定义：
包含多级的放大器。

放大器链包含一系列的放大器，可以逐级放大信号光。第一级通常称为前置放大器，最后一级则称为功率放大器。不仅在电子学中很常见，在这里的激光技术中也很常用，因为相比于单级放大器，放大器链的概念具有很多优势包括： 

• 在得到高的饱和输出功率和高增益之间需要一些权衡。例如，若要得到高的饱和输出功率需要在放大器的最后部分具有大的模式面积，然而前置放大器则当模式面积很小时具有更好的增益效率。总体性能的提高可以通过将放大器分成多级，然后分级优化来实现。在超短脉冲放大器中，功率放大器也需要增加模式面积来降低非线性效应。也可以同时将不同的放大器结合一起使用，例如将正反馈放大器作为高增益前置放大器，将中等程度增益的多通放大器作为功率放大器，或者采用光参量放大器和一个激光放大器。 
• 在有些情况下，需要在多级放大器链中加入一些其它光学器件。例如，在很多高增益放大器链中，在各级放大器中间加入光学隔离器是为了减小背向散射和ASE效应。带通滤波器可以在前后向极大减小ASE的强度。放大器应用于超短脉冲放大时，各级之间的光学调制器（例如声光调制器）仅仅在很短时间间隔内打开，这样脉冲可以传输到下一级。 
• 采用放大器链可以方便模块化，这样可以通过结合已有的不同级数的放大器模块从而很简单的获得不同的性能。

Definition: amplifiers consisting of several stages

An optical amplifier chain is a sequence of several optical amplifiers, which can subsequently amplify some signal. The first stage is often called the preamplifier and the last stage a power amplifier. Such schemes are common in electronics, but also in laser technology (as considered here), because the concept of an amplifier chain can have advantages compared with an approach where the full performance in expected from a single amplifier stage:

• There are certain trade-offs, for example between obtaining a high saturated output power and a high gain. For example, a high saturated output power calls for a large mode area in the last section of the amplifier, while the preamplifier can have a better gain efficiency when the effective mode area is chosen small. The overall performance can then be improved by splitting the amplifier into different amplifier stages which can be independently optimized. In ultrashort pulse amplifiers, the power amplifier may also need increased mode areas for reducing nonlinear effects.
• It is also possible to combine different kinds of amplifiers, e.g. a regenerative amplifier as a high-gain preamplifier and a multipass amplifier as a power amplifier with moderate gain, or an optical parametric amplifier with a laser amplifier.
• Sometimes it is necessary to insert certain optical elements between different stages of an amplifier chain. Some examples:
• In many high-gain amplifiers an optical isolator between the stages reduces the sensitivity to ASE and back-reflections.
• A bandpass filter can strongly reduce the total ASE power for both propagation directions.
• In amplifiers for ultrashort pulse amplification, an optical modulator (e.g. an acousto-optic modulator) between the stages may be opened only for some short time interval during which a pulse is transmitted to the next stage.
• The use of amplifier chains allows for a more modular approach where different performance numbers can be obtained simply by differently combining existing amplifier stages (modules).