Femtosecond optical comb frequency automatic locking system and method for photogenerated ultra-stable microwave source

Abstract

The present invention discloses a femtosecond optical comb frequency automatic locking system and method for an optically generated ultra-stable microwave source, comprising: an optical frequency comb, a frequency difference voltage generating circuit, a voltage conditioning circuit and a phase-locked loop circuit; the optical frequency comb outputs an optical comb signal; the frequency difference voltage generating circuit determines the frequency difference between an input optical comb signal and an input reference signal, and converts the frequency difference into a voltage signal; the voltage conditioning circuit conditions the voltage signal to obtain a conditioned voltage signal, and feeds the conditioned voltage signal back to the optical frequency comb; the optical frequency comb is also used to change the frequency of the output optical comb signal according to the conditioned voltage signal; the phase-locked loop circuit is used to phase-lock the input reference signal and the input frequency-adjusted optical comb signal, obtain a phase difference signal and feed it back to the optical frequency comb, and the optical frequency comb locks the phase of the optical comb signal according to the phase difference signal. The present invention can realize automatic locking, is simpler to realize, has high stability, strong reliability, and can automatically operate stably for a long time.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical frequency combs, and in particular relates to a femtosecond optical comb frequency automatic locking system and method for a photogenerated ultra-stable microwave source. Background Art

[0002] The optical frequency comb can stabilize the frequency or phase of the laser to an external reference source. Locking and controlling the frequency and phase of electromagnetic radiation (visible light, infrared, microwaves and other electromagnetic waves) can improve the accuracy and stability of the laser. It is used in high-performance frequency standards, radar, navigation and other fields, and is also an important component of the photogenerated ultra-stable microwave source. The photogenerated ultra-stable microwave source is based on the technology of ultra-stable laser and optical frequency comb. It can convert the ultra-stable laser frequency signal with ultra-high stability into the microwave frequency band to generate an ultra-stable microwave source. It is currently the microwave frequency source with the highest frequency stability. The photogenerated ultra-stable microwave source is also the basis for the promotion and application of future frequency standards (optical frequency standards). Whether it is the generation of time or the vast majority of precision measurements, it is necessary to convert the output laser of the optical frequency standard into an ultra-stable baseband frequency signal before it can be realized.

[0003] Optical frequency combs have important application value in locking the frequency of electromagnetic radiation, and can realize accurate measurement and control of electromagnetic frequency. Optical frequency combs are devices that generate ultra-stable microwave signals. To achieve this goal, the repetition frequency and carrier envelope frequency shift of the optical frequency comb need to be locked to a stable reference signal respectively, so that each frequency tooth of the optical frequency comb has a certain value. The commonly used locking method is to use phase-locked loop technology for locking. In addition, in the application of optical frequency combs, the frequency of the optical frequency comb needs to be locked to the reference frequency. Usually, the frequency of the optical frequency comb needs to be manually adjusted to the reference frequency to lock it. Due to the complexity of the operation, the operator needs to have certain professional knowledge and be very familiar with the equipment. The manual adjustment process usually takes a long time, and frequent debugging and calibration will take up a lot of time. When locking the optical beat frequency signal fbeat, since the signal frequency change is very sensitive to the adjustment amount, a high adjustment accuracy is required, and manual locking is difficult to achieve. When the lock is lost, manual supervision and re-locking are required, which is not conducive to the long-term operation of the equipment.

[0004] In other words, the existing optical comb frequency locking process requires manual intervention, is complex to operate, requires a high level of professionalism from the operator, takes a long time to lock, has low locking accuracy, and is not conducive to long-term operation of the equipment. Summary of the invention

[0005] In order to solve the above problems existing in the prior art, the present invention provides a femtosecond optical comb frequency automatic locking system and method for a photogenerated ultra-stable microwave source.

[0006] The technical problem to be solved by the present invention is achieved through the following technical solutions:

[0007] The present invention provides a femtosecond optical comb frequency automatic locking system for a photogenerated ultra-stable microwave source, comprising:

[0008] An optical frequency comb, a frequency difference voltage generating circuit, a voltage conditioning circuit and a phase-locked loop circuit; the optical frequency comb, the frequency difference voltage generating circuit and the voltage conditioning circuit constitute a frequency-locked loop circuit, and the frequency-locked loop circuit is connected in parallel with the phase-locked loop circuit; wherein the output end of the optical frequency comb is electrically connected to the input end of the frequency difference voltage generating circuit and the input end of the phase-locked loop circuit respectively, one input end of the frequency difference voltage generating circuit and one input end of the phase-locked loop circuit are also used to access a reference signal, and the output end of the frequency difference voltage generating circuit is electrically connected to the input end of the voltage conditioning circuit;

