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在弱渐变假定下,研究了抛物型渐变光纤传导模式的截止频率对折射率参量的依赖关系。采用矢量场法,得到了在弱导条件下传导模式的特征方程和截止频率的近似计算公式。引入了介电比γ,它是由光纤三个折射率参量所确定的常数。在弱导近似的条件下,归一化截止频率仅与γ这一个变量有关,任一渐变抛物型光纤的实际截止频率可通过γ而由归一化截止频率简单求得,从而找到了渐变光纤的实际截止频率与归一化截止频率间的联系。给出了归一化截止频率随γ的变化曲线,归一化截止频率随γ的增加而单调上升,但HElm模截止频率的上升规律与其他模式不同。
Under the weak gradient assumption, the dependence of the cut-off frequency of the parabolic-gradient optical fiber transmission mode on the refractive index parameters is studied. By using the vector field method, the approximate formula of the characteristic equation and the cut-off frequency of the conduction mode under weak conduction condition is obtained. The dielectric ratio γ is introduced, which is a constant determined by the three refractive index parameters of the fiber. In the case of weak approximation, the normalized cut-off frequency is only related to a variable of γ, and the actual cut-off frequency of any graded parabolic fiber can be simply calculated from the normalized cut-off frequency by γ, finding a graduated fiber The actual cut-off frequency and the normalized cutoff frequency link. The curve of normalized cutoff frequency with γ is given. The normalized cutoff frequency increases monotonically with the increase of γ, but the rising law of cutoff frequency of HElm mode is different from other modes.