Research On The Application Of Optical Fiber Sensor Based On Self-injection Locking Technology

Fiber optic sensing technology has good development potential in military,electric power,structure monitoring and civil engineering,especially fiber Bragg grating sensing technology,which has the advantages of fast response speed and wide measurement range.The corresponding demodulation technique is used to demodulate the center wavelength of fiber Bragg grating(FBG),the drift of wavelength is obtained accurately,and the corresponding sensing parameters are demodulated.In this paper,the fiber sensing technology based on the self-injection locking technique of fiber laser is proposed.The output laser of the laser is locked at the reflection wavelength of the sensing grating by using the self-injection locking method,and the chirped grating has good large dispersion performance.The length of the laser resonator changes with the wavelength of the laser,and the sensing demodulation is realized by measuring the wavelength of the laser by laser beat frequency.Using beat frequency as measured data can not only simplify the demodulation system,but also reduce the cost of the system.Generally,most of the fiber grating sensors are used as part of the laser resonator directly,in the experimental system which uses the laser beat frequency technology to realize the sensing measurement.With the constant change of sensing distance in practical application,the measuring device with fiber laser structure can not fix the exact length of its own resonator,so it is difficult to stabilize the frequency band of laser beat frequency measurement,which brings difficulties to the practical fast sensing measurement.Especially in long range sensing,the relative cavity length decreases and the sensitivity decreases with the increase of laser cavity length.Therefore,we introduce the self-injection locking technique to fix the demodulation unit in this paper,so that the demodulation frequency range is fixed in the corresponding frequency band to ensure the sensitivity of the system.The sensing distance of the system is no longer limited by the specific cavity length.In the experimental design of optical fiber sensing based on self-injection locking,the experimental structure is divided into two parts: demodulation part and sensing part.The general principle of grating sensing is explained,and the best observation frequency is obtained by theoretical analysis in this paper.The self-injection locking method is used to lock the working wavelength of the laser.The variation of the working wavelength of the laser will be changed into the length of the cavity of the laser under the action of the dispersion characteristic of the chirped grating.The actual wavelength change of the sensing grating can be obtained by measuring the laser beat frequency,and then the grating sensing demodulation can be realized.In this paper,the temperature sensing scheme is used to measure the temperature.In the range of 23.8?-65.8?,the temperature of the sensor is changed step by step.The measuring steps and process of temperature parameters are described in detail.The measured temperature change curve is drawn by software,and the linear curve relation between beat frequency and temperature is obtained,and the influence of error in all aspects is analyzed synthetically.