| Because of the excellent characteristics, such as natural compatibility with fiber, fine reflectivity performance, low insertion loss, small volume, low cost and high sensitivity to the changes of environmental temperature, stress and strain, etc, fiber gratings have been and will be used in fiber communication and fiber sensing domain extensively. With the rapid development of Tri-Networks Integration and All-Optical Network, fiber grating will play a more and more important role in these areas.Firstly, this article studies several special spectral fiber gratings such as sampled fiber Bragg grating, phase-shifted fiber Bragg grating, triangular fiber Bragg grating, and tiled fiber Bragg grating using the couple mode theory, transfer matrix method, and discrete layer peeling. Among of them, the multi-channel grating filters are designed and analyzed in a focused manner and two main results are listed as following.(1) Design a new kind of Sinc-sampled fiber Bragg grating which is fabricated in the high birefringence fiber. The sampled grating has two sets of reflection spectra along two perpendicularly polarization directions. The grating's channel number can be doubled by approximately designing the refractive index difference between the fast and slow axes of the fiber, which enhances the utilization ratio and reduces the claim for photosensitivity of the fiber. The group delay characteristics are theoretically studied and side-lobes are depressed by apodization technique in order to get optimized spectra. The results show that the comb-like spectra of the grating enable it have promising applications in both multi-wavelength polarized fiber laser and fiber sensing network.(2) The discrete layer-peeling method for designing multi-channel fiber Bragg grating is optimized. In the new method, after inserting different phase changes at different channels, the coupling coefficients is then fitted by Gaussian function to get a lower and more smooth refractive index modulation. The simulation results show that a 8-channel fiber Bragg grating is successfully designed by using the new method with the maximum refractive index modulation of 0.0005, much lower than that of traditional DLP method (0.0013), which decreases the requirement of fiber's optical sensitivity. Meanwhile, the difficulty of inscribing a fiber grating is reduced by smoothing the refractive index modulation. Secondly, the application of GratingMOD module of Rsoft software in analyzing and synthesizing fiber gratings is introduced. By using the GratingMOD, fiber Bragg grating, rectangular-sampled fiber grating, 8-channel sampled fiber grating and triangular fiber grating are simulated. The relevant results are compared to those by the MATLAB method. And the results show that the software can deal with the grating filter's design problems conveniently and rapidly.Lastly, a wavelength switchable linear polarization Yb-doped double clad fiber laser is proposed, in which the resonant cavity is composed of a polarization-maintaining fiber Bragg grating as the lower reflective mirror and a chirped fiber grating as the higher reflective mirror. A 8-meter single mode polarization maintaining double clad Yb-doped fiber is used as the gain material. Two lasting wavelength of laser at 1070.08 nm and 1070.39 nm are realized and the two wavelength can be switched by changing the polarization state of the cavity. The other characteristics of the laser, such as power of 1 W, extinction ratio of 48 dB, slope efficiency of 52% and FWHM of 0.022 nm, are tested. The polarization characteristics are studied by a Glan-Thompson-type prism polarizers. |
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