A frequency self-scanning single-frequency continuous wave laser ranging system

Abstract

A frequency self-scanning single-frequency continuous wave laser ranging system, comprising a frequency self-scanning single-frequency fiber laser, a doped fiber amplifier and a measurement and analysis system; the frequency self-scanning single-frequency fiber laser is used to generate a frequency self-scanning single-frequency laser; the doped fiber amplifier amplifies the power of the frequency self-scanning single-frequency laser; the measurement and analysis system uses the frequency self-scanning single-frequency laser after power amplification to act on the measured object, and realizes ranging based on the echo signal. The present invention applies the wavelength self-scanning fiber laser to coherent ranging, uses the pulse and spectral characteristics of the self-scanning laser to detect the distance, and has the advantages of the pulse method, amplitude modulation method and frequency modulation method in laser ranging, with high resolution, long measurement distance, simple operation and analysis, and can improve the ranging performance through the good coherence of the light source and the wide bandwidth. And it does not rely on expensive light sources, modulators and timing analysis systems, which can greatly reduce costs and has good economic benefits.

Description

Technical Field

[0001] The invention belongs to the technical field of distance measurement, relates to laser distance measurement, and particularly relates to a frequency self-scanning single-frequency continuous wave laser distance measurement system. Background Art

[0002] Laser rangefinders have important application value in the fields of military, people's livelihood and industrial production. Laser ranging is based on the speed of light to measure the optical path through the flight time and finally obtain the distance information. Therefore, a precise timer device is required to accurately measure the flight time of the laser. In addition, the laser can also be modulated in other ways to obtain the exact value of the flight time. Typical methods include pulse method, amplitude modulation and frequency modulation. These three methods have their own advantages and disadvantages. The pulse method is suitable for long-distance detection, and the amplitude modulation method is suitable for short-distance detection, but the resolution of both is low. The frequency modulation method converts the time information into the beat frequency information of the reference signal and the echo signal through calculation, which increases the resolution of the ranging to a certain extent. However, it is difficult to play a role in long-distance ranging due to the modulation bandwidth and coherence distance of the laser. Therefore, it is very necessary to develop a laser rangefinder that can be applied to a variety of scenarios. Whether a laser rangefinder that combines the advantages of the above three methods can be developed is also the goal of scientific research. Summary of the invention

[0003] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a frequency self-scanning single-frequency continuous wave laser ranging system to solve the technical problem that the ranging resolution cannot be improved in long-distance ranging, so that laser ranging can be applied to a variety of scenarios.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is:

[0005] A frequency self-scanning single-frequency continuous wave laser ranging system, comprising a frequency self-scanning single-frequency fiber laser, a doped fiber amplifier and a measurement and analysis system;

[0006] The frequency self-sweeping single-frequency fiber laser is used to generate frequency self-sweeping single-frequency laser;

[0007] The doped optical fiber amplifier amplifies the power of the frequency self-scanning single-frequency laser;

[0008] The measurement and analysis system uses a power-amplified frequency self-scanning single-frequency laser to act on the object to be measured, and realizes distance measurement based on the echo signal.

[0009] In one embodiment, the frequency self-scanning single-frequency fiber laser includes a first pump source, the output end of the first pump source is connected to the blue end of the first wavelength division multiplexer, the common end of the first wavelength division multiplexer is connected to one end of the first doped fiber, the other end of the first doped fiber is connected to port 1 of the first fiber circulator, port 2 of the first fiber circulator is connected to one end of the second doped fiber, the other end of the second doped fiber is connected to the reflection end, port 3 of the first fiber circulator is connected to the input end of the first output coupler, one output end of the first output coupler is connected to the red end of the first wavelength division multiplexer to form a ring cavity, the other output end of the first output coupler is connected to the doped fiber amplifier, and the output frequency self-scanning single-frequency laser is output.

[0010] In one embodiment, the doped fiber amplifier includes a second pump source, a third pump source and a second wavelength division multiplexer, the output ends of the second pump source and the third pump source are connected to the blue end of the second wavelength division multiplexer, the frequency self-scanning single-frequency laser is connected to the red end of the second wavelength division multiplexer, the common end of the second wavelength division multiplexer is connected to one end of the third doped fiber, and the other end of the third doped fiber is connected to the measurement and analysis system.

