<p>A Mach–Zehnder interferometer based on processed hollow-core fiber (HCF) is proposed and experimentally demonstrated for gas pressure sensing. The fiber sensor is fabricated by splicing a segment of HCF between the two coreless fibers. One end of the HCF is processed into an open cavity, which allows gas pressure of the air-core to be equivalent to that of the external environment. Gas pressure change induces refractive index change of the air-core, thus the measurement of gas pressure can be achieved by monitoring wavelength shift of the interference pattern. The proposed fiber sensor exhibits a high gas pressure sensitivity of 9.35 nm / MPa in the range from 0.1 to 0.04 MPa and a temperature sensitivity of 30 pm / ° C in the range from 30°C to 90°C. Furthermore, the fiber sensor processes the advantages of compactness, low cost, and all-fiber configuration, which makes it suitable for gas pressure measurement.</p>
An in-line optical fiber Mach–Zehnder interferometric (MZI) sensor is proposed and experimentally demonstrated for magnetic field measurement. The fabrication mechanism of the optical fiber microstructures by CO2 laser is described in detail. The sensor with symmetrical structure is fabricated by splicing a 7-mm length of seven-core fiber and two fiber peanuts, which is encapsulated with magnetic fluid in the capillary. The transmission spectrum of the MZI is modulated by the refractive index of the magnetic fluid, which is affected by the magnetic field. The experimental results indicate that the mode interference is sensitive to the magnetic field and different dips of the interference spectrum have different sensitivities. Hence, simultaneous measurement of the temperature and magnetic field can be achieved by simultaneously monitoring two different dips. The sensitivities of the magnetic field and temperature can reach up to 0.062 nm / Gs and 0.081 nm / ° C, respectively. The proposed Mach–Zehnder interference sensor has a more compact structure, simple manufacturing process, and high reliability, which would find potential applications in weak magnetic sensing fields.
FBG(fiber Bragg grating) strain sensor are widely applied in structure health monitoring, the temperature compensation problem is a key issue that impact the performance of the strain sensor, many kinds of temperature compensation method also have been put forward, but the compensation result get from these method can’t meet the engineering requirements very well, especially when the ambient temperature changes rapidly due to the sunshine, the wind, the rain or other factors, and these impact can’t avoid when monitoring an open-air structure project. Through engineering case and experiments test found that, the inaccurate compensation temperature is the key reason lead to test result error, and closer analysis could found that the temperature from strain sensitive FBG and temperature sensitive FBG have non synchronous phenomenon, and the error could be reach 1 degrees Celsius, so use the temperature from the same moment to compensate the strain calculation also can’t get accurate results. The author thinks that the temperature non synchronous phenomenon may be caused by the temperature sensitive FBG and strain sensitive FBG have different package structure or package material, also may be installed on different positions, because all of these factors may lead to inconsistent temperature response speed between the two FBG when the ambient temperature changed rapidly. In order to confirm this conclusion, designed a FBG strain sensor package structure, the temperature sensitive FBG and strain sensitive FBG are packaged in one and the same structure with special stress isolation mechanism. Through temperature chamber test and engineering simulation experiment verified that the compensation temperature error could be reduced to 0.1 degrees Celsius, this will greatly improve the accuracy of temperature compensation for the FBG strain sensor.
A demodulation method for a quasi-distributed sensor based on an original interrogating
system for concatenated low reflective Fiber Grating is proposed. The system is based on
Optical Frequency Domain Reflectometer technology for which a commercial device has
been extended to a wavelength-tunable device. This interrogation system has the
advantage of allowing a large number of gratings to be addressed simultaneously. In our
application, except of the first grating (it has 20 times higher reflective than others) all
other gratings have low reflective (about 0.5% and 1 nm bandwidth at 3 dB) and have a
Fiber Bragg Grating central wavelength of about 1535 nm. Compare to conventional
Optical Frequency Domain Reflectometer technology, this interrogating system has very
fast measurement capability and higher precision.
There are many vibration damages happen in the world, such as Pipeline broken, Historical Relics stolen,
even for the board destroy. With conventional vibration detection methods there is a gap between what you
believe is occurring along area and what is actually happening. This information gap can result a delay in
your discovering and locating broken. Based on the non-linear optical scattering theory, we have developed
a new fiber grating vibration-monitoring system. This new system overcomes the limitations of
measurement technologies available today, thus closing the monitoring gap and improving system integrity
Modern oil production in the oilfield management needs a sensor which enable fast, reliable and cost-effective through highly integrated optical measurement systems. A sensor for accurate and long-term fluid high pressure and temperature monitoring in oil down-hole based on optical fiber Bragg grating is presented. This sensor, using fiber Bragg grating written in side-hole single mode fiber, has small size and simple construct. At different temperature, the pressure measurements from atmospheric pressure to 40 Mpa has been made. It has very linear relationship between peak separation and pressure.