The principle of gap-loss is used in optical attenuators to reduce the optical power level by inserting the device in the fiber path using an inline configuration. The attenuator circuit will allow a known source of power to be reduced by a predetermined factor, which is usually expressed as decibels. Key requirements include minimal effect on the beam profile, low wavelength and polarization dependence, and sufficient power handling capability. Fiber-optic systems use a wide variety of relays, switches, amplifiers, and other devices that are connected by fiber-optic cables. In some cases, these devices can be several dozen kilometers apart.