CN117572443A - Rapid high-precision sweep frequency interferometry nonlinear correction system and method based on non-uniform zero-insertion filtering - Google Patents
Rapid high-precision sweep frequency interferometry nonlinear correction system and method based on non-uniform zero-insertion filtering Download PDFInfo
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- 238000012952 Resampling Methods 0.000 claims abstract description 14
- 238000005259 measurement Methods 0.000 claims description 70
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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
- G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
- G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
- G01S17/06—Systems determining position data of a target
- G01S17/08—Systems determining position data of a target for measuring distance only
- G01S17/32—Systems determining position data of a target for measuring distance only using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated
- G01S17/34—Systems determining position data of a target for measuring distance only using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated using transmission of continuous, frequency-modulated waves while heterodyning the received signal, or a signal derived therefrom, with a locally-generated signal related to the contemporaneously transmitted signal
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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
- G01S7/491—Details of non-pulse systems
- G01S7/493—Extracting wanted echo signals
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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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- Instruments For Measurement Of Length By Optical Means (AREA)
Abstract
A nonlinear correction system and method for rapid high-precision sweep frequency interferometry based on non-uniform zero-insertion filtering relate to the technical field of laser ranging. The method solves the problems of low precision and low efficiency of the traditional nonlinear correction method. The system adopts a sweep frequency light emitting path to emit sweep frequency light into a measuring path; the measuring path divides incident light into local oscillation light and measuring light, heterodynes the local oscillation light and the measuring light to form a measuring beat frequency signal, converts the measuring beat frequency signal into a measuring electric signal, sends the measuring electric signal to the collecting and processing unit, and sends the incident light to the correcting path; the optical frequency comb laser emission path emits optical frequency comb laser to the correction path; the correction path carries out I/Q modulation after heterodyne interference of the optical frequency comb laser and the sweep frequency light, converts the modulated optical signal into a beat frequency signal and sends the beat frequency signal to the acquisition and processing unit; the acquisition and processing unit corrects the nonlinearity of the sweep frequency of the laser by measuring the electric signal and the beat frequency signal. The invention is suitable for the problem of equal frequency interval resampling of non-uniform sampling sequences.
Description
Technical Field
The invention relates to the technical field of laser ranging.
Background
The Frequency Modulation Continuous Wave (FMCW) laser ranging technique is widely used in modern industry because of its high accuracy, large range, no need for cooperative target measurement, etc. However, in the FMCW laser ranging system, sweep nonlinearity is one of the main factors affecting measurement accuracy. In recent years, nonlinear correction methods have been widely studied.
The existing nonlinear correction methods comprise negative feedback phase-locked control active linearization, an equal optical frequency interval resampling method, an optical frequency comb correction method and a phase ratio method. The negative feedback phase-locked control active linearization method has high measurement accuracy, but has high requirements on hardware and is easily influenced by environmental factors. The equal optical frequency interval resampling method has simple structure and lower requirement on signal to noise ratio, but has slightly lower precision. The optical frequency comb correction method has high and stable precision, but has certain challenges in practical application. The phase ratio method has high accuracy, but has high requirements on signal to noise ratio. The method based on the optical frequency comb correction can improve the measurement accuracy, but is required to be coherent with the optical frequency comb, so that the application range of the method is limited. In addition, in the design of the existing FPGA-based sweep frequency interferometry signal processing system, most of the FPGA design is focused on the aspect of active linearization of the negative feedback phase-locked laser, and the FPGA design for other nonlinear correction methods is less, so that the FPGA-based sweep frequency interferometry nonlinear correction method is necessary to be further explored so as to solve the problems of the existing nonlinear correction method.
Disclosure of Invention
The invention solves the problems of low precision and low efficiency of the traditional nonlinear correction method.
In order to achieve the above object, the present invention provides the following solutions:
the invention provides a non-linear correction system for rapid high-precision sweep frequency interferometry based on non-uniform zero-insertion filtering, which comprises a sweep frequency light emitting path, an optical frequency comb laser emitting path, a measuring path, a correction path and an acquisition and processing unit;
the sweep light emission path emits sweep light and irradiates the sweep light into the measurement path;
the measuring path is used for dividing incident light into local oscillation light and measuring light, heterodyning the local oscillation light and the measuring light to interfere with each other, forming a measuring beat frequency signal, converting the measuring beat frequency signal into a measuring electric signal, and transmitting the measuring electric signal to the collecting and processing unit, and also used for transmitting the incident light to the correcting path;
the optical frequency comb laser emission path emits optical frequency comb laser and emits the optical frequency comb laser into the correction path;
the correction circuit is used for performing I/Q modulation after heterodyne interference of the optical frequency comb laser and the received sweep frequency light, and is also used for converting the optical signals subjected to the I/Q modulation into orthogonal beat frequency signals and sending the orthogonal beat frequency signals to the acquisition and processing unit;
the acquisition and processing unit is used for correcting the nonlinearity of the sweep frequency of the laser according to the received measurement electric signals and the orthogonal beat frequency signals.
Further, in a preferred embodiment, the swept optical emission path includes an external cavity swept continuous wave laser source and a swept optical isolator;
the optical frequency comb laser emission path comprises a femtosecond optical frequency comb and an optical frequency comb isolator;
the external cavity type sweep continuous wave laser source emits sweep light, the sweep light is emitted into the sweep optical isolator, and the sweep optical isolator optically isolates the incident light and emits the incident light into the measuring path;
the femtosecond optical frequency comb emits optical frequency comb laser and irradiates the optical frequency comb isolator, and the optical frequency comb isolator optically isolates incident light and irradiates the incident light into the correction path.
