A slow frequency-modulated continuous wave semiconductor laser ranging device and method

Abstract

The application discloses a kind of slowly varying frequency-modulated continuous wave semiconductor laser ranging device and method, the device includes tunable semiconductor laser, beam splitter, coupler, photoelectric detector, band-pass filter, detector and operation control unit;The beam splitter is located at the light-emitting side of the tunable semiconductor laser, and the laser beam is split into local reference light and echo reflected light, the coupler is used to simultaneously receive local reference light and echo reflected light;The photoelectric detector is used to convert the beat frequency microwave signal into analog electrical signal;The band-pass filter is used for frequency selection processing to analog electrical signal;The detector is used to collect the beat frequency electrical signal after filtering and output direct current voltage signal capable of representing the size of microwave energy;The operation control unit is used to collect the direct current voltage signal output by the detector, and completes the distance determination and operation of the measured object.The present application effectively shortens the operation time of single ranging, meets the real-time detection demand in dynamic scene.

Description

Technical Field

[0001] This invention relates to the field of laser ranging technology. Specifically, it relates to a slowly frequency-modulated continuous wave semiconductor laser ranging device and method. Background Technology

[0002] Frequency-modulated continuous-wave laser ranging (FM-CWL) emits a laser beam with a continuously varying time-frequency. The target echo is coherently interfered with the local oscillator reference beam to generate a beat frequency signal. The target distance is then calculated based on the relationship between the beat frequency and the optical path difference. This technology offers high ranging accuracy, eliminates blind spots at close range, and exhibits excellent resistance to ambient light interference. It is now widely used in industrial precision inspection, precision machining, autonomous driving, and mobile robot navigation, demonstrating significant practical value.

[0003] However, existing traditional FMCW laser rangefinders still have many shortcomings in practical applications:

[0004] Firstly, traditional devices rely on high-speed acquisition equipment and complex spectrum analysis algorithms to extract frequency information of beat frequency signals. High-speed acquisition cards and high-performance computing chips increase the overall hardware cost. Furthermore, they have significant computational latency, which limits real-time performance. In particular, traditional solutions often fail to meet the requirements of real-time processing in dynamic measurement scenarios that require rapid response.

[0005] Secondly, existing systems lack sufficient sensitivity for detecting minute distance changes, such as variations in pipe depth or tiny protrusions on workpiece surfaces. The beat frequency shift caused by minute distance changes is extremely small, making it difficult to distinguish using conventional spectral analysis methods. The industry's conventional solution is to increase the sampling rate and improve hardware resolution, further increasing system cost and hardware architecture complexity.

[0006] Third, the common semiconductor lasers used in the system have inherent shortcomings: a wider laser linewidth will shorten the coherence length, resulting in a decrease in the signal-to-noise ratio and ranging accuracy in long-distance measurements; frequency modulation nonlinear distortion will broaden the spectrum of the beat frequency signal, directly reducing the ranging resolution and stability.

[0007] Therefore, there is an urgent need for a slowly variable frequency modulated continuous wave semiconductor laser ranging device and method that can simplify the signal processing link, reduce hardware costs, and have high sensitivity to minute distance changes. Summary of the Invention

[0008] Therefore, the technical problem to be solved by the present invention is to provide a slowly variable frequency modulated continuous wave semiconductor laser ranging device and method. The laser ranging device effectively solves the problems of complex hardware architecture, high computing power, and insufficient sensitivity for detecting small deformations in traditional FMCW laser ranging systems by means of the coordinated linkage between a tunable semiconductor laser capable of slowly variable frequency modulation, a bandpass filter with narrow band characteristics, a detector, and an operation and control unit with threshold discrimination logic.

[0009] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0010] A slowly varying frequency modulated continuous wave semiconductor laser ranging device includes:

[0011] Tunable semiconductor lasers are used to output laser beams whose frequency varies slowly over time in a triangular wave pattern.

