通过研究各向同性以及各向异性介质中电磁场的波矢量与波印廷矢量之间的角度关系，给出了利用电磁场的单位波矢量与单位群速度的点积值来判断光子晶体介质性质及其手性特征的一种方法.并指出，可以利用光子晶体手性特征临界点的特性来解决多光束的合束问题.最后，利用解析计算讨论了上述结论.上述研究结果为进一步丰富“电动力学”等相关课程的教学内容打下了基础.

By studying the angle relationship between the wave vector and the Poynting vector of the electro-magnetic field in isotropic or anisotropic media，the method for determining the dielectric properties and chiral characteristics of photonic crystals by using the dot product between the unit wave vector and the unit group velocity of

　　the electromagnetic field has been given. It is pointed out that the criterion for the critical value of the chiral charac

　　teristic of photonic crystals can be used to solve the problem of multi-beam combination. At last，the above conclu

　　sions are discussed by analytic calculation. The above results have laid a foundation for further enriching the con

　　tents of electrodynamics and other related course.