定义：随着缓变的传播参数变化的孤子脉冲压缩技术。

绝热孤子压缩是在光纤中时间压缩超短脉冲的技术。下面会介绍其具体的工作原理。孤子脉冲在光纤中传播时，其脉冲能量与脉冲时间的乘积与群速度色散除以光纤的非线性成正比。因此，当色散减小的情况下要保持脉冲能量不变，需要相应的减小脉冲长度。因此，脉冲在色散缓变光纤中传播时能实现显著的脉冲压缩。但是，还需要满足下列条件：

•  初始脉冲在入射光纤端口需要满足孤子条件。
• 光纤色散变化非常缓慢，脉冲随着缓变的光纤参数发生绝热变化（否则，脉冲会发生畸变）。更准确的说，色散在一个孤子周期的长度范围内不发生显著变化。由于脉冲周期与脉冲长度的平方成正比，那么如果初始脉冲大于1ps时则需要相当长的光纤。
• 在整个压缩脉冲的光谱范围内，光纤色散需要保持不变。也就是说，高阶色散必须很弱。但是在脉冲光谱两侧存在比较小的正常色散是有利的。

还有一种情况是在拉曼散射和高阶色散共同作用下脉冲压缩是绝热的，尽管上述任意一个单独的效应都会引起很严重的脉冲畸变。
这种技术非常有用，但是有一个限制是必须使用色散缓变光纤。很多其它方法中不需要采用后者，而只需要色散不变的光纤，以及在光纤中掺杂激光活性物质来实现脉冲的放大。这时，在固定色散情况下提高脉冲能量也能实现时间压缩。

如果不采用色散缓变光纤，还可以将具有不同色散的光纤连接在一起。这样可以得到可重复性的结果，但是由于这时色散并不是连续变化，压缩因子和脉冲质量会受到影响。

一般来说，绝热孤子压缩局限于脉冲能量比较低的情况，因为光纤中的孤子能量不可能非常高。因此，这一技术通常用于高脉冲重复速率的脉冲列，例如，在光纤通信中。 

Definition: a pulse compression technique based on the adaptation of solitons to slowly varying propagation parameters

More general term: pulse compression

Adiabatic soliton compression is a technique for the temporal compression of ultrashort pulses in a fiber. The principle of operation is described in the following. For a fundamental soliton pulse in a fiber, the product of pulse energy and pulse duration is proportional to the group velocity dispersion divided by the nonlinearity of the fiber. Thus, the pulse duration must be reduced if the dispersion is reduced while keeping constant the pulse energy. Significant pulse compression can therefore be obtained by propagating the pulses through a dispersion-decreasing fiber. However, the following conditions must be satisfied:

• The initial pulses must fulfill the soliton condition at the input fiber end.
• The fiber dispersion must be varied sufficiently slowly to allow adiabatic adaptation of the pulses to the fiber parameters (otherwise, the pulses can become distorted). More precisely stated, the dispersion must not vary substantially over a length scale of a soliton period. As the latter scales with the square of the pulse duration, rather long fibers are required if the initial pulses are longer than e.g. 1 ps.
• The fiber dispersion must stay sufficiently constant over the whole spectral range of the compressed pulses. In other words, higher-order dispersion must be sufficiently weak. However, it has been shown that slightly normal dispersion in the wings of the generated pulse spectrum can be beneficial.

Interestingly, there are situations where Raman scattering and higher-order dispersion combine in such a way that the pulse compression stays adiabatic, even though each of the mentioned effects separately would lead to severe pulse distortion [5].

Even though the method is elegant and powerful, it suffers from the need to use a dispersion-decreasing fiber. The latter requirement is eliminated by a variant of the method, where the fiber has constant dispersion but contains a laser-active dopant which allows the amplification of the pulses. Here, an increasing pulse energy for constant dispersion also results in temporal compression.

Instead of using a dispersion-decreasing fiber, it is also possible to concatenate (fusion-splice) different fibers with different dispersion values. This may lead to more reproducible results, but as the dispersion does not vary continuously, the compression factor and/or the pulse quality can be compromised.

Generally, adiabatic soliton compression is limited to fairly low pulse energies, since the soliton energies of pulses in fibers cannot be made very high. Therefore, the technique is mainly applied to high repetition rate pulse trains, e.g. in the context of optical fiber communications.

Bibliography