Measured in decibels (dB), return loss is calculated by comparing the input (or incident) power to the reflected power using the following formula: Return Loss = 10*log (incident power/reflected power) in +dB The result is always a positive number, and a higher value is better. Return loss is the ratio of signal power injected from a source compared to the amount that is returned or reflected back toward the source. It is a critical performance parameter in both copper twisted pair and fiber optic cabling systems, because it can interfere with the transmitted signal and. In the test report for a fiber cable, you may often see some data related to fiber insertion loss (IL) and return loss (RL), but do you know what insertion loss and return loss actually mean? How do the values of IL and RL impact the quality of the fiber cable? Are higher values better, or lower. Reflectance (which has also been called "back reflection" or optical return loss) of a connection is the amount of light that is reflected back up the fiber toward the source by light reflections off the interface of the polished end surface of the mated connectors and air. Reflectance occurs at point discontinuities, for example connector interfaces, splice interfaces, etc. An Optical Power Meter and Laser Light Source will be used to measure power loss on each completed ring or distribution span to verify continuity between fibers (no fibers incorrectly spliced. To ensure the proper performance of an optical transmission system, various parameters—such as attenuation and optical return loss (ORL)—must be within the acceptable tolerance levels of both the transmission and receiving equipment.
