Dual-frequency optical frequency locking method, system and computing device based on single-photon detection

Abstract

The present invention discloses a dual-frequency optical frequency locking method, system and computing equipment based on single-photon detection, relating to the technical field of wind measurement radars, and solving the technical problem of unstable system frequency caused by the long-term drift of the laser and the low temperature control precision of the resonant cavity in the single-photon radar system. The present invention performs two amplitude modulations on a continuous laser to form dual-frequency continuous light, and constructs a transmittance curve of the resonant cavity based on the dual-frequency continuous light. The dual-frequency continuous light is chopped into dual-frequency pulsed light. If the dual-frequency pulsed light is asymmetrically locked in the transmittance curve or is in an unstable state within the rising and falling edges preset in the transmittance curve, a time-to-digital converter is used to obtain the timestamp of the dual-frequency pulsed light signal received by the single-photon detector, and the number of photons of the dual-frequency pulsed light is calculated based on the number of timestamps. The photon number is calibrated in the transmittance curve by frequency tuning of the laser to complete laser frequency locking. The present invention can achieve frequency locking without extremely high temperature control precision.

Description

Technical Field

[0001] The present invention belongs to the field of wind measurement radar and relates to laser detection technology, in particular to a dual-frequency optical frequency locking method, system and computing equipment based on single-photon detection. Background Art

[0002] Traditional coherent detection lidar receives the Mie scattering signal of aerosols in the atmosphere and obtains the Doppler frequency shift by heterodyning the beat frequency with the intrinsic signal of the laser emission end. Direct detection lidar requires the use of a discriminator to measure the Doppler frequency shift of the aerosol signal. This discriminator is usually a high-performance resonant cavity. When the outgoing laser is scattered by the aerosol, the laser frequency changes due to the Doppler frequency shift. Therefore, the transmittance of the echo signal will change after entering the resonant cavity. Based on the change in transmittance, the Doppler frequency shift can be inverted and the wind speed can be calculated. This method of determining the frequency shift by measuring the change in light intensity after passing through the discriminator is also called edge technology. At the same time, since the limit of light detection capability is to achieve single-photon detection, a single-photon detector is selected as the optical signal receiving device;

[0003] However, as the core component of the direct detection wind measurement system, the discriminator has the advantage of high resolution, but it is also more susceptible to the system's frequency instability factors. Since the discriminator is a resonant cavity, its resonant peak wavelength changes with temperature, and the intrinsic frequency of the laser light source will also drift over time. By using a tunable laser to change the tuning process of the injected current, the tuning process is nonlinear, and repeated changes in current will also cause frequency drift and slight temperature fluctuations, resulting in technical problems such as unstable output wavelength. Summary of the Invention

[0004] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention proposes a dual-frequency optical frequency locking method, system and computing device based on single-photon detection, which are used to solve the technical problem that the tuning process of a tunable laser changing the injection current in the prior art is nonlinear, and repeated changes in current will also cause frequency drift and slight temperature fluctuations, thereby leading to unstable output wavelength.

[0005] To achieve the above objectives, a first aspect of the present invention provides a dual-frequency optical frequency locking method based on single-photon detection, comprising:

[0006] The continuous light emitted by the laser is split by an optical switch to obtain two beams of light with the same frequency;

[0007] Performing frequency shifting on the two light beams with the same frequency to obtain two light beams with different frequencies;

[0008] chopping the two light beams of different frequencies to obtain dual-frequency pulsed light;

[0009] Inputting the dual-frequency pulsed light into a resonant cavity, and determining the number of photons of different frequencies output by the resonant cavity within a preset time period;

[0010] The regulating voltage of the laser is determined based on the number of photons of different frequencies; the regulating voltage is used to make the number of photons of different frequencies output by the resonant cavity the same.

