Optimization the coupling coefficient of large mode area PCF using 2D FDTD method

The 2D FDTD method is used to design a tapered photonic crystal fiber, where large mode area is prominently coupled to optical fiber. For the first time, we observed that the mode area is stabilized with respect to possible fabrication tolerance by implementing a secondary surrounding waveguide with configuration of large air holes in the outer ring. The mode field area can be obtained in tapered region using a full vectorial H field technique. Beside these, the coupling coefficient can be optimizing by using least square boundary residual technique.