Laser radar with wavelength locking function

Abstract

A laser radar according to the present disclosure is provided with: a laser light source (1) that oscillates laser light; an optical branching device (2) that branches laser light into two systems; a modulator (3) that phase-modulates laser light sent from the optical branching device (2); a gas cell (4); and a wavelength control device (7) for controlling the wavelength of the laser light source (1), the laser light source (1) being capable of temperature control, and a target spectrum detection device (6) for performing temperature scanning control and constant temperature control of the laser light source (1).

Description

Technical Field

[0001] The disclosed technology relates to a laser radar with a wavelength locking function. Background Art

[0002] The wavelength locking function is used, for example, in a device that performs various measurements by irradiating laser light. An example of a device that performs various measurements by irradiating laser light is a laser radar (LiDAR: Light Detection and Ranging or Laser Imaging Detection and Ranging).

[0003] For example, Non-Patent Document 1 discloses a technique for simultaneously measuring water vapor density and wind speed using a coherent differential absorption LiDAR (DIAL) having a wavelength of 1.53 [μm].

[0004] The differential absorption laser radar of Non-Patent Document 1 has an output wavelength (λ ON ) and a laser light source that outputs a laser with a wavelength (λ OFF ) is a laser light source that emits laser light of the same wavelength as the output wavelength (λ ON )'s laser light source uses a wavelength locking circuit (Wavelength Locking Circuit) that fixes the wavelength to a certain target value.

[0005] The differential absorption laser radar of non-patent document 1 uses an HCN gas cell for the purpose of obtaining information on the wavelength that serves as an absolute reference. The differential absorption laser radar of non-patent document 1 irradiates the gas (HCN) in the gas cell with laser light and generates a feedback signal for wavelength locking based on the absorption line spectrum information obtained from the transmitted light.

[0006] Prior art literature

[0007] Non-patent literature

[0008] Non-patent document 1: M. IMAKI et al., Optics Express 28(18)27078-27096, August 31, 2020. Summary of the invention

[0009] Problem that the invention aims to solve

[0010] When observing the absorption line spectrum of HCN gas, there are about 50 absorption line peaks (hereinafter referred to as "absorption line spectrum peaks") in the wavelength range of 1525 [nm] to 1565 [nm] (refer to Figure 5 ).

[0011] A laser radar that simultaneously measures water vapor density and wind speed needs to correctly select an absorption line of a specific wavelength in an absorption line spectrum peak, such as an absorption line of 1531.276 [nm], for the wavelength of the laser, and generate a feedback signal for wavelength locking.

[0012] The following situation may occur in a laser radar that simultaneously measures water vapor density and wind speed: when the laser oscillator is in an unstable state, such as just after the power is turned on, although the air chamber is used, the wrong absorption line in the absorption line spectrum peak is selected, and the wavelength of the laser is locked to an unintended wavelength.

[0013] Means used to solve problems

[0014] The laser radar of the disclosed technology includes a laser light source, which oscillates laser; an optical branching device, which branches the laser to two systems; a modulator, which phase-modulates the laser sent from the optical branching device; an air chamber; a light detector, which detects the transmitted laser after passing through the air chamber and converts it into an electrical signal; and a wavelength control device, which controls the wavelength of the laser light source. The laser light source can be temperature controlled. The laser radar also includes a target spectrum detection device, which performs temperature scanning control and constant temperature control of the laser light source.

[0015] Effects of the Invention

[0016] Since the laser radar with a wavelength locking function of the disclosed technology has the above-mentioned structure, it is possible to prevent the following situation from occurring: the wavelength of the laser is locked to an unintended wavelength due to the selection of an erroneous absorption line in the absorption line spectrum peak. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a block diagram showing the functional structure of a laser radar with a wavelength locking function according to embodiment 1.

[0018] Figure 2 This is a flowchart showing the processing steps performed by the laser radar with wavelength locking function in embodiment 1.

[0019] Figure 3 This is a block diagram showing the functional structure of a laser radar with a wavelength locking function according to embodiment 2.

[0020] Figure 4 This is a flowchart showing the detailed steps of the main processing (ST50) performed by the laser radar with a wavelength locking function according to the second embodiment.

[0021] Figure 5 This is a graph showing the absorption line spectrum of HCN gas.