Further, in a preferred embodiment, the external cavity type sweep continuous wave laser source is implemented by using a linear tuning laser.
Further, in a preferred embodiment, the measuring path includes a measuring path first coupler, a measuring path second coupler, a circulator, an optical fiber mirror, a measuring path third coupler, and a measuring path balance detector;
the correction circuit comprises a 90-degree optical mixer;
the sweep frequency optical isolator optically isolates incident light and then emits the incident light into the first coupler of the measuring path, and the first coupler of the measuring path divides the incident light into two beams of sweep frequency light and emits the two beams of sweep frequency light into the 90-degree optical mixer and the second coupler of the measuring path respectively;
the second coupler of the measuring path divides incident light into vibration light and measuring light, the measuring light is injected into the circulator, and the vibration light is injected into the third coupler of the measuring path;
the circulator transmits the processed incident light to the third coupler of the measuring path through the optical fiber reflector, the third coupler of the measuring path performs heterodyne interference on the received light beam and local oscillation light to obtain a measurement beat frequency signal, and the measurement beat frequency signal is sent to the balance detector of the measuring path, and the balance detector of the measuring path converts the measurement beat frequency signal into an electric signal and sends the electric signal to the acquisition and processing unit.
Further, in a preferred embodiment, the first coupler of the measuring path, the second coupler of the measuring path and the third coupler of the measuring path are all implemented by 50:50 couplers.
Further, in a preferred embodiment, the correction circuit further includes a polarization controller, an attenuator, a correction circuit first balance detector, a correction circuit second balance detector, a first low-pass filter, and a second low-pass filter;
the optical frequency comb isolator optically isolates incident light and then emits the incident light into the polarization controller, the polarization controller adjusts the polarization of the incident light and emits the incident light into the attenuator, the attenuator adjusts the signal intensity of the incident light and emits the incident light into the 90-degree optical mixer, the 90-degree optical mixer heterodynes the incident light and the received swept light and modulates the incident light into I/Q (input/output) signals, the I/Q signals are respectively emitted into the first balance detector and the second balance detector of the correction path, the first balance detector of the correction path converts the light signal of the incident light into a beat signal and emits the beat signal into the first low-pass filter, and the first low-pass filter filters the beat signal and sends the beat signal to the acquisition and processing unit;
the second balance detector of the correction circuit converts the optical signal of the incident light into a beat signal and transmits the beat signal to the second low-pass filter, and the second low-pass filter filters the beat signal and transmits the beat signal to the acquisition and processing unit.
Further, in a preferred embodiment, the collection and processing unit includes a TRIG trigger source, a CLK clock source, and a collection card;
the TRIG trigger source is used for taking sweep frequency light emitted by the linear harmonic laser as a trigger signal of the acquisition card;
the CLK clock source is used for taking optical frequency comb laser emitted by the femtosecond optical frequency comb as an external clock source of the acquisition card;
the acquisition card is used for receiving the measurement electric signal and the beat frequency signal.
Further, in a preferred embodiment, the wavelength of the emission of the linearly tuned laser and the femtosecond optical frequency comb is 1550nm.
The invention also provides a non-uniform zero-insertion filtering-based rapid high-precision sweep-frequency interferometry nonlinear correction method, which is realized based on the non-uniform zero-insertion filtering-based rapid high-precision sweep-frequency interferometry nonlinear correction system, and comprises the following steps:
s1, heterodyne interference is carried out on optical frequency comb laser emitted by a femtosecond optical frequency comb and sweep frequency light emitted by a linear tuning laser at the input end of a 90-degree optical mixer to generate heterodyne signals, the heterodyne signals are subjected to I/Q modulation through the 90-degree optical mixer to obtain two paths of modulated signals, and photoelectric conversion is carried out on the two paths of modulated signals by a correction path first balance detector and a correction path second balance detector to obtain two paths of intersected beat frequency signals;
s2, processing signals of heterodyne interference of sweep frequency light and optical frequency comb laser by adopting a sweep frequency relative frequency algorithm to obtain a frequency difference value of the sweep frequency laser relative to a sweep starting frequency;
s3, carrying out non-uniform zero interpolation by adopting a fixed step length according to the frequency difference value of the sweep frequency laser relative to the scanning initial frequency to obtain an equidistant frequency sequence;
s4, determining a new time sampling point by adopting a judging program and combining an original resolving frequency and an original sampling time point, and determining a new time sampling point corresponding to the equidistant frequency sequence;
s5, non-uniform zero interpolation is carried out on the measurement path signal at the new time sampling point, and meanwhile, low-pass filtering processing is carried out, so that accurate interpolation value of the inserted zero point is obtained;
and S6, extracting the measurement path signal at the new time sampling point according to the new time sampling point corresponding to the equidistant frequency sequence to realize equidistant resampling, and obtaining the measurement path signal after the nonlinear correction of the frequency sweep, wherein the measurement path signal is used for obtaining a rapid high-precision frequency sweep interferometry result.
