Double-frequency light frequency locking method and system based on single photon detection and computing equipment

Abstract

The invention discloses a double-frequency light frequency locking method and system based on single-photon detection and computing equipment, relates to the technical field of wind measurement radars, and solves the technical problem of unstable system frequency caused by long-term drift of a laser and low temperature control precision of a resonant cavity in a single-photon radar system. The method comprises the following steps: performing amplitude modulation on continuous laser twice to form double-frequency continuous light, and constructing a transmittance curve of a resonant cavity based on the double-frequency continuous light; chopping the double-frequency continuous light into double-frequency pulse light, and if the double-frequency pulse light is asymmetrically locked in a transmittance curve or is in an unstable state in a rising edge and a falling edge preset in the transmittance curve, acquiring a timestamp of a double-frequency pulse light signal received by a single-photon detector by using a time-to-digital converter; calculating the number of photons of the dual-frequency pulsed light based on the number of timestamps; the photon number is calibrated on a transmittance curve through frequency tuning of the laser, and laser frequency locking is completed; according to the invention, frequency locking can be realized without extremely high temperature control precision.

Description

Technical Field

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

[0002] Traditional coherent detection lidars obtain the Doppler frequency shift by receiving the Mie scattering signal of aerosols in the atmosphere and heterodyne beating with the intrinsic signal at the laser emission end. A direct detection lidar needs to use a frequency discriminator to measure the Doppler frequency shift of the aerosol signal. This kind of frequency discriminator is usually a high-performance resonant cavity. When the emitted laser is scattered by aerosols, due to the Doppler frequency shift, the laser frequency changes. Therefore, the transmittance of the echo signal will change after entering the resonant cavity. According to 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 amount by measuring the change in light intensity after passing through the frequency discrimination device is also called the edge technique. At the same time, since the limit of optical detection ability is to achieve single-photon detection, a single-photon detector is selected as the optical signal receiving device; However, as the core device of the direct detection wind measurement system, although the frequency discriminator has the advantage of high resolution, it is more vulnerable to the influence of system frequency instability factors. Since the frequency discriminator is a resonant cavity, the resonant peak wavelength changes with temperature, and the intrinsic frequency of the laser light source also drifts over time. By using a tunable laser to change the injection current during the tuning process, the tuning process is nonlinear, and the repeated change of the current will also cause frequency drift and weak temperature fluctuations, resulting in the technical problem of unstable output wavelength. Summary of the Invention

[0003] The present invention aims to solve at least one of the technical problems existing in the prior art; for this purpose, the present invention proposes a dual-frequency optical frequency locking method, system, and computing device based on single-photon detection to solve the technical problem that in the prior art, during the tuning process of changing the injection current of a tunable laser, the tuning process is nonlinear, and the repeated change of the current will also cause frequency drift and weak temperature fluctuations, resulting in unstable output wavelength.

[0004] To achieve the above object, the first aspect of the present invention provides a dual-frequency optical frequency locking method based on single-photon detection, including: Splitting the continuous light emitted by a laser through an optical switch to obtain two beams of light with the same frequency; Shifting the frequencies of the two beams of light with the same frequency respectively to obtain two beams of light with different frequencies; Chopping the two beams of light with different frequencies to obtain dual-frequency pulsed light; Inputting the dual-frequency pulsed light into a resonant cavity and determining the number of photons with different frequencies output by the resonant cavity within a preset time period; Determine the adjustment voltage of the laser based on the photon numbers of different frequencies; the adjustment voltage is used to make the photon numbers of different frequencies output by the resonant cavity the same.

[0005] Preferably, the optical switch splits the continuous light based on a square wave signal; the frequency of the continuous light is ; Perform frequency shifting on the two beams of light with the same frequency respectively to obtain two beams of light with different frequencies, including: Input the first beam of the two beams of light with the same frequency into the acousto-optic modulator AOM1 and the first attenuator to obtain a second beam, where the acousto-optic modulator AOM1 is used to perform frequency shifting on the first beam , and the first attenuator is used to attenuate the frequency-shifted first beam; the frequency of the second beam ; Input the third beam of the two beams of light with the same frequency into the acousto-optic modulator AOM2 and the second attenuator to obtain a fourth beam, where the acousto-optic modulator AOM2 is used to perform frequency shifting on the third beam , and the second attenuator is used to attenuate the frequency-shifted third beam; the frequency of the fourth beam .