[0012] A beam splitter is located on the light-emitting side of the tunable semiconductor laser. It is used to receive the laser beam and split the laser beam into a probe signal light and a local oscillator reference light. The probe signal light is projected onto the surface of the object under test and is reflected by the object under test to form an echo reflection light.

[0013] A coupler is used to simultaneously receive the local oscillator reference light and the echo reflected light, so that the local oscillator reference light and the echo reflected light interfere and beat frequency inside the coupler and output a beat frequency microwave signal.

[0014] A photodetector, the input end of which is connected to the output end of a coupler, is used to convert the beat frequency microwave signal into an analog electrical signal;

[0015] A bandpass filter, the input of which is connected to the output of a photodetector, is used to perform frequency selection processing on analog electrical signals, retaining only beat frequency electrical signals within a preset range;

[0016] A detector, the input of which is connected to the output of a bandpass filter, is used to acquire the filtered beat frequency electrical signal and output a DC voltage signal that can characterize the magnitude of microwave energy.

[0017] The arithmetic control unit is used to acquire the DC voltage signal output by the detector and to complete the distance determination and calculation of the object under test.

[0018] The aforementioned slowly frequency-modulated continuous wave semiconductor laser ranging device, wherein the operational control unit is electrically connected to the tunable semiconductor laser and the detector, and its operational logic is as follows:

[0019] When the frequency of the beat frequency electrical signal falls within the frequency range of the bandpass filter, the detector detects a DC voltage signal characterizing microwave energy. The operation and control unit determines whether the laser frequency is locked within the bandwidth based on the DC voltage signal. When it is determined that the laser frequency is locked within the bandwidth, the operation and control unit reads the output frequency of the tunable semiconductor laser and calculates the distance to the object under test by combining it with the center frequency of the bandpass filter.

[0020] In the aforementioned slowly frequency-modulated continuous wave semiconductor laser ranging device, the operation and control unit determines whether the laser frequency is locked within the bandwidth based on the DC voltage signal characterizing microwave energy. When it is determined that the laser frequency is not locked within the bandwidth, the operation and control unit continuously drives the tunable semiconductor laser to slowly sweep the frequency until the laser frequency falls into the bandwidth range of the bandpass filter.

[0021] The aforementioned frequency-modulated continuous wave semiconductor laser ranging device includes a beam splitter with an input terminal, a first output terminal, and a second output terminal. The input terminal of the beam splitter is connected to the output terminal of the tunable semiconductor laser, so that the laser beam enters the beam splitter through the input terminal. After being split by the beam splitter, the laser beam outputs the detection signal light from the first output terminal and the local oscillator reference light from the second output terminal.

[0022] The aforementioned slowly varying frequency modulated continuous wave semiconductor laser ranging device includes a coupler configured with a first input terminal, a second input terminal, and an output terminal. The local oscillator reference light is input into the coupler through the first input terminal, and the echo reflected light is input into the coupler through the second input terminal. The local oscillator reference light and the echo reflected light interfere and beat within the coupler, causing the beat frequency microwave signal to be output from the output terminal of the coupler.

[0023] The aforementioned slowly modulated continuous wave semiconductor laser ranging device changes the beat frequency corresponding to a fixed distance to be measured by adjusting the frequency modulation slope of the tunable semiconductor laser, thereby matching the beat frequency to the passband range of the bandpass filter.

[0024] The aforementioned slowly variable frequency modulated continuous wave semiconductor laser ranging device has a preset beat frequency of 10MHz corresponding to the target distance to be measured.

[0025] The aforementioned slowly varying frequency modulated continuous wave semiconductor laser ranging device has a bandpass filter that is a SAW filter with narrow bandwidth characteristics. The bandwidth of the SAW filter is 0.1% to 5% of the center frequency. When the center frequency is set to 10MHz to match the expected beat frequency, the bandwidth is 10kHz to 500kHz.

[0026] The aforementioned slowly frequency modulated continuous wave semiconductor laser ranging device uses a DFB tunable semiconductor laser.

