Filtering Characteristics of Coated Phase Shifted Long-Period Fiber Grating

The filtering characteristics of coated phase-shifted long-period fiber grating (LPFG) is analyzed by the coupled- mode theory together with the transfer matrix method. The effects of introducing single and multiple phase shifts at various locations along a LPFG are analyzed, and the influences of the film parameters on the spectral characteristics are also studied. It is shown that the number, location and value of the phase shifts will affect the LPFG filtering characteristics. The loss peak of transmission spectrum decreases with the increase of film thickness, and the peak position shifts with the film refractive index. Compared with the non-coated phase-shifted LPFG, the coated phase-shifted LPFG not only has the similar desirable filtering characteristics, but also has a flexible adjustment ability to transmission properties.