[0006] In the present invention, by using two acousto-optic modulators to modulate the continuous light respectively, the frequency shifts of the dual-frequency continuous light are equal in magnitude but opposite in direction, thereby ensuring the link symmetry.

[0007] Preferably, obtaining the dual-frequency pulsed light obtained by coupling the two beams of light with different frequencies includes: Measure the output power of the attenuator connected to the acousto-optic modulator AOM1, denoted as P1; measure the output power of the attenuator connected to the acousto-optic modulator AOM2, denoted as P2; If P1 is greater than P2, adjust the attenuator connected to the acousto-optic modulator AOM1, and at the same time use an optical power meter to measure the output power P3 of the attenuator until P3 is equal to P2, then mark it as the completion of adjustment; If P1 is less than P2, adjust the attenuator connected to the acousto-optic modulator AOM2, and at the same time use an optical power meter to measure the output power P4 of the attenuator until P4 is equal to P2, then mark it as the completion of adjustment; Based on the chopping technique, modulate the coupled beams with the same power by the acousto-optic modulator AOM3 to form dual-frequency pulsed light, so that the frequency shifts of the dual-frequency pulsed light are both increased ; where, one of the optical frequencies in the dual-frequency pulsed light is , and the other optical frequency is .

[0008] The present invention optimizes the signal-to-noise ratio synchronization of two signals in real time by adjusting the attenuator, ensuring the symmetry of the link and improving the stability of the link operation.

[0009] Preferably, the determining the number of photons of different frequencies output by the resonant cavity within a preset duration includes: Set a pre-locking period, count the number of timestamps within a square wave period, and accumulate the number of timestamps collected during the high level and low level of the square wave respectively. Take the quotient of the pre-locking period and the square wave period as the accumulation multiple; Count the number of timestamps within a square wave period, and accumulate the number of timestamps collected during the high level and low level of the square wave respectively. Set the locking period to 10 times the square wave period of 10n; where n is a positive integer; For all the high-level times of the square wave within the locking period The number of timestamps of the pulses is used as The number of photons one within the locking period; For all the low-level times of the square wave within the locking period The number of timestamps of the pulses is used as The number of photons two within the locking period.

[0010] The present invention calculates the number of photons of the dual-frequency pulsed light based on the number of timestamps, which is beneficial for subsequent rapid frequency calibration.

[0011] Preferably, the obtaining method of the number of timestamps includes: Input the dual-frequency pulsed light into a single-photon detector, use the single-photon detector to receive the single-photon signal of the dual-frequency pulsed light, collect the timestamps corresponding to the single-photon pulse signal through a time-to-digital converter TDC, and count the number of timestamps.

[0012] 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 at a high level, only the optical signal with an optical frequency of passes through; if the square wave is at a low level, then the optical signal with an optical frequency of passes through.

[0013] The present invention avoids statistical deviation caused by insufficient measurement time by setting a locking period and accumulating data of multiple square wave periods; Preferably, the adjusting voltage for making the number of photons of different frequencies output by the resonant cavity the same includes: Count the number of photons of different frequencies output by the resonant cavity within the preset duration to generate a transmittance curve; Determine the adjusting voltage of the laser based on the number of photons of different frequencies, including: Record the laser sweep voltage corresponding to the peak position of the transmittance curve , take the transmittance corresponding in the transmittance curve 1 as the central reference position; Set the optical distribution of the optical signal with a frequency of in the rising edge of the transmittance curve, and record the transmittance corresponding to the optical signal with a frequency of as 2; Set the optical distribution of the optical signal with a frequency of in the falling edge of the transmittance curve, and record the transmittance corresponding to the optical signal with a frequency of as 3; If there is no | | within the interval [0, 1 - 2| = | 3 - 1| corresponding tuning port voltage value, then mark the tuning port voltage corresponding to the optical signal with a frequency of as the adjustment direction is reverse, and adjust the tuning port voltage of the laser until | 1 - 2| = | 3 - 1|, then mark it as the completion of the photon number calibration of the dual - frequency pulsed light in the transmittance curve.

