Intensity Demodulation Fiber Bragg Grating Laser Senso

This paper builds a ring-cavity laser using Fiber Bragg Grating（FBG）as a filter and introduces a conical structure as the sensitive element of the sensor.By demodulating the intensity variation of the output laser,refractive index（RI）and curvature are measured,and the interference of temperature to the sensor is explored.The main contents are as follows:（1）Explored the composition and working principles of the fiber Bragg laser,described the basic principles of FBG,including the transmission characteristics of FBG and its sensing characteristics under temperature variation,axial stress and radial strain;analyzed the characteristics of the chirped wave and the intensity demodulation principle.（2）Built a single-grating fiber optic laser sensor,compared and analyzed the output differences of the laser under different central wavelengths of the fiber Bragg gratings.Then introduced the conical auxiliary structure to test the temperature and RI sensitivities of the sensor under passive and active conditions.The results showed that the spectrum showed consistent red shift characteristics under passive and active conditions,and the temperature sensitivities were 12.24 pm/℃and 12.36 pm/℃,respectively.When the conical diameter was the same,the RI sensitivity of the active structure was significantly higher than that of the passive structure.In the radial strain test,the sensitivities under passive and active conditions were-2.2 d B/m^-1and-0.674d B/m^-1,respectively,and the sensitivity was inversely proportional to the diameter of the conical.（3）A cascaded fiber grating with different center wavelengths was used to achieve dual-wavelength laser output,and the characteristics of bending sensors were tested.Due to the mode competition relation,the outputs of the two lasers appeared reverse variation features with the curvature changes,and the sensitivity is related to the wavelength spacing.The experimental results showed that,when the center wavelengths of the FBGs were 1558.82 nm and 1543.15 nm,the maximum curvature sensitivity was-2.045 d B/m^-1 and 6.15 d B/m^-1,respectively.In addition,a tapered structure was prepared and tested for arm bending state monitoring,which could detect the frequency and position of the arm bending,and was suitable for state detection of moving objects such as arms.