Frequency shift real-time online calibration device

Abstract

The present invention discloses a real-time online calibration device for frequency shift, which can realize time-division monitoring of seed laser and atmospheric echo based on time division multiplexing of a first chopper and a second chopper through a simple structure, and then accurately identify the frequency drift of the seed laser through the electrical signals detected by the first photodetector and the second photodetector before and after the optical frequency discriminator, and the seed laser is shifted to a known fixed frequency by an acousto-optic frequency shifter before being injected into the laser pulse generator, and then the frequency shift of the emitted laser pulse relative to the injected continuous wave seed laser is detected by beam combining. By correcting these two frequency shift errors, accurate detection of Doppler frequency shift can be achieved. In summary, the present invention is not only simple in structure and cost-saving, but also can accurately detect and correct the Doppler frequency shift of the laser radar, and the detection and correction results are relatively accurate.

Description

Technical Field

[0001] The present invention relates to the field of laser radar, and in particular to a frequency shift real-time online calibration device. Background Art

[0002] In the field of laser remote sensing of wind farms, an optical discriminator is an optical device with a steep monotonic transmittance characteristic near the working laser frequency. There is a photodetector before and after the optical discriminator, and the ratio of the detection signals of the two detectors is its transmittance. Due to its sensitivity, a slight change in the laser frequency will cause a significant change in the measured transmittance. The change in the incident laser frequency can be deduced from the change in the discriminator transmittance. Direct detection wind measurement technology uses such an optical discriminator to receive atmospheric echo signals. When the system is initially calibrated, the transmittance of the working frequency point of zero wind speed (no Doppler shift) is first determined, that is, the transmittance of the working frequency point of the emitted laser. Then, the transmittance of the atmospheric echo through the optical discriminator is measured, and the frequency shift value of the atmospheric echo relative to the zero wind speed frequency point of the initial calibration of the system can be calculated in real time using the transmittance curve (also called the discriminator curve).

[0003] If the laser emission frequency is stable, the optical discriminator performance is stable, and the pulse laser frequency emitted into the atmosphere is consistent with the continuous wave laser frequency of the seed laser, then the frequency shift value of the atmospheric echo measured by the above method relative to the zero wind speed frequency point of the system initial calibration is the Doppler frequency shift value caused by the line of sight wind speed. In fact, there are various factors that make the above ideal assumptions invalid, such as the short-term fluctuations and long-term drifts in the laser emission frequency of the seed laser, the long-term drifts in the performance of the optical discriminator, the degradation of the detection performance of the photodetector, the inconsistency between the emitted pulse laser frequency and the injected continuous wave seed laser frequency, etc. At this time, the frequency shift value directly measured is not a pure Doppler frequency shift value, and must be strictly corrected to obtain the Doppler frequency shift.

[0004] In practice, domestic research teams or users of related equipment often do not make relevant corrections in the early stage, and generally clear the accumulated errors by increasing the frequency of system calibration. For example, a system calibration is performed before observation every day, and the system is assumed to be stable during the subsequent observation on the same day. Another system calibration is performed before observation on the second day to clear the accumulated errors of the previous day. Although this observation strategy simplifies the equipment functions (no frequency shift monitoring and correction functions), frequent system calibration increases the workload of users, requires high professional skills of operators, and is prone to errors. Summary of the invention

[0005] In view of the above problems, the present invention provides a frequency shift real-time online calibration device that overcomes the above problems or at least partially solves the above problems.

[0006] A frequency shift real-time online calibration device, comprising: a first optical path, a second optical path, a third optical path, a fourth optical path, a fifth optical path, a sixth optical path, a first photodetector, a second photodetector, a third photodetector and a calibration module;

[0007] The first optical path includes, in sequence: a seed laser, a first beam splitter for reflection, a first attenuator, a first chopper, and a second beam splitter for transmission;

[0008] The second optical path includes, in sequence: the seed laser, the first beam splitter for transmission, the third beam splitter for transmission, an acousto-optic frequency shifter, a laser pulse generator, a fourth beam splitter for transmission, a second chopper and the second beam splitter for reflection, wherein the first chopper and the second chopper perform time division multiplexing;

[0009] The first photodetector is used to receive the first laser signal transmitted by the second beam splitter in the first optical path and to receive the first atmospheric echo signal reflected by the second beam splitter in the second optical path, and to obtain corresponding first electrical signals and second electrical signals based on the first laser signal and the first atmospheric echo signal, wherein the first laser signal corresponds to the first electrical signal, and the first atmospheric echo signal corresponds to the second electrical signal;

[0010] The third optical path includes, in sequence: the seed laser, the first beam splitter for reflection, the first attenuator, the first chopper, the second beam splitter for reflection and an optical frequency discriminator;

[0011] The fourth optical path includes, in sequence: the seed laser, the first beam splitter for transmission, the third beam splitter for transmission, the acousto-optic frequency shifter, the laser pulse generator, the fourth beam splitter for transmission, the second chopper, the second beam splitter for transmission and the optical frequency discriminator;

[0012] The second photodetector is used to receive the second laser signal transmitted by the optical discriminator in the third optical path and the second atmospheric echo signal transmitted by the optical discriminator in the fourth optical path, and obtain a corresponding third electrical signal and a fourth electrical signal based on the second laser signal and the second atmospheric echo signal, wherein the second laser signal corresponds to the third electrical signal, and the second atmospheric echo signal corresponds to the fourth electrical signal;

