CN115327515B - Double-sweep frequency interference dynamic measurement system and measurement method based on phase transmission - Google Patents
Double-sweep frequency interference dynamic measurement system and measurement method based on phase transmission Download PDFInfo
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- CN115327515B CN115327515B CN202210957840.1A CN202210957840A CN115327515B CN 115327515 B CN115327515 B CN 115327515B CN 202210957840 A CN202210957840 A CN 202210957840A CN 115327515 B CN115327515 B CN 115327515B
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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
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
- G01S7/497—Means for monitoring or calibrating
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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
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
- G01S7/497—Means for monitoring or calibrating
- G01S7/4972—Alignment of sensor
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
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Abstract
The invention provides a double-sweep frequency interference dynamic measurement system and a measurement method based on phase transmission; the frequency sweep bandwidths of the two frequency sweep light sources are not overlapped on a frequency domain, the light path part of the measuring interferometer is used for resolving the target absolute distance, the light path part of the auxiliary interferometer 1 is used for providing a phase frequency coordinate of frequency modulation nonlinear correction, the light path part of the auxiliary interferometer 2 and the light path part of the air chamber are used for calibrating the light path part of the auxiliary interferometer 1 on line, and the acousto-optic modulation signal is used for implementing phase demodulation on the signal of the auxiliary interferometer 1; the invention has the advantages of simple structure, stronger noise resistance, short auxiliary interferometer, greatly reduced sampling rate, no influence of dispersion mismatch and environmental change, realization of non-cooperative target dynamic high-precision measurement and online tracing and the like.
Description
Technical Field
The invention belongs to the technical field of frequency modulation continuous wave FMCW laser radar nonlinear correction and frequency sweep interference measurement (FSI), and particularly relates to a double-frequency sweep interference dynamic measurement system and a double-frequency sweep interference dynamic measurement method based on phase transfer.
Background
The sweep frequency interference measurement has the advantages of low emission power, no range finding ambiguity and the like, and can realize high-resolution and high-precision measurement without the cooperation of a guide rail and a cooperative target, so that the sweep frequency interference measurement has wide application in the fields of high-precision absolute distance measurement and the like, such as frequency modulation continuous wave radar (FMCW), optical Frequency Domain Reflectometer (OFDR), optical Coherence Tomography (OCT) and the like. The technical idea is derived from a microwave radar, the target distance is determined by utilizing the frequency difference generated between the emission sweep light and the sweep light reflected by the measured target due to the time difference, and the distance parameter of the target is reflected according to the frequency domain characteristics. In order to ensure that the target distance information can be accurately determined through frequency domain characteristics, the problem that the measurement capability is reduced due to three types of nonlinearity (frequency modulation nonlinearity of a frequency modulation laser, doppler effect introduced by target motion, and optical fiber-free space dispersion mismatch) existing in a measurement system needs to be effectively solved at a high speed;
the existing main methods are divided into a hardware method and a software method, wherein the hardware method is used for scanning in different directions by using a double-scanning-frequency laser or triangular-wave scanning by using one laser, although the scheme can inhibit the influence of three types of nonlinearity on measurement, the former method causes a complex system, and the latter method cannot finish effective distance measurement compensation on a fast moving target; the optical sweep nonlinearity is directly eliminated by utilizing the photoelectric phase-locked loop, the scheme can improve the signal-to-noise ratio of the measured return light, but the scheme is complex and difficult to realize, and the nonlinear correction of the full frequency modulation range of the laser cannot be realized. The software method is simple in structure and easy to implement, but is more easily influenced by the roughness of the surface of the target due to the fact that the scheme utilizes the phase relation to measure the absolute distance of the target; if the auxiliary interferometer is used for resampling, the method is limited by the fact that a long auxiliary interferometer must be used in the sampling theorem, and the overlong auxiliary interferometer not only aggravates the acquisition pressure, but also makes the measurement system more sensitive to environmental changes.
Disclosure of Invention
The invention provides a double-sweep frequency interference dynamic measurement system and a measurement method based on phase transmission, aiming at the problems in the existing frequency modulation nonlinear correction method, and realizes high-precision absolute distance measurement of a free space target.
The invention is realized by the following technical scheme:
a double-sweep frequency interference dynamic measurement system based on phase transfer comprises:
the system comprises: the system comprises a gas chamber, a measurement interferometer, an auxiliary interferometer 1 and an auxiliary interferometer 2;
the frequency-sweeping bandwidths of the two frequency-sweeping light sources are not overlapped on a frequency domain, the light path part of the measuring interferometer is used for resolving the target absolute distance, the light path part of the auxiliary interferometer 1 is used for providing a phase frequency coordinate for frequency modulation nonlinear correction, the light path part of the auxiliary interferometer 2 and the light path part of the air chamber are used for calibrating the light path part of the auxiliary interferometer 1 on line, and the acousto-optic modulation signal is used for implementing phase demodulation on the signal of the auxiliary interferometer 1.
