Enhanced sensitivity distributed sensing of magnetic fields in optical fiber using random Bragg grating

We show that the use of Random Optical Grating using UV Exposure (ROGUE) can significantly reduce the noise floor of an optical frequency domain reflectometry (OFDR) measurement of Faraday rotation in the polarization. We compare it with unexposed spun fiber which shows a S/P minimum ratio (signal noise floor) 20 dB higher than when using our ROGUE. High sensitivity magnetic field measurements are achieved by spatially filtering (setting a gage length) the derivative of the S/P ratio's evolution. Example of a calibrated electromagnet spatially resolved B-field measurement is demonstrated, which can measure fields down to 10 mT with 10 cm spatial resolution. The potential for current sensing using such ROGUE apparatus is discussed and simulation shows a noise floor of around 1 A with 40 probing loops spatial resolution.