[0013] The fifth optical path includes, in sequence: the seed laser, the first beam splitter for transmission, the third beam splitter for reflection, a second attenuator, a reflector and a beam combiner;

[0014] The sixth optical path includes, in sequence: the seed laser, the first beam splitter for transmission, the third beam splitter for transmission, the acousto-optic frequency shifter, the laser pulse generator, the fourth beam splitter for reflection, the third attenuator and the beam combiner;

[0015] The beam combiner is used to combine the laser light in the fifth optical path with the laser light in the sixth optical path to obtain a third laser signal;

[0016] The third photoelectric detection is used to receive the third laser signal and obtain a fifth electrical signal based on the third laser signal;

[0017] The calibration module is used to detect the frequency drift of the seed laser and the frequency domain offset of the laser pulse generator according to the first electrical signal, the second electrical signal, the third electrical signal, the fourth electrical signal and the fifth electrical signal, so as to correct the Doppler frequency shift to be corrected, wherein the frequency domain offset is the frequency offset of the emitted laser pulse relative to the injected continuous wave seed laser.

[0018] Optionally, in some optional embodiments, the calibration module includes: a first correction unit, a second correction unit, a measurement unit to be corrected, and a Doppler correction unit;

[0019] The first correction amount unit is used to obtain a first correction amount of the emitted pulse laser relative to the continuous wave seed laser according to the fifth electrical signal;

[0020] The second correction unit is used to obtain a second correction value for initial calibration of the seed laser relative to the wind laser radar according to the first electrical signal and the third electrical signal;

[0021] The to-be-corrected measurement unit is used to obtain the uncorrected to-be-corrected Doppler frequency shift of the atmospheric echo signal according to the second electrical signal and the fourth electrical signal;

[0022] The Doppler correction unit is used to correct the Doppler frequency shift to be corrected according to the first correction amount and the second correction amount.

[0023] Optionally, in some optional implementations, the first correction unit is specifically used to:

[0024] Performing Fourier transform on the fifth electrical signal to obtain a corresponding power spectrum;

[0025] Using a spectrum peak recognition algorithm to identify the power spectrum, to obtain a signal peak position in the power spectrum;

[0026] The first correction amount is obtained based on the frequency of the signal peak position.

[0027] Optionally, in some optional implementations, the second correction unit is specifically used to:

[0028] Obtaining transmittance of the seed laser relative to the optical discriminator according to the first electrical signal and the third electrical signal;

[0029] Based on the transmittance, a pre-calibrated discrimination curve is queried to obtain a second correction value for the initial calibration of the seed laser relative to the wind laser radar.

[0030] Optionally, in some optional implementations, the measurement unit to be corrected is specifically used to:

[0031] Obtaining a transmittance of the atmospheric echo signal relative to the optical discriminator according to the second electrical signal and the fourth electrical signal;

[0032] Based on the transmittance, a pre-calibrated discrimination curve is queried to obtain an uncorrected Doppler frequency shift of the atmospheric echo signal.

[0033] Optionally, in some optional implementations, the Doppler correction unit is specifically used to:

[0034] Adding the first correction value and the second correction value to obtain a Doppler correction value;

[0035] The Doppler frequency shift to be corrected is corrected based on the Doppler correction amount.

[0036] Optionally, in some optional embodiments, when the wind laser radar just starts to emit laser pulses into the atmosphere: the first chopper is turned on and the second chopper is turned off;

[0037] After the laser pulse emitted by the laser pulse generator is transmitted to the atmospheric altitude layer to be measured: the first chopper is turned off and the second chopper is turned on.

[0038] Optionally, in certain optional embodiments, the optical discriminator is a gas atom discriminator, a gas molecule discriminator or an optical processing discriminator such as an etalon;

[0039] The optical discriminator laser operating frequency is set on the edge of a transmittance curve having a steep absorption peak or transmission peak edge feature.

