Optical transmission system

An optical transmission system comprising:

• an optical transmitter, the optical transmitter including:
• a signal generation unit configured to generate, using input information data, an N-value symbol that is Gray-coded, the N being an integer of 2 or greater;
• a signal coding unit configured to perform nonlinear trellis coding, which corresponds to nonlinear calculation, on the N-value symbol to generate an N+2-value symbol;
• and
• a modulator configured to modulate the N+2-value symbol and transmit an optical signal corresponding to the N+2-value symbol to an optical receiver, and
• the optical receiver, the optical receiver including:
• a light receiving unit configured to receive the optical signal and convert the received optical signal into an electrical signal;
• and
• a digital signal processing unit configured to perform digital signal processing on the electrical signal to reconstruct the N+2-value symbol.