[0011] In one embodiment, the doped fiber amplifier further includes a first fiber isolator and a second fiber isolator, wherein the first fiber isolator is connected between the output end of the frequency self-scanning single-frequency fiber laser and the red end of the second wavelength division multiplexer, and the second fiber isolator is connected between the other end of the third doped fiber and the input end of the measurement and analysis system.

[0012] In one embodiment, the doped fiber amplifier uses a one-stage amplification or multi-stage amplification structure to amplify the frequency self-scanning single-frequency laser to obtain output light of watts to kilowatts.

[0013] In one embodiment, the measurement and analysis system includes a second output coupler, the output end of the doped fiber amplifier is connected to the input end of the second output coupler, one output end of the second output coupler outputs a reference signal and is connected to a data analysis device, and the other output end is connected to a light receiving and transmitting device, the light receiving and transmitting device outputs laser to the object to be measured and receives an echo signal, the output end of the light receiving and transmitting device is connected to the data analysis device, and the data analysis device realizes ranging based on the frequency difference between the reference signal and the echo signal.

[0014] In one embodiment, the measurement and analysis system further comprises a second optical fiber circulator, port 1 of which is connected to the other output end of the second output coupler, port 2 is connected to the optical receiving and transmitting device, and port 3 is connected to the data analysis device.

[0015] In one embodiment, the light receiving and emitting device is a collimator.

[0016] In one embodiment, the method for the data analysis device to implement ranging based on the frequency difference between the reference signal and the echo signal is as follows:

[0017] Beat the echo signal with the reference signal and record the frequency difference;

[0018] By comparing the peak pulse and the frequency difference signal, the accurate ranging time is obtained;

[0019] For short-distance ranging scenarios, the reference signal and the echo signal will only have a phase difference of the sinusoidal signal, and the amplitude modulation method is used for analysis;

[0020] For long-distance ranging scenarios, the frequency difference is first determined by the beat frequency signal of the reference signal and the echo signal, and then the delay of the pulse signal is compared to obtain accurate time information to determine the target distance.

[0021] In one embodiment, the first doped optical fiber, the second doped optical fiber and the third doped optical fiber are all ytterbium-doped optical fibers.

[0022] Compared with the prior art, the present invention applies wavelength self-scanning fiber lasers to coherent ranging, and uses the pulse and spectral characteristics of the self-scanning laser to detect distance. This technical solution combines the advantages of the pulse method, amplitude modulation method, and frequency modulation method in laser ranging, and has the advantages of high resolution, long measurement distance, simple operation and analysis, and can improve the ranging performance through the good coherence and wide bandwidth of the light source. As for the system itself, this ranging solution does not rely on expensive light sources, modulators, and timing analysis systems, which can greatly reduce costs and has good economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a diagram of the frequency self-scanning single-frequency continuous wave (FSCW) laser ranging system.

[0024] Figure 2 It is a self-scanning laser output pulse diagram with a fiber Bragg grating at the reflection end, where (b) is a high-precision curve diagram of a pulse signal in (a).

[0025] Figure 3 It is a self-scanning spectrum diagram of a fiber Bragg grating with a reflection end, where (a) is a time-wavelength relationship diagram and (b) is a wavelength-intensity relationship diagram. DETAILED DESCRIPTION

[0026] The embodiments of the present invention are described in detail below with reference to the accompanying drawings and examples.

[0027] The key to laser ranging is to obtain the flight time of the laser. The existing pulse method, amplitude modulation method and frequency modulation method cannot meet the requirements of high resolution under long-distance ranging when obtaining the precise value of the flight time. Therefore, the present invention provides a frequency self-scanning single-frequency continuous wave laser ranging system, which mainly includes a frequency self-scanning single-frequency fiber laser, a doped fiber amplifier and a measurement and analysis system.

[0028] Among them, the frequency self-scanning single-frequency fiber laser is used to generate a frequency self-scanning single-frequency laser, the doped fiber amplifier is used to amplify and adjust the power of the frequency self-scanning single-frequency laser so that it reaches the power required for the ranging scenario, and the measurement and analysis system uses the frequency self-scanning single-frequency laser obtained after amplification and adjustment to act on the object to be measured.