[0040] By means of the above technical scheme, a frequency shift real-time online calibration device provided by the present invention comprises: a first optical path, a second optical path, a third optical path, a fourth optical path, a fifth optical path, a sixth optical path, a first photodetector, a second photodetector, a third photodetector and a calibration module; the first optical path comprises in sequence: a seed laser, a first beam splitter for reflection, a first attenuator, a first chopper and a second beam splitter for transmission; the second optical path comprises in sequence: the seed laser, the first beam splitter for transmission, the third beam splitter for transmission, an acousto-optic frequency shifter, a laser pulse generator, a fourth beam splitter for transmission, a second chopper and the second beam splitter for reflection, wherein the first chopper and The second chopper performs time division multiplexing; the first photodetector is used to receive the first laser signal transmitted by the second beam splitter in the first optical path and the first atmospheric echo signal reflected by the second beam splitter in the second optical path, and obtain corresponding first electrical signals and second electrical signals based on the first laser signal and the first atmospheric echo signal, wherein the first laser signal corresponds to the first electrical signal, and the first atmospheric echo signal corresponds to the second electrical signal; the third optical path includes, in sequence: the seed laser, the first beam splitter for reflection, the first attenuator, the first chopper, the second beam splitter for reflection and an optical frequency discriminator; the fourth optical The optical path includes, in sequence: the seed laser, the first beam splitter for transmission, the third beam splitter for transmission, the acousto-optic frequency shifter, the laser pulse generator, the fourth beam splitter for transmission, the second chopper, the second beam splitter for transmission and the optical discriminator; the second photodetector is used to receive the second laser signal transmitted by the optical discriminator in the third optical path and the second atmospheric echo signal transmitted by the optical discriminator in the fourth optical path, and obtain a corresponding third electrical signal and a fourth electrical signal based on the second laser signal and the second atmospheric echo signal, wherein the second laser signal corresponds to the third electrical signal, and the second atmospheric echo signal corresponds to The fourth electrical signal corresponds to; the fifth optical path includes in sequence: the seed laser, the first beam splitter for transmission, the third beam splitter for reflection, the second attenuator, a reflector and a beam combiner; the sixth optical path includes in sequence: the seed laser, the first beam splitter for transmission, the third beam splitter for transmission, the acousto-optic frequency shifter, the laser pulse generator, the fourth beam splitter for reflection, the third attenuator and the beam combiner; the beam combiner is used to combine the laser in the fifth optical path with the laser in the sixth optical path to obtain a third laser signal; the third photoelectric detection is used to receive the third laser signal and obtain a fifth electrical signal based on the third laser signal;The calibration module is used to perform Doppler frequency correction on the frequency drift error of the seed laser in the wind laser radar and the performance error of the optical discriminator according to the first electrical signal, the second electrical signal, the third electrical signal, the fourth electrical signal and the fifth electrical signal. It can be seen that the present invention is based on the time-division multiplexing of the first chopper and the second chopper, and realizes the time-division monitoring of the seed laser and the atmospheric echo through a simple structure, and then accurately identifies the performance error of the optical discriminator through the electrical signals detected by the first photodetector and the second photodetector before and after the optical discriminator. In addition, the present invention uses an acousto-optic frequency shifter to shift the seed laser to a known fixed frequency before injecting it into the laser pulse generator, and then combines the beams to detect the frequency drift error of the seed laser, thereby avoiding the problem that the final error result cannot distinguish between positive and negative due to the inconsistency between the emitted laser pulse frequency and the injected continuous wave seed laser frequency. In summary, the present invention is not only simple in structure and cost-saving, but also more accurate in error detection. ;

[0041] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention, it can be implemented according to the contents of the specification. In order to make the above and other purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present invention. Moreover, the same reference symbols are used throughout the accompanying drawings to represent the same components. In the accompanying drawings:

[0043] Figure 1 A schematic structural diagram of a frequency shift real-time online calibration device provided by the present invention is shown;

[0044] Figure 2 A timing diagram of time division multiplexing of a chopper provided by the present invention is shown;

[0045] Figure 3 A signal schematic diagram of a pulse-continuous wave laser frequency shift coherent detection provided by the present invention is shown;

[0046] Figure 4 A frequency schematic diagram of direct detection of seed laser frequency shift provided by the present invention is shown;

[0047] Figure 5 A schematic diagram of the transmittance of an optical frequency discriminator provided by the present invention is shown. DETAILED DESCRIPTION

[0048] The exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided in order to enable a more thorough understanding of the present invention and to enable the scope of the present invention to be fully communicated to those skilled in the art.

[0049] like Figure 1 As shown, the present invention provides a frequency shift real-time online calibration device, including: 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 first photodetector 1001, a second photodetector 1002, a third photodetector 1003 and a calibration module 10;

[0050] The first optical path LP1 includes, in sequence: a seed laser 1, a first beam splitter 201 for reflection, a first attenuator 501, a first chopper 601, and a second beam splitter 202 for transmission;

[0051] Optional, such as Figure 1 As shown, the first optical path LP1 mentioned in the present invention is specifically as follows: the laser emitted by the seed laser 1 is projected onto the first beam splitter 201, the first beam splitter 201 reflects a portion of the laser to the first attenuator 501, the first attenuator 501 attenuates the intensity of the laser it receives to a suitable level that can be detected by the subsequent first photodetector 1001, the first chopper 601 is configured on the seed laser monitoring channel and cooperates with the second chopper 602 for time division multiplexing, and time-division detection of the seed laser and the atmospheric echo, the laser passing through the first chopper 601 hits the second beam splitter 202, the second beam splitter 202 transmits a portion of the laser to hit the subsequent first photodetector 1001, and the present invention does not impose any limitation on this.

[0052] Optionally, the seed laser 1 emits single-frequency continuous wave laser and is configured to lock the emitted laser to a certain fixed operating frequency point.

[0053] Optional. Since there is only one set of frequency detection equipment, when measuring one signal, the other signal must be blocked. Otherwise, if two lasers hit a photodetector at the same time, the obtained signal will be unusable because the amplitude of a single signal is unknown. Therefore, it is necessary to measure them separately through time division multiplexing. For details, please refer to Figure 2 In the timing diagram shown, the first chopper 601 and the second chopper 602 are respectively turned on and off at different time periods to collect signals on different optical paths, which is not limited in the present invention.

