Miniature fiber optic towed array for AUV applications

The towed array sensor fit is a real challenge in AUVs due to its space constraints. Only miniature arrays are possible, that too with minimal length. The major components needed for a compatible array are the miniature hydrophones, with less h/w components and minimal cabling & connectors, thus achieving a miniature towed array. The fully electrically passive nature of fiber optic (FO) arrays where sensors can be remotely located through a fiber optic cable, without electrical power, is well suited for towed array sonar applications. This paper aims at the design of miniature mandrel FO hydrophones, its interrogation method and the ultra thin towed array. Considering the hydrostatic pressure tolerance at water depths, a composite mandrel with metal base and foaming layer is proposed for a miniature mandrel FO hydrophone. Small diameter fiber and fiber bragg grating written on to the fiber through the coating eliminates couplers and mirrors thus reducing the components are proposed. An array design with 16 hydrophones using path-matched differential interferometry (PMDI) scheme based on heterodyne interrogator technique is used.