CN112946611B - Sweep frequency nonlinear correction distance measurement method based on similar triangular interpolation sampling - Google Patents
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
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- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
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- G01S17/08—Systems determining position data of a target for measuring distance only
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- G—PHYSICS
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- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
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Abstract
A frequency sweep nonlinear correction ranging method based on similar triangular interpolation sampling relates to the technical fields of Frequency Sweep Interferometry (FSI) measurement, FMCW laser radar and the like, aims at solving the problems that an accurate resampling sequence cannot be provided by the existing method, and the frequency sweep nonlinearity is not thoroughly eliminated to cause the reduction of the frequency sweep interferometry precision, is used for eliminating the frequency spectrum broadening effect generated by the frequency sweep nonlinearity of a frequency sweep laser, and can effectively improve the excellent property of measuring the full width at half maximum of a frequency spectrum. Especially for measuring extreme distances, the error is smaller than taking a near zero point as a sampling point. Meanwhile, similar interpolation algorithms are faster in signal processing speed due to the use of matrix multiplication. The invention ensures the high-precision and high-real-time processing of the measurement result when the absolute distance measurement system carries out remote measurement.
Description
Technical Field
The invention relates to the technical fields of Frequency Sweep Interferometry (FSI) measurement, FMCW laser radar and the like, in particular to a frequency sweep nonlinear correction ranging system and method based on similar triangular interpolation sampling.
Background
The sweep frequency interference measurement has the advantages of low emission power, no range finding ambiguity, no guide rail matching, applicability to cooperative target measurement, capability of realizing high-resolution measurement and the like, so that the sweep frequency interference measurement is widely applied to the field of high-precision absolute distance measurement, such as the fields of frequency modulation continuous laser radar, optical frequency meters, optical coherence tomography and the like. The basic principle is that a fixed frequency difference is formed between an emitted measuring optical signal and a swept frequency measuring optical signal reflected by a measured target to determine the absolute distance of the target, and the absolute distance parameter of the target is reflected by means of signal frequency domain characteristics which are easy to process. High distance resolution and measurement accuracy can be obtained by high-linearity broadband frequency sweep measurement light, but a linear tuned laser in the current market cannot meet the condition of high-linearity linear frequency sweep, nonlinear frequency sweep brings difficulty to signal frequency domain characteristic analysis, and a non-single frequency beat signal not only can reduce the distance resolution, but also greatly reduces the measurement accuracy. In the existing method, an auxiliary interferometer is adopted to sample sweep frequency optical signals, and a sampling sequence is formed by extracting the zero crossing point of the auxiliary interferometer signals to collect measurement interferometer signals. However, the zero crossing point of the auxiliary interferometer signal is not necessarily positioned in the auxiliary interferometer signal sampling, so that the resampling sequence cannot be accurately determined, the sweep nonlinearity cannot be completely eliminated, and the precision of sweep interference measurement is reduced.
Disclosure of Invention
The purpose of the invention is: aiming at the problems that the existing method can not provide an accurate resampling sequence and sweep frequency nonlinearity elimination is not thorough, so that sweep frequency interference measurement precision is reduced, a sweep frequency nonlinearity correction distance measurement method based on similar triangular interpolation sampling is provided.