[0054] The second optical path LP2 includes, in sequence: the seed laser 1, the first beam splitter 201 for transmission, the third beam splitter 203 for transmission, the acousto-optic frequency shifter 3, the laser pulse generator 4, the fourth beam splitter 204 for transmission, the second chopper 602 and the second beam splitter 202 for reflection, wherein the first chopper 601 and the second chopper 602 perform time division multiplexing;

[0055] Optional, such as Figure 1 As shown, the second optical path LP2 mentioned in the present invention is specifically as follows: the laser emitted by the seed laser 1 is incident on the first beam splitter 201, the first beam splitter 201 transmits a part of the laser to the third beam splitter 203, the third beam splitter 203 transmits a part of the laser to the acousto-optic frequency shifter 3, the acousto-optic frequency shifter 3 actively shifts the frequency of the incident laser by a certain fixed amount, and then the laser after frequency shift (generally a low-power laser) is emitted to the laser pulse generator 4 (of course, it can also be replaced with an amplifier), the laser pulse generator 4 amplifies the input laser and converts it into a high-energy pulse laser, the laser pulse generator 4 outputs a pulse laser and emits it to the fourth beam splitter 204, the fourth beam splitter 204 transmits a part of the laser into the atmosphere, the atmospheric echo reflected by the atmosphere passes through the second chopper 602 (time-division multiplexed with the first chopper 601), and then is emitted to the second beam splitter 202, the second beam splitter 202 reflects a part of the laser to the subsequent first photodetector 1001, and the present invention does not limit this.

[0056] Optionally, the laser pulse generator 4 is a complete laser, also known as a master oscillator. Even without the injection of single-frequency seed light, the laser pulse generator 4 will output high-energy laser pulses, but the laser frequency is non-single-frequency. Using the seed injection technology, the laser frequency emitted by the laser pulse generator 4 will be locked near the injected seed laser frequency to achieve single-frequency output. However, this technical solution has a disadvantage, that is, the emitted laser pulse frequency is inconsistent with the injected continuous wave seed laser frequency, and the two will have random frequency shifts. If the acousto-optic frequency shifter 3 is not added, the seed laser and the pulse laser are directly combined, and the frequency shift is obtained by the coherent detection method. In this way, only the magnitude of the frequency shift can be obtained, and its positive or negative value is unknown. Because, the present invention first uses the acousto-optic frequency shifter 3 to shift the seed laser to a known fixed frequency, and the absolute value of this frequency must be greater than the amplitude of the random frequency shift of the pulse-continuous wave. In this way, the seed laser after active frequency shifting is injected into the main oscillator, and then the coherent detection technology is used to determine the random frequency shift amount. The sign of the frequency shift amount is also known (consistent with the fixed frequency shift sign introduced by the acousto-optic frequency shifter 3), so it can be used as the first correction amount to participate in the subsequent Doppler frequency correction.

[0057] Optionally, if the laser pulse generator 4 is replaced by an amplifier, the continuous wave seed laser passes through the acousto-optic frequency shifter 3, is modulated into a pulse train by the acousto-optic frequency shifter 3, and then amplified and output by the amplifier. This scheme also uses the acousto-optic frequency shifter 3, and the frequency shift introduced by the acousto-optic frequency shifter 3 is also monitored in real time by the coherent detection technology in the present invention, and participates in the subsequent correction.

[0058] The first photodetector 1001 is used to receive the first laser signal transmitted by the second beam splitter 202 in the first optical path LP1 and to receive the first atmospheric echo signal reflected by the second beam splitter 202 in the second optical path LP2, and to obtain corresponding first electrical signals and second electrical signals based on the first laser signal and the first atmospheric echo signal, wherein the first laser signal corresponds to the first electrical signal, and the first atmospheric echo signal corresponds to the second electrical signal;

[0059] Optionally, the photodetector can convert the light signal incident on its photosensitive surface into an electrical signal, which can be collected and processed by a subsequent acquisition card (which can be separate or configured in the calibration module 10).

[0060] The third optical path LP3 includes, in sequence: the seed laser 1, the first beam splitter 201 for reflection, the first attenuator 501, the first chopper 601, the second beam splitter 202 for reflection and an optical discriminator 8;

[0061] Optional, such as Figure 1 As shown, the third optical path LP3 mentioned in the present invention is specifically as follows: the laser emitted by the seed laser 1 is projected onto the first beam splitter 201, the first beam splitter 201 reflects a portion of the laser to the first attenuator 501, the first attenuator 501 attenuates the intensity of the laser it receives to an appropriate level that can be detected by the subsequent first photodetector 1001, the first chopper 601 is configured on the seed laser monitoring channel and cooperates with the second chopper 602 for time division multiplexing, and time-division detection of the seed laser and the atmospheric echo, the laser passing through the first chopper 601 hits the second beam splitter 202, the second beam splitter 202 reflects a portion of the laser to the optical discriminator 8, the laser passes through the optical discriminator 8 and hits the subsequent second photodetector 1002, and the present invention does not impose any limitation on this.

[0062] It should be noted that the optical frequency discriminator 8 is an optical frequency measuring instrument with high spectral resolution, which can precisely measure the laser frequency by the transmittance of the laser beam passing through it.

