Studying For Online Writing FBG On The Drawing Optical Fiber

Fiber Bragg grating (FBG) is a photonic device appeared in the late1970s.Using a UV laser to irradiate the optical fiber though a phase mask, due to thephotosensitivity, the refractive index of fiber core will change periodically along thefiber to form a spatial phase grating. A function of FBG is to form a narrow-bandreflector, by which, FBGs may be made into optical fiber temperature sensors,optical fiber strain/stress sensors, optical fiber displacement sensors, optical fibervibration sensors, and so on.By connecting a certain number of FBGs in series along an optical fiber to formthe sensing network and using wavelength division multiplexing, the FBGs may beused to the large engineering monitoring. But this method will bring great loss andweak tensile strength due to the many welded joins along the fiber. By comparison,the online writing weak FBG sensor array on the drawing optical fiber has attractedmany attentions in the large engineer monitoring because of its low cost, lowcrosstalk and strong multiplexing capacity. In this paper, the main work is asfollows:Conclude the photosensitivity, attenuation and dispersion characteristics of theoptical fiber; introduce the effects of the material composition, the geometricstructure and bending of the optical fiber on the photosensitive, the attenuation anddispersion characteristics of the fiber.For the optical fiber in the drawing process, establish the vibration model of theaxial moving fiber, and the coupled nonlinear equations of transverse vibration andlongitudinal vibration; Study the transverse vibration law of the optical fiber in thespecial case of axial velocity is zero. Deduce the index refractive fluctuation alongthe optical fiber produced by its longitudinal vibration.Based on the coupled-mode equations of fiber Bragg gratings undergoingnonlinear strain and, use numerical simulation method to investigate the effects ofnonlinear strain on the reflection spectrum of fiber Bragg grating, and obtain thedependence relationship of the wavelength shift, full width at half high and themaximum intensity upon strain gradient.To improve the wavelength consistency of all FBGs in the optical grating array, propose a measurement method based on the FBG group and end reflection rate, the first isto measure the total reflection rate of weak grating group, then calculate the reflection rate ofsingle FBG. Finish the aging training of the FBGs array in ordinary single-mode fiber to finda suitable aging condition and ensure the FBGs array has long-term stability andrepeatability in the engineering application.