Abstract
Dispersive fibers whose refractive index differences change greatly with wavelength are fabricated from optical glasses with different index dispersions. The fibers have several guided modes, and are changed into single-mode fibers by annealing under suitable conditions. The number of guided modes is investigated by measuring the bending loss and the mode lines of annealed dispersive fibers. The annealed single-mode fibers support only the fundamental mode over broad spectral ranges and no second guided mode at any wavelength.