Optical transmission system and transmitter

An optical transmission system comprising:

• a transmitter;
• and
• a receiver that receives signal light transmitted from the transmitter via a transmission line;
• wherein the transmitter includes:
• a generator that generates a second digital signal including a first digital signal and a third signal, the first digital signal including a first signal corresponding to a pilot symbol and a second signal corresponding to a data signal, the third signal including information related to a carrier phase of the first signal after Tomlinson-Harashima Precoding (THP) processing is performed;
• a THP processor that performs the THP processing on the second digital signal;
• and
• a transmission circuit that transmits, to the transmission line, signal light generated based on a third digital signal which is a signal after the THP processing is performed on the second digital signal;
• and
• wherein the receiver includes:
• a reception circuit that receives the signal light from the transmission line;
• and
• a compensator that compensates for an error of the second signal based on the first signal and the third signal, both of which are included in the third digital signal generated based on the signal light received by the reception circuit.