Modified in-line Sagnac interferometer with passive demodulation technique for environmental immunity of a fiber-optic current sensor.
A modified in-line Sagnac interferometer (MISI) with passive demodulation Technique (PDT) was proposed to immunize the fiber-optic current sensor (FOCS) from environmental perturbations. A large vibration to simulate the environmental perturbations with acceleration up to 12 g was applied to the lead fiber of the FOCS. The noise floor could be significantly suppressed (20 dB) by the MISI better than by a conventional interferometer. In the same dynamic environments, the PDT could make the FOCS achieve a good linear demodulation with average distortion rates always lower than 0.9%. In addition, all the sensitivities measured in both static and dynamic environments are all approximately 4.5 microrad/(A(rms) turns), which is close to the literatural data measured in static environments. These considerable achievements of high sensitivity, environmental immunity, and free electric shock concerns may lead FOCS's to field-monitoring applications of power delivery lines.