Enhancement of free spectral range in the resonance peaks in a long-period fiber grating by controlling clad mode material dispersion

Summary form only given.We propose a new method to control the long period fibre grating (LPG) spectrum by introducing material dispersion into cladding modes. Previous studies in LPGs were focused only on the change of refractive index profiles of the core region leaving the cladding modes behind. To change material dispersion of cladding modes, we propose transition metal doping, such as Cr/sup 3+/ into the cladding region. Because the transition metals have absorption peaks in visible range, they effectively introduce changes of refractive index and dispersive characteristics in silica host at the optical communication windows. We calculated the refractive index of transition metal doped silica glasses using Kramers Kronig relation.