A frequency discrimination curve calibration system, method and device

Abstract

The application discloses a frequency discrimination curve calibration system, method and device, and relates to the technical field of laser remote sensing. The system locks the output laser frequency of a first laser on an atom or molecule absorption peak with low concentration, and obtains an accurate frequency standard. The output laser of a second laser is combined with the output laser of the first laser to generate a tuning control signal of the second laser from a frequency difference extracted from a power spectrum of a beat frequency signal, and the output laser frequency of the second laser is locked at any preset frequency offset. The whole laser radar system uses an electrically controlled optical switch to realize the conversion between a calibration state and a detection state. In the calibration state, the laser from the second laser is selected to calibrate the frequency discrimination curve. In the detection state, the received atmospheric backwave signal light is selected for atmospheric remote sensing detection. Therefore, the calibration cost of the frequency discrimination curve is reduced, and the calibration efficiency of the frequency discrimination curve is improved on the basis of ensuring the calibration accuracy and stability of the frequency discrimination curve.

Description

Technical Field

[0001] This application relates to the field of laser remote sensing technology, and in particular to a frequency discrimination curve calibration system, method and apparatus. Background Technology

[0002] In the field of laser remote sensing of wind fields, direct measurement technology is one of the two major technologies alongside coherent measurement technology, and it is often the only choice for measuring wind fields in the upper atmosphere. Direct measurement technology uses an optical frequency discriminator to extract the Doppler frequency shift information of atmospheric backscattered echoes relative to the emitted laser, thereby retrieving line-of-sight wind speed. An optical frequency discriminator is an optical device with a steep, monotonic transmittance characteristic near the laser's operating frequency, and the calibration of its monotonic transmittance characteristic curve (i.e., the frequency discriminant curve) is one of the crucial aspects of a lidar system.

[0003] Traditional frequency discrimination curve calibration requires the use of lasers and high-precision spectrometers to build the test optical path. After calibration, the original detection optical path needs to be restored. This method is not only time-consuming and labor-intensive, but also requires highly skilled technicians to operate, resulting in high calibration costs and unstable calibration results, which can easily cause errors in the measurement system.

[0004] Therefore, how to reduce the cost and improve the efficiency of frequency discrimination curve calibration while ensuring the accuracy and stability of the calibration has become an urgent technical problem to be solved. Summary of the Invention

[0005] The main purpose of this application is to provide a frequency discrimination curve calibration system, method and apparatus, which aims to solve the technical problems of time-consuming, labor-intensive, inefficient and costly frequency discrimination curve calibration in related technologies.

[0006] To achieve the above objectives, the first aspect of this application provides a frequency discrimination curve calibration system, the system comprising:

[0007] The first optical path originates from the first laser, passes sequentially through the first beam splitter, the electro-optic modulator, and the atomic / molecular absorption cell, and is incident on the first photodetector.

[0008] The second optical path originates from the first laser, passes sequentially through the first beam splitter and beam combiner, and is incident on the second photodetector.

[0009] The third optical path originates from the second laser, passes sequentially through the second beam splitter and the beam combiner, and is incident on the second photodetector.

[0010] The fourth optical path originates from the second laser, passes sequentially through the second beam splitter, the third beam splitter, the attenuator, the electrically controlled optical switch, and the fourth beam splitter, and is incident on the third photodetector.

[0011] The fifth optical path originates from the second laser, passes sequentially through the second beam splitter, the third beam splitter, the acousto-optic frequency shifter, and the laser pulse generator, and is emitted into the atmosphere to obtain an atmospheric echo. It then passes sequentially through the electrically controlled optical switch and the fourth beam splitter, and the resulting first atmospheric echo signal is incident on the third photodetector.

[0012] The sixth optical path originates from the second laser, passes sequentially through the second beam splitter, the third beam splitter, the attenuator, the electrically controlled optical switch, the fourth beam splitter, and the optical frequency discriminator, and is incident on the fourth photodetector;

[0013] The seventh optical path originates from the second laser, passes sequentially through the second beam splitter, the third beam splitter, the acousto-optic frequency shifter, and the laser pulse generator, and is emitted into the atmosphere to obtain an atmospheric echo. It then passes sequentially through the electrically controlled optical switch, the fourth beam splitter, and the optical frequency discriminator to obtain a second atmospheric echo signal which is incident on the fourth photodetector.

[0014] The calibration module is used to control the output laser frequency of the second laser to scan and change within a preset operating frequency range based on the first photoelectric signal and the second photoelectric signal; and to determine the frequency discrimination curve of the optical frequency discriminator based on the third photoelectric signal and the fourth photoelectric signal.

[0015] Wherein, the first photoelectric signal is determined by the first photodetector based on the first laser signal received from the atomic / molecular absorption cell in the first optical path; the second photoelectric signal is determined by the second photodetector based on the second laser signal received from the beam combiner after combining the second and third optical paths; the third photoelectric signal is determined by the third photodetector based on the third laser signal received from the fourth beam splitter in the fourth optical path; and the fourth photoelectric signal is determined by the fourth photodetector based on the fourth laser signal received from the optical frequency discriminator in the sixth optical path.

[0016] The calibration module includes a frequency locking unit, which generates a first control signal acting on the first laser based on the first photoelectric signal, so as to control the output laser frequency of the first laser to be locked at the absorption peak of the atomic / molecular absorption cell through the first control signal.

[0017] A frequency bias unit is used to generate a second control signal acting on the second laser based on the second photoelectric signal, so as to control the output laser frequency of the second laser to be locked to a frequency that deviates from the output laser frequency of the first main laser by the second control signal.

[0018] The transmittance measurement module is used to determine, in the calibration state, the calibrated transmittance of the output laser of the second laser relative to the optical frequency discriminator based on the third photoelectric signal and the fourth photoelectric signal, so as to determine the frequency discrimination curve based on the calibrated transmittance; and is used to determine, in the detection state, the transmittance of the current atmospheric echo signal relative to the optical frequency discriminator based on the fifth photoelectric signal, the sixth photoelectric signal and the frequency discrimination curve.

[0019] The fifth photoelectric signal is determined by the third photodetector based on the first atmospheric echo signal received from the fourth beam splitter in the fifth optical path; the sixth photoelectric signal is determined by the fourth photodetector based on the second atmospheric echo signal received from the optical frequency discriminator in the seventh optical path.

[0020] Optionally, the frequency locking unit is specifically used for:

[0021] Based on the driving signal of the electro-optic modulator, the first photoelectric signal is subjected to lock-in amplification processing to obtain the first control signal:

[0022] The frequency tuning device of the first laser is driven according to the first control signal so that the output laser frequency of the first laser is locked at the absorption peak of the atomic / molecular absorption cell.

[0023] Optionally, the frequency bias unit is specifically used for:

[0024] Perform a Fourier transform on the second photoelectric signal to obtain the corresponding power spectrum;

[0025] Peak identification is performed on the power spectrum to determine the signal peaks in the power spectrum;

[0026] Based on the frequency of the signal peak and the preset frequency offset, the second control signal is determined, and the frequency tuning range of the second laser is determined according to the second control signal, so that the output laser frequency of the second laser is locked to a frequency that deviates from the preset frequency offset of the output laser frequency of the first laser.

