Y-shaped microstructured fibers with Ge-doped core

Y-shaped microstructured optical fibers (MOF) are gaining increasing attention due to its simplicity, since the cross section of this fiber is formed by a solid-core and only three large air holes in the cladding. In the fabrication process, in order to provide a Ge-doped core, a step-index multimode Ge-doped fiber can be inserted in the interstitial hole between the three capillaries. We have found that the filling of a Ge-doped Y-shaped MOF with a liquid of refractive index higher than the index of silica but lower than the index of the Ge-doped core produces a cutoff of the fundamental mode. This cutoff is very sensitive to small changes of the relative refractive index values of the liquid, as well as of in the silica and the Ge-doped core. Finally, we use the Ge-doped fiber to inscribe fiber bragg gratings (FBG) and see the spectral shift when the grating is put down strain and temperature changes.