中文说明：在前面1维FDTD的基础上给出了2维的FDTD程序。可以帮助我们解决比如波导，光纤中的电磁场计算问题。尤其是给出了边界条件的设置方法。
English Description：
Based on the previous 1-D FDTD, a 2-D FDTD program is given. It can help us to solve the electromagnetic field calculation problems in waveguides and optical fibers. In particular, the setting method of boundary conditions is given.