1. At a discontinuity or impedance mismatch, e.g., in a transmission line , the ratio of the incident power to the reflected power. ( 188 ) Note 1: Reflection loss is usually expressed in dB . Note 2: The reflection loss, L r , is given by
where Z 1 and Z 2 are the respective impedances, and the vertical bars designate absolute magnitude. ( 188 ) 2. In an optical fiber , the loss that takes place at any discontinuity of refractive index , especially at an air- glass interface such as a fiber endface, at which a fraction of the optical signal is reflected back toward the source. Note: This reflection phenomenon is also called " Fresnel reflection loss," or simply, "Fresnel loss." At normal incidence, the fraction of reflected power is expressed by the formula,
where n 1 and n 2 are the respective indices of refraction .