[0011] Preferably, the optical switch splits the continuous light based on a square wave signal; the frequency of the continuous light is ;

[0012] The two light beams with the same frequency are frequency-shifted to obtain two light beams with different frequencies, including:

[0013] The first light beam of the two light beams with the same frequency is input into the acousto-optic modulator AOM1 and the first attenuator to obtain the second light beam, wherein the acousto-optic modulator AOM1 is used to adjust the frequency of the first light beam. , the first attenuator is used to attenuate the first light beam after frequency shift; the frequency of the second light beam ;

[0014] The third light beam of the two light beams with the same frequency is input into the acousto-optic modulator AOM2 and the second attenuator to obtain a fourth light beam, wherein the acousto-optic modulator AOM2 is used to adjust the frequency of the third light beam. , the second attenuator is used to attenuate the frequency-shifted third light beam; the frequency of the fourth light beam .

[0015] The present invention uses two acousto-optic modulators to modulate continuous light respectively, so that the frequency shift magnitudes of the dual-frequency continuous light are equal but the frequency shift directions are opposite, thereby ensuring the symmetry of the link.

[0016] Preferably, obtaining dual-frequency pulsed light obtained by coupling the two light beams of different frequencies includes:

[0017] Measure the output power of the first attenuator connected to the acousto-optic modulator AOM1, recorded as P1; measure the output power of the second attenuator connected to the acousto-optic modulator AOM2, recorded as P2;

[0018] If P1 is greater than P2, adjust the first attenuator connected to the acousto-optic modulator AOM1 and use an optical power meter to measure the output power P3 of the first attenuator until P3 equals P2, marking the adjustment as completed.

[0019] If P1 is less than P2, adjust the second attenuator connected to the acousto-optic modulator AOM2 and use an optical power meter to measure the output power P4 of the second attenuator until P4 equals P2. This marks the adjustment as complete.

[0020] The coupled light beams with the same power are modulated by the acousto-optic modulator AOM3 based on the chopping technology to form dual-frequency pulse light, so that the frequency of the dual-frequency pulse light is increased. ; Among them, the optical frequency of the dual-frequency pulse light is , the optical frequency is .

[0021] The present invention achieves synchronous optimization of the signal-to-noise ratio of two signals by adjusting the attenuator in real time, thereby ensuring the symmetry of the link and improving the stability of the link operation.

[0022] Preferably, the determining the number of photons of different frequencies output by the resonant cavity within a preset time period includes:

[0023] Set the pre-lock period, count the number of timestamps within a square wave period, and accumulate the timestamps collected when the square wave is high and low, respectively. The quotient of the pre-lock period and the square wave period is used as the accumulation multiple.

[0024] Count the number of timestamps within a square wave period, and accumulate the timestamps collected when the square wave is high and low respectively. Set the lock period to 10n times the square wave period (10), where n is a positive integer.

[0025] All square wave high level time within the lock cycle The number of timestamps of the pulse is given as The number of photons in the locking period is one;

[0026] All square wave low level time within the lock cycle The number of timestamps of the pulse is given as The number of photons in the locking period is two.

[0027] The present invention obtains the number of photons of dual-frequency pulse light by calculation based on the number of timestamps, which is beneficial to subsequent rapid frequency calibration.

[0028] Preferably, the method for obtaining the number of timestamps includes:

[0029] The dual-frequency pulse light is input into a single-photon detector, and the single-photon signal of the dual-frequency pulse light is received by the single-photon detector. The timestamp corresponding to the single-photon pulse signal is collected through the time-to-digital converter (TDC), and the number of timestamps is counted.

[0030] It should be noted that the trigger signal of the TDC has the same frequency as the drive signal of the optical switch, and both are square waves. If the square wave is high, there is only the optical frequency in the link. The optical signal passes through; if the square wave is low level, the optical frequency is The light signal passes through.

[0031] The present invention accumulates data from multiple square wave periods by setting a locking period, thereby avoiding statistical deviations caused by insufficient measurement time.