[0063] The fourth optical path LP4 includes, in sequence: the seed laser 1, the first beam splitter 201 for transmission, the third beam splitter 203 for transmission, the acousto-optic frequency shifter 3, the laser pulse generator 4, the fourth beam splitter 204 for transmission, the second chopper 602, the second beam splitter 202 for transmission and the optical frequency discriminator 8;

[0064] Optional, such as Figure 1 As shown, the fourth optical path LP4 of the present invention is specifically as follows: the laser emitted by the seed laser 1 is incident on the first beam splitter 201, the first beam splitter 201 transmits a part of the laser to the third beam splitter 203, the third beam splitter 203 transmits a part of the laser to the acousto-optic frequency shifter 3, the acousto-optic frequency shifter 3 actively shifts the frequency of the incident laser by a certain fixed amount, and then the laser after frequency shift (generally a low-power laser) is emitted to the laser pulse generator 4 (of course, it can also be replaced by an amplifier), and the laser pulse generator 4 transmits the output The input laser is amplified and converted into a high-energy pulse laser. The laser pulse generator 4 outputs a pulse laser and emits it to the fourth beam splitter 204. The fourth beam splitter 204 transmits a part of the laser into the atmosphere. The atmospheric echo reflected by the atmosphere passes through the second chopper 602 (time-division multiplexed with the first chopper 601), and then enters the second beam splitter 202. The second beam splitter 202 transmits a part of the laser to the optical discriminator 8. The laser passing through the optical discriminator 8 hits the subsequent second photodetector 1002. The present invention does not impose any limitation on this.

[0065] The second photodetector 1002 is used to receive the second laser signal transmitted by the optical discriminator 8 in the third optical path LP3 and the second atmospheric echo signal transmitted by the optical discriminator 8 in the fourth optical path LP4, and obtain a corresponding third electrical signal and a fourth electrical signal based on the second laser signal and the second atmospheric echo signal, wherein the second laser signal corresponds to the third electrical signal, and the second atmospheric echo signal corresponds to the fourth electrical signal;

[0066] Optionally, the laser beam detected by the first photodetector 1001 is a signal that has not passed through the optical discriminator 8, and its value is assumed to be S1; and the second photodetector 1002 measures the signal after the laser beam passes through the optical discriminator 8, and its value is assumed to be S2, then the transmittance T of the optical discriminator 8 = S2 / S1. This is the transmittance without normalization, so its value can be greater than 1. Normalization is not required, as long as the caliber is unified when the discriminator curve is initially obtained and in subsequent applications.

[0067] The fifth optical path LP5 includes, in sequence: the seed laser 1, the first beam splitter 201 for transmission, the third beam splitter 203 for reflection, the second attenuator 502, the reflector 7 and the beam combiner 9;

[0068] Optional, such as Figure 1 As shown, the fifth optical path LP5 mentioned in the present invention is specifically as follows: the laser emitted by the seed laser 1 is incident on the first beam splitter 201, the first beam splitter 201 transmits a part of the laser to the third beam splitter 203, the third beam splitter 203 reflects a part of the laser to the second attenuator 502, the second attenuator 502 attenuates the intensity of the laser it receives to a suitable level that can be detected by the subsequent third photodetector 1003, the second attenuator 502 emits the attenuated laser to the reflector 7, and the reflector 7 reflects the laser to the beam combiner 9, and the present invention does not impose any limitation on this.

[0069] Optionally, the combiner 9 optically combines and mixes a portion of the emitted pulsed laser (the pulsed laser of the sixth optical path LP6) and a portion of the continuous wave seed laser (the laser of the fifth optical path LP5), and then projects them onto the third photodetector 1003, which is not limited by the present invention.

[0070] The sixth optical path LP6 includes, in sequence: the seed laser 1, the first beam splitter 201 for transmission, the third beam splitter 203 for transmission, the acousto-optic frequency shifter 3, the laser pulse generator 4, the fourth beam splitter 204 for reflection, the third attenuator 503 and the beam combiner 9;

[0071] Optional, combined Figure 1 As shown, the sixth optical path LP6 mentioned in the present invention is specifically as follows: the laser emitted by the seed laser 1 is incident on the first beam splitter 201, the first beam splitter 201 transmits a part of the laser to the third beam splitter 203, the third beam splitter 203 transmits a part of the laser to the acousto-optic frequency shifter 3, the acousto-optic frequency shifter 3 actively shifts the frequency of the incident laser by a certain fixed amount, and the laser after frequency shift (generally a low-power laser) is incident on the laser pulse generator 4 (of course, it can also be replaced with an amplifier), the laser pulse generator 4 amplifies the input laser and converts it into a high-energy pulse laser, the laser pulse generator 4 outputs a pulse laser and emits it to the fourth beam splitter 204, the fourth beam splitter 204 reflects a part of the laser to the third attenuator 503, the third attenuator 503 attenuates the intensity of the laser it receives to a suitable level that can be detected by the subsequent third photodetector 1003, and the third attenuator 503 emits the attenuated laser to the beam combiner 9, and the present invention does not impose any limitation on this.

[0072] The beam combiner 9 is used to combine the laser light in the fifth optical path LP5 with the laser light in the sixth optical path LP6 to obtain a third laser signal;

[0073] Optionally, the beam combiner 9 is a partially reflective and partially transmissive cube (the transmission-reflection ratio is generally 1:1), so that one path of light is transmitted and the other path of vertically incident light is reflected inside the cube, and as a result, the two paths of light are output simultaneously in one optical path, which is beam combining.

