A four-channel fabry-perot frequency discriminator module closed-loop feedback control system

Abstract

The application provides a four-channel Fabry-Perot frequency discrimination module closed-loop feedback control system, which comprises a laser, a four-channel Fabry-Perot frequency discrimination module and a control module; the four-channel Fabry-Perot frequency discrimination module comprises three optical channels composed of Fabry-Perot etalons and a fourth channel allowing laser to be completely transmitted; two of the three optical channels are used as frequency discrimination channels, and the other one is used as a locking channel; the locking channel and the fourth channel respectively receive laser signals emitted by the laser and transmit the transmitted laser signals to the control module; the control module calculates the transmittance of the locking channel according to the signal intensity of the laser signals transmitted through the two channels, and generates a driving signal according to the preset transmittance to adjust the mirror distance of the three optical channels, so as to realize the locking of the transmittance of the locking channel. The application effectively reduces the influence of laser frequency jitter, external environmental temperature change and vibration factors on frequency discrimination, and improves the frequency discrimination precision and reliability.

Description

Technical Field

[0001] This invention belongs to the field of laser echo signal frequency discrimination technology, and specifically relates to a closed-loop feedback control system for a four-channel Fabry-Perot frequency discrimination module. Background Technology

[0002] Incoherent wind lidar is the preferred laser remote sensing instrument for high-precision and high-resolution global atmospheric wind field measurement. It can be widely used in the fields of low-to-mid-altitude to mid-to-high-altitude atmospheric wind fields, turbulence, cyclones, local thunderstorms and other extreme weather warnings and measurements, climate research.

[0003] In common incoherent wind lidar systems, the frequency discrimination methods for laser echo signals include fringe discrimination, single-edge discrimination, and double-edge discrimination. The fringe method determines wind speed movement by judging the movement of interference fringes formed by the interferometer through the echo signal, while single-edge and double-edge discrimination invert and measure wind speed changes by comparing the transmittance changes caused by the intensity changes of the laser echo signal before and after passing through the frequency discrimination component.

[0004] The advantage of using the fringe method for frequency discrimination is its direct connection to the Fizeau interferometer and linear CCD array. This method is simple, but it suffers from limitations in addressing the interference of laser center frequency fluctuations and external environmental factors on the interferometer's frequency discrimination accuracy, leading to unreliability in laser wind speed radar frequency discrimination measurements. Furthermore, traditional single-edge and double-edge frequency discrimination methods employ open-loop control of dual- or triple-channel FP frequency discrimination modules. This approach cannot resolve the impact of laser center frequency drift on the accuracy of wind measurement lasers. Additionally, changes in ambient temperature and vibration can also degrade the frequency discrimination capability of the FP frequency discrimination module. Summary of the Invention

[0005] The technical problem solved by this invention is to overcome the shortcomings of the prior art and provide a four-channel Fabry-Perot frequency discrimination module closed-loop feedback control system, which effectively reduces the influence of laser frequency jitter, external environmental temperature changes and vibration factors on laser echo signal frequency discrimination, and improves frequency discrimination accuracy and reliability.

[0006] The technical solution of this invention is:

[0007] A closed-loop feedback control system for a four-channel Fabry-Perot frequency discrimination module is characterized by comprising a laser, a four-channel Fabry-Perot frequency discrimination module, and a control module; the laser emits laser signals; the four-channel Fabry-Perot frequency discrimination module includes a first channel, a second channel, a third channel, a fourth channel, and a frequency discrimination module, wherein the first, second, and third channels are optical channels composed of Fabry-Perot etalons; each optical channel includes two parallel flat glass plates and is equipped with piezoelectric ceramics for adjusting the distance between the flat glass plates; the fourth channel allows complete transmission of the laser; two of the first, second, and third channels serve as frequency discrimination channels, and the other serves as a locking channel; the two frequency discrimination channels respectively receive atmospheric signals. The echo signal of the laser signal is discriminated by the frequency discrimination module based on the echo signal after transmission through the two frequency discrimination channels. The locking channel and the fourth channel respectively receive the laser signal and transmit the transmitted laser signal to the control module. The control module receives the laser signal after transmission through the locking channel and the laser signal after transmission through the fourth channel, calculates the transmittance of the locking channel based on the signal intensity of the received laser signal after transmission through the two channels, and then determines whether the transmittance of the locking channel is equal to the preset transmittance. If they are not equal, the control module outputs a control signal to control the driving voltage of the piezoelectric ceramics of the first, second, and third channels until the transmittance value of the locking channel is equal to the preset transmittance value. If they are equal, the driving voltage of the piezoelectric ceramics of each channel remains unchanged.

