A method for super-resolution error compensation in a pulsed laser ranging system

Abstract

A super-resolution error compensation method for a pulsed laser ranging system is disclosed. The method comprises five steps: constructing a time deviation parameter set, constructing a phase compensation sequence, calculating the correlation coefficient, obtaining the time deviation, and performing phase compensation on the signal sequence. The pulsed laser ranging system consists of five parts: a pulsed laser source, a laser transmitter and receiver, a photoelectric converter, a signal acquisition and preprocessor, and a signal analysis and output unit. This invention designs the algorithm from the perspective of improving error compensation accuracy, considering the characteristics of the laser ranging device itself, saving hardware resources, reducing the requirements for device stability and real-time performance, and lowering the cost of error compensation. It can enhance the accuracy of error compensation even under extremely subtle jitter in the laser ranging device, improving the signal-to-noise ratio and data accuracy.

Description

Technical Field

[0001] This invention belongs to the field of laser measurement technology, specifically relating to a super-resolution error compensation method for a pulsed laser ranging system. Background Technology

[0002] With the development of ultrafast laser technology, the use of optical pulse sequences in ranging has significantly improved the dynamic range and distance resolution of measurements. However, the inherent instability of the laser itself, signal drift caused by inherent jitter in the measuring device, and the reduction in signal-to-noise ratio all affect the accuracy of distance measurement, severely limiting the performance of high-precision distance measurement systems. Current solutions focus on stabilizing the system at the hardware level, including using motorized translation stages with feedback control and high-degree-of-freedom servo systems. Compensating for system jitter through hardware improvements is expensive, and it is difficult to eliminate the extremely fine jitter introduced by the device itself.

[0003] Currently, software-based jitter compensation for measurement signals containing distance information still lags behind hardware-based compensation methods in terms of efficiency and accuracy. Traditional compensation methods cannot overcome the inherent time resolution of the signal and are insensitive to minute jitter inherent in the system itself, preventing further improvement in error compensation accuracy and leading to the problem of ineffective control of measurement errors in distance measurements. Summary of the Invention

[0004] To address the aforementioned problems, this invention aims to provide a super-resolution error compensation method for pulsed laser ranging systems.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A super-resolution error compensation method for a pulsed laser ranging system is disclosed. The super-resolution error compensation method consists of five steps: constructing a time deviation parameter set, constructing a phase compensation sequence, calculating the correlation coefficient, obtaining the time deviation, and performing phase compensation on the signal sequence.

[0007] The pulsed laser ranging system consists of five parts: a pulsed laser source, a laser transmitter and receiver, a photoelectric converter, a signal acquisition and preprocessor, and a signal analysis and output unit.

[0008] The signal acquisition and preprocessor will generate a periodic discrete signal sequence containing ranging information, and through repeated measurements, obtain a signal sequence set Y1, Y2…Y N Each of these sequences corresponds to a set of equally spaced (Δt) time series T = {t1, t2, ..., tt}. N} T .

[0009] Using Y1 as the reference signal sequence, sequentially process the sequences Y2…Y in the set. N The overall time and position error compensation method consists of five steps, as follows:

[0010] Step 1: Construct the time deviation parameter set Γ={τ1,τ2,…,τ m}, where the minimum difference between parameter values ​​can be less than Δt;

[0011] Step 2: Select a time deviation parameter τ i Construct the phase compensation sequence Φ of the signal in the frequency domain. i = exp{jWτ i / Δt}( That is, an equally spaced frequency sequence, for the signal Y to be compensated k (k>1), perform the operation: Y k,i =IFFT{FFT{Y k}·Φ i}, where FFT and IFFT represent the Discrete Fourier Transform and Inverse Fourier Transform, respectively;

[0012] Step 3: Calculate Y k,i Correlation coefficient with Y1: C k,i =∑{Y k,i ·Y1};

[0013] Step 4: For all parameters in the time deviation parameter set, perform the operations of Step 2 and Step 3 to obtain the corresponding correlation coefficients, and select the time deviation τ corresponding to the maximum value of the coefficient from all the correlation coefficients. x ∈Γ, that is, signal Y k Regarding the overall time deviation estimate of Y1, Y k,x That is, the compensated signal sequence;