[0027] A method for ranging using a slowly varying frequency modulated continuous wave semiconductor laser, implemented based on the aforementioned laser ranging device, includes the following steps:

[0028] Step P1: Control the output frequency of the tunable semiconductor laser to be a laser beam whose frequency changes slowly with time in a triangular wave pattern.

[0029] Step P2: The laser beam is split into a probe signal beam and a local oscillator reference beam by a beam splitter. The probe signal beam is projected onto the surface of the object under test and is reflected by the object to form an echo reflection beam.

[0030] Step P3: The local oscillator reference light and the echo reflection light are input into the coupler, and the two beams interfere and beat within the coupler to output a beat frequency light signal;

[0031] Step P4: The beat frequency optical signal is input into the photodetector and converted into an analog electrical signal. The analog electrical signal is input into the bandpass filter for frequency selection processing to filter out noise components outside the preset passband and retain only the beat frequency electrical signal within the passband.

[0032] Step P5: The filtered beat frequency electrical signal is input into the detector, and the detector outputs a DC voltage signal that represents the current microwave energy level.

[0033] Step P6: The arithmetic control unit acquires the DC voltage signal output by the detector and determines whether the current beat frequency electrical signal falls within the bandwidth of the bandpass filter based on the DC voltage signal.

[0034] If it is determined that the beat frequency signal is not locked within the bandwidth of the bandpass filter, the tunable semiconductor laser is continuously controlled to slowly sweep the frequency and steps P1 to P6 are repeated.

[0035] If the beat frequency signal is determined to be locked within the bandwidth of the bandpass filter, the output frequency of the tunable semiconductor laser is read, and the distance to the object under test is calculated by combining it with the preset center frequency of the bandpass filter.

[0036] The technical solution of the present invention achieves the following beneficial technical effects:

[0037] This application abandons the high-speed data acquisition module and complex FFT spectrum analysis algorithm required for traditional FMCW laser ranging. Instead, it utilizes a narrowband bandpass filter in conjunction with a detector to transform the traditional method of directly measuring the beat frequency into microwave energy amplitude detection. This eliminates the need for high-frequency sampling hardware, high-performance computing chips, and large-scale spectrum iteration calculations, significantly reducing the overall hardware procurement and circuit construction costs, drastically decreasing the amount of backend data processing, and effectively shortening the single ranging calculation time, thus meeting the real-time detection requirements in dynamic scenarios.

[0038] The laser ranging device of this application utilizes the frequency selectivity of a narrowband bandpass filter to convert the beat frequency shift caused by minute distance changes into a significant decrease in the detector's output energy. When the object under test experiences micron-level distance fluctuations, the beat frequency shifts only slightly, yet this causes a sharp change in the microwave energy passing through the filter, which is visually reflected in a significant rise or fall in the detector's output DC voltage. Compared to traditional solutions that rely on spectrum resolution to distinguish minute frequency shifts, this device can capture weak displacement signals without increasing the resolution of the acquisition hardware. It exhibits extremely high detection sensitivity for scenarios involving the detection of minute defects such as pipe depth fluctuations, minute protrusions on the workpiece surface, and thin-wall deformation, and has a stronger ability to identify minute-sized defects.

[0039] The laser ranging device of this application uses a tunable semiconductor laser to output a slowly varying triangular wave frequency-modulated laser. The frequency modulation slope can be flexibly adjusted, which on the one hand can match different ranges of distance to be measured, so that the corresponding beat frequency falls accurately within the passband range of the bandpass filter, ensuring effective ranging; on the other hand, the gentle low-slope frequency sweep can suppress the nonlinearity defects of the laser's own frequency modulation, eliminating the need for additional pre-distortion correction circuits. The entire optical path and circuit architecture is simplified, with fewer components, a simple assembly and debugging process, and low difficulty in miniaturization and integration, making it easy to mass-produce and integrate with various industrial equipment.