[0027] Optionally, the transmittance measurement module is specifically used for:

[0028] In the calibration state, the second laser is controlled to scan and change stepwise within the working frequency range according to the preset frequency offset amount of the frequency offset unit;

[0029] Calculate the ratio of the fourth photoelectric signal to the third photoelectric signal after each frequency change to obtain the frequency discrimination curve of the output laser of the second laser relative to the optical frequency discriminator.

[0030] Optionally, the transmittance measurement module is specifically used for:

[0031] During the detection state, the preset frequency offset amount of the frequency offset unit is fixed at a preset fixed value to lock the output laser frequency of the second laser.

[0032] The ratio of the sixth photoelectric signal to the fifth photoelectric signal is calculated to obtain the transmittance of the current atmospheric echo signal relative to the optical frequency discriminator.

[0033] Optionally, both the first laser and the second laser are single-frequency continuous-wave tunable lasers.

[0034] Optionally, the electro-optical switch is a two-input, one-output gating switch, used to select the laser signal from the fourth optical path and the atmospheric echo signal from the fifth optical path.

[0035] Secondly, embodiments of this application also provide a frequency discrimination curve calibration method, wherein the frequency discrimination curve calibration method is applied to the frequency discrimination curve calibration system as described in any of the preceding claims, and the method includes:

[0036] Based on the first optical path, second optical path, third optical path, fourth optical path, fifth optical path, sixth optical path, and seventh optical path, the first photoelectric signal, second photoelectric signal, third photoelectric signal, and fourth photoelectric signal are obtained;

[0037] Based on the first photoelectric signal and the second photoelectric signal, the output laser frequency of the second laser is controlled to scan and change within a preset operating frequency range;

[0038] The frequency discrimination curve of the optical frequency discriminator is determined based on the third photoelectric signal and the fourth photoelectric signal.

[0039] Thirdly, embodiments of this application also provide a frequency discrimination curve calibration device, which is applied to the frequency discrimination curve calibration system as described in any of the above claims, the device comprising:

[0040] The acquisition unit is used to obtain the first photoelectric signal, the second photoelectric signal, the third photoelectric signal, and the fourth photoelectric signal based on the first optical path, the second optical path, the third optical path, the fourth optical path, the fifth optical path, the sixth optical path, and the seventh optical path;

[0041] The control unit is used to control the output laser frequency of the second laser to scan and change within a preset operating frequency range based on the first photoelectric signal and the second photoelectric signal.

[0042] The calculation unit is used to determine the frequency discrimination curve of the optical frequency discriminator based on the third photoelectric signal and the fourth photoelectric signal.

[0043] As can be seen from the above, in the scheme of this application, the first optical path of the frequency discrimination curve calibration system is emitted from the first laser, passes sequentially through the first beam splitter, electro-optic modulator, and atomic / molecular absorption cell, and is incident on the first photodetector; the second optical path is emitted from the first laser, passes sequentially through the first beam splitter and beam combiner, and is incident on the second photodetector; the third optical path is emitted from the second laser, passes sequentially through the second beam splitter and beam combiner, and is incident on the second photodetector; the fourth optical path is emitted from the second laser, passes sequentially through the second beam splitter, third beam splitter, attenuator, electro-optical switch, and fourth beam splitter, and is incident on the third photodetector; the fifth optical path is emitted from the second laser, passes sequentially through the second beam splitter, third beam splitter, acousto-optical frequency shifter, and laser pulse generator, is emitted into the atmosphere to obtain an echo signal, and then passes sequentially through the electro-optical switch, the first beam splitter, the ... the attenuator, and the atomic / molecular absorption cell, and is incident on the third photodetector; the fifth optical path is emitted from the second laser, passes sequentially through the second beam splitter, third beam splitter, acousto-optical frequency shifter, and laser pulse generator, is emitted into the atmosphere to obtain an echo signal, and then passes sequentially through the electro-optical switch, the first beam splitter, the third beam splitter, the attenuator, and the fourth beam splitter, and is incident on the third photodetector; the sixth optical path is emitted from the second laser, passes sequentially through the second beam splitter, third beam splitter, acousto-optical frequency shifter, and laser pulse generator, is emitted into the atmosphere to obtain an echo signal, and then passes sequentially through the electro-optic The fourth optical path, originating from the second laser, passes through the second and third beam splitters, an attenuator, an electrically controlled optical switch, a fourth beam splitter, and an optical frequency discriminator before reaching the fourth photodetector. The seventh optical path, also originating from the second laser, passes through the second and third beam splitters, an acousto-optic frequency shifter, and a laser pulse generator before reaching the atmosphere and obtaining an atmospheric echo. This echo then passes through the electrically controlled optical switch, the fourth beam splitter, and the optical frequency discriminator before reaching the fourth photodetector. The calibration module controls the output laser frequency of the second laser to scan and vary within a preset operating frequency range based on the first and second photoelectric signals. It also determines the frequency discrimination curve of the optical frequency discriminator based on the third and fourth photoelectric signals.

[0044] Compared to existing technologies, the frequency discrimination curve calibration system provided in this application utilizes two single-frequency lasers (a first laser and a second laser), frequency locking, and offset techniques, with an atomic / molecular absorption cell as the frequency standard. This gives the system's own lasers high frequency stability and frequency sweeping capabilities, allowing them to be directly used for frequency discrimination curve calibration without the need for additional frequency sweeping lasers and high-precision wavelength meters or other spectral analysis instruments. Compared to traditional solutions, the frequency discrimination curve calibration system provided in this application not only performs frequency discrimination curve calibration but also directly detects the current wind field by measuring transmittance after calibration. Switching between calibration and detection states is achieved via a photoelectric switch, eliminating the need for highly skilled technicians, saving time and effort, significantly reducing system maintenance costs, and improving utilization efficiency. While ensuring the accuracy and stability of frequency discrimination curve calibration, it reduces calibration costs and improves calibration efficiency. Attached Figure Description

[0045] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0046] Figure 1 This is a schematic diagram of the appearance of the Fabry-Perot etalon provided in the embodiments of this application;

[0047] Figure 2 This is a schematic diagram of the appearance of the iodine molecule frequency discriminator provided in the embodiments of this application;

[0048] Figure 3 This is a schematic diagram of the single-edge frequency discrimination principle of the optical frequency discriminator provided in the embodiments of this application;

[0049] Figure 4 This is a schematic diagram of the frequency discrimination curve of the optical frequency discriminator provided in the embodiments of this application;

[0050] Figure 5 This is a schematic diagram of the frequency discrimination curve of the iodine molecule frequency discriminator provided in the embodiments of this application;

[0051] Figure 6 This is a schematic diagram of the dual-edge frequency discrimination principle of the optical frequency discriminator provided in the embodiments of this application;

[0052] Figure 7 This is provided by the embodiments of this application. Figure 6 The transmittance curves for dual-edge frequency discrimination are shown.