[0022] Figure 6 Graphs showing wavelength characteristics of a DFB laser (left graph: relative to temperature, right graph: relative to injection current).

[0023] Figure 7 This is an explanatory diagram for explaining a feedback signal used in a current control loop of a wavelength locking circuit. DETAILED DESCRIPTION

[0024] 《About the specifications required in the disclosed technology》

[0025] The wavelength (λ) absorbed by molecules in the atmosphere among the system parameters disclosed in Non-Patent Document 1 ON ) is 1531.3814 [nm], the wavelength that is not absorbed by molecules in the atmosphere (λ OFF ) is 1531.5537 [nm]. That is, the accuracy of the wavelength in the specification required by the disclosed technology is on the order of 0.001 [nm]. This is 1 / 100 compared to the accuracy of the wavelength required in the technical field of so-called gas sensing, specifically, on the order of 0.1 [nm].

[0026] In addition, a Michelson interferometer is generally cited as a device for achieving wavelength measurement of the order of 0.001 [nm]. However, a device based on the Michelson interferometer inevitably becomes large in size due to its principle, and therefore, it is not discussed in this specification.

[0027] Implementation method 1.

[0028] Figure 1 1 is a block diagram showing the functional structure of a laser radar with a wavelength locking function according to Embodiment 1. Figure 1 As shown, the laser radar with wavelength locking function of embodiment 1 includes a laser light source 1, an optical branching device 2, a modulator 3, a gas chamber 4, a light detector 5, a target spectrum detection device 6 and a wavelength control device 7.

[0029] 《Laser Light Source 1》

[0030] The laser light source 1 can be implemented by a DFB laser (DFB: Distributed Feedback) covering a wavelength region of 1.53 [μm]. Generally, the wavelength stability of a DFB laser is very high, oscillates in a single mode, and has a very narrow line width. Therefore, a DFB laser is suitable as a light source for a laser radar with a wavelength locking function. However, the oscillation wavelength of a DFB laser also changes depending on the injected current (hereinafter referred to as "injected current") and the ambient temperature.

[0031] The laser light source 1 of the disclosed technology can be temperature-controlled by an external signal. Specifically, the laser light source 1 of the disclosed technology can be realized by, for example, a DFB laser having a TEC (Thermo-Electric Cooling), that is, a micro-Peltier element, and having a TEC terminal.

[0032] Figure 6 Graphs showing the wavelength characteristics of a DFB laser (left graph: relative to temperature, right graph: relative to injection current). Figure 6 As shown in the left graph, as the temperature rises, the wavelength of the laser light emitted by the DFB laser becomes longer. Figure 6 As shown in the right graph, when the injection current increases, the wavelength of the laser light radiated by the DFB laser becomes longer.

[0033] Laser light generated by the laser light source 1 is sent to the light branching device 2 .

[0034] Light Branching Device 2

[0035] The optical branching device 2 is a component that branches the incoming laser light into two systems.

[0036] One of the laser beams branched by the light branching device 2 is sent to the modulator 3 .

[0037] Modulator 3

[0038] The modulator 3 is a component that performs phase modulation on the laser beam sent. The modulator 3 starts phase modulation when a modulation start signal is input. If no modulation start signal is input, the modulator 3 does not process the laser beam sent and outputs it as it is.

[0039] Gas Chamber 4

[0040] As described above, the gas cell 4 is a component for obtaining information of a wavelength serving as an absolute reference. Specifically, the gas cell 4 of the disclosed technology uses a hydrogen cyanide (HCN) gas as a medium.

[0041] When the measurement target is water vapor density, the absorption line of HCN is used instead of the absorption line of H2O because the absorption rate of H2O is small. If the gas cell 4 using water vapor as a medium is used for realization, the gas cell 4 has the same scale as the observation field, which is unrealistic.

[0042] Figure 5 is a graph showing the absorption line spectrum of HCN gas. Figure 5 In the graph shown, the vertical axis represents the normalized transmittance, and the horizontal axis represents the wavelength. Figure 5 As shown, when the absorption line spectrum of the HCN gas is observed, there are absorption line spectrum peaks showing about 50 absorption lines in the wavelength range of 1525 [nm] to 1565 [nm].

[0043] The laser light that has been transmitted through the gas cell 4 and in which a specific spectrum is absorbed (hereinafter referred to as “transmitted laser light”) is sent to the photodetector 5 .