[0014] Step 5: For the repeatedly acquired signal sequence set, perform time deviation compensation sequentially to obtain the compensated signal sequence set {Y1, Y...} 2，x …,Y n，x The averaged signal sequence is} and the set of time bias estimates {τ1, τ 2,x …,τ n,x}, its average value is Finally, from this set of signal sequences, the error-compensated signal sequence with statistical average significance is extracted, that is:

[0015] The pulsed laser source emits laser pulses with a fixed time period, a repetition frequency of 64 MHz, a repetition frequency phase noise of approximately -140 dBc / Hz at a 1 kHz offset, a pulse width of approximately 1 ps, and a power of 13 mW.

[0016] The laser emitting and receiving device is a set of Michelson interferometers. The emitting optical path includes a probe optical path and a local reference optical path. The probe optical path emits a pulsed laser at the target object. After the light is reflected on the surface of the target object, it is received by the receiving device. The local reference light source is generated by splitting the pulsed laser light source and changing the time period of the laser pulse through a periodically changing laser delay line. The maximum delay of the laser delay line is 50 ps, ​​and the delay changes in a sinusoidal curve with a period of 0.5s. The received probe light signal interferes with the reference light source. The intensity of the light signal after interference changes with the laser delay, resulting in a time-varying laser interference signal with periodicity.

[0017] The local reference light source in the laser emitting and receiving device can also be another pulsed laser light source with a different time period.

[0018] The photoelectric converter converts the laser interference signal into a time-varying periodic electrical signal.

[0019] The signal acquisition and preprocessor described above digitally discretizes the periodic electrical signal and performs digital filtering and amplification operations on the periodic electrical signal to form a set of periodic discrete signal sequences: Y i ={y i1 ,y i2 ,…,y iN} T To prevent the DC quantity carried by the original signal from affecting the distance resolution, the obtained discrete-time signal sequence Y is... i Take the average value Then in the signal sequence Y i Subtract its average value from each corresponding point. Obtain the time discrete signal sequence Y without DC flow. i (i.e., Y) i The mean is 0);

[0020] The signal acquisition and preprocessor includes a 12-bit analog-to-digital converter with a sampling rate of up to 1.8 GSa / s, and acquires discrete sequences with a time length of 8ms within one period.

[0021] The parameter values ​​in the time deviation parameter set are evenly distributed, and the distribution range is set to the time span corresponding to the interval of the interference signal fringe, which is about 20 μs. The fixed difference between the parameters is determined by the size of the parameter set, and this fixed difference also determines the resolution of the compensation method.

[0022] In step 4, the selection order of time deviation parameters can be based on their numerical values, or by referring to the time deviation estimates of preceding signal sequences and prioritizing parameters with similar values. After step 4 and before step 5, the time deviation parameter set Γ can be modified multiple times, including adjusting the numerical distribution range of the parameters, reducing the numerical differences between parameters, and repeating the operations from steps 1 to 4. This improves the estimation accuracy of the time deviation of the signal sequence. Simultaneously, increasing the number of signal sequences (n) under a single measurement condition can enhance the accuracy of the signal sequence estimation. This improves the signal-to-noise ratio and time accuracy, thereby enhancing the accuracy and sensitivity of the ranging system. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the specific embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of a super-resolution error compensation system for a pulsed laser ranging system according to an embodiment of the present invention;

[0025] Figure 2 This is a flowchart illustrating a super-resolution error compensation method for a pulsed laser ranging system according to an example of the present invention.

[0026] Figure 3 This is a schematic diagram illustrating the structural principle of a pulsed laser source in an example of the present invention.

[0027] Figure 4 This is a schematic diagram of a Michelson interferometer used as a laser emitting and receiving device in an example of the present invention.

