High-precision laser phase ranging system and method for co-path optical path

Abstract

The invention provides a high-precision laser phase ranging system and method for a co-path optical path. The system comprises an arbitrary waveform generator, a semiconductor laser, a loop unit, an optical fiber collimation unit, a photoelectric detector, a data collector and a processor. The optical fiber collimation unit transmits a part of the laser signal to a target, collects object light reflected by the target and reflects a part of the laser signal to form reference light, and the object light received by the optical fiber collimation unit and the reference light are transmitted in a common-path mode; the loop unit receives object light and reference light which are transmitted in a co-pass mode, and the object light and the reference light are transmitted to the processor after being processed by the photoelectric detector and the data collector; and the processor calculates a phase difference based on the intensity signals of the interference light corresponding to the position before and after the target moves, and obtains a relative distance measurement value. According to the invention, the reference light and the object light share the same optical path, so that the measurement error is reduced, the optical path structure is simplified, the external interference is reduced, the stability and precision of distance measurement are improved, and high-resolution and high-precision displacement measurement is realized.

Description

Technical Field

[0001] The present invention relates to the field of laser radar technology, and more specifically to a high-precision laser phase ranging system and method for a common optical path. Background Art

[0002] LiDAR uses laser as light source and photoelectric detection technology to realize active detection technology of target distance. It has the advantages of high precision, high speed and small size, and is widely used in fields such as autonomous driving, drones, intelligent robots, 3D modeling, and geographic mapping. For example, LiDAR can help robots accurately locate and navigate in complex environments and update environmental maps in real time; in the manufacturing process, LiDAR can be used to detect changes in the size and shape of mechanical parts, monitor the position and movement of objects on the production line in real time, and ensure accurate control of the production process. How to ensure the ranging accuracy of LiDAR has always been an important research topic in this field.

[0003] The existing laser radar ranging methods are: 1. Time-of-flight ranging method, which directly measures the distance by detecting the round-trip time of pulse light reflected from the light source through the surface of the object and then back to the detector. This method has a simple structure, but is seriously interfered by background light. In complex environments, the reflected signal may be interfered by multipath. 2. Frequency-modulated continuous wave ranging method, which indirectly measures the distance by detecting the beat frequency signal between the reference light and the signal light reflected from the surface of the object. This method is anti-interference, but has strict requirements on the frequency modulation linearity of the light source, because the nonlinearity of frequency modulation will seriously affect the measurement accuracy.

[0004] In order to further improve the ranging accuracy, Zhang Enyao et al. disclosed in the document "Improvement of the Performance of Fiber Heterodyne Interferometry Displacement Sensor" that a dual-path fiber Fizeau interferometer is composed of semiconductor laser (LD), optical isolator, fiber directional coupler, self-focusing lens, etc., and uses triangular wave current modulation, upper and lower edge beat frequency signal differential phase detection method to improve the measurement sensitivity and displacement response speed, and uses an auxiliary interferometer to detect the phase drift of the system, and feedback control of the LD emission wavelength to improve the stability of the system. However, the optical path structure in this technology is complex, which affects the measurement efficiency, and requires the use of a coupler for splitting. The optical path difference between the reference light and the object light is large. External factors (such as air turbulence, mechanical vibration, etc.) will have different effects on the phase of the two beams of light, resulting in increased phase noise, thereby reducing the stability and accuracy of the measurement. Summary of the invention

[0005] The purpose of the present invention is to provide a high-precision laser phase ranging system and method for a common optical path, which reduces measurement errors by using a common optical path between reference light and object light, simplifies the optical path structure, reduces external interference, improves the stability and accuracy of ranging, and is conducive to achieving high-resolution and high-precision displacement measurement.