[0044] Light Detector 5

[0045] The photodetector 5 is a component that detects the transmitted laser light and converts it into an electrical signal. The electrical signal generated by the photodetector 5 is sent to the target spectrum detection device 6 and the wavelength control device 7.

[0046] 《Target spectrum detection device 6》

[0047] The target spectrum detection device 6 is a structural element unique to the disclosed technology that does not exist in the conventional laser radar device. The target spectrum detection device 6 generally implements two temperature controls. The first temperature control is the control of scanning the temperature of the laser light source 1 (hereinafter referred to as "temperature scanning control"). The second temperature control is the control of keeping the temperature of the laser light source 1 constant (hereinafter referred to as "constant temperature control").

[0048] The temperature scan performed in the first temperature control of the target spectrum detection device 6 is specifically as follows: after the power is turned on, the TEC of the laser light source 1 is temporarily increased from 0 [°C] to 60 [°C] at a speed of 6 to 60 [°C / min], and then the TEC of the laser light source 1 is decreased from 60 [°C] to 0 [°C] at a speed of 6 to 60 [°C / min].

[0049] The two temperature controls performed by the target spectrum detection device 6 are realized by inputting a control signal to the TEC terminal of the laser light source 1. Figure 1 In the block diagram shown, the loop consisting of laser light source 1 → light branching device 2 → modulator 3 → gas cell 4 → light detector 5 → target spectrum detection device 6 → laser light source 1 represents a temperature control loop.

[0050] The details of the processing steps performed by the target spectrum detection device 6 will become clear from the following description.

[0051] 《Wavelength Control Device 7》

[0052] The wavelength control device 7 is a component that controls the wavelength of the laser light source 1. Specifically, the wavelength control device 7 controls the wavelength of the laser light source 1 by controlling the injection current injected into the laser light source 1. Figure 1 In the block diagram shown, a loop consisting of laser light source 1 →light branching device 2 →modulator 3 →gas cell 4 →photodetector 5 →wavelength control device 7 →laser light source 1 represents a current control loop.

[0053] The temperature control loop described above functions as a portion for performing rough adjustment of the wavelength, whereas the current control loop functions as a portion for performing fine adjustment of the wavelength.

[0054] "Processing contents of laser radar with wavelength locking function according to implementation mode 1"

[0055] Figure 2 This is a flowchart showing the processing steps performed by the laser radar with wavelength locking function in embodiment 1.

[0056] like Figure 2 As shown, the processing steps implemented by the laser radar with wavelength locking function of embodiment 1 include preparation processing (ST10) and main processing (ST50). The action implemented by the preparation processing (ST10) is to stabilize the output of the laser light source 1, so it is similar to a warm-up operation.

[0057] The preparation process (ST10) includes a process of scanning the temperature (ST11), a process of detecting the wavelength and the temperature (ST12), and a process of setting the temperature (ST13). In the preparation process (ST10), the wavelength control device 7 does not control the current control loop. The injection current injected into the laser light source 1 is set to a predetermined value, specifically, a value of 90 [mA] to 280 [mA] that serves as a reference. The method of determining the injection current amount that serves as the reference (hereinafter referred to as the "reference injection current amount") will become clear from the description to be described later.

[0058] The main process (ST50) includes at least a wavelength locking control process (ST55). In the wavelength locking control process (ST55), the wavelength control device 7 first controls the current control loop.

[0059] The temperature scanning process (ST11) is a process step performed by the target spectrum detection device 6. In the temperature scanning process (ST11), the target spectrum detection device 6 performs the temperature scanning control of the laser light source 1 described above. As described above, as the temperature rises, the wavelength of the laser irradiated by the DFB laser becomes longer. More specifically, as Figure 6 As shown in the left graph, when the temperature (T) rises by 10[°C], the wavelength of the DFB laser increases by about 1[nm].

[0060] As mentioned above, Figure 5 This is a graph showing the absorption line spectrum of HCN gas. Figure 5 The absorption line spectrum shown is divided into the distribution on the left side of the diagram (in Figure 5 The distribution from 1525 [nm] to 1542 [nm] recorded as "R Branch" in the figure) and the distribution on the right side of the graph (in Figure 5 In the R Branch, there are absorption line peaks numbered 0 to 26. In the P Branch, there are absorption line peaks numbered 1 to 27.

