CN114488199A - Semiconductor seed laser frequency locking system of high-spectral-resolution laser radar - Google Patents
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- 239000004065 semiconductor Substances 0.000 title claims abstract description 52
- 238000010521 absorption reaction Methods 0.000 claims abstract description 44
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- 238000012545 processing Methods 0.000 claims abstract description 14
- 238000000926 separation method Methods 0.000 claims abstract description 5
- 229910052740 iodine Inorganic materials 0.000 claims description 8
- 239000011630 iodine Substances 0.000 claims description 8
- ZCYVEMRRCGMTRW-UHFFFAOYSA-N 7553-56-2 Chemical compound [I] ZCYVEMRRCGMTRW-UHFFFAOYSA-N 0.000 claims description 7
- 238000000034 method Methods 0.000 claims description 7
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- 239000000443 aerosol Substances 0.000 description 7
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- QWVYNEUUYROOSZ-UHFFFAOYSA-N trioxido(oxo)vanadium;yttrium(3+) Chemical compound [Y+3].[O-][V]([O-])([O-])=O QWVYNEUUYROOSZ-UHFFFAOYSA-N 0.000 description 1
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- G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
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Abstract
The invention discloses a semiconductor seed laser frequency locking system of a high-spectral-resolution laser radar, which comprises a semiconductor seed laser, a laser amplification frequency doubling module, a frequency discrimination receiving system and a feedback control module, wherein the semiconductor seed laser is connected with the frequency discrimination receiving system through a frequency discrimination receiving module; the frequency discrimination receiving system comprises a beam splitter prism, an iodine molecule absorption cell frequency discrimination module, a detection channel photoelectric detector and a reference channel photoelectric detector; the feedback control module comprises a micro control unit and a control signal processing circuit. The system of the invention utilizes the frequency discrimination characteristic of one side of the iodine molecule absorption line, adopts a pure current tuning mode and divides a control signal into a bias value and a compensation value, thereby realizing the long-time locking of the laser frequency of the seed laser in the laser radar with high spectral resolution. The invention realizes the long-term locking of the frequency of the high-spectral-resolution laser radar light source on the premise of simple light path and circuit structure, thereby ensuring that the iodine molecule absorption cell spectrum frequency discriminator can carry out effective spectrum separation on the atmosphere echo signal.
Description
Technical Field
The invention belongs to the technical field of atmospheric aerosol remote sensing laser radars, and particularly relates to a semiconductor seed laser frequency locking system of a high-spectral-resolution laser radar.
Background
The acquisition of the accurate aerosol vertical profile has a crucial significance for atmospheric research. The high spectral resolution laser radar is a novel laser radar system which can accurately invert aerosol and cloud optical characteristic parameters without assuming the ratio of extinction coefficient to backscattering coefficient (also called laser radar ratio), introduces a spectrum frequency discriminator as a key characteristic device compared with a common backscattering laser radar, and can carry out spectrum separation on molecular components of atmosphere backscattering signals and aerosol components.
For example, chinese patent publication No. CN110441777A discloses an inversion method of aerosol vertical profile based on lidar, which combines the working principle of the mie scattering lidar and the radiation transmission process of laser in the atmosphere, establishes an inversion model of mass concentration and particle spectrum of the mie scattering lidar aerosol, and after calculating the optical thickness of the aerosol, can directly invert the near-ground mass concentration of the aerosol from the optical remote sensing image.
The seed injection mode is adopted as a good selection of a single-frequency laser light source by most of high-spectral-resolution laser radars, and is often matched with an iodine molecule absorption cell spectrum discriminator with a plurality of absorption spectral lines at a 532nm waveband. However, since the absorption spectrum line frequency of the iodine molecule is fixed, the laser frequency of the seed laser must be accurately locked, so that the laser frequency output by the radar system is ensured to be positioned in the center of the absorption spectrum line of the iodine molecule, and further, the spectrum separation ratio required by the atmospheric data inversion is ensured.