Further, the optical path of the gas chamber comprises a swept-frequency laser 1, a polarization-maintaining isolator 1, a coupler 2, a gas chamber and a balance detector 1;
the sweep light output from the sweep laser 1 passes through the polarization maintaining isolator 1, and is input into a laser system with a splitting ratio of 99:5, where 5% of the swept light enters 95:5 coupler 2, 95% of the beam enters the coupler 2,5% of the beam enters the gas absorption cell, and finally the signal output by the gas absorption cell is received by the balanced detector 1.
Further, the optical path of the measuring interferometer comprises a frequency-sweeping laser 1, a frequency-sweeping laser 2, a polarization-preserving isolator 1, a polarization-preserving isolator 2, a coupler 1, a wavelength division multiplexer 1, a coupler 4, a coupler 5, a circulator 2, a coupler 7, a wavelength division multiplexer 4, a wavelength division multiplexer 5, a focusing mirror group, a measured target, a balance detector 5 and a balance detector 6;
the sweep light emitted from the sweep laser 1 passes through the polarization maintaining isolator 1 and is input into a splitting ratio of 95:5, the light beams of 95 percent of the coupler 1 enter the wavelength division multiplexing 1, and the sweep frequency light emitted from the sweep frequency laser 2 enters the wavelength division multiplexing 1 through the polarization-preserving isolator 2;
the two beams of light are combined into one beam after being subjected to wavelength division multiplexing 1, and then the combined beam is subjected to 99:5 coupler 4,5% of the beam enters the splitting ratio of 50:50 coupler 3, 95% of the beam enters the split ratio 99:1, wherein 99% of the light enters the measurement arms as measurement light and 1% of the light enters the reference arms as reference light, respectively;
wherein, the measuring light passes through the circulator 2 and focuses on the target surface through the focusing mirror group, and the return light of the target surface enters the splitting ratio of 50 through the focusing mirror group and the circulator: 50 of the coupler 7; the reference light directly enters a coupler 7, and two beams of sweep-frequency light with different frequencies are separated on a frequency domain by utilizing wavelength division multiplexing 4 and 5;
finally, the measuring interferometer signal with the laser output from the swept-frequency laser 1 as the light source is received by the detector 5, and the measuring interferometer signal with the laser output from the swept-frequency laser 2 as the light source is received by the detector 6.
Further, the optical path of the auxiliary interferometer 1 includes a coupler 4, a coupler 3, an acousto-optic modulator, a coupler 6, a circulator 1, a wavelength division multiplexer 2, a wavelength division multiplexer 3, a balanced detector 3 and a balanced detector 4;
the splitting ratio is 50:50, the coupler 3 receives the light transmitted by the coupler 4 and equally divides the light into measuring light and reference light;
wherein, the measuring light enters the splitting ratio of 50 through the single mode fiber and the acousto-optic modulator: 50, the reference light directly enters the coupler 6 with the splitting ratio of 50:50 of the coupler 6;
wherein, 50% of the output light passes through the circulator 1 and is subjected to wavelength division multiplexing 2, and the light beams of the frequency-sweeping laser 1 and the frequency-sweeping laser 2 are separated on a frequency domain; the other beam of 50% output light is subjected to wavelength division multiplexing 3, and light beams of the frequency-swept laser 1 and the frequency-swept laser 2 are separated on a frequency domain;
finally, a detector 3 receives the signal of the auxiliary interferometer 1 taking the laser output by the frequency-swept laser 1 as a light source, and a detector 4 receives the signal of the auxiliary interferometer 1 taking the laser output by the frequency-swept laser 2 as a light source;
the optical path of the auxiliary interferometer 2 comprises a coupler 2, a circulator 1, a coupler 3, a coupler 6 and a balance detector 2;
the splitting ratio is 95: the coupler 2 of 5 receives the sweep light of the coupler 1, 95% of the light beam is input into the circulator 1, and the sweep light is divided into a first light beam and a second light beam by a splitting ratio of 50: the 50 coupler 6 is divided into 50% of measuring light and 50% of reference light, and the measuring light enters a splitting ratio of 50:50, reference light enters the coupler 3 with a splitting ratio of 50:50, and finally receiving interference signals of the measuring light and the reference light of the auxiliary interferometer 2 by the balanced detector 2.
Further, the system also comprises a data acquisition card;
the data acquisition card performs analog-to-digital conversion on the signals of the balance detectors 1, 2, 3, 4,5 and 6 and the reference signal, and finally performs data processing and analysis on an upper computer;
the reference signal is an acousto-optic modulation signal directly input into the data acquisition card.