[0014] It should be noted that, due to the fixed frequency difference between the optical signal with a frequency of and the optical signal with a frequency of being 2 , then during the process of adjusting the tuning port voltage, from the perspective of the transmittance curve, the optical signal with a frequency of and the optical signal with a frequency of move simultaneously; there is a proportional mapping relationship between the photon number and the transmittance. When the transmittance of the dual - frequency pulsed light is symmetric in the transmittance curve with 1 as the axis of symmetry, that is, the photon number of the dual - frequency pulsed light is symmetrically locked in the transmittance curve.

[0015] In the present invention, since the photon number is in a proportional relationship with the transmittance, when the transmittance is made symmetric in the transmittance curve by adjusting the tuning port voltage, that is, the photon number is symmetric in the transmittance curve, without directly adjusting the tuning frequency of the laser, thus effectively suppressing the frequency drift phenomenon in the link.

[0016] Preferably, the obtaining method of the transmittance curve includes: Measure the optical power P0 of the dual - frequency pulsed light before entering the resonant cavity by an optical power meter; Turn on the laser frequency sweep, and mark the laser tuning frequency corresponding to the moment when the laser frequency sweep is turned on as ; Measure the power Pc at the output port of the resonator, and use the quotient of Pc and P0 as the transmittance ; Where: a.u. represents arbitrary unit; Construct the transmittance curve of the resonator with the transmittance as the ordinate and the laser tuning frequency as the abscissa.

[0017] It should be noted that since the tuning frequency of the laser has a linear relationship with the voltage of the laser tuning port of 1 GHz / V, the abscissa of the transmittance curve can be expressed as both the tuning port voltage and the laser tuning frequency; since both Pc and P0 are powers, the unit of Pc / P0 cancels out and it is dimensionless.

[0018] To achieve the above object, the second aspect of the present invention provides a dual-frequency optical frequency locking system based on single-photon detection, including: a data processing module, a photon number calculation module, and a calibration module; Data processing module: Split the continuous light emitted by the laser through an optical switch to obtain two beams of light with the same frequency; Shift the frequencies of the two beams of light with the same frequency respectively to obtain two beams of light with different frequencies; Chop the two beams of light with different frequencies to obtain dual-frequency pulsed light; Photon number calculation module; Input the dual-frequency pulsed light into the resonator, and determine the number of photons with different frequencies output by the resonator within a preset time; Calibration module: Determine the adjustment voltage of the laser based on the number of photons with different frequencies; the adjustment voltage is used to make the number of photons with different frequencies output by the resonator the same.

[0019] Preferably, the system further includes: a signal feedback module: used to call a multifunctional I / O device, and feedback the optical distribution setting of the optical signal with frequencies of and to the laser through the multifunctional I / O device, and adjust the output frequency of the laser to the laser tuning frequency corresponding to the tuning port voltage value when | 1 - 2| = | 3 - 1|.

[0020] To achieve the above object, the third aspect of the present invention provides a dual-frequency optical frequency locking calculation device based on single-photon detection, including: A memory and a processor, where the memory stores executable instructions for the processor; wherein, the processor is configured to execute the method for dual-frequency optical frequency locking based on single-photon detection provided in the first aspect by executing the executable instructions.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. In the present invention, the output of a tunable laser passes through two acousto-optic modulators with the same frequency and opposite frequency shift directions respectively, thereby generating two lights with different frequencies. Through the laser feedback frequency locking technology, the number of photons with different frequencies output by the resonant cavity is the same, that is, these two lights with different frequencies are symmetrically locked at the two edges of the resonant cavity transmittance curve, which is equivalent to locking the intrinsic frequency of the laser at the peak position of the resonant cavity transmittance curve. In addition, this technology uses a single-photon detector as the optical signal detector, which can give full play to the advantages of the single-photon detector in the field of weak signal reception, and improves the detection efficiency while meeting the wind measurement requirements.

