Method and apparatus for automatically controlling bias voltage of optical modulator

An apparatus for automatically controlling a bias voltage of an IQ optical modulator, wherein the IQ optical modulator comprises an I modulation module, a Q modulation module and a P phase shifting module, the I modulation module and the Q modulation module being configured to parallelly receive an input optical signal, the P phase shifting module being connected in series to the Q modulation module, the optical signal being modulated by the Q modulation module being input to the P phase shifting module for modulation, the optical signal output by the P phase shifting module being combined with the optical signal output by the I modulation module and then being output;

• wherein the apparatus comprises:
• a processor, an optical-electrical converter, a filter, and an output device;
• wherein
• the processor is configured to:
• obtain an I dither amplitude and an initial I bias voltage with respect to the I modulation module, a Q dither amplitude and an initial Q bias voltage with respect to the Q modulation module, and an initial P bias voltage with respect to the P phase shifting module;
• obtain an I reference phase and an I error feedback coefficient with respect to the I modulation module, a Q reference phase and a Q error feedback coefficient with respect to the Q modulation module, and a P reference phase and a P error feedback coefficient with respect to the P phase shifting module;
• use the initial I bias voltage as an I bias voltage, use the initial P bias voltage as a P bias voltage, and use the initial Q bias voltage as a Q bias voltage;
• and send the Q bias voltage, the I bias voltage and the P bias voltage to the output device;
• the output device is configured to:
• input the I bias voltage and an I dither signal to the I modulation module, input the Q bias voltage and a Q dither signal to the Q modulation module, and input the P bias voltage to the P phase shifting module, wherein an amplitude of the I dither signal is the I dither amplitude, and an amplitude of the Q dither signal is the Q dither amplitude;
• the optical-electrical converter is configured to:
• acquire, via a light splitter, an output optical signal that is modulated by the I modulation module based on the I bias voltage, the I dither signal and an input I radio frequency signal, modulated by the Q modulation module based on the Q bias voltage, the Q dither signal and an input Q radio frequency signal, and modulated by the P phase shifting module based on the P bias voltage, and convert the output optical signal into an electrical signal;
• the filter is configured to extract an alternating current component from the electrical signal;
• the processor is configured to extract an I harmonic component with respect to the I modulation module, a Q harmonic component with respect to the Q modulation module, and a P feedback signal with respect to the P phase shifting module from the alternating current component;
• the processor is configured to:
• calculate an I harmonic amplitude and an I harmonic phase of the I harmonic component, a Q harmonic amplitude and a Q harmonic phase of the Q harmonic component, and a P feedback signal amplitude and a P feedback signal phase of the P feedback signal;
• calculate a new I bias voltage based on the I harmonic phase and the I reference phase in combination with the I error feedback coefficient, the I bias voltage and the I harmonic amplitude, calculate a new Q bias voltage based on the Q harmonic phase and the Q reference phase in combination with the Q error feedback coefficient, the Q bias voltage and the Q harmonic amplitude, and calculate a new P bias voltage based on the P feedback signal phase and the P reference phase in combination with the P error feedback coefficient, the P bias voltage and the P feedback signal amplitude;
• and use the new I bias voltage as the I bias voltage, use the new Q bias voltage as the Q bias voltage, use the new P bias voltage as the P bias voltage, and send the Q bias voltage, the I bias voltage and the P bias voltage to the output device, such that the output device inputs the I bias voltage and the I dither signal to the I modulation module, and inputs the Q bias voltage and the Q dither signal to the Q modulation module, and inputs the P bias voltage to the P phase shifting module.