[0061] The absorption line spectrum peak marked with number 18 in the R Branch (hereinafter referred to as the "18th absorption line spectrum peak") is the peak of 1531.276 [nm], the wavelength to be tuned this time. In addition, the absorption line spectrum peak marked with number 9 in the R Branch (hereinafter referred to as the "9th absorption line spectrum peak") is the peak with the lowest transmittance in the whole, and is a peak with a wavelength of about 1536 [nm].

[0062] In the process of scanning the temperature (ST11), the target spectrum detection device 6 scans the wavelength of the laser irradiated by the laser light source 1 within a width including the wavelength of the 9th absorption line spectrum peak and the wavelength of the 18th absorption line spectrum peak. When the temperature (T) that can be temperature scanned is considered to be 0 [℃] to 60 [℃], the wavelength change width of the laser light source 1 is about 6 [nm]. If calculated in reverse from this, the reference injection current amount injected into the laser light source 1 can be determined to be approximately 1531 [nm] when the temperature (T) of the laser light source 1 is 0 [℃]. By determining the reference injection current amount in this way, when the temperature (T) of the laser light source 1 is 60 [℃], the wavelength of the laser becomes approximately 1537 [nm]. The width of the wavelength scanned based on this temperature scan also includes the wavelength of the 8th absorption line spectrum peak whose wavelength is longer than the 9th absorption line spectrum peak.

[0063] The wavelength and temperature detection process (ST12) is a processing step implemented by the target spectrum detection device 6. In the wavelength and temperature detection process (ST12), the target spectrum detection device 6 performs temperature scanning control of the laser light source 1 and simultaneously detects the wavelength and temperature of the laser light source 1. However, the detection of the wavelength of the laser light source 1 implemented in the wavelength and temperature detection process (ST12) is based on the information of the absorption line spectrum of the HCN gas.

[0064] The laser radar with wavelength locking function of the disclosed technology is stored in the form of a data table, for example Figure 5 By retaining this information, the laser radar with wavelength locking function of the disclosed technology can monitor the intensity of light transmitted through the gas chamber 4 (hereinafter referred to as "transmitted light intensity"), determine the peak with the lowest transmittance to be the 9th absorption line spectrum peak, and determine the 18th absorption line spectrum peak obtained by counting 9 in the direction of shorter wavelength from this point to be the peak of the wavelength to be tuned this time, that is, 1531.276 [nm].

[0065] The temperature setting process (ST13) is a process step implemented by the target spectrum detection device 6. In the temperature setting process (ST13), the target spectrum detection device 6 sets the temperature of the laser light source 1 to a temperature corresponding to the wavelength of the 18th absorption line spectrum peak obtained in the wavelength and temperature detection process (ST12). In addition, in this specification, the wavelength to be tuned is set to the wavelength of the 18th absorption line spectrum peak (1531.276 [nm]), but the disclosed technology is not limited to this. The wavelength to be tuned can be appropriately determined according to the purpose of use of the laser radar.

[0066] The target spectrum detection device 6 implements constant temperature control on the laser light source 1 , and after the temperature of the laser light source 1 is stabilized at a set temperature, a “control start signal” that serves as a trigger for starting current control is sent to the wavelength control device 7 .

[0067] The wavelength locking control process (ST55) is a process step performed by the wavelength control device 7. The wavelength control device 7, which receives the control start signal, starts the current control of the current control loop. The wavelength control device 7 sends a "modulation start signal" as a trigger to the modulator 3 at the same time as the start of the current control of the current control loop.

[0068] Figure 7 This is an explanatory diagram for explaining the feedback signal used in the current control loop of the wavelength locking circuit. When the laser is phase modulated by the modulator 3, sideband waves appear on the positive and negative sides of the center frequency of the laser. The phases of the sideband waves appearing on the positive and negative sides differ by 180 degrees. By taking the correlation between the laser after phase modulation and the transmitted light after passing through the gas cell 4, we can obtain Figure 7The feedback signal shown in the lower graph. In the wavelength locking control process (ST55), the wavelength control device 7 performs current control of the current control loop based on the feedback signal.

