Interaction mechanics of interferometric optical fiber sensors embedded in a monolithic structure

The mechanical and optical interaction of an optical fiber strain sensor which is structurally embedded in a monolithic host material is explored with closed form solutions, finite element methods, and fiber interferometry. A stripped single mode optical fiber is embedded in a four-point bend specimen to investigate both the stress state induced in the specimen by the fiber acting as an elastic inclusion, and the phase-shift induced in the optical fiber by the specimen strain field. Generalized plane strain elasticity solutions are combined with a 3D phase-strain model developed for embedded sensors to predict the strain induced optical retardation of the light propagating in the fiber sensor. The closed form solutions are used in conjunction with finite element solutions to investigate the local stress state induced by the presence of the fiber.