[0006] To achieve the above object, the present invention provides the following solutions: A high-precision laser phase ranging system for a common optical path, comprising an arbitrary waveform generator, a semiconductor laser, a loop unit, an optical fiber collimation unit, a photoelectric detector, a data collector and a processor; The arbitrary waveform generator generates a frequency modulation signal, and performs frequency modulation on the laser signal of the semiconductor laser by controlling the driving current of the semiconductor laser; The output end of the semiconductor laser is connected to the loop unit via an optical fiber; The loop unit is connected to the optical fiber collimation unit via an optical fiber, and is used to transmit the laser signal to the optical fiber collimation unit; The optical fiber collimation unit is used to transmit a part of the laser signal to the target, collect the object light reflected by the target, and reflect a part of the laser signal to form a reference light. The object light received by the optical fiber collimation unit and the reference light are transmitted in the same way. The loop unit receives the object light and the reference light transmitted back by the optical fiber collimation unit, and transmits them to the photoelectric detector; The photoelectric detector is used to convert the intensity signal of the interference light of the object light and the reference light into an electrical signal, and transmit it to the data acquisition device; The data collector is used to receive the electrical signal converted by the photoelectric detector and transmit it to the processor; The processor is used to receive the electrical signal, and calculate the phase difference based on the intensity signal of the interference light corresponding to the position of the target before and after movement, to obtain a relative distance measurement value, where the relative distance measurement value is the distance moved by the target.

[0007] Furthermore, the arbitrary waveform generator is also used to generate a synchronous electrical signal, which is transmitted to a data collector, and the synchronous electrical signal has the same frequency as the frequency modulation signal.

[0008] Furthermore, the signal transmission mode between the loop unit and the photodetector includes: one or more of optical fiber transmission, collimator conversion transmission, and free space optical transmission.

[0009] Furthermore, the loop unit is provided with three interfaces, namely, port a, port b and port c, wherein port a is used to receive a laser signal from a DFB laser, port b is used to output the laser signal to a fiber collimation unit and receive object light and reference light, and port c is used to transmit the object light and reference light to a photodetector.

[0010] Furthermore, the optical fiber collimation unit adopts an optical fiber collimator with a PC-type interface, a lens with transmission and reflection functions, or a combination structure of an optical fiber and a collimator.

[0011] Furthermore, the loop unit adopts an optical fiber circulator.

[0012] Furthermore, the frequency modulation signal is a symmetrical triangle wave or a sawtooth wave, and the synchronous electrical signal is a square wave with a duty cycle of 50%.

[0013] The present invention also provides a high-precision laser phase ranging method for a common optical path, which is applied to the high-precision laser phase ranging system for the common optical path, and comprises the following steps: The arbitrary waveform generator generates a frequency modulation signal, transmits it to the semiconductor laser, and performs frequency modulation on the laser signal of the semiconductor laser; The frequency modulated laser signal is transmitted to the optical fiber collimation unit through the loop unit; The fiber collimation unit transmits a part of the laser signal to the target, collects the object light reflected by the target, and reflects a part of the laser signal to form a reference light; The object light received by the optical fiber collimation unit and the reference light reflected at the end face of the optical fiber collimation unit are transmitted together and transmitted to the photoelectric detector via the loop unit; The photoelectric detector converts the intensity signal of the interference light of the object light and the reference light into an electrical signal and transmits it to the data collector; The data collector receives the electrical signal converted by the photodetector and transmits it to the processor; The processor receives the electrical signal, calculates the phase difference based on the intensity signal of the interference light corresponding to the position of the target before and after the movement, and obtains a relative distance measurement value, where the relative distance measurement value is the distance the target moves; The calculation formula for the relative distance measurement value is as follows: In the formula, Relative distance measurement indicating the position of the target before and after the movement; The time difference corresponding to the optical path difference between the object light and the reference light when measuring the distance to the position of the target before it moves; The time difference corresponding to the optical path difference between the object light and the reference light when measuring the distance to the target after it moves; The phase difference is actually measured based on the intensity signal of the interference light corresponding to the position of the target before and after movement; is the initial frequency of the laser signal; The speed of light.

[0014] Further, the phase difference is calculated based on the intensity signal of the interference light corresponding to the position of the target before and after the movement to obtain the relative distance measurement value, which specifically includes: When measuring the distance at the position where the target moves before, the time domain expression of the difference frequency signal intensity obtained after the interference of the object light and the reference light is: In the formula, , They are respectively the light intensity at the rising and falling edges of the difference frequency signal obtained after the interference of the object light and the reference light when measuring the distance at the position before the target moves; , are the intensities of the reference light and the object light, respectively; The time difference corresponding to the optical path difference between the object light and the reference light when measuring the distance to the position of the target before it moves; is the frequency modulation rate, that is, the slope of the rising edge of the triangle wave, is the FM bandwidth, is the frequency modulation period; When measuring the distance at the position where the target moved before, the phase difference between the rising and falling edges is ; Similarly, when measuring the distance at the position where the target moves, the time difference corresponding to the optical path difference between the object light and the reference light is , then when measuring the distance at the position where the target moves, the phase difference between the rising and falling edges is ; Based on the intensity signal of the interference light corresponding to the position of the target before and after movement, the phase difference is calculated: ; Depend on , we can conclude ; but, .