[0074] One laser has a frequency of f1 and the other has a frequency of f2. If the two beams are coherent, the combined laser electric field will have two components: sum frequency (f1+f2) and difference frequency (f1-f2). This is optical mixing. Such combined and mixed laser beams hit the photodetector and are converted into electrical signals. The sum frequency (f1+f2) component is outside the response bandwidth of the detector, and the output electrical signal component is DC; the difference frequency (f1-f2) component is within the response bandwidth, and the electrical signal completely retains the spectrum component. The acquisition card is used to collect and convert it into a digital signal, and then the difference frequency (f1-f2) can be obtained through FFT transformation and spectrum recognition technology.

[0075] The third photodetector 1003 is used to receive the third laser signal and obtain a fifth electrical signal based on the third laser signal;

[0076] The calibration module 10 is used to detect the frequency drift of the seed laser and the frequency domain offset of the laser pulse generator according to the first electrical signal, the second electrical signal, the third electrical signal, the fourth electrical signal and the fifth electrical signal, so as to correct the Doppler frequency shift to be corrected, wherein the frequency domain offset is the frequency offset of the emitted laser pulse relative to the injected continuous wave seed laser.

[0077] Optionally, in some optional implementations, the calibration module 10 includes: a first correction unit, a second correction unit, a measurement unit to be corrected, and a Doppler correction unit;

[0078] The first correction amount unit is used to obtain a first correction amount of the emitted pulse laser relative to the continuous wave seed laser according to the fifth electrical signal;

[0079] The second correction unit is used to obtain a second correction value for initial calibration of the seed laser relative to the wind laser radar according to the first electrical signal and the third electrical signal;

[0080] The to-be-corrected measurement unit is used to obtain the uncorrected to-be-corrected Doppler frequency shift of the atmospheric echo signal according to the second electrical signal and the fourth electrical signal;

[0081] The Doppler correction unit is used to correct the Doppler frequency shift to be corrected according to the first correction amount and the second correction amount.

[0082] Optionally, in some optional implementations, the first correction unit is specifically used to:

[0083] Performing Fourier transform on the fifth electrical signal to obtain a corresponding power spectrum;

[0084] Using a spectrum peak recognition algorithm to identify the power spectrum, to obtain a signal peak position in the power spectrum;

[0085] The first correction amount is obtained based on the frequency of the signal peak position.

[0086] Optionally, in some optional implementations, the second correction unit is specifically used to:

[0087] Obtaining transmittance of the seed laser relative to the optical discriminator 8 according to the first electrical signal and the third electrical signal;

[0088] Based on the transmittance, a pre-calibrated discrimination curve is queried to obtain a second correction value for the initial calibration of the seed laser relative to the wind laser radar.

[0089] Optionally, in some optional implementations, the measurement unit to be corrected is specifically used to:

[0090] Obtaining the transmittance of the atmospheric echo signal relative to the optical discriminator 8 according to the second electrical signal and the fourth electrical signal;

[0091] Based on the transmittance, a pre-calibrated discrimination curve is queried to obtain an uncorrected Doppler frequency shift of the atmospheric echo signal.

[0092] Optionally, in some optional implementations, the Doppler correction unit is specifically used to:

[0093] Adding the first correction value and the second correction value to obtain a Doppler correction value;

[0094] The Doppler frequency shift to be corrected is corrected based on the Doppler correction amount.

[0095] Optionally, in some optional embodiments, when the wind laser radar just starts to emit laser pulses to the atmosphere: the first chopper 601 is turned on and the second chopper 602 is turned off;

[0096] After the laser pulse emitted by the laser pulse generator 4 is transmitted to the atmospheric altitude layer to be measured: the first chopper 601 is turned off and the second chopper 602 is turned on.

[0097] Optionally, in some optional embodiments, the optical discriminator 8 is an optical processing discriminator such as a gas atom discriminator, a gas molecule discriminator or an etalon;

[0098] The laser operating frequency of the optical discriminator 8 is set on the edge of the transmittance curve with a steep absorption peak or transmission peak edge feature.

[0099] Optionally, the optical discriminator 8 is an artificially coated Fabry-Perot etalon discriminator, and its laser operating frequency may be on the edge of a steep transmittance curve, which is not limited in the present invention.

[0100] It should be noted that the laser operating frequency of the optical discriminator 8 is on the edge of a steep transmittance curve, which means that the optical discriminator 8 is more sensitive and has a higher accuracy.

[0101] Optionally, the edge of the steep absorption peak used by the optical discriminator 8 has the laser frequency on the abscissa and the optical transmittance of the discriminator on the ordinate. According to this curve, the laser frequency can be converted by measuring the transmittance. The greater the slope of this curve (that is, the "steeper"), the greater the transmittance change caused by the same frequency shift, that is, the higher the detection sensitivity.