[0008] Preferably, the control module calculates the transmittance of the locking channel based on the signal intensity of the laser signal transmitted through the two channels. Specifically, the transmittance of the locking channel is equal to the ratio of the signal intensity of the laser signal transmitted through the locking channel to the signal intensity of the laser signal transmitted through the fourth channel.

[0009] Preferably, the control module includes a closed-loop controller and a boost module. The closed-loop controller generates a drive voltage control signal based on the calculated transmittance of the locked channel and a preset transmittance. The drive control signal includes a first channel drive voltage control signal, a second channel drive voltage control signal, and a third channel drive voltage control signal. The boost module boosts the drive voltage control signal to the drive voltage range of the piezoelectric ceramic.

[0010] Preferably, the control module controls the driving voltage of the piezoelectric ceramics in the first, second, and third channels, specifically by the closed-loop controller generating a step-by-step driving voltage control signal based on a preset initial driving voltage value and a driving voltage step value.

[0011] Preferably, the voltage range of the drive voltage control signal is 0 to 10V, and the voltage range of the boosted drive voltage control signal is 0 to 100V.

[0012] Preferably, it also includes a first fiber-optic coupling lens and a second fiber-optic coupling lens. The fourth channel transmits the transmitted laser signal to the control module through the first fiber-optic coupling lens, and the locking channel transmits the transmitted laser signal to the control module through the second fiber-optic coupling lens.

[0013] Preferably, the first, second, third, and fourth channels are parallel to each other and parallel to the direction of the laser signal emitted by the laser, and the incident directions of the first, second, third, and fourth channels are opposite to the direction of the laser signal.

[0014] Preferably, the system further includes a first plane mirror, a beam-splitting prism, and a second plane mirror. The laser signal emitted by the laser is reflected by the first plane mirror to the beam-splitting prism. The laser signal reflected by the beam-splitting prism is incident on the fourth channel. The laser signal transmitted by the beam-splitting prism is incident on the second plane mirror and, after reflection, is incident on the locking channel. The angle between the normal direction of the first plane mirror and the direction of the laser signal emitted by the laser is 45°. The beam-splitting prism is perpendicular to the first plane mirror, and the second plane mirror is parallel to the beam-splitting prism.

[0015] Preferably, the wavelength of the laser signal emitted by the laser is 355nm.

[0016] Preferably, the transmittance of the lock channel preset by the control module is in the range of 0.6 to 0.8.

[0017] The advantages of this invention compared to the prior art are:

[0018] (1) This invention proposes a four-channel Fabry-Perot frequency discrimination module closed-loop feedback control system. By real-time detection of the transmittance of the locked channel through the laser signal transmitted through the locked channel and the fourth channel, and adjusting the lens distance of each Fabry-Perot etalon according to the transmittance set value, the real-time closed-loop control of the transmittance of the locked channel is realized. This provides closed-loop feedback control for incoherent laser wind radar based on dual-edge frequency discrimination detection, effectively reducing the impact of laser frequency jitter, external environmental temperature changes and vibration factors on the reliability of laser echo signal frequency discrimination, and improving the frequency discrimination accuracy of the system.

[0019] (2) The present invention uses a pigtail coupling lens to perform laser signal fiber coupling on the two locking signals of the fourth channel and the locking channel, thereby improving the utilization rate of the laser signal of the locking channel. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the closed-loop feedback system of the four-channel Fabry-Perot frequency discrimination module of the present invention;

[0021] Figure 2 This is a schematic diagram of the present invention using the second channel as the locking channel;

[0022] Figure 3 This is a schematic diagram of the present invention using a third channel as the locking channel. Detailed Implementation

[0023] The features and advantages of the present invention will become clearer and more explicit through the following detailed description.

[0024] This invention provides a four-channel Fabry-Perot frequency discrimination module closed-loop feedback system, such as... Figure 1 As shown, it consists of a laser, a four-channel Fabry-Perot frequency discrimination module 4, and a control module.

[0025] Specifically, the laser is a 355nm laser system that emits 355nm pulsed laser signals.