Further, in a preferred embodiment, the step S2 specifically includes:
s21, carrying out phase analysis and unwrapping on two paths of intersected beat signals by adopting a sweep frequency relative frequency algorithm to obtain the phase of a corrected road beat signal;
s22, calculating the frequency based on the phase derivation of the time according to the phase of the correction road beat signal, and obtaining the frequency difference value between the sweep frequency laser and the nearest light comb teeth;
s23, unwrapping the frequency difference value between the sweep frequency laser and the nearest optical comb teeth to obtain a frequency value of the sweep frequency laser relative to the scanning initial frequency.
The beneficial effects of the invention are as follows:
1. the invention provides a non-linear correction system for quick high-precision sweep frequency interferometry based on non-uniform zero-insertion filtering, which adopts a measuring path to separate sweep frequency light emitted by a sweep frequency light emitting path into local oscillation light and vibration light, and heterodynes the local oscillation light and vibration to generate a measurement beat frequency signal and then converts the measurement beat frequency signal into a measurement electric signal; and performing heterodyne interference on the sweep frequency light and the optical frequency comb laser emitted by the optical frequency comb laser emission circuit by adopting a correction circuit to generate heterodyne signals, and performing I/Q modulation to convert the modulated signals into orthogonal beat frequency signals. The system has the advantages of simple structure, good nonlinear correction effect, high processing speed and high stability, is not influenced by dispersion mismatch and environmental change, and realizes rapid high-precision equal optical frequency interval resampling.
2. The invention provides a non-linear correction method for rapid high-precision sweep frequency interferometry based on non-uniform zero-insertion filtering, which combines a sweep frequency relative frequency algorithm with non-uniform zero-insertion filtering, solves the problem of equal-frequency interval resampling of a non-uniform sampling sequence, reduces algorithm complexity, is suitable for embedded systems such as FPGA (field programmable gate array) and the like, has the characteristics of high efficiency and low power consumption, and can improve system performance and efficiency.
The invention is suitable for the problem of equal-frequency interval resampling of a non-uniform sampling sequence.
Drawings
FIG. 1 is a schematic diagram of a fast high-precision swept-frequency interferometry nonlinear correction system based on non-uniform zero-insertion filtering according to embodiments one to seven;
FIG. 2 is an algorithm flow chart of a fast high-precision swept-frequency interferometry nonlinear correction method based on non-uniform zero-insertion filtering according to an embodiment nine;
FIG. 3 (a) is a range spectrum before correction according to the eleventh embodiment;
fig. 3 (b) is a corrected distance spectrum according to the eleventh embodiment.
Detailed Description
The following describes in further detail the embodiments of the present invention with reference to the drawings and examples. The following examples will assist those skilled in the art in further understanding the present invention, but are not intended to limit the invention in any way. It should be noted that variations and modifications can be made by those skilled in the art without departing from the spirit of the invention, which falls within the scope of the invention.
Referring to fig. 1, the first embodiment is described, and the present embodiment provides a fast high-precision sweep frequency interferometry nonlinear correction system based on non-uniform zero-insertion filtering, where the system includes a sweep frequency light emission path, an optical frequency comb laser emission path, a measurement path, a correction path, and an acquisition and processing unit;
the sweep light emission path emits sweep light and irradiates the sweep light into the measurement path;
the measuring path is used for dividing incident light into local oscillation light and measuring light, heterodyning the local oscillation light and the measuring light to interfere with each other, forming a measuring beat frequency signal, converting the measuring beat frequency signal into a measuring electric signal, and transmitting the measuring electric signal to the collecting and processing unit, and also used for transmitting the incident light to the correcting path;
the optical frequency comb laser emission path emits optical frequency comb laser and emits the optical frequency comb laser into the correction path;
the correction circuit is used for performing I/Q modulation after heterodyne interference of the optical frequency comb laser and the received sweep frequency light, and is also used for converting the optical signals subjected to the I/Q modulation into orthogonal beat frequency signals and sending the orthogonal beat frequency signals to the acquisition and processing unit;
the acquisition and processing unit is used for correcting the nonlinearity of the sweep frequency of the laser according to the received measurement electric signals and the orthogonal beat frequency signals.
In practical application, as shown in fig. 1, the swept-frequency light emitting path emits swept-frequency light, and the swept-frequency light is emitted into the measuring path; the measuring path divides the incident sweep frequency light into local oscillation light and measuring light, processes the measuring light, heterodynes the processed measuring light with the local oscillation light to form a measuring beat frequency signal, and then converts the measuring beat frequency signal into a measuring electric signal. The measuring circuit also transmits the sweep frequency light to the correcting circuit, the correcting circuit heterodynes the sweep frequency light with the optical frequency comb laser emitted by the optical frequency comb laser emitting circuit, and meanwhile carries out I/Q modulation, and the optical signals subjected to the I/Q modulation are converted into orthogonal beat frequency signals, so that the correction of the sweep frequency nonlinearity of the laser is realized.
The embodiment provides a non-linear correction system for rapid high-precision sweep frequency interferometry based on non-uniform zero-insertion filtering, which adopts a measuring path to separate sweep frequency light emitted by a sweep frequency light emitting path into local oscillation light and vibration light, and heterodynes the local oscillation light and vibration to generate a measurement beat frequency signal and then converts the measurement beat frequency signal into a measurement electric signal; and performing heterodyne interference on the sweep frequency light and the optical frequency comb laser emitted by the optical frequency comb laser emission circuit by adopting a correction circuit to generate heterodyne signals, and performing I/Q modulation to convert the modulated signals into orthogonal beat frequency signals. The system has the advantages of simple structure, good nonlinear correction effect, high processing speed and high stability, is not influenced by dispersion mismatch and environmental change, and realizes rapid high-precision equal optical frequency interval resampling.
