Optical fiber, dispersion compensator using optical fiber, optical transmission line using optical fiber, and optical transmission system using optical fiber

An optical fiber which comprises a core and a clad including an innermost layer and an outermost layer, and has a refractive index distribution structure satisfying conditions of 0.8%≦Δ1≦1.3% and −0.7%≦Δ2≦−0.4%, where Δ1 represents a relative refractive index difference of the core with respect to the outermost layer of the clad, and Δ2 represents a relative refractive index difference of the innermost layer of the clad with respect to the outermost layer of the clad, and also satisfying the conditions of −20≦D≦0, −0.1≦S<0 and 0≦(D/S)≦200 in specified wavelength band having a band width of at least 20 nm in a 1.5 μm wavelength band, where D represents the chromatic dispersion (ps/nm/km) at a specified wavelength in a 1.5 μm wavelength band, and S represents the dispersion slope (ps/nm2/km).