Compact, remote optical waveguide magnetic field sensing using double-pass Faraday rotation-induced optical attenuation

Compact, magnetic field, B sensing is proposed and demonstrated by combining the two Faraday rotation elements and beam displacement crystals within a micro-optical fiber circulator with a fiber reflector and ferromagnets to allow high contrast attenuation in an optical fiber arm. Low optical noise sensing is measured at λ =1550nm as a change in attenuation, α , of optical light propagating through the optical noise sensing rotators and back. The circulator’s double-pass configuration, using a gold mirror as a reflector, achieves a magnetic field sensitivity s =Δ α /Δ B =(0.26±0.02)dB/mT with a resolution of Δ B =0.01mT, over a detection range B =0−89mT. The circulator as a platform provides direct connectivity to the Internet, allowing remote sensing to occur. The method described here is amenable to multisensor combinations, including with other sensor technologies, particularly in future integrated waveguide Faraday optical circuits and devices, extending its utility beyond point magnetic field sensing applications.