Referring to fig. 1, the second embodiment is described, where the first embodiment is an example of a swept-frequency optical emission path and an optical-frequency comb laser emission path in the fast high-precision swept-frequency interferometry nonlinear correction system based on non-uniform zero-insertion filtering, where the swept-frequency optical emission path includes an external cavity swept-frequency continuous-wave laser source and a swept-frequency optical isolator;
the optical frequency comb laser emission path comprises a femtosecond optical frequency comb and an optical frequency comb isolator;
the external cavity type sweep continuous wave laser source emits sweep light, the sweep light is emitted into the sweep optical isolator, and the sweep optical isolator optically isolates the incident light and emits the incident light into the measuring path;
the femtosecond optical frequency comb emits optical frequency comb laser and irradiates the optical frequency comb isolator, and the optical frequency comb isolator optically isolates incident light and irradiates the incident light into the correction path.
In practical application, as shown in fig. 1, the external cavity type sweep continuous wave laser source emits sweep light, and the sweep light is injected into the sweep optical isolator, and the sweep optical isolator optically isolates the incident light and then injects the incident light into the measurement path; the linear sweep light passing through the sweep optical isolator is optically isolated, and the echo and the interference of the optical signal are prevented. And similarly, the second optical frequency comb emits optical frequency comb laser and irradiates the optical frequency comb isolator, and the optical frequency comb isolator optically isolates incident light and irradiates the incident light into the correction path, so that echo and interference of optical signals can be prevented.
Referring to fig. 1, the third embodiment is described by illustrating an external cavity type sweep-frequency continuous wave laser source in the non-linear correction system for high-speed high-precision sweep-frequency interferometry based on non-uniform zero-insertion filtering according to the second embodiment, wherein the external cavity type sweep-frequency continuous wave laser source is implemented by using a linear tuning laser.
In practical application, the external cavity type sweep frequency continuous wave laser source is realized by adopting a linear tuning laser, the linear tuning laser emits linear sweep frequency light, the linear tuning laser emits the linear sweep frequency light into a sweep frequency optical isolator, and the sweep frequency optical isolator optically isolates the incident light and emits the linear sweep frequency light into the measuring path; the linear sweep light passing through the sweep optical isolator is optically isolated, and meanwhile, the linear sweep light can be ensured to propagate in one specific direction only, and can be prevented in the other direction, so that the echo and the interference of an optical signal are prevented.
In the fourth embodiment, referring to fig. 1, the present embodiment is an example of a measurement path in the fast high-precision sweep-frequency interferometry nonlinear correction system based on non-uniform zero-insertion filtering according to the third embodiment, where the measurement path includes a first measurement path coupler, a second measurement path coupler, a circulator, an optical fiber mirror, a third measurement path coupler, and a measurement path balance detector;
the correction circuit comprises a 90-degree optical mixer;
the sweep frequency optical isolator optically isolates incident light and then emits the incident light into the first coupler of the measuring path, and the first coupler of the measuring path divides the incident light into two beams of sweep frequency light and emits the two beams of sweep frequency light into the 90-degree optical mixer and the second coupler of the measuring path respectively;
the second coupler of the measuring path divides incident light into vibration light and measuring light, the measuring light is injected into the circulator, and the vibration light is injected into the third coupler of the measuring path;
the circulator transmits the processed incident light to the third coupler of the measuring path through the optical fiber reflector, the third coupler of the measuring path performs heterodyne interference on the received light beam and local oscillation light to obtain a measurement beat frequency signal, and the measurement beat frequency signal is sent to the balance detector of the measuring path, and the balance detector of the measuring path converts the measurement beat frequency signal into an electric signal and sends the electric signal to the acquisition and processing unit.
In practical application, as shown in fig. 1, the second coupler of the measuring path splits incident light into oscillation light and measuring light, and the measuring light is injected into the circulator, and the oscillation light is injected into the third coupler of the measuring path; the circulator transmits incident light to the optical transmitting/receiving system through the optical fiber reflector, then the incident light is output to the third coupler of the measuring path through the circulator to heterodyne interference with local oscillation light, a measurement beat frequency signal is formed, then the measurement beat frequency signal is converted into a measurement electric signal through the balance detector of the measuring path, and the measurement electric signal is sent to the acquisition and processing unit.
Because the frequency of the simple optical signal is too high to be used as a signal for correction processing, the measuring path carries out heterodyne interference on local oscillation light and measuring light, and then the measuring beat frequency signal is converted into a measuring electric signal through the balance detector, so that the signal which can be used as the signal for correction processing is realized.
Referring to fig. 1, the fourth embodiment is an illustration of a first measuring path coupler, a second measuring path coupler and a third measuring path coupler in the fast high-precision sweep-frequency interferometry nonlinear correction system based on non-uniform zero-insertion filtering, wherein the first measuring path coupler, the second measuring path coupler and the third measuring path coupler are all implemented by 50:50 couplers.
In practical application, as shown in fig. 1, the first coupler of the measuring path, the second coupler of the measuring path and the third coupler of the measuring path all adopt 50:50 couplers, so that light with the same proportion is split.