The selected iodine molecule absorption spectral line has the absorption characteristic close to a rectangle and the line width of 1GHz, so that relatively harsh frequency locking precision of a kHz order is not pursued in the actual working process of the 532nm high-spectral-resolution laser radar, and the adaptability of the laser frequency to the external environment is emphasized. Therefore, the conventional beat-demodulation frequency locking method is no longer suitable, the cost is high, the structure is relatively complex, and a new semiconductor seed laser frequency locking system needs to be designed.
Disclosure of Invention
The invention provides a semiconductor seed laser frequency locking system of a high-spectral-resolution laser radar, which can stably lock the laser frequency of the high-spectral-resolution laser radar for a long time.
A semiconductor seed laser frequency locking system of a high-spectral-resolution laser radar comprises a semiconductor seed laser, a laser amplification frequency doubling module, a frequency discrimination receiving system and a feedback control module;
the semiconductor seed laser is used for receiving a control signal to control the current flowing through the laser diode inside the semiconductor seed laser so as to generate single-frequency seed laser;
the laser amplification frequency doubling module is used for chopping single-frequency seed laser generated by the semiconductor seed laser into quasi-continuous light, then amplifying the power of the quasi-continuous light, performing frequency doubling and finally outputting the quasi-continuous laser;
the frequency discrimination receiving system comprises a beam splitter prism, an iodine molecule absorption cell frequency discrimination module, a detection channel photoelectric detector and a reference channel photoelectric detector; the beam splitter prism divides the quasi-continuous laser into two beams, one beam is transmitted through the iodine molecule absorption cell frequency discrimination module and then received by the detection channel photoelectric detector, and the other beam is directly received by the reference channel photoelectric detector; the detection channel photoelectric detector and the reference channel photoelectric detector have the same structure and are used for converting quasi-continuous laser into continuous voltage signals to be output;
and the feedback control module is used for realizing feedback control on the semiconductor seed laser according to the continuous voltage signal output of the detection channel photoelectric detector and the reference channel photoelectric detector.
Furthermore, the iodine molecule absorption spectrum line selected by the frequency discrimination receiving system is consistent with the iodine molecule absorption spectrum line of the high-spectral resolution laser radar playing a spectrum separation role.
Preferably, the temperature of the iodine vapor in the iodine molecule absorption cell and frequency discrimination module is controlled to be 25-40 ℃.
Furthermore, the iodine molecule absorption cell frequency discrimination module utilizes one side of the iodine molecule absorption line transmittance curve as a frequency discrimination interval.
Furthermore, the detection channel photoelectric detector and the reference channel photoelectric detector both comprise a photodiode, a transimpedance amplification circuit and a filtering amplification circuit.
Furthermore, the feedback control module comprises a micro control unit and a control signal processing circuit; the feedback control module realizes the specific process of feedback control on the semiconductor seed laser as follows:
s1, the micro control unit performs analog-to-digital conversion and collection on signals output by the photoelectric detector of the detection channel and the photoelectric detector of the reference channel, and obtains the transmissivity of the iodine molecule absorption cell frequency discrimination module to the current incident laser according to the ratio of the signals after smooth filtering;
s2, subtracting the transmittance of the current incident laser from the transmittance corresponding to the set laser frequency value to obtain an error signal, obtaining a required offset value and a compensation value by using proportional-integral-differential operation, and converting the offset value and the compensation value into an offset voltage signal and a compensation voltage signal to be output;
s3, the control signal processing circuit receives the bias voltage signal and the compensation voltage signal output by the micro control unit and then respectively amplifies the signals to different degrees; the amplified bias voltage signal has large-range tuning capacity and is used for following large-range and slowly-changed frequency deviation caused by environmental change, so that double frequency of the output frequency of the seed laser is ensured to be positioned at the locked iodine molecule absorption line; the compensation voltage signal has high tuning precision after being amplified and is used for compensating small-amplitude transient frequency errors so as to keep double times of the laser frequency of the semiconductor seed laser locked at a specific position on one side of a transmission spectrum of an iodine molecule absorption line;
and S4, adding the two amplified signals in a control signal processing circuit to obtain a control signal, and outputting the control signal to the semiconductor seed laser to form closed-loop feedback to realize frequency locking.
