A variable optical attenuator (VOA) for use in an optical fiber communication system has a substrate, a thermal gradient prism and a heating element deposited on the prism. Heat is applied to the thermal gradient prism through the heating element. An optical signal is input into the prism via an optical signal input source. The optical signal traveling through the prism may be deflected due to a thermal gradient of the prism. The deflected optical signal is output into an optical signal output carrying medium. An optical signal strength measuring apparatus may measure a parameter related to the strength of the optical signal output into the optical signal output carrying medium.