A double-sweep frequency interference dynamic measurement method based on phase transfer comprises the following steps:
the method specifically comprises the following steps:
step 1, synchronously acquiring a measurement interferometer, an auxiliary interferometer 1, an auxiliary interferometer 2 and a gas chamber signal;
Step 3, utilizing the auxiliary interferometer 2 and the air chamber signal, and realizing the L of the auxiliary interferometer 2 based on an online air chamber calibration method f Calibrating;
and 4, eliminating the nonlinear effect of the measuring interferometer: auxiliary interferometer 1 phase demodulating step 3
As new sampling coordinates, the time domain coordinates are replaced one by one according to the sampling sequence, and at the moment, the signal of the measuring interferometer can be greater or less by utilizing methods such as cubic spline interpolation and the like>
Is converted into a measurement interferometer signal of uniform phase samples->
And 5, eliminating the Doppler effect and dispersion mismatch influence of the measuring interferometer: measuring the reconstructed interferometer signal
Performing mixing and high-pass filtering to obtain->
And 6, performing spectrum analysis on the range-finding interferometer signal subjected to nonlinear correction to obtain the range-finding interferometer signal frequency, converting the range-finding interferometer signal frequency into the absolute distance of a target by using an online air chamber calibration result, and completing the dynamic measurement of double-sweep frequency interference.
Further, the specific method of frequency modulation nonlinearity is as follows: hilbert transformation is carried out on the acousto-optic modulation signal to obtain an orthogonal basis used for demodulating the signal phase of the auxiliary interferometer 1 and the auxiliary interferometer 2, wherein the orthogonal basis sr (n) and si (n) contain acousto-optic modulator frequency shift information;
sr(n)＝cos(2πf AOM n) n＝1,2,3,…N (1)
si(n)＝sin(2πf AOM n) n＝1,2,3,…N (2)
wherein sr (n) and si (n) are real part and imaginary part of orthogonal base, f AOM Acousto-optic frequency shift;
using the generated quadrature basis to respectively communicate with the auxiliary interferometer 2 signals
Performs mixing and low-pass filtering to obtain the quadrature basis of the signal of the auxiliary interferometer 2. The quadrature basis->
Wherein f is g2 (n) is the frequency modulation function of the auxiliary interferometer 2 under the influence of the fiber dispersion, R f Is the arm length difference of the auxiliary interferometer 1, and c is the speed of light;
subjecting the orthogonal base obtained above to
Performing arc tangent demodulation and phase unwrapping to obtain auxiliaryPhase of interferometer 2>
The phase of the signal of the auxiliary interferometer 1 can be obtained in the same way
Respectively an up-scan modulation function and a down-scan modulation function under the influence of optical fiber dispersion, and taking the signal phase of the auxiliary interferometer 1 as a ranging interferometer signal->
The new coordinate of (2) can be used for constructing the distance measuring interferometer signal of equal phase sampling by utilizing methods such as cubic spline interpolation and the like
Mixing the signals of the two distance measuring interferometers, and obtaining a signal which is subjected to nonlinear correction by a high-pass filter>
Wherein HPF is high pass filtering, R mf For measuring interferometer fibre arm length difference, R m0 Is the distance of the object in free space, R m (t) is the absolute position change of the target,
up-scan and down-scan modulation functions, f, respectively under the influence of free-space dispersion 0 For the initial optical frequency, L, of the frequency-modulated laser f For the calibration result of the air chamber, is selected>
Phase frequency coordinates provided for an auxiliary interferometer>
For a sampling interval at equal phase sampling, <' >>
For the refractive index of the optical fiber corresponding to the initial optical frequency of the frequency-modulated laser, d f Is the fiber dispersion coefficient in the frequency modulation band;
the effect of the non-linearity in the signal on the measurement is now eliminated, as shown in equation (6).
Further, the calibration method of the air chamber comprises the following steps: providing gas by adopting an HCN gas chamber, enabling absorption peaks to correspond to K absolute optical frequency values delta f (m) and K corresponding samples m, and determining K phases of signals of the auxiliary interferometer 1 according to the K samples m
Using the relationship between the optical frequency and the phase of the signal of the auxiliary interferometer 1, the optical length L of the signal of the auxiliary interferometer 1 f And (3) solving:
an electronic device comprising a memory storing a computer program and a processor implementing the steps of any of the above methods when the processor executes the computer program.
A computer readable storage medium storing computer instructions which, when executed by a processor, implement the steps of any of the above methods.
The invention has the beneficial effects that
1. The invention can realize the whole correction process by using the double frequency modulation laser and the short auxiliary interferometer, relieves the system acquisition pressure, reduces the data processing pressure, has no dispersion mismatch influence, has high measurement reference repeatability and is not easily influenced by environmental factors.
2. The gas chamber is used for carrying out online calibration on the group delay of the auxiliary interferometer, and a higher-precision online measurement reference is provided for the system.
3. And the phase discrimination method of orthogonal demodulation is adopted, so that the frequency modulation nonlinear correction effect of the scheme is improved, and the performance of the measurement system is improved.