[0029] In the measurement and analysis system, the laser is divided into two parts, a small part is used as a reference signal, and the remaining part is reflected by the object to be measured to obtain an echo signal. Based on the reference signal and the echo signal, the distance measurement can be achieved as follows:

[0030] 1. Beat the echo signal with the reference signal and record the frequency difference;

[0031] 2. By comparing the peak pulse and frequency difference signal, the accurate ranging time can be obtained.

[0032] For short-distance ranging scenarios, there will only be a phase difference of the sinusoidal signal between the reference signal and the echo signal, and the amplitude modulation method can be directly used for analysis.

[0033] For long-distance ranging scenarios, the frequency difference is first determined by the beat frequency signal of the reference signal and the echo signal, and then the delay of the pulse signal is compared to obtain accurate time information to determine the target distance.

[0034] In the present invention, short distance is generally defined as 0-100m, and long distance is generally defined as greater than 1000m.

[0035] In the present invention, the frequency self-scanning single-frequency laser refers to an output laser that can produce periodic linear frequency changes and maintain high monochromaticity (line width at the kHz level) at the same time.

[0036] In one embodiment of the present invention, a structure of a frequency self-scanning single-frequency fiber laser, a doped fiber amplifier, and a measurement and analysis system are provided.

[0037] The core of laser ranging is the frequency self-scanning single-frequency fiber optic light source. Figure 1 The frequency self-scanning single-frequency fiber laser of the present invention is Figure 1Phase 1 in the embodiment is a ring cavity composed of a first pump source 11, a first wavelength division multiplexer 21, a first doped fiber 31, a first fiber circulator 41, a second doped fiber 32, a reflective end 5 and a first output coupler 61. The output end of the first pump source 1 is connected to the blue end of the first wavelength division multiplexer 21, the common end of the first wavelength division multiplexer 21 is connected to the 1 port of the first fiber circulator 41 through the first doped fiber 31, the 2 port of the first fiber circulator 41 is connected to the reflective end 5 through the second doped fiber 32, the 3 port of the first fiber circulator 41 is connected to the input end of the first output coupler 61, one output end of the first output coupler 61 is connected to the red end of the first wavelength division multiplexer 21 to form a ring cavity, and the other output end is connected to the doped fiber amplifier to output a self-scanning single-frequency laser.

[0038] In this structure, the first doped optical fiber 31 acts as a gain medium and can generate excitation light, which is transmitted to the reflection end 5 via the second doped optical fiber 32. After being reflected at the reflection end 5, the excitation light returns to the ring cavity along the original path of the second doped optical fiber 32 and continues to be transmitted downstream along the ring cavity. The second doped optical fiber 32 acts as a saturable absorber, in which the excitation light forms a standing wave structure, and forms a dynamic grating to realize the self-scanning operation of the laser frequency. The bandwidth of the reflection end 5 determines the wavelength range of the frequency self-scanning.

[0039] The pulse intensity and frequency characteristics of the frequency self-scanning fiber light source are the key to distance measurement. It combines the advantages of pulse method and frequency modulation method. In actual measurement, the delayed light and reference light that have traveled a long distance show hysteresis in the pulse, while the frequency self-scanning laser has different frequencies before and after the peak pulse, but a continuous wave with a constant frequency interval. After the light delay reaches the millisecond level, the beat frequency signal of the delayed light and the reference light can be used to obtain multiples of the frequency interval, and the delay time can be further obtained through the pulse sequence of the delayed light and the reference light, and finally the target distance can be obtained. Doped fiber amplifiers are Figure 1 Phase 2 in the embodiment mainly includes a second pump source 12, a third pump source 13 and a second wavelength division multiplexer 22. The output ends of the second pump source 12 and the third pump source 13 are connected to the 976nm (blue) end of the second wavelength division multiplexer 22, the frequency self-sweeping single-frequency laser is connected to the 1064nm (red) end of the second wavelength division multiplexer 22, and the common (black) end of the second wavelength division multiplexer 22 is connected to the measurement and analysis system through the third doped optical fiber 33. The frequency self-sweeping single-frequency laser output by the frequency self-sweeping single-frequency fiber laser can be amplified and a suitable laser power can be obtained through the second pump source 12, the third pump source 13 and the third doped optical fiber 33.

