A method and device for self-locking frequency of a wide-band optical frequency comb

Abstract

The present invention discloses a method and device for self-locking the frequency of a wide-band optical frequency comb, which converts the repetition frequency and offset frequency optical signals of the optical frequency comb into the repetition frequency signal f of the optical frequency comb at the microwave frequency. r And the offset frequency signal f0; for f r After the signal is filtered, it is mixed with the reference signal to obtain the error signal, which is generated by the frequency synthesizer; the error signal is converted into a voltage signal in one way, and the output frequency of the frequency synthesizer is adjusted according to the direction of the error signal and the voltage signal until the error signal is lower than 10Hz; after the output frequency of the frequency synthesizer is adjusted, the error signal is collected by the analog-to-digital converter in another way, and then processed by the adaptive PID controller, and the control signal is output by the digital-to-analog converter, and the f is realized by controlling the piezoelectric ceramics. r Signal locking; filter the f0 signal, divide the frequency, and then phase-detect with the reference signal to obtain an error signal; the error signal is divided into two paths, one of which is converted into a voltage signal after frequency reduction, and the output frequency of the frequency synthesizer is adjusted according to the direction of the error signal and the voltage signal until the error signal is lower than 100Hz; after the output frequency adjustment is completed, the error signal is collected by the analog-to-digital converter and processed by the adaptive PID controller, and the control voltage is output by the digital-to-analog converter, and then applied to the pump laser after current conversion to achieve f0 signal locking. The present invention can achieve self-locking of the repetition frequency and offset frequency of the optical frequency comb.

Description

Technical Field

[0001] The present invention relates to the field of frequency control technology, and in particular to a method and device for self-locking the broadband and large-range frequency of an optical frequency comb. Background Art

[0002] As one of the greatest inventions of the 21st century, the optical frequency comb has become the most effective optical frequency measurement tool to date. It can simply and accurately connect microwave atomic frequency standards and optical frequency standards, laying the foundation for the development of extremely high-precision frequency standards. At the same time, due to the relationship between parameters such as time, length and wavelength, the optical frequency comb can also provide a more ideal research tool for absolute measurement technology on a spatial scale, and has broad application space in manned space flight, spectral imaging, modern manufacturing and other fields.

[0003] In order to make the measurement results based on the optical frequency comb highly reliable, the repetition frequency and offset frequency of the optical frequency comb need to be locked with high precision and for a long time. The repetition frequency of the optical frequency comb is the spacing between each "comb tooth" of the optical frequency comb in the frequency domain, and the offset frequency is the offset of the first "comb tooth" of the optical frequency comb relative to the zero frequency. The repetition frequency of the optical frequency comb is directly affected by the cavity length. Temperature changes or mechanical vibrations will affect the cavity length, causing the repetition frequency of the optical frequency comb to drift; the offset frequency of the optical frequency comb is affected by the pump current and temperature. Fluctuations in temperature or pump current will cause the offset frequency of the optical frequency comb to drift. At present, the frequency locking of the optical frequency comb is mostly achieved by analog locking technology. A phase-locked loop is built through an operational amplifier to achieve closed-loop control. When actually locking, it is often necessary for the operator to perform more complex adjustments to complete the locking, which increases the complexity of the optical frequency comb system. At the same time, after being exposed to factors such as temperature and micro-vibration for a long time, the frequency of the optical frequency comb cannot continue to be locked after it is out of lock, which limits the accuracy of the optical frequency comb to a certain extent. For the automatic locking of the optical frequency comb frequency, the publicly available methods mostly use the upper computer to adjust the parameters of the lower computer, which requires the upper computer and the lower computer to work in coordination and has a large amount of communication data, thereby reducing the bandwidth of the phase-locked loop and the locking accuracy of the optical frequency comb, affecting the measurement accuracy of the optical frequency comb. At the same time, if there is a communication error, it will directly cause the optical frequency comb to be unlocked. Summary of the invention

[0004] In view of this, the present invention provides a method and device for self-locking the frequency of an optical frequency comb over a wide bandwidth and a large range, which can achieve self-locking of the repetition frequency and the offset frequency of the optical frequency comb.

