Optical relaying apparatus, optical transmission system, and optical-signal reproducing and relaying method

An optical repeater comprising:

• a first signal converter to convert a received optical signal into an electric signal, demodulate and output the electric signal, and modulate an input electric signal in a first modulation scheme and convert the electric signal into an optical signal and transmit the optical signal;
• and
• a second signal converter to modulate the electric signal output from the first signal converter in a second modulation scheme and convert the electric signal into an optical signal and transmit the optical signal, and convert a received optical signal into an electric signal, demodulate the electric signal, and output the electric signal as an electric signal input to the first signal converter;
• further comprising an optical switcher to perform first switch processing for inputting, to the first signal converter, an optical signal output from a first communication circuit and outputting an optical signal output from the first signal converter toward the first communication circuit and inputting, to the second signal converter, an optical signal output from a second communication circuit and outputting an optical signal output from the second signal converter toward the second communication circuit or second switch processing for inputting, to the first signal converter, the optical signal output from the second communication circuit and outputting the optical signal output from the first signal converter toward the second communication circuit and inputting, to the second signal converter, the optical signal output from the first communication circuit and outputting the optical signal output from the second signal converter toward the first communication circuit.