Fiber Grating Temperature And Stress Sensing System Based On Scanning Laser Source

Optical fiber sensor becomes promising with the development of optical fiber and devices. Compared to traditional electric sensing technology, optical fiber sensing technology has much more advantages. As the manufacturing process of fiber bragg grating (FBG) gets more and more mature, fiber grating plays a very essential role in the sensing field and shows vast development potential. Based on the above background, we conduct a research on temperature and strain characterization of fiber bragg grating sensor.The fiber grating coupled-mode theory is introduced. Then on this basis, the spectral property analytical expressions of FBG and LPG (Long Period Grating) are obtained with boundary conditions taken into account. In addition, strain and temperature sensing properties of fiber bragg grating are analyzed and photosensitivity mechanism of optical fiber is stated.A fiber grating temperature and strain sensing system using a scanning laser is proposed and developed. In the system, an oscilloscope instead of a spectrograph is used to detect the reflection spectra of FBG. Several gratings are also used in the system for quasi-distributed sensing, among which the first grating is for reference while the others are for sensing. With the system:(1) FBG temperature properties in the water and in the air are studied individually. And experimental results reveal that FBG wavelength moves towards long wave region when temperature rises and vise versa. Furthermore, the wavelength shift is basically linear to the temperature change. And the slope when gratings are in the water is different from that in the air. (2) FBG stress and strain properties are investigated. And experimental results show that FBG wavelength moves towards long wave region when stress increases. And the wavelength shift keeps linear relationship with the change of stress. Relationship between FBG wavelength shift and strain is further calculated. (3) Higher accuracy is achieved by using an oscilloscope to detect the reflection spectra of FBG than using a spectrograph.