Synchronous demodulation of high-sensitivity fiber-optic sensor for harsh environment electrical applications

A new approach of demodulating high-sensitivity fiber-optic sensors is presented for harsh environment electrical applications where a reference of synchronism is ever available by using the power-line signal. The principal goal of the demodulation system is to obtain the optical phase shift which is linearly related to the measurand, but the optoelectronic interrogation system that is required before shows a raised cosine transference function. Multi-cycle outputs present excellent benefits for obtaining the read-out of the optical phase evolution due to dynamic parameters, except for the ambiguity of the shift. This problem is also satisfactorily solved here with a synchronous sampling/demodulation based on the availability of a reference signal of synchronism. This technique can find multiple applications, among which the measurements at electrical equipment are highlighted. Experimental results with a vibration sensor inside power-transformers are presented here, where a fiber-optic technology is needed because of the harsh-environment, as well as a very high sensitivity for the typical magnitudes of interest. Resolution better than 1 nm of deformed elements/displacements is achieved with the sensor design and a range to resolution better than 50 dB.