Effective Refractive Index：
Definition: a number quantifying the pha delay per unit length in a waveguide, relative to the pha delay in vacuum
荷花几月开In homogeneous transparent media, the refractive index 网页没有声音n can be ud to quantify the increa in the wavenumber (pha change per unit length) caud by the medium由于介质的存在而造成的波数的增加: the wavenumber is n times higher than it would be in vacuum介质中的波数是真空中的n倍. The effective refractive index neff has the analogous meaning for light propagation in a waveguide朱自清的文章在波导中，有效折射率neff有着相类似的意义; the propagation constant of the waveguide is the effective index times the vacuum wavenumber:在波导中的传输常数是真空中的neff倍
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Note that the effective refractive index depends not only on the wavelength but also (for multimode waveguides) on the mode in which the light propagates.有效折射率不仅仅和波
长相关，也和模式相关， For this reason, it is also called modal index.因此也称为模式折射率 Obviously, the effective index is not just a material property, but depends on the whole waveguide design.有效折射率不仅仅是一种材料的性质，它也依赖于整个波导的设计 Its value can be obtained with numerical mode calculations, for example. 它的数值可以通过数值模式计算得到It can vary substantially near a mode cut-off.
The effective index may be a complex quantity. In that ca, the imaginary part describes 去滑雪的英文gain中国的传统文化有哪些 or loss – e the article on propagation constant for more details.有效折射率是一个复杂的物理量，在有效折射率中，虚部描述的是损耗或者损耗。
A common but wrong belief常见的错误是 is that the effective refractive index有效折射率 is a kind of weighted average of the refractive index of core and cladding of the waveguide,是波导的覆层和芯层折射率的加权平均值 with the weight factors determined by the fractions of the optical power propagating in the core and cladding. This impression may result from the common obrvation that higher-order modes, e.g. of a fiber, have a lower effective index and also a lower mode overlap with the core. However,
a step-index multimode waveguide with a high numerical aperture and large core diameter. Here, all modes overlap to nearly 100% with the core (i.e. the mode overlaps are very similar), whereas the effective indices differ substantially.