[0069] 《Modification of wavelength detection by target spectrum detection device 6》

[0070] In the wavelength and temperature detection process (ST12), the target spectrum detection device 6 finds the 18th absorption line spectrum peak by counting 9 from the 9th absorption line spectrum peak for the peak with the lowest transmittance. However, if the transmittance of the laser light transmitted through the gas cell 4 is directly obtained, the target spectrum detection device 6 can also directly obtain the wavelength corresponding to which absorption line spectrum peak when scanning the wavelength based on the transmittance.

[0071] Since the feedback signal is a signal obtained by taking the correlation between the laser with sideband waves and the transmitted light after passing through the gas chamber 4, the magnitude of the feedback signal in the wavelength scan based on the temperature scan, for example, Figure 7 The difference between the “maximum value” and the “minimum value” described in the graph on the lower layer can be used to estimate the magnitude of the absorption line spectrum peak.

[0072] In the wavelength and temperature detection process (ST12), the target spectrum detection device 6 may find the 18th absorption line spectrum peak by estimating the size of the absorption line spectrum peak based on the size of the feedback signal instead of counting 9 from the 9th absorption line spectrum peak to find the 18th absorption line spectrum peak for the peak with the lowest transmittance.

[0073] When wavelength detection is performed using a feedback signal, the modulator 3 needs to phase modulate the laser light even in the preparation process (ST10). When this modification is adopted, the modulator 3 always performs phase modulation, so a "modulation start signal" as a trigger is not required.

[0074] As described above, since the laser radar of Embodiment 1 has the above-mentioned structure, it is possible to prevent the following situation from occurring: the wavelength of the laser light is locked to an unintended wavelength due to selection of an erroneous absorption line in the absorption line spectrum peak.

[0075] Implementation method 2.

[0076] The laser radar with wavelength locking function of embodiment 2 is a modified example of the laser radar of the disclosed technology. More specifically, the laser radar with wavelength locking function of embodiment 2 is a laser radar of a configuration scheme that concretizes the main processing (ST50) of the disclosed technology. Unless otherwise specified, in embodiment 2, the same reference numerals as those used in embodiment 1 are used. In addition, in embodiment 2, the descriptions repeated in embodiment 1 are appropriately omitted.

[0077] Figure 3 : is a block diagram showing the functional structure of a laser radar with a wavelength locking function according to Embodiment 2. Figure 3 As shown, the laser radar with wavelength locking function of embodiment 2 has the structural elements shown in embodiment 1 (refer to Figure 1 ), it also includes a fixed wavelength shift device 9, a second laser light source 10, an optical switch 11, a second optical branching device 12, a pulse modulator 13, an optical amplifier 14, a transceiver optical system 15, a light receiver 16, an AD converter 17, a signal processing device 18, a wavelength control abnormality judgment device 19 and a wavelength control resetting device 20.

[0078] 《Fixed wavelength shift device 9》

[0079] The fixed wavelength shifting device 9 is a structural element that shifts the wavelength of the input light by a predetermined fixed wavelength amount. More specifically, the fixed wavelength shifting device 9 shifts the wavelength of the laser light sent from the optical branching device 2 by a fixed wavelength amount and converts it into a wavelength (λ ON ) lasers of the same wavelength.

[0080] The wavelength of the laser light oscillated by the laser light source 1 is tuned to the wavelength of the 18th absorption line spectrum peak, which is 1531.276 [nm]. On the other hand, the wavelength (λ ON ) is, for example, 1531.3814 [nm] described in Non-Patent Document 1. In this case, the wavelength shift amount performed by the fixed wavelength shifting device 9 is 0.1054 [nm].

[0081] 《Second laser light source 10》

[0082] The second laser light source 10 is used to oscillate a wavelength (λ OFF )Structural elements of lasers with the same wavelength.

[0083] The wavelength (λ) of the laser beam oscillated by the second laser light source 10 is OFF ) For example, it is 1531.5537 [nm] recorded in non-patent document 1.

[0084] The laser light oscillated by the second laser light source 10 is sent to the optical switch 11 .

[0085] Light Switch 11

[0086] The optical switch 11 is a structural element that switches multiple optical paths according to an input optical switch control signal and selectively outputs light. More specifically, the optical switch 11 selectively outputs wavelengths (λ) absorbed by molecules in the atmosphere by switching paths. ON) of laser light and a wavelength (λ OFF ) of the laser.

[0087] The laser light selectively output by the optical switch 11 is sent to the second optical branching device 12 .

