health monitoring of composite materials. It is known that bending an optical fiber beyond a critical curvature leads to loss of optical power through the curved region. The optical power loss depends on the radius of curvature of the loop. The optical power can be measured by a photodetector and a change in the power due a change to the curvature can be measured. In the present research optical fiber-optic loop-sensors are developed that can exploit this concept. Single-mode optical fiber sensors having different loop radii, from 6-10 mm, are fabricated and calibrated for applied strain on the loop. The calibration is carried out using a 0.098 N load cell and a computer controlled translation stage having 50 nm step resolution. Results show that the sensors provide highly repeatable curves for loading and unloading cycles. Smaller loop radii lead to higher optical power losses, resulting in higher sensitivity. Calibration results show that such sensors can be used in structural health monitoring applications. In this approach the coating and cladding of optical fibers are maintained intact; therefore, the sensors are robust and can withstand several composites fabrication processes.

대변위 측정을 위한 다중화된 광섬유 센서

A multiplexed bend loss type single-mode fiber-optic sensor system was prepared to measure the displacement of several cm of the civil engineering structures such as many bridges, tunnels and various buildings. This bend loss type fiber-optic sensor used the signal difference between two reflection signals due to various bend losses generating at a pair of optical connectors by using OTDR (optical time domain reflectometer) for measuring displacements. And the experiments were conducted for showing the measurement feasibility on the range of 10 cm, and the multiplexing experiments were also performed to measure the displacements of 5 measuring positions of an object by setting these 5 fiber-optic sensors on a single mode fiber simultaneously.

광커넥터의 반사를 이용한 다중화된 굽힘 손실형 단일모드 광섬유 변위센서

교량과 각종 건물을 비롯한 대형 토목 구조물에서 발생하는 수 mm의 변위를 한 개의 광섬유로 간편하게 측정하기 위하여 광커넥터에서 반사가 굽힘 손실에 의하여 변하는 현상을 이용한 새로운 다중화된 광섬유 변위센서를 제안하고 실험하였다. 한 쌍의 광커넥터 양끝에서 반사광의 신호차이가 두 광커넥터 사이에서 발생한 굽힘 변위에 의해서 달라지는 것을 Optical Time Domain Reflectometer로 측정하여 선형으로 그 변화가 측정되는 변위센서를 만들고, 이 센서 4개를 직렬형으로 배열하여 여러 지점의 변위를 동사에 측정이 가능한 다중화 센서 시스템을 구성하고 실험하였다. 그 결과 이 변위센서를 이용하면 4개 지점에서 각각 최대 6 mm까지의 변위를 6%의 오차범위 내에서 0.9942의 선형성을 가지고 변위를 측정할 수 있음을 확인하였다. We propose and present a new multiplexed bend loss type single-mode fiber-optic sensor system for displacement measurement in order to measure the displacement of several mm of civil engineering structures such as bridges and buildings. We make a bend loss type fiber-optic sensor for measuring displacements using the signal difference between two reflection signals due to various bend losses generating at a pair of optical connectors by using the optical time domain reflectometer. And we fabricate a multiplexed bend loss type fiber-optic sensor detecting linear displacements of 4 measuring positions of an object by setting these new 4 fiber-optic sensors on a single mode fiber simultaneously. We find that the multiplexed fiber-optics displacement sensor has linearity of 0.9942, maximum displacement of 6 mm, and accuracy of 6% for 4 measuring points.

Fabrication and characterization of pH sensor based on side polished single mode optical fiber

Abstract Fabrication and characterization of side-polished single mode optical fiber pH sensor utilizing evanescent field absorption spectroscopy and dye doped sol–gel immobilization technology are presented. The sensor is prepared by fixing the fiber in a groove made on one of the surfaces of a fused silica block. To make the surface sensitive to pH it is polished up to the core of the fiber and a film containing a mixture of three pH sensitive dyes is coated on it using sol–gel technology. The influence of the radius of curvature of the groove on the sensitivity of the sensor is studied. The decrease in the radius of curvature of the groove increases the sensitivity. This occurs due to the increase in the evanescent field and hence its interaction with the pH sensitive dyes entrapped in the film. The advantage of the side-polished single mode optical fiber sensor is that only 0.1 ml of sample is sufficient to measure the pH of the fluid. This is important when the procurement of the sample in large quantity is not possible.

Single-mode fiber-based reflex sensor for internal surface in-line measurement of small products

Abstract This paper describes experiments concerning dimension and surface shape measurement with a single-mode fiber-optic sensor and improvement of the measurement principle. The sensor probe was well designed with a small structure and a compensation network. The novel optical fiber probe arrangement as well as the possibilities for complex measurement problems is explained by measuring an internal screw thread as an example. The size of the fiber-based sensor probe is about 5 mm, which is very suitable for the internal surface measurement of small precision products. The experimental results show that the measurement uncertainty of the internal screw thread minor diameter can reach ±10 μm, and the stability of the measurement system is better than 0.1%. Compared the measurement results obtained by the developed sensor system with those by a Universal Tool Maker’s Microscope, the measurement results of an external screw thread are satisfactory. The maximum deviation of the thread pitch measurement is about 1 μm, and that of the major diameter measurement is better than 3 μm.

Shape measurement based on fiber-optic technique for complex internal surface

Reverse engineering based on fiber-optic technique is a very new topic in CAD/CAM fields. A novel single-mode fiber-optic sensor is presented based on the principle of beam reflection to implement the digitizing of complex surface shape. The fibers in the sensor probe are arranged like a spoke with eight symmetrically cross-arranged receiving fibers and one centered emitting fiber. Thus, the sensor can compensate for the offsets caused by fluctuations of surface reflectivity and light power and is fit for application under rough and formidable conditions with noncontact, fast shape measurement. A prototype was developed based on the simulation results to verify the feasibility. With the GRIN lens on the exit end of the single-mode emitting fiber, the lateral resolution was greatly improved compared with former multimode fiber-optic displacement sensors. Preliminary experiments indicated that the estimated uncertainty of displacement measurement was better than ±2 μm, and the uncertainty of ±5.6 μm can be obtained when measuring a MJ20×1.5 thread.