Fabrication of dispersive fibers and their application to long wavelength-pass filters

Dispersive fibers are fabricated in which the refractive index dispersions of the core and cladding cross at a certain wavelength. The core and cladding were made of different types of optical glasses. To pass a long wavelength light (to suppress short wavelength light), the refractive index of the core was chosen to be lower than that of the cladding in the short wavelength region. In the fabricated dispersive fibers, no waveguide mode was observed in the short wavelength region, indicating that the fibers play the role of a long wavelength pass filter. To evaluate the fibers as an optical filter, the transmission loss and insertion loss were investigated and it was found that the pass wavelength region could be controlled by changing the curvature of the fibers.