[0009] The optical frequency comb is used to output an optical comb signal; the frequency difference voltage generating circuit is used to determine a voltage signal representing the frequency difference between an input optical comb signal and an input reference signal; the voltage conditioning circuit is used to condition the voltage signal to obtain a conditioned voltage signal corresponding to the optical comb signal, and feed the conditioned voltage signal back to the optical frequency comb; the optical frequency comb is also used to change the frequency of the output optical comb signal according to the conditioned voltage signal; the phase-locked loop circuit is used to lock the input reference signal and the input optical comb signal after frequency adjustment by the frequency-locked loop circuit to obtain a phase difference signal, and feed the phase difference signal back to the optical frequency comb; the optical frequency comb is also used to phase-lock the frequency-adjusted optical comb signal according to the phase difference signal.

[0010] In some embodiments, the frequency difference voltage generating circuit includes: a frequency difference generating subunit and a voltage generating subunit; wherein, one input end of the frequency difference generating subunit is electrically connected to the output end of the optical frequency comb, another input end of the frequency difference generating subunit is used to access the reference signal, the output end of the frequency difference generating subunit is electrically connected to the input end of the voltage generating subunit, and the output end of the voltage generating subunit is electrically connected to the input end of the voltage conditioning circuit;

[0011] The frequency difference generating subunit is used to determine the difference frequency signal according to the input optical comb signal and the input reference signal;

[0012] The voltage generating subunit is used to generate a voltage signal representing the frequency difference between the input optical comb signal and the input reference signal according to the difference frequency signal.

[0013] In some embodiments, the frequency difference generating subunit includes: a mixer and a low-pass filter; wherein, one input end of the mixer is electrically connected to the output end of the optical frequency comb, the other input end of the mixer is used to access the reference signal, the output end of the mixer is electrically connected to the input end of the low-pass filter, and the output end of the low-pass filter is electrically connected to the input end of the voltage generating subunit.

[0014] In some embodiments, the voltage generating subunit is a frequency discriminator.

[0015] In some embodiments, the voltage conditioning circuit includes a PID circuit having preset PID parameters, wherein the preset PID parameters are used to control a frequency range when the frequency locked loop circuit performs signal locking.

[0016] In some embodiments, the system comprises: a frequency difference voltage generating circuit, a voltage conditioning circuit and a phase-locked loop circuit; the optical frequency comb, the frequency difference voltage generating circuit and the voltage conditioning circuit constitute a frequency-locked loop circuit, and the optical comb signal comprises: any one of a carrier envelope phase shift frequency signal fceo, a repetition frequency signal fr and an optical beat frequency signal fbeat;

[0017] Wherein, the voltage conditioning circuit is used to feed back the conditioned voltage signal corresponding to the repetition frequency signal fr or the optical beat frequency signal fbeat to the electro-optic modulator and piezoelectric ceramic in the optical frequency comb, or to feed back the conditioned voltage signal corresponding to the carrier-envelope phase shift frequency signal fceo to the pump driver in the optical frequency comb; the optical frequency comb is also used to change the frequency of the output optical comb signal according to the conditioned voltage signal fed back to the electro-optic modulator and the piezoelectric ceramic, or to change the frequency of the output optical comb signal according to the conditioned voltage signal fed back to the pump driver.

[0018] In some embodiments, the system includes: two frequency difference voltage generating circuits, two voltage conditioning circuits and two phase-locked loop circuits, and the optical comb signal includes a carrier envelope phase shift frequency signal fceo and also includes a repetition frequency signal fr or an optical beat frequency signal fbeat;

[0019] Wherein, the optical frequency comb, the first frequency difference voltage generating circuit and the first voltage conditioning circuit constitute the first frequency locked loop circuit, and the first frequency locked loop circuit is connected in parallel with the first phase locked loop circuit; and an input end of the first frequency difference voltage generating circuit is used to input the repetition frequency signal fr or the optical beat frequency signal fbeat; another input end of the first frequency difference voltage generating circuit and an input end of the first phase locked loop circuit are also used to access the reference signal, and the first voltage conditioning circuit is used to convert the repetition frequency signal fr or the optical beat frequency signal fbeat into a reference signal. The conditioned voltage signal corresponding to the rate signal fbeat is fed back to the electro-optic modulator and the piezoelectric ceramic in the optical frequency comb; the optical frequency comb is also used to change the frequency of the output optical comb signal according to the conditioned voltage signal fed back to the electro-optic modulator and the piezoelectric ceramic; the first phase-locked loop circuit is used to lock the input reference signal and the input optical comb signal after frequency adjustment by the first frequency-locked loop circuit to obtain a phase difference signal, and feed the phase difference signal back to the optical frequency comb; the optical frequency comb is also used to phase lock the optical comb signal after frequency adjustment according to the phase difference signal;