Referring to fig. 1, the present embodiment is described by way of example of a correction path in a fast high-precision swept-frequency interferometry nonlinear correction system based on non-uniform zero-insertion filtering according to the fifth embodiment, where the correction path further includes a polarization controller, an attenuator, a correction path first balance detector, a correction path second balance detector, a first low-pass filter, and a second low-pass filter;
the optical frequency comb isolator optically isolates incident light and then emits the incident light into the polarization controller, the polarization controller adjusts the polarization of the incident light and emits the incident light into the attenuator, the attenuator adjusts the signal intensity of the incident light and emits the incident light into the 90-degree optical mixer, the 90-degree optical mixer heterodynes the incident light and the received swept light and modulates the incident light into I/Q (input/output) signals, the I/Q signals are respectively emitted into the first balance detector and the second balance detector of the correction path, the first balance detector of the correction path converts the light signal of the incident light into a beat signal and emits the beat signal into the first low-pass filter, and the first low-pass filter filters the beat signal and sends the beat signal to the acquisition and processing unit;
the second balance detector of the correction circuit converts the optical signal of the incident light into a beat signal and transmits the beat signal to the second low-pass filter, and the second low-pass filter filters the beat signal and transmits the beat signal to the acquisition and processing unit.
In practical application, as shown in fig. 1, polarization control adjusts the polarization of the optical frequency comb laser after optical isolation, then transmits the optical frequency comb laser to an attenuator, the attenuator strengthens the signal intensity of incident light and then transmits the optical frequency comb laser into a 90-degree optical mixer, heterodyne interference is carried out on the optical frequency comb laser with the received sweep light, and then the 90-degree optical mixer carries out I/Q modulation, so that two paths of modulated signals are respectively transmitted to a first balance detector of a correction path and a second balance detector of the correction path, the first balance detector of the correction path converts the optical signal of the incident light into a beat signal and then transmits the beat signal to the first low-pass filter, and the first low-pass filter filters the beat signal and then transmits the beat signal to the acquisition and processing unit; the positive path second balance detector converts the optical signal of the incident light into a beat frequency signal and transmits the beat frequency signal to the second low-pass filter, and the second low-pass filter filters the beat frequency signal and transmits the beat frequency signal to the acquisition and processing unit. At this time, the acquisition and processing unit corrects the nonlinearity of the sweep frequency of the laser by using the received measurement electric signals and the orthogonal beat frequency signals.
Because the frequency of the simple optical signal is too high to be used as a signal for correction processing, the correction circuit carries out heterodyne interference on the sweep frequency light and the optical frequency comb laser and carries out I/Q modulation to obtain an orthogonal beat frequency signal, so that the signal which can be used as the signal for correction processing is realized.
The seventh embodiment is described with reference to fig. 1, which illustrates an acquisition and processing unit in a fast high-precision swept-frequency interferometry nonlinear correction system based on non-uniform zero-insertion filtering according to the sixth embodiment,
the acquisition and processing unit comprises a TRIG trigger source, a CLK clock source and an acquisition card;
the TRIG trigger source is used for taking sweep frequency light emitted by the linear harmonic laser as a trigger signal of the acquisition card;
the CLK clock source is used for taking optical frequency comb laser emitted by the femtosecond optical frequency comb as an external clock source of the acquisition card;
the acquisition card is used for receiving the measurement electric signal and the beat frequency signal.
In practical application, as shown in fig. 1, the TRIG trigger source of this embodiment: the start of the sweep frequency of the linear tuning laser generates a trigger signal for synchronizing the start of the acquisition card.
CLK clock source: the femtosecond optical frequency comb also outputs square wave signals containing optical comb repetition frequency information as an external clock source of the acquisition card to realize synchronous acquisition of beat signals.
In the eighth embodiment, the wavelengths of the emission of the linear tuning laser and the femtosecond optical frequency comb in the fast high-precision sweep-frequency interferometry nonlinear correction system based on the non-uniform zero insertion filtering are exemplified, and the wavelengths of the emission of the linear tuning laser and the femtosecond optical frequency comb are 1550nm.
Referring to fig. 2, the present embodiment provides a method for nonlinear correction of a fast high-precision frequency-sweep interferometry based on non-uniform zero-insertion filtering, where the method is implemented based on the fast high-precision frequency-sweep interferometry nonlinear correction system based on non-uniform zero-insertion filtering described in any one of the first to eighth embodiments, and the method includes:
s1, heterodyne interference is carried out on optical frequency comb laser emitted by a femtosecond optical frequency comb and sweep frequency light emitted by a linear tuning laser at the input end of a 90-degree optical mixer to generate heterodyne signals, the heterodyne signals are subjected to I/Q modulation through the 90-degree optical mixer to obtain two paths of modulated signals, and photoelectric conversion is carried out on the two paths of modulated signals by a correction path first balance detector and a correction path second balance detector to obtain two paths of intersected beat frequency signals;
s2, processing signals of heterodyne interference of sweep frequency light and optical frequency comb laser by adopting a sweep frequency relative frequency algorithm to obtain a frequency difference value of the sweep frequency laser relative to a sweep starting frequency;
s3, carrying out non-uniform zero interpolation by adopting a fixed step length according to the frequency difference value of the sweep frequency laser relative to the scanning initial frequency to obtain an equidistant frequency sequence;
s4, determining a new time sampling point by adopting a judging program and combining an original resolving frequency and an original sampling time point, and determining a new time sampling point corresponding to the equidistant frequency sequence;
s5, non-uniform zero interpolation is carried out on the measurement path signal at the new time sampling point, and meanwhile, low-pass filtering processing is carried out, so that accurate interpolation value of the inserted zero point is obtained;
and S6, extracting the measurement path signal at the new time sampling point according to the new time sampling point corresponding to the equidistant frequency sequence to realize equidistant resampling, and obtaining the measurement path signal after the nonlinear correction of the frequency sweep, wherein the measurement path signal is used for obtaining a rapid high-precision frequency sweep interferometry result.