[0005] The technical solution adopted by the present invention is as follows:

[0006] A broadband and large-range frequency self-locking method for an optical frequency comb, which converts the repetition frequency and offset frequency optical signals of the optical frequency comb into the repetition frequency signal f at microwave frequency. r And the offset frequency signal f0;

[0007] For f r The signal is filtered and mixed with the reference signal to obtain an error signal, which is generated by a frequency synthesizer. The error signal is divided into two paths, one of which is converted into a voltage signal. The output frequency of the frequency synthesizer is adjusted according to the direction of the error signal and the voltage signal until the error signal is lower than 10Hz. After the output frequency of the frequency synthesizer is adjusted, the error signal is collected by the analog-to-digital converter and processed by the adaptive PID controller. The control signal is output by the digital-to-analog converter, and the piezoelectric ceramic driver is amplified to realize the control of the piezoelectric ceramic and thus realize f r The signal is automatically locked;

[0008] For the f0 signal, the frequency is divided after filtering and then phase-detected with the reference signal to obtain the error signal; the error signal is divided into two paths, one of which is converted into a voltage signal after frequency reduction, and the output frequency of the frequency synthesizer is adjusted according to the direction of the error signal and the voltage signal until the error signal is lower than 100Hz; after the output frequency adjustment of the frequency synthesizer is completed, the other path of the error signal is collected by the analog-to-digital converter and processed by the adaptive PID controller, and the control voltage is output by the digital-to-analog converter, which is applied to the pump laser after current conversion to achieve automatic locking of the f0 signal.

[0009] The present invention also provides a wide-band and large-range frequency self-locking device for an optical frequency comb, comprising a repetition frequency automatic locking unit and an offset frequency automatic locking unit;

[0010] The repetition frequency automatic locking unit includes a photodetector Ⅰ, a bandpass filter amplifier Ⅰ, a digital phase detector, a power divider Ⅰ, a frequency-voltage converter Ⅰ, a digital-to-analog converter Ⅰ, a microcontroller, a rubidium atomic clock, a frequency synthesizer, an adaptive PID controller Ⅰ, an analog-to-digital converter, and a piezoelectric ceramic driver;

[0011] The photoelectric detector I is used to perform photoelectric conversion on the optical frequency comb repetition frequency optical signal generated by the optical frequency comb optical system to obtain the microwave field optical frequency comb repetition frequency signal f r ;

[0012] The bandpass filter amplifier I is used to re-sample the optical frequency comb signal f r Perform filtering;

[0013] The digital phase detector is used to convert the filtered optical frequency comb repetition frequency signal f r Mixing and phase detection with reference signal I to obtain an error signal; the reference signal I is generated by a frequency synthesizer traceable to a rubidium atomic clock, and the frequency synthesizer is controlled by a microcontroller;

[0014] The power divider I is used to divide the error signal into two paths, one of which is transmitted to the frequency-voltage converter I, and the frequency-voltage converter I is used for frequency-voltage conversion, and the converted voltage is collected by the analog-to-digital converter; the microcontroller adjusts the output frequency of the frequency synthesizer according to the collected voltage and the direction of the error signal until the frequency value of the error signal is lower than 10Hz;

[0015] After the adjustment of the frequency synthesizer output frequency is completed, the error signal is collected by the microcontroller through the analog-to-digital converter. The collected signal is processed by the adaptive PID controller I and then outputs the control signal by the digital-to-analog converter I.

[0016] The piezoelectric ceramic driver receives the control signal, amplifies it and outputs it to achieve f r Automatic signal locking;

[0017] The offset frequency automatic locking unit includes a photodetector II, a bandpass filter amplifier II, a frequency divider I, a high-speed phase detector, a power divider II, a frequency divider II, a frequency-voltage converter II, an adaptive PID controller II, a digital-to-analog converter II, a V / I converter and a pump laser; at the same time, the offset frequency automatic locking unit and the repetition frequency automatic locking unit share the analog-to-digital converter, a microcontroller, a rubidium atomic clock and a frequency synthesizer;

[0018] The photodetector II is used to perform photoelectric conversion on the optical frequency comb offset frequency optical signal generated by the optical frequency comb optical system to obtain the microwave field optical frequency comb offset frequency signal f0;

[0019] The bandpass filter amplifier II is used to filter the optical frequency comb offset frequency signal f0;

[0020] The frequency divider I is used to divide the frequency of the optical frequency comb offset signal f0 after filtering;

[0021] The high-speed phase detector is used to perform phase detection on the divided optical frequency comb offset signal f0 and the reference signal II to obtain an error signal; the reference signal II is generated by a frequency synthesizer traceable to a rubidium atomic clock, and the frequency synthesizer is controlled by a microcontroller;

[0022] The power divider II is used to divide the error signal into two paths, one of which is divided by the frequency divider II and input into the frequency-voltage converter II; the frequency-voltage converter II is used for frequency-voltage conversion, and the converted voltage is collected by the analog-to-digital converter; the microcontroller adjusts the output frequency of the frequency synthesizer according to the collected voltage and the direction of the error signal until the frequency value of the error signal is lower than 100Hz;

[0023] After the frequency synthesizer output frequency is adjusted, the error signal is collected by the microcontroller through the analog-to-digital converter. The collected signal is processed by the adaptive PID controller II and then outputs the control voltage by the digital-to-analog converter II.