The technical scheme adopted by the invention to solve the technical problems is as follows:
a sweep frequency nonlinear correction ranging method based on similar triangular interpolation sampling is realized by utilizing a sweep frequency nonlinear correction device;
the frequency sweep nonlinear correction device comprises: the system comprises a measuring interferometer, an auxiliary interferometer and an acquisition card;
the measuring interferometer comprises a PBS, a focusing optical system, a 1/4 wave plate and a balanced detector;
the auxiliary interferometer comprises two 3dB optical fiber couplers;
the sweep laser beam splitting ratio is 95: after the optical fiber coupler of 5 splits light, 95% sweep light and 5% sweep light are obtained, and the splitting ratio of the 95% sweep light is 99: the optical fiber coupler of 1 is divided into measuring light of a measuring interferometer and reference light of the measuring interferometer, the measuring light of the measuring interferometer sequentially passes through a PBS (polarization beam splitter), a focusing optical system and a 1/4 wave plate and then is emitted, and after being reflected by a measuring target, an original path returns and is mixed with the reference light of the measuring interferometer on a detection plane of a balance detector to obtain a beat frequency signal of the measuring interferometer, namely an optical signal of the measuring interferometer;
the 5% sweep light is divided into 50% by a 3dB fiber coupler: measuring light of an auxiliary interferometer and reference light of the auxiliary interferometer of 50, combining the measuring light of the auxiliary interferometer and the reference light of the auxiliary interferometer by a 3dB optical fiber coupler, and mixing on a balance detector to obtain a beat frequency signal of the auxiliary interferometer, namely an optical signal of the auxiliary interferometer;
the acquisition card is used for acquiring and storing a beat frequency signal of the measuring interferometer and a beat frequency signal of the auxiliary interferometer;
the sweep frequency nonlinear correction ranging method based on similar triangular interpolation sampling comprises the following specific steps:
the method comprises the following steps: obtaining a measurement interferometer optical signal ImcAnd auxiliary interferometer optical signal IdcAnd obtaining a measurement interferometer signal sequence I according to the measurement interferometer optical signal and the auxiliary interferometer optical signalmAnd an auxiliary interferometer signal sequence Id；
Step two: extracting a signal sequence I of the measuring interferometermAnd an auxiliary interferometer signal sequence IdIn odd order1m、I1dAnd even-order data sequences I2m、I2d；
Step three: will I1dAnd I2dCorresponding multiplication is carried out, the multiplication results are screened to obtain a plurality of groups of adjacent data points with zero points between two points, then data point labels are recorded, and a set I is formedo；
Step four: will be set IoPerforming similar fitting on each group of adjacent data points to obtain a zero horizontal coordinate value set A between each group of adjacent data pointsoAfter that, the set A isoAfter arrangement, determining a resampling sequence Bo；
Step five: using set IoData point index pair I of two adjacent points in which zero exists1mAnd I2mReading data to obtain a resampling sequence BoMeasuring interferometer data points I corresponding to two sides1mo、I2moThen use I1mo、I2moAnd a resampling sequence BoTo I1mo、I2moPerforming similar interpolation to obtain a corrected signal of the measuring interferometer;
step six: and carrying out spectrum analysis on the corrected measuring interferometer signal, searching for the maximum value of the spectrum peak value, and carrying out corresponding linear transformation to obtain a corrected distance measuring result.
Further, the swept laser is obtained by an external cavity laser.
Further, the frequency of the beat frequency signal of the measuring interferometer is determined according to the arm length difference of the measuring interferometer and the measuring distance.
Further, the measurement interferometer optical signal is represented as:
wherein, AmFor measuring interferometer optical signal amplitude, 2RmTo measure the interferometer arm length difference, Δ f (t) is the sweep frequency variation, and c is the speed of light.
Further, the auxiliary interferometer light signal is represented as:
wherein A is0To assist the interferometer in amplitude of the optical signal, R0To assist interferometer arm length difference, Δ f (t) is sweep frequency variation, and c is speed of light.
Further, the sweep variation Δ f (t) is expressed as:
wherein k is the resample sequence sample sequence index.
Further, the interferometer signal measured in the fifth step is expressed as:
the beneficial effects of the invention are:
the method is used for eliminating the spectrum broadening effect generated by the non-linearity of the sweep frequency laser, and can effectively improve the excellent property of measuring the full width at half maximum of the spectrum. Especially for measuring extreme distances, the error is smaller than taking a near zero point as a sampling point. Meanwhile, similar interpolation algorithms are faster in signal processing speed due to the use of matrix multiplication. The invention ensures the high-precision and high-real-time processing of the measuring result when the absolute distance measuring system carries out remote measurement.