In practical application, the optical frequency comb laser of a correction path and sweep frequency light emitted by a linear tuning laser in a fast high-precision sweep frequency interferometry nonlinear correction system based on non-uniform zero-insertion filtering are adopted to perform heterodyne interference at the input end of a 90-degree optical mixer to generate heterodyne signals, the heterodyne signals are subjected to I/Q modulation through the 90-degree optical mixer, and two paths of modulated signals are converted through a balance detector to obtain two paths of crossed beat signals; processing a signal of heterodyne interference of the sweep light and the optical frequency comb laser by adopting a sweep relative frequency algorithm to obtain a frequency difference value of the sweep laser relative to a sweep initial frequency; the method comprises the following steps: carrying out phase analysis and unwrapping on two paths of intersected beat signals by adopting a sweep frequency relative frequency algorithm to obtain the phase of a corrected path beat signal; calculating the frequency based on the derivation of the phase to time according to the phase of the correction road beat signal, and obtaining the frequency difference between the sweep frequency laser and the nearest light comb teeth; and unwrapping the frequency difference value of the sweep frequency laser and the nearest optical comb teeth to obtain the frequency value of the sweep frequency laser relative to the scanning initial frequency. According to the frequency difference value of the sweep frequency laser relative to the sweep initial frequency, adopting a fixed step length to carry out non-uniform zero interpolation to obtain an equidistant frequency sequence; determining a new time sampling point by combining the original resolving frequency and the original sampling time point by a judging program, and determining a new time sampling point corresponding to the equidistant frequency sequence; then non-uniform zero insertion is carried out on the measurement path signal at the new time sampling point, and low-pass filtering processing is carried out at the same time, so that accurate interpolation value of the inserted zero point is obtained; and extracting the measurement path signal at the new time sampling point according to the new time sampling point corresponding to the equidistant frequency sequence and the accurate interpolation value of the inserted zero point, and realizing equidistant resampling to obtain the measurement path signal after the nonlinear correction of the frequency sweep, wherein the measurement path signal is used for obtaining a rapid high-precision frequency sweep interferometry result.
The embodiment provides a fast high-precision sweep frequency interferometry nonlinear correction method based on non-uniform zero-insertion filtering, which combines a sweep frequency relative frequency algorithm with non-uniform zero-insertion filtering, solves the problem of equal-frequency interval resampling of a non-uniform sampling sequence, reduces algorithm complexity, is suitable for embedded systems such as FPGA (field programmable gate array) and the like, has the characteristics of high efficiency and low power consumption, and can improve system performance and efficiency.
The specific principle is as follows: the complex amplitude expression of the linear tuning laser is:
wherein,f swept (t) is the sweep frequency f swept (t)＝f 0 +Δf (t), Δf (t) being the amount of frequency with nonlinearity;
the femtosecond optical frequency comb complex amplitude expression is:
the interference signals of the femtosecond optical frequency comb and the linear tuning laser in the correction path are as follows:
the phase of the nonlinear sweep frequency contained in the beat frequency is:
wherein,
from phase to frequency relationshipThe resolvable frequencies are:
f(t)＝f swept (t-mT)-f c ；
the instantaneous frequency of the sweep frequency laser can be obtained;
the measurement light beat signal output in the measurement path is converted into a voltage signal V after passing through the photoelectric detector R (t) expressed as:
wherein τ m To measure the corresponding time delay after the light reaches the target m =2r/c, R is distance, c is speed of light;
from the calculated instantaneous frequency f of the sweep swept Replacing the measurement path signal from a function of time to a frequency f swept Is a function of (2);
under the condition of ensuring that the laser frequency calculation and the distance measurement are acquired simultaneously, replacing the time of a measuring path by the frequency calculated by a correction path, and then carrying out Fourier transform on the measuring signal with respect to the frequency to obtain a measured distance spectrum, wherein the influence of the sweep frequency on a distance result is eliminated;
wherein, the distance spectrum expression is:
wherein B is bandwidth, R is distance, and c is speed of light. Extracting a distance corresponding to the distance spectrum peak value, namely a measured distance value R, wherein the distance resolution is as follows: Δr=c/(2B).
In a tenth embodiment, the step s2 in the fast high-precision sweep-frequency interferometry nonlinear correction method based on non-uniform zero-insertion filtering according to the ninth embodiment is illustrated, and the step two specifically includes:
s21, carrying out phase analysis and unwrapping on two paths of intersected beat signals by adopting a sweep frequency relative frequency algorithm to obtain the phase of a corrected road beat signal;
s22, calculating the frequency based on the phase derivation of the time according to the phase of the correction road beat signal, and obtaining the frequency difference value between the sweep frequency laser and the nearest light comb teeth;
s23, unwrapping the frequency difference value between the sweep frequency laser and the nearest optical comb teeth to obtain a frequency value of the sweep frequency laser relative to the scanning initial frequency.