[0053] Figure 8 This is a schematic diagram of the structure of a conventional frequency discrimination curve calibration system provided in an embodiment of this application;

[0054] Figure 9 This is a schematic diagram of the system structure of the frequency discrimination curve calibration system provided in the embodiments of this application;

[0055] Figure 10 This is a schematic diagram of the structure of the frequency locking unit provided in the embodiments of this application;

[0056] Figure 11 This is a schematic diagram of the frequency discrimination curve provided in the embodiments of this application;

[0057] Figure 12 A flowchart of a frequency discrimination curve calibration system provided in this application embodiment is shown. Detailed Implementation

[0058] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of this application. However, those skilled in the art will understand that this application may also be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods are omitted so as not to obscure the description of this application with unnecessary detail.

[0059] It should be understood that, when used in this specification and the appended claims, the term "comprising" indicates the presence of the described features, integrals, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0060] It should also be understood that the terminology used in this application specification is for the purpose of describing particular embodiments only and is not intended to limit the application. As used in this application specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0061] It should also be further understood that the term “and / or” as used in this application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0062] As used in this specification and the appended claims, the term "if" may be interpreted, depending on the context, as "when," "once," "in response to determination," or "in response to classification." Similarly, the phrases "if determined" or "if classified to [the described condition or event]" may be interpreted, depending on the context, as meaning "once determined," "in response to determination," "once classified to [the described condition or event]," or "in response to classification to [the described condition or event]."

[0063] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0064] Many specific details are set forth in the following description in order to provide a full understanding of this application. However, this application may also be implemented in other ways different from those described herein. Those skilled in the art can make similar extensions without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0065] An optical frequency discriminator is an optical device that exhibits a steep, monotonic transmittance characteristic near the laser's operating frequency. The calibration of its monotonic transmittance characteristic curve (i.e., the frequency discriminator curve) is a crucial step in lidar systems. Currently, optical frequency discriminators are mainly divided into two categories: one is entirely artificially fabricated optical components, such as Fabry-Perot etalons (e.g.,...). Figure 1 The diagram shows the appearance of the Fabry-Perot etalon, Fizeau interferometer, various gratings, etc.; another type is optical devices made using the energy level structure of a certain gaseous molecule (which can be a monatomic molecule, such as alkali metal vapor; or a polyatomic molecule, such as iodine vapor), for example... Figure 2 The iodine molecule frequency discriminator shown.

[0066] Figure 3 This is a schematic diagram of the single-edge frequency discrimination principle of an optical frequency discriminator, as shown below. Figure 3 As shown, atmospheric echo signal

[0067] The laser radar's receiving optical path is split into two paths by a beam splitter: one path is directly received by the optical detector and converted into an electrical signal with an amplitude of [missing value]. This path is called the reference channel; the other path, after passing through a frequency discriminator, is received by another optical detector, with a signal amplitude of... This path is called the measurement channel. Ratio This refers to the transmittance of the optical frequency discriminator for the current atmospheric echo signal. The relationship between the transmittance of the optical frequency discriminator and the incident light frequency, i.e., the frequency discrimination curve of the optical frequency discriminator, is shown below. Figure 4 As shown, it has steep, monotonous edge features. For example... Figure 4 As shown in the figure For the laser emission frequency, This represents the transmittance of the corresponding optical frequency discriminator. For example... Figure 4 As shown, when atmospheric echoes generate a Doppler effect When the frequency shifts, the transmittance will deviate. Conversely, if the current atmospheric echo transmittance can be measured, the Doppler frequency shift can be calculated using the frequency discrimination curve, and then the line-of-sight wind speed can be inferred. Figure 5 The frequency discrimination curve of an iodine molecule frequency discriminator is shown below, taking the iodine molecule frequency discriminator as an example. Figure 5 As shown, the steeper the curve edge, the greater the transmittance change will be for the same amount of frequency shift, which means higher detection sensitivity.

[0068] Understandable, Figure 4 The frequency discrimination curve shown only illustrates the falling edge; in actual operation, both the rising and falling edges can be used. Figure 5As shown in the figure, the two steep edges inside the ellipse can be selected as the operating frequency range of the optical frequency discriminator. Figure 5 The shape and amplitude of the transmittance curve shown are related to the temperature control of the iodine molecule frequency discriminator, the pressure of the iodine vapor, and the performance of the optical detector used to measure transmittance. It represents the ratio of the signal amplitudes measured by the two optical detectors in the experiment, and is not strictly speaking the transmittance value. A strictly defined transmittance value must be no greater than 1. Figure 5 The largest amplitude is greater than 1. Figure 5 The curve shown is merely the unnormalized transmittance curve. In actual use of lidar systems, the unnormalized transmittance curve is used only as the frequency discrimination curve. Its function is to establish a connection between the measurement signals of the two optical detectors and the laser frequency, not to actually measure the precise transmittance of the optical frequency discriminator.

[0069] like Figure 3 As shown, the optical frequency discriminator is based on single-edge technology, which utilizes only the steep edge of a single transmittance curve of the optical frequency discriminator. In addition, double-edge technology can also be used. Among these, Figure 6 This is a schematic diagram of the dual-edge frequency discrimination principle of an optical frequency discriminator. Figure 7 for Figure 6 The transmittance curves for dual-edge frequency discrimination are shown. Figure 7 As shown, the frequency discrimination curve is still the ratio of the signal amplitudes measured by the two optical detectors, but at this time the ratio is no longer a simple transmittance, but a ratio of the transmittance of the two channels, but it still has the characteristic of steep and monotonic change with frequency shift.

[0070] The frequency discrimination curve calibration system, method, and apparatus provided in this application do not involve specific technical implementation methods of optical frequency discriminators, and can be adopted as follows: Figure 3 The single-edge frequency discrimination shown can be used as follows: Figure 6 The dual-edge frequency discrimination is shown.

[0071] For ease of explanation, the embodiments of this application employ the following methods: Figure 3 As shown in the single-edge diagram, it is understood that other forms of optical frequency discrimination technology may also be used in this application, which are not specifically limited in this application.

[0072] Because the frequency discrimination curve needs to be measured and recorded before the lidar is used, and the saved curve data needs to be retrieved later to convert the measured transmittance into Doppler frequency shift, and because the optical frequency discriminator must operate in a very stable environment during subsequent use to ensure that the frequency discrimination curve does not change, thus reducing inversion system errors, accurate measurement of the frequency discrimination curve is crucial.

[0073] The traditional frequency discrimination curve calibration process is as follows: First, a low-power, single-frequency tunable continuous-wave laser is prepared as the measurement light source. The laser wavelength tuning range should cover the operating frequency curve of the optical frequency discrimination in the lidar system (e.g., Figure 4 (The steep, sloping edge of the frequency discrimination curve shown). Figure 8 This is a schematic diagram of a traditional frequency discrimination curve calibration system, such as... Figure 8 As shown, a portion of the laser light is injected into the atmospheric echo signal optical channel of the lidar system for transmittance measurement (i.e., the vertical axis of the frequency discrimination curve); another portion of the light enters a high-precision wavelength meter or other spectral analyzer for laser wavelength detection (i.e., the horizontal axis of the frequency discrimination curve); then the laser frequency is swept, and the output of the wavelength meter and the output of the two optical detectors are recorded simultaneously to obtain the frequency discrimination curve.

