Signal modulation and demodulation method and system, and apparatus

A signal modulation apparatus, applied to an intensity-modulation and direct-detection (IMDD) system, the apparatus comprising:

• a pulse amplitude modulation (PAM) encoder configured to perform PAM encoding on an input signal to obtain a PAM signal;
• a first filter configured to electrically modulate the PAM signal;
• a digital-to-analog converter (DAC) configured to convert the electrically modulated PAM signal into an analog signal;
• and
• an electro-optic modulator configured to:
• optically modulate the analog signal to obtain an optical signal, wherein a bias voltage of the electro-optic modulator is M+Vpi, Vpi is a variation value of the bias voltage in any cycle of a modulation curve of the electro-optic modulator when an output optical power of the electro-optic modulator varies from a maximum value to a minimum value or varies from a minimum value to a maximum value, the modulation curve is a curve corresponding to a function whose independent variable is the bias voltage and dependent variable is the output optical power, and M is a value of the bias voltage when the output optical power is the largest, and
• send the optical signal.

A signal modulation and demodulation system, applied to an intensity-modulation and direct-detection (IMDD) system, the signal modulation and demodulation system comprising:

• a signal modulation apparatus comprising,
• a pulse amplitude modulation (PAM) encoder configured to perform PAM encoding on an input signal to obtain a PAM signal,
• a first filter configured to electrically modulate the PAM signal,
• a digital-to-analog converter (DAC) configured to convert the electrically modulated PAM signal into an analog signal, and
• an electro-optic modulator configured to:
• optically modulate the analog signal to obtain an optical signal, wherein a bias voltage of the electro-optic modulator is M+Vpi, Vpi is a variation value of the bias voltage in any cycle of a modulation curve of the electro-optic modulator when an output optical power of the electro-optic modulator varies from a maximum value to a minimum value or varies from a minimum value to a maximum value, the modulation curve is a curve corresponding to a function whose independent variable is the bias voltage and dependent variable is the output optical power, and M is a value of the bias voltage when the output optical power is the largest;
• and
• send the optical signal;
• and
• a signal demodulation apparatus comprising.
• a receiver configured to receive the optical signal and convert the optical signal into an electrical signal, wherein an absolute value of a difference between 0 and a power of an optical carrier of the optical signal falls within a second preset range,
• a second filter configured to electrically demodulate the electrical signal, and
• a PAM decoder configured to perform PAM decoding on the electrically demodulated electrical signal to obtain a restored input signal.