Sensitivity Enhanced Sensing With Fast/Slow Light In Fiber Bragg Gratings

Fiber Bragg gratings(FBGs)has been attracted much attention in the field of fiber communication systems,fiber lasers,and fiber sensors by researchers owing to its some advantages such as simple structure,high measurement accuracy,ease of multiplexing and integration,distributed sensing and so on.In the field of fiber sensors,FBG sensors based on optical fiber Mach-Zehnder(M-Z)interferometer detection method achieved high-sensitivity strain measurement.However,the sensitivity of the sensor is limited by interferometer arm length difference.At the same time,the research shows that the sensitivity of the interferometer can be improved with fast/slow light in fibers.According to the special performance in fiber sensing field of FBG and fast/slow light technology application in the field of high-precision sensing.The paper presents a scheme of sensitivity enhanced fiber sensor with fast/slow light in FBGs.In experiment,based on the Michelson's interferometer,a sensing system with slow light in a uniform FBG was established.First of all,the correspondence between the phase shift sensitivity of the sensor and the group delay was studied by vary the wavelength of incident light.Comparing the measured phase change of the signal light and the delay of the theoretical group with the curve of the wavelength,we concluded that the phase-shift sensitivity of the sensor has a good correlation with the group delay.Compared with the traditional FBG sensor,the sensitivity of the sensor will be enhanced.Secondly,on the basis of the above experiments,the active uniform FBG was introduced into the interferometer,and the relationship between the phase shift sensitivity of the sensor and the group delay was studied by vary the pump light power.The same conclusion was drawn.The development of this experiment will lay the foundation for the experimental research of fast and slow light sensing of double-Lorentzian fiber Bragg grating(DL-FBG)with high sensitivity.In theory,we analyzed the fast/slow light in a DL-FBG in detail.A sensing model of high sensitivity fiber sensor using DL-FBG was established.We inserted DL-FBG into the Michelson's interferometric fiber sensor.High sensitivity sensing could be achieved by constructing a push-pull configuration which introduced fast and slow light in the two arms of the interferometer,respectively.The relation among the sensitivity of sensor,signal light group delay and grating reflectivity was deduced.In addition,we will use active FBG fast/slow light to further improve the sensitivity.