The invention has the advantages of simple structure, stronger noise resistance, short auxiliary interferometer, greatly reduced sampling rate, no influence of dispersion mismatch and environmental change, realization of non-cooperative target dynamic high-precision measurement and online tracing and the like.
Drawings
FIG. 1 is a schematic diagram of the optical path of the system of the present invention;
FIG. 2 is a diagram of an auxiliary interferometer group delay calibration scheme;
FIG. 3 is a comparison graph of SNR before and after non-linear correction, wherein (a) is SNR before correction and (b) is SNR after correction.
Detailed Description
The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without making any creative effort based on the embodiments in the present invention, belong to the protection scope of the present invention.
A double-sweep frequency interference dynamic measurement system based on phase transfer comprises:
the system comprises: the system comprises a gas chamber, a measurement interferometer, an auxiliary interferometer 1 and an auxiliary interferometer 2;
the frequency sweep bandwidths of the two frequency sweep light sources are not overlapped on a frequency domain, the light path part of the measuring interferometer is mainly applied to target absolute distance calculation, the light path of the auxiliary interferometer 1 is used for providing a phase frequency coordinate of frequency modulation nonlinear correction, the light path part of the auxiliary interferometer 2 and the light path part of the air chamber are used for calibrating the light path of the auxiliary interferometer 1 on line, and acousto-optic modulation signals are used for implementing phase demodulation on signals of the auxiliary interferometer 1.
The optical path of the gas chamber comprises a swept-frequency laser 1, a polarization-maintaining isolator 1, a coupler 2, a gas chamber and a balance detector 1;
the sweep light output from the sweep laser 1 passes through the polarization maintaining isolator 1, and is input into a laser system with a splitting ratio of 99:5, where 5% of the swept light enters 95:5, 95% of the light beam enters the coupler 2,5% of the light beam enters the gas absorption cell, and finally the signal output by the gas absorption cell is received by the balanced detector 1.
The light path of the measuring interferometer comprises a frequency-sweeping laser 1, a frequency-sweeping laser 2, a polarization-preserving isolator 1, a polarization-preserving isolator 2, a coupler 1, a wavelength division multiplexer 1, a coupler 4, a coupler 5, a circulator 2, a coupler 7, a wavelength division multiplexer 4, a wavelength division multiplexer 5, a focusing mirror group, a measured target, a balance detector 5 and a balance detector 6;
the sweep light emitted from the sweep laser 1 passes through the polarization maintaining isolator 1 and is input into a splitting ratio of 95:5, the light beams of 95 percent of the coupler 1 enter the wavelength division multiplexing 1, and the sweep frequency light emitted from the sweep frequency laser 2 enters the wavelength division multiplexing 1 through the polarization-preserving isolator 2;
the two beams of light are combined into one beam after being subjected to wavelength division multiplexing 1, and then the two beams of light are subjected to 99:5 coupler 4,5% of the beam enters the splitting ratio of 50:50 coupler 3, 95% of the beam enters the split ratio 99:1, wherein 99% of the light enters the measurement arms as measurement light and 1% of the light enters the reference arms as reference light, respectively;
wherein the measuring light passes through the circulator 2 and is focused on the target surface through the focusing mirror group, and the return light of the target surface enters the splitting ratio of 50 through the focusing mirror group and the circulator: 50 of the coupler 7; the reference light directly enters a coupler 7, and two beams of sweep-frequency light with different frequencies are separated on a frequency domain by utilizing wavelength division multiplexing 4 and 5;
finally, the balance detector 5 receives the measurement interferometer signal using the laser output from the swept-frequency laser 1 as a light source, and the balance detector 6 receives the measurement interferometer signal using the laser output from the swept-frequency laser 2 as a light source.
The optical path of the auxiliary interferometer 1 comprises a coupler 4, a coupler 3, an acousto-optic modulator, a coupler 6, a circulator 1, a wavelength division multiplexer 2, a wavelength division multiplexer 3, a balance detector 3 and a balance detector 4;
the splitting ratio is 50:50, the coupler 3 receives the light transmitted by the coupler 4 and equally divides the light into measuring light and reference light;
wherein, the measuring light enters the splitting ratio of 50 through the single mode fiber and the acousto-optic modulator: 50, the reference light directly enters the coupler 6 with the splitting ratio of 50:50 of the coupler 6;
wherein, 50% of output light passes through the circulator 1 and the wavelength division multiplexer 2, and the beams of the frequency-swept laser 1 and the frequency-swept laser 2 are separated on the frequency domain; the other beam of 50% output light is subjected to wavelength division multiplexing 3, and light beams of the frequency-swept laser 1 and the frequency-swept laser 2 are separated on a frequency domain;
finally, a balance detector 3 receives the signal of the auxiliary interferometer 1 taking the laser output by the frequency-swept laser 1 as a light source, and a balance detector 4 receives the signal of the auxiliary interferometer 1 taking the laser output by the frequency-swept laser 2 as a light source;
the optical path of the auxiliary interferometer 2 comprises a coupler 2, a circulator 1, a coupler 3, a coupler 6 and a balance detector 2;
the splitting ratio is 95: the coupler 2 of 5 receives the sweep light of the coupler 1, 95% of the light beam is input into the circulator 1, and the sweep light is divided into a first light beam and a second light beam by a splitting ratio of 50: the coupler 6 of 50 is divided into 50% measuring light and 50% reference light, and the measuring light enters the splitting ratio of 50:50, reference light enters the coupler 3 with a splitting ratio of 50:50, and finally receiving interference signals of the measuring light and the reference light of the auxiliary interferometer 2 by the balanced detector 2.
