Self Powered Fiber Optical Sensors

The problem of supplying power to optical and in particular fiber-optical sensors may be solved by generating electrical energy locally. This idea is illustrated here with several optical sensors, taken primarily from mechanical measurement applications. Incremental rotary encoders for transducing shaft position in rotating machinery are described which have a mechanical shaft input and 50/125μm fiber-optical signal outputs. They combine a DC generator or AC alternator with an internal fiber coupled optical emitter, allowing self-contained operation, independant of dedicated optical or electrical supplies. Incremental pulse generation is effected either by an encoder disc, or directly from the voltage periodicity of the AC alternator output. Applications include machine control, flow measurement, and limit detection in electrically noisy environments. A second class of sensors is demonstrated, transient optical sensors, which generate an optical output only for a short duration on activation of a particular transducer. With appropriate local intelligence in the form of low-power electronics, and suitable codes and transmission protocols, several sensor heads may be multiplexed onto a common optical bus.