[0015] Further, The range is 0- ,when hour, but The value range is 0- ,in, is the wavelength of the laser signal.

[0016] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects: in the high-precision laser phase ranging system and method for a common optical path provided by the present invention, the object light received by the optical fiber collimation unit and the reference light reflected at the end face of the optical fiber collimation unit are transmitted in a co-path; the processor calculates the phase difference based on the intensity signal of the interference light corresponding to the position of the target before and after movement, and obtains the relative distance measurement value.

[0017] First, in the existing distance measurement system, in the case of non-co-path, the normal state of the light will change, and the difference in normal state between the object light and the reference light will seriously affect the contrast of the signal; while the present invention combines the characteristics of the co-path, the object light received by the optical fiber collimation unit and the reference light reflected at the end face of the optical fiber collimation unit are co-transmitted to form interference light, which is transmitted to the photoelectric detector through the loop unit. When measuring the distance, the phase difference is calculated based on the intensity signal of the interference light corresponding to the position before and after the target moves. Since the object light and the reference light are co-transmitted, the influence of the interference of the external environment (such as temperature, pressure, vibration, etc.) on the object light and the reference light is consistent. When calculating the phase difference, the external interference can be offset by phase subtraction, thereby maximizing the measurement accuracy. Secondly, the present invention obtains relative distance measurements: This formula calculates the distance the target moves. Since there is no need to directly measure the distance between the target and the fiber collimation unit, there is no need to consider the transmission distance of the laser signal in the fiber optical path, thus avoiding the measurement error caused by this part of the transmission distance. At the same time, in the case of co-path transmission, the skew-normal effects of the object light and the reference light are the same, canceling each other out, and the contrast of the interference light is improved, thereby further improving the measurement accuracy.

[0018] This application adopts heterodyne measurement to avoid effective information being carried on the DC signal, which is convenient for signal amplification, filtering, etc. In summary, the present invention combines the strong anti-interference of the common optical path, the high precision of the phase method, and the convenience of heterodyne interference signal processing to comprehensively improve the laser ranging effect.

[0019] In addition, the present invention reduces the use of couplers. In traditional methods, multiple couplers are needed to split and combine light, which increases the complexity and cost of the system. The use of optical fiber collimation units to reflect and form reference light can reduce the use of these couplers, reduce the energy loss caused by the couplers, and improve the overall efficiency of the system; at the same time, various errors introduced by the couplers (such as insertion loss, reflection loss, etc.) are reduced. At the same time, the object light received by the optical fiber collimation unit and the reference light are transmitted in the same way, which reduces non-co-path errors and further improves the ranging accuracy. It can be seen that the method of using collimator reflection to form reference light not only reduces the use of couplers and simplifies system design, but also significantly improves the ranging accuracy.

[0020] In summary, the present invention calculates the phase difference based on the intensity signal of the interference light corresponding to the position of the target before and after movement to obtain the relative distance measurement value and obtain the ranging result. Compared with the traditional frequency difference ranging method, the phase difference ranging method adopted by the present invention can achieve higher measurement accuracy, is very sensitive to tiny distance changes, can detect very subtle displacements, and is suitable for ranging applications requiring extremely high resolution. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0022] Figure 1 It is a structural schematic diagram of the high-precision laser phase ranging system of the common optical path of the present invention; Figure 2 This is a schematic diagram of a triangular wave frequency modulation signal according to an embodiment of the present invention; Figure 3 It is a schematic diagram of the structure of a typical FMCW laser radar ranging system in the prior art; Figure 4 This is a beat frequency signal diagram obtained by a typical FMCW laser radar ranging system in the prior art; Figure 5 This is a beat frequency signal diagram obtained after improving the optical path of the high-precision laser phase ranging system using the common optical path of the present invention; Figure 6 A schematic diagram of the structure of a fiber collimation unit formed by a combination of an optical fiber and a collimating lens; Description of reference numerals: 1. Arbitrary waveform generator; 2. Semiconductor laser; 3. Loop unit (divided into three ports a, b, and c, port a input and port b output, port b input and port c output); 4. Fiber collimation unit; 5. Photoelectric detector; 6. Data acquisition device (two-way input); 7. Processor; 8. The position of the target before moving; 8', the position of the target after moving; 3-1, tunable laser; 3-2, isolator; 3-3, coupler 1; 3-4, circulator; 3-5, lens; 3-6, target; 3-7, coupler 2; 3-8, balanced detector; 6-1. Optical fiber; 6-2. Collimating lens. DETAILED DESCRIPTION

