Research On Temperature Sensing Characteristics Based On Brillouin Scattering Effect

Temperature monitoring is critical in many engineering fields of today's society.And many engineering fields need to work in extremely harsh environment such as strong electromagnetic radiation,strong corrosiveness,high temperature,humidity and so on.In such environment,it is difficult to guarantee long-term effective work for the traditional electrical temperature sensors,which limits its application.Optical fiber temperature sensors use optical fiber as the transmission medium for sensing signal,and fiber's main component is silicon dioxide which has some good chemical and physical properties,such as anti-electromagnetic interference,corrosion resistance,high temperature resistance and so on.In addition,its light and flexible mechanical properties enable it to be embedded in various engineering structures and composite materials.Therefore,researchers all over the world have devoted a lot of researches on optical fiber temperature sensor,and has obtained many important research achievements.Among many optical fiber temperature sensors,the point or quasi-distributed temperature sensors based on fiber grating,and distributed optical fiber temperature sensors based on the optical scattering effects have been developing rapidly and widely used.Both sensors can achieve high resolution,high measurement precision,high sensitivity and other excellent sensing performances.However,the signal processing process is very complicated,making the cost of such sensors generally higher.The optical fiber temperature sensors based on laser beat frequency technology only needs to demodulate the frequency of the sensing signal in signal processing,which simplifies signal processing and makes the cost cheaper.Multiwavelength laser output by multiwavelength fiber laser based on Brillouin scattering has stable Brillouin frequency shift interval,therefore,the stable laser beat frequency signal can be obtained by combining it with the laser beat frequency technology,which can accurately reflect the information of the environmental temperature.And the beat frequency signal generated by high order scattered light has higher temperature sensing sensitivity,therefore,the study of optical fiber temperature sensor based on Brillouin scattering multi-wavelength optical fiber laser combined with laser beat frequency technology is of certain significance.In this paper,the temperature sensing experiment based on a simple structure of multi-wavelength optical fiber laser with double Brillouin frequency shift interval combined with laser beat frequency technology has been studied.The experimental results obtained are as follows:1.The experimental scheme is simpler in the similar schemes.It has more temperature sensing signals of 9 sets beat frequency microwave sensing signals,and higher temperature sensing sensitivity of 19.93MHz/°C by using the 18^th order stokes light pair to generate the beat frequency signal,the temperature measurement error is±0.125°C.2.The experimental scheme of moving the sensing signal to the high frequency region to avoid the noise interference near the zero frequency position meanwhile retaining the sensitivity of the sensing signal is proposed and verified for the first time.By using two kinds of gain fiber in the system structure,two beams of second-order Brillouin Stokes light output from two kinds of fiber respectively are used to obtain a beat frequency microwave signal with a frequency turning out to be1.625 GHz,and the temperature sensing experiment is made based on the signal,thus,realizing the shift of the sensing signal to the high frequency position and improving the signal-to-noise ratio of the signal,therefore,it is more conductive to terminal demodulation.