如上图所示，定向耦合器由完全相同的直波导与弯曲波导构成，波

导芯为宽高比相同（均为 a） 的正方形， 其工作波长，波导材料

对 TE 模式的折射率，及圆弧形弯曲波导的半径 r 等参数如图所

示，若波长为 1550 nm， 归一化光功率为 1 的光波从直波导输

入，请选择适当的满足单模工作的波导宽度 a， 然后给出从圆形弯

曲波导输出的归一化光功率 P4与两波导边缘的间距 d-Directional coupler by the same straight and curved waveguides constituting the waveguide, waves

Conducting core is the same aspect ratio (are a) square, its operating wavelength, the waveguide material

The refractive index of the TE mode and the arc-shaped curved waveguide of radius r and other parameters as shown

Shown, if the wavelength of 1550 nm, normalized optical power　a light straight waveguide input

In,　the appropriate work to meet the single-mode waveguide width a, and then is given　a circular bend

Curved waveguide output normalized optical power P4 and two edges of the waveguide spacing d