[0028] Figure 5 This is a schematic diagram of a discrete sequence collected within one period in an example of the present invention;

[0029] Figure 6a This is a stacked diagram of multiple signal sequences obtained under a single measurement condition through repeated acquisition in an example of the present invention;

[0030] Figure 6b This is a stacked diagram of multiple signal sequences after compensation in an example of the present invention;

[0031] Figure 7 This is a scatter plot of the overall time deviation estimate in an example of the present invention;

[0032] Figure 8 This is a schematic diagram of the compensation result in an example of the present invention;

[0033] Figure 9 This is a schematic diagram of the signal-to-noise ratio improvement result in an example of the present invention;

[0034] In the diagram, 1-The pulsed laser ranging system consists of a pulsed laser source; 2-Laser transmitter and receiver; 3-Photoelectric converter; 4-Signal acquisition and preprocessor; 5-Signal analysis and output unit. Detailed Implementation

[0035] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. However, it should not be construed that the scope of the subject matter of the present invention is limited to the following embodiments. All modifications, substitutions and alterations made based on ordinary technical knowledge and common practices in the art without departing from the above-described technical concept of the present invention are included within the scope of the present invention.

[0036] Reference Figure 1 In the example, the pulsed laser ranging system Y i Generated by a pulsed laser ranging system, which consists of five parts: a pulsed laser source (1), a laser transmitter and receiver (2), a photoelectric converter (3), a signal acquisition and preprocessor (4), and a signal analysis and output unit (5). The reference signal sequence is Y1Y1, Y2…Y1…Y ... N Generated by a pulsed laser ranging system.

[0037] Reference Figure 2 In this example, to compensate for the minute time jitter in the signal caused by the error of the ranging system itself, Y1 is used as the reference signal sequence. Following steps 1 to 5 of the super-resolution error compensation method mentioned in the invention, calculation program code is written on the data processing platform to sequentially process the sequences Y2…Y1 in the set. N Perform overall time and position error compensation.

[0038] First, input the reference signal sequence Y1 and assign values ​​to Y. ref Construct a loop to iterate through the sequence Y2…Y in the set to be compensated. N Enter Y2…Y in sequence N And assign the value to Y in A frequency sequence W is constructed with equal intervals within a range of 2π, containing the same number of points as the signal sequence.

[0039] Construct the time deviation parameter set Γ={τ1,τ2,…,τ mThe values ​​of the time deviation parameter are evenly distributed, and the distribution range is set to the time span corresponding to the interval of the interference signal fringe, which is about 20 μs. The fixed difference between the parameters is determined by the size of the parameter set. This fixed difference also determines the resolution of the compensation method, which in principle can be less than the signal time interval Δt.

[0040] Create a data space C to store the results of the correlation coefficient calculation.

[0041] Construct a loop to iterate through each parameter in the time deviation parameter set Γ. Select the time deviation parameter τ in sequence. i Construct the phase compensation sequence Φ of the signal in the frequency domain. i =exp{jWτ i / Δt}, for the signal Y to be compensated in Perform the operation: Y in =IFFT{FFT{Y in}·Φi}, and calculate Y in With Y ref Correlation coefficient: Ci=∑{Y in ·Y ref}

[0042] After traversing all the parameters in the time deviation parameter set, a sequence of correlation coefficients, namely Y, can be obtained. in With Y ref Corresponding to each time deviation parameter τ i The correlation coefficient. The time deviation τ corresponding to the maximum value of the correlation coefficient is selected using the max function. x , that is, signal Y in About Y ref The overall time deviation estimate. Finally, for signal Y... in Compensation for the corresponding time deviation τ x Get Y out =IFFT{FFT{Y in}·exp{jWτ x / Δt}} is the compensated signal sequence, such as Figure 6b As shown.

[0043] Iterate through all sequences Y2…Y to be compensated N Then, the compensated signal sequence set {Y1,Y} is obtained. 2,x …,Y n,x The averaged signal sequence is calculated as follows: And Y2…Y N For the set of overall time deviation estimates of Y1 {τ1, τ 2,x …,τ n,x},like Figure 7 As shown, its average value is calculated as follows. Finally, from this set of signal sequences, the error-compensated signal sequence with statistical average significance is extracted, that is:

[0044] Reference Figure 3 In the example, the pulsed laser-based ranging system uses a fully polarization-maintaining mode-locked fiber laser as the pulsed laser source 1, with a repetition frequency of 64MHz and a repetition-frequency phase noise of approximately -140 dBc / Hz at a 1kHz offset. The pulse width is approximately 1ps, and the power is 13mW.