In step S1, the micro control unit performs analog-to-digital conversion on the signals output by the detection channel photodetector and the reference channel photodetector at a sampling rate of 10kHz and collects the signals.
In step S2, the micro control unit determines whether the current output compensation value is close to the full-scale output by monitoring the current output compensation value in real time, and accordingly fine-tunes the output of the offset value, and keeps the tuning range of the compensation value to include the frequency discrimination interval of the selected iodine absorption line, thereby preventing the compensation voltage signal from exceeding the appropriate control range and adapting to the environmental temperature change.
The micro control unit is communicated with the high-spectral-resolution laser radar upper computer through a serial port, so that remote operation of the whole set of locking process and monitoring during locking are realized, and the control period of the micro control unit is less than 1 ms.
Compared with the prior art, the invention has the following beneficial effects:
1. because the traditional frequency locking system has limited piezoelectric ceramic (PZT) tuning range for controlling the semiconductor seed laser in a feedback mode, and the semiconductor seed laser is extremely sensitive to temperature, the phenomenon that the laser frequency is unlocked due to the fact that the tuning range of the PZT is shifted when the environment temperature changes is difficult to avoid even the temperature is controlled with high precision is avoided. Aiming at the problem, on the basis of a temperature control system of a semiconductor seed laser, a pure current tuning mode, namely a large-range tuning mode, is adopted to lock the frequency and divide the current into two parts, one part is used for compensating the slowly-varying frequency drift caused by the environmental temperature, and the other part is specially used for locking the current frequency error, so that the high-spectral-resolution laser radar can normally work when being positioned in a severe environment to carry out long-time observation experiments.
2. The system of the invention does not need a modulation and demodulation link, directly locks the laser frequency to a specific value at one side of an iodine molecule absorption spectral line, so that the laser frequency finally output by the radar system is locked to a spectral line absorption peak, greatly simplifies the light path and the circuit structure on the premise of ensuring the normal work of the radar system, fully controls the cost, and promotes the engineering application and the domestic development of the high-spectral-resolution laser radar system.
Drawings
FIG. 1 is a schematic diagram of a semiconductor seed laser frequency locking system of a high spectral resolution lidar according to the present invention.
In the figure: the system comprises a 1-semiconductor seed laser, a 2-laser amplification frequency doubling module, a 3-frequency discrimination receiving system, a 31-beam splitter prism, a 32-iodine molecule absorption cell frequency discriminator, a 33-detection channel photoelectric detector, a 34-reference channel photoelectric detector, a 4-feedback control module, a 41-micro control unit and a 42-control signal processing circuit.
Detailed Description
The invention will be described in further detail below with reference to the drawings and examples, which are intended to facilitate the understanding of the invention without limiting it in any way.
As shown in fig. 1, a semiconductor seed laser frequency locking system of a high spectral resolution lidar includes a semiconductor seed laser 1, a laser amplification frequency doubling module 2, a frequency discrimination receiving system 3, and a feedback control module 4.
The frequency discrimination receiving system 3 comprises a beam splitter prism 31, an iodine molecule absorption cell frequency discriminator 32, a detection channel photoelectric detector 33 and a reference channel photoelectric detector 34; the feedback control module 4 comprises a micro control unit 41 and a control signal processing circuit 42.