In an eleventh embodiment, referring to fig. 3, the present embodiment is a verification description of a fast high-precision frequency-sweep interferometry nonlinear correction method based on non-uniform zero-insertion filtering described in embodiment nine or embodiment ten, where a distance spectrum before correction is shown in fig. 3 (a), and a corrected distance spectrum is shown in fig. 3 (b), so that the correction precision of the fast high-precision frequency-sweep interferometry nonlinear correction method based on non-uniform zero-insertion filtering described in the present embodiment is greatly improved.
According to the fast high-precision sweep frequency interferometry nonlinear correction method based on the non-uniform zero-insertion filtering, a sweep frequency relative frequency algorithm is combined with the non-uniform zero-insertion filtering, the problem of equal-frequency interval resampling of a non-uniform sampling sequence is solved, meanwhile, algorithm complexity is reduced, the method is suitable for embedded systems such as FPGA (field programmable gate array) and has the characteristics of high efficiency and low power consumption, and system performance and efficiency can be improved. The correction method is realized based on a correction system, the correction system adopts a measurement path to separate sweep light emitted by a sweep light emission path into local oscillation light and vibration light, heterodyne interference is carried out on the local oscillation light and vibration to generate a measurement beat frequency signal, and then the measurement beat frequency signal is converted into a measurement electric signal; and performing heterodyne interference on the sweep frequency light and the optical frequency comb laser emitted by the optical frequency comb laser emission circuit by adopting a correction circuit to generate heterodyne signals, and performing I/Q modulation to convert the modulated signals into orthogonal beat frequency signals. The system has the advantages of simple structure, good nonlinear correction effect, high processing speed and high stability, is not influenced by dispersion mismatch and environmental change, and realizes rapid high-precision equal optical frequency interval resampling.
Furthermore, the terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include at least one such feature. In the description of the present invention, the meaning of "plurality" means at least two, for example, two, three, etc., unless specifically defined otherwise.
In the description of the present specification, a description referring to terms "one embodiment," "some embodiments," "examples," "specific examples," or "some examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms are not necessarily directed to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, the different embodiments or examples described in this specification and the features of the different embodiments or examples may be combined and combined by those skilled in the art without contradiction.
The above description is only an example of the present invention and is not limited to the present invention, but various modifications and changes will be apparent to those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the scope of the claims of the present invention.
Claims (10)
1. The rapid high-precision sweep frequency interferometry nonlinear correction system based on non-uniform zero-insertion filtering is characterized by comprising a sweep frequency light emitting path, an optical frequency comb laser emitting path, a measuring path, a correction path and an acquisition and processing unit;
the sweep light emission path emits sweep light and irradiates the sweep light into the measurement path;
the measuring path is used for dividing incident light into local oscillation light and measuring light, heterodyning the local oscillation light and the measuring light to interfere with each other, forming a measuring beat frequency signal, converting the measuring beat frequency signal into a measuring electric signal, and transmitting the measuring electric signal to the collecting and processing unit, and also used for transmitting the incident light to the correcting path;
the optical frequency comb laser emission path emits optical frequency comb laser and emits the optical frequency comb laser into the correction path;
the correction circuit is used for performing I/Q modulation after heterodyne interference of the optical frequency comb laser and the received sweep frequency light, and is also used for converting the optical signals subjected to the I/Q modulation into orthogonal beat frequency signals and sending the orthogonal beat frequency signals to the acquisition and processing unit;
the acquisition and processing unit is used for correcting the nonlinearity of the sweep frequency of the laser according to the received measurement electric signals and the orthogonal beat frequency signals.
2. The non-uniform zero-insertion filtering-based rapid high-precision swept-frequency interferometry nonlinear correction system according to claim 1, wherein the swept-frequency optical emission path comprises an external cavity type swept-frequency continuous-wave laser source and a swept-frequency optical isolator;
the optical frequency comb laser emission path comprises a femtosecond optical frequency comb and an optical frequency comb isolator;
the external cavity type sweep continuous wave laser source emits sweep light, the sweep light is emitted into the sweep optical isolator, and the sweep optical isolator optically isolates the incident light and emits the incident light into the measuring path;
the femtosecond optical frequency comb emits optical frequency comb laser and irradiates the optical frequency comb isolator, and the optical frequency comb isolator optically isolates incident light and irradiates the incident light into the correction path.
3. The non-uniform zero-insertion filtering-based rapid high-precision swept-frequency interferometry nonlinear correction system according to claim 2, wherein the external cavity type swept-frequency continuous wave laser source is implemented by a linear tuning laser.
4. The non-uniform zero-insertion filtering-based rapid high-precision sweep interferometry nonlinear correction system according to claim 3, wherein the measurement path comprises a measurement path first coupler, a measurement path second coupler, a circulator, an optical fiber reflector, a measurement path third coupler and a measurement path balance detector;
the correction circuit comprises a 90-degree optical mixer;
the sweep frequency optical isolator optically isolates incident light and then emits the incident light into the first coupler of the measuring path, and the first coupler of the measuring path divides the incident light into two beams of sweep frequency light and emits the two beams of sweep frequency light into the 90-degree optical mixer and the second coupler of the measuring path respectively;
the second coupler of the measuring path divides incident light into vibration light and measuring light, the measuring light is injected into the circulator, and the vibration light is injected into the third coupler of the measuring path;
the circulator transmits the processed incident light to the third coupler of the measuring path through the optical fiber reflector, the third coupler of the measuring path performs heterodyne interference on the received light beam and local oscillation light to obtain a measurement beat frequency signal, and the measurement beat frequency signal is sent to the balance detector of the measuring path, and the balance detector of the measuring path converts the measurement beat frequency signal into an electric signal and sends the electric signal to the acquisition and processing unit.
