An optical fiber has a core region and a first cladding region surrounding the core. The first cladding region is doped to increase the fiber's refractive index volume. A second cladding region surrounds the first cladding region. The second cladding region is doped to reduce the fiber's cutoff wavelength, offsetting an increase in the fiber's cutoff wavelength caused by the first cladding region. An outer cladding surrounds the cutoff reduction region. In a further embodiment, the volume increasing region is doped to have a refractive index profile that is sloped to increase from the region's outer circumference towards its inner circumference. In another embodiment, the cutoff reduction region has a step refractive index profile that may have more than one section.