[0032] Preferably, the voltage adjustment is used to make the number of photons of different frequencies output by the resonant cavity the same, including:

[0033] Counting the number of photons of different frequencies output by the resonant cavity within the preset time period to generate a transmittance curve;

[0034] Determining a regulating voltage of the laser based on the number of photons of different frequencies includes:

[0035] Record the laser sweep voltage corresponding to the peak position of the transmittance curve ,Will The corresponding transmittance in the transmittance curve 1 as the center reference position;

[0036] The frequency of the resonant cavity is The light distribution of the optical signal is set at the rising edge of the transmittance curve, and the frequency is The transmittance of the light signal in the transmittance curve is recorded as 2;

[0037] The frequency is The light distribution of the optical signal is set at the falling edge of the transmittance curve, and the frequency is The transmittance of the light signal in the transmittance curve is recorded as 3;

[0038] If in the interval [0, ] does not exist | 1- 2|=| 3- 1|The corresponding tuning port voltage value, then the frequency is The tuning port voltage corresponding to the optical signal is marked as the adjustment direction is reverse, and the laser tuning port voltage is adjusted until | 1- 2|=| 3- 1|, it marks the completion of the photon number calibration of the dual-frequency pulse light in the transmittance curve.

[0039] It should be noted that since the frequency is The optical signal and frequency are The fixed frequency difference of the optical signal is 2 , in the process of adjusting the tuning port voltage, from the transmittance curve, the frequency is The optical signal and frequency are The light signal moves simultaneously; there is a positive proportional mapping relationship between the number of photons and the transmittance. When the transmittance of the dual-frequency pulse light is 1 is the symmetry axis in the transmittance curve, that is, the number of photons of the dual-frequency pulse light is symmetrically locked in the transmittance curve.

[0040] In the present invention, since the number of photons is directly proportional to the transmittance, when the transmittance is symmetrical in the transmittance curve by adjusting the tuning port voltage, that is, the number of photons is symmetrical in the transmittance curve, there is no need to directly adjust the laser tuning frequency, thereby effectively suppressing the frequency drift phenomenon in the link.

[0041] Preferably, the method for obtaining the transmittance curve includes:

[0042] Use an optical power meter to measure the optical power P0 of the dual-frequency pulse light before it enters the resonant cavity;

[0043] Turn on the laser sweep and mark the laser tuning frequency corresponding to the moment when the laser sweep is turned on as ; Measure the power Pc at the output port of the resonant cavity and take the quotient of Pc and P0 as the transmittance ; Where: au represents arbitrary unit;

[0044] The transmittance curve of the resonant cavity is constructed with transmittance as the ordinate and the laser tuning frequency as the abscissa.

[0045] It should be noted that since the tuning frequency of the laser and the laser tuning port voltage have a linear relationship of 1 GHz / V, the horizontal axis of the transmittance curve represents both the tuning port voltage and the laser tuning frequency; since Pc and P0 are both power, the Pc / P0 units cancel each other out and are dimensionless.

[0046] To achieve the above-mentioned object, a second aspect of the present invention provides a dual-frequency optical frequency locking system based on single-photon detection, comprising: a data processing module, a photon number calculation module, and a calibration module;

[0047] Data processing module: splits the continuous light emitted by the laser through an optical switch to obtain two beams of light with the same frequency;

[0048] Performing frequency shifting on the two light beams with the same frequency to obtain two light beams with different frequencies;

[0049] chopping the two light beams of different frequencies to obtain dual-frequency pulsed light;

[0050] Photon number calculation module: inputs the dual-frequency pulse light into the resonant cavity and determines the number of photons of different frequencies output by the resonant cavity within a preset time length;

[0051] Calibration module: determines the adjustment voltage of the laser based on the number of photons of different frequencies; the adjustment voltage is used to make the number of photons of different frequencies output by the resonant cavity the same.

[0052] Preferably, the system further comprises: a signal feedback module for calling a multifunctional I / O device and transmitting the frequency as well as The light distribution setting of the optical signal is fed back to the laser, and the output frequency of the laser is adjusted to | 1- 2|=| 3- The laser tuning frequency corresponding to the tuning port voltage value when 1|.

