Research On Seven-Core And Bandgap Yb-Doped Photonic Crystal Fiber

High-power lasers have wide application prospects in laser cutting, laser welding and laser weapons and other areas, governments are increasingly attach importance to the development of high-power lasers. Due to the area of fiber core, nonlinear effects and other factors, output power of single-core fiber laser is limited. Because photonic crystal fiber (PCF) can be while maintaining a large mode field area and single-mode transmission, but also easy to implement multi-core arrangement, is expected to be high power and high beam quality laser output. Seven cores and band gap Yb-doped PCF conducted the following studies in this article.Firstly, According to characteristics of the seven-core PCF's supermode intensity distribution, give a calculation method of the coupling length of the seven-core PCF, revealing the intrinsic link between supermode of seven-core PCF and coupling characteristics. To use of finite difference beam propagation method (FD-BPM) analysis of the coupling characteristics of seven-core PCF, Also analyzed the impact of horizontal nonuniformity,vertical nonuniformity and position deviation of seven-core PCF on coupling characteristics, for design of the structure of the seven-core Yb-doped PCF provides a theoretical basis.Secondly, To raise output power of the seven-core Yb-doped PCF laser, the effective strength mode area of seven-core Yb-doped PCF must be increased, and need strong coupling among cores to ensure that the same phase output. Through continuous optimization of the structural parameters of seven-core photonic crystal fiber, a seven-core Yb-doped PCF with large outer layer air holes and small inner layer air holes was designed, its mode area as high as 3 703μm2 and coupling length is 13 310μm.Finally, bandgap PCF with Yb-doped cladding was simulated by Plane Wave Method (PWM). Through analyzing the impact of structural parameters on band-gap position and characteristics, we design a bandgap PCF with a band-gap in the vicinity of 976 nm, provides a new approach for improving pumping efficiency.