Drawings
FIG. 1 is a diagram of the optical path of the hardware system of the present application;
FIG. 2 is a schematic diagram of a linear fit similarity difference algorithm;
FIG. 3 is a flow chart of swept nonlinear correction ranging with similar triangular interpolation sampling;
FIG. 4 is a schematic diagram of a 0.1s sweep time simulation;
FIG. 5 is a schematic diagram of a 0.105s sweep time simulation;
FIG. 6 is a schematic diagram of a sweep time 0.110s simulation;
FIG. 7 is a schematic diagram of a 0.115s sweep time simulation;
FIG. 8 is a schematic diagram of a sweep time 0.12s simulation;
FIG. 9 is a schematic diagram of a sweep time 0.125s simulation;
FIG. 10 is a schematic diagram of a sweep time 0.13s simulation;
FIG. 11 is a schematic diagram of a sweep time of 0.135s simulation;
FIG. 12 is a schematic diagram of a 0.14s sweep time simulation;
FIG. 13 is a schematic diagram of a sweep time 0.145s simulation;
FIG. 14 is a schematic diagram of a 0.15s sweep time simulation;
FIG. 15 is a schematic diagram of a sweep time 0.155s simulation;
FIG. 16 is a schematic diagram of a 0.16s sweep time simulation;
FIG. 17 is a schematic diagram of a sweep time 0.165s simulation;
FIG. 18 is a schematic diagram of a 0.17s sweep time simulation;
FIG. 19 is a schematic diagram of a sweep time 0.175s simulation;
FIG. 20 is a schematic diagram of a sweep time 0.18s simulation;
FIG. 21 is a schematic diagram of a sweep time 0.185s simulation;
FIG. 22 is a schematic diagram of a sweep time 0.19s simulation;
fig. 23 is a simulation diagram of sweep time 0.195s.
Detailed Description
It should be noted that, in the case of conflict, the various embodiments disclosed in the present application may be combined with each other.
The first specific implementation way is as follows: specifically describing the present embodiment with reference to fig. 1, fig. 2 and fig. 3, the method for distance measurement based on sweep frequency nonlinear correction of similar triangular interpolation sampling according to the present embodiment is implemented by using a sweep frequency nonlinear correction device;
the frequency sweep nonlinear correction device comprises: the system comprises a measuring interferometer, an auxiliary interferometer and an acquisition card;
the measuring interferometer comprises a PBS, a focusing optical system, a 1/4 wave plate and a balanced detector;
the auxiliary interferometer comprises two 3dB optical fiber couplers;
the sweep laser beam splitting ratio is 95: after the optical fiber coupler of 5 splits light, 95% sweep light and 5% sweep light are obtained, and the splitting ratio of the 95% sweep light is 99: the optical fiber coupler of 1 is divided into measuring light of a measuring interferometer and reference light of the measuring interferometer, the measuring light of the measuring interferometer sequentially passes through a PBS (polarization beam splitter), a focusing optical system and a 1/4 wave plate and then is emitted, and after being reflected by a measuring target, an original path returns and is mixed with the reference light of the measuring interferometer on a detection plane of a balance detector to obtain a beat frequency signal of the measuring interferometer, namely an optical signal of the measuring interferometer;
the 5% sweep light is divided into 50% by a 3dB fiber coupler: measuring light of an auxiliary interferometer and reference light of the auxiliary interferometer of 50, combining the measuring light of the auxiliary interferometer and the reference light of the auxiliary interferometer by a 3dB optical fiber coupler, and mixing on a balance detector to obtain a beat frequency signal of the auxiliary interferometer, namely an optical signal of the auxiliary interferometer;
the acquisition card is used for acquiring and storing the beat frequency signal of the measurement interferometer and the beat frequency signal of the auxiliary interferometer;
the sweep frequency nonlinear correction ranging method based on similar triangular interpolation sampling comprises the following specific steps:
the method comprises the following steps: obtaining measurement interferometer optical signals ImcAnd auxiliary interferometer optical signal IdcAnd obtaining a measurement interferometer signal sequence I according to the measurement interferometer optical signal and the auxiliary interferometer optical signalmAnd an auxiliary interferometer signal sequence Id；
Step two: extracting a signal sequence I of the measuring interferometermAnd auxiliary interferometer signal sequence IdIn odd order1m、I1dAnd even-order data sequences I2m、I2d；
Step three: will I1dAnd I2dCorresponding multiplication is carried out, the multiplication results are screened to obtain a plurality of groups of adjacent data points with zero point between two points, then data point labels are recorded, and a set I is formedo；