[0053] To achieve the above objectives, a third aspect of the present invention provides a dual-frequency optical frequency-locked computing device based on single-photon detection, comprising:

[0054] A memory and a processor, wherein the memory stores executable instructions of the processor; wherein the processor is configured to implement the dual-frequency optical frequency locking method based on single-photon detection provided by the first aspect by executing the executable instructions.

[0055] Compared with the prior art, the present invention has the following beneficial effects:

[0056] 1. This invention generates two light beams of different frequencies by passing the output of a tunable laser through two acousto-optic modulators with the same frequency but opposite frequency shift directions. Laser feedback frequency locking ensures that the number of photons of different frequencies output by the resonant cavity is the same. This symmetrical locking of the two light beams at the two edges of the resonant cavity transmittance curve is equivalent to locking the laser's intrinsic frequency at the peak of the resonant cavity transmittance curve. Furthermore, this technology utilizes single-photon detectors as optical signal detectors, leveraging their advantages in weak signal reception. This improves detection efficiency while meeting wind measurement requirements.

[0057] 2. The present invention uses a resonant cavity as a standard frequency reference. Under good temperature control, its resonant peak frequency will fluctuate within a very small range. In contrast, the frequency drift of the laser is larger. Therefore, the laser light from the laser is modulated to generate two lights of different frequencies, which pass through the resonant cavity. The two beams of light are locked to the two edges of the transmittance curve of the resonant cavity. The locking method is laser PZT tuning (PZT - piezoelectric ceramic, used to accurately adjust the cavity length of the laser's internal resonant cavity and thus change the light frequency). Through PZT tuning, the frequency drift generated by the laser is corrected in the opposite direction, thereby suppressing the laser's frequency drift. At the same time, the drift of the laser and the resonant cavity are also consistent, stabilizing the system frequency. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0059] Figure 1 Schematic diagram of the specific steps of frequency locking of the present invention;

[0060] Figure 2 A schematic diagram of the connection relationship of the components used in the present invention;

[0061] Figure 3 A schematic diagram of the specific steps for obtaining the transmittance curve of the resonant cavity according to the present invention;

[0062] Figure 4 Schematic diagram of the symmetrical locking steps of the dual-frequency pulse light in the transmittance curve of the present invention;

[0063] Figure 5 This is a schematic diagram of the relationship between the modules included in the present invention. DETAILED DESCRIPTION

[0064] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0065] See also Figure 1-Figure 2 The first embodiment of the present invention provides a dual-frequency optical frequency locking method based on single-photon detection, comprising:

[0066] The continuous light emitted by the laser is split by an optical switch to obtain two beams of light with the same frequency;

[0067] Performing frequency shifting on the two light beams with the same frequency to obtain two light beams with different frequencies;

[0068] chopping the two light beams of different frequencies to obtain dual-frequency pulsed light;

[0069] Inputting the dual-frequency pulsed light into a resonant cavity, and determining the number of photons of different frequencies output by the resonant cavity within a preset time period;

[0070] The regulating voltage of the laser is determined based on the number of photons of different frequencies; the regulating voltage is used to make the number of photons of different frequencies output by the resonant cavity the same.

[0071] See also Figure 3 , the specific steps to obtain the transmittance curve of the resonant cavity: set the frequency of the continuous light to ;

[0072] Two beams of the same frequency are frequency-shifted to obtain two beams of different frequencies, including:

[0073] The first beam of the two beams of the same frequency is input into the acousto-optic modulator AOM1 and the first attenuator to obtain the second beam, wherein the acousto-optic modulator AOM1 is used to adjust the frequency of the first beam. The first attenuator is used to attenuate the frequency-shifted first light beam; the frequency of the second light beam ;

[0074] The third beam of the two beams of the same frequency is input into the acousto-optic modulator AOM2 and the second attenuator to obtain a fourth beam, wherein the acousto-optic modulator AOM2 is used to adjust the frequency of the third beam. The second attenuator is used to attenuate the frequency-shifted third light beam; the frequency of the fourth light beam is ;

[0075] Measure the output power of the attenuator connected to the AOM1, recorded as P1; measure the output power of the attenuator connected to the AOM2, recorded as P2;

[0076] If P1 is greater than P2, adjust the first attenuator connected to the AOM1 and use an optical power meter to measure the output power P3 of the first attenuator until P3 equals P2, marking the adjustment complete. If P1 is less than P2, adjust the second attenuator connected to the AOM2 and use an optical power meter to measure the output power P4 of the second attenuator until P4 equals P2, marking the adjustment complete.