[0040] This application sets up an energy threshold determination logic, which only performs distance calculation when the beat frequency is stably within the filter bandwidth. It automatically filters out invalid noise signals caused by laser sweep frequency inflection point, optical mode hopping, and ambient stray light, avoids invalid data from participating in the calculation, reduces ranging jumps and measurement distortion problems, and significantly improves measurement stability and data reliability. Attached Figure Description

[0041] Figure 1 A schematic diagram of the structure of a slowly varying frequency modulated continuous wave semiconductor laser ranging device according to the present invention.

[0042] In the attached diagram, 1-tunable semiconductor laser; 2-beam splitter; 3-coupler; 4-photodetector; 5-bandpass filter; 6-detector; 7-operation control unit; 8-object under test. Detailed Implementation

[0043] Example 1: This example discloses a slowly varying frequency modulated continuous wave semiconductor laser ranging device, such as... Figure 1 As shown, it includes a tunable semiconductor laser 1, a beam splitter 2, a coupler 3, a photodetector 4, a bandpass filter 5, a detector 6, and a computation and control unit 7;

[0044] The tunable semiconductor laser 1 is a DFB tunable semiconductor laser, used to output a laser beam whose frequency changes periodically with time in a triangular wave pattern. By adjusting the frequency modulation slope of the tunable semiconductor laser 1, on the one hand, the beat frequency corresponding to a fixed distance is changed, thereby adjusting the matching state between the beat frequency and the passband of the bandpass filter 5; on the other hand, the offset amplitude of the beat frequency under small distance disturbances is changed, thereby changing the fluctuation amplitude of the microwave energy output by the detector 6, realizing the control of the sensitivity of micro-deformation detection; at the same time, the low frequency modulation slope can reduce the nonlinear distortion of the laser frequency modulation, reduce the beat frequency band, eliminate the need for high-speed acquisition and spectrum calculation hardware, and balance the measurement sensitivity and the overall hardware cost.

[0045] The beam splitter 2 is disposed on the light-emitting side of the tunable semiconductor laser 1, and is used to receive the laser beam and split the laser beam into a probe signal light and a local oscillator reference light. The probe signal light is projected onto the surface of the object under test 8 and is reflected by the object under test 8 to form an echo reflection light. The beam splitter 2 is configured with an input end, a first output end and a second output end. The input end of the beam splitter 2 is connected to the output end of the tunable semiconductor laser 1 so that the laser beam enters the beam splitter 2 through the input end of the beam splitter 2. After being split by the beam splitter 2, the probe signal light is output from the first output end and the local oscillator reference light is output from the second output end.

[0046] The coupler 3 is configured with a first input terminal, a second input terminal, and an output terminal. The local oscillator reference light is input into the coupler 3 through the first input terminal, and the echo reflected light is input into the coupler 3 through the second input terminal. The local oscillator reference light and the echo reflected light interfere and beat within the coupler 3, causing a beat frequency microwave signal to be output from the output terminal of the coupler 3. This output terminal is used to simultaneously receive the local oscillator reference light and the echo reflected light, causing the local oscillator reference light and the echo reflected light to interfere and beat within the coupler 3 and output a beat frequency microwave signal.

[0047] The input terminal of the photodetector 4 is connected to the output terminal of the coupler 3, and is used to convert the beat frequency microwave signal into an analog electrical signal;

[0048] The input of the bandpass filter 5 is connected to the output of the photodetector 4, and is used to perform frequency selection processing on the analog electrical signal, retaining only the beat frequency electrical signal within a preset range; the expected beat frequency corresponding to the preset target distance is set to 10MHz. The bandpass filter 5 is a SAW filter with narrow bandwidth characteristics (low insertion loss; good rectangular coefficient; small size; low cost, especially suitable for mass industrial applications). The bandwidth of the SAW filter is 0.1% to 5% of the center frequency. When the center frequency is set to 10MHz to match the expected beat frequency, the bandwidth is 10kHz to 500kHz. In this example, the bandwidth is 100kHz. When the actual beat frequency is close to 10MHz and falls within the passband range of 9.95MHz to 10.05MHz, the detector 6 outputs effective microwave energy, determines beat frequency lock, and performs distance calculation for the object under test 8. Aligning the filter's center frequency with the expected beat frequency ensures that the beat frequency is centered in the passband at the standard measurement distance, maximizing microwave energy amplitude. Beat frequency shifts caused by minute distance disturbances result in significant energy changes, further enhancing the detection sensitivity for minute distance variations. Narrowband SAW filters only allow signals close to the expected beat frequency to pass through, filtering out other noise and reducing the probability of misjudgment in ranging.