[0022] 2. In the present invention, by using the resonant cavity as a standard frequency reference, under the condition of good temperature control, the resonant peak frequency will fluctuate within a very small range, while the frequency drift of the laser is larger. Therefore, the laser output from the laser is modulated to generate two lights with different frequencies and pass through the resonant cavity; the two beams of light are locked at the two edges of the resonant cavity transmittance curve, and the locking means is the PZT tuning of the laser (PZT - piezoelectric ceramic, used to precisely adjust the cavity length of the internal resonant cavity of the laser to change the optical frequency); through the PZT tuning, the frequency drift direction generated by the laser is corrected in the opposite direction, so the frequency drift of the laser is suppressed, and at the same time, the laser and the resonant cavity drift in unison, stabilizing the system frequency. Description of the Drawings

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0024] Figure 1 It is a schematic diagram of the specific steps of the frequency locking of the present invention; Figure 2 It is a schematic diagram of the connection relationship of the components used in the present invention; Figure 3 It is a schematic diagram of the specific steps of obtaining the transmittance curve of the resonant cavity in the present invention; Figure 4 It is a schematic diagram of the symmetric locking step of the dual-frequency pulsed light in the transmittance curve of the present invention; Figure 5Schematic diagram of the module relationship included in the present invention. Detailed implementation manners

[0025] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0026] Please refer to Figure 1 - Figure 2 , an embodiment of the first aspect of the present invention provides a dual-frequency optical frequency locking method based on single-photon detection, including: Splitting the continuous light emitted by the laser through an optical switch to obtain two beams of light with the same frequency; Performing frequency shift on the two beams of light with the same frequency respectively to obtain two beams of light with different frequencies; Performing chopping on the two beams of light with different frequencies to obtain dual-frequency pulsed light; Inputting the dual-frequency pulsed light into the resonant cavity, and determining the number of photons with different frequencies output by the resonant cavity within a preset time duration; Determining the adjustment voltage of the laser based on the number of photons with different frequencies; the adjustment voltage is used to make the number of photons with different frequencies output by the resonant cavity the same.

[0027] Please refer to Figure 3 , the specific steps for obtaining the transmittance curve of the resonant cavity: setting the frequency of the continuous light as ; Performing frequency shift on the two beams of light with the same frequency respectively to obtain two beams of light with different frequencies, including: Inputting the first beam in the two beams of light with the same frequency into the acousto-optic modulator AOM1 and the first attenuator to obtain the second beam, where the acousto-optic modulator AOM1 is used to perform frequency shift on the first beam The first attenuator is used to attenuate the frequency-shifted first beam; the frequency of the second beam ; Inputting the third beam in the two beams of light with the same frequency into the acousto-optic modulator AOM2 and the second attenuator to obtain the fourth beam, where the acousto-optic modulator AOM2 is used to perform frequency shift on the third beam , the second attenuator is used to attenuate the frequency-shifted third beam; the frequency of the fourth beam ; Measuring the output power of the attenuator connected to the acousto-optic modulator AOM1, denoted as P1; measuring the output power of the attenuator connected to the acousto-optic modulator AOM2, denoted as P2; If P1 is greater than P2, adjust the attenuator connected to the acousto-optic modulator AOM1, and at the same time use an optical power meter to measure the output power P3 of the attenuator until P3 is equal to P2, then mark it as the adjustment completed; if P1 is less than P2, adjust the attenuator connected to the acousto-optic modulator AOM2, and at the same time use an optical power meter to measure the output power P4 of the attenuator until P4 is equal to P2, then mark it as the adjustment completed; The continuous dual-frequency light with the same power is modulated by the acousto-optic modulator AOM3 based on the chopping technique to form dual-frequency pulsed light, and the frequency shift of the dual-frequency pulsed light increases ; where one of the optical frequencies in the dual-frequency pulsed light is , and the other optical frequency is ; Measure the optical power P0 of the dual-frequency pulsed light before entering the resonant cavity with an optical power meter; Turn on the laser frequency sweep, and mark the laser tuning frequency corresponding to the moment when the laser frequency 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 ; In the formula: a.u. represents arbitrary unit; Construct the transmittance curve of the resonant cavity with the transmittance as the ordinate and the laser tuning frequency as the abscissa.

[0028] For example, the laser changes the length of the resonant cavity inside the laser through the built-in piezoelectric ceramic, the tuning range is 10 GHz, and the tuning port voltage range is 0 - 10 V; record the laser output frequency as , and pass through an optical switch, and the optical switch is set to be driven by a square wave with a high level of 4 V and a low level of -4 V; the uplink is frequency-shifted by AOM1 , the frequency is , the downlink passes through AOM2, and the frequency is shifted , and the optical frequency becomes .