Step four: set IoPerforming similar fitting on each group of adjacent data points to obtain a zero horizontal coordinate value set A between each group of adjacent data pointsoAfter that, the set A isoDetermining a resampling sequence B after the arrangemento；
Step five: using set IoData point index pair I of two adjacent points in which zero exists1mAnd I2mReading data to obtain a resample sequence BoMeasuring interferometer data points I corresponding to two sides1mo、I2moThen use I1mo、I2moAnd a resampling sequence BoTo I1mo、I2moPerforming similar interpolation to obtain a corrected signal of the measuring interferometer;
step six: and carrying out spectrum analysis on the corrected measuring interferometer signal, searching for the maximum value of the spectrum peak value, and carrying out corresponding linear transformation to obtain a corrected distance measuring result.
According to the method and the device, the sampling points of the auxiliary interferometer are found, the sampling points are fine enough, linear fitting can be conducted on the sampling points on two sides of the zero crossing point, and the time domain coordinate of the zero crossing point of the auxiliary interferometer is found accurately through corresponding operation of similar triangles. Compared with the traditional method, the method provided by the patent improves the measurement precision of the signal of the measuring interferometer. In simulation, the fact that when the optical path difference of the auxiliary interferometer is 2 times of the optical path difference of the measuring interferometer, the spectrum peak of the measuring signal changes after the zero-crossing point resampling is not accurately positioned at the moment, and finally micrometer-level deviation is generated in absolute distance measurement.
The method is used for eliminating the spectrum broadening effect generated by the non-linearity of the sweep frequency laser, and can effectively improve the excellent property of measuring the full width at half maximum of the spectrum. Especially for measuring extreme distances, the error is smaller than taking a near zero point as a sampling point. Meanwhile, similar interpolation algorithms are faster in signal processing speed due to the use of matrix multiplication. The high-precision and high-real-time processing of the measurement result when the absolute distance measurement system carries out remote measurement is ensured.
The hardware part of the invention is mainly divided into a sweep frequency interference distance measuring light path, an auxiliary interferometer 1 and an acquisition card. The frequency sweep interference distance measuring optical path mainly comprises a Mach-Zehnder interferometer formed by a plurality of fiber-coupled PBS, WDM, a focusing optical system, a 1/4 wave plate and a balance detector, the frequency sweep nonlinearity is measured by an auxiliary interferometer, and the signal of the measuring interferometer is resampled by adopting a frequency sampling method of software to eliminate the nonlinear phase introduced by frequency sweep laser. Since the sampling points hardly coincide with the theoretical zero crossings, the sequence of frequency samples generated on the basis of the auxiliary interferometer cannot be determined accurately when the auxiliary interferometer signal frequency drops, and at the same time re-sampling on the basis of this sequence will not completely eliminate the non-linearity of the measuring interferometer. Therefore, the patent proposes to judge the real zero crossing point of the signal based on the triangular similarity, and further improve the nonlinear elimination effect of the frequency sampling method.
Two paths of optical signals are generated in the optical path, wherein one path of optical signal passes through a measurement target, and a return optical beat frequency signal of the optical signal is called as a measurement interferometer optical signal; and the other optical signal passes through the optical path of the auxiliary interferometer, the optical beat frequency signal received by the detector is called as the optical signal of the auxiliary interferometer, and the two optical signals are expressed mathematically as follows:
in the formula Im(t)、I0(t) measuring the interferometer light signal on the auxiliary interferometer light signal, Am、A0For measuring the amplitude of the optical signal of the interferometer at the amplitude of the optical signal of the auxiliary interferometer, 2Rm、R0In order to measure the interferometer arm length difference and the auxiliary interferometer arm length difference, Δ f (t) is the sweep frequency variation.
