Fiber optic attenuators are devices used to reduce or monitor the power level of a fiber optic signal. Basic types of fixed attenuation include single mode, dual window and multimode in D4/PC, FC, FC/UPC, MU, SC, SC/APC and UPC, ST and ST/UPC style connectors. Optical attenuators usually work by absorbing light, much like sunglasses absorb extra light energy.