The system also comprises a data acquisition card;
the data acquisition card performs analog-to-digital conversion on the signals of the balance detectors 1, 2, 3, 4,5 and 6 and the reference signal, and finally performs data processing and analysis on an upper computer;
the reference signal is an acousto-optic modulation signal directly input into the data acquisition card.
A double-sweep frequency interference dynamic measurement method based on phase transfer comprises the following steps:
the method specifically comprises the following steps:
step 1, synchronously acquiring signals of a measurement interferometer, an auxiliary interferometer 1, an auxiliary interferometer 2 and an air chamber through an optical path shown in figure 1;
Step 3, utilizing the auxiliary interferometer 2 and the air chamber signal, and realizing the L of the auxiliary interferometer 2 based on an online air chamber calibration method f Calibrating;
and 4, eliminating the nonlinear effect of the measuring interferometer: auxiliary interferometer 1 phase demodulating step 3
As new sampling coordinates, the time domain coordinates are replaced one by one according to the sampling sequence, and at the moment, the signal of the measuring interferometer can be greater or less by utilizing methods such as cubic spline interpolation and the like>
Is converted into a measurement interferometer signal of uniform phase samples->
At this point, the nonlinear effects of the measuring interferometer signal have been eliminated;
and 5, eliminating the Doppler effect and dispersion mismatch influence of the measuring interferometer: measuring the reconstructed interferometer signal
Performing mixing and high-pass filtering to obtain->
At the moment, the Doppler effect and dispersion mismatch influence in the signal of the measuring interferometer can be corrected;
and 6, performing spectrum analysis on the range-finding interferometer signal subjected to nonlinear correction to obtain the range-finding interferometer signal frequency, and converting the range-finding interferometer signal frequency into the absolute distance of a target by using the online air chamber calibration result to complete the dynamic measurement of double-sweep interference.
The specific method of frequency modulation nonlinearity is as follows: hilbert transformation is carried out on the acousto-optic modulation signal to obtain an orthogonal basis used for demodulating the signal phase of the auxiliary interferometer 1 and the auxiliary interferometer 2, wherein the orthogonal basis sr (n) and si (n) contain acousto-optic modulator frequency shift information;
sr(n)＝cos(2πf AOM n) n＝1,2,3,…N (1)
si(n)＝sin(2πf AOM n) n＝1,2,3,…N (2)
wherein sr (n) and si (n) are real part and imaginary part of orthogonal base, f AOM Acousto-optic frequency shift;
using the generated quadrature basis to respectively signal with the auxiliary interferometer 2
Performs mixing and low-pass filtering to obtain the quadrature basis of the signal of the auxiliary interferometer 2. The quadrature basis->
Wherein f is g2 (n) is the frequency modulation function of the auxiliary interferometer 2 under the influence of the fiber dispersion, R f Is the arm length difference of the auxiliary interferometer 1, c is the speed of light;
subjecting the orthogonal base obtained above to
Performing inverse tangent demodulation and phase unwrapping to obtain the phase of the auxiliary interferometer 2>
The phase of the signal of the auxiliary interferometer 1 can be obtained in the same way
Respectively an up-scan modulation function and a down-scan modulation function under the influence of optical fiber dispersion, and taking the signal phase of the auxiliary interferometer 1 as a ranging interferometer signal->
The new coordinate of (2) can utilize methods such as cubic spline interpolation to construct the ranging interferometer signal(s) sampled at equal phase>
Mixing the signals of the two distance measuring interferometers, and obtaining a signal which is subjected to nonlinear correction by a high-pass filter>
Wherein HPF is high pass filtering, R mf For measuring interferometer fibre arm length difference, R m0 Is the distance of the object in free space, R m (t) is the absolute position change of the target,
up-scan and down-scan modulation functions, f, respectively under the influence of free-space dispersion 0 For the initial optical frequency, L, of the frequency-modulated laser f For the calibration result of the air chamber, is selected>
Phase frequency coordinates provided for an auxiliary interferometer>
For a sampling interval at equal phase sampling, <' >>
Refractive index of optical fiber corresponding to initial optical frequency of frequency-modulated laser, d f Is the fiber dispersion coefficient in the frequency modulation wave band;
the effect of the non-linearity in the signal on the measurement is now eliminated, as shown in equation (6).
