文章中提到These four basic waves are assumed to have identical field profiles in the z direction, denoted by Θ(z), which is the same as the field profile of the fundamental waveguide mode for a waveguide with no periodic structure.有一个疑问，这里的no periodic structure指的是忽略空气孔按照缘草寮折射率算，还是按照有空气孔的有效折射率算呢？