[0026] Specifically, the four-channel Fabry-Perot frequency discrimination module 4 consists of a three-channel etalon module structure, an FP (Fabry-Perot) optical frequency discrimination module, and a fourth channel. The FP optical frequency discrimination module includes three optical channels formed by Fabry-Perot etalons: the first channel (channel A in the figure), the second channel (channel B in the figure), and the third channel (channel C in the figure). Each channel consists of two parallel flat glass plates. Each optical channel is equipped with a piezoelectric ceramic for adjusting the distance between the flat glass plates. The distance between the flat glass plates can be adjusted by adjusting the driving voltage of the piezoelectric ceramic. During operation, two of the channels act as frequency discrimination channels, receiving laser echo signals from the atmosphere in proportion to the laser signal emitted by the laser. By comparing the relative changes in the intensity of the echo signals from the two frequency discrimination channels, the frequency of the laser echo signal can be identified. The third channel acts as a locking channel, working with the fourth channel to lock the laser emission frequency. The fourth channel consists only of structural components, allowing complete laser transmission.

[0027] Furthermore, the three-channel etalon module structure adopts an integrated structural design, which integrates components such as the fourth channel and the FP optical frequency discrimination module into one unit.

[0028] Specifically, the control module includes a closed-loop control circuit module 7, an open-loop controller 8, a power supply module 9, and control software 10. The main function of the closed-loop control circuit module 7 is to connect the four-channel Fabry-Perot frequency discriminator module 4 to the open-loop controller 8. The output laser signal of the four-channel Fabry-Perot frequency discriminator module 4 is input to the closed-loop control circuit module 7. After internal processing according to the internal algorithm and the setting parameters provided by the control software 10, the closed-loop control circuit module 7 outputs a voltage control signal, which is then input to...

[0029] Open-loop controller 8. After converting the voltage control signal into a high-voltage signal, the open-loop controller 8 inputs it to the four-channel Fabry-Perot frequency discriminator module 4, thereby controlling the distance between the front and rear lenses of the four-channel Fabry-Perot frequency discriminator module 4. The main function of the power supply module 9 is to provide power to the closed-loop control circuit module 7 and the open-loop controller 8. The main function of the control software 10 is to send instructions to the closed-loop control circuit module 7 according to preset parameters, and simultaneously receive the parameters fed back from it, performing real-time communication and processing.

[0030] Furthermore, the closed-loop control circuit module 7 primarily processes electronic signals. It has two optical signal inputs, one power signal input port, one communication control signal port, and three DC voltage signal outputs. The two optical signal inputs are laser signals transmitted through a locked channel from the first fiber-optic coupling lens 5, and laser signals transmitted through a fourth channel from the second fiber-optic coupling lens 6. The three DC voltage signal outputs are the first open-loop input drive control line 15, the second...

[0031] The voltage range of the three drive control lines 5 (two open-loop input drive control lines 16 and three open-loop input drive control lines 17) is between 0 and 10V. One communication control signal is output via the control software 10.

[0032] The communication control cable 11 is used to exchange signals with the control software.

[0033] Furthermore, the open-loop controller 8 converts the voltage control signal into a high-voltage signal and inputs it to the four-channel Fabry-Perot frequency discriminator module 4 to control the distance between the front and rear lenses of the four-channel Fabry-Perot frequency discriminator module 4.

[0034] It has 3 input signals, 3 output signals, and 1 power input signal. The 3 input signals originate from the 3 output signals of the closed-loop control circuit module 7, which are driven by the first open-loop input control.

[0035] Line 15, the second open-loop input drive control line 16, and the third open-loop input drive control line 17 output DC regulated signals, all with a voltage range between 0 and 10V. The three output signals, via the first PZT RF drive control line 12, the second PZT RF drive control line 13, and the third PZT RF drive control line 14, respectively output DC regulated signals to control the drive voltage of the piezoelectric ceramics in the first channel, the second channel 5, and the third channel of the FP optical frequency discriminator module. The voltage range of these three signals is between 0 and 100V. One power input signal is a 12V DC regulated signal.

[0036] Furthermore, the power module 9 has one 12V / 5A DC regulated signal and one 220V / 5A AC signal.

[0037] Furthermore, the main function of the control software 10 is to send instructions to the closed-loop control circuit module 7 according to preset parameters, and at the same time receive the parameters fed back from it, performing real-time communication and processing. The preset parameters include: scanning mode, transmittance lock, scanning start voltage, scanning end voltage, scanning step voltage, transmittance value, and whether the lock is active.

[0038] In one specific embodiment, the first, second, third, and fourth channels of the four-channel Fabry-Perot frequency discrimination module are parallel to each other and parallel to the direction of the laser signal emitted by the laser. The incident directions of the first, second, third, and fourth channels are opposite to the direction of the laser signal.

