Coherent detection method, apparatus, and system

A coherent detection method, comprising:

• performing, by a transmitting end, intensity modulation on an original signal to obtain an intensity-modulated optical signal, wherein the intensity-modulated optical signal excludes a phase-modulated optical signal;
• and
• performing, by a receiving end, phase modulation on a local oscillator optical signal to obtain a phase-modulated local oscillator optical signal, mixing the phase-modulated local oscillator optical signal and the intensity-modulated optical signal transmitted by the transmitting end, and then performing photoelectric detection, analog-to-digital conversion, and digital signal receiving processing in sequence to recover the original signal;
• wherein performing, by a receiving end, phase modulation on a local oscillator optical signal to obtain a phase-modulated local oscillator optical signal comprises:
• performing phase modulation on the local oscillator optical signal in each symbol period to obtain a phase-modulated local oscillator optical signal, wherein a modulation frequency of the phase-modulated local oscillator optical signal is consistent with a symbol rate of the intensity-modulated optical signal;
• or
• performing phase modulation twice on the local oscillator optical signal in each symbol period to obtain in sequence two phase-modulated local oscillator optical signals with different phases, wherein a modulation frequency of each of the phase-modulated local oscillator optical signals is twice a symbol rate of the intensity-modulated optical signal.

A coherent detection apparatus, comprising:

• a signal receiving module configured to receive an intensity-modulated optical signal transmitted by a transmitting end, wherein the intensity-modulated optical signal is obtained by intensity modulation performed by the transmitting end on an original signal, wherein the intensity-modulated optical signal excludes a phase-modulated optical signal;
• a phase modulation module configured to perform phase modulation on a local oscillator optical signal to obtain a phase-modulated local oscillator optical signal;
• and
• a signal recovery module configured to mix the intensity-modulated optical signal and the phase-modulated local oscillator optical signal, and then perform photoelectric detection, analog-to-digital conversion, and digital signal receiving processing in sequence to recover the original signal;
• wherein the phase modulation module comprises:
• an adjustable electrical delay line configured to control phase modulation on the local oscillator optical signal;
• a phase modulator configured to:
• under the control of the adjustable electrical delay line, perform phase modulation on the local oscillator optical signal in each symbol period to obtain the phase-modulated local oscillator optical signal, wherein a modulation frequency of the phase-modulated local oscillator optical signal is consistent with a symbol rate of the intensity-modulated optical signal;
• or
• perform phase modulation twice on the local oscillator optical signal in each symbol period to obtain in sequence two phase-modulated local oscillator optical signals with different phases, wherein a modulation frequency of each of the phase- modulated local oscillator optical signals is twice a symbol rate of the intensity- modulated optical signal.