[0023] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] The purpose of the present invention is to provide a high-precision laser phase ranging system and method with a common optical path, which reduces measurement errors by using a common optical path between reference light and object light, simplifies the optical path structure, reduces external interference, improves the stability and accuracy of ranging, and is conducive to increasing the measurement range and realizing high-resolution and high-precision displacement measurement.

[0025] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0026] like Figure 1 As shown, the high-precision laser phase ranging system for a common optical path provided by the present invention comprises an arbitrary waveform generator 1, a semiconductor laser 2, a loop unit 3, a fiber collimation unit 4, a photodetector 5, a data collector 6 and a processor 7; The arbitrary waveform generator 1 generates a frequency modulation signal, and performs frequency modulation on the laser signal of the semiconductor laser 2 by controlling the driving current of the semiconductor laser 2; The output end of the semiconductor laser 2 is connected to the loop unit 3 via an optical fiber; The loop unit 3 is connected to the optical fiber collimation unit 4 via an optical fiber, and is used to transmit the laser signal to the optical fiber collimation unit 4; The optical fiber collimation unit 4 is used to transmit a part of the laser signal to the target, collect the object light reflected by the target, and reflect a part of the laser signal to form a reference light. The object light received by the optical fiber collimation unit 4 and the reference light are transmitted together. The loop unit 3 receives the object light and the reference light transmitted back by the optical fiber collimation unit 4, and transmits them to the photodetector 5; The photoelectric detector 5 is used to convert the intensity signal of the interference light of the object light and the reference light into an electrical signal, and transmit it to the data acquisition device 6; The data collector 6 is used to receive the electrical signal converted by the photodetector 5 and transmit it to the processor 7; The processor 7 is used to receive the electrical signal, and calculate the phase difference based on the intensity signal of the interference light corresponding to the position of the target before and after movement, to obtain a relative distance measurement value, where the relative distance measurement value is the distance moved by the target.

[0027] The distance measurement result described in the present invention refers to the difference between the positions of the target before and after the target moves, that is, the distance the target moves, that is, the relative displacement of the target can be measured when the optical fiber collimation unit 4 is fixed. Figure 1 middle , They respectively represent the distances from the position 8 before the target moves and the position 8' after the target moves to the optical fiber collimation unit 4, Indicates the distance the target moves.

[0028] The arbitrary waveform generator 1 is also used to generate a synchronous electrical signal and transmit it to the data collector 6. The synchronous electrical signal has the same frequency as the frequency modulation signal, for example, 1 kHz. For example, the frequency modulation signal is a symmetrical triangle wave or a sawtooth wave, and other waveforms can also be used. The synchronous electrical signal is a square wave with a duty cycle of 50%. The embodiment of the present invention takes a triangle wave frequency modulation signal as an example.

[0029] For example, the semiconductor laser 2 may be a narrow line width semiconductor laser, such as a DFB (Distributed Feedback Laser) laser; the loop unit 3 may be an optical fiber circulator.

[0030] For example, the signal transmission mode between the loop unit 3 and the photodetector 5 includes: one or more of optical fiber transmission, collimator conversion transmission, and free space optical transmission.

[0031] Specifically, the loop unit 3 is provided with three interfaces, namely, port a, port b and port c, wherein port a is used to receive the laser signal from the DFB laser 2, port b is used to output the laser signal to the fiber collimation unit 4 and receive the object light and the reference light, and port c is used to transmit the object light and the reference light to the photodetector 5.

[0032] For example, the optical fiber collimation unit 4 may be a fiber collimator with a PC-type interface, a lens with transmission and reflection functions, or a combination structure of an optical fiber and a collimator. Figure 6 As shown. The present invention does not limit the selection of the optical fiber collimation unit 4, and only requires that the optical fiber collimation unit 4 can realize the transmission and reflection functions of the laser signal, and the laser signal is reflected at the end face of the optical fiber collimation unit 4 to form a reference light. After the object light passes through the optical fiber collimation unit 4, it is transmitted to the photodetector 5 through the loop unit 3 with the reference light, so that the optical path difference between the measured reference light and the object light is closer to the distance to be measured, reducing the measurement error.

