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A simple single-polarization single-mode (SPSM) photonic crystal fiber (PCF) coupler with two cores is introduced. The full-vector finite-element method (FEM) is applied to analyze the modal interference phenomenon of the even and odd modes of two orthogonal polarizations and the power propagation within the two cores. Meanwhile, the SPSM coupling wavelength range and its corresponding coupling length for different structure parameters are numerically analyzed. The numerical results show that SPSM coupling can be realized with a broad range of wavelength, and the coupling length can be of millimeter magnitude. Moreover, the SPSM coupling wavelength range and the coupling length can be optimized by designing proper mirco-structure parameters of the coupler.

Based on the special structure of high-power Yb3+-doped double-clad fiber lasers, a heat dissipation model and the corresponding steady-state heat equations with consideration of both convective and radiative heat transfer are constructed. The temperature distributions along the radial and axial directions of the fiber for forward pump of 1000 W and two-end pump of 500 W each side are calculated numerically by using the steady-state rate equations and the heat equations. The results show that the temperature distribution for two-end pump mode is more even than that for forward pump mode and the maximum temperature in the fiber decreases by 139.8°C. Finally, a comparison between the temperature distributions with and without consideration of radiative heat transfer is performed, the results of which indicate that radiative heat transfer plays an important role in heat dissipation of high-power fiber lasers. Therefore, radiative heat transfer has to be considered in the thermal, stress, and thermo-optic eff...