Amplitude coherent detection for pulse amplitude modulation signals

A method for digital communication, implemented at an optical receiver, the method comprising:

• receiving an optical signal comprising a signal based on pulse amplitude modulation and a pre-distortion operation, wherein the pre-distortion operation is based on amplitude levels of the pulse amplitude modulation;
• performing a coherent detection operation on the optical signal, wherein the coherent detection comprises an equally-spaced amplitude distribution;
• converting an output of the coherent detection operation from an optical domain to an electrical domain by digitizing the output;
• filtering an output of the digitizing using a pulse shaping filter;
• and
• demodulating an output of the filtering using a pulse amplitude modulation demodulator.

An apparatus for digital communication, comprising:

• a modulator configured to modulate an input signal based on pulse amplitude modulation;
• a processor configured to perform a pre-distortion operation on an output of the modulator, wherein the pre-distortion operation is based on amplitude levels of the pulse amplitude modulation;
• a pulse shaping filter configured to filter an output of the pre-distortion operation;
• and
• an optical transmitter configured to transmit an output of the filtering using intensity modulation, wherein the intensity modulation comprises an equally-spaced amplitude distribution.

An apparatus for digital communication, comprising:

• an optical receiver configured to receive an optical signal comprising a signal based on pulse amplitude modulation and a pre-distortion operation, wherein the pre-distortion operation is based on amplitude levels of the pulse amplitude modulation;
• a heterodyne coherent receiver configured to perform a coherent detection operation on an output of the optical receiver, wherein the coherent detection comprises an equally-spaced amplitude distribution;
• an analog-to-digital converter configured to convert an output of the heterodyne coherent receiver from an optical domain to an electrical domain;
• a pulse shaping filter configured to filter an output of the analog-to-digital converter;
• and
• a pulse amplitude modulation demodulator configured to demodulate an output of the pulse shaping filter.