[0049] The input terminal of the detector 6 is connected to the output terminal of the bandpass filter 5, and is used to acquire the filtered beat frequency electrical signal and output a DC voltage signal that can characterize the magnitude of microwave energy.

[0050] The operation and control unit 7 is used to acquire the DC voltage signal output by the detector 6 and to perform distance determination and calculation for the object under test 8. The operation and control unit 7 is electrically connected to the tunable semiconductor laser 1 and the detector 6, and its operation logic is as follows:

[0051] When the beat frequency signal falls within the frequency range of the bandpass filter 5, the detector 6 detects a DC voltage signal characterizing microwave energy. The calculation control unit 7 determines whether the laser frequency is locked within the bandwidth based on the DC voltage signal. When the laser frequency is locked within the bandwidth, the calculation control unit 7 reads the output frequency of the tunable semiconductor laser 1 and calculates the distance to the object under test 8 by combining it with the center frequency of the bandpass filter 5. When the laser frequency is not locked within the bandwidth, the calculation control unit 7 continuously drives the tunable semiconductor laser 1 to slowly sweep the frequency until the laser frequency falls within the bandwidth range of the bandpass filter 5. The effective measurement range is determined by the DC voltage amplitude output by the detector 6. Distance calculation is only performed when the beat frequency signal matches the bandwidth of the bandpass filter 5 and the signal is deemed valid. Invalid signals such as out-of-band noise, sweep frequency inflection points, and laser mode skipping directly skip the calculation steps. This logic completely abandons the high-speed acquisition module and FFT spectrum analysis program that are essential for traditional equipment, significantly reducing the backend hardware specifications and overall production costs; at the same time, it reduces a large number of redundant calculations, significantly shortens the single ranging processing time, meets the real-time usage requirements in dynamic scenarios, and effectively improves the stability of measurement data and detection accuracy.

[0052] This device can be used for depth measurement of unknown pipe fittings and detection of protrusion defects on the surface of workpieces. During the test, the pipe fitting to be tested is fixed on the translation device, and the spot of the detection signal light moves at a constant speed along the axial direction of the pipe fitting to complete the full-line scan.

[0053] When the light spot scans to different depths at the bottom of the pipe, the change in distance causes a change in the beat frequency, and the DC voltage amplitude output by detector 6 changes synchronously. By comparing the real-time collected voltage amplitude with the preset calibration curve, the actual depth value of each position of the pipe can be calculated.

[0054] When the light spot sweeps across the raised area on the workpiece surface, a slight change in distance results in a small shift in the beat frequency of only a few hundred hertz. This application leverages the attenuation characteristics of the narrowband bandpass filter 5; even with only a slight shift, the microwave energy passing through the filter will show significant attenuation, resulting in a significant reduction in the output voltage of the detector 6. This application eliminates the need for high-precision, high-speed acquisition equipment and complex spectrum analysis algorithms; it can quickly identify minute raised defects based on simple changes in energy amplitude, achieving ultra-high defect detection sensitivity while controlling hardware costs.