[0020] The optical frequency comb, the second frequency difference voltage generating circuit and the second voltage conditioning circuit constitute a second frequency locked loop circuit, and the second frequency locked loop circuit is connected in parallel with the second phase locked loop circuit; and one input end of the second frequency difference voltage generating circuit is used to input the carrier envelope phase shift frequency signal fceo; the other input end of the second frequency difference voltage generating circuit and one input end of the second phase locked loop circuit are also used to access the reference signal, and the second voltage conditioning circuit is used to feed back the conditioned voltage signal corresponding to the carrier envelope phase shift frequency signal fceo to the pump drive in the optical frequency comb; the optical frequency comb is also used to change the frequency of the output optical comb signal according to the conditioned voltage signal fed back to the pump drive; the second phase locked loop circuit is used to lock the input reference signal and the input optical comb signal after frequency adjustment by the second frequency locked loop circuit to obtain a phase difference signal, and feed back the phase difference signal to the optical frequency comb; the optical frequency comb is also used to phase lock the optical comb signal after frequency adjustment according to the phase difference signal.

[0021] In some embodiments, the PID circuit is a proportional-integral-derivative circuit.

[0022] The present invention also provides a method for automatically locking the frequency of a femtosecond optical comb for a photogenerated ultra-stable microwave source, which is applied to the above-mentioned automatic locking system for the frequency of a femtosecond optical comb for a photogenerated ultra-stable microwave source. The method comprises:

[0023] Outputting optical comb signal;

[0024] Determine a voltage signal representing a frequency difference between a current optical comb signal and an input reference signal, condition the determined voltage signal to obtain a conditioned voltage signal corresponding to the current optical comb signal, and change the frequency of the current optical comb signal according to the conditioned voltage signal corresponding to the current optical comb signal to obtain a current frequency-adjusted optical comb signal;

[0025] Phase-locking the current frequency-adjusted optical comb signal and the input reference signal to obtain a current phase difference signal, phase-locking the frequency-adjusted optical comb signal according to the current phase difference signal, and outputting the next optical comb signal when phase locking fails;

[0026] Determine a voltage signal representing a frequency difference between the next optical comb signal and an input reference signal, and condition the determined voltage signal to obtain a conditioned voltage signal corresponding to the next optical comb signal, and change the frequency of the next optical comb signal according to the conditioned voltage signal corresponding to the next optical comb signal to obtain a frequency-adjusted optical comb signal for the next time;

[0027] The optical comb signal after the next frequency adjustment is phase-locked with the input reference signal to obtain the next phase difference signal, and the phase of the optical comb signal after the frequency adjustment is phase-locked according to the next phase difference signal, and this is repeated until the phase locking is successful. After the phase locking is successful, the frequency adjustment of the optical comb signal is terminated.

[0028] In some embodiments, determining a voltage signal representing a frequency difference between a current optical comb signal and an input reference signal comprises:

[0029] Mixing the current optical comb signal with the currently input reference signal to obtain a mixed signal;

[0030] Performing low-pass filtering on the mixed signal to obtain a difference frequency signal;

[0031] The difference frequency signal is converted into a voltage signal; wherein the voltage signal represents the frequency difference between the current optical comb signal and the input reference signal.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] The present invention measures the frequency difference between a reference signal and an optical comb frequency signal through a frequency-locked loop circuit composed of an optical frequency comb, a frequency difference voltage generating circuit and a voltage conditioning circuit, and then obtains a voltage signal proportional to the frequency difference. Then, the voltage signal is conditioned, and the frequency of the optical comb signal is adjusted according to the conditioned voltage signal. In addition, the input reference signal and the input optical comb signal after the frequency adjustment by the frequency-locked loop circuit are phase-locked through a phase-locked loop circuit to obtain a phase difference signal and feed it back to the optical frequency comb. The optical frequency comb then locks the phase of the optical comb signal according to the phase difference signal, and this cycle is repeated until the phase is successfully locked. In this way, the frequency of the optical comb can be automatically adjusted to match the reference frequency, thus overcoming the shortcomings of manual adjustment such as complex operation, time consumption, limited accuracy, insufficient stability, poor repeatability and high labor cost, so that locking can be achieved quickly and automatically. The locking process is completely controlled by the circuit without the need for human intervention or program control. Moreover, when loss of lock occurs, the frequency of the optical comb signal can be spontaneously controlled in time and re-locked with the reference signal. The locking is faster, more accurate and easier to achieve, and has the advantages of high stability, simple operation, high repeatability, reduced labor costs, real-time monitoring and adjustment, strong adaptability and improved system reliability. The efficiency and effect of optical comb frequency locking are significantly improved, so that the optical frequency comb can be automatically operated for a long time and stably, which can make the application of optical frequency comb in high-precision frequency measurement, time standards, optical communications, quantum technology and multidisciplinary cross-disciplinary research more efficient and extensive.