[0077] The dual-frequency continuous light with the same power is modulated into dual-frequency pulse light based on the chopping technology by the acousto-optic modulator AOM3, and the frequency of the dual-frequency pulse light is increased. ; Among them, the optical frequency of the dual-frequency pulse light is , the optical frequency is ;

[0078] Use an optical power meter to measure the optical power P0 of the dual-frequency pulse light before it enters the resonant cavity;

[0079] Turn on the laser sweep and mark the laser tuning frequency corresponding to the moment when the laser sweep is turned on as ; Measure the power Pc at the output port of the resonant cavity and take the quotient of Pc and P0 as the transmittance ; Where: au represents arbitrary unit;

[0080] The transmittance curve of the resonant cavity is constructed with transmittance as the ordinate and the laser tuning frequency as the abscissa.

[0081] For example, the laser changes the resonant cavity length in the laser through the built-in piezoelectric ceramic, the tuning range is 10GHz, and the tuning port voltage range is 0-10V; the laser emission frequency is recorded as , and after The optical switch is set to be driven by a square wave with a high level of 4V and a low level of -4V; the uplink is frequency shifted by AOM1 , the frequency is , downlink passes through AOM2, frequency shift , the light frequency becomes .

[0082] First, adjust the attenuator to make the two lights have the same power after passing through the coupler. Then, perform 3-wave chopping through the acousto-optic modulator to modulate the dual-frequency continuous light into dual-frequency pulse light and shift the frequency at the same time. , at this time the frequencies of the dual-frequency pulse light are as well as and incident into the resonant cavity;

[0083] After the laser signal light is attenuated, it is directly connected to the resonant cavity, and the optical power before entering the resonant cavity is measured. Then, the laser is turned on for frequency sweeping, and the resonant cavity output power is measured to obtain the transmittance curve of the resonant cavity.

[0084] See also Figure 4 , the dual-frequency pulse light has symmetrical locking steps in the transmittance curve:

[0085] Count the number of timestamps within a square wave period, and accumulate the timestamps collected when the square wave is high and low respectively. Set the lock period to an integer multiple of 10 of the square wave period.

[0086] All square wave high level time within the lock cycle The number of timestamps of the pulse is given as The number of photons in the locking period is one;

[0087] All square wave low level time within the lock cycle The number of timestamps of the pulse is given as The number of photons in the locking period is two.

[0088] Record the laser sweep voltage corresponding to the peak position of the transmittance curve ,Will The corresponding transmittance in the transmittance curve 1 as the center reference position;

[0089] The frequency of the resonant cavity is The light distribution of the optical signal is set at the rising edge of the transmittance curve, and the frequency is The transmittance of the light signal in the transmittance curve is recorded as 2;

[0090] The frequency is The light distribution of the optical signal is set at the falling edge of the transmittance curve, and the frequency is The transmittance of the light signal in the transmittance curve is recorded as 3;

[0091] If in the interval [0, ] does not exist | 1- 2|=| 3- 1|The corresponding tuning port voltage value, then the frequency is The tuning port voltage corresponding to the optical signal is marked as the adjustment direction is reverse, and the tuning port voltage in the transmittance curve is adjusted until | 1- 2|=| 3- 1|, it marks the completion of the photon number calibration of the dual-frequency pulse light in the transmittance curve.

