A waveguide is characterized by a region of high refractive index bounded by regions of lower index.

波导就是折射率高的区域由折射率低的区域包裹的结构。

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The core has a high index of refraction, whereas the surrounding cladding, with its air holes interspersed with silica, has a lower index.

核心的石英折射系数高，环绕在外的外层石英与孔洞交错，所以折射系数较低。

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The covering material that encases the core of an optical fiber. the cladding material usually has a lower index of refraction than the core material and may be either glass or plastic.

一种包装光纤芯的保护材料。保护材料的折射率通常比光纤芯的折射率低，它一般是玻璃或塑料。

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Eating a lower glycemic index diet may help improve your cholesterol ratios.

CNN: Is instant oatmeal just as healthy as traditional?

Lower glycemic index diets have been linked to a reduced risk of heart disease, diabetes and age-related macular degeneration, the leading cause of blindness in Americans.

CNN: Is quick brown rice as healthy as regular?

The lower the index, the healthier the nation.

ECONOMIST: European health