A sensor array includes an array of nodes coupled to an optical transmission line. The nodes include a transducer, and encoder, and a transmitter. The transducer senses an environmental condition such as temperature and pressure. The encoder encodes readings from the transducer by means of a characteristic frequency to indicate which node generated the reading. The transmitter transmits the encoded reading to a decoder located near the opening of the oil well, or other blind hole. Power is transmitted to the nodes through the transmission line. A photo-electric converter at the node converts the optical power to electrical energy that is stored to power the node.