[0055] In summary, this application effectively solves the problems of complex hardware architecture, high computing power, and insufficient sensitivity for detecting minute deformations in traditional FMCW laser ranging systems by using a tunable semiconductor laser 1 capable of gradual frequency modulation, a bandpass filter 5 with narrowband characteristics, a detector 6, and a computational control unit 7 with threshold discrimination logic in synergistic operation. The tunable semiconductor laser 1 outputs a gradually triangular frequency-modulated laser with an adjustable slope, which can both match the beat frequency to the passband of the filter and suppress the laser's frequency modulation nonlinearity, eliminating the need for a pre-distortion correction circuit. The narrowband bandpass filter 5 converts the beat frequency deviation into a microwave energy amplitude change, which is then converted into a DC voltage signal by the detector 6. This replaces the high-speed data acquisition and FFT spectrum analysis process of traditional solutions, significantly reducing hardware configuration costs and backend computational load. The operational control unit 7 determines the valid measurement signal based on the output voltage of the detector 6. When there is a beat frequency mismatch, it automatically drives the laser to perform a gradual frequency sweep to complete self-calibration. The distance is calculated only when the signal is valid by the difference between the instantaneous output frequency of the laser and the center frequency of the filter, reducing redundant calculations and improving the real-time performance of the detection. At the same time, it filters out interference such as sweep frequency inflection points, optical mode hopping, and environmental clutter, optimizing measurement stability. In addition, the low frequency slope can amplify the beat frequency offset corresponding to a small displacement. Combined with the fast energy attenuation characteristics of the narrowband filter, quantitative measurement of pipe depth and highly sensitive identification of micron-level surface protrusions can be achieved without high-precision acquisition hardware.

[0056] Example 2: A method for ranging using a slowly varying frequency modulated continuous wave semiconductor laser, implemented based on the laser ranging device described in Example 1, includes the following steps:

[0057] Step P1: The fixed center frequency of the bandpass filter 5, the DC voltage threshold for determining the effective signal, and the slowly varying triangular wave frequency modulation slope parameters are pre-entered into the operation control unit 7; The operation control unit 7 outputs a drive signal to control the output laser beam of the tunable semiconductor laser 1 to change the frequency of the laser beam slowly and linearly with the triangular wave periodicity over time. The low frequency modulation slope, which is much lower than that of traditional high-speed chirped frequency modulation, is used to gradually change the output optical frequency, thereby suppressing the frequency nonlinear distortion caused by laser current frequency modulation.

[0058] Step P2: The laser beam emitted by the tunable semiconductor laser 1 is transmitted to the beam splitter 2. The beam splitter 2 performs beam splitting. One beam forms a local oscillator reference beam that is directly sent into the coupler 3, and the other beam forms a probe signal beam that is projected onto the surface of the object under test 8. After the probe signal beam contacts the object under test 8, it is reflected. The reflected beam that is folded back along the original optical path forms an echo reflection beam, which is synchronously transmitted to the coupler 3.

[0059] Step P3: The local oscillator reference light enters the coupler 3 through the first input terminal of the coupler 3, and the reflected light enters the coupler 3 through the second input terminal of the coupler 3. The two beams interfere in the coupler 3, and the light of different frequencies superimposes to generate a beat frequency light signal carrying the distance information to be measured, which is then output from the output terminal of the coupler 3.

[0060] In step P4, the beat frequency optical signal output by coupler 3 is connected to photodetector 4. Photodetector 4 uses the photoelectric conversion effect to convert the beat frequency optical signal into a continuous analog electrical signal. The analog electrical signal is sent to bandpass filter 5. Bandpass filter 5 performs frequency selection processing on the analog electrical signal according to the preset center frequency and fixed passband width, filtering out ambient stray light, circuit power frequency noise, sweep frequency sideband noise and other noise components outside the passband, and retaining only the beat frequency electrical signal that falls within the passband range and effectively reflects the distance to be measured.

[0061] Step P5: The beat frequency electrical signal after being filtered by bandpass filter 5 is connected to detector 6. Detector 6 performs detection processing on the beat frequency electrical signal, converting the alternating frequency signal into a DC voltage signal whose amplitude is positively correlated with microwave energy. The DC voltage amplitude directly corresponds to the degree of deviation between the current beat frequency signal and the center frequency of the filter. The closer the beat frequency is to the center frequency, the higher the output DC voltage.

