Research on the Theory of Nonlinear Directional Coupler and its Application to Optical Devices

1.作为非线性光波导数值计算的有力工具，我们提出了基于有限差分格式的正交配置法和光束传播法。实际应用表明，这些方法对于分析NLDC.2是非常有效的。发展了一种基于奇异微扰技术的严格耦合模理论。结果表明，只包含线性耦合系数和非线性自相位调制系数的耦合模方程可以较好地描述不同NLDC结构中功率传输的整体特征。对于平面NLDC结构，给出了这两个系数的闭合形式。给出了对称平面NLDC中光开关的耦合长度和临界功率。提出了一种新型的非对称非对称NLDC结构，它由一个公共的线性包层隔开一个非线性波导和一个线性波导组成。结果表明，通过适当设置输入和输出端，所提出的NLDC可用于构建功率带通滤波器、功率带阻滤波器和光脉冲调制器。分析了由三个平行的非线性波导组成的NLDC的功率传输特性。结果表明，光开关的输入/输出特性优于传统的NLDC.6。讨论了光波在具有表面波纹的非线性波导中的传播特性，为研制波长选择性NLDC结构奠定了基础。

1. As the powerful numerical approches for the nonlinear optical waveguides, we have proposed the orthogonal collocation method and the beam propagatin method based on the finite difference scheme. It was shown from the practical applications that those methods are very effective for the analysis of NLDC.2. A rigorous coupled-mode theory based on the singular perturbation technique has been developed. It was shown that the global features of power transfer along various NLDC structures can be reasonably described by the coupled-mode equations which include only the linear coupling coefficient and the nonlinear self-phase modulation coefficient. The closed forms of those two coefficients were derived for the planar NLDC structure.3. The coupling length and the critical powers for optical switching in a symmetric planar NLDC has veen brought out.4. A novel asymmetric NLDC structure has been proposed, which consists of a nonlinear waveguide and a linear waveguide separated by a common linear cladding layr. It was shown that the proposed NLDC is useful for constructing a power band-pass filter, a power band-reject filter, and an optical pulse modulator, by setting the input and output ends properly.5. The power transfer characteristics in the NLDC composed of three parallel nonlinear waveguides have been analyzed. It was shown that the input/output characteristics for optical switching are superior to those of the conventional NLDC.6. The characteristics of optical waves propagating along a nonlinear waveguide with a surface corrugation have been discussed as the basic research for developing the wavelength selective NLDC structure.