[0045] Reference Figure 4 In this example, a Michelson interferometer is used as the laser transmitting and receiving device 2. The reference light source in the receiving device is generated by beam splitting from a pulsed laser source 1, and the time period of the laser pulse is changed by a periodically varying laser delay line. The maximum delay of the laser delay line is 50 ps, ​​and the delay varies in a sinusoidal curve with a period of 0.5 s. The received probe light signal interferes with the reference light source, and the intensity of the interfering light signal changes with the laser delay, thus forming a set of periodically varying optical intensity signals.

[0046] The photoelectric converter 3 (>300MHz) converts the signal into a time-varying periodic electrical signal.

[0047] Reference Figure 5 In this example, the signal acquisition and preprocessor 4 includes a 12-bit analog-to-digital converter with a sampling rate of up to 1.8 GSa / s, and acquires discrete sequences with a time length of 8 ms within one period;

[0048] The discrete sequence contains a relatively complete laser interferometry signal. After digital filtering and amplification, a one-period discrete-time signal sequence Y is finally obtained. i ={y i1 ,y i2 ,…,y iN} T .

[0049] To prevent the DC quantity carried by the original signal from affecting the distance resolution, the obtained discrete-time signal sequence Y is processed. i Take the average value Then in the signal sequence Y i Subtract its average value from each corresponding point. Obtain the time discrete signal sequence Y without DC flow. i Construct a set of equally spaced (Δt) time series T = {t1, t2, ..., tt} corresponding to the discrete-time signal sequence. N} TThe time window corresponds to the scan period of the scan delay line, which is 0.5s. Through repeated acquisitions, multiple signal sequences under a single measurement condition can be obtained, forming the set Y1, Y2…, Y… n},like Figure 6a As shown in the figure, it is clear from the figure that due to the error of the ranging system itself, the overall signal strength and time position of the acquired signal undergo random changes. The range of time variation (σ) is shown in the figure. t It can be smaller than the time series interval (σ) corresponding to the signal. t <Δt), which is the amount of error below the signal time resolution (over-resolution error).

[0050] Figure 8 The image shows a comparison between the final compensated signal sequence and the initial sequence set. The thick line represents the signal sequence after error compensation, which has statistical significance. It can be seen that the compensated signal sequence has less time jitter than the uncompensated signal, which is the result of compensating for the time offset introduced by the system's own errors. The thick line can be considered as the interference signal that best reflects distance information within that measurement time.

[0051] By calculating the peak-to-peak value V of the signal pp With the noise root mean square error σ noise The signal-to-noise ratio (SNR) was calculated to be SNR = 10·log 10 (V pp / 2·σ noise ),like Figure 9 As shown. Signal The signal-to-noise ratio (SNR) increases with the number of signal sequences (n) under a single measurement condition. This increased SNR improves timing accuracy, thereby enhancing the accuracy and sensitivity of the ranging system.

[0052] The super-resolution error compensation method for a pulsed laser ranging system provided by this invention has been described in detail above. Specific examples have been used to illustrate the structure and working principle of this invention. The descriptions of the embodiments above are only for the purpose of helping to understand the method and core ideas of this invention. It should be noted that those skilled in the art can make several improvements and modifications to this invention without departing from the principles of this invention, and these improvements and modifications also fall within the scope of protection of the claims of this invention.

Claims

1. A super-resolution error compensation method for a pulsed laser ranging system, characterized in that: The super-resolution error compensation method consists of five steps: constructing a time deviation parameter set, constructing a phase compensation sequence in the frequency domain, calculating the correlation coefficient, obtaining the time deviation, and compensating the phase of the signal sequence. A periodic discrete signal sequence containing ranging information is generated through signal acquisition and preprocessor (4), and a signal sequence set is obtained through repeated measurements. , Each of these sequences corresponds to a set of equally spaced sequences. time series ;by Using the reference signal sequence, sequentially process the sequences in the set. The overall time and position error compensation method consists of five steps, as follows: Step 1: Construct the time deviation parameter set The minimum difference between parameter values ​​can be less than ; Step 2: Select a time deviation parameter Construct a phase compensation sequence for the signal in the frequency domain. That is, an equally spaced frequency sequence, for the signal to be compensated. Perform the operation: ,in FFT and IFFT Represents the Discrete Fourier Transform and its inverse; Step 3: Calculation and Correlation coefficient: ; Step 4: For all parameters in the time deviation parameter set, perform the operations of Step 2 and Step 3 to obtain the corresponding correlation coefficients, and select the time deviation corresponding to the maximum value of the coefficient from all the correlation coefficients. signal about The overall time deviation estimate, That is, the compensated signal sequence; Step 5: For the repeatedly acquired signal sequence set, perform time offset compensation sequentially to obtain the compensated signal sequence set. The averaged signal sequence is and a set of time deviation estimates Its average value is Finally, from this set of signal sequences, the error-compensated signal sequence with statistical average significance is extracted, i.e.: .