[0039] Furthermore, it also includes a first plane mirror 1, a beam splitter prism 2, and a second plane mirror 3. The laser signal emitted by the laser is reflected by the first plane mirror 1 to the beam splitter prism 2. The laser signal reflected by the beam splitter prism 2 is incident on the fourth channel. The laser signal transmitted by the beam splitter prism 2 is incident on the second plane mirror 3 and then incident on the locking channel after reflection. The angle between the normal direction of the first plane mirror 1 and the direction of the laser signal emitted by the laser is 45°. The beam splitter prism 2 is perpendicular to the first plane mirror 1, and the second plane mirror 3 is parallel to the beam splitter prism 2.

[0040] Preferably, the reflectivity of the first plane mirror 1 and the second plane mirror 3 to the 355nm laser wavelength is ≥99%@45°; the reflection-to-transmission ratio of the beam splitter prism 2 is 5:95.

[0041] The working process of the four-channel Fabry-Perot frequency discrimination module closed-loop feedback system of this invention is as follows:

[0042] First, the first channel of the FP optical frequency discriminator module is used as the locking channel. The 355nm pulsed laser signal emitted by the 355nm laser system is reflected by the first plane mirror 1 and then shines on the beam splitter prism 2. 5% of the laser beam, after being reflected by the beam splitter prism 2, enters the closed-loop control circuit module 7 directly through the fourth channel and the second fiber-optic coupling lens 6. The remaining 95% of the laser beam transmitted through the beam splitter prism 2 shines on the second plane mirror 3 at a 45° incident angle and is reflected at a 45° angle. After being transmitted through the first channel of the FP optical frequency discriminator module of the four-channel Fabry-Perot frequency discriminator module 4, it enters the closed-loop control circuit module 7 through the first fiber-optic coupling lens 5. The first channel of the FP optical frequency discriminator module is the locking channel, while the second and third channels are frequency discriminator channels used to receive laser echo signals of equal proportion. By comparing the relative changes in the intensity of the echo signals from the two frequency discriminator channels, the frequency of the laser echo signal can be identified. The closed-loop control circuit module performs real-time detection and calculation of the 355nm laser signal intensity transmitted through the first fiber-optic coupling lens 5 and the second fiber-optic coupling lens 6, obtaining the transmittance value of the 355nm laser through the locked channel. This transmittance value is equal to the ratio of the signal intensity transmitted through the locked channel to the signal intensity transmitted through the fourth channel. In the control software, automatic locking parameters can be set, with the range between the cutoff voltage and the start voltage covering two cycles of frequency discrimination in the four-channel Fabry-Perot frequency discriminator module 4. Typically, the transmittance value in the control software 10 is set to any value between 0.6 and 0.8, the PZT scan voltage step size is set to 0.01V, the PZT start scan voltage is set to 0.1V, and the cutoff scan voltage is set to 3V. After the control software is started, it uploads the above three parameters to the closed-loop control circuit. At the same time, the closed-loop control circuit module collects the laser signal intensity input from the first fiber-coupled lens 5 and the second fiber-coupled lens 6, calculates the transmittance coefficient of both, and compares the coefficient with the lock-in transmittance value set in the control software. If the values ​​are consistent, the closed-loop control circuit module will no longer adjust the PZT output voltage. That is, the voltage values ​​output by the first open-loop input drive control line 15, the second open-loop input drive control line 16, and the third open-loop input drive control line 17 of the closed-loop controller remain unchanged. The voltage signals output by the open-loop controller to the four-channel Fabry-Perot frequency discriminator module 4 via the first PZT RF drive control line 12, the second PZT RF drive control line 13, and the third PZT RF drive control line 14 also remain unchanged. The voltage range of these three signals depends on the hardware setting of the open-loop controller, which includes 75V, 100V, and 150V.If the ratio of the laser signal intensity input to the first fiber-optic coupling lens 5 and the second fiber-optic coupling lens 6, calculated by the closed-loop control circuit module, is inconsistent with the parameters set by the control software, the automatic search algorithm in the closed-loop control circuit module will be invoked to adjust the voltage values ​​output through the first open-loop input drive control line 15, the second open-loop input drive control line 16, and the third open-loop input drive control line 17 in real time. The voltage values ​​will then be output to the four-channel Fabry-Perot frequency discriminator module through the first PZT RF drive control line 12, the second PZT RF drive control line 13, and the third PZT RF drive control line 14 output by the open-loop controller. The distance between the front and rear surfaces of the four-channel Fabry-Perot frequency discriminator module will be adjusted in real time until the ratio of the laser signal intensity input to the first fiber-optic coupling lens 5 and the second fiber-optic coupling lens 6 is equal to the lockout transmittance value set by the control software.