[0033] In FMCW laser ranging, a triangle wave is generally used as the modulation waveform to linearly modulate the frequency of the laser, such as Figure 2 As shown in the figure, the variation of laser frequency over time under the modulation of periodic triangle wave, the solid line trace represents the optical frequency of reference light, and the dotted line trace represents the optical frequency of object light. Because there is a time delay between them, there is a difference in the frequency of the two when mixing occurs. In one frequency modulation cycle, the frequency difference will jump, but because the change time is extremely short, the impact can be ignored, so the difference frequency signal obtained by mixing can be regarded as a sine wave with a fixed frequency.

[0034] After the frequency modulation signal modulates the laser signal, the photodetector 5 receives a sine wave with a phase mutation within the T / 2 period, which is an AC signal. The AC signal processing method can be used for filtering and signal amplification. If there is no frequency modulation signal, at a measurement position, the photodetector 5 obtains a DC signal.

[0035] Under the rising edge modulation of the triangle wave, the instantaneous frequency of the reference light is expressed as: , in, represents the initial frequency of the laser, is the frequency modulation rate, that is, the slope of the rising edge of the triangle wave, is the FM bandwidth.

[0036] In a frequency modulation cycle The reference light signal expression is: ; The expression of the object light signal is: {E}_{r}\left ( {t} \right )={E}_{2}exp\left [ {2\pi {f}_{0}\left ( {t-\tau} \right )+\pi \alpha \left ( {t-\tau} \right )^{2}+{\varphi}_{0}} \right ] ; in, is the initial phase of the reference light, is the amplitude of the reference light, is the amplitude of the object light.

[0037] After mixing interference, the time domain expression of the difference frequency signal intensity can be obtained as follows: {I}_{rising}=\left [ {{E}_{e}\left ( {t} \right )+{E}_{r}\left ( {t} \right )} \right ]={I}_{1}+{I}_{2}+2\sqrt {{I}_{1}{I}_{2}}\cos {\left ( {2\pi \alpha \tau t+2\pi {f}_{0}\tau -\pi \alpha {\tau}^{2}} \right )} Since the quadratic term is much smaller than the phase term, ignoring the quadratic term yields: When the falling edge occurs, the instantaneous frequency of the reference signal is expressed as , , similarly we can get: According to the odd function properties of the cosine function, we can get: The synchronized square wave generated by the arbitrary waveform generator can be used to separate the rising and falling edge signals of the triangle wave at the data acquisition device. From the expression, we can know that the phase difference between the rising and falling edges is .

[0038] in, express relatively time delay.

[0039] The distance measurement result of the present invention can only be used for relative distance measurement, because the phase difference is greater than a 2 π Phase winding will occur, and the specific phase value cannot be determined. In addition, when performing relative distance measurement, the phase corresponding to the distance change between two measurements must also be less than 2 π .

[0040] Based on the above principle, the present invention provides a high-precision laser phase ranging method for a common optical path, which is applied to the high-precision laser phase ranging system for the common optical path, and includes the following steps: The arbitrary waveform generator 1 generates a frequency modulation signal, transmits it to the semiconductor laser 2, and performs frequency modulation on the laser signal of the semiconductor laser 2; The frequency modulated laser signal is transmitted to the optical fiber collimation unit 4 through the loop unit 3; The optical fiber collimation unit 4 transmits a part of the laser signal to the target, collects the object light reflected by the target, and reflects a part of the laser signal to form a reference light; The object light received by the optical fiber collimation unit 4 is transmitted together with the reference light and transmitted to the photodetector 5 via the loop unit 3; The photodetector 5 converts the intensity signal of the interference light of the object light and the reference light into an electrical signal and transmits it to the data collector 6; The data collector 6 receives the electrical signal converted by the photodetector 5 and transmits it to the processor 7; The processor 7 receives the electrical signal, calculates the phase difference based on the intensity signal of the interference light corresponding to the position of the target before and after movement, and obtains a relative distance measurement value, where the relative distance measurement value is the distance moved by the target.