The calibration method of the air chamber comprises the following steps: providing gas in the wavelength range of 1525nm to 1565nm by adopting an HCN gas chamber, wherein K absolute light frequency values delta f (m) corresponding to absorption peaks and K corresponding sampling peaksSample m, determining K phases of the signal of the auxiliary interferometer 1 simultaneously from K samples m
As shown in fig. 2.
Using the relationship between the optical frequency and the phase of the signal of the auxiliary interferometer 1, the optical length L of the signal of the auxiliary interferometer 1 f And (3) solving:
an electronic device comprising a memory storing a computer program and a processor implementing the steps of any of the above methods when the processor executes the computer program.
A computer readable storage medium storing computer instructions which, when executed by a processor, implement the steps of any of the above methods.
The memory in the embodiments of the present application may be either volatile memory or nonvolatile memory, or may include both volatile and nonvolatile memory. The non-volatile memory may be a Read Only Memory (ROM), a Programmable ROM (PROM), an Erasable PROM (EPROM), an electrically Erasable EPROM (EEPROM), or a flash memory. Volatile memory can be Random Access Memory (RAM), which acts as external cache memory. By way of example, and not limitation, many forms of RAM are available, such as Static Random Access Memory (SRAM), dynamic random access memory (dynamic RAM, DRAM), synchronous Dynamic Random Access Memory (SDRAM), double data rate synchronous dynamic random access memory (DDR SDRAM), enhanced synchronous SDRAM (ESDRAM), synchronous Link DRAM (SLDRAM), and direct rambus RAM (DR RAM). It should be noted that the memories of the methods described herein are intended to comprise, without being limited to, these and any other suitable types of memories.
In the above embodiments, the implementation may be wholly or partially realized by software, hardware, firmware, or any combination thereof. When implemented in software, may be implemented in whole or in part in the form of a computer program product. The computer program product includes one or more computer instructions. When loaded and executed on a computer, cause the processes or functions described in accordance with the embodiments of the application to occur, in whole or in part. The computer may be a general purpose computer, a special purpose computer, a network of computers, or other programmable device. The computer instructions may be stored on a computer readable storage medium or transmitted from one computer readable storage medium to another, for example, from one website, computer, server, or data center to another website, computer, server, or data center via wire (e.g., coaxial cable, fiber optic, digital Subscriber Line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.). The computer-readable storage medium can be any available medium that can be accessed by a computer or a data storage device, such as a server, a data center, etc., that includes one or more available media. The usable medium may be a magnetic medium (e.g., a floppy disk, a hard disk, a magnetic tape), an optical medium (e.g., a Digital Video Disk (DVD)), or a semiconductor medium (e.g., a Solid State Disk (SSD)), among others.
In implementation, the steps of the above method may be performed by integrated logic circuits of hardware in a processor or instructions in the form of software. The steps of a method disclosed in connection with the embodiments of the present application may be directly implemented by a hardware processor, or may be implemented by a combination of hardware and software modules in a processor. The software module may be located in ram, flash memory, rom, prom, or eprom, registers, etc. storage media as is well known in the art. The storage medium is located in a memory, and a processor reads information in the memory and completes the steps of the method in combination with hardware of the processor. To avoid repetition, it is not described in detail here.
It should be noted that the processor in the embodiments of the present application may be an integrated circuit chip having signal processing capabilities. In implementation, the steps of the above method embodiments may be performed by integrated logic circuits of hardware in a processor or by instructions in the form of software. The processor described above may be a general purpose processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components. The various methods, steps, and logic blocks disclosed in the embodiments of the present application may be implemented or performed. A general purpose processor may be a microprocessor or the processor may be any conventional processor or the like. The steps of the method disclosed in connection with the embodiments of the present application may be directly implemented by a hardware decoding processor, or implemented by a combination of hardware and software modules in the decoding processor. The software module may be located in ram, flash memory, rom, prom, or eprom, registers, etc. storage media as is well known in the art. The storage medium is located in a memory, and a processor reads information in the memory and completes the steps of the method in combination with hardware of the processor.
The double-sweep frequency interference dynamic measurement method based on phase transmission provided by the invention is introduced in detail, the principle and the implementation mode of the invention are explained, and the description of the embodiment is only used for helping to understand the method and the core idea of the invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, the specific embodiments and the application range may be changed, and in summary, the content of the present specification should not be construed as a limitation to the present invention.
