An optical sensor system and method for determining the position, displacement and/or angle of a member (for example, a seal plate or valve gate) within a system (for example, a valve assembly in an aircraft turbine engine system or environmental control system). The system has, in one embodiment, a controller in communication with an encoder via a fiber optic line or similar light transmitter and the encoder further has an optically layered element. The optically layered element has at least one coating whose optical characteristics vary over the angles (or distance) of interest to provide feedback based on the position displacement and/or angle of the valve member. The system may communicate and/or be controlled by a computing system via a data communication network.