[0043] Then, the first channel and the second channel of the FP optical frequency discrimination module are respectively used as the locking channels, such as... Figure 2 , Figure 3 As shown, by repeating the above process, the transmittance of each optical channel can be locked.

[0044] During the operation of the four-channel Fabry-Perot frequency discrimination module, one of the channels is used as the locked channel. The closed-loop feedback system of this invention is used to perform real-time closed-loop feedback control on the transmittance of the locked channel, which can effectively reduce the influence of laser frequency jitter, external environmental temperature changes and vibration factors on laser echo signal frequency discrimination, and improve the frequency discrimination accuracy and reliability.

[0045] The contents not described in detail in this specification are common knowledge to those skilled in the art.

Claims

1. A four-channel Fabry-Perot frequency discrimination module closed-loop feedback control system, characterized in that, The system includes a laser, a four-channel Fabry-Perot frequency discrimination module, and a control module. The laser emits laser signals. The four-channel Fabry-Perot frequency discrimination module includes a first channel, a second channel, a third channel, a fourth channel, and a frequency discrimination module. The first, second, and third channels are optical channels constructed from Fabry-Perot etalons. Each optical channel includes two parallel flat glass plates and is equipped with piezoelectric ceramics for adjusting the distance between the glass plates. The fourth channel allows complete laser transmission. Two of the first, second, and third channels serve as frequency discrimination channels, and the third channel serves as a locking channel. The two frequency discrimination channels respectively receive atmospheric signals related to the laser. The echo signal is received by the frequency discrimination module, which performs frequency discrimination on the echo signal after transmission through the two frequency discrimination channels. The locking channel and the fourth channel respectively receive the laser signal and transmit the transmitted laser signal to the control module. The control module receives the laser signal after transmission through the locking channel and the laser signal after transmission through the fourth channel, calculates the transmittance of the locking channel based on the signal intensity of the received laser signal after transmission through the two channels, and then determines whether the transmittance of the locking channel is equal to the preset transmittance. If they are not equal, the control module outputs a control signal to control the driving voltage of the piezoelectric ceramics of the first channel, the second channel and the third channel until the transmittance value of the locking channel is equal to the preset transmittance value. If they are equal, the driving voltage of the piezoelectric ceramics in each channel remains unchanged; The control module calculates the transmittance of the locking channel based on the signal intensity of the laser signal transmitted through the two channels. Specifically, the transmittance of the locking channel is equal to the ratio of the signal intensity of the laser signal transmitted through the locking channel to the signal intensity of the laser signal transmitted through the fourth channel. The control module includes a closed-loop controller and a boost module. The closed-loop controller generates a drive voltage control signal based on the calculated transmittance of the locked channel and a preset transmittance. The drive voltage control signal includes a first channel drive voltage control signal, a second channel drive voltage control signal, and a third channel drive voltage control signal. The boost module boosts the drive voltage control signal to the drive voltage range of the piezoelectric ceramic. The control module controls the driving voltage of the piezoelectric ceramics in the first, second, and third channels. Specifically, the closed-loop controller generates a step-by-step driving voltage control signal based on the preset initial driving voltage value and the driving voltage step value. The voltage range of the drive voltage control signal is 0~10V, and the voltage range of the boosted drive voltage control signal is 0~100V; It also includes a first fiber optic coupling lens and a second fiber optic coupling lens. The fourth channel transmits the transmitted laser signal to the control module through the first fiber optic coupling lens, and the locking channel transmits the transmitted laser signal to the control module through the second fiber optic coupling lens. The first, second, third, and fourth channels are parallel to each other and parallel to the direction of the laser signal emitted by the laser. The incident directions of the first, second, third, and fourth channels are opposite to the direction of the laser signal. It also includes a first plane mirror, a beam splitter prism, and a second plane mirror. The laser signal emitted by the laser is reflected by the first plane mirror to the beam splitter prism. The laser signal reflected by the beam splitter prism is incident on the fourth channel. The laser signal transmitted by the beam splitter prism is incident on the second plane mirror and then incident on the locking channel after reflection. The angle between the normal direction of the first plane mirror and the direction of the laser signal emitted by the laser is 45°. The beam splitter prism is perpendicular to the first plane mirror, and the second plane mirror is parallel to the beam splitter prism.

2. The four-channel Fabry-Perot frequency discrimination module closed-loop feedback control system according to claim 1, characterized in that, The laser emits a laser signal with a wavelength of 355nm.

3. The four-channel Fabry-Perot frequency discrimination module closed-loop feedback control system according to claim 1, characterized in that, The control module presets the transmittance of the locking channel to a range of 0.6 to 0.8.

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