The Research Of Yb Doped Double-Cladding Photonic Crystal Fiber For High Power Amplifier

Compared to the ordinary step-index optical fiber, the photonic crystal fiber has originality which lies in that the micron or even nanometer micro structure has been introduced into the design of fiber section, relying on that micro structure has characteristics which are different from the general homogeneous materials' dispersion and band characteristics, the photonic crystal fiber has some unique light guiding performances that are different from the traditional optical fiber, such as single mode operation during the full-wave band, large mode field area and dispersion characteristics. And photonic crystal fibers have many parameters can be adjusted flexibly, which make a significant contribution to increase the degree of freedom during the designing. So in recent years, photonic crystal fiber(PCF) is applied more and more widely, especially in the field of fiber lasers, due to its large mode field characteristics, which makes it be able to support high power without an optical damage, and to ensure good beam quality meanwhile. This paper is based on the index guiding photonic crystal fibers,and then do a design that the fiber core is doped with ytterbium ions and introduce air holes in outer cladding to make a kind of fiber for high power fiber lasers which is called Yb doped double-clad Photonic Crystal Fiber, then we will do a series of research of its characteristics, the research details go as follows:(1) Use the Comsol software which is based on finite element method to analyze the infulences that the air hole size, interval and number of layers will make on the characteristics of index guiding photonic crystal fibers,such as effective refractive index, the area of fundmental mode and the confinement losses.(2) Use the Comsol software to do numerical simulation for Yb doped double cladding photonic crystal fibers, to find the single mode operation conditions and analyze what infulences will the refractive index and the raduis of Yb doped area make on the characteristics of fundamental mode, such as mode field diameter, meanwhile to analyze what changes will the numerical aperture of the clad take while the clad air hole size varies. And then discuss the bending and polarization maintaining characterics.(3) Do theoretical analysis for the Yb doped double cladding photonic crystal lasers, the pump method we use is pumping forward, then use Matlab to model the laser, basing on the rate energy equation of Yb ion, to calculate the fiber absorption coefficient, slope efficiency and optimum length under a certain doping concentration.(4) Use the existing conditions to do experiment rearches for Yb doped double cladding photonic crystal fibers, constructing laser platform to test the fiber's absorption coefficient, slop efficiency and optimum length.After a series of studies, a kind of Yb doped double cladding photonic crystal fiber that keeps single-mode operation in full-wave band has been designed, the mode field diameter at 1.06 um can reach up to 19.3 um, and the experiment shows that its slope efficient reaches 81%, the cladding absorption coefficient reaches 2.7 dB per meter.