Olshansky R, Keck D B
Appl Opt. 1976 Feb 1;15(2):483-91. doi: 10.1364/AO.15.000483.
This paper reports on some theoretical and experimental investigations of the radial refractive index gradient that maximizes the information-carrying capacity of a multimode optical waveguide. The primary difference between this work and previous studies is that the dispersive nature of core and cladding materials is taken into consideration. This leads to a new expression for the index gradient parameter alpha(c) which characterizes the optimal profile. Using the best available refractive index data, it is found that in high-silica waveguides, the dispersive properties of the glasses significantly influence the pulse broadening of near-parabolic fibers, and that the parameter alpha(c) must be altered by 10-20% to compensate for dispersion differences between core and cladding glasses. These predictions are supported by pulse broadening measurements of two graded-index fibers. A comparison is made between the widths and shapes of measured pulses and pulses calculated using the WKB approximation and the near-field measurement of the index profiles. The good agreement found between theory and experiment not only supports the predictions made for the value of alpha(c), but demonstrates an ability to predict pulse broadening in fibers having general index gradients.
本文报道了一些关于径向折射率梯度的理论和实验研究，该梯度能使多模光波导的信息承载能力最大化。这项工作与先前研究的主要区别在于考虑了纤芯和包层材料的色散特性。这导致了用于表征最佳折射率分布的折射率梯度参数α(c)的新表达式。利用现有的最佳折射率数据发现，在高硅光波导中，玻璃的色散特性对近抛物线型光纤的脉冲展宽有显著影响，并且参数α(c)必须改变10% - 20%以补偿纤芯和包层玻璃之间的色散差异。两根渐变折射率光纤的脉冲展宽测量结果支持了这些预测。对测量脉冲的宽度和形状与使用WKB近似计算的脉冲以及折射率分布的近场测量结果进行了比较。理论与实验之间的良好一致性不仅支持了对α(c)值的预测，还证明了预测具有一般折射率梯度的光纤中脉冲展宽的能力。