[0074] Therefore, it is evident that additional test lasers and high-precision wavelength meters or other spectral measurement instruments are required during the frequency discrimination curve calibration process. Traditional offline frequency discrimination calibration methods are time-consuming to set up the test optical path, and the original measurement optical path needs to be restored after calibration, requiring a high level of expertise from operators. This necessitates on-site operation by specialized technicians at the lidar system installation site. Furthermore, various factors in reality affect the stability of the frequency discrimination curve, such as optical path deviation caused by stress release in the mechanical structure, optical path deviation caused by thermal deformation due to temperature changes, and performance degradation of the optical detector. Changes in the frequency discrimination curve affect the accuracy of wind field measurements in the lidar system, leading to errors. Therefore, the frequency discrimination curve needs to be recalibrated periodically, significantly increasing equipment maintenance costs.

[0075] Based on this, embodiments of this application provide a frequency discrimination curve calibration system, method, and apparatus to reduce the cost of frequency discrimination curve calibration and improve the efficiency of frequency discrimination curve calibration while ensuring the accuracy and stability of frequency discrimination curve calibration.

[0076] Figure 9 This is a schematic diagram of a frequency discrimination curve calibration system provided in an embodiment of this application. Figure 9 As shown, the frequency discrimination curve calibration system provided in this application embodiment includes: a first optical path LP1, a second optical path LP2, a third optical path LP3, a fourth optical path LP4, a fifth optical path LP5, a sixth optical path LP6, a seventh optical path LP7, a first photodetector 601, a second photodetector 602, a third photodetector 603, a fourth photodetector 604, and a calibration module 13.

[0077] like Figure 9As shown, the first optical path LP1 includes: a first laser 1, a first beam splitter 301, an electro-optic modulator 4, and an atomic / molecular absorption cell 5. It can be understood that the atomic / molecular absorption cell can also be called an atomic or molecular absorption cell.

[0078] The light emitted from the first laser 1 passes sequentially through the first beam splitter 301, the electro-optic modulator 4, and the atomic / molecular absorption cell 5 before being incident on the first photodetector 601.

[0079] Specifically, such as Figure 9 As shown, the first laser 1 in the first optical path LP1 emits a laser beam that is incident on the first beam splitter 301. The first beam splitter 301 transmits a portion of the laser beam to the electro-optic modulator 4, and then, after passing through the atomic / molecular absorption cell 5, it is incident on the first photodetector 601.

[0080] In some embodiments of this application, the first laser emitter 1 is a single-frequency continuous-wave tunable laser, that is, the emitted laser is a single-frequency continuous-wave tunable laser. The tuning method of the first laser emitter can be pump current, temperature or piezoelectric actuator, and its tuning element is controlled by an external control signal, which is not specifically limited in this application.

[0081] In some embodiments of this application, the electro-optic modulator 4 described above can be a Pockel cell, which is driven by an external sinusoidal signal to perform phase modulation on the electric field of the incident laser beam.

[0082] In some embodiments of this application, the atomic / molecular absorption cell 5 is filled with alkali metal atomic vapor or halogen molecular vapor. To ensure accurate and stable subsequent laser frequency locking, the absorption peak of the atomic / molecular absorption cell 5 should be as sharp as possible, requiring a very low vapor concentration to reduce spectral line collision broadening. However, a low concentration also results in minimal signal attenuation. Therefore, to increase the attenuation of the incident laser beam by the atomic / molecular absorption cell 5 and thus improve screen locking accuracy, the atomic / molecular absorption cell 5 in this embodiment is configured for multi-path reflection, allowing the outgoing laser beam to exit from the same end incident on the atomic / molecular absorption cell 5. This application does not impose specific limitations on this aspect.

[0083] like Figure 9 As shown, the first photodetector 601 is used to receive the first laser signal transmitted from the atomic / molecular absorption cell 5 in the first optical path LP1, and to obtain the first photoelectric signal based on the first laser signal.

[0084] In this embodiment, the second optical path LP2 includes a first laser 1, a first beam splitter 301, and a beam combiner 7. The second optical path LP2 originates from the first laser 1, passes sequentially through the first beam splitter 301 and the beam combiner 7, and then enters the second photodetector 602. Figure 9 As shown.

[0085] Specifically, such as Figure 9 As shown, the second optical path LP2 emits a laser from the first laser 1 and is incident on the first beam splitter 301. The first beam splitter 301 reflects a portion of the laser to the beam combiner 7, and then the laser is incident on the second photodetector 602 through the beam combiner 7.

[0086] In the embodiments of this application, the third optical path LP3 includes: a second laser 2, a second beam splitter 302, and a beam combiner 7. The third optical path LP3 is emitted from the second laser 2, passes sequentially through the second beam splitter 302 and the beam combiner 7, and is incident on the second photodetector 602.

[0087] Specifically, such as Figure 9 As shown, the third optical path LP3 emits a laser from the second laser 2 and is incident on the second beam splitter 302. The second beam splitter 302 reflects a portion of the laser to the beam combiner 7. After passing through the beam combiner 7, the laser is then incident on the subsequent second photodetector 602.

[0088] As can be seen from the above, a portion of the laser emitted from the first laser 1 via the second optical path LP2, and a portion of the laser emitted from the second laser 2 via the third optical path LP3, are both incident on the beam combiner 7. Therefore, in this embodiment, the beam combiner 7 is used to combine the laser from the second optical path LP2 with the laser from the third optical path LP3 to obtain the second laser signal.

[0089] In some embodiments of this application, the combiner 7 is a two-in-one fiber combiner with two optical inputs and one optical output.

[0090] like Figure 9 As shown, the second photodetector 602 is used to receive the second laser signal obtained by the beam combiner 7 after beam combining in the second optical path LP2 and the third optical path LP3, and to obtain the second photoelectric signal based on the second laser signal.

[0091] Because both lasers in the combined beam are single-frequency lasers, the photoelectric field of the second laser signal after beam combining contains two components: sum frequency and difference frequency. The sum frequency component far exceeds the response bandwidth of the second photodetector 602, and is a DC component after conversion to an electrical signal. The difference frequency component is within the response bandwidth of the second photodetector 602, and becomes the effective part of the second photoelectric signal after conversion to an electrical signal.

[0092] like Figure 9As shown, the fourth optical path LP4 sequentially includes: a second laser 2, a second beam splitter 302, a third beam splitter 303, an attenuator 10, an electrically controlled optical switch 11, and a fourth beam splitter 304. The fourth optical path LP4 originates from the second laser 2, passes sequentially through the second beam splitter 202, the third beam splitter 303, the attenuator 10, the electrically controlled optical switch 11, and the fourth beam splitter 304, and then enters the third photodetector 603.

[0093] Specifically, in the fourth optical path LP4, the second laser 2 emits a laser beam that is incident on the second beam splitter 302. The transmitted beam is then incident on the third beam splitter 303. The third beam splitter 303 reflects a portion of the laser beam, which is then incident on the attenuator 10. The attenuator 10 attenuates the intensity of the received laser beam to a level detectable by the subsequent third photodetector 603. The laser beam is then incident on the electrically controlled optical switch 11. The beam emitted from the electrically controlled optical switch 11 is partially reflected by the fourth beam splitter 304 onto the subsequent third photodetector 603. Figure 9 As shown.