To eliminate the sweep nonlinearity caused by Δ f (t), the signal processing procedure is called frequency sampling method by determining the zero crossings of equation 2 and then resampling equation 1 by the sampling sequence generated by these zero crossings. The sampling mode of the frequency sampling method is shown in formula 3, in the sampling process, the sweep frequency nonlinearity delta f (t) in the formula can be represented by a linear sequence, and a measurement interferometer signal after the frequency sampling method is shown in formula 4, so that a single-frequency signal related to the measurement distance is obtained theoretically. Fig. 3 shows a flow chart of the method adopted by the patent.
The determination of zero crossings by linear fitting will prove to be more effective than the determination of sampling points near zero in the following simulations, which can be illustrated by the following simulations.
The simulation conditions are set such that the measurement interferometer arm length difference setting range is 1m to 54m, the auxiliary interferometer arm length difference is 109m, the sampling frequency of the signal in the simulation is set to 10MHz, and the sweep time is set to 0.1s, 0.105s, 0.11s, 0.115s, 0.120s, 0.125s, 0.130s, 0.135s, 0.140s, 0.145s, 0.150s, 0.155s, 0.160s, 0.165s, 0.170s, 0.175s, 0.180s, 0.185s, 0.190s, 0.195s. The simulation shows that the measurement error generated when the measurement distance approaches the arm length difference of the auxiliary interferometer can be eliminated to a great extent, and the algorithm value deviation caused by data processing is eliminated. In the simulation diagram, linear refers to simulation data points by adopting a Linear fitting method of similar triangles, and Near refers to simulation data points by adopting a sampling point method Near a zero point.
Simulation description:
according to the description of fig. 4 to fig. 23, simulation is performed, the distance from the measurement target to the balanced detector in the simulation is a variable from 1m to 54m, and it can be seen from each simulation that when the measurement interferometer arm length difference gradually approaches to half of the auxiliary interferometer arm length difference, the sampling method using the proximity point as the resampling sequence cannot completely eliminate the influence of the sweep frequency nonlinearity on the measurement interferometer frequency spectrum, and the nonlinear correction method using the similarity fitting to determine the resampling sequence has smaller measurement error. The method adopting the near point as the resampling sequence is sensitive to the parameter of the sequence length, and the distance demodulation error and the sequence length are in a nonlinear relation in simulation. As demonstrated in the above simulations, the sampling method employed in this patent can ensure the effect on the cancellation of non-linear errors in fast distance measurements, attenuating the errors introduced by clock jitter. In the actual measurement process, the method adopted by the patent effectively avoids errors introduced by an algorithm.
It should be noted that the detailed description is only for explaining and explaining the technical solution of the present invention, and the scope of protection of the claims is not limited thereby. It is intended that all such modifications and variations be included within the scope of the invention as defined in the following claims and the description.