[0092] It should be noted that since the frequency is The optical signal and frequency are The fixed frequency difference of the optical signal is 2 , in the process of adjusting the voltage, from the transmittance curve, the frequency is The optical signal and frequency are The light signal moves simultaneously; there is a positive proportional mapping relationship between the number of photons and the transmittance. When the transmittance of the dual-frequency pulse light is 1 is the symmetry axis in the transmittance curve, that is, the number of photons of the dual-frequency pulse light is symmetrically locked in the transmittance curve.

[0093] For example, in this solution, the TDC trigger signal and the optical switch drive signal have the same frequency, both are 100Hz square waves. When the square wave is high, only the signal with a frequency of The optical signal passes through, when the level is low, the frequency is The light signal passes through.

[0094] The temperature control accuracy of the resonant cavity is set to 10mK, and the frequency drift of the laser is 100 MHz / day. Therefore, it is sufficient to lock once every 1s. The square wave period is set to 10ms. The timestamps collected when the square wave is high and low are accumulated to obtain the frequency The optical signal and frequency are The number of photons accumulated in the optical signal within 10ms is 100 square wave cycles, so the frequency within 1s is The optical signal and frequency are The number of photons of the optical signal; the initial voltage supplied to the laser through the multi-function I / O device is , then the frequency entering the resonant cavity is set to The optical signal light is distributed on the rising edge of the transmittance curve, and the frequency is The light distribution of the optical signal is on the falling edge of the transmittance curve, so the comparison frequency is The optical signal and frequency are The number of photons in the optical signal is large, and the frequency is obtained as The number of photons in the optical signal is greater than the frequency The number of photons in the optical signal will be The corresponding transmittance in the transmittance curve 1 is used as the center reference position, and the voltage output by the I / O device is adjusted. At this time, the frequency is The optical signal and frequency are The number of photons (transmittance) of the optical signal is not equal, so the frequency of the optical signal entering the resonant cavity is adjusted to The optical signal light is distributed on the falling edge of the transmittance curve, and the frequency is The light distribution of the optical signal is on the rising edge of the transmittance curve, and the DC voltage signal is fed back to the laser through the multi-function I / O device, thereby changing the laser frequency and completing the symmetrical locking of the photon number of the dual-frequency pulse light in the transmittance curve.

[0095] It should be noted that the process of adjusting the direction to the reverse direction can be achieved by reversing the voltage output in the program setting, and this process is completed in real time by the processor executing the computer code.

[0096] See also Figure 5 , a second aspect of the present invention provides a dual-frequency optical frequency locking system based on single-photon detection, comprising: a data processing module, a photon number calculation module, a calibration module and a signal feedback module;

[0097] Data processing module: splits the continuous light emitted by the laser through an optical switch to obtain two beams of light with the same frequency;

[0098] Performing frequency shifting on the two light beams with the same frequency to obtain two light beams with different frequencies;

[0099] chopping the two light beams of different frequencies to obtain dual-frequency pulsed light;

[0100] Photon number calculation module: inputs the dual-frequency pulse light into the resonant cavity and determines the number of photons of different frequencies output by the resonant cavity within a preset time length;

[0101] Calibration module: determining an adjustment voltage of the laser based on the number of photons of different frequencies; the adjustment voltage is used to make the number of photons of different frequencies output by the resonant cavity the same;

[0102] Signal feedback module: used to call the multi-function I / O device and transmit the frequency to the as well as The light distribution setting of the optical signal is fed back to the laser and the output frequency of the laser is adjusted.

[0103] An embodiment of the third aspect of the present invention provides a dual-frequency optical frequency locking computing device based on single-photon detection, comprising: a memory and a processor, wherein the memory stores executable instructions of the processor; wherein the processor is configured to execute the executable instructions to implement the dual-frequency optical frequency locking system based on single-photon detection provided by the second aspect.

[0104] Some of the data in the above formula are dimensionless and calculated numerically. The formula is a formula that is closest to the actual situation obtained by software simulation of a large amount of collected data; the preset parameters and preset thresholds in the formula are set by technicians in this field according to the actual selected resonant cavity and laser characteristics.