[0062] Step P6: The operation and control unit 7 collects the DC voltage signal output by the detector 6 in real time, compares the collected actual voltage value with the system's preset voltage threshold, and determines whether the current beat frequency electrical signal stably falls within the bandwidth of the bandpass filter 5.

[0063] If the actual DC voltage is lower than the preset threshold, it is determined that the beat frequency signal is not locked within the bandwidth of the bandpass filter 5, which means that the beat frequency corresponding to the current distance deviates from the filter window, and the distance calculation operation is not performed. The operation control unit 7 continuously outputs a slowly changing drive signal to control the tunable semiconductor laser 1 to slowly sweep the frequency and change the output optical frequency. Then, steps P1 to P6 are repeated in a loop to continuously match the filter passband.

[0064] If the actual DC voltage is higher than the preset threshold, the beat frequency signal is determined to be stably locked within the bandwidth of the bandpass filter 5, and the current signal is a valid measurement signal. The operation and control unit 7 reads the instantaneous output optical frequency of the tunable semiconductor laser 1 in real time, retrieves the fixed center frequency of the pre-stored bandpass filter 5, and obtains the current real beat frequency value by performing a difference calculation between the two. Then, according to the beat frequency-distance conversion relationship pre-calibrated by the device, the actual distance from the laser to the object under test 8 is obtained by substituting into the calculation, and the distance measurement result is output and stored.

[0065] The above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of the claims of this patent application.

Claims

1. A slowly varying frequency modulated continuous wave semiconductor laser ranging device, characterized in that, include: A tunable semiconductor laser (1) is used to output a laser beam whose frequency changes slowly with time as a triangular wave. A beam splitter (2) is provided on the light-emitting side of the tunable semiconductor laser (1) to receive the laser beam and split the laser beam into a probe signal light and a local oscillator reference light. The probe signal light is projected onto the surface of the object under test (8) and is reflected by the object under test (8) to form an echo reflection light. Coupler (3) is used to simultaneously receive the local oscillator reference light and the echo reflected light, so that the local oscillator reference light and the echo reflected light interfere and beat frequency inside the coupler (3) and output beat frequency microwave signal; A photodetector (4) is provided, the input end of which is connected to the output end of a coupler (3) for converting the beat frequency microwave signal into an analog electrical signal. A bandpass filter (5) is connected to the output of a photodetector (4) for frequency selection of analog electrical signals, retaining only beat frequency electrical signals within a preset range. Detector (6), the input end of which is connected to the output end of bandpass filter (5), is used to acquire the filtered beat frequency electrical signal and output a DC voltage signal that can characterize the magnitude of microwave energy; The operation control unit (7) is used to acquire the DC voltage signal output by the detector (6) and to complete the distance determination and calculation of the object under test (8).

2. The slowly varying frequency modulated continuous wave semiconductor laser ranging device according to claim 1, characterized in that, The arithmetic control unit (7) is electrically connected to the tunable semiconductor laser (1) and the detector (6), and its arithmetic logic is as follows: When the frequency of the beat frequency electrical signal falls within the frequency range of the bandpass filter (5), the detector (6) detects a DC voltage signal characterizing microwave energy. The operation control unit (7) determines whether the laser frequency is locked within the bandwidth based on the DC voltage signal. When it is determined that the laser frequency is locked within the bandwidth, the operation control unit (7) reads the output frequency of the tunable semiconductor laser (1) and calculates the distance to the object under test (8) by combining it with the center frequency of the bandpass filter (5).

3. The slowly varying frequency modulated continuous wave semiconductor laser ranging device according to claim 2, characterized in that, The operation control unit (7) determines whether the laser frequency is locked within the bandwidth based on the DC voltage signal characterizing microwave energy. When it is determined that the laser frequency is not locked within the bandwidth, the operation control unit (7) continuously drives the tunable semiconductor laser (1) to slowly sweep the frequency until the laser frequency falls into the bandwidth range of the bandpass filter (5).