[0041] The calculation formula for the relative distance measurement value is as follows: In the formula, Relative distance measurement indicating the position of the target before and after the movement; The time difference corresponding to the optical path difference between the object light and the reference light when measuring the distance to the position of the target before it moves; The time difference corresponding to the optical path difference between the object light and the reference light when measuring the distance to the target after it moves; It is the phase difference actually measured based on the intensity signal of the interference light at the position of the target before and after movement; is the initial frequency of the laser signal; The speed of light.

[0042] Specifically, based on the intensity signal of the interference light corresponding to the position of the target before and after movement, the phase difference is calculated to obtain the relative distance measurement value, which specifically includes: When measuring the distance at the position where the target moves before, the time domain expression of the difference frequency signal intensity obtained after the interference of the object light and the reference light is: In the formula, , They are respectively the light intensity at the rising and falling edges of the difference frequency signal obtained after the interference of the object light and the reference light when measuring the distance at the position before the target moves; , are the intensities of the reference light and the object light, respectively; The time difference corresponding to the optical path difference between the object light and the reference light when measuring the distance to the position of the target before it moves; is the frequency modulation rate, that is, the slope of the rising edge of the triangle wave, is the FM bandwidth, is the frequency modulation period; When measuring the distance at the position where the target moved before, the phase difference between the rising and falling edges is ; Similarly, when measuring the distance at the position where the target moves, the time difference corresponding to the optical path difference between the object light and the reference light is , the time domain expression of the difference frequency signal intensity obtained after the interference of the object light and the reference light is: In the formula, , They are the light intensity at the rising and falling edges of the difference frequency signal obtained after the interference of the object light and the reference light when measuring the distance to the position of the target after it moves; When measuring the distance at the position where the target moves, the phase difference between the rising and falling edges is ; The combined phase difference is calculated based on the intensity signal of the interference light at the position before and after the target moves: ; Depend on , we can conclude ; Among them, because the phase difference of the light intensity at the rising edge and the falling edge is doubled, the corresponding measured phase difference also needs to be doubled, which is ; but, .

[0043] The range is 0- ,when hour, but The value range is 0- ,in, is the wavelength of the laser signal.

[0044] For phase difference ranging, the maximum ranging distance depends on the wavelength of the laser signal, and the ranging accuracy depends on the resolution of the phase difference.

[0045] The present invention further calculates the combined phase difference of the intensity signals of the interference light at the position before and after the target moves based on the phase difference of the light intensity at the rising edge and the falling edge, and uses the combined phase difference of the rising edge and the falling edge to obtain the distance difference. Compared with measuring the distance by comparing the phase difference of the two rising edges, the distance accuracy is doubled at the same phase difference resolution.

[0046] In the above, the phase difference actually measured is based on the intensity signal of the interference light at the position before and after the target moves. Specifically, it can be calculated using the existing technologies in the field, such as the cross-correlation method, the fast Fourier transform method, the Hilbert transform method, the zero-crossing method (interpolation method), etc. The cross-correlation method: perform cross-correlation on two discrete signals, find the position of the correlation peak, calculate the time offset, and then convert it into a phase difference in combination with the sampling frequency. It is suitable for processing periodic signals and non-periodic signals; the fast Fourier transform (FFT) method: perform FFT on the signal to obtain the phase information in the spectrum, and then calculate the phase difference between the two signals at the same frequency point. This method is suitable for sinusoidal signals with stable frequencies; the Hilbert transform method: perform Hilbert transform on the signal to obtain the analytical signal (including amplitude and phase information), and then calculate the phase difference; the zero-crossing method (interpolation method): find the zero-crossing point in the sampled data, accurately locate the time difference of the zero-crossing point by the interpolation method, and calculate the phase difference accordingly. It is suitable for data with high sampling rates.

[0047] In addition, the following embodiments may also be used for calculating the phase difference: When performing signal processing, the phase difference can also be directly obtained by referring to only the rising edge part when measuring the positions of the front and rear targets before and after they move, that is: Depend on , we can conclude ; Similarly, we get the above, .

[0048] like Figure 3 This is a typical FMCW laser radar ranging system in the prior art. Two couplers are set up. The reference light and the object light are not transmitted in the fiber collimation unit. The beat frequency signal obtained by the system during ranging is as follows: Figure 4 As shown, it can be seen that before the optical path is improved in the present invention, the beat frequency signal does not have obvious sinusoidal characteristics, it is difficult to observe an obvious sinusoidal signal from the signal, and its phase cannot be determined.