[0094] like Figure 9 As shown, the fifth optical path LP5 includes: a second laser 2, a second beam splitter 302, a third beam splitter 303, an acousto-optic frequency shifter 8, a laser pulse generator 9, an electro-optical switch 11, and a fourth beam splitter 304.

[0095] Among them, the fifth optical path LP5 is emitted from the second laser 2, passes through the second beam splitter 302, the third beam splitter 303, the acousto-optic frequency shifter 8, and the laser pulse generator 9 in sequence, and is emitted into the atmosphere to obtain an echo signal. Then, it passes through the electronically controlled optical switch 11 and the fourth beam splitter 304 in sequence and is incident on the third photodetector 603.

[0096] Specifically, such as Figure 9 As shown, in the fifth optical path LP5, the second laser 2 emits a laser beam that is incident on the second beam splitter 302. The transmitted beam is then incident on the third beam splitter 303. The transmitted beam is incident on the acousto-optic frequency shifter 8. The laser emitted from the acousto-optic frequency shifter 8 is incident on the laser pulse generator 9. The pulsed laser output by the laser pulse generator 9 is emitted into the atmosphere. The echo signal backscattered from the atmosphere is incident on the fourth beam splitter 304 through the electronically controlled optical switch 11. The fourth beam splitter 304 reflects a portion of the incident light onto the subsequent third photodetector 603.

[0097] In some embodiments of this application, the acousto-optic frequency shifter 8 chops the continuous wave laser incident on it into a frequency-shifted low-energy pulsed laser. At this time, the laser pulse generator 9 is simply a laser amplifier, which amplifies the low-energy frequency-shifted laser pulse into a high-energy laser pulse for atmospheric remote sensing.

[0098] In some embodiments of this application, the acousto-optic frequency shifter 8 is used to shift the frequency of the continuous-wave laser incident upon it without chopping it, and the output laser is still a continuous-wave laser. In this case, the subsequent laser pulse emitter 9 is a laser oscillator, which can use seed injection technology to achieve single-frequency high-energy laser pulse output after single-frequency light injection. This application does not impose specific limitations on this.

[0099] In some embodiments of this application, the electrically controlled optical switch 11 is a two-input, one-output gating switch, used to select the laser signal from the fourth optical path LP4 and the atmospheric echo signal from the fifth optical path LP5. Specifically, in the calibration state, the laser from the second laser 2 is selected for frequency discrimination curve calibration; in the detection state, the received atmospheric echo signal is selected for atmospheric remote sensing detection.

[0100] In some embodiments of this application, the electrically controlled optical switch 11 is a two-input, one-output micromechanical fiber optic device, and an external electrical signal can quickly control the selection and switching state of the electrically controlled optical switch 11.

[0101] In this embodiment, the use of the two-input, one-output gating optical switch 11 enables time-division multiplexing of the calibration optical path and the atmospheric echo detection optical path for the optical frequency discriminator, thus enabling the lidar system to have an online calibration function for the frequency discrimination curve without the need for offline calibration.

[0102] In this embodiment, the third photodetector 603 is used to receive the third laser signal obtained from the fourth beam splitter 304 in the fourth optical path LP4 and the first atmospheric echo signal obtained from the fourth beam splitter 304 in the fifth optical path LP5, and to obtain the third photoelectric signal based on the third laser signal, and the fifth photoelectric signal based on the first atmospheric echo signal. It can be seen that the third laser signal corresponds to the third photoelectric signal, and the first atmospheric echo signal corresponds to the fifth photoelectric signal.

[0103] like Figure 9 As shown, the sixth optical path LP6 includes: a second laser 2, a second beam splitter 302, a third beam splitter 303, an attenuator 10, an electrically controlled optical switch 11, a fourth beam splitter 304, and an optical frequency discriminator 12. The sixth optical path LP6 originates from the second laser 2, passes sequentially through the second beam splitter 302, the third beam splitter 303, the attenuator 10, the electrically controlled optical switch 11, the fourth beam splitter 304, and the optical frequency discriminator 12, and then enters the fourth photodetector 604.

[0104] Specifically, in the sixth optical path LP6 of this application embodiment, the second laser 2 emits a laser beam that is incident on the second beam splitter 302. The transmitted beam is then incident on the third beam splitter 303. The third beam splitter 303 reflects a portion of the laser beam and it is incident on the attenuator 10. The attenuator 10 attenuates the intensity of the laser beam it receives to the intensity that can be detected by the subsequent third photodetector 603, and then it is incident on the electronically controlled optical switch 11. The output beam of the electronically controlled optical switch 11 is transmitted through the fourth beam splitter 304 and enters the optical frequency discriminator 12. The output beam of the optical frequency discriminator 12 is incident on the subsequent fourth photodetector 604.

[0105] Optionally, the optical frequency discriminator 12 is one of the optically fabricated frequency discriminators such as a gas atom frequency discriminator, a gas molecule frequency discriminator, or a standard etalon. A gas frequency discriminator uses the energy levels of atoms or molecules in a canister gas to provide the absorption lines required for frequency discrimination, while an optically fabricated frequency discriminator uses optical processing techniques such as optical coating and etching to artificially create the required optical transmission (or reflection) characteristics on optical materials such as glass and ceramics. Figure 5 This is a schematic diagram of the transmittance curve of an iodine molecule frequency discriminator. Its operating frequency range can be selected at the left or right edge of the absorption peak, with the operating frequency point set near the midpoint of the edge. When the gas absorption cell is used as an optical frequency discriminator, the gas is supersaturated (high concentration) to ensure a steep edge to the transmittance curve and high frequency discrimination sensitivity. Figure 5 The mid-absorption peak no longer has a peak-like structure but a flat bottom, which is different from the peak structure when used as a frequency standard. Figure 4 The differences.

[0106] like Figure 9 As shown, the seventh optical path LP7 includes: a second laser 2, a second beam splitter 302, a third beam splitter 303, an acousto-optic frequency shifter 8, a laser pulse generator 9, an electrically controlled optical switch 11, a fourth beam splitter 4, and an optical frequency discriminator 12. The seventh optical path LP7 originates from the second laser 2, passes sequentially through the second beam splitter 302, the third beam splitter 303, the acousto-optic frequency shifter 8, and the laser pulse generator 9, and is emitted into the atmosphere to obtain an echo signal. This echo signal then passes sequentially through the electrically controlled optical switch 11, the fourth beam splitter 304, and the optical frequency discriminator 12 before being incident on the fourth photodetector 604.

[0107] Specifically, in the seventh optical path LP7 of this application embodiment, the laser emitted by the second laser 2 is incident on the second beam splitter 302, and the transmitted beam is then incident on the third beam splitter 303. The transmitted beam is incident on the acousto-optic frequency shifter 8, and the laser emitted from the acousto-optic frequency shifter 8 is incident on the laser pulse generator 9. The pulsed laser output by the laser pulse generator 9 is emitted into the atmosphere, and the echo signal backscattered from the atmosphere is incident on the fourth beam splitter 304 through the electrically controlled optical switch 11. The fourth beam splitter 304 transmits a portion of the incident light to the optical frequency discriminator 12, such as...Figure 9 As shown.

