Method and device for automatically locking repetition frequency and carrier-envelop offset frequency of optical frequency comb

A device for automatically locking repetition frequency and carrier-envelope offset frequency of optical frequency comb, comprising:

• a repetition frequency automatic locking unit;
• and
• a carrier-envelope offset frequency automatic locking unit;
• wherein the repetition frequency automatic locking unit comprises:
• a first photodetector;
• a first band-pass filter amplifier;
• a digital phase detector;
• a first power splitter;
• a first frequency-to-voltage converter;
• a first digital-to-analog converter;
• a microcontroller;
• a rubidium atomic clock;
• a frequency synthesizer;
• a first adaptive PID controller;
• an analog-to-digital converter;
• and
• a piezoelectric ceramic driver;
• wherein the first photodetector is configured to convert a repetition frequency optical signal of the optical frequency comb under a microwave frequency into a microwave repetition frequency signal fr;
• wherein a repetition frequency refers to a reciprocal of a time interval between two adjacent pulses in an optical pulse train;
• the repetition frequency represents a pulse period in a time domain;
• the repetition frequency represents a spacing between adjacent comb teeth in the frequency domain;
• the first band-pass filter amplifier is configured to filter the microwave repetition frequency signal fr to obtain a filtered repetition frequency signal;
• the digital phase detector is configured to mix the filtered repetition frequency signal with a first reference signal for phase discrimination to obtain a first error signal;
• wherein the first reference signal is generated by the frequency synthesizer;
• the frequency synthesizer is traceable to the rubidium atomic clock and is controlled by the microcontroller;
• the first power splitter is configured to split the first error signal into a first sub-signal and a second sub-signal;
• wherein the first sub-signal is transmitted to the first frequency-to-voltage converter;
• the first frequency-to-voltage converter is configured to convert the first sub-signal into a first voltage signal;
• the analog-to-digital converter is configured to acquire the first voltage signal;
• the microcontroller is configured to adjust a first output frequency of the frequency synthesizer based on a direction of the first voltage signal and the first error signal until a frequency of the first error signal is below 10 Hz;
• the analog-to-digital converter is configured to acquire the second sub-signal after adjustment of the first output frequency of the frequency synthesizer;
• the first adaptive PID controller is configured to process the second sub-signal to obtain a first processed signal;
• the first digital-to-analog converter is configured to convert the first processed signal into a first control signal;
• and
• the piezoelectric ceramic driver is configured to amplify the first control signal, so as to achieve automatic locking of the microwave repetition frequency signal fr;
• wherein the carrier-envelope offset frequency automatic locking unit comprises:
• a second photodetector;
• a second band-pass filter amplifier;
• a first frequency divider;
• a high-speed phase detector;
• a second power splitter;
• a second frequency divider;
• a second frequency-to-voltage converter;
• a second adaptive PID controller;
• a second digital-to-analog converter,
• a voltage to current (V/I) converter;
• a pump laser;
• the analog-to-digital converter;
• the microcontroller;
• the rubidium atomic clock;
• and
• the frequency synthesizer;
• wherein the second photodetector is configured to convert a carrier-envelope offset frequency optical signal of the optical frequency comb under the microwave frequency into a microwave carrier-envelope offset frequency signal f0;
• a carrier-envelope offset frequency represents an overall frequency offset of the optical pulse train;
• the second band-pass filter amplifier is configured to filter the microwave carrier-envelope offset frequency signal f0 to obtain a filtered carrier-envelope offset frequency signal;
• the first frequency divider is configured to divide the filtered carrier-envelope offset frequency signal to obtain a divided carrier-envelope offset frequency signal;
• the high-speed phase detector is configured to perform phase discrimination for the divided carrier-envelope offset frequency signal and a second reference signal to obtain a second error signal;
• wherein the second reference signal is generated by the frequency synthesizer;
• the second power splitter is configured to split the second error signal into a third sub-signal and a fourth sub-signal;
• the second frequency divider is configured to divide the third sub-signal into a divided sub-signal;
• the second frequency-to-voltage converter is configured to convert the divided sub-signal into a second voltage signal;
• the analog-to-digital converter is configured to acquire the second voltage signal;
• the microcontroller is further configured to adjust a second output frequency of the frequency synthesizer based on a direction of the second voltage signal and the second error signal until a frequency of the second error signal is below 100 Hz;
• the analog-to-digital converter is further configured to acquire the fourth sub-signal after adjustment of the second output frequency of the frequency synthesizer;
• the second adaptive PID controller is configured to process the fourth sub-signal to obtain a second processed signal;
• and
• the second digital-to-analog converter is configured to convert the first processed signal into a second control signal;
• the V/I converter is configured to convert the second control signal into a control current, which is applied to the pump laser;
• and
• the pump laser is configured to control an output light intensity of the pump laser based on the control current, so as to achieve automatic locking of the microwave carrier-envelope offset frequency signal f0.