Investigation of application of fiber structures based on a section of double-cladding fiber for bend and refractive index sensing

A fiber optic structure based on transformation of core and cladding modes coupled at a splice of two fibers having different refractive index profiles is investigated. The structure is formed by splicing a section of double-cladding fiber with small core (SM630) between two standard fibers SMF-28. The transmission spectra of the proposed structure under bending are measured. A shift of resonances to longer wavelengths with increasing curvature was observed. The dependences of the shift on the fiber section length, bending orientation, and refractive index of the external medium are investigated.