Coherent detection method and apparatus, and optical transmission system

A coherent detection device, comprising:

• an optical coupling module configured to acquire an optical transmission signal and a local oscillator signal and couple the optical transmission signal and the local oscillator signal to obtain only one coupled signal, wherein a frequency value of the local oscillator signal differs from a frequency value of the optical transmission signal by a preset offset frequency value, the preset offset frequency value being smaller than a symbol rate value of the optical transmission signal, wherein the coupled signal has values on both an in-phase component and a quadrature component;
• an optoelectronic detection module connected to the optical coupling module and configured to convert the coupled signal into an analog signal;
• an analog-to-digital conversion module connected to the optoelectronic detection module and configured to sample the analog signal according to a preset sampling frequency value and convert the analog signal into a plurality of digital signals, wherein the plurality of digital signals comprises the in-phase component and the quadrature component;
• and
• a digital processing module connected to the analog-to-digital conversion module and configured to process two digital signals among the plurality of digital signals so that a phase difference between the two digital signals is 90 degrees, wherein the two digital signals are derived from a same signal symbol in the optical transmission signal.

An optical transmission system, comprising a coherent detection device, wherein the coherent detection device comprises:

• an optical coupling module configured to acquire an optical transmission signal and a local oscillator signal and couple the optical transmission signal and the local oscillator signal to obtain only one coupled signal, wherein a frequency value of the local oscillator signal differs from a frequency value of the optical transmission signal by a preset offset frequency value, the preset offset frequency value being smaller than a symbol rate value of the optical transmission signal, wherein the coupled signal has values on both an in-phase component and a quadrature component;
• an optoelectronic detection module connected to the optical coupling module and configured to convert the coupled signal into an analog signal;
• an analog-to-digital conversion module connected to the optoelectronic detection module and configured to sample the analog signal according to a preset sampling frequency value and convert the analog signal into a plurality of digital signals, wherein the plurality of digital signals comprises the in-phase component and the quadrature component;
• and
• a digital processing module connected to the analog-to-digital conversion module and configured to process two digital signals among the plurality of digital signals so that a phase difference between the two digital signals is 90 degrees, wherein the two digital signals are derived from a same signal symbol in the optical transmission signal.