[0108] The fourth photodetector 604 is used to receive the fourth laser signal obtained by the optical frequency discriminator 12 in the sixth optical path LP6 and the second atmospheric echo signal obtained by the optical frequency discriminator 12 in the seventh optical path, and to obtain the fourth photoelectric signal based on the fourth laser signal, and the sixth photoelectric signal based on the second atmospheric echo signal. It can be seen that the fourth laser signal corresponds to the fourth photoelectric signal, and the second atmospheric echo signal corresponds to the sixth photoelectric signal.

[0109] As described above, in this embodiment, the laser beam detected by the third photodetector 603 is a signal that has not yet passed through the optical frequency discriminator 12, while the laser beam detected by the fourth photodetector 604 is a signal that has passed through the optical frequency discriminator 12. Let the amplitude of the third photoelectric signal be... The amplitude of the fourth photoelectric signal is The transmittance of the optical frequency discriminator 12 during frequency discrimination curve calibration is: Let the amplitude of the fifth photoelectric signal be... The amplitude of the sixth photoelectric signal is The transmittance of the optical frequency discriminator 12 during wind speed detection is... At this point, the transmittance is not normalized, and its value can be greater than 1. It is understood that the transmittance in the embodiments of this application does not need to be normalized, as long as the standard is consistent when initially calibrating the frequency discrimination curve and during application. and Use the same form of definition.

[0110] In some embodiments of this application, the calibration module 13 may include: a frequency locking unit, a frequency biasing unit, and a transmittance measurement unit.

[0111] The frequency locking unit is used to generate a first control signal acting on the first laser 1 based on the first photoelectric signal, so as to control the output laser frequency of the first laser 1 to be locked at the absorption peak of the atomic / molecular absorption cell through the first control signal, for example... Figure 11 In the above sub-graph Frequency point.

[0112] Furthermore, the frequency locking unit is specifically used to: perform locking amplification processing on the first photoelectric signal according to the driving signal of the electro-optic modulator 4 to obtain the first control signal; and drive the frequency tuning device of the first laser 1 according to the first control signal so that the output laser frequency of the first laser 1 is locked on the absorption peak of the atomic / molecular absorption cell.

[0113] Figure 10 This is a schematic diagram of the structure of the frequency locking unit provided in the embodiments of this application, as shown below. Figure 10As shown, the first photoelectric signal of the first photodetector 601 and the driving signal of the electro-optic modulator 4 are mixed, and the output signal contains a DC component and a series of harmonic components. After subsequent low-pass filtering to remove the higher-order harmonic components, only the DC component is retained. This DC component is the error signal for controlling the first laser controller 1 to lock the atomic / molecular absorption line. This error signal is input to the servo amplifier to obtain the first control signal for driving the frequency tuning device inside the first laser 1. It can be understood that the above-mentioned servo amplifier can be a simple proportional amplifier, a proportional-integral amplifier, or a proportional-integral-differential amplifier, and no specific limitation is made in this application.

[0114] In this embodiment, the frequency biasing unit is used to generate a second control signal acting on the second laser 2 based on the second photoelectric signal, so as to control the output laser frequency of the second laser 2 to be locked to a preset frequency bias amount that deviates from the output laser frequency of the first laser 1. The frequency, for example Figure 11 The SFR frequency range is shown in the sub-figure below.

[0115] Furthermore, the frequency offset unit is specifically used to: perform Fourier transform on the second photoelectric signal to obtain the corresponding power spectrum; identify the peaks in the power spectrum to determine the signal peaks; and determine the second control signal based on the frequency of the signal peaks and the preset frequency offset amount, so as to lock the output laser frequency of the second laser 2 to a frequency that deviates from the output laser frequency of the first laser 1 by the preset frequency offset amount.

[0116] In the embodiments of this application, a peak identification algorithm can be used to identify the power spectrum and determine the position of the signal peak in the power spectrum.

[0117] Furthermore, based on the frequency of the signal peak and a preset frequency offset, an offset locking error signal is determined. Specifically, the difference between the frequency of the signal peak and the preset frequency offset is used as the initial error signal, which is then input to a servo amplifier. The servo amplifier processes the initial error signal to obtain the offset locking error signal, i.e., the second control signal. It is understood that the aforementioned servo amplifier can be a simple proportional amplifier, a proportional-integral amplifier, or a proportional-integral-differential amplifier; no specific limitation is made in this application.

[0118] The transmittance measurement unit is used to determine the calibrated transmittance of the output laser of the second laser 2 relative to the optical frequency discriminator 12 based on the third photoelectric signal and the fourth photoelectric signal during the calibration state, so as to determine the frequency discrimination curve based on the calibrated transmittance; and is used to determine the transmittance of the current atmospheric echo signal relative to the optical frequency discriminator based on the fifth photoelectric signal, the sixth photoelectric signal and the frequency discrimination curve during the detection state.

[0119] In this embodiment, the transmittance measurement unit operates in both calibration and detection states. It is understood that the calibration state in this embodiment refers to the operating state of the frequency discrimination curve calibration system for frequency discrimination curve calibration; the detection state refers to the operating state of the frequency discrimination curve calibration system for wind speed detection.

[0120] During calibration, the transmittance measurement unit calculates and records the offset at different preset frequencies based on the third and fourth photoelectric signals. The output laser of the second laser 2 relative to the calibrated transmittance of the optical frequency discriminator 12 Through each standard transmittance Frequency discrimination curves can then be plotted. In the detection state, the transmittance measurement unit is used to calculate the transmittance of the current atmospheric echo signal relative to the optical frequency discriminator 12 based on the fifth and sixth photoelectric signals and the aforementioned frequency discrimination curve. .

[0121] Furthermore, the transmittance measurement module is specifically used to: control the second laser 2 to scan and change stepwise within the working frequency range according to the preset frequency bias amount of the frequency bias unit during calibration; calculate the ratio of the fourth photoelectric signal and the third photoelectric signal after each step of frequency change, and obtain the frequency discrimination curve of the output laser of the second laser 2 relative to the optical frequency discriminator 12.

[0122] The transmittance measurement module is also specifically used to control the preset frequency offset of the frequency offset unit to be fixed at a preset fixed value during the detection state, so as to lock the output laser frequency of the second laser 2; calculate the ratio of the sixth optical signal and the fifth photoelectric signal to obtain the transmittance of the current atmospheric echo signal relative to the optical frequency discriminator 12.

[0123] The frequency discrimination curve calibration system provided in this application embodiment can perform the following process:

[0124] The frequency locking unit of the calibration module 13 generates a first control signal acting on the first laser 1 based on the first photoelectric signal, and locks the output laser frequency of the first laser 1 to the absorption peak of the atomic / molecular absorption cell.

