Spectral Characteristics And Sensing Characteristics Investigation Of The Long-period Fiber Grating

Because long-period fiber grating(LPFG)has very long period ,usually is dozen ofμm toseveral hundredμm. And the mode coupling is met by the core mode and cladding modes in thesame direction. So its resonance wavelength and loss peak are all very sensitive to externalenvironmental changes. And LPFG has higher sensitivity than FBG, which of this determines theLPFG have wider application prospects in the optical communications field.First, the spectral characteristic of single LPFG is analyzed by coupled-mode theory. Then, theinfluence on the DC and AC coupling ratio of LPFG when modulation depth changed are analyzed .Also the spectral of LPFG at difference coupling strength are analyzed. Finally, the normalizedwavelength and bandwidth with the change of wavelength are got.Second, uniform and non-uniform cascaded long-period grating are analyzed by transfermatrix method. For two uniform cascaded grating, the two grating spacing, phase shift and thelength of the two gratings are researched. And also the phase shift and sampling grating arediscussed too. For cascaded phase shift grating, the ordinary phase shift, number ofπphase shiftand phase shift increments is discussed. Sampled grating can be well applied to the WDM channelisolator. Afterwards, number of long-period grating cascaded is researched.Finally, the LPFG sensing mechanism is described and discussed the characteristics oftemperature and stress sensors.The results show that the spectral of cascaded long period fiber grating is rich and easy tocontrol and can be well applied to DWDM systems, WDM channel isolation and comb filter and soon. The sensing characteristic of long period grating is also more prominent. And LPFG will havegood application in the sensing field.