定义：光纤链的传输距离和最大数据速率的乘积

带宽距离积一词通常在出现在光纤通信中。它通常被定义为一个光纤链路的长度和最大光谱宽度的乘积。
而后者与数据传输速率（Gbit/s）强烈相关，它们之间的转换因子取决于采用的调制形式。
带宽距离积通常受限于高数据传输速率时比特误码率骤然增加的情况。 
通过比较带宽距离积可以对比不同的光纤链路的性能。然而带宽距离积的定义表示其并不是与光纤长度无关的，是否是这种情形则需要视情况而定。
基于多模光纤中的链路的容量是受限于模间色散的，实际上，带宽距离积也大多在这种领域中应用。
（渐变折射率光纤的典型值为1 GHz km，而阶跃光纤的值则会小一个数量级）另外，基于单模光纤链路的容量在没有任何色散补偿手段的情况下是受限于色散的
数据传输速率增加一倍会使得传输距离减少为1/4。此时带宽距离积则相应的减少一半。
当然，通过在两个光纤链路间利用电学正反馈可以使传输距离加倍。

Definition: product of length and maximum signal bandwidth of a fiber-optic link

Alternative term: bandwidth–length product

The term bandwidth–distance product (or bandwidth–length product) is often used in the context of optical fiber communications. It is usually defined as the product of the length of a fiber-optic link and its maximum signal bandwidth. That bandwidth is strongly related to the data rate (in Gbit/s), with a conversion factor which depends on the used modulation format. The bandwidth–distance product is typically limited by the phenomenon that the bit error rate rises sharply for too high data rates.

The concept of the bandwidth–distance product is helpful e.g. for comparing the performance of different types of fiber-optic links. However, the definition by no means implies that the achievable bandwidth–distance product is independent of the chosen fiber length. Whether this is the case, depends on the circumstances. It can be true for a link based on multimode fiber, the capacity of which is limited by intermodal dispersion; indeed, the bandwidth–distance product (based on the modal bandwidth) is mostly used in that domain. (A typical value may then be of the order of a few GHz·km for a graded-index fiber, or an order of magnitude less for step-index fibers.) On the other hand, in a link based on single-mode fiber, which is limited by chromatic dispersion and which does not contain means for dispersion compensation, a doubling of the data rate may enforce a reduction in the fiber length by a factor of four. The bandwidth–distance product is then effectively reduced by a factor of two. However, the transmission distance may of course also be doubled by concatenating two fiber-optic links with electronic regeneration between them.