Research On The Dual-Period Fiber Grating

The fiber grating that used in fiber grating sensors mainly include Short-Period Fiber Grating(SPFG) and Long-Period Fiber Grating(LPFG). The grating called Short-Period Grating is ordinary equi-period Bragg grating(FBG). The Short-Period Grating has been utilized widely in sensing field, for its good sensing properties and mature demodulation technology. The Long-Period Grating has developed later than the Short-Period Grating, and has not utilized widely. But Long-Period Grating has its unique sensing properties, such as quite sensitive properties of strain, temperature and birefringence, sensitive to exterior medium. Because Long-Period Grating has those properties, more and more people paid their attention to the sensors based on it.The LPFG and SPFG are written in the same position of the fiber, and the new grating has the characteristics of the LPFG and SPFG. We called it as dual-period fiber grating (DPFG). The signal of the SPFG and the LPFG do not interfere each other. At the reflected end of the fiber, the signal of the SPFG can be detected only. But at the transmission end of the fiber, the signal of the both gratings can be detected. The transmission spectrum of the SPFG do not effect the measurement of the transmission spectrum of the LPFG. The paper researched the fabrication and the sensing properties of the DPFG, and discussed three application of the DPFG based on above research:1. the simultaneous measurement for the temperature and axial strain,2.the simultaneous measurement for multi-axial strain,3. the multiple wavelength techniques of encoding which based on DPFG.And the paper researched from theories and experiments on theabove three aspects.The contributions of this paper are:1.To research the fabrication of the DPFG,2. To analyse the sensing properties of the DPFG from theory,3. To research simultaneous measurement for the temperature and axial strain based on the DPFG,4. To research simultaneous measurement for multi-axial strain based on the DPFG,5. To research multiple wavelength techniques of encoding based on the DPFG.