[0024] The V / I converter is used to convert the control voltage into a current to obtain a control current and apply it to the pump laser;

[0025] The pump laser can be used to achieve automatic locking of the f0 signal.

[0026] Beneficial effects:

[0027] 1. The present invention can well solve the problem of complexity of frequency locking operation of optical frequency comb in analog locking circuit, and can also solve the problem of large communication data volume and reduced reliability between lower and upper computers in digital locking of optical frequency comb. It can realize automatic locking of repetition frequency and offset frequency (carrier envelope phase shift frequency) of optical frequency comb after the optical frequency comb is turned on and stabilized, greatly increasing the application range of optical frequency comb. Secondly, the present invention can adjust the frequency synthesizer in a relatively large range (adjustment in the order of hundreds of kHz), thereby realizing self-locking of wide-range frequency of optical frequency comb.

[0028] 2. The present invention can adjust the reference signal frequency in a timely manner according to the locking state of the optical frequency comb to achieve tracking locking.

[0029] 3. When the optical frequency comb is unlocked due to sudden environmental factors such as vibration, the present invention can achieve re-locking within a time better than 200ms.

[0030] 4. Since the repetition frequency and offset frequency of the optical frequency comb are greatly affected by temperature, the present invention controls TEC to achieve a stable temperature environment in the laser cavity, ensuring that the optical system of the optical frequency comb is in a constant temperature state, thereby reducing the frequency drift of the repetition frequency and offset frequency of the optical frequency comb, and laying the foundation for achieving long-term frequency locking of the optical frequency comb.

[0031] 5. The device of the present invention can get rid of the analog devices and peripheral instruments such as the host computer in the process of frequency locking of the optical frequency comb, and can realize the function of frequency locking of the optical frequency comb in a very small space, which provides support for the miniaturization development of the optical frequency comb. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The figure is a schematic diagram of the composition of the device of the present invention. DETAILED DESCRIPTION

[0033] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0034] The present invention provides a broadband and large-range frequency self-locking method for an optical frequency comb, which uses a digital phase-locked loop control method to achieve automatic locking of the repetition frequency and offset frequency of the optical frequency comb, and can also achieve tracking locking and re-locking after being released from locking.

[0035] Optical frequency comb f rThe signal generating optical system is a femtosecond laser oscillator. Since the repetition frequency and offset frequency of the optical frequency comb are greatly affected by temperature, it is necessary to first achieve a constant temperature in the laser cavity of the femtosecond laser oscillator. Specifically, a thermistor with a resistance of 10K at standard temperature is used as the temperature sensor in the cavity. The microcontroller controls the analog-to-digital converter to read the resistance of the thermistor in real time, and converts it through an empirical formula to realize temperature reading. According to the current temperature, the microcontroller controls the heating or cooling of the TEC cooler in the cavity through the PID controller to stabilize the temperature in the cavity to 25±0.05℃, thereby reducing the frequency drift of the repetition frequency and offset frequency of the optical frequency comb, laying the foundation for achieving long-term frequency locking of the optical frequency comb.

[0036] After the temperature in the laser cavity is stabilized, the repetition frequency f of the optical frequency comb is then r The optical frequency comb f is locked to the offset frequency f0. r The signal generating optical system and the f0 signal generating optical system generate optical frequency comb repetition frequency and offset frequency optical signals respectively. The repetition frequency optical signal and the offset frequency optical signal are converted into photoelectric signals through a photodetector (PD), thereby converting the optical signal into a microwave signal, and then obtaining the optical frequency comb repetition frequency signal and offset frequency signal at the microwave frequency.

[0037] For the optical frequency comb f at microwave frequencies r signal, in order to effectively extract the microwave f r The baseband signal is filtered out by bandpass filter amplifier I r High-order harmonic signals, thereby retaining the fundamental frequency signal, the f r The signal is mixed with a reference signal I (the reference signal is a frequency signal) in a digital phase detector, and the output of the digital phase detector is a triangular wave error signal. The reference signal I is output by a frequency synthesizer traceable to a rubidium atomic clock, and the frequency synthesizer is controlled by a microcontroller.

