Interferometric fiber-optic current sensor with inherent source wavelength shift compensation

Fiber-optic current sensors utilize the Faraday effect in fused silica fiber to measure electric current. Since the effect is wavelength dependent, high sensor accuracy requires a stable source wavelength. Commonly used semiconductor sources require temperature stabilization within ≈0.1°C for adequate wavelength stability that adds extra cost. Here, we theoretically and experimentally demonstrate a novel method for inherent (passive) compensation of source wavelength shifts in interferometric fiber-optic current sensors. The method is based on an appropriately detuned fiber-optic half-wave retarder that generates wavelength dependent cross-coupling between the two orthogonal polarization modes of the sensor which compensates the change of the Faraday effect with wavelength. It is shown that at a wavelength shift over 14 nm (near 1305 nm), which corresponds to a source temperature change of 24°C, the scale factor variation is reduced from 2% to <;0.2%.