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通过芯径渐缩、指数型连续渐缩或阶梯型离散渐缩的方法，可获得色散随距离下降的光纤，能补偿光纤损耗对孤子传输的影响。但芯径的连续变化，将导致模耦合。分析发现，在连续渐缩光纤中，即使Ｖ＜２．４０４８始终满足，仍可存在两种模式：其一是Ｚ→∞的稳态模，另一为兼有导模和辐射模部分性质的一种特殊模式，称为“过渡模”，该模式的模式场是一系列ＬＰ０ｍ′的模式场的迭加，它包括导模ＬＰ０１′的模式场和辐射模ＬＰ０ｍ′（ｍ≥２）的模式场，随着ｒ→∞不是迅速衰减而是振荡着缓慢衰减。它具有与激励模相同的传输常数，但幅度却以芯径渐缩的速率衰减。尽管指数型渐缩光纤可增加孤子的传输距离，但“过渡模”的影响始终存在，而离散型光纤不存在“过渡模”。为了估计稳态模的基态孤子在芯径渐缩光纤中的传输长度，可利用该模的本地功率与阈值功率之比来计算，称该比值为“裕度”。如果在进入渐缩光纤之前，基态孤子已经处于阈值临界状态，则在渐缩光纤中稳态模孤子的裕度恰好等于孤子阶数参量Ｎ２的变化比。本文给出了在高斯近似下的过渡模和稳态模的功率计算公式，并得到孤子传输的裕度公式及计算曲线
Through the core diameter taper, exponential continuous tapering or step-type discrete taper method, the optical fiber with dispersion decreasing with distance can be obtained, which can compensate the influence of fiber loss on the soliton transmission. However, continuous changes in core diameter will result in mode coupling. It is found that there are still two modes in the continuous-tapered fiber even if V <2.4048 is always satisfied: one is the steady state mode of Z → ∞ and the other is the mode of both guided mode and radiation mode A special mode, referred to as a “transitional mode”, whose mode field is a superposition of a series of LP0m ’mode fields including the mode field of the guided mode LP01’ and the mode of the radiation mode LP0m ’(m≥2) Field, with r → ∞ not decaying rapidly but oscillating slowly decaying. It has the same transfer constant as the excitation mode, but the amplitude decays at a rate that the core diameter tapers. Although exponential tapered fiber can increase the soliton transmission distance, the influence of “transition mode” always exists, but there is no “transition mode” in discrete optical fiber. In order to estimate the propagation length of the ground state soliton in the steady-state mode in the core-tapered optical fiber, it can be calculated by using the ratio of the local power to the threshold power of the mode, which is called “margin”. If the ground state soliton is already at the threshold critical state before entering the tapered fiber, the margin of the steady mode soliton in the tapered fiber is exactly equal to the change ratio of the soliton order parameter N2. In this paper, the power calculation formulas of transitional mode and steady-state mode under Gaussian approximation are given, and the marginal formula and calculation curve of soliton transmission are obtained