5. The non-uniform zero insertion filtering-based rapid high-precision sweep frequency interferometry nonlinear correction system according to claim 4, wherein the first measuring path coupler, the second measuring path coupler and the third measuring path coupler are all implemented by adopting 50:50 couplers.
6. The non-uniform zero-insertion filtering based rapid high-precision swept-frequency interferometry nonlinear correction system according to claim 5, wherein the correction path further comprises a polarization controller, an attenuator, a correction path first balanced detector, a correction path second balanced detector, a first low-pass filter, and a second low-pass filter;
the optical frequency comb isolator optically isolates incident light and then emits the incident light into the polarization controller, the polarization controller adjusts the polarization of the incident light and emits the incident light into the attenuator, the attenuator adjusts the signal intensity of the incident light and emits the incident light into the 90-degree optical mixer, the 90-degree optical mixer heterodynes the incident light and the received swept light and modulates the incident light into I/Q (input/output) signals, the I/Q signals are respectively emitted into the first balance detector and the second balance detector of the correction path, the first balance detector of the correction path converts the light signal of the incident light into a beat signal and emits the beat signal into the first low-pass filter, and the first low-pass filter filters the beat signal and sends the beat signal to the acquisition and processing unit;
the second balance detector of the correction circuit converts the optical signal of the incident light into a beat signal and transmits the beat signal to the second low-pass filter, and the second low-pass filter filters the beat signal and transmits the beat signal to the acquisition and processing unit.
7. The non-uniform zero-insertion filtering-based rapid high-precision swept-frequency interferometry nonlinear correction system according to claim 6, wherein the acquisition and processing unit comprises a TRIG trigger source, a CLK clock source, and an acquisition card;
the TRIG trigger source is used for taking sweep frequency light emitted by the linear harmonic laser as a trigger signal of the acquisition card;
the CLK clock source is used for taking optical frequency comb laser emitted by the femtosecond optical frequency comb as an external clock source of the acquisition card;
the acquisition card is used for receiving the measurement electric signal and the beat frequency signal.
8. The non-uniform zero-insertion filtering based rapid high-precision swept-frequency interferometry nonlinear correction system according to claim 7, wherein the wavelength of the emissions of the linearly tuned laser and the femtosecond optical frequency comb are each 1550nm.
9. A method for nonlinear correction of fast high-precision sweep frequency interferometry based on non-uniform zero-insertion filtering, characterized in that the method is realized based on the fast high-precision sweep frequency interferometry nonlinear correction system based on non-uniform zero-insertion filtering according to any one of claims 1-8, and the method comprises the following steps:
s1, heterodyne interference is carried out on optical frequency comb laser emitted by a femtosecond optical frequency comb and sweep frequency light emitted by a linear tuning laser at the input end of a 90-degree optical mixer to generate heterodyne signals, the heterodyne signals are subjected to I/Q modulation through the 90-degree optical mixer to obtain two paths of modulated signals, and photoelectric conversion is carried out on the two paths of modulated signals by a correction path first balance detector and a correction path second balance detector to obtain two paths of intersected beat frequency signals;
s2, processing signals of heterodyne interference of sweep frequency light and optical frequency comb laser by adopting a sweep frequency relative frequency algorithm to obtain a frequency difference value of the sweep frequency laser relative to a sweep starting frequency;
s3, carrying out non-uniform zero interpolation by adopting a fixed step length according to the frequency difference value of the sweep frequency laser relative to the scanning initial frequency to obtain an equidistant frequency sequence;
s4, determining a new time sampling point by adopting a judging program and combining an original resolving frequency and an original sampling time point, and determining a new time sampling point corresponding to the equidistant frequency sequence;
s5, non-uniform zero interpolation is carried out on the measurement path signal at the new time sampling point, and meanwhile, low-pass filtering processing is carried out, so that accurate interpolation value of the inserted zero point is obtained;
and S6, extracting the measurement path signal at the new time sampling point according to the new time sampling point corresponding to the equidistant frequency sequence to realize equidistant resampling, and obtaining the measurement path signal after the nonlinear correction of the frequency sweep, wherein the measurement path signal is used for obtaining a rapid high-precision frequency sweep interferometry result.
10. The method for nonlinear correction of fast high-precision sweep interferometry based on non-uniform zero-insertion filtering according to claim 9, wherein the step S2 is specifically:
s21, carrying out phase analysis and unwrapping on two paths of intersected beat signals by adopting a sweep frequency relative frequency algorithm to obtain the phase of a corrected road beat signal;
s22, calculating the frequency based on the phase derivation of the time according to the phase of the correction road beat signal, and obtaining the frequency difference value between the sweep frequency laser and the nearest light comb teeth;
s23, unwrapping the frequency difference value between the sweep frequency laser and the nearest optical comb teeth to obtain a frequency value of the sweep frequency laser relative to the scanning initial frequency.
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