[0102] Optionally, a portion of the single-frequency continuous wave laser of the seed laser 1 is combined with a portion of the pulsed laser injected into the laser pulse generator 4 or the amplifier output after frequency shifting by the acousto-optic frequency shifter 3 to perform beat frequency combination, and a first frequency shift correction value is extracted from the beat frequency signal power spectrum; two choppers are used to respectively control the timing of the atmospheric echo signal receiving channel and the seed laser monitoring channel in the direct detection wind measurement laser radar system, and the same set of demodulation system is used to perform alternating demodulation measurement on the two channel signals in a time-division multiplexing manner, and the frequency shift value obtained by the demodulation measurement of the seed laser monitoring channel is the second frequency shift correction value; the first correction value and the second correction value are used to correct the demodulation result of the atmospheric echo signal, thereby eliminating the Doppler frequency shift measurement error caused by the emission laser frequency offset (including the seed laser drift and the pulse-continuous wave laser frequency shift) and the optical demodulator 8 and the error in the wind speed detection of the direct detection wind measurement laser radar, thereby improving the accuracy of wind field detection.

[0103] The present invention takes into account the difference between the seed laser 1 and the laser pulse frequency emitted into the atmosphere, and uses coherent detection technology to monitor and correct the frequency difference in real time. In addition, by controlling the switching timing of the two choppers, time division multiplexing of only one frequency discrimination system on the atmospheric echo receiving channel and the seed laser monitoring channel is cleverly achieved. It not only simplifies the structure and saves costs, but also eliminates the standard transmission error problem caused by the dual-frequency standard solution. The drift of the seed laser frequency will produce a non-zero second correction amount, and the unstable characteristics of the optical discriminator 8 will also produce a non-zero second correction amount. Therefore, with the use of the second correction amount in the present invention, not only the error caused by the frequency drift of the seed laser 1 is corrected, but also the sum error of the optical discriminator 8 is corrected at the same time.

[0104] In summary, the frequency shift real-time online calibration device disclosed in the present invention can specifically perform the following process:

[0105] When the wind laser radar starts to emit laser pulses into the atmosphere, the first chopper 601 is turned on and the second chopper 602 is turned off;

[0106] The electrical signal converted by the third photodetector 1003 after the beam combiner 9 is collected and Fourier transformed to obtain the power spectrum of the mixed signal, and then the signal peak position is determined by using the spectrum peak recognition algorithm to obtain the frequency shift of the emitted laser pulse relative to the continuous wave seed laser, that is, the first frequency shift correction amount;

[0107] The photoelectric detectors located before and after the optical discriminator 8 of the laser radar system measure the transmittance of the current seed laser relative to the optical discriminator 8, and use the discriminator curve to determine the frequency shift of the current seed laser relative to the initial calibration of the system, that is, the second correction value of the frequency shift;

[0108] After the laser pulse is transmitted to the atmospheric altitude layer to be measured, the first chopper 601 is turned off and the second chopper 602 is turned on;

[0109] The photoelectric detectors located before and after the optical discriminator 8 of the laser radar system measure the transmittance of the current atmospheric echo signal relative to the optical discriminator 8, and use the discriminator curve to determine the frequency shift of the current atmospheric echo relative to the initial calibration of the system, that is, the Doppler frequency shift to be corrected;

[0110] The corrected Doppler frequency shift is obtained by subtracting the first correction amount and the second correction amount from the Doppler frequency shift to be corrected.

[0111] Optionally, the pulse laser is applied to the third photodetector 1003 to obtain Figure 3 The signal shown in the upper part of the figure is transformed by Fourier transform to obtain Figure 3 The signal shown in the lower half of the figure is not limited in the present invention.

[0112] Optionally, the discrimination curve is Figure 4 The discriminator transmittance curve shown in the figure is determined by pre-calibration of the entire laser radar system before use, and requires the use of other standard measuring instruments, namely, high-precision wavelength meters. The frequency of the seed laser 1 can be tuned. While changing the frequency of the seed laser 1 and recording it with a wavelength meter, the values ​​of the first photodetector 1001 and the second photodetector 1002 are measured on the other hand, and the transmittance T is calculated, and the following is obtained: Figure 4 The frequency discrimination curve is shown.

[0113] Combination Figure 4 The curve graph shown, ( , ) represents the working point during the initial calibration (the horizontal axis represents the initial laser frequency, and the vertical axis represents the initial transmittance), ( , ) represents the current working point. By measuring the current transmittance of the seed laser, the current seed laser frequency can be obtained, and the second correction value can be obtained by subtracting them.

[0114] Optional, such as Figure 5 As shown, a schematic diagram of the transmittance of an iodine molecular discriminator is shown, and both steep edges (falling edge and rising edge) surrounded by the dotted ellipse can be used. That is, the operating frequency point of the laser radar can be selected and set from the falling edge or the rising edge of the transmittance of the iodine molecular discriminator, and the present invention does not limit this.

[0115] In the present invention, relational terms such as first and second, etc. are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprise", "include" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the statement "comprise a ..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0116] Each embodiment in this specification is described in a related manner, and the same or similar parts between the embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment.

[0117] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined in the present invention may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown in the present invention, but will conform to the widest scope consistent with the principles and novel features disclosed in the present invention.

[0118] The above description is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention are included in the protection scope of the present invention.

