The return loss of an attenuator is defined as the ratio of reflected power to incident power. In essence, it measures how effectively the attenuator prevents signal. Fiber-optic attenuators are a specific type of optical attenuators which are used in fiber optics, e. FC/PC or LC/APC). Beginning with software release 1. 8, OptiFiber is able to measure optical return loss. Losses can be divided into intrinsic and extrinsic types: Intrinsic losses: caused by the fiber material and core structure, including absorption, scattering, and. 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.