The hottest high-resolution optical fiber sensor c

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High resolution optical fiber sensors come out with a resolution of one centimeter

in order to repair aging infrastructure and monitor existing bridges, dams and other large buildings, distributed optical fiber sensors need a new light source to monitor the stress and temperature changes borne by buildings. However, this common optical fiber sensor, an optical phenomenon based on stimulated Brillouin scattering (SBS), is limited by the insurmountable spatial range and resolution

researchers in Spain and Switzerland have solved these difficulties. They have developed a method that can detect temperature or stress changes of one millionth of a millionth in a short time with a centimeter level spatial resolution within a range of 10 kilometers. The team believes that the high resolution of the scheme enables it to find a place in the biomedical environment with long-distance infrastructure monitoring and more precise flame retardant rating of UL 94 V if the fixture is divided by structure -0

signal distortion

sbs optical fiber sensor sends a pulse laser signal, that is, a pump pulse, which propagates through a certain length of optical fiber and meets the back-propagation continuous wave (CW) probe laser beam. (in fact, in order to prevent some systematic errors, these systems usually use two CW probe waves and distinguish the two trains of waves with the modulation frequency related to the material characteristics of the optical fiber, that is, the so-called double sideband method.) Stimulated Brillouin scattering (SBS), inelastic Stokes and anti Stokes scattering are produced by the nonlinear interaction between the pump pulse and the optical fiber. This scattering will change the frequency distribution of the pulse optical signal. This so-called Brillouin frequency shift depends on the interactive, interesting and open way to show industry insiders the material properties of optical fibers that bring infinite flexibility to industry innovation as "partners of technical cooperation" with stress and temperature; Therefore, the changes of those parameters along the fiber length can be detected by analyzing the Brillouin frequency shift

although optical fiber sensing based on SBS has found its place in the construction of various infrastructures, it still has some problems. One of the problems is the limited scope of monitoring. Recent analysis shows that the power required by the probe with a span of several kilometers (as well as the stress and temperature changes on the optical fiber) may distort the pump pulse signal, seriously affecting the accurate detection of Brillouin frequency shift

another problem is the limited spatial resolution. Because SBS depends on the nonlinear interaction between light and matter to produce sound waves, there is a small but obvious time lag in spatial resolution in time domain technology. Other technologies in the frequency and correlation domain can make up for the shortcomings of SBS, but it takes longer - it takes about an hour or more to measure onemillion points distributed along the fiber

about scanning problems

the joint research team of Spain and Switzerland, as well as scientists from the University of Alcala in Spain and the Federal Institute of Technology (EPFL) in Lausanne, Switzerland, seem to have found ways to solve these problems. Through in-depth study of the actual details of signal scanning, they obtained the Brillouin frequency shift related to stress or temperature changes

in most time-domain SBS based optical fiber sensing schemes, the frequency shift is determined by symmetrically scanning the offset of the two sideband detection beams relative to the fixed pump pulse frequency. However, it has been proved that this scanning method is the main source of pulse distortion at high probe power. This is because it is difficult to quantify the asymmetric energy transfer between the two probe sidebands and pump pulses - an effect that increases with the increase of probe power

the joint research team found that by changing the scanning method, the sideband detection beam maintains a fixed frequency difference (related to the Stokes and anti Stokes frequencies of the optical fiber), and scans the input pump beam with the related frequency - which can significantly reduce the signal distortion. This method means that the upper limit of detection beam power becomes higher, and the span of optical fiber sensing system becomes longer. In addition, by eliminating the signal distortion in the pump pulse, the system also has a higher spatial resolution

the resolution can reach one centimeter

researchers used differential pulse width pairs and Brillouin optical time domain analysis (dpp-botda) experiments to test 10 km long single-mode fibers. They found that this method can detect the Brillouin frequency shift of onemillion points distributed along the optical fiber, with a resolution of up to one centimeter, and can detect three centimeter "hot spots" at the far end of the optical fiber. Moreover, since the system remains in the time domain, this method can realize these functions in 20 minutes, which is far less than the time spent in using the frequency correlation domain method

the research team believes that in addition to the application in infrastructure, this technology can also be used in other fields. Alejandro Dominguez Lopez of the University of Alcala said, "because we have such a large density of monitoring points, sensors can also be used in fields such as avionics and aerospace to monitor every inch of aircraft wings." Researchers also believe that the higher resolution of the system may promote the development of some biomedical applications, such as the detection of temperature deviation in breast cancer

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