[0034] The present invention will be further described in detail below with reference to the accompanying drawings and specific implementation methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a structural schematic diagram of a femtosecond optical comb frequency automatic locking system for a photogenerated ultra-stable microwave source provided by an embodiment of the present invention;

[0036] Figure 2 It is an exemplary structural diagram of a femtosecond optical comb frequency automatic locking system for a photogenerated ultra-stable microwave source provided by an embodiment of the present invention;

[0037] Figure 3 is another exemplary structural schematic diagram of a femtosecond optical comb frequency automatic locking system for a photogenerated ultra-stable microwave source provided by an embodiment of the present invention;

[0038] Figure 4 The present invention is a flowchart of a method for automatically locking the frequency of a femtosecond optical comb for a photogenerated ultrastable microwave source provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0039] The present invention is further described in detail below with reference to specific embodiments, but the embodiments of the present invention are not limited thereto.

[0040] Figure 1 The present invention provides a femtosecond optical comb frequency automatic locking system for an optically generated ultra-stable microwave source. Figure 1 As shown, the system includes: an optical frequency comb, a frequency difference voltage generating circuit, a voltage conditioning circuit and a phase-locked loop circuit. The optical frequency comb, the frequency difference voltage generating circuit and the voltage conditioning circuit constitute a frequency-locked loop circuit, and the frequency-locked loop circuit is connected in parallel with the phase-locked loop circuit; wherein the output end of the optical frequency comb is electrically connected to the input end of the frequency difference voltage generating circuit and the input end of the phase-locked loop circuit respectively, one input end of the frequency difference voltage generating circuit and one input end of the phase-locked loop circuit are also used to access a reference signal, and the output end of the frequency difference voltage generating circuit is electrically connected to the input end of the voltage conditioning circuit.

[0041] The optical frequency comb is used to output an optical comb signal; the frequency difference voltage generating circuit is used to determine a voltage signal representing the frequency difference between an input optical comb signal and an input reference signal; the voltage conditioning circuit is used to condition the voltage signal to obtain a conditioned voltage signal corresponding to the optical comb signal, and feed the conditioned voltage signal back to the optical frequency comb; the optical frequency comb is also used to change the frequency of the output optical comb signal according to the conditioned voltage signal; the phase-locked loop circuit is used to lock the input reference signal and the input optical comb signal after frequency adjustment by the frequency-locked loop circuit to obtain a phase difference signal, and feed the phase difference signal back to the optical frequency comb; the optical frequency comb is also used to phase lock the frequency-adjusted optical comb signal according to the phase difference signal.

[0042] Here, the frequency of the optical comb signal is adjusted first each time, and then the phase of the frequency-adjusted optical comb signal is locked. When the phase of the frequency-adjusted optical comb signal is successfully locked, the frequency locking function of the frequency-locked loop circuit ends, and then the phase lock is maintained. In this way, the optical comb signal can be first locked to a position convenient for phase locking with the assistance of the frequency-locked loop circuit, and then the phase lock is performed, which not only improves the locking efficiency of the optical comb signal, but also improves the locking success rate of the optical comb signal.

[0043] In some embodiments, the frequency difference voltage generating circuit includes: a frequency difference generating subunit and a voltage generating subunit; wherein one input end of the frequency difference generating subunit is electrically connected to the output end of the optical frequency comb, another input end of the frequency difference generating subunit is used to access the reference signal, the output end of the frequency difference generating subunit is electrically connected to the input end of the voltage generating subunit, and the output end of the voltage generating subunit is electrically connected to the input end of the voltage conditioning unit. The frequency difference generating subunit is used to determine the difference frequency signal according to the input optical comb signal and the input reference signal; the voltage generating subunit is used to generate a voltage signal representing the frequency difference between the input optical comb signal and the input reference signal according to the difference frequency signal.