[0088] <<Second optical branching device 12>>

[0089] The second optical branching device 12 is a structural element that splits the input light at a predetermined power ratio and outputs it. More specifically, the second optical branching device 12 splits the laser light sent from the optical switch 11 into a transmission laser light and a reference laser light at a predetermined power ratio and outputs them. Generally, the reference laser light may have a smaller power than the transmission laser light.

[0090] The transmission laser light is sent to the pulse modulator 13 , and the reference laser light is sent to the photoreceiver 16 .

[0091] Pulse Modulator 13

[0092] The pulse modulator 13 is a component that pulses the input transmission laser light at a timing based on a trigger signal from the signal processing device 18 and modulates the optical frequency of the transmission laser light to a preset value.

[0093] The laser light pulsed and modulated by the pulse modulator 13 is sent to the optical amplifier 14 .

[0094] Optical Amplifier 14

[0095] The optical amplifier 14 is a component that amplifies the laser light sent from the pulse modulator 13 and outputs the amplified laser light.

[0096] The laser light amplified by the optical amplifier 14 is sent to the transmitting and receiving optical system 15 .

[0097] 《Transmitting and receiving optical system 15》

[0098] The transceiver optical system 15 is a structural element having both a transmission optical system for transmitting light and a reception optical system for receiving light. The transmission optical system in the transceiver optical system 15 irradiates the atmosphere with laser light sent from the optical amplifier 14. The light scattered and reflected by the aerosol in the atmosphere is received by the reception optical system in the transceiver optical system 15 and sent to the light receiver 16.

[0099] 《Light Receiver 16》

[0100] The optical receiver 16 is a component that combines the reference laser light sent from the second optical branching device 12 and the reflected light sent from the transmitting and receiving optical system 15 and converts the combined light into an analog electric signal.

[0101] The analog electric signal generated by the light receiver 16 is sent to the AD converter 17 .

[0102] AD Converter 17

[0103] The AD converter 17 is a component that converts an analog electric signal sent from the light receiver 16 into a digital electric signal. The timing of the digital conversion by the AD converter 17, that is, the sampling, follows a trigger signal from the signal processing device 18.

[0104] The digital electric signal generated by the AD converter 17 is often referred to as a beat signal.

[0105] 《Signal Processing Device 18》

[0106] The signal processing device 18 is a structural element that performs various signal processing. The signal processing device 18 is composed of, for example, a signal processing circuit. The main processing performed by the signal processing device 18 is the detection of the frequency of the beat signal (hereinafter referred to as the "beat signal frequency") and the intensity of the beat signal (hereinafter referred to as the "beat signal intensity"). The signal processing device 18 also calculates the wind speed based on the beat signal frequency and calculates the molecular weight of the observed object based on the beat signal intensity (hereinafter referred to as the "observed object molecular weight"). In addition, the wind speed calculated based on the beat signal frequency is strictly speaking the wind speed of the laser irradiation direction component.

[0107] The signal processing device 18 also generates a trigger signal for the pulse modulator 13 and a trigger signal for the AD converter 17 .

[0108] The signal processing device 18 receives the "stable control signal" which is a signal from the wavelength control device 7 and starts to operate. In the wavelength control device 7, when the magnitude of the feedback signal is less than a predetermined threshold value for a period of more than a certain fixed period, the wavelength control device 7 can send the "stable control signal" to the signal processing device 18.

[0109] In addition, when the signal processing device 18 receives the reset signal from the wavelength control reset device 20, it stops the operation and returns the state to the initial state.

[0110] The details of the processing performed by the signal processing device 18 will become clear from the following description.

[0111] The beat signal intensity and the observed object molecular weight calculated by the signal processing device 18 are sent to the wavelength control abnormality determination device 19 .

[0112] 《Wavelength control abnormality determination device 19》

[0113] The wavelength control abnormality determination device 19 is a component that monitors the wavelength control performed by the wavelength control device 7 in a manner that no abnormality occurs. In other words, the wavelength control abnormality determination device 19 performs abnormality determination of the wavelength control performed by the wavelength control device 7. The abnormality determination performed by the wavelength control abnormality determination device 19 is performed based on the beat signal intensity sent from the signal processing device 18 and the observed object molecular weight. Specifically, the wavelength control abnormality determination device 19 determines that there is a wavelength control abnormality when the beat signal intensity exceeds the intensity threshold and the observed object molecular weight is lower than the molecular weight threshold.