[0040] In the present invention, the wavelength range of the frequency self-sweeping single-frequency laser output by the frequency self-sweeping single-frequency optical fiber light source can reach 4nm, and the power range can reach 10mW. After amplification and adjustment, the output laser power can reach W level.

[0041] For example, the doped fiber amplifier may further include a first fiber isolator 71 and a second fiber isolator 72, wherein the first fiber isolator 71 is connected between the output end of the frequency self-scanning single-frequency fiber laser and the 1064nm (red) end of the second wavelength division multiplexer 22, and the second fiber isolator 72 is connected between the third doped fiber 33 and the input end of the measurement and analysis system. The main function of the first fiber isolator 71 and the second fiber isolator 72 is to isolate the generated reverse Brillouin scattered light to prevent interference with the seed source.

[0042] In the present invention, the structure can be determined according to the required optical power, and a single-stage amplification or multi-stage amplification structure can be used to amplify the frequency self-scanning single-frequency laser to obtain watt-level or even kilowatt-level output light.

[0043] Measurement and analysis system Figure 1 Phase 3 in the measurement and analysis system mainly includes a second output coupler 62, a data analysis device 10 and a light receiving and transmitting device 8, wherein the output end of the doped fiber amplifier is connected to the input end of the second output coupler 62, one output end of the second output coupler 62 outputs a reference signal and is connected to the data analysis device 10, and the other output end is connected to the light receiving and transmitting device 8, the light receiving and transmitting device 8 outputs laser to the object 9 to be measured and receives an echo signal, the output end of the light receiving and transmitting device 8 is connected to the data analysis device 10, and the data analysis device 10 realizes ranging based on the frequency difference between the reference signal and the echo signal. By way of example, the measurement and analysis system also includes a second fiber circulator 42, whose port 1 is connected to the other output end of the second output coupler 62, port 2 is connected to the light receiving and transmitting device 8, and port 3 is connected to the data analysis device 10.

[0044] The amplified laser is divided into two paths through the second output coupler 62. One path is directly passed into the data analysis device 10, and the other path is output by the light receiving and transmitting device 8 after passing through the second optical fiber circulator 42. After the light wave is reflected by the object to be measured 9, the echo signal re-enters the second optical fiber circulator 42 through the light receiving and transmitting device 8, and finally enters the data analysis device 10.

[0045] In the measurement and analysis system of the present invention, most of the laser light is emitted from the light receiving and emitting device 8 through the second fiber optic circulator 42, and an echo signal is obtained after being reflected by the object to be measured 9. The echo signal returns to the light receiving and emitting device 8 and enters the data analysis device 10 together with another small part as a reference signal laser.

[0046] In the present invention, the light receiving and transmitting device 8 can be a collimator. The reflecting end 5 can be a reflecting device such as an optical fiber Bragg fiber, an optical fiber Sagnac total reflector, an optical fiber circulator, etc. to realize a frequency self-scanning optical fiber light source with controllable bandwidth. Figure 2 and Figure 3 The pulse and spectrum of the self-sweeping laser are shown when the reflective end 5 is a fiber Bragg grating. It can be seen that due to the frequency sweeping characteristics of the seed laser, the output will have the characteristics of a self-sweeping laser output.

[0047] In the present invention, each pump source emits 980nm light, and the first doped fiber 31, the second doped fiber 32 and the third doped fiber 33 are all ytterbium-doped fibers that can generate excitation light near 1μm. Of course, doped fibers of other wavelengths and other doping media can also be used, as long as the role of the doped fiber in the present invention can be achieved, they are within the protection scope of the present invention. In addition, the working wavelengths of each pump source, wavelength division multiplexer, fiber circulator, light receiving and transmitting device and output coupler are consistent with the excitation wavelength of the doped fiber. At the same time, the connections between each pump source, wavelength division multiplexer, fiber circulator, light receiving and transmitting device and output coupler are all single-mode fiber connections.