[0044] For example, Figure 2As shown in FIG, the frequency difference generating subunit is a mixer and a low-pass filter; the voltage generating subunit is a frequency discriminator. Figure 2 As shown, one input end of the mixer is electrically connected to the output end of the optical frequency comb, the other input end of the mixer is used to access the reference signal, the output end of the mixer is electrically connected to the input end of the low-pass filter, and the output end of the low-pass filter is electrically connected to the input end of the discriminator.

[0045] In some embodiments, the voltage conditioning circuit includes a PID circuit having preset PID parameters, wherein the preset PID (full spelling in English: Proportional Integral Derivative) parameters are used to control the frequency range when the frequency-locked loop circuit performs signal locking. Here, the preset PID parameters can be set according to actual needs. Exemplarily, the PID circuit is a proportional integral differential circuit.

[0046] In some embodiments, the system includes: a frequency difference voltage generating circuit, a voltage conditioning circuit and a phase-locked loop circuit; and the optical frequency comb, the frequency difference voltage generating circuit and the voltage conditioning circuit constitute a frequency-locked loop circuit, and the optical comb signal is any one of the carrier-envelope phase-shifted frequency signal fceo, the repetition frequency signal fr and the optical beat frequency signal fbeat. The voltage conditioning circuit is used to feed back the conditioned voltage signal corresponding to the repetition frequency signal fr or the optical beat frequency signal fbeat to the electro-optic modulator and the piezoelectric ceramic in the optical frequency comb, or the voltage conditioning circuit is used to feed back the conditioned voltage signal corresponding to the carrier-envelope phase-shifted frequency signal fceo to the pump drive in the optical frequency comb. The optical frequency comb is also used to change the frequency of the output optical comb signal according to the conditioned voltage signal fed back to the electro-optic modulator and the piezoelectric ceramic, or the optical frequency comb is also used to change the frequency of the output optical comb signal according to the conditioned voltage signal fed back to the pump drive.

[0047] In some embodiments, Figure 3As shown, the system includes: two frequency difference voltage generating circuits, two voltage conditioning circuits and two phase-locked loop circuits. The optical comb signal includes a carrier envelope phase shift frequency signal fceo and a repetition frequency signal fr, or the optical comb signal includes a carrier envelope phase shift frequency signal fceo and an optical beat frequency signal fbeat. The optical frequency comb, the first frequency difference voltage generating circuit and the first voltage conditioning circuit constitute a first frequency locked loop circuit, and the first frequency locked loop circuit is connected in parallel with the first phase locked loop circuit; and one input end of the first frequency difference voltage generating circuit is used to input a repetition frequency signal fr or an optical beat frequency signal fbeat; the other input end of the first frequency difference voltage generating circuit and one input end of the first phase locked loop circuit are also used to access a reference signal, and the first voltage conditioning circuit is used to feed back a conditioned voltage signal corresponding to the repetition frequency signal fr or the optical beat frequency signal fbeat to an electro-optic modulator and piezoelectric ceramics in the optical frequency comb; the optical frequency comb is also used to change the frequency of an output optical comb signal (i.e., the repetition frequency signal fr or the optical beat frequency signal fbeat) according to the conditioned voltage signal fed back to the electro-optic modulator and the piezoelectric ceramics; the first phase locked loop circuit is used to lock the input reference signal and the input optical comb signal after frequency adjustment by the first frequency locked loop circuit, obtain a phase difference signal, and feed back the phase difference signal to the optical frequency comb; the optical frequency comb is also used to phase lock the optical comb signal after frequency adjustment according to the phase difference signal. The optical frequency comb, the second frequency difference voltage generating circuit and the second voltage conditioning circuit constitute a second frequency locked loop circuit, and the second frequency locked loop circuit is connected in parallel with the second phase locked loop circuit; and one input end of the second frequency difference voltage generating circuit is used to input the carrier envelope phase shift frequency signal fceo; the other input end of the second frequency difference voltage generating circuit and one input end of the second phase locked loop circuit are also used to access the reference signal, and the second voltage conditioning circuit is used to feed back the conditioned voltage signal corresponding to the carrier envelope phase shift frequency signal fceo to the pump drive in the optical frequency comb; the optical frequency comb is also used to change the frequency of the output optical comb signal (i.e., the carrier envelope phase shift frequency signal fceo) according to the conditioned voltage signal fed back to the pump drive; the second phase locked loop circuit is used to lock the input reference signal and the input optical comb signal after frequency adjustment by the second frequency locked loop circuit to obtain a phase difference signal, and feed the phase difference signal back to the optical frequency comb; the optical frequency comb is also used to phase lock the optical comb signal after frequency adjustment according to the phase difference signal.