[0038] In order to optimize the optical frequency comb f r In the signal locking state, the error signal is divided into two paths through the power divider I. One path converts the frequency error signal into a DC voltage signal through the frequency-to-voltage converter I (the effective conversion bandwidth is 20kHz, and the corresponding DC conversion voltage is 0-5V). The DC voltage value represents the magnitude of the current frequency error signal. Since the phase error signal identified by the digital phase detector can only determine the previous f r The difference between the signal and the reference signal I cannot determine f rThe microcontroller needs to record the voltage value after sampling the voltage through the analog-to-digital converter, and then adjust the frequency of the frequency synthesizer appropriately after 5ms according to the different voltage values ​​obtained by sampling. Then the microcontroller records the voltage collected by the adjusted analog-to-digital converter, and judges the current f by comparing it with the previously recorded voltage value. r The direction of the error signal generated after the phase detection between the signal and the reference signal I. Then the microcontroller adjusts the frequency synthesizer again according to the direction of the current error signal and the frequency value of the error signal corresponding to the voltage signal after the frequency-voltage conversion, so that it can be close enough to f r The frequency of the signal (the frequency value of the error signal is less than 10Hz) is adjusted to ensure that it can be locked directly in the future. After the microcontroller completes the adjustment of the output frequency of the frequency synthesizer, the other signal separated by the power divider I is directly collected by the microcontroller through the analog-to-digital converter, and the collected error signal is processed. After the error signal is calculated by the adaptive PID controller I, the adaptive PID controller I adjusts the proportional, integral and differential parameters in real time according to the signal state to achieve parameter optimization. The result of the adaptive PID controller I is output through the digital-to-analog converter I (the output voltage of the digital-to-analog converter I is 0-5V, and the default intermediate state output is 2.5V). The output result is amplified by 30 times the control signal through the PZT driver (piezoelectric ceramic driver) to achieve an output of 0-150V, thereby controlling the PZT expansion and contraction in the cavity to achieve cavity length adjustment, thereby realizing the optical frequency comb f r Negative feedback of the signal automatically locks.

[0039] Implementing an optical frequency comb in a microcontroller r During the process of continuous signal locking, the microcontroller monitors the output voltage of the digital-to-analog converter I in real time. When the output voltage is 0.2V away from the threshold voltage, the threshold voltage is the maximum and minimum values ​​of the output voltage of the digital-to-analog converter I. According to the change direction of the output voltage of the digital-to-analog converter I, the output frequency of the frequency synthesizer is adjusted (for example, when the output voltage of the digital-to-analog converter I is close to 0V, it is necessary to slowly reduce the frequency of the reference signal I so that the output voltage of the digital-to-analog converter I is close to 2.5V again; conversely, when the output voltage of the digital-to-analog converter I is close to 5V, it is necessary to slowly increase the frequency of the reference signal I so that the output voltage of the digital-to-analog converter I is close to 2.5V again) until the adjusted output voltage of the digital-to-analog converter I returns to the output voltage when the optical frequency comb repetition frequency is locked, thereby achieving tracking and locking of the optical frequency comb repetition frequency.

[0040] When the optical frequency comb is out of lock due to external factors, the microcontroller determines that the system is out of lock based on the change in the output voltage of the frequency-to-voltage converter I, and then turns off the closed-loop control of the adaptive PID controller I. Then, according to the method of automatic locking of the optical frequency comb repetition frequency, the search for the best reference frequency output by the frequency synthesizer (the error signal frequency value is less than 10Hz) is carried out, and the closed-loop lock is re-performed after the adjustment of the frequency synthesizer output frequency, thereby achieving the re-locking of the optical frequency comb repetition frequency after it is out of lock.

