An optical transmitter, comprising: an optical signal generator, N spreaders (3021,3022,...,302n), N pairs of data modulators (3031a, 3031b; 3032a, 3032b;...; 303na,303nb), and a combiner, wherein N is a positive integer; and the optical signal generator is configured to generate N optical carriers with a single wavelength; characterized in that: an i th spreader is configured to: spread an i th optical carrier generated by the optical signal generator, to obtain a spread optical signal having two subcarriers, wherein frequencies of spread optical signals generated by different spreaders are different; and split the spread optical signal into two signals, wherein the two signals are a first optical signal and a second optical signal, and delay the second optical signal to obtain a third optical signal; an i th pair of data modulators are configured to: perform data modulation on the first optical signal and the third optical signal that are obtained by the i th spreader through processing, to obtain a pair of modulated optical signals, and transmit the pair of modulated optical signals to the combiner, wherein the pair of modulated optical signals reaching the combiner differ by 1/(4 f si) in time domain, f si represents a spreading frequency of the i th spreader, and i is any positive integer not greater than N; and the combiner is configured to: combine, into one optical signal, N pairs of modulated optical signals transmitted by the N pairs of data modulators (3031a, 3031b; 3032a, 3032b;...; 303na,303nb), and send the optical signal. an optical signal generator, N spreaders (3021,3022,...,302n), N pairs of data modulators (3031a, 3031b; 3032a, 3032b;...; 303na,303nb), and a combiner, wherein N is a positive integer; and the optical signal generator is configured to generate N optical carriers with a single wavelength; characterized in that: an i th spreader is configured to: spread an i th optical carrier generated by the optical signal generator, to obtain a spread optical signal having two subcarriers, wherein frequencies of spread optical signals generated by different spreaders are different; and split the spread optical signal into two signals, wherein the two signals are a first optical signal and a second optical signal, and delay the second optical signal to obtain a third optical signal; an i th pair of data modulators are configured to: perform data modulation on the first optical signal and the third optical signal that are obtained by the i th spreader through processing, to obtain a pair of modulated optical signals, and transmit the pair of modulated optical signals to the combiner, wherein the pair of modulated optical signals reaching the combiner differ by 1/(4 f si) in time domain, f si represents a spreading frequency of the i th spreader, and i is any positive integer not greater than N; and the combiner is configured to: combine, into one optical signal, N pairs of modulated optical signals transmitted by the N pairs of data modulators (3031a, 3031b; 3032a, 3032b;...; 303na,303nb), and send the optical signal. an i th spreader is configured to: spread an i th optical carrier generated by the optical signal generator, to obtain a spread optical signal having two subcarriers, wherein frequencies of spread optical signals generated by different spreaders are different; and split the spread optical signal into two signals, wherein the two signals are a first optical signal and a second optical signal, and delay the second optical signal to obtain a third optical signal; an i th pair of data modulators are configured to: perform data modulation on the first optical signal and the third optical signal that are obtained by the i th spreader through processing, to obtain a pair of modulated optical signals, and transmit the pair of modulated optical signals to the combiner, wherein the pair of modulated optical signals reaching the combiner differ by 1/(4 f si) in time domain, f si represents a spreading frequency of the i th spreader, and i is any positive integer not greater than N; and the combiner is configured to: combine, into one optical signal, N pairs of modulated optical signals transmitted by the N pairs of data modulators (3031a, 3031b; 3032a, 3032b;...; 303na,303nb), and send the optical signal.