Specifically, the semiconductor seed laser 1 is composed of a 1064nm Distributed Bragg Reflector (DBR) laser and a semiconductor laser driver, the semiconductor laser driver receives an external control voltage signal, linearly converts the external control voltage signal into a drive current, and provides the drive current for the DBR laser to realize laser output and tuning, and the semiconductor laser driver utilizes a thermistor probe and a semiconductor refrigerator which are arranged in the DBR laser to control the temperature of the DBR laser; the 1064nm laser is input into the laser amplification frequency doubling module 2 through an optical fiber, chopped into quasi-continuous light with the repetition frequency of 50kHz, amplified by a laser crystal, and frequency doubled by a frequency doubling crystal to obtain 532nm quasi-continuous light. The beam splitter prism 31 is a 5:5 beam splitter prism, which divides the 532nm quasi-continuous light into two beams, wherein one beam is transmitted through the iodine molecule absorption cell frequency discriminator 32 and is used as a detection beam to be received by the detection channel photoelectric detector 33, the other beam is used as a reference beam to be received by the reference channel photoelectric detector 34, and due to the frequency discrimination characteristic of iodine molecule absorption lines, the error of laser frequency can be reflected on the transmissivity of the iodine molecule absorption cell frequency discriminator 32 to the detection beam; the detection channel photoelectric detector 33 and the reference channel photoelectric detector 34 are respectively used for receiving the detection light beam and the reference light beam by a photodiode, a transimpedance amplification circuit and a filtering amplification circuit, converting quasi-continuous optical signals into continuous voltage signals, and acquiring the voltage signals after analog-to-digital conversion processing of the micro control unit 41; the micro control unit 41 not only sets a bias value according to the selected iodine molecule absorption line, but also compares the acquired detection signal with a reference signal to obtain the transmissivity of the iodine molecule absorption cell discriminator 32 to the detection light beam, and subtracts the transmissivity corresponding to the set frequency value to obtain an error signal, and after carrying out proportional-integral-differential operation on the error signal, the most initial feedback control quantity, namely a compensation value for the frequency error is obtained; the offset value and the compensation value are subjected to digital-to-analog conversion and then input to the control signal processing circuit 42, and a final control signal obtained after the processing is output to the semiconductor seed laser 1.
In the present invention, the lock point frequency set by the micro control unit 41 corresponds to a specific position of the iodine molecule absorption line where one side has a frequency discrimination slope portion, and the temperature of the iodine vapor inside the iodine molecule absorption cell discriminator 32 is controlled to a temperature between 25 ℃ and 40 ℃, so that the iodine molecule absorption cell discriminator 32 has both good frequency discrimination sensitivity and a sufficiently large frequency discrimination interval for the probe beam.
In the control signal processing circuit 42, the bias signal and the compensation signal are respectively amplified to the tuning precision of MHz and kHz magnitude by the amplifying circuit, and then the bias signal and the compensation signal are added by the adding circuit to obtain a final control signal; the tuning range of the bias value component of the MHz tuning precision in the control signal is large, and the tunable semiconductor seed laser 1 enables the frequency of 1064nm laser output by the tunable semiconductor seed laser to be twice of the selected iodine molecule absorption line, so that the tuning range of the compensation value component of the kHz tuning precision in the control signal can include the frequency discrimination curve part of the iodine molecule absorption line, and the compensation value component can realize the compensation of the current laser frequency error;
although the temperature of the DBR laser is well controlled, the semiconductor laser frequency is very sensitive to the temperature, and in addition, the thermistor probe inside the DBR laser and the laser diode have a slight temperature difference, which causes the change of the ambient temperature under the condition to have a great influence on the laser frequency. Therefore, after the laser frequency is locked, the micro control unit 41 determines whether the laser frequency is affected by the ambient temperature according to whether the current compensation value is too high or too low, so as to correspondingly adjust the offset value, and further adapt to the change of the ambient temperature.
In this embodiment, the semiconductor seed laser 1 is assembled by using a Distributed Bragg Reflector (DBR) laser of DBR1064PN of Thorlabs, usa and an L0116 semiconductor laser driver of shenzhen micro-optical ocean electronics ltd.