Claims (7)
1. The sweep frequency nonlinear correction distance measurement method based on similar triangular interpolation sampling is characterized in that the method is realized by utilizing a sweep frequency nonlinear correction device;
the frequency sweep nonlinear correction device comprises: the system comprises a measuring interferometer, an auxiliary interferometer and an acquisition card;
the measuring interferometer comprises a PBS, a focusing optical system, a 1/4 wave plate and a balanced detector;
the auxiliary interferometer comprises two 3dB optical fiber couplers;
the sweep laser beam splitting ratio is 95: after the optical fiber coupler of 5 splits light, 95% sweep light and 5% sweep light are obtained, and the splitting ratio of the 95% sweep light is 99: the optical fiber coupler of 1 is divided into measuring light of a measuring interferometer and reference light of the measuring interferometer, the measuring light of the measuring interferometer sequentially passes through a PBS (polarization beam splitter), a focusing optical system and a 1/4 wave plate and then is emitted, and after being reflected by a measuring target, an original path returns and is mixed with the reference light of the measuring interferometer on a detection plane of a balance detector to obtain a beat frequency signal of the measuring interferometer, namely an optical signal of the measuring interferometer;
the 5% sweep light is divided into 50% by a 3dB fiber coupler: 50, combining the measuring light of the auxiliary interferometer and the reference light of the auxiliary interferometer by a 3dB optical fiber coupler, and mixing on a balance detector to obtain an auxiliary interferometer beat frequency signal, namely an auxiliary interferometer optical signal;
the acquisition card is used for acquiring and storing the beat frequency signal of the measurement interferometer and the beat frequency signal of the auxiliary interferometer;
the sweep frequency nonlinear correction ranging method based on similar triangular interpolation sampling comprises the following specific steps:
the method comprises the following steps: obtaining a measurement interferometer optical signal ImcAnd auxiliary interferometer optical signal IdcAnd obtaining a measurement interferometer signal sequence I according to the measurement interferometer optical signal and the auxiliary interferometer optical signalmAnd an auxiliary interferometer signal sequence Id；
Step two: extracting a signal sequence I of the measuring interferometermAnd an auxiliary interferometer signal sequence IdIn odd order1m、I1dAnd even-order data sequences I2m、I2d；
Step three: will I1dAnd I2dCorresponding multiplication is carried out, the multiplication results are screened to obtain a plurality of groups of adjacent data points with zero point between two points, then data point labels are recorded, and a set I is formedo；
Step four: will be set IoPerforming similar fitting on each group of adjacent data points to obtain a zero horizontal coordinate value set A between each group of adjacent data pointsoAfter that, the set A isoDetermining a resampling sequence B after the arrangemento；
Step five: using set IoData point index pair I of two adjacent points in which zero exists1mAnd I2mReading data to obtain a resample sequence BoMeasuring interferometer data points I corresponding to two sides1mo、I2moThen use I1mo、I2moAnd a resampling sequence BoTo I1mo、I2moPerforming similar interpolation to obtain a corrected signal of the measuring interferometer;
step six: and carrying out spectrum analysis on the corrected measuring interferometer signal, searching for the maximum value of the spectrum peak value, and carrying out corresponding linear transformation to obtain a corrected distance measuring result.
2. A swept frequency nonlinear correction ranging method based on similar triangular interpolation sampling according to claim 1, wherein the swept frequency laser is obtained by an external cavity laser.
3. A swept frequency nonlinear correction ranging method based on similar triangular interpolation sampling according to claim 2, wherein the frequency of the beat signal of the measuring interferometer is determined according to the arm length difference and the measuring distance of the measuring interferometer.
4. A swept frequency nonlinear correction ranging method based on similar triangular interpolation sampling according to claim 1, characterized in that the measurement interferometer optical signal is represented as:
wherein A ismFor measuring interferometer optical signal amplitude, 2RmTo measure the interferometer arm length difference, Δ f (t) is the sweep frequency variation, and c is the speed of light.
5. A swept frequency nonlinear correction ranging method based on similar triangular interpolation sampling according to claim 1, characterized in that the auxiliary interferometer optical signal is represented as:
wherein A is0To assist the interferometer in amplitude of the optical signal, R0To assist the interferometer arm length difference, Δ f (t) is the sweep frequency variation, and c is the speed of light.
6. A swept frequency nonlinear correction ranging method based on similar triangular interpolation sampling according to claim 4 or 5, characterized in that the sweep frequency variation Δ f (t) is expressed as:
wherein k is the resample sequence sample sequence index.
7. A swept frequency nonlinear correction ranging method based on similar triangular interpolation sampling according to claim 6, wherein the measured interferometer signal in the fifth step is represented as:
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| CN115327515B (en) * | 2022-08-10 | 2023-04-18 | 哈尔滨工业大学 | Double-sweep frequency interference dynamic measurement system and measurement method based on phase transmission |
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