[0041] For the optical frequency comb f0 signal at microwave frequency and the repetition frequency signal f r Similarly, according to the characteristics of the f0 signal, a suitable bandpass filter amplifier II is selected to realize the effective extraction and signal amplification of the f0 signal. Since the optical frequency comb f0 signal drifts very fast, reaching the order of hundreds of kHz or even MHz, this drift speed is generally impossible for conventional mixers or phase detectors to effectively detect the phase. Therefore, it is first divided by the frequency divider I, and the frequency divider I is selected to be 16 divisions or more, which can ensure that the frequency drift of the optical frequency comb f0 signal is reduced to a lower speed. Although the signal is divided, the frequency drift speed at this time is still relatively fast, reaching the order of tens of kHz. Therefore, the effective phase detection between the optical frequency comb f0 signal and the reference signal II is realized by a high-speed phase detector, and the reference signal II is output by a frequency synthesizer traced back to the rubidium atomic clock. The effective phase detection bandwidth of the high-speed phase detector reaches the order of MHz, ensuring that there is a good high signal-to-noise ratio error signal output under MHz range jitter. After completing the phase detection, in order to optimize the locking state of the optical frequency comb f0 signal, the error signal is divided into two paths through the power divider II, one of which is divided by the frequency divider II to ensure that the error signal input to the frequency-to-voltage converter II (effective conversion bandwidth is 20kHz, corresponding to the DC conversion voltage of 0~5V) is lower than 20kHz. rThe signal is similar, and the error signal cannot determine the signal size relationship between the f0 signal and the reference signal II. Therefore, the output voltage result of the frequency-voltage converter II is converted by the analog-to-digital converter and collected by the microcontroller. The collected voltage is recorded, and then the frequency synthesizer is adjusted in a larger range (kHz level adjustment) according to the current collected voltage. The size of the output voltage of the frequency-voltage converter II after the change is recorded, so as to avoid the state misjudgment caused by the jitter of the f0 signal, and then realize the judgment of the current error signal direction. Then the microcontroller adjusts the output frequency of the frequency synthesizer according to the direction of the current error signal and the collected voltage value of the frequency-voltage converter II, so that the reference signal II is close enough to the f0 signal frequency (lower than 100Hz after frequency division). After the output frequency of the frequency synthesizer is adjusted, the microcontroller collects another error signal through the analog-to-digital converter, inputs it into the adaptive PID controller II, processes the signal, and sends the processing result to the digital-to-analog converter II to form the output voltage (the output voltage of the digital-to-analog converter II is 0-3V, and the default is 1.5V intermediate state output). Since the optical frequency comb f0 signal is locked by current regulation, the control voltage output by the digital-to-analog converter II is converted to current by the V / I converter (0-3V corresponds to 0-20mA), and the control current is applied to the pump laser to achieve automatic locking of the optical frequency comb f0 signal. The stability of the optical frequency comb offset signal f0 is directly affected by the temperature and the output stability of the pump laser. After the temperature control of the laser cavity of the femtosecond laser oscillator is completed, the control current generated after the closed-loop locking is applied to the pump laser, and the pump laser optical power can be modulated, thereby effectively improving the stability of the pump laser output optical power and achieving offset signal locking.

[0042] In the process of the microcontroller realizing continuous locking of the optical frequency comb f0 signal, the microcontroller monitors the output voltage of the digital-to-analog converter II in real time. When the output voltage is 0.1V away from the threshold voltage, the threshold voltage is the maximum and minimum values ​​of the output voltage of the digital-to-analog converter II. According to the change direction of the output voltage of the digital-to-analog converter II, the output frequency of the frequency synthesizer is adjusted (for example, when the output voltage of the digital-to-analog converter II is close to 0V, it is necessary to slowly reduce the frequency of the reference signal II so that the output voltage of the digital-to-analog converter II is close to 1.5V again; conversely, when the output voltage of the digital-to-analog converter II is close to 3V, it is necessary to slowly increase the frequency of the reference signal II so that the output voltage of the digital-to-analog converter II is close to 1.5V again) until the output voltage of the digital-to-analog converter II after adjustment returns to the output voltage when the optical frequency comb offset frequency is locked, thereby realizing tracking and locking of the optical frequency comb offset frequency.

[0043] When the optical frequency comb is out of lock due to external factors, the microcontroller determines that the system is out of lock based on the change in the output voltage of the frequency-voltage converter II, and then turns off the closed-loop control of the adaptive PID controller II. Then, according to the method of automatic locking of the offset frequency of the optical frequency comb (searching for the best reference frequency output by the frequency synthesizer, and re-locking the closed loop after adjusting the output frequency of the frequency synthesizer), the offset frequency of the optical frequency comb is re-locked after being out of lock.

[0044] The present invention also provides a wide-band and large-range frequency self-locking device for an optical frequency comb, comprising a temperature control unit, a repetition frequency automatic locking unit and an offset frequency automatic locking unit;

[0045] The temperature control unit includes a TEC cooler and a thermistor. The TEC cooler and the thermistor are both set in the laser cavity. The thermistor is used as a temperature sensor to monitor the temperature in the cavity. A thermistor with a resistance of 10K at standard temperature is used. The microcontroller controls the analog-to-digital converter to read the thermistor resistance in real time and converts it through an empirical formula to achieve temperature reading. The TEC cooler is used to adjust the temperature in the cavity. The microcontroller controls the TEC cooler to heat or cool according to the current temperature through the PID controller, so as to stabilize the temperature in the cavity to 25±0.05℃.