The laser amplification frequency doubling module 2 adopts a Z-1064-L-T-D0.3-T-A-K acousto-optic modulator of Shanghai Qingjin photoelectricity to chop the laser into quasi-continuous light with repetition frequency of 50kHz, the laser crystal adopts yttrium vanadate crystal, the frequency doubling crystal adopts KTP crystal, and finally 532nm quasi-continuous light with 500 muW is output.
The beam splitter 31 may optionally be a 5:5 splitting ratio 532nm beam splitter such as BS004 available from Thorlabs, USA.
The iodine cell of the iodine molecule absorption cell discriminator 32 adopts a saturated iodine molecule absorption cell, the length is 5cm, the internal iodine vapor is controlled at 35 ℃, and the wavelength of an iodine molecule absorption spectral line selected during frequency discrimination is 532.26 nm. In the above-mentioned detection channel photodetector 33 and the reference channel photodetector 34, the photodiode can be any photodiode responding to the 532nm band, and the transimpedance amplifier circuit and the filter amplifier circuit can be implemented by common operational amplifier chips, such as AD8622 of Analog Devices in the united states.
The micro control unit 41 adopts STM32F103ZET6 from STMicroelectronics, Italy.
The amplification and addition circuitry of the control signal processing circuit 42 described above is implemented using a Texas Instruments LM 358B.
The invention has been applied to a 532nm high spectral resolution atmospheric lidar instrument.
The embodiments described above are intended to illustrate the technical solutions and advantages of the present invention, and it should be understood that the above-mentioned embodiments are only specific embodiments of the present invention, and are not intended to limit the present invention, and any modifications, additions and equivalents made within the scope of the principles of the present invention should be included in the scope of the present invention.
Claims (9)
1. A semiconductor seed laser frequency locking system of a high-spectral-resolution laser radar is characterized by comprising a semiconductor seed laser (1), a laser amplification frequency doubling module (2), a frequency discrimination receiving system (3) and a feedback control module (4);
the semiconductor seed laser (1) is used for receiving a control signal to control the current flowing through a laser diode inside the semiconductor seed laser to generate single-frequency seed laser;
the laser amplification frequency doubling module (2) is used for chopping single-frequency seed laser generated by the semiconductor seed laser (1) into quasi-continuous light, then amplifying the power of the quasi-continuous light, doubling the frequency and finally outputting the quasi-continuous laser;
the frequency discrimination receiving system (3) comprises a beam splitter prism (31), an iodine molecule absorption cell frequency discrimination module (32), a detection channel photoelectric detector (33) and a reference channel photoelectric detector (34); the beam splitter prism (31) splits the quasi-continuous laser into two beams, one beam is transmitted through the iodine molecular absorption cell frequency discrimination module (32) and then received by the detection channel photoelectric detector (33), and the other beam is directly received by the reference channel photoelectric detector (34); the detection channel photoelectric detector (33) and the reference channel photoelectric detector (34) have the same structure and are used for converting quasi-continuous laser into continuous voltage signals to be output;
and the feedback control module (4) is used for realizing feedback control on the semiconductor seed laser (1) according to continuous voltage signal output of the detection channel photoelectric detector (33) and the reference channel photoelectric detector (34).
2. The semiconductor seed laser frequency locking system of the high spectral resolution lidar according to claim 1, wherein the iodine molecule absorption line selected by the frequency discrimination receiving system (3) is consistent with an iodine molecule absorption line of the high spectral resolution lidar for spectral separation.
3. The semiconductor seed laser frequency locking system of high spectral resolution lidar according to claim 1, wherein the temperature of the iodine vapor inside the iodine molecule absorption cell discriminator module (32) is controlled to be 25-40 ℃.
4. The semiconductor seed laser frequency locking system of high spectral resolution lidar of claim 1, wherein the iodine molecule absorption cell discriminator module (32) utilizes one side of an iodine molecule absorption line transmittance curve as a discriminator interval.