[0049] Figure 5 The beat frequency signal obtained by improving the optical path of the high-precision laser phase ranging system of the common optical path of the present invention is shown. Figure 4 By comparison, it can be seen that the present invention can observe the part with obvious sinusoidal signal characteristics, which can be used to obtain phase information after fitting, and the waveform integrity is significantly improved compared with the signal before the optical path is improved. It can be seen that the present invention has better technical effects than the traditional FMCW laser radar ranging system and achieves technical improvement.

[0050] In addition, compared with the typical FMCW laser radar ranging system in the prior art, the present invention adopts the fiber collimation unit to reflect and form the reference light, which can reduce the use of couplers, reduce the energy loss caused by the couplers, and improve the overall efficiency of the system; at the same time, it reduces various errors introduced by the couplers, and at the same time, the object light received by the fiber collimation unit and the reference light are transmitted in the same way, which reduces the non-co-path error and further improves the ranging accuracy.

[0051] In summary, the high-precision laser phase ranging system and method of the co-path optical path provided by the present invention, compared with the traditional ranging optical path, generates reflected light as reference light at the end face of the optical fiber collimation unit, avoiding the additional optical path introduced by the splitting scheme. The present invention combines the characteristics of the optical path. The object light received by the optical fiber collimation unit and the reference light reflected at the end face of the optical fiber collimation unit are co-transmitted to form interference light, which is transmitted to the photodetector through the loop unit. When measuring the distance, the phase difference is calculated based on the intensity signal of the interference light corresponding to the position before and after the target moves. Since the object light and the reference light are co-transmitted, the interference of the external environment (such as temperature, pressure, vibration, etc.) has the same effect on the object light and the reference light. When calculating the phase difference, the external interference can be offset by phase subtraction, thereby maximizing the measurement accuracy. The present invention obtains the distance moved by the target. Since there is no need to directly measure the distance between the target and the optical fiber collimation unit, there is no need to consider the transmission distance of the laser signal in the optical fiber optical path, thereby avoiding the measurement error caused by this part of the transmission distance. The present invention uses the phase difference method for measurement, which greatly improves the measurement accuracy.

[0052] In summary, the present invention combines the strong anti-interference ability of the common optical path, the high precision of the phase method and the convenience of heterodyne interference signal processing to comprehensively improve the laser ranging effect.

[0053] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A high-precision laser phase ranging system for a common optical path, characterized in that: It comprises an arbitrary waveform generator (1), a semiconductor laser (2), a loop unit (3), an optical fiber collimation unit (4), a photodetector (5), a data acquisition device (6), and a processor (7); The arbitrary waveform generator (1) generates a frequency modulation signal, and performs frequency modulation on the laser signal of the semiconductor laser (2) by controlling the driving current of the semiconductor laser (2); The output end of the semiconductor laser (2) is connected to the loop unit (3) via an optical fiber; The loop unit (3) is connected to the optical fiber collimation unit (4) via an optical fiber, and is used to transmit the laser signal to the optical fiber collimation unit (4); The optical fiber collimation unit (4) is used to transmit a part of the laser signal to the target and collect the object light reflected by the target, and at the same time reflect a part of the laser signal to form reference light, and the object light received by the optical fiber collimation unit (4) and the reference light are transmitted in the same way; The loop unit (3) receives the object light and the reference light transmitted back by the optical fiber collimation unit (4), and transmits them to the photoelectric detector (5); The photoelectric detector (5) is used to convert the intensity signal of the interference light of the object light and the reference light into an electrical signal, and transmit it to the data acquisition device (6); The data collector (6) is used to receive the electrical signal converted by the photoelectric detector (5) and transmit it to the processor (7); The processor (7) is used to receive the electrical signal and calculate the phase difference based on the intensity signal of the interference light corresponding to the position of the target before and after movement, so as to obtain a relative distance measurement value, wherein the relative distance measurement value is the distance moved by the target.

2. The high-precision laser phase ranging system for common optical paths according to claim 1, characterized in that: The arbitrary waveform generator (1) is also used to generate a synchronous electrical signal, which is transmitted to a data collector (6), wherein the synchronous electrical signal has the same frequency as the frequency modulation signal.