[0048] The present invention measures the frequency difference between a reference signal and an optical comb frequency signal through a frequency-locked loop circuit composed of an optical frequency comb, a frequency difference voltage generating circuit and a voltage conditioning circuit, and then obtains a voltage signal proportional to the frequency difference. Then, the voltage signal is conditioned, and the frequency of the optical comb signal is adjusted according to the conditioned voltage signal. In addition, the input reference signal and the input optical comb signal after the frequency adjustment by the frequency-locked loop circuit are phase-locked through a phase-locked loop circuit to obtain a phase difference signal and feed it back to the optical frequency comb. The optical frequency comb then locks the phase of the optical comb signal according to the phase difference signal, and the cycle is repeated until the phase is successfully locked. In this way, the frequency of the optical comb can be automatically adjusted to match the reference frequency, thus overcoming the shortcomings of manual adjustment such as complex operation, time consumption, limited accuracy, insufficient stability, poor repeatability and high labor cost, so that locking can be achieved quickly and automatically. The locking process is completely controlled by the circuit without the need for human intervention or program control. Moreover, when loss of lock occurs, the frequency of the optical comb signal can be spontaneously controlled in time and re-locked with the reference signal. The locking is faster, more accurate and easier to achieve, and has the advantages of high stability, simple operation, high repeatability, reduced labor costs, real-time monitoring and adjustment, strong adaptability and improved system reliability. The efficiency and effect of optical comb frequency locking are significantly improved, so that the optical frequency comb can be automatically operated for a long time and stably, which can make the application of optical frequency comb in high-precision frequency measurement, time standards, optical communications, quantum technology and multidisciplinary cross-disciplinary research more efficient and extensive.

[0049] The present invention also provides a method for automatically locking the frequency of a femtosecond optical comb for an optically generated ultra-stable microwave source. The method is applied to the above-mentioned automatic locking system for the frequency of a femtosecond optical comb for an optically generated ultra-stable microwave source. Figure 4 As shown, the method includes:

[0050] S101. Output an optical comb signal.

[0051] S102. Determine a voltage signal representing the frequency difference between a current optical comb signal and an input reference signal, and condition the determined voltage signal to obtain a conditioned voltage signal corresponding to the current optical comb signal, and change the frequency of the current optical comb signal according to the conditioned voltage signal corresponding to the current optical comb signal to obtain a current frequency-adjusted optical comb signal.

[0052] Specifically, the current optical comb signal is mixed with the input reference signal to obtain a mixed signal; the mixed signal is low-pass filtered to obtain a difference frequency signal; and the difference frequency signal is converted into a voltage signal representing the frequency difference between the current optical comb signal and the input reference signal.

[0053] S103, phase-locking the current frequency-adjusted optical comb signal and the input reference signal to obtain a current phase difference signal, phase-locking the frequency-adjusted optical comb signal according to the current phase difference signal, and outputting the next optical comb signal when phase locking fails.

[0054] Here, the phase locking of the current frequency-adjusted optical comb signal is performed according to the current phase difference signal.

[0055] S104. Determine a voltage signal representing the frequency difference between the next optical comb signal and the input reference signal, and condition the determined voltage signal to obtain a conditioned voltage signal corresponding to the next optical comb signal, and change the frequency of the next optical comb signal according to the conditioned voltage signal corresponding to the next optical comb signal to obtain the next frequency-adjusted optical comb signal.

[0056] S105. Phase-lock the optical comb signal after the next frequency adjustment and the input reference signal to obtain the next phase difference signal, and phase-lock the optical comb signal after the frequency adjustment according to the next phase difference signal, and so on until the phase locking is successful. After the phase locking is successful, the frequency adjustment of the optical comb signal is terminated to maintain the phase lock.

[0057] Here, the phase locking of the optical comb signal after the next frequency adjustment is performed based on the next phase difference signal.

[0058] It should be noted that after successful locking, the locked optical comb signal and the input reference signal have close frequencies and are phase synchronized.

[0059] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification.

[0060] In the specification, the word "comprising" does not exclude other components or steps, and "a" or "an" does not exclude a plurality of components. Certain measures are recorded in different embodiments, but this does not mean that these measures cannot be combined to produce good effects.

[0061] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as falling within the protection scope of the present invention.

