Transmitting, receiving and communication systems of optical network and method for modulating signal

A receiving system of an optical network, comprising:

• an M-order digital demodulator, configured to demodulate a received M-order digital signal into a binary digital signal and output the binary digital signal, wherein the received M-order digital signal is a signal modulated by a transmitting system through an M-order digital modulator, and each transmission symbol in the M-order digital signal carries information of N=log2M bits, where N is a natural number greater than 1 and M is a natural number;
• second Passive Optical Network (PON) equipment, configured to receive the demodulated binary digital signal, and perform corresponding operation according to the demodulated binary digital signal;
• wherein the second PON equipment comprises one of:
• an Optical Line Terminal (OLT) and an Optical Network Unit (ONU);
• wherein the received M-order digital signal is modulated by a M-order digital modulator, wherein the M-order digital modulator is configured to modulate the binary digital signal into an M-order digital signal, and output the M-order digital signal to the M-order digital demodulator, wherein before modulating the input binary digital signal into the M-order digital signal, the M-order digital modulator further configured to judge whether to perform modulation by the M-order digital modulator or not;
• and based on that a judgment result is not to perform modulation by the M-order digital modulator, perform modulation through a binary digital modulator;
• wherein before judging whether to perform modulation by the M-order digital modulator or not, the the M-order digital modulator further configured to:
• judge whether to output both paths of received binary digital signals or not based on that a judgment result is to output both paths of received binary digital signals, modulate the two paths of binary digital signals by the binary digital modulator and the M-order digital modulator respectively;
• and based on that a judgment result is not to output both paths of received binary digital signals, judge whether to perform modulation by the M-order digital modulator or not.

A method for modulating a signal, comprising:

• modulating an input two paths of binary digital signal into an M-order digital signal by an M-order digital modulator, wherein each transmission symbol in the M-order digital signal carries information of N=log2M bits, where N is a natural number greater than 1 and M is a natural number;
• outputting the M-order digital signal by an optical network;
• wherein before modulating the input binary digital signal into the M-order digital signal by the M-order digital modulator, the method further comprises:
• judging whether to perform modulation by the M-order digital modulator or not;
• and based on that a judgment result is not to perform modulation by the M-order digital modulator, performing modulation through a binary digital modulator;
• wherein before judging whether to perform modulation by the M-order digital modulator or not, the method further comprises:
• judging whether to output both paths of received binary digital signals or not;
• based on that a judgment result is to output both paths of received binary digital signals, modulating the two paths of binary digital signals by the binary digital modulator and the M-order digital modulator respectively;
• and based on that a judgment result is not to output both paths of received binary digital signals, judging whether to perform modulation by the M-order digital modulator or not.