[0046] like Figure 1 As shown, the repetition frequency automatic locking unit includes a photodetector Ⅰ, a bandpass filter amplifier Ⅰ, a digital phase detector, a power divider Ⅰ, a frequency-voltage converter Ⅰ, a digital-to-analog converter Ⅰ, a microcontroller, a rubidium atomic clock, a frequency synthesizer, an adaptive PID controller Ⅰ, an analog-to-digital converter, and a piezoelectric ceramic driver;

[0047] Photodetector I is used to perform photoelectric conversion on the optical frequency comb repetition frequency optical signal generated by the optical frequency comb optical system to obtain the microwave field optical frequency comb repetition frequency signal f r ;

[0048] Bandpass filter amplifier I is used to re-sample the optical frequency comb signal f r Perform filtering;

[0049] The digital phase detector is used to re-occur the filtered optical frequency comb signal f r Mixing and phase detection are performed with reference signal I to obtain error signal I; reference signal I is generated by a frequency synthesizer traceable to a rubidium atomic clock, and the frequency synthesizer is controlled by a microcontroller;

[0050] The power divider I is used to divide the error signal I into two paths, one of which is transmitted to the frequency-voltage converter I. The frequency-voltage converter I is used for frequency-voltage conversion, and the converted voltage is collected by the analog-to-digital converter; the microcontroller adjusts the output frequency of the frequency synthesizer according to the collected voltage and the direction of the error signal I until the frequency value of the error signal I is lower than 10Hz;

[0051] After the adjustment of the frequency synthesizer output frequency is completed, the error signal I is collected by the microcontroller through the analog-to-digital converter. The collected signal is processed by the adaptive PID controller I and then outputs the control signal by the digital-to-analog converter I.

[0052] The piezoelectric ceramic driver receives the control signal and amplifies it to output, realizing f r Automatic locking of the signal.

[0053] The offset frequency automatic locking unit includes a photodetector II, a bandpass filter amplifier II, a frequency divider I, a high-speed phase detector, a power divider II, a frequency divider II, a frequency-voltage converter II, an adaptive PID controller II, a digital-to-analog converter II, a V / I converter and a pump laser; at the same time, the offset frequency automatic locking unit and the repetition frequency automatic locking unit share the analog-to-digital converter, a microcontroller, a rubidium atomic clock and a frequency synthesizer;

[0054] Photodetector II is used to perform photoelectric conversion on the optical frequency comb offset frequency optical signal generated by the optical frequency comb optical system to obtain the optical frequency comb offset frequency signal f0 in the microwave field;

[0055] The bandpass filter amplifier II is used to filter the optical frequency comb offset frequency signal f0;

[0056] Frequency divider I is used to divide the frequency of the filtered optical frequency comb offset signal f0;

[0057] The high-speed phase detector is used to detect the phase of the divided optical frequency comb offset signal f0 and the reference signal II to obtain the error signal II; the reference signal II is generated by a frequency synthesizer traceable to a rubidium atomic clock, and the frequency synthesizer is controlled by a microcontroller;

[0058] The power divider II is used to divide the error signal II into two paths, one of which is divided by the frequency divider II and input into the frequency-voltage converter II; the frequency-voltage converter II is used for frequency-voltage conversion, and the converted voltage is collected by the analog-to-digital converter; the microcontroller adjusts the output frequency of the frequency synthesizer according to the collected voltage and the direction of the error signal II until the frequency value of the error signal II is lower than 100Hz;

[0059] After the adjustment of the frequency synthesizer output frequency is completed, the error signal II is collected by the microcontroller through the analog-to-digital converter. The collected signal is processed by the adaptive PID controller II and then outputs the control voltage by the digital-to-analog converter II.

[0060] The V / I converter is used to convert the control voltage into a current to obtain a control current and apply it to the pump laser;

[0061] The pump laser is an actuator for realizing automatic locking of the f0 signal and can be used to realize automatic locking of the f0 signal.