2. The super-resolution error compensation method for the pulsed laser ranging system according to claim 1, characterized in that: The pulsed laser ranging system consists of five parts: a pulsed laser source (1), a laser transmitting and receiving device (2), a photoelectric converter (3), a signal acquisition and preprocessor (4), and a signal analysis and output unit (5).

3. The super-resolution error compensation method for the pulsed laser ranging system according to claim 2, characterized in that: The pulsed laser source (1) emits laser pulses with a fixed time period, a repetition frequency of 64MHz, a repetition frequency phase noise of about -140dBc / Hz at a 1kHz offset, a pulse width of about 1ps, and a power of 13mW. The laser emitting and receiving device (2) is a set of Michelson interferometers. The emitting optical path includes a probe optical path and a local reference optical path. The probe optical path emits a pulsed laser at the target object. After the light is reflected on the surface of the target object, it is received by the receiving device. The local reference light source is generated by splitting the pulsed laser light source and changing the time period of the laser pulse through a periodically changing laser delay line. The maximum delay of the laser delay line is 50 ps, ​​and the delay changes in a sinusoidal curve with a period of 0.5 s. The received probe light signal interferes with the reference light source. The intensity of the light signal after interference will change with the change of the laser delay, and a laser interference signal that changes with time is obtained. This laser interference signal has a time periodicity. The local reference light source in the laser emitting and receiving device (2) can also be another pulsed laser light source with a different time period; The photoelectric converter (3) converts the laser interference signal into a time-varying periodic electrical signal.

4. The super-resolution error compensation method for the pulsed laser ranging system according to claim 2, characterized in that: The signal acquisition and preprocessor (4) digitally discretizes the periodic electrical signal and performs digital filtering and digital amplification operations on the periodic electrical signal to form a set of periodic discrete signal sequences: To prevent the DC quantity carried by the original signal from affecting the distance resolution, the obtained discrete-time signal sequence is... Take the average value In the signal sequence Subtract its average value from each corresponding point. This yields a time-discrete signal sequence without direct current. ,Right now The mean is 0; The signal acquisition and preprocessor (4) includes a 12-bit analog-to-digital converter with a sampling rate of up to 1.8GSa / s, and acquires discrete sequences with a time length of 8ms within one cycle.

5. The super-resolution error compensation method for the pulsed laser ranging system according to claim 2, characterized in that: The parameter values ​​in the time deviation parameter set are evenly distributed, and the distribution range is set to the time span corresponding to the interval of the interference signal fringe, which is about 20µs. The fixed difference between the parameters is determined by the size of the parameter set, and this fixed difference also determines the resolution of the compensation method.

6. The super-resolution error compensation method for the pulsed laser ranging system according to claim 2, characterized in that: In step 4, the selection order of time deviation parameters can be based on their numerical values, or the time deviation estimates of the preceding signal sequence can be referenced, prioritizing parameters with similar values. After step 4 and before step 5, the set of time deviation parameters can be modified multiple times. This includes adjusting the numerical distribution range of the parameter set, reducing the numerical differences between parameters, and repeating steps 1 to 4 to improve the estimation accuracy of the time deviation of the signal sequence. Simultaneously, increasing the number of signal sequences n under a single measurement condition can improve the accuracy of the signal sequence estimation. This improves the signal-to-noise ratio and time accuracy, thereby enhancing the accuracy and sensitivity of the ranging system.

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