Working principle of optical attenuator

Optical attenuators are commonly used in, 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 is achieved. However, such arrangements are unreliable, since the stressed fiber tends to. [pdf]