[0114] When the wavelength control abnormality determination device 19 determines that the wavelength control is abnormal, it transmits a “wavelength control abnormality signal” as the signal to the wavelength control resetting device 20 .

[0115] 《Wavelength Control Reset Device 20》

[0116] The wavelength control reset device 20 is a component that resets the target spectrum detection device 6, the wavelength control device 7, and the signal processing device 18 to return to the initial state when a wavelength control abnormality signal is sent from the wavelength control abnormality determination device 19. The wavelength control reset device 20 may be configured to send a reset signal to each device so that the target spectrum detection device 6, the wavelength control device 7, and the signal processing device 18 are reset.

[0117] "Processing contents of laser radar with wavelength locking function according to implementation mode 2"

[0118] Figure 4 1 is a flowchart showing the detailed steps of the main processing (ST50) performed by the laser radar with wavelength locking function according to the second embodiment. Figure 4 As shown, the main process (ST50) includes a stability determination process (ST51), an observation process (ST52), an abnormality determination process (ST53), and a wavelength locking control process (ST55).

[0119] The stability determination process (ST51) is a process step performed by the wavelength control device 7. In the stability determination process (ST51), the wavelength control device 7 determines whether the magnitude of the feedback signal is less than a predetermined threshold value for a period of more than a certain fixed period. When the magnitude of the feedback signal is less than the predetermined threshold value for a period of more than a certain fixed period, the wavelength control device 7 sends a "stable control signal" as a signal to the signal processing device 18.

[0120] The observation process (ST52) is a processing step implemented by the signal processing device 18. In the observation process (ST52), the signal processing device 18 detects the beat signal frequency and the beat signal strength. The signal processing device 18 also calculates the wind speed based on the beat signal frequency and calculates the observed object molecular weight based on the beat signal strength. In the observation process (ST52), the signal processing device 18 also generates a trigger signal for the pulse modulator 13 and a trigger signal for the AD converter 17.

[0121] The abnormality determination process (ST53) is a process step performed by the wavelength control abnormality determination device 19. In the abnormality determination process (ST53), the wavelength control abnormality determination device 19 determines that there is a wavelength control abnormality when the beat signal intensity exceeds the intensity threshold and the observed molecular weight is lower than the molecular weight threshold.

[0122] As described above, since the laser radar of the second embodiment has the above-mentioned structure, it is possible to exert the effects described in the first embodiment and to simultaneously measure the water vapor density and wind speed in the atmosphere.

[0123] Industrial Applicability

[0124] The disclosed technology can be applied to a measuring device that simultaneously measures the water vapor density and wind speed in the atmosphere, and therefore has industrial applicability.

[0125] Description of Reference Numerals

[0126] 1 laser light source, 2 optical branching device, 3 modulator, 4 gas chamber, 5 optical detector, 6 target spectrum detection device, 7 wavelength control device, 9 fixed wavelength shift device, 10 second laser light source, 11 optical switch, 12 second optical branching device, 13 pulse modulator, 14 optical amplifier, 15 transceiver optical system, 16 light receiver, 17 AD converter, 18 signal processing device, 19 wavelength control abnormality determination device, 20 wavelength control reset device.

Claims

1. A laser radar, wherein: The laser radar has: a laser light source which oscillates laser light; An optical branching device that branches the laser light to two systems; a modulator for phase-modulating the laser light sent from the optical branching device; Air chamber; a light detector that detects the transmitted laser light after passing through the gas cell and converts the detected laser light into an electrical signal; and a wavelength control device, which controls the wavelength of the laser light source through a current control loop, The laser light source can be temperature controlled. The laser radar also includes a target spectrum detection device, which performs temperature scanning control and constant temperature control of the laser light source.

2. A laser radar having a laser light source capable of temperature control, wherein: After the power is turned on, the temperature of the laser light source temporarily rises from 0[°C] to 60[°C] at a rate of 6-60[°C / min], and then drops from 60[°C] to 0[°C] at a rate of 6-60[°C / min].

3. The laser radar according to claim 1 or 2, wherein: The laser radar also includes a signal processing device, which calculates the wind speed based on the beat signal frequency and calculates the molecular weight of the observed object based on the beat signal intensity.

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