Claims (7)
1. A dynamic measurement method of a double-sweep frequency interference dynamic measurement system based on phase transmission is characterized in that:
the system comprises: the system comprises a gas chamber, a measurement interferometer, an auxiliary interferometer 1 and an auxiliary interferometer 2;
the frequency sweep bandwidths of the two frequency sweep light sources are not overlapped on a frequency domain, the light path part of the measuring interferometer is used for resolving the target absolute distance, the light path part of the auxiliary interferometer 1 is used for providing a phase frequency coordinate of frequency modulation nonlinear correction, the light path part of the auxiliary interferometer 2 and the light path part of the air chamber are used for calibrating the light path part of the auxiliary interferometer 1 on line, and the acousto-optic modulation signal is used for implementing phase demodulation on the signal of the auxiliary interferometer 1;
the method specifically comprises the following steps:
step 1, synchronously acquiring signals of a measurement interferometer, an auxiliary interferometer 1, an auxiliary interferometer 2 and an air chamber;
step 2, hilbert transformation is carried out on the acousto-optic modulation signal to generate a group of orthogonal bases sr (n) and si (n), and the orthogonal bases sr (n) and si (n) are respectively connected with signals of the auxiliary interferometer 1
Auxiliary interferometer 2 signal->
Mixing and low-pass filtering, performing arc tangent demodulation and phase unwrapping on the generated orthogonal base signal to obtain auxiliary interferometer 1 phase->
Phase->
Step 3, utilizing the auxiliary interferometer 2 and the air chamber signal to realize the L of the auxiliary interferometer 1 based on the online air chamber calibration method f Calibrating;
the calibration method of the air chamber comprises the following steps: providing gas by adopting an HCN gas chamber, enabling absorption peaks to correspond to K absolute light frequency values delta f (m) and K corresponding samples m, and determining K of signals of the auxiliary interferometer 1 according to the K samples mA phase position
Using the relationship between the optical frequency and the phase of the signal of the auxiliary interferometer 1, the optical length L of the signal of the auxiliary interferometer 1 f And (3) solving:
and 4, eliminating the nonlinear effect of the measuring interferometer: auxiliary interferometer 1 phase demodulating step 3
As new sampling coordinates, the time domain coordinates are replaced one by one according to the sampling sequence, and the signal of the measuring interferometer can be greater or less than the set value by utilizing a cubic spline interpolation method>
Is converted into a measurement interferometer signal of uniform phase samples->
The specific method of frequency modulation nonlinearity is as follows: hilbert transformation is carried out on the acousto-optic modulation signal to obtain an orthogonal basis used for demodulating the signal phase of the auxiliary interferometer 1 and the auxiliary interferometer 2, wherein the orthogonal basis sr (n) and si (n) contain acousto-optic modulator frequency shift information;
sr(n)＝cos(2πf AOM n)n＝1,2,3,…N (1)
si(n)＝sin(2πf AOM n)n＝1,2,3,…N (2)
wherein sr (n) and si (n) are real part and imaginary part of orthogonal base, f AOM Acousto-optic frequency shift;
using the generated quadrature basis to respectively communicate with the auxiliary interferometer 2 signals
Performs mixing and low-pass filtering to obtain the quadrature basis of the signal of the auxiliary interferometer 2. The quadrature basis->
/>
Wherein f is g2 (n) is the frequency modulation function of the auxiliary interferometer 2 under the influence of the fiber dispersion, R f Is the arm length difference of the auxiliary interferometer 1, c is the speed of light;
subjecting the orthogonal base obtained above to
Performing inverse tangent demodulation and phase unwrapping to obtain the phase of the auxiliary interferometer 2>
The phase of the signal of the auxiliary interferometer 1 can be obtained in the same way
Respectively an up-scan modulation frequency function and a down-scan modulation frequency function under the influence of optical fiber dispersion, and respectively taking the signal phase of the auxiliary interferometer 1 as a ranging interferometer signal
Using cubic spline interpolation method to construct equal phase sampling distance measuring interferometer signal
Mixing the signals of the two distance measuring interferometers, and obtaining a signal which is subjected to nonlinear correction by a high-pass filter>
Wherein HPF is high pass filtering, R mf For measuring interferometer fibre arm length difference, R m0 Is the distance of the object in free space, R m (t) is the absolute position change of the target,
up-scan and down-scan modulation functions, f, respectively under the influence of free-space dispersion 0 For initiating the light frequency of the frequency-modulated laser, is>
Phase frequency coordinates provided for an auxiliary interferometer>
For a sampling interval at equal phase sampling, <' >>
Optical fiber corresponding to initial optical frequency of frequency-modulated laserRefractive index, d f Is the fiber dispersion coefficient in the frequency modulation wave band;
as shown in equation (6), the effect of the non-linearity in the signal on the measurement has been eliminated;
and 5, eliminating the Doppler effect and dispersion mismatch influence of the measurement interferometer: measuring the reconstructed interferometer signal
Performing mixing and high-pass filtering to obtain->
And 6, performing spectrum analysis on the range-finding interferometer signal subjected to nonlinear correction to obtain the range-finding interferometer signal frequency, converting the range-finding interferometer signal frequency into the absolute distance of a target by using an online air chamber calibration result, and completing the dynamic measurement of double-sweep frequency interference.
