Wavelength-insensitive couplers made of annealed dispersive fibers

Wavelength-insensitive fiber couplers are made of the annealed single-mode dispersive fibers whose index differences between the core and the cladding glasses increase with wavelength. Since the produced dispersive fibers support several guided modes, they are changed into single-mode fibers with dissimilar index differences by annealing under various conditions. It becomes evident that the wavelength-insensitive region of the fabricated fiber couplers can be shifted and broadened by choosing proper annealing conditions.