[0029] First, adjust the attenuator so that the powers of the two beams of light are the same after passing through the coupler. Secondly, perform chopping through the acousto-optic modulator to modulate the continuous dual-frequency light into dual-frequency pulsed light, and at the same time shift the frequency , and at this time the frequencies of the dual-frequency pulsed light are respectively and and then incident into the resonant cavity; Attenuate the laser signal light and directly connect it to the resonant cavity, measure the optical power before entering the resonant cavity, and then turn on the laser frequency sweep and measure the output power of the resonant cavity to obtain the transmittance curve of the resonant cavity.

[0030] Please refer to Figure 4 , the symmetric locking steps of the dual-frequency pulsed light in the transmittance curve: Count the number of timestamps within a square wave period, and accumulate the number of timestamps collected during the high and low levels of the square wave respectively. Set the locking period to an integer multiple of 10 times the square wave period; All the timestamps of the pulses during the high level time of the square wave within the locking period are used as the number of photons within the locking period; All the timestamps of the pulses during the low level time of the square wave within the locking period are used as the number of photons within the locking period.

[0031] Record the laser sweep voltage corresponding to the peak position of the transmittance curve , and use the transmittance corresponding to it in the transmittance curve 1 as the central reference position; Set the light distribution of the optical signal with a frequency of on the rising edge of the transmittance curve, and record the transmittance corresponding to the optical signal with a frequency of in the transmittance curve as 2; Set the light distribution of the optical signal with a frequency of on the falling edge of the transmittance curve, and record the transmittance corresponding to the optical signal with a frequency of in the transmittance curve as 3; If there is no value of the tuning port voltage corresponding to | within the interval [0, 1 - 2| = | 3 - 1|, then mark the tuning port voltage corresponding to the optical signal with a frequency of as having an adjustment direction of reverse, and adjust the tuning port voltage in the transmittance curve until | 1 - 2| = | 3 - 1|, then mark it as completed the calibration of the number of photons of the dual-frequency pulsed light in the transmittance curve.

[0032] It should be noted that since the fixed frequency difference between the optical signal with a frequency of and the optical signal with a frequency of is 2 , then during the voltage adjustment process, from the perspective of the transmittance curve, the optical signal with a frequency of and the optical signal with a frequency of The optical signals move simultaneously; there is a proportional mapping relationship between the number of photons and the light transmittance. When the light transmittance of the dual-frequency pulsed light is symmetric in the transmittance curve with 1 as the axis of symmetry, that is, the number of photons of the dual-frequency pulsed light is symmetrically locked in the transmittance curve. 1 is symmetric in the transmittance curve with 1 as the axis of symmetry, that is, the number of photons of the dual-frequency pulsed light is symmetrically locked in the transmittance curve.

[0033] For example, in this solution, the TDC trigger signal has the same frequency as the optical switch drive signal, both are 100Hz square waves. When the square wave is at a high level, only the optical signal with a frequency of passes through the link. When the square wave is at a low level, the optical signal with a frequency of passes through.

[0034] Set the temperature control accuracy of the resonant cavity to the order of 10mK. At the same time, the frequency drift of the laser is hundreds of megahertz per day. Therefore, locking can be achieved once every 1s. Set a square wave period to 10ms. Accumulate the number of timestamps collected when the square wave is at a high level and a low level respectively, and the number of photons accumulated by the optical signal with a frequency of and the optical signal with a frequency of within 10ms can be obtained. Accumulate 100 square wave periods, and then the number of photons of the optical signal with a frequency of and the optical signal with a frequency of within 1s can be obtained; the initial voltage provided to the laser by the multi-functional I / O device is , then set the frequency of the optical signal with a frequency of entering the resonant cavity to be distributed on the rising edge of the transmittance curve, and the optical signal with a frequency of is distributed on the falling edge of the transmittance curve. Then compare the number of photons of the optical signal with a frequency of with the number of photons of the optical signal with a frequency of . It is concluded that the number of photons of the optical signal with a frequency of is greater than the number of photons of the optical signal with a frequency of . Take the corresponding light transmittance in the transmittance curve 1 as the central reference position, adjust the voltage output by the I / O device. At this time, the number of photons (light transmittance) of the optical signal with a frequency of and the optical signal with a frequency of are not equal. Adjust the set frequency of the optical signal entering the resonant cavity to be distributed on the falling edge of the transmittance curve with a frequency of , and the optical signal with a frequency of is distributed on the rising edge of the transmittance curve. And feedback the DC voltage signal to the laser through the multi-functional I / O device, thereby changing the laser frequency and completing the symmetric locking of the number of photons of the dual-frequency pulsed light in the transmittance curve.

