An optical attenuator, or fiber optic attenuator, is a device used to reduce the power level of an optical signal, either in free space or in an optical fiber. The basic types of optical attenuators are fixed, step-wise variable, and continuously variable.
Fiber optic attenuators are devices which reduce (attenuate) the strength of a fiber optic signal within a fiber optic network. Attenuators are usually used when the signal arriving at the receiver is too strong and hence may overpower the receiving elements. This may occur because of a mismatch between the transmitters/receivers (transceivers, media converters), or because the media converters are designed for a much longer distance than for which they are being used. Sometimes attenuators are also used for stress testing a network link by incrementally reducing the signal strength (increasing the dB attenuation) until the optical link fails, thus determining the signal existing safety margin.
Optical attenuators are commonly used in fiber-optic communications, either to test power level margins by temporarily adding a calibrated amount of signal loss, or installed permanently to properly match transmitter and receiver levels. Sharp bends stress optic fibers and can cause losses. If a received signal is too strong a temporary fix is to wrap the cable around a pencil until the desired level of attenuation is achieved.