Multicore fiber with integrated fiber Bragg gratings for background-free Raman sensing

In the last years a variety of fiber optic Raman probes emerged, which are only partly suited for in-vivo applications. The in-vivo capability is often limited by the bulkiness of the probes. The size is associated with the required filtering of the probes, which is necessary due to Raman scattering inside the fibers. We propose a fiber optic Raman probe with in-line fiber Bragg gratings (FBG), employed as notch filter for the collection path. Multicore single-mode fibers (MCSMF) were designed and drawn integrating 19 single-mode cores to achieve better collection efficiency. A Raman probe was assembled with one excitation fiber and six MCSMF with inscribed FBGs as collection fibers. The probe was characterized regarding Raman background suppression, collection efficiency and distance dependence. First Raman measurements on brain tissue are presented.