Optical transmission system

The invention discloses an optical transmission system, which comprises a polarization beam combination optical path, a mutual excitation optical path and two paths of semiconductor optical amplification units, and is characterized in that each path of semiconductor optical amplification unit comprises a first lens, a semiconductor optical amplifier chip and a second lens which are arranged in sequence; the polarization beam combination light path is arranged on the side, back to the semiconductor optical amplifier chip, of the first lens, and the mutual excitation light path is arranged on the side, back to the semiconductor optical amplifier chip, of the second lens. Light beams output by the rear ends of the two semiconductor optical amplifier chips can pass through the mutual excitation light path and then are respectively input into the different semiconductor optical amplifier chips to form two gain light beams, and the two gain light beams are integrated into one beam of parallel light through the pola