[0125] The electro-optical switch 11 selects and calibrates the laser, and the frequency discrimination curve calibration system enters the calibration state;

[0126] The preset frequency offset of the frequency offset unit of calibration module 13 is scanned and varied stepwise within the preset operating frequency range.

[0127] The transmittance measurement unit of calibration module 13 calculates and records the ratio of the fourth photoelectric signal to the third photoelectric signal after each frequency change, thus obtaining the transmittance curve of the second laser output laser relative to the optical frequency discriminator 12. This refers to the frequency discrimination curve. The horizontal axis of the frequency discrimination curve represents the laser frequency.

[0128] Figure 12 This is a schematic flowchart of a frequency discrimination curve calibration system provided in an embodiment of this application, as shown below. Figure 12 As shown, in step S1201, the electro-optical switch selects the calibration reference laser channel and closes the atmospheric echo signal optical channel, and the frequency discrimination curve calibration system enters the calibration state; in step S1202, the initial bias amount of the frequency bias unit... The laser emission frequency of the second laser 2 is configured to be located at one end of the operating frequency range of the optical frequency discriminator, i.e. Step S1203, the bias amount of the frequency bias unit. The step increment increases to the other end of the operating frequency range of the optical frequency discriminator 12, i.e. Record the amplitude of the third photoelectric signal detected by the third photodetector 603 at each step of frequency change. and the amplitude of the fourth photoelectric signal detected by the fourth photodetector 604 Step S1204: Determine the frequency discrimination curve, whose horizontal axis is... The vertical axis is Step S1204: The electronically controlled optical switch selects the atmospheric echo signal optical channel and closes the calibration reference laser channel, and the frequency discrimination curve calibration system exits the calibration state.

[0129] The electronically controlled optical switch 11 selects the atmospheric echo signal, and the frequency discrimination curve calibration system enters the detection state.

[0130] The preset frequency offset of the frequency offset unit of the calibration module 13 is fixed at a preset fixed value to lock the output laser frequency of the second laser 2.

[0131] The transmittance measurement unit of calibration module 13 calculates the ratio of the sixth photoelectric signal to the fifth photoelectric signal to obtain the transmittance of the current atmospheric echo signal relative to the optical frequency discriminator 12. ;

[0132] By querying the frequency discrimination curve recorded during calibration, the transmittance can be obtained. The corresponding standard atmospheric echo signal frequency This allows us to obtain the frequency shift of the current atmospheric echo signal relative to the emitted laser. That is, Doppler frequency shift;

[0133] The line-of-sight wind speed profile for the current atmosphere is calculated based on the Doppler frequency shift.

[0134] The frequency discrimination curve calibration system provided in this application locks the output laser frequency of the first laser at the low-concentration atomic or molecular absorption peaks to obtain a precise frequency standard. Then, it uses the output laser of the second laser to perform beam combining and frequency beating with the output laser of the first laser. The frequency difference is extracted from the power spectrum of the beating signal to generate a tuning control signal for the second laser, locking its output laser frequency at any preset frequency offset. The entire lidar system uses an electrically controlled optical switch to switch between calibration and detection states: in calibration state, the laser from the second laser is selected for frequency discrimination curve calibration; in detection state, the received atmospheric echo signal light is selected for atmospheric remote sensing. Based on this, the system reduces the cost and improves the efficiency of frequency discrimination curve calibration while ensuring accuracy and stability.

[0135] Compared to existing technologies, the frequency discrimination curve calibration system provided in this application utilizes two single-frequency lasers (a first laser and a second laser), frequency locking, and offset techniques, with an atomic / molecular absorption cell as the frequency standard. This gives the system's own lasers high frequency stability and frequency sweeping capabilities, allowing them to be directly used for frequency discrimination curve calibration without the need for additional frequency sweeping lasers and high-precision wavelength meters or other spectral analysis instruments. Compared to traditional solutions, the frequency discrimination curve calibration system provided in this application not only performs frequency discrimination curve calibration but also directly detects the transmittance of the current wind field after calibration. It eliminates the need for additional calibration lasers and spectrometers, as well as highly skilled technicians, saving time and effort, significantly reducing system maintenance costs, and improving utilization efficiency. While ensuring the accuracy and stability of frequency discrimination curve calibration, it reduces calibration costs and improves calibration efficiency.

[0136] Secondly, embodiments of this application also provide a frequency discrimination curve calibration method, wherein the frequency discrimination curve calibration method is applied to the frequency discrimination curve calibration system as described in any of the preceding claims, and the method includes:

[0137] Based on the first optical path, second optical path, third optical path, fourth optical path, fifth optical path, sixth optical path, and seventh optical path, the first photoelectric signal, second photoelectric signal, third photoelectric signal, and fourth photoelectric signal are obtained;

[0138] Based on the first photoelectric signal and the second photoelectric signal, the output laser frequency of the second laser is controlled to scan and change within a preset operating frequency range;

[0139] The frequency discrimination curve of the optical frequency discriminator is determined based on the third photoelectric signal and the fourth photoelectric signal.

[0140] Thirdly, embodiments of this application also provide a frequency discrimination curve calibration device, which is applied to the frequency discrimination curve calibration system as described in any of the above claims, the device comprising:

[0141] The acquisition unit is used to obtain the first photoelectric signal, the second photoelectric signal, the third photoelectric signal, and the fourth photoelectric signal based on the first optical path, the second optical path, the third optical path, the fourth optical path, the fifth optical path, the sixth optical path, and the seventh optical path;

[0142] The control unit is used to control the output laser frequency of the second laser to scan and change within a preset operating frequency range based on the first photoelectric signal and the second photoelectric signal.

[0143] The calculation unit is used to determine the frequency discrimination curve of the optical frequency discriminator based on the third photoelectric signal and the fourth photoelectric signal.

[0144] It should be noted that the specific structure and implementation of the frequency discrimination curve calibration device and its various modules or units can be referred to the corresponding description in the method embodiment, and will not be repeated here.

[0145] It should be noted that the division of the modules of the frequency discrimination curve calibration device is not unique and is not intended as a specific limitation.

[0146] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0147] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is merely an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the above device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiments can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit. Furthermore, the specific names of the functional units and modules are only for easy differentiation and are not intended to limit the scope of protection of this application. The specific working process of the units and modules in the above device can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.

[0148] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0149] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0150] In the embodiments provided in this application, it should be understood that the disclosed systems / terminal devices and methods can be implemented in other ways. For example, the system / terminal device embodiments described above are merely illustrative. For instance, the division of modules or units described above is merely a logical functional division, and in actual implementation, it can be divided in other ways. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed.

[0151] If the integrated modules / units described above are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the methods of the above embodiments can also be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the various method embodiments described above. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include: any entity or device capable of carrying the computer program code, recording media, USB flash drives, portable hard drives, magnetic disks, optical disks, computer memory, read-only memory (ROM), random access memory (RAM), electrical carrier signals, electrical signals, and software distribution media, etc. It should be noted that the content included in the computer-readable storage medium can be appropriately increased or decreased according to the requirements of legislation and patent practice in the jurisdiction.