[0105] The working principle of the present invention is as follows: the output of a tunable laser is passed through two acousto-optic modulators with the same frequency but opposite frequency shift directions, thereby generating two lights of different frequencies. Based on the difference in photon counts of the two beams after passing through the resonant cavity, the laser frequency is tuned in real time, so that the two lights of different frequencies are respectively and symmetrically distributed on the rising and falling edges of the resonant cavity transmittance curve. This is equivalent to locking the laser's eigenfrequency at the center of the resonant cavity transmittance curve.

[0106] The above embodiments are only used to illustrate the technical method of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical method of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical method of the present invention.

Claims

1. A dual-frequency optical frequency locking method based on single-photon detection, characterized in that: include: The continuous light emitted by the laser is split by an optical switch to obtain two beams of light with the same frequency; Performing frequency shifting on the two light beams with the same frequency to obtain two light beams with different frequencies; chopping the two light beams of different frequencies to obtain dual-frequency pulsed light; Inputting the dual-frequency pulsed light into a resonant cavity, and determining the number of photons of different frequencies output by the resonant cavity within a preset time period; The regulating voltage of the laser is determined based on the number of photons of different frequencies; the regulating voltage is used to make the number of photons of different frequencies output by the resonant cavity the same.

2. The dual-frequency optical frequency locking method based on single-photon detection according to claim 1, characterized in that: The optical switch splits the continuous light based on the square wave signal; the frequency of the continuous light is ; The two light beams with the same frequency are frequency-shifted to obtain two light beams with different frequencies, including: The first light beam of the two light beams with the same frequency is input into the acousto-optic modulator AOM1 and the first attenuator to obtain the second light beam, wherein the acousto-optic modulator AOM1 is used to adjust the frequency of the first light beam. , the first attenuator is used to attenuate the first light beam after frequency shift; the frequency of the second light beam ; The third light beam of the two light beams with the same frequency is input into the acousto-optic modulator AOM2 and the second attenuator to obtain a fourth light beam, wherein the acousto-optic modulator AOM2 is used to adjust the frequency of the third light beam. , the second attenuator is used to attenuate the frequency-shifted third light beam; the frequency of the fourth light beam .

3. The dual-frequency optical frequency locking method based on single-photon detection according to claim 1, characterized in that: Obtaining dual-frequency pulsed light obtained by coupling the two light beams of different frequencies, comprising: Measure the output power of the first attenuator connected to the AOM1, recorded as P1; measure the output power of the second attenuator connected to the AOM2, recorded as P2; If P1 is greater than P2, adjust the first attenuator connected to the acousto-optic modulator AOM1 and use an optical power meter to measure the output power P3 of the first attenuator until P3 equals P2, marking the adjustment as completed. If P1 is less than P2, adjust the second attenuator connected to the acousto-optic modulator AOM2 and use an optical power meter to measure the output power P4 of the second attenuator until P4 equals P2, marking the adjustment as completed. The coupled light beams with the same power are modulated by the acousto-optic modulator AOM3 based on the chopping technology to form dual-frequency pulse light, so that the frequency of the dual-frequency pulse light is increased. ; Among them, the optical frequency of the dual-frequency pulse light is , the optical frequency is .

4. The dual-frequency optical frequency locking method based on single-photon detection according to claim 1, characterized in that: The determining the number of photons of different frequencies output by the resonant cavity within a preset time period includes: Count the number of timestamps within a square wave period, and accumulate the timestamps collected when the square wave is high and low, respectively. Set the lock period to an integer multiple of the square wave period. All square wave high level time within the lock cycle The number of timestamps of the pulse is given as The number of photons in the locking period is one; All square wave low level time within the lock cycle The number of timestamps of the pulse is given as The number of photons in the locking period is two.

5. The dual-frequency optical frequency locking method based on single-photon detection according to claim 4, characterized in that: Methods for obtaining the number of timestamps include: The dual-frequency pulse light is input into a single-photon detector, and the single-photon signal of the dual-frequency pulse light is received by the single-photon detector. The timestamp corresponding to the single-photon pulse signal is collected through the time-to-digital converter (TDC), and the number of timestamps is counted.