5. The semiconductor seed laser frequency locking system of a high spectral resolution lidar according to claim 1, wherein the detection channel photodetector (33) and the reference channel photodetector (34) each comprise a photodiode, a transimpedance amplifier circuit, and a filter amplifier circuit.
6. The semiconductor seed laser frequency locking system of a high spectral resolution lidar according to claim 1, wherein the feedback control module (4) comprises a micro control unit (41) and a control signal processing circuit (42); the feedback control module (4) realizes the specific process of feedback control on the semiconductor seed laser (1) as follows:
s1, the micro control unit (41) performs analog-to-digital conversion and collection on signals output by the detection channel photoelectric detector (33) and the reference channel photoelectric detector (34), and obtains the transmissivity of the iodine molecule absorption pool frequency discrimination module (32) to the current incident laser according to the ratio of the signals after smooth filtering;
s2, subtracting the transmittance of the current incident laser from the transmittance corresponding to the set laser frequency value to obtain an error signal, obtaining a required offset value and a compensation value by using proportional-integral-differential operation, and converting the offset value and the compensation value into an offset voltage signal and a compensation voltage signal to be output;
s3, the control signal processing circuit (42) receives the bias voltage signal and the compensation voltage signal output by the micro control unit (41) and then respectively amplifies the bias voltage signal and the compensation voltage signal to different degrees; the amplified bias voltage signal has large-range tuning capability and is used for following large-range and slowly-changed frequency deviation caused by environmental change, so that the double frequency of the output frequency of the seed laser is ensured to be positioned at the locked iodine molecule absorption line; the compensation voltage signal has high tuning precision after being amplified and is used for compensating small-amplitude transient frequency errors so as to keep the double locking of the laser frequency of the semiconductor seed laser at a specific position on one side of the transmission spectrum of the iodine molecule absorption line;
and S4, adding the two amplified signals in the control signal processing circuit (42) to obtain a control signal, and outputting the control signal to the semiconductor seed laser (1) to form closed-loop feedback to realize frequency locking.
7. The semiconductor seed laser frequency locking system of high spectral resolution lidar according to claim 6, wherein in step S1, the micro control unit (41) performs analog-to-digital conversion and collection on the signals output by the detection channel photodetector (33) and the reference channel photodetector (34) at a sampling rate of 10 kHz.
8. The semiconductor seed laser frequency locking system of the high spectral resolution lidar of claim 6, wherein in step S2, the micro control unit (41) determines whether the current output compensation value is close to full scale output by monitoring the current output compensation value in real time and adjusts the output of the offset value accordingly, keeping the tuning range of the compensation value to include the frequency discrimination interval of the selected iodine absorption line, thereby avoiding the compensation voltage signal from exceeding a proper control range and adapting to the environmental temperature change.
9. The semiconductor seed laser frequency locking system of the high spectral resolution lidar according to claim 6, wherein the micro control unit (41) communicates with the high spectral resolution lidar host computer through a serial port to realize remote operation of the whole locking process and monitoring during locking, and a control period of the micro control unit (41) is less than 1 ms.
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| JPH0712509A (en) * | 1993-03-26 | 1995-01-17 | Agency Of Ind Science & Technol | High-accuracy interference distance meter |
| CN103308926A (en) * | 2013-06-18 | 2013-09-18 | 浙江大学 | Laser radar set with high spectral resolution |
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Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH0712509A (en) * | 1993-03-26 | 1995-01-17 | Agency Of Ind Science & Technol | High-accuracy interference distance meter |
| CN103308926A (en) * | 2013-06-18 | 2013-09-18 | 浙江大学 | Laser radar set with high spectral resolution |
Non-Patent Citations (1)
| Title |
|---|
| 闫庆等: "基于分子吸收的脉冲激光锁频方法研究", 光学学报, vol. 39, no. 10, pages 2 * |
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