[0152] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions are not in essence a departure from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A frequency discrimination curve calibration system, characterized in that, The system includes: The first optical path originates from the first laser, passes sequentially through the first beam splitter, the electro-optic modulator, and the atomic / molecular absorption cell, and is incident on the first photodetector. The second optical path originates from the first laser, passes sequentially through the first beam splitter and beam combiner, and is incident on the second photodetector. The third optical path originates from the second laser, passes sequentially through the second beam splitter and the beam combiner, and is incident on the second photodetector. The fourth optical path originates from the second laser, passes sequentially through the second beam splitter, the third beam splitter, the attenuator, the electrically controlled optical switch, and the fourth beam splitter, and is incident on the third photodetector. The fifth optical path originates from the second laser, passes sequentially through the second beam splitter, the third beam splitter, the acousto-optic frequency shifter, and the laser pulse generator, and is emitted into the atmosphere to obtain an atmospheric echo. It then passes sequentially through the electrically controlled optical switch and the fourth beam splitter to obtain a first atmospheric echo signal which is incident on the third photodetector. The sixth optical path originates from the second laser, passes sequentially through the second beam splitter, the third beam splitter, the attenuator, the electrically controlled optical switch, the fourth beam splitter, and the optical frequency discriminator, and is incident on the fourth photodetector. The seventh optical path originates from the second laser, passes sequentially through the second beam splitter, the third beam splitter, the acousto-optic frequency shifter, and the laser pulse generator, and is emitted into the atmosphere to obtain an atmospheric echo. It then passes sequentially through the electrically controlled optical switch, the fourth beam splitter, and the optical frequency discriminator to obtain a second atmospheric echo signal which is incident on the fourth photodetector. The calibration module is used to control the output laser frequency of the second laser to scan and change within a preset operating frequency range based on the first photoelectric signal and the second photoelectric signal; and to determine the frequency discrimination curve of the optical frequency discriminator based on the third photoelectric signal and the fourth photoelectric signal. Wherein, the first photoelectric signal is determined by the first photodetector based on the first laser signal received from the atomic / molecular absorption cell in the first optical path; the second photoelectric signal is determined by the second photodetector based on the second laser signal received from the beam combiner after combining the second and third optical paths; the third photoelectric signal is determined by the third photodetector based on the third laser signal received from the fourth beam splitter in the fourth optical path; and the fourth photoelectric signal is determined by the fourth photodetector based on the fourth laser signal received from the optical frequency discriminator in the sixth optical path. The calibration module includes a frequency locking unit, which generates a first control signal acting on the first laser based on the first photoelectric signal, so as to control the output laser frequency of the first laser to be locked at the absorption peak of the atomic / molecular absorption cell through the first control signal. A frequency bias unit is used to generate a second control signal acting on the second laser based on the second photoelectric signal, so as to control the output laser frequency of the second laser to be locked to a frequency that deviates from the output laser frequency of the first laser by the second control signal. The transmittance measurement module is used to determine, in calibration mode, the calibrated transmittance of the output laser of the second laser relative to the optical frequency discriminator based on the third photoelectric signal and the fourth photoelectric signal, so as to determine the frequency discrimination curve based on the calibrated transmittance; and is used to determine, in detection mode, the transmittance of the current atmospheric echo signal relative to the optical frequency discriminator based on the fifth photoelectric signal, the sixth photoelectric signal and the frequency discrimination curve. The fifth photoelectric signal is determined by the third photodetector based on the first atmospheric echo signal received from the fourth beam splitter in the fifth optical path; the sixth photoelectric signal is determined by the fourth photodetector based on the second atmospheric echo signal received from the optical frequency discriminator in the seventh optical path.

2. The frequency discrimination curve calibration system according to claim 1, characterized in that, The frequency locking unit is specifically used for: Based on the driving signal of the electro-optic modulator, the first photoelectric signal is subjected to lock-in amplification processing to obtain the first control signal: The frequency tuning device of the first laser is driven according to the first control signal so that the output laser frequency of the first laser is locked at the absorption peak of the atomic / molecular absorption cell.

3. The frequency discrimination curve calibration system according to claim 1, characterized in that, The frequency bias unit is specifically used for: Perform a Fourier transform on the second photoelectric signal to obtain the corresponding power spectrum; Peak identification is performed on the power spectrum to determine the signal peaks in the power spectrum; Based on the frequency of the signal peak and the preset frequency offset, the second control signal is determined, and the frequency tuning range of the second laser is determined according to the second control signal, so that the output laser frequency of the second laser is locked to a frequency that deviates from the preset frequency offset of the output laser frequency of the first laser.

4. The frequency discrimination curve calibration system according to claim 1, characterized in that, The transmittance measurement module is specifically used for: In the calibration state, the second laser is controlled to scan and change stepwise within the working frequency range according to the preset frequency offset amount of the frequency offset unit; Calculate the ratio of the fourth photoelectric signal to the third photoelectric signal after each frequency change to obtain the frequency discrimination curve of the output laser of the second laser relative to the optical frequency discriminator.

5. The frequency discrimination curve calibration system according to claim 1, characterized in that, The transmittance measurement module is specifically used for: During the detection state, the preset frequency offset amount of the frequency offset unit is fixed at a preset fixed value to lock the output laser frequency of the second laser. The ratio of the sixth photoelectric signal to the fifth photoelectric signal is calculated to obtain the transmittance of the current atmospheric echo signal relative to the optical frequency discriminator.

6. The frequency discrimination curve calibration system according to claim 1, characterized in that, Both the first laser and the second laser are single-frequency continuous-wave tunable lasers.

7. The frequency discrimination curve calibration system according to claim 1, characterized in that, The electro-optical switch is a two-input, one-output gating switch, used to select the output laser from the fourth optical path and to select the first atmospheric echo signal from the fifth optical path.

8. A method for calibrating a frequency discrimination curve, characterized in that, The frequency discrimination curve calibration method is applied to the frequency discrimination curve calibration system as described in any one of claims 1-7, and the method includes: Based on the first optical path, second optical path, third optical path, fourth optical path, fifth optical path, sixth optical path, and seventh optical path, the first photoelectric signal, second photoelectric signal, third photoelectric signal, and fourth photoelectric signal are obtained; Based on the first photoelectric signal and the second photoelectric signal, the output laser frequency of the second laser is controlled to scan and change within a preset operating frequency range; The frequency discrimination curve of the optical frequency discriminator is determined based on the third photoelectric signal and the fourth photoelectric signal.

9. A frequency discrimination curve calibration device, characterized in that, The frequency discrimination curve calibration device is applied to the frequency discrimination curve calibration system as described in any one of claims 1-7, and the device comprises: The acquisition unit is used to obtain the first photoelectric signal, the second photoelectric signal, the third photoelectric signal, and the fourth photoelectric signal based on the first optical path, the second optical path, the third optical path, the fourth optical path, the fifth optical path, the sixth optical path, and the seventh optical path; The control unit is used to control the output laser frequency of the second laser to scan and change within a preset operating frequency range based on the first photoelectric signal and the second photoelectric signal. The calculation unit is used to determine the frequency discrimination curve of the optical frequency discriminator based on the third photoelectric signal and the fourth photoelectric signal.

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