2. The method of claim 1, wherein:
the optical path of the gas chamber comprises a frequency-sweeping laser 1, a polarization-maintaining isolator 1, a coupler 2, a gas chamber and a balance detector 1;
the sweep light output from the sweep laser 1 passes through the polarization maintaining isolator 1, and is input into a laser system with a splitting ratio of 99:5, where 5% of the swept light enters 95:5 coupler 2, 95% of the beam enters the coupler 2,5% of the beam enters the gas absorption cell, and finally the signal output by the gas absorption cell is received by the balanced detector 1.
3. The method of claim 2, further comprising:
the light path of the measuring interferometer comprises a frequency-sweeping laser 1, a frequency-sweeping laser 2, a polarization-preserving isolator 1, a polarization-preserving isolator 2, a coupler 1, a wavelength division multiplexer 1, a coupler 4, a coupler 5, a circulator 2, a coupler 7, a wavelength division multiplexer 4, a wavelength division multiplexer 5, a focusing mirror group, a measured target, a balance detector 5 and a balance detector 6;
the sweep light emitted from the sweep laser 1 passes through the polarization maintaining isolator 1 and is input into a splitting ratio of 95:5, the light beams of 95% of the coupler 1 enter a wavelength division multiplexer 1, and the sweep frequency light emitted from the sweep frequency laser 2 enters the wavelength division multiplexer 1 through a polarization-preserving isolator 2;
the two beams of light are combined into one beam after being subjected to wavelength division multiplexing 1, and then the combined beam is subjected to 99:5 coupler 4,5% of the beam enters the splitting ratio of 50:50 coupler 3, 95% of the beam enters the split ratio 99:1, wherein 99% of the light enters the measurement arms as measurement light and 1% of the light enters the reference arms as reference light, respectively;
wherein the measuring light passes through the circulator 2 and is focused on the target surface through the focusing mirror group, and the return light of the target surface enters the splitting ratio of 50 through the focusing mirror group and the circulator: 50, coupler 7; the reference light directly enters a coupler 7, and two beams of frequency-sweeping light with different frequencies are separated on a frequency domain by utilizing wavelength division multiplexing 4 and 5;
finally, the measuring interferometer signal with the laser output from the swept-frequency laser 1 as the light source is received by the detector 5, and the measuring interferometer signal with the laser output from the swept-frequency laser 2 as the light source is received by the detector 6.
4. The method of claim 3, wherein:
the optical path of the auxiliary interferometer 1 comprises a coupler 4, a coupler 3, an acousto-optic modulator, a coupler 6, a circulator 1, a wavelength division multiplexer 2, a wavelength division multiplexer 3, a balance detector 3 and a balance detector 4;
the splitting ratio is 50:50, the coupler 3 receives the light transmitted by the coupler 4 and equally divides the light into measuring light and reference light;
wherein, the measuring light enters the splitting ratio of 50 through the single mode fiber and the acousto-optic modulator: 50, the reference light directly enters the coupler 6 with the splitting ratio of 50:50 of the coupler 6;
wherein, 50% of output light passes through the circulator 1 and the wavelength division multiplexer 2, and the beams of the frequency-swept laser 1 and the frequency-swept laser 2 are separated on the frequency domain; the other beam of 50% output light is subjected to wavelength division multiplexing 3, and light beams of the frequency-swept laser 1 and the frequency-swept laser 2 are separated on a frequency domain;
finally, a detector 3 receives the signal of the auxiliary interferometer 1 taking the laser output by the frequency-swept laser 1 as a light source, and a detector 4 receives the signal of the auxiliary interferometer 1 taking the laser output by the frequency-swept laser 2 as a light source;
the optical path of the auxiliary interferometer 2 comprises a coupler 2, a circulator 1, a coupler 3, a coupler 6 and a balance detector 2;
the splitting ratio is 95: the coupler 2 of 5 receives the sweep light of the coupler 1, 95% of the light beam is input into the circulator 1, and the sweep light is divided into a first light beam and a second light beam by a splitting ratio of 50: the coupler 6 of 50 is divided into 50% measuring light and 50% reference light, and the measuring light enters the splitting ratio of 50:50, reference light enters the coupler 3 with a splitting ratio of 50:50, and finally, the interference signal of the measurement light and the reference light of the auxiliary interferometer 2 is received by the balanced detector 2.
5. The method of claim 4, wherein:
the system also comprises a data acquisition card;
the data acquisition card performs analog-to-digital conversion on the signals of the balance detectors 1, 2, 3, 4,5 and 6 and the reference signal, and finally performs data processing and analysis on an upper computer;
the reference signal is an acousto-optic modulation signal directly input into the data acquisition card.
6. An electronic device comprising a memory and a processor, the memory storing a computer program, wherein the processor implements the steps of the method of any one of claims 1 to 5 when executing the computer program.
7. A computer readable storage medium storing computer instructions, which when executed by a processor implement the steps of the method of any one of claims 1 to 5.
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