Optical transmission system

An optical transmission system comprising:

• an optical fiber transmission line having a zero-dispersion wavelength of 1350 nm to 1440 rim and a cable cutoff wavelength band of less than 1368 nm, said optical fiber transmission line transmitting signal light at least in a wavelength band from 1450 nm to 1530 nm (S band) and Raman-amplifying said signal light in S band when Raman amplification Dumping light is supplied thereto, said optical fiber transmission line also transmits signal light in a wavelength band from 1530 nm to 1565 nm (C band) or signal light in a wavelength band from 1565 rim to 1625 nm (L band);
• Raman amplification pumping light supplying means for supplying said Raman amplification pumping light to said optical fiber transmission line;
• and
• an Er-doped optical fiber amplifier for optically amplifying said signal light in C band or L band when Pumping light is supplied thereto,
• wherein said Raman amplification pumping light supplying means propagates said Raman amplification pumping light from an introducing position for said Raman amplification pumping light into said optical fiber transmission line in a direction opposite from that directed to the Er-doped optical fiber amplifier whose distance from said introducing position along said optical fiber transmission line is the shortest.