Abstract: A system for measuring magnetic field gradients comprising a multi-bay support structure with a series of raised contact shoulders separated from each other by voids. An optical fiber is spaced along the length of the multi-cell support structure and traverses all the raised contact points and voids. The optical fiber has a plurality of Fiber Bragg gratings (FBGs) spaced lengthwise, each FBG suspended in a void. In addition, a plurality of ferromagnetic members are strung onto the optical fiber, each suspended in a void. Magnetic field gradients act on the ferromagnetic member to create localized tension in the optical fiber. The FBG's refractive indices are monitored, tension is calculated therefrom, and the tension is correlated to the magnetic field gradient. This greatly simplifies mechanical, optical, electronic and computational complexity and is bay suited for any FOSS array for measuring magnetic fields using many dense measurement points.