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业已研制出VAD凹陷包层的单模光纤。所制备的光纤在纤芯中掺锗,折射率差为△~+=0.2～0.3％;在包层中掺氟,负折射率差为△~-=0.1～0.4％。包层与芯径之比为5到9,1.3μm波长处传输损耗小于0.5 dB/km。已发现,凹陷包层光纤侧向压力引起的弯曲损耗增加值与匹配包层光纤弯曲损耗增加值相等,匹配包层光纤的折射率差等于凹陷包层光纤折射率差的总和(△=△~++△~-)。但是,凹陷包层光纤的色散与纤芯中具有同样含锗量的匹配包层光纤的色散极其相似,即具有相同的正折射率(△=△~+),使得1.3μm波长处的色散比较低。此外本文还证实了,这种光纤的熔融接头损耗与匹配包层光纤的熔融接头损耗一样小,在整个成缆过程中传输损耗始终很低。
Single-mode optical fibers have been developed with VAD depressed cladding. The prepared optical fiber is doped with germanium in the core, the difference of the refractive index is Δ ~ + = 0.2-0.3%; and the difference of the refractive index of the cladding in the cladding is Δ ~ - = 0.1-0.4%. The cladding to core diameter ratio is 5 to 9 and the transmission loss at 1.3 μm wavelength is less than 0.5 dB / km. It has been found that the added value of the bending loss caused by the lateral pressure of the depressed clad fiber is equal to the added value of the bending loss of the matched clad fiber and the difference of the refraction index of the matched clad fiber is equal to the sum of the refractive index differences of the depressed clad fiber (Δ = ++ △ ~ -). However, the dispersion of the depressed clad fiber is very similar to the dispersion of the matched cladding fiber with the same germanium content in the core, ie has the same positive refractive index (Δ = Δ ~ +), so that the dispersion at 1.3 μm wavelength is compared low. In addition, this paper also confirms that the melting loss of this fiber is as small as the melting loss of the cladding cladding fiber, and the transmission loss is always low throughout the cable formation.