Study On Fiber Grating Based Fiber Lasers, Filters And Tilted Fiber Gratings

The fiber phase grating is an important candidate in fiber technology,and has found many useful applications in fiber communication and fiber sensing.Under the supports of national 863 high technology program and national nature science foundation,this thesis is devoted to the detailed theoretical and experimental researches on fiber gratings and fiber grating based devices,mainly including proposing and optimizing the structures of fiber lasers and filters,deeply investigating the characteristics of tilted fiber gratings.And the main achievements of this thesis are listed as follows:1.A novel all fiber two-cavity Fabry-Perot configuration based on fiber Bragg gratings is proposed.The design guidelines of the cavity structure are presented to realize the single mode operation at the center wavelength of the fiber grating.The fabrication error tolerances of the structures,including inaccurate cavity lengths and index modulations of fiber gratings,are calculated and discussed,providing the principles for the design of short linear-cavity fiber laser and narrow-band filters in ring cavity fiber laser.2.A single-longitudinal-mode erbium-doped linear-type fiber laser is proposed and experimentally realized,which consists of three fiber Bragg gratings directly written in a piece of photosensitive erbium-doped fiber.The laser has no intra-cavity fusion splices,and the linewidth of less than 5-kHz is acquired.3.A switchable dual-wavelength erbium-doped fiber laser is proposed and experimentally demonstrated,which is constructed by a polarization-maintaining fiber Sagnac loop mirror and two fiber gratings with different wavelengths. Wavelength switching operation was achieved by properly adjusting the polarization controller in the polarization-maintaining fiber Sagnac loop mirror. Stable single- or dual-wavelength lasing output can be realized.4.An all fiber multi-cavity configuration based on fiber Bragg gratings is proposed and used as a filter,in order to improve the filtering performance of the single-cavity structures such as flatness of the top and steepness at the edge of transmission peak.The characteristics of the transmission spectra for the configuration are analyzed and modeled in detail.The results show that the steepness of the peak slope can be improved by increase of fiber grating reflectivites,and required band-width of the peak can be obtained by adjusting the cavity lengths in different applications.The comparison of the transmission peaks of four-cavity,two-cavity,and single-cavity structures demonstrates the improved performance of filters.5.A simplified model for refective tilted fiber gratings of uniform periods is presented to investigate the spectral characteristics,on the basis of the coupled-mode theory.Explicit expressions are derived for the spectral parameters of reflection and transmission loss spectra,including wavelength related reflectivity, maximum reflectivity,peak-reflection wavelength and transmission loss,among which the expression of transmission loss is derived for the first time.Numerical simulations are carried on to show the dependences of grating spectral responses on the structural parameters,such as tilt angle,grating length,index modulation amplitude and polarization states,and qualitative explanations of the spectral behaviors are presented.6.Based on the coupled-mode theory and Mueller matrix method,the polarization properties of tilted fiber gratings are analyzed quantitatively for the first time.The explicit expression of wavelength-dependent polarization-dependent loss for tilted fiber gratings is derived.The polarization capability of tilted fiber gratings with different tilt angles are compared by simulating the corresponding polarization-dependent loss.