Claims

1. A femtosecond optical comb frequency automatic locking system for optically generated ultra-stable microwave sources, characterized in that: include: An optical frequency comb, a frequency difference voltage generating circuit, a voltage conditioning circuit and a phase-locked loop circuit; the optical frequency comb, the frequency difference voltage generating circuit and the voltage conditioning circuit constitute a frequency-locked loop circuit, and the frequency-locked loop circuit is connected in parallel with the phase-locked loop circuit; wherein the output end of the optical frequency comb is electrically connected to the input end of the frequency difference voltage generating circuit and the input end of the phase-locked loop circuit respectively, one input end of the frequency difference voltage generating circuit and one input end of the phase-locked loop circuit are also used to access a reference signal, and the output end of the frequency difference voltage generating circuit is electrically connected to the input end of the voltage conditioning circuit; The optical frequency comb is used to output an optical comb signal; the frequency difference voltage generating circuit is used to determine a voltage signal representing the frequency difference between an input optical comb signal and an input reference signal; the voltage conditioning circuit is used to condition the voltage signal to obtain a conditioned voltage signal corresponding to the optical comb signal, and feed the conditioned voltage signal back to the optical frequency comb; the optical frequency comb is also used to change the frequency of the output optical comb signal according to the conditioned voltage signal; the phase-locked loop circuit is used to lock the input reference signal and the input optical comb signal after frequency adjustment by the frequency-locked loop circuit to obtain a phase difference signal, and feed the phase difference signal back to the optical frequency comb; the optical frequency comb is also used to phase-lock the frequency-adjusted optical comb signal according to the phase difference signal.

2. The femtosecond optical comb frequency automatic locking system for optically generated ultra-stable microwave source according to claim 1, characterized in that: The frequency difference voltage generating circuit comprises: a frequency difference generating subunit and a voltage generating subunit; wherein, one input end of the frequency difference generating subunit is electrically connected to the output end of the optical frequency comb, another input end of the frequency difference generating subunit is used to access the reference signal, the output end of the frequency difference generating subunit is electrically connected to the input end of the voltage generating subunit, and the output end of the voltage generating subunit is electrically connected to the input end of the voltage conditioning circuit; The frequency difference generating subunit is used to determine the difference frequency signal according to the input optical comb signal and the input reference signal; The voltage generating subunit is used to generate a voltage signal representing the frequency difference between the input optical comb signal and the input reference signal according to the difference frequency signal.

3. The femtosecond optical comb frequency automatic locking system for optically generated ultra-stable microwave source according to claim 2, characterized in that: The frequency difference generating subunit includes: a mixer and a low-pass filter; wherein, one input end of the mixer is electrically connected to the output end of the optical frequency comb, the other input end of the mixer is used to access the reference signal, the output end of the mixer is electrically connected to the input end of the low-pass filter, and the output end of the low-pass filter is electrically connected to the input end of the voltage generating subunit.

4. The femtosecond optical comb frequency automatic locking system for optically generated ultrastable microwave source according to claim 2, characterized in that: The voltage generating subunit is a frequency discriminator.

5. The femtosecond optical comb frequency automatic locking system for optically generated ultra-stable microwave source according to claim 1, characterized in that: The voltage conditioning circuit includes a PID circuit with preset PID parameters, wherein the preset PID parameters are used to control the frequency range of the frequency locked loop circuit when performing signal locking.

6. The femtosecond optical comb frequency automatic locking system for optically generated ultra-stable microwave source according to claim 1, characterized in that: The system comprises: a frequency difference voltage generating circuit, a voltage conditioning circuit and a phase-locked loop circuit; the optical frequency comb, the frequency difference voltage generating circuit and the voltage conditioning circuit constitute a frequency-locked loop circuit, and the optical comb signal comprises: any one of a carrier envelope phase shift frequency signal fceo, a repetition frequency signal fr and an optical beat frequency signal fbeat; Wherein, the voltage conditioning circuit is used to feed back the conditioned voltage signal corresponding to the repetition frequency signal fr or the optical beat frequency signal fbeat to the electro-optic modulator and piezoelectric ceramic in the optical frequency comb, or to feed back the conditioned voltage signal corresponding to the carrier-envelope phase shift frequency signal fceo to the pump driver in the optical frequency comb; the optical frequency comb is also used to change the frequency of the output optical comb signal according to the conditioned voltage signal fed back to the electro-optic modulator and the piezoelectric ceramic, or to change the frequency of the output optical comb signal according to the conditioned voltage signal fed back to the pump driver.

