Theoretical And Experimental Study On High Power Photonics Crystal Fiber Amplifiers

Thanks to their high luminance, favorable radiation of heat, high conversion efficiency, high beam quality and compactness, photonic crystal fiber based amplifiers/lasers have been extensively researched. Photonic crystal fiber has a relatively bigger inner cladding numerical aperture, larger model area and endless single mode area, so the fiber amplifier based on photonic crystal fiber has important investigation value and great application potential in the high power laser field. In this paper, the amplification characteristics of the high power Yb³⁺-doped photonic crystal fiber amplifiers were investigated theoretically and experimentally. The research contents mainly include:1. Based on the time-independent steady-state rate equations for fiber amplifiers, the analytical expression between the output characteristics and parameters of the fiber amplifier is obtained. The output characteristics of Yb³⁺ -doped double cladding fiber amplifier are numerically investigated. Meanwhile, the influence of the amplifier parameters to the output characteristics, such as fiber length, the reflection of end face, doped concentration, the pump way, was also analyzed.2. Based on the thermal distribution functions for fiber amplifier, the temperature distribution in the gain fiber of double cladding fiber amplifier was simulated. The factors which impact the thermal effect were analyzed. Meanwhile the relationship between the nonlinear effects and temperature distribution in the gain fiber is also simulated, because the generation of nonlinear effects in the fiber is directly related to the temperature distribution.3. The gain characterization of fiber amplifier which is based on Yb³⁺-doped large modal area photonic crystal fiber and high power semiconductor laser diodes is experimentally studied. A home-made oscillator was used as a seed source, and the corresponding wavelength was 1064 nm. The Yb³⁺-doped large modal area photonic crystal fiber was adopted as gain medium. The gain characters for different pumping technique and different pumping powers are obtained experimentally. When the power of the probe light is 8 W and the pump power is 150.2 W, the output power, up to 72 W, has been achieved eventually using the double-side pumping technique. Using the reverse pumping technique, when the power of the probe light is 6 W and the pump power is 160 W, the output power, up to 104 W, has been achieved eventually.