3. The high-precision laser phase ranging system for common optical paths according to claim 1, characterized in that: The signal transmission method between the loop unit (3) and the photoelectric detector (5) includes: one or more of optical fiber transmission, collimator conversion transmission, and free space optical transmission.

4. The high-precision laser phase ranging system for common optical paths according to claim 1, characterized in that: The loop unit (3) is provided with three interfaces, namely, port a, port b and port c, wherein port a is used to receive a laser signal from a DFB laser (2), port b is used to output the laser signal to a fiber collimation unit (4) and receive object light and reference light, and port c is used to transmit the object light and reference light to a photoelectric detector (5).

5. The high-precision laser phase ranging system for common optical paths according to claim 1, characterized in that: The optical fiber collimation unit (4) adopts an optical fiber collimator with a PC-type interface, a lens with transmission and reflection functions, or a combined structure of an optical fiber and a collimator.

6. The high-precision laser phase ranging system for common optical paths according to claim 1, characterized in that: The loop unit (3) adopts an optical fiber circulator.

7. The high-precision laser phase ranging system for common optical paths according to claim 2, characterized in that: The frequency modulation signal is a symmetrical triangle wave or a sawtooth wave, and the synchronous electrical signal is a square wave with a duty cycle of 50%.

8. A high-precision laser phase ranging method for a common optical path, applied to the high-precision laser phase ranging system for a common optical path according to any one of claims 1 to 7, characterized in that: The steps include: The arbitrary waveform generator (1) generates a frequency modulation signal and transmits it to the semiconductor laser (2), thereby frequency modulating the laser signal of the semiconductor laser (2); The frequency modulated laser signal is transmitted to the optical fiber collimation unit (4) through the loop unit (3); The optical fiber collimation unit (4) transmits a part of the laser signal to the target, collects the object light reflected by the target, and reflects a part of the laser signal to form a reference light; The object light received by the optical fiber collimation unit (4) and the reference light reflected at the end face of the optical fiber collimation unit (4) are transmitted together and transmitted to the photoelectric detector (5) via the loop unit (3); The photodetector (5) converts the intensity signal of the interference light between the object light and the reference light into an electrical signal and transmits it to the data acquisition device (6); The data collector (6) receives the electrical signal converted by the photodetector (5) and transmits it to the processor (7); The processor (7) receives the electrical signal, calculates the phase difference based on the intensity signal of the interference light corresponding to the position of the target before and after the movement, and obtains a relative distance measurement value, wherein the relative distance measurement value is the distance the target moves; The calculation formula of the relative distance measurement value is as follows: In the formula, Relative distance measurement indicating the position of the target before and after the movement; The time difference corresponding to the optical path difference between the object light and the reference light when measuring the distance to the position of the target before it moves; The time difference corresponding to the optical path difference between the object light and the reference light when measuring the distance to the target after it moves; The phase difference is actually measured based on the intensity signal of the interference light corresponding to the position of the target before and after movement; is the initial frequency of the laser signal; The speed of light.

9. The high-precision laser phase ranging method for a common optical path according to claim 8, characterized in that: The phase difference is calculated based on the intensity signal of the interference light corresponding to the position of the target before and after the movement to obtain the relative distance measurement value, which specifically includes: When measuring the distance at the position where the target moves before, the time domain expression of the difference frequency signal intensity obtained after the interference of the object light and the reference light is: In the formula, , They are respectively the light intensity at the rising and falling edges of the difference frequency signal obtained after the interference of the object light and the reference light when measuring the distance at the position before the target moves; , are the intensities of the reference light and the object light, respectively; The time difference corresponding to the optical path difference between the object light and the reference light when measuring the distance to the position of the target before it moves; is the frequency modulation rate, that is, the slope of the rising edge of the triangle wave, is the FM bandwidth, is the frequency modulation period; When measuring the distance at the position where the target moved before, the phase difference between the rising and falling edges is ; Similarly, when measuring the distance at the position where the target moves, the time difference corresponding to the optical path difference between the object light and the reference light is , then when measuring the distance at the position where the target moves, the phase difference between the rising and falling edges is ; Based on the intensity signal of the interference light corresponding to the position of the target before and after movement, the phase difference is calculated: ; Depend on , we can conclude ; but, .

10. The high-precision laser phase ranging method for a common optical path according to claim 9, characterized in that: The range is 0- ,when hour, but The value range is 0- ,in, is the wavelength of the laser signal.

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