4. The slowly varying frequency modulated continuous wave semiconductor laser ranging device according to claim 1, characterized in that, The beam splitter (2) is configured with an input terminal, a first output terminal and a second output terminal. The input terminal of the beam splitter (2) is connected to the output terminal of the tunable semiconductor laser (1) so that the laser beam enters the beam splitter (2) through the input terminal of the beam splitter (2). After the laser beam is split by the beam splitter (2), the detection signal light is output from the first output terminal and the local oscillator reference light is output from the second output terminal.

5. The slowly varying frequency modulated continuous wave semiconductor laser ranging device according to claim 1, characterized in that, The coupler (3) is configured with a first input terminal, a second input terminal and an output terminal. The local oscillator reference light is input into the coupler (3) through the first input terminal of the coupler (3), and the echo reflected light is input into the coupler (3) through the second input terminal of the coupler (3). The local oscillator reference light and the echo reflected light interfere and beat frequency in the coupler (3), so that the beat frequency microwave signal is output from the output terminal of the coupler (3).

6. The slowly varying frequency modulated continuous wave semiconductor laser ranging device according to claim 1, characterized in that, By adjusting the frequency modulation slope of the tunable semiconductor laser (1), the beat frequency corresponding to the fixed distance to be measured is changed, thereby making the beat frequency match the passband range of the bandpass filter.

7. The slowly varying frequency modulated continuous wave semiconductor laser ranging device according to claim 1, characterized in that, The expected beat frequency corresponding to the target distance to be measured is 10MHz.

8. The slowly varying frequency modulated continuous wave semiconductor laser ranging device according to claim 7, characterized in that, The bandpass filter (5) is a SAW filter with narrow bandwidth characteristics. The bandwidth of the SAW filter is 0.1% to 5% of the center frequency. When the center frequency is set to 10MHz to match the expected beat frequency, the bandwidth is 10kHz to 500kHz.

9. The slowly varying frequency modulated continuous wave semiconductor laser ranging device according to claim 1, characterized in that, The tunable semiconductor laser (1) is a DFB tunable semiconductor laser (1).

10. A method for ranging using a slowly varying frequency modulated continuous wave semiconductor laser, implemented based on the laser ranging device according to any one of claims 1-9, characterized in that, Includes the following steps: Step P1: Control the tunable semiconductor laser (1) to output a laser beam whose frequency changes slowly with time in a triangular wave pattern. Step P2: The laser beam is split into a probe signal light and a local oscillator reference light by a beam splitter (2). The probe signal light is projected onto the surface of the object under test (8) and is reflected by the object under test (8) to form an echo reflection light. Step P3: The local oscillator reference light and the echo reflection light are input into the coupler (3). The two beams interfere and beat within the coupler (3), and output a beat frequency light signal. Step P4: The beat frequency optical signal is input into the photodetector (4) and converted into an analog electrical signal. The analog electrical signal is input into the bandpass filter (5) for frequency selection processing to filter out the noise components outside the preset passband and retain only the beat frequency electrical signal in the passband. Step P5: The filtered beat frequency electrical signal is input into the detector (6), and the detector (6) outputs a DC voltage signal that represents the current microwave energy level. Step P6: The arithmetic control unit (7) acquires the DC voltage signal output by the detector (6) and determines whether the current beat frequency electrical signal falls within the bandwidth of the bandpass filter (5) based on the DC voltage signal. If it is determined that the beat frequency signal is not locked within the bandwidth of the bandpass filter (5), the tunable semiconductor laser (1) is continuously controlled to slowly sweep the frequency and steps P1 to P6 are repeated. If the beat frequency signal is determined to be locked within the bandwidth of the bandpass filter (5), the output frequency of the tunable semiconductor laser (1) is read, and the distance to the object under test (8) is calculated by combining the preset center frequency of the bandpass filter (5).

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