6. The dual-frequency optical frequency locking method based on single-photon detection according to claim 1, characterized in that: The voltage adjustment is used to make the number of photons of different frequencies output by the resonant cavity the same, and includes: Count the number of photons of different frequencies output by the resonant cavity and generate a transmittance curve; Determining a regulating voltage of the laser based on the number of photons of different frequencies includes: Record the laser sweep voltage corresponding to the peak position of the transmittance curve ,Will The corresponding transmittance in the transmittance curve 1 as the center reference position; The frequency of the resonant cavity is The light distribution of the optical signal is set at the rising edge of the transmittance curve, and the frequency is The transmittance of the light signal in the transmittance curve is recorded as 2; The frequency is The light distribution of the optical signal is set at the falling edge of the transmittance curve, and the frequency is The transmittance of the light signal in the transmittance curve is recorded as 3; If in the interval [0, ] does not exist | 1- 2|=| 3- 1|The corresponding tuning port voltage value, then the frequency is The tuning port voltage corresponding to the optical signal is marked as the adjustment direction is reverse, and the laser tuning port voltage is adjusted until | 1- 2|=| 3- 1|, it marks the completion of the photon number calibration of the dual-frequency pulse light in the transmittance curve.

7. The dual-frequency optical frequency locking method based on single-photon detection according to claim 6, characterized in that: The method for obtaining the transmittance curve includes: Use an optical power meter to measure the optical power P0 of the dual-frequency pulse light before it enters the resonant cavity; Turn on the laser sweep and mark the laser tuning frequency corresponding to the moment when the laser sweep is turned on as ; Measure the power Pc at the output port of the resonant cavity and take the quotient of Pc and P0 as the transmittance ; Where: au represents arbitrary unit; The transmittance curve of the resonant cavity is constructed with transmittance as the ordinate and the laser tuning frequency as the abscissa.

8. A dual-frequency optical frequency locking system based on single-photon detection, adapted to the dual-frequency optical frequency locking method based on single-photon detection according to any one of claims 1 to 7, characterized in that: include: Data processing module, photon number calculation module and calibration module; Data processing module: splits the continuous light emitted by the laser through an optical switch to obtain two beams of light with the same frequency; Performing frequency shifting on the two light beams with the same frequency to obtain two light beams with different frequencies; chopping the two light beams of different frequencies to obtain dual-frequency pulsed light; Photon number calculation module: inputs the dual-frequency pulse light into the resonant cavity and determines the number of photons of different frequencies output by the resonant cavity within a preset time length; Calibration module: determines the adjustment voltage of the laser based on the number of photons of different frequencies; the adjustment voltage is used to make the number of photons of different frequencies output by the resonant cavity the same.

9. The dual-frequency optical frequency locking system based on single-photon detection according to claim 8, characterized in that: Also includes: Signal feedback module: used to call the multi-function I / O device and transmit the frequency to the as well as The light distribution setting of the optical signal is fed back to the laser, and the output frequency of the laser is adjusted to | 1- 2|=| 3- The laser tuning frequency corresponding to the tuning port voltage value when 1|; where, is the optical frequency 1 in the dual-frequency pulse light, is the second frequency of the dual-frequency pulse light; 1 is the laser sweep voltage corresponding to the peak position of the transmittance curve The corresponding transmittance, frequency is The transmittance of the light signal in the transmittance curve is recorded as 2, the frequency is The transmittance of the light signal in the transmittance curve is recorded as 3. The transmittance curve is generated based on the number of photons of different frequencies output by the resonant cavity.

10. A dual-frequency optical frequency-locked computing device based on single-photon detection, characterized in that: include: A memory and a processor, wherein the memory stores executable instructions of the processor; wherein the processor is configured to execute the dual-frequency optical frequency locking system based on single-photon detection according to any one of claims 8 to 9 by executing the executable instructions.

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