IEC 61300-3-6:2008介绍了被测光纤设备（DUT）回波损耗（RL）的测量程序。本标准中使用的RL是入射或进入DUT的功率（Pi）与DUT反射的总功率（Pr）之比，以分贝表示。第三版取消并取代了2003年出版的第二版。这是一项技术性修订。与前一版相比的变化是重新考虑文件的构成和多模光纤的发射条件。

IEC 61300-3-6:2008 presents procedures for the measurement of the return loss (RL) of a fibre optic device under test (DUT). RL, as used in this standard, is the ratio of the power (Pi) incident on, or entering, the DUT to the total power reflected (Pr) by the DUT, expressed in decibels. This third edition cancels and replaces the second edition published in 2003. It constitutes a technical revision. The changes with respect to the previous edition are to reconsider the constitution of the document and launch conditions for multimode fibres.