Claims

1. A frequency self-scanning single-frequency continuous wave laser ranging system, characterized in that: Including frequency self-scanning single-frequency fiber laser, doped fiber amplifier and measurement and analysis system; The frequency self-sweeping single-frequency fiber laser is used to generate frequency self-sweeping single-frequency laser; The doped optical fiber amplifier amplifies the power of the frequency self-scanning single-frequency laser; The measurement and analysis system uses a power-amplified frequency self-scanning single-frequency laser to act on the object to be measured (9), and realizes distance measurement based on the echo signal; The measurement and analysis system comprises a second output coupler (62), the output end of the doped optical fiber amplifier is connected to the input end of the second output coupler (62), one output end of the second output coupler (62) outputs a reference signal and is connected to a data analysis device (10), and the other output end is connected to a light receiving and transmitting device (8), the light receiving and transmitting device (8) outputs laser light to the measured object (9) and receives an echo signal, the output end of the light receiving and transmitting device (8) is connected to the data analysis device (10), and the data analysis device (10) implements distance measurement based on the frequency difference between the reference signal and the echo signal, and the method is as follows: (1) Beat the echo signal with the reference signal and record the frequency difference; (2) Obtain accurate ranging time by comparing the peak pulse and frequency difference signal; For short-distance ranging scenarios, the reference signal and the echo signal will only have a phase difference of the sinusoidal signal, and the amplitude modulation method is used for analysis; For long-distance ranging scenarios, the frequency difference is first determined by the beat frequency signal of the reference signal and the echo signal, and then the delay of the pulse signal is compared to obtain accurate time information to determine the target distance.

2. The frequency self-scanning single-frequency continuous wave laser ranging system according to claim 1, characterized in that: The frequency self-scanning single-frequency fiber laser comprises a first pump source (11), the output end of the first pump source (11) is connected to the blue end of the first wavelength division multiplexer (21), the common end of the first wavelength division multiplexer (21) is connected to one end of a first doped fiber (31), the other end of the first doped fiber (31) is connected to port 1 of a first fiber circulator (41), port 2 of the first fiber circulator (41) is connected to one end of a second doped fiber (32), the other end of the second doped fiber (32) is connected to a reflection end (5), port 3 of the first fiber circulator (41) is connected to the input end of a first output coupler (61), one output end of the first output coupler (61) is connected to the red end of the first wavelength division multiplexer (21) to form a ring cavity, the other output end of the first output coupler (61) is connected to a doped fiber amplifier, and a frequency self-scanning single-frequency laser is output.

3. The frequency self-scanning single-frequency continuous wave laser ranging system according to claim 2, characterized in that: The light receiving and emitting device (8) is a collimator.

4. The frequency self-scanning single-frequency continuous wave laser ranging system according to claim 2, characterized in that: The doped fiber amplifier comprises a second pump source (12), a third pump source (13) and a second wavelength division multiplexer (22); the output ends of the second pump source (12) and the third pump source (13) are connected to the blue end of the second wavelength division multiplexer (22); the frequency self-scanning single-frequency laser is connected to the red end of the second wavelength division multiplexer (22); the common end of the second wavelength division multiplexer (22) is connected to one end of the third doped fiber (33); and the other end of the third doped fiber (33) is connected to the measurement and analysis system.

5. The frequency self-scanning single-frequency continuous wave laser ranging system according to claim 4, characterized in that: The first doped optical fiber (31), the second doped optical fiber (32) and the third doped optical fiber (33) are all ytterbium-doped optical fibers.

6. The frequency self-scanning single-frequency continuous wave laser ranging system according to claim 4, characterized in that: The doped fiber amplifier further comprises a first fiber isolator (71) and a second fiber isolator (72), wherein the first fiber isolator (71) is connected between the output end of the frequency self-scanning single-frequency fiber laser and the red end of the second wavelength division multiplexer (22), and the second fiber isolator (72) is connected between the other end of the third doped fiber (33) and the input end of the measurement and analysis system.

7. The frequency self-scanning single-frequency continuous wave laser ranging system according to claim 6, characterized in that: The doped optical fiber amplifier adopts a one-stage amplification or multi-stage amplification structure to amplify the frequency self-scanning single-frequency laser to obtain output light of watt level to kilowatt level.

8. The frequency self-scanning single-frequency continuous wave laser ranging system according to claim 1, characterized in that: The measurement and analysis system also includes a second optical fiber circulator (42), port 1 of which is connected to the other output end of the second output coupler (62), port 2 of which is connected to the optical receiving and transmitting device (8), and port 3 of which is connected to the data analysis device (10).

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