[0062] In summary, the above are only preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for self-locking the frequency of a wide-range optical frequency comb, characterized in that: Convert the repetition frequency and offset frequency optical signals of the optical frequency comb into the repetition frequency signal f at microwave frequency r And the offset frequency signal f0; For f r The signal is filtered and mixed with the reference signal to obtain an error signal, which is generated by a frequency synthesizer. The error signal is divided into two paths, one of which is converted into a voltage signal. The output frequency of the frequency synthesizer is adjusted according to the direction of the error signal and the voltage signal until the error signal is lower than 10Hz. After the output frequency of the frequency synthesizer is adjusted, the error signal is collected by the analog-to-digital converter and processed by the adaptive PID controller. The control signal is output by the digital-to-analog converter, and the piezoelectric ceramic driver is amplified to realize the control of the piezoelectric ceramic and thus realize f r The signal is automatically locked; For the f0 signal, the error signal is obtained by filtering, dividing the frequency, and then phase detection with the reference signal; The error signal is divided into two paths. One path is converted into a voltage signal after frequency reduction. The output frequency of the frequency synthesizer is adjusted according to the direction of the error signal and the voltage signal until the error signal is lower than 100Hz. After the output frequency adjustment of the frequency synthesizer is completed, the error signal is collected by the analog-to-digital converter and processed by the adaptive PID controller. The control voltage is output by the digital-to-analog converter, and then applied to the pump laser after current conversion to achieve automatic locking of the f0 signal.

2. The optical frequency comb broadband large range frequency self-locking method as claimed in claim 1, characterized in that: The frequency synthesizer is traceable to a rubidium atomic clock and is controlled by a microcontroller.

3. The optical frequency comb broadband large range frequency self-locking method as claimed in claim 1, characterized in that: For f r The method for adjusting the output frequency of the frequency synthesizer is as follows: the microcontroller records the voltage collected by the analog-to-digital converter, and then adjusts the frequency of the frequency synthesizer after a set time interval according to the different voltage values ​​obtained by sampling, and then the microcontroller records the voltage collected by the analog-to-digital converter after adjustment, and judges the current frequency by comparing it with the previously recorded voltage value. r The direction of the error signal generated after phase detection between the signal and the reference signal; The microcontroller adjusts the frequency of the frequency synthesizer again according to the direction of the current error signal and the frequency value of the error signal corresponding to the voltage signal after the collected frequency-voltage conversion, until the frequency value of the error signal is lower than 10Hz; For the f0 signal, the method for adjusting the output frequency of the frequency synthesizer is as follows: the microcontroller records the voltage collected by the analog-to-digital converter, and then adjusts the frequency of the frequency synthesizer after a set time interval according to the different voltage values ​​obtained by sampling, and then the microcontroller records the voltage collected by the analog-to-digital converter after adjustment, and judges the direction of the error signal generated after the phase detection between the current f0 signal and the reference signal according to the comparison with the previously recorded voltage value; The microcontroller adjusts the frequency of the frequency synthesizer again according to the direction of the current error signal and the frequency value of the error signal corresponding to the voltage signal after the collected frequency-voltage conversion, until the frequency value of the error signal is lower than 100 Hz.

4. The optical frequency comb broadband large range frequency self-locking method as claimed in claim 1, characterized in that: Implementing an optical frequency comb in a microcontroller r During the process of continuous signal locking, when the microcontroller detects that the output voltage of the digital-to-analog converter controlled by itself is 0.2V away from the threshold voltage, the frequency synthesizer is adjusted according to the change direction of the output voltage of the digital-to-analog converter until the output voltage of the adjusted digital-to-analog converter returns to the output voltage when the optical frequency comb repetition frequency is locked, thereby achieving tracking and locking of the optical frequency comb repetition frequency.

5. The optical frequency comb broadband large range frequency self-locking method as claimed in claim 1, characterized in that: If the repetition frequency of the optical frequency comb is out of lock, the closed-loop control of the adaptive PID controller is turned off, and then the output frequency of the frequency synthesizer is adjusted and automatically locked again according to the method of automatically locking the repetition frequency of the optical frequency comb.

6. The optical frequency comb broadband large range frequency self-locking method as claimed in claim 1, characterized in that: In the process of the microcontroller realizing continuous locking of the optical frequency comb f0 signal, when the microcontroller detects that the output voltage of the digital-to-analog converter controlled by itself is 0.1V away from the threshold voltage, the frequency synthesizer is adjusted according to the change direction of the output voltage of the digital-to-analog converter to achieve tracking and locking of the optical frequency comb offset frequency.

7. The optical frequency comb broadband large range frequency self-locking method as claimed in claim 1, characterized in that: If the optical frequency comb offset frequency is out of lock, the closed-loop control of the adaptive PID controller is turned off, and then the output frequency of the frequency synthesizer is adjusted according to the method of automatic locking of the optical frequency comb offset frequency, and then negative feedback is automatically locked again.