[0035] It should be noted that the process of reversing the adjustment 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.

[0036] Please refer to Figure 5 , the second aspect embodiment of the present invention provides a dual-frequency optical frequency locking system based on single-photon detection, including: a data processing module, a photon number calculation module, a calibration module, and a signal feedback 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; Frequency shift is respectively performed on the two beams of light with the same frequency to obtain two beams of light with different frequencies; Chopping is performed on the two beams of light with different frequencies to obtain dual-frequency pulsed light; Photon number calculation module; inputs the dual-frequency pulsed light into the resonant cavity and determines the number of photons with different frequencies output by the resonant cavity within a preset time duration; Calibration module: Determines the adjustment voltage of the laser based on the number of photons with different frequencies; the adjustment voltage is used to make the number of photons with different frequencies output by the resonant cavity the same; Signal feedback module: Used to call a multifunctional I / O device, and feedback the optical distribution setting of the optical signal with frequencies of and to the laser, and adjust the output frequency of the laser.

[0037] The third aspect embodiment of the present invention provides a dual-frequency optical frequency locking calculation device based on single-photon detection, including: a memory and a processor, and executable instructions of the processor are stored in the memory; wherein, the processor is configured to execute the dual-frequency optical frequency locking system provided in the second aspect via executing the executable instructions.

[0038] Some data in the above formula are calculated by removing the dimension and taking their numerical values. The formula is obtained by software simulation of a large amount of collected data to get a formula closest to the actual situation; the preset parameters and preset thresholds in the formula are set by those skilled in the art according to the characteristics of the resonant cavity and the laser actually selected.

[0039] The working principle of the present invention: The present invention passes the output of an adjustable laser through two acousto-optic modulators with the same frequency and opposite frequency shift directions respectively, thereby generating two lights with different frequencies. According to the difference in photon counting of the two lights after passing through the resonant cavity, the frequency of the laser is tuned in real time, so that the two lights with different frequencies are respectively and symmetrically distributed on the rising edge and the falling edge of the resonant cavity transmittance curve, that is, equivalently locking the intrinsic frequency of the laser at the center position of the resonant cavity transmittance curve.

[0040] The above embodiments are only used to illustrate the technical method of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical method of the present invention can be modified or equivalently replaced 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, Comprising: Splitting 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 beams of light with the same frequency respectively to obtain two beams of light with different frequencies; Chopping the two beams of light with different frequencies to obtain dual-frequency pulsed light; Inputting the dual-frequency pulsed light into the resonant cavity and determining the number of photons with different frequencies output by the resonant cavity within a preset time duration; Determining the adjustment voltage of the laser based on the number of photons with different frequencies; the adjustment voltage is used to make the number of photons with 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, wherein The optical switch splits the continuous light based on a square wave signal; the frequency of the continuous light is ; Performing frequency shifting on the two beams of light with the same frequency respectively to obtain two beams of light with different frequencies, including: Input the first beam of the two beams with the same frequency into the acousto-optic modulator AOM1 and the first attenuator to obtain a second beam, where the acousto-optic modulator AOM1 is used to shift the frequency of the first beam , and the first attenuator is used to attenuate the first beam after frequency shift; the frequency of the second beam ; Input the third beam in the two beams with the same frequency into the acousto-optic modulator AOM2 and the second attenuator to obtain a fourth beam, where the acousto-optic modulator AOM2 is used to shift the frequency of the third beam , and the second attenuator is used to attenuate the frequency-shifted third beam; the frequency of the fourth beam .

