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.