7. The femtosecond optical comb frequency automatic locking system for optically generated ultra-stable microwave source according to claim 1, characterized in that: The system comprises: two frequency difference voltage generating circuits, two voltage conditioning circuits and two phase-locked loop circuits, and the optical comb signal comprises a carrier envelope phase shift frequency signal fceo and also comprises a repetition frequency signal fr or an optical beat frequency signal fbeat; Wherein, the optical frequency comb, the first frequency difference voltage generating circuit and the first voltage conditioning circuit constitute the first frequency locked loop circuit, and the first frequency locked loop circuit is connected in parallel with the first phase locked loop circuit; and an input end of the first frequency difference voltage generating circuit is used to input the repetition frequency signal fr or the optical beat frequency signal fbeat; another input end of the first frequency difference voltage generating circuit and an input end of the first phase locked loop circuit are also used to access the reference signal, and the first voltage conditioning circuit is used to convert the repetition frequency signal fr or the optical beat frequency signal fbeat into a reference signal. The conditioned voltage signal corresponding to the rate signal fbeat is fed back to the electro-optic modulator and the piezoelectric ceramic in the optical frequency comb; the optical frequency comb is also used to change the frequency of the output optical comb signal according to the conditioned voltage signal fed back to the electro-optic modulator and the piezoelectric ceramic; the first phase-locked loop circuit is used to lock the input reference signal and the input optical comb signal after frequency adjustment by the first frequency-locked loop circuit to obtain a phase difference signal, and feed the phase difference signal back to the optical frequency comb; the optical frequency comb is also used to phase lock the optical comb signal after frequency adjustment according to the phase difference signal; The optical frequency comb, the second frequency difference voltage generating circuit and the second voltage conditioning circuit constitute a second frequency locked loop circuit, and the second frequency locked loop circuit is connected in parallel with the second phase locked loop circuit; and one input end of the second frequency difference voltage generating circuit is used to input the carrier envelope phase shift frequency signal fceo; the other input end of the second frequency difference voltage generating circuit and one input end of the second phase locked loop circuit are also used to access the reference signal, and the second voltage conditioning circuit is used to feed back the conditioned voltage signal corresponding to the carrier envelope phase shift frequency signal fceo to the pump drive in the optical frequency comb; the optical frequency comb is also used to change the frequency of the output optical comb signal according to the conditioned voltage signal fed back to the pump drive; the second phase locked loop circuit is used to lock the input reference signal and the input optical comb signal after frequency adjustment by the second frequency locked loop circuit to obtain a phase difference signal, and feed back the phase difference signal to the optical frequency comb; the optical frequency comb is also used to phase lock the optical comb signal after frequency adjustment according to the phase difference signal.

8. The femtosecond optical comb frequency automatic locking system for optically generated ultra-stable microwave source according to claim 5, characterized in that: The PID circuit is a proportional-integral-differential circuit.

9. A method for automatically locking the frequency of a femtosecond optical comb for an optically generated ultrastable microwave source, characterized in that: The method for the automatic frequency locking system of a femtosecond optical comb for a photogenerated ultrastable microwave source as claimed in any one of claims 1 to 8 comprises: Outputting optical comb signal; Determine a voltage signal representing a frequency difference between a current optical comb signal and an input reference signal, condition the determined voltage signal to obtain a conditioned voltage signal corresponding to the current optical comb signal, and change the frequency of the current optical comb signal according to the conditioned voltage signal corresponding to the current optical comb signal to obtain a current frequency-adjusted optical comb signal; Phase-locking the current frequency-adjusted optical comb signal and the input reference signal to obtain a current phase difference signal, phase-locking the frequency-adjusted optical comb signal according to the current phase difference signal, and outputting the next optical comb signal when phase locking fails; Determine a voltage signal representing a frequency difference between the next optical comb signal and an input reference signal, and condition the determined voltage signal to obtain a conditioned voltage signal corresponding to the next optical comb signal, and change the frequency of the next optical comb signal according to the conditioned voltage signal corresponding to the next optical comb signal to obtain a frequency-adjusted optical comb signal for the next time; The optical comb signal after the next frequency adjustment is phase-locked with the input reference signal to obtain the next phase difference signal, and the phase of the optical comb signal after the frequency adjustment is phase-locked according to the next phase difference signal, and this is repeated until the phase locking is successful. After the phase locking is successful, the frequency adjustment of the optical comb signal is terminated.

10. The method for automatically locking the frequency of a femtosecond optical comb for an optically generated ultrastable microwave source according to claim 9, characterized in that: The step of determining a voltage signal representing a frequency difference between a current optical comb signal and an input reference signal comprises: Mixing the current optical comb signal with an input reference signal to obtain a mixed signal; Performing low-pass filtering on the mixed signal to obtain a difference frequency signal; The difference frequency signal is converted into a voltage signal; wherein the voltage signal represents the frequency difference between the current optical comb signal and the input reference signal.

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