3. The dual-frequency optical frequency locking method based on single-photon detection according to claim 1, wherein Obtaining the dual-frequency pulsed light coupled by the two beams of light with different frequencies, including: Measuring the output power of the attenuator connected to the acousto-optic modulator AOM1, denoted as P1; measuring the output power of the attenuator connected to the acousto-optic modulator AOM2, denoted as P2; If P1 is greater than P2, adjusting the attenuator connected to the acousto-optic modulator AOM1, and simultaneously measuring the output power P3 of the attenuator using an optical power meter until P3 is equal to P2, then marking it as the completion of adjustment; If P1 is less than P2, adjusting the attenuator connected to the acousto-optic modulator AOM2, and simultaneously measuring the output power P4 of the attenuator using an optical power meter until P4 is equal to P2, then marking it as the completion of adjustment; The coupled light beams with the same power are modulated by the acou-optic modulator AOM3 based on the chopping technique to form a dual-frequency pulsed light, so that the frequency shifts of the dual-frequency pulsed light are both increased. Among them, one of the optical frequencies in the dual-frequency pulsed light is , and the other 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 with different frequencies output by the resonant cavity within a preset time duration includes: Counting the number of timestamps within a square wave period, and respectively accumulating the number of timestamps collected at the high level and low level of the square wave, and setting the locking period as an integer multiple of the square wave period; During all high-level times of the square wave within the locking period, the number of timestamps of the pulses is used as the number of photons within the locking period; The number of timestamps of the pulses during all low-level times of the square wave within the locking period is used as the number of photons within the locking period II.

5. The dual-frequency optical frequency locking method based on single-photon detection according to claim 4, characterized in that The obtaining method of the number of timestamps includes: Inputting the dual-frequency pulsed light into a single-photon detector, using the single-photon detector to receive the single-photon signal of the dual-frequency pulsed light, collecting the timestamps corresponding to the single-photon pulse signal through a time-to-digital converter TDC, and counting the number of timestamps.

6. The dual-frequency optical frequency locking method based on single-photon detection according to claim 1, wherein The adjustment voltage is used to make the number of photons with different frequencies output by the resonant cavity the same, including: Counting the number of photons with different frequencies output by the resonant cavity and generating a transmittance curve; Determining the adjustment voltage of the laser based on the number of photons with different frequencies, including: The laser sweep voltage corresponding to the peak position of the recorded transmittance curve , take The transmittance corresponding to it in the transmittance curve 1 as the central reference position; Set the optical distribution of the optical signal with a frequency of entering the resonant cavity on the rising edge of the transmittance curve, and denote the transmittance corresponding to the optical signal with a frequency of in the transmittance curve as 2; Set the optical distribution of the optical signal with a frequency of at the descending edge of the transmittance curve, and denote the transmittance corresponding to the optical signal with a frequency of in the transmittance curve as 3; If there is no corresponding tuning port voltage value for | within the interval [0, 1 - 2| = | 3 - 1|, then mark the tuning port voltage corresponding to the optical signal with a frequency of as having an adjustment direction of reverse, and adjust the laser tuning port voltage until | 1 - 2| = | 3 - 1|, and then mark it as completed the calibration of the number of photons in the transmittance curve of the dual - frequency pulsed light.

7. The dual-frequency optical frequency locking method based on single-photon detection according to claim 6, characterized in that, The obtaining method of the transmittance curve includes: Measuring the optical power P0 of the dual-frequency pulsed light before entering the resonant cavity through an optical power meter; Turn on the laser frequency sweep, and mark the laser tuning frequency corresponding to the moment when the laser frequency sweep is turned on as ; Measure the power Pc at the output port of the resonator, and take the quotient of Pc and P0 as the transmittance ; Where: a.u. represents arbitrary unit; Constructing the transmittance curve of the resonant cavity with the 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 1-7, characterized in that, Comprising: A data processing module, a photon number calculation module, and a calibration module; Data processing module: Splitting 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 beams of light with the same frequency respectively to obtain two beams of light with different frequencies; Chopping the two beams of light with different frequencies to obtain dual-frequency pulsed light; Photon number calculation module; Inputting the dual-frequency pulsed light into the resonant cavity and determining the number of photons with different frequencies output by the resonant cavity within a preset time duration; Calibration module: Determining the adjustment voltage of the laser based on the number of photons with different frequencies; the adjustment voltage is used to make the number of photons with 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, wherein, Further comprising: Signal feedback module: used to call a multi-functional I / O device, and through the multi-functional I / O device, feed back the light distribution settings of optical signals with frequencies of and to the laser, and adjust the output frequency of the laser to | 1 - 2| = | 3 - 1|, which is the laser tuning frequency corresponding to the tuned port voltage value.

10. A dual-frequency optical frequency locking calculation device based on single-photon detection, characterized in that Comprising: 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 8-9 by executing the executable instructions.

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