Development Of Frequency-modulated Continuous Wave Interference Optical Fiber Temperature Sensor Optical System

In this paper,an extrinsic fiber temperature sensor is developed based on Frequency modulated continuous wave(FMCW)interference.The temperature sensor consists of an optical system,a temperature probe,and a signal acquisition and processing system.The optical system uses an optical fiber Fabry-Perot(F-P)interferometer in which the signal light and the reference light are in the same optical path and the temperature probe is easy to manufacture,The temperature sensing probe uses a stainless-steel tube with a higher expansion coefficient and chemical stability as the F-P cavity,and uses a fiber collimator to couple the fiber to the F-P cavity.The FMCW interference is used to demodulate the cavity length variation caused by thermal expansion and contraction of the F-P cavity to realize temperature sensing.The signal acquisition and processing system takes the STM32F407 chip as the core,and combines the amplifying filter circuit to realize the DFB laser drive,signal acquisition and amplification,and phase discrimination of the digital cosine signal.Experiments show that the temperature sensing probe of the fiber temperature sensor is 200mm in length,the temperature measurement resolution reaches 0,0002?,and the temperature measurement sensitivity reaches 3.022?m/?.The optical fiber FMCW temperature sensor has high sensitivity and resolution,However,the interference signal obtained by the FMCW laser interference is a periodic cosine signal,only the relative temperature and continuity measurement can be realized.In the discontinuous measurement process,when the phase change of the interfering cosine signal exceeds one cycle,the number of cycles of the interference level will not be known.In response to this problem,this paper presents a new measurement method--Dual wavelength fractional comparison.The F-P cavity was measured simultaneously by two frequency-modulated continuous wave optical fiber temperature sensors with different central wavelengths of two light sources.Finally,the fractional parts of the interference level measured by the two-channel interferometer is used to calculate the number of cycles of the interference level.The sensor based on the dual wavelength fractional comparison method can not only achieve discontinuous measurement,but also maintain the accuracy of single-channel FMCW interferometry,which is of great significance for FMCW interferometry.