Claims

1. A frequency shift real-time online calibration device, characterized in that: include: A first optical path, a second optical path, a third optical path, a fourth optical path, a fifth optical path, a sixth optical path, a first photodetector, a second photodetector, a third photodetector and a calibration module; The first optical path includes, in sequence: a seed laser, a first beam splitter for reflection, a first attenuator, a first chopper, and a second beam splitter for transmission; The second optical path includes, in sequence: the seed laser, the first beam splitter for transmission, the third beam splitter for transmission, an acousto-optic frequency shifter, a laser pulse generator, a fourth beam splitter for transmission, a second chopper and the second beam splitter for reflection, wherein the first chopper and the second chopper perform time division multiplexing; The first photodetector is used to receive the first laser signal transmitted by the second beam splitter in the first optical path and to receive the first atmospheric echo signal reflected by the second beam splitter in the second optical path, and to obtain corresponding first electrical signals and second electrical signals based on the first laser signal and the first atmospheric echo signal, wherein the first laser signal corresponds to the first electrical signal, and the first atmospheric echo signal corresponds to the second electrical signal; The third optical path includes, in sequence: the seed laser, the first beam splitter for reflection, the first attenuator, the first chopper, the second beam splitter for reflection and an optical frequency discriminator; The fourth optical path includes, in sequence: the seed laser, the first beam splitter for transmission, the third beam splitter for transmission, the acousto-optic frequency shifter, the laser pulse generator, the fourth beam splitter for transmission, the second chopper, the second beam splitter for transmission and the optical frequency discriminator; The second photodetector is used to receive the second laser signal transmitted by the optical discriminator in the third optical path and the second atmospheric echo signal transmitted by the optical discriminator in the fourth optical path, and obtain a corresponding third electrical signal and a fourth electrical signal based on the second laser signal and the second atmospheric echo signal, wherein the second laser signal corresponds to the third electrical signal, and the second atmospheric echo signal corresponds to the fourth electrical signal; The fifth optical path includes, in sequence: the seed laser, the first beam splitter for transmission, the third beam splitter for reflection, a second attenuator, a reflector and a beam combiner; The sixth optical path includes, in sequence: the seed laser, the first beam splitter for transmission, the third beam splitter for transmission, the acousto-optic frequency shifter, the laser pulse generator, the fourth beam splitter for reflection, the third attenuator and the beam combiner; The beam combiner is used to combine the laser light in the fifth optical path with the laser light in the sixth optical path to obtain a third laser signal; The third photoelectric detection is used to receive the third laser signal and obtain a fifth electrical signal based on the third laser signal; The calibration module is used to detect the frequency drift of the seed laser and the frequency domain offset of the laser pulse generator according to the first electrical signal, the second electrical signal, the third electrical signal, the fourth electrical signal and the fifth electrical signal, so as to correct the Doppler frequency shift to be corrected, wherein the frequency domain offset is the frequency offset of the emitted laser pulse relative to the injected continuous wave seed laser.

2. The device according to claim 1, characterized in that The calibration module includes: a first correction unit, a second correction unit, a measurement unit to be corrected and a Doppler correction unit; The first correction amount unit is used to obtain a first correction amount of the emitted pulse laser relative to the continuous wave seed laser according to the fifth electrical signal; The second correction unit is used to obtain a second correction value for initial calibration of the seed laser relative to the wind laser radar according to the first electrical signal and the third electrical signal; The to-be-corrected measurement unit is used to obtain the uncorrected to-be-corrected Doppler frequency shift of the atmospheric echo signal according to the second electrical signal and the fourth electrical signal; The Doppler correction unit is used to correct the Doppler frequency shift to be corrected according to the first correction amount and the second correction amount.

3. The device according to claim 2, characterized in that The first correction unit is specifically used for: Performing Fourier transform on the fifth electrical signal to obtain a corresponding power spectrum; Using a spectrum peak recognition algorithm to identify the power spectrum, to obtain a signal peak position in the power spectrum; The first correction amount is obtained based on the frequency of the signal peak position.

4. The device according to claim 2, characterized in that The second correction unit is specifically used for: Obtaining transmittance of the seed laser relative to the optical discriminator according to the first electrical signal and the third electrical signal; Based on the transmittance, a pre-calibrated discrimination curve is queried to obtain a second correction value for the initial calibration of the seed laser relative to the wind laser radar.

5. The device according to claim 2, characterized in that The measurement unit to be corrected is specifically used for: Obtaining a transmittance of the atmospheric echo signal relative to the optical discriminator according to the second electrical signal and the fourth electrical signal; Based on the transmittance, a pre-calibrated discrimination curve is queried to obtain an uncorrected Doppler frequency shift of the atmospheric echo signal.

6. The device according to claim 2, characterized in that The Doppler correction unit is specifically used for: Adding the first correction value and the second correction value to obtain a Doppler correction value; The Doppler frequency shift to be corrected is corrected based on the Doppler correction amount.

7. The device according to claim 1, characterized in that When the wind laser radar just starts to emit laser pulses into the atmosphere: the first chopper is turned on and the second chopper is turned off; After the laser pulse emitted by the laser pulse generator is transmitted to the atmospheric altitude layer to be measured: the first chopper is turned off and the second chopper is turned on.

8. The device according to claim 1, characterized in that The optical frequency discriminator is a gas atom frequency discriminator, a gas molecule frequency discriminator or an etalon; The optical discriminator laser operating frequency is set on the edge of a transmittance curve having a steep absorption peak or transmission peak edge feature.

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