8. The optical frequency comb broadband large range frequency self-locking method according to any one of claims 1 to 7, characterized in that: According to the collected temperature inside the laser cavity, the PID controller is used to control the heating or cooling of the TEC cooler inside the cavity to stabilize the temperature inside the cavity to 25±0.05℃.

9. An optical frequency comb broadband large range frequency self-locking device, characterized in that: It includes a repetition frequency automatic locking unit and an offset frequency automatic locking unit; The repetition frequency automatic locking unit includes a photodetector I, a bandpass filter amplifier I, a digital phase detector, a power divider I, a frequency-voltage converter I, a digital-to-analog converter I, a microcontroller, a rubidium atomic clock, a frequency synthesizer, an adaptive PID controller I, an analog-to-digital converter, and a piezoelectric ceramic driver; The photoelectric detector I is used to perform photoelectric conversion on the optical frequency comb repetition frequency optical signal generated by the optical frequency comb optical system to obtain the microwave field optical frequency comb repetition frequency signal f r ; The bandpass filter amplifier I is used to re-sample the optical frequency comb signal f r Perform filtering; The digital phase detector is used to convert the filtered optical frequency comb repetition frequency signal f r Mixing and phase detection with reference signal I to obtain an error signal; the reference signal I is generated by a frequency synthesizer traceable to a rubidium atomic clock, and the frequency synthesizer is controlled by a microcontroller; The power divider I is used to divide the error signal into two paths, one of which is transmitted to the frequency-voltage converter I, and the frequency-voltage converter I is used for frequency-voltage conversion, and the converted voltage is collected by the analog-to-digital converter; the microcontroller adjusts the output frequency of the frequency synthesizer according to the collected voltage and the direction of the error signal until the frequency value of the error signal is lower than 10Hz; After the adjustment of the frequency synthesizer output frequency is completed, the error signal is collected by the microcontroller through the analog-to-digital converter. The collected signal is processed by the adaptive PID controller I and then outputs the control signal by the digital-to-analog converter I. The piezoelectric ceramic driver receives the control signal, amplifies it and outputs it to achieve f r Automatic signal locking; The offset frequency automatic locking unit includes a photodetector II, a bandpass filter amplifier II, a frequency divider I, a high-speed phase detector, a power divider II, a frequency divider II, a frequency-voltage converter II, an adaptive PID controller II, a digital-to-analog converter II, a V / I converter and a pump laser; at the same time, the offset frequency automatic locking unit and the repetition frequency automatic locking unit share the analog-to-digital converter, a microcontroller, a rubidium atomic clock and a frequency synthesizer; The photodetector II is used to perform photoelectric conversion on the optical frequency comb offset frequency optical signal generated by the optical frequency comb optical system to obtain the microwave field optical frequency comb offset frequency signal f0; The bandpass filter amplifier II is used to filter the optical frequency comb offset frequency signal f0; The frequency divider I is used to divide the frequency of the optical frequency comb offset signal f0 after filtering; The high-speed phase detector is used to perform phase detection on the divided optical frequency comb offset signal f0 and the reference signal II to obtain an error signal; the reference signal II is generated by a frequency synthesizer traceable to a rubidium atomic clock, and the frequency synthesizer is controlled by a microcontroller; The power divider II is used to divide the error signal into two paths, one of which is divided by the frequency divider II and input into the frequency-voltage converter II; the frequency-voltage converter II is used for frequency-voltage conversion, and the converted voltage is collected by the analog-to-digital converter; the microcontroller adjusts the output frequency of the frequency synthesizer according to the collected voltage and the direction of the error signal until the frequency value of the error signal is lower than 100Hz; After the frequency synthesizer output frequency is adjusted, the error signal is collected by the microcontroller through the analog-to-digital converter. The collected signal is processed by the adaptive PID controller II and then outputs the control voltage by the digital-to-analog converter II. The V / I converter is used to convert the control voltage into a current to obtain a control current and apply it to the pump laser; The pump laser can be used to achieve automatic locking of the f0 signal.

10. The optical frequency comb broadband large range frequency self-locking device as claimed in claim 9, characterized in that: It also includes a temperature control unit, which includes a TEC cooler and a thermistor. The TEC cooler and the thermistor are both arranged in the laser cavity. The thermistor is used as a temperature sensor to monitor the temperature in the cavity; the TEC cooler is used to adjust the temperature in the cavity.

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