Single-mode optical fiber having multiple cladding regions for dispersion compensation

A dispersion-compensating fiber for compensating for a dispersion of a single-mode optical fiber having a predetermined length and a zero-dispersion wavelength near 1.3 μm, said dispersion-compensating fiber comprising:

• a core region extending along a predetermined reference axis and having an outer diameter 2a;
• and
• a cladding region which is a region provided on the outer periphery of said core region, said cladding region comprising:
• a first cladding provided on the outer periphery of said core and having an outer diameter 2b;
• a second cladding provided on the outer periphery of said first cladding and having an outer diameter 2c;
• and
• a third cladding provided on the outer periphery of said second cladding,
• wherein a refractive index n1 of said core, a refractive index n2 of said first cladding, a refractive index n3 of said second cladding, and a refractive index n4 of said third cladding satisfy
• n1>n3>n4>n2;
• wherein relative refractive index difference Δ1 of said core and relative refractive index difference Δ2 of said first cladding, which are defined with reference to the refractive index n4 of said third cladding satisfy
• 1%≦Δ1≦3%,
• and
• Δ2≦−0.3%;
• wherein the ratio of the outer diameter of said core with respect to the outer diameter of said second cladding satisfies
• 2a/2c≦0.3;
• and
• wherein, when said single-mode optical fiber with the predetermined length and said dispersion-compensating fiber having a length sufficient for compensating for the dispersion of said single-mode optical fiber are optically connected to each other to constitute an optical transmission system, said dispersion-compensating fiber causes a total dispersion slope in said optical transmission system to have an absolute value of 0.024 ps/nm2/km or less with respect to light having a shortest wavelength and light having a longest wavelength in signal wavelengths within a wavelength band in use.