CN110375864B - Method for expanding frequency modulation continuous wave laser interference measurement range - Google Patents
Method for expanding frequency modulation continuous wave laser interference measurement range Download PDFInfo
- Publication number
- CN110375864B CN110375864B CN201910648286.7A CN201910648286A CN110375864B CN 110375864 B CN110375864 B CN 110375864B CN 201910648286 A CN201910648286 A CN 201910648286A CN 110375864 B CN110375864 B CN 110375864B
- Authority
- CN
- China
- Prior art keywords
- frequency
- modulation
- continuous wave
- laser
- signal
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Active
Links
- 238000000034 method Methods 0.000 title claims abstract description 13
- 238000005259 measurement Methods 0.000 title claims description 10
- 230000035559 beat frequency Effects 0.000 claims abstract description 39
- 238000004556 laser interferometry Methods 0.000 claims abstract description 5
- 230000003247 decreasing effect Effects 0.000 claims 1
- 230000003287 optical effect Effects 0.000 abstract description 17
- 238000005305 interferometry Methods 0.000 abstract description 3
- 239000004065 semiconductor Substances 0.000 description 2
- 238000004458 analytical method Methods 0.000 description 1
- 238000006073 displacement reaction Methods 0.000 description 1
- 238000000691 measurement method Methods 0.000 description 1
- 238000005070 sampling Methods 0.000 description 1
Images
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J9/00—Measuring optical phase difference; Determining degree of coherence; Measuring optical wavelength
- G01J9/02—Measuring optical phase difference; Determining degree of coherence; Measuring optical wavelength by interferometric methods
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J9/00—Measuring optical phase difference; Determining degree of coherence; Measuring optical wavelength
- G01J9/02—Measuring optical phase difference; Determining degree of coherence; Measuring optical wavelength by interferometric methods
- G01J2009/0249—Measuring optical phase difference; Determining degree of coherence; Measuring optical wavelength by interferometric methods with modulation
Abstract
The invention relates to the technical field of optical frequency modulation continuous wave interferometry, in particular to a method for expanding the laser interferometry range of frequency modulation continuous wave. The frequency modulation continuous wave laser interference obtains a dynamic beat frequency signal, the frequency and the initial phase of the dynamic beat frequency signal are related to the optical path difference between signal light and reference light in the interferometer, and when the optical path difference is small or large, the initial phase or the optical path difference cannot be identified normally and accurately, so that the frequency modulation continuous wave laser interference has two dead zones. The technical scheme provided by the invention is as follows: the beat frequency of the current interference signal is measured, and the laser frequency modulation degree of the frequency modulation continuous wave laser light source is changed, so that the beat frequency of the interference signal is always in the frequency range capable of effectively demodulating the phase. The invention has the advantages that: not only can reduce the front dead zone when the optical path difference is small, but also can eliminate the back dead zone when the optical path difference is large, thereby greatly enlarging the measuring range of frequency modulation continuous wave laser interference.
Description
The technical field is as follows:
the invention relates to the technical field of optical frequency modulation continuous wave interferometry, in particular to a method for expanding the laser interferometry range of frequency modulation continuous wave.
Background art:
optical Frequency Modulated Continuous Wave (FMCW) interferometry is a new precision measurement technique. This optical interference technique uses a laser light source whose light frequency is periodically continuously linearly modulated. When the signal light and the reference light in the interference device meet and interfere, the generated interference signal is a dynamic beat frequency signal, and the frequency and the initial phase of the dynamic beat frequency signal are related to the optical path difference between the signal light and the reference light. When the optical path difference is small, the initial phase and the change direction thereof may not be identified due to the low beat frequency, and theoretical analysis indicates that the initial phase can be normally identified only if the beat frequency is greater than or equal to 2.5 times of the modulation frequency of the laser. The frequency modulation continuous wave laser interference has two dead zones, the corresponding dead zone is called as a front dead zone when the optical path difference is small, when the optical path difference is large, the beat frequency is high, because the ADC sampling frequency in the digital signal processing circuit is fixed by the country, the signal data volume in each beat frequency period is inevitably reduced, the measurement accuracy is seriously influenced, and even the measurement cannot be carried out, the dead zone is called as a back dead zone. The existence of the dead zone limits the measuring range of frequency modulation continuous wave laser interference.
The invention content is as follows:
the invention provides a method for expanding the measuring range of frequency modulation continuous wave laser interference, which aims to solve the problem that the measuring range of frequency modulation continuous wave laser interference is limited in the prior art.
In order to achieve the purpose of the invention, the technical scheme provided by the invention is as follows: a method for expanding the measuring range of frequency modulation continuous wave laser interferometry is characterized in that: by measuring the beat frequency of the current interference signal, wherein the beat frequency is linear modulation, the laser frequency modulation degree of the frequency modulation continuous wave laser light source is changed, so that the beat frequency of the interference signal is always in the frequency range capable of effectively demodulating the phase, the initial phase and the change of the initial phase of the interference signal can be accurately measured, and the frequency modulation continuous wave laser interference measurement range is greatly expanded.
When the beat frequency is less than 3 multiplied by the modulation frequency, the slope of the modulation straight line of the laser driving signal is increased according to the 2/3 geometric progression, and the linear modulation data table is updated until the beat frequency is more than 3 multiplied by the modulation frequency.
When the beat frequency > is 10 × modulation frequency, the slope of the interpolation line is reduced to k according to the proportional series of 2/3, and the linear modulation data table is updated until the beat frequency <10 × modulation frequency.
Compared with the prior art, the invention has the advantages that:
1. by the method, the beat frequency of the interference signal is always in a proper frequency range, so that the initial phase and the change of the initial phase of the interference signal can be accurately measured.
2. The method can not only reduce the front dead zone, but also eliminate the back dead zone, thereby greatly enlarging the measuring range of frequency modulation continuous wave laser interference measurement.
3. The method is not only suitable for sawtooth wave modulation frequency modulation continuous wave interference, but also suitable for triangular wave modulation frequency modulation continuous wave interference.
Description of the drawings:
fig. 1 shows waveforms of drive currents having different k values when a drive signal of a semiconductor laser has a sawtooth waveform.
The specific implementation mode is as follows:
the present invention will be described in detail below with reference to the drawings and examples.
According to the theory of optically chirped continuous wave interference, if the laser frequency is linearly modulated (e.g., sawtooth modulation or triangular modulation), the light intensity I (τ, t) of the interference signal can be expressed as
I(τ，t)＝I0[1+Vcos(ατt+ω0τ)] (1)
Wherein, I0Is the average light intensity (I) of the interference signal0＝I1+I2，I1To reference the light intensity, I2Signal light intensity), V is the contrast of the interference signal
ω0For the central angular frequency of the laser, τ is the delay time of the signal light relative to the reference light (τ is OPD/c, OPD is the optical path difference of the signal light relative to the reference light, c is the speed of light), α is the angular frequency modulation rate of the laser (α is Δ ω/T)mΔ ω is the angular frequency modulation range of the laser, TmA modulation signal period).
The above formula shows that the chirp-continuous-wave interference signal is a dynamic signal whose beat frequency and initial phase are both proportional to the delay time τ (or the optical path difference between the two) of the signal light relative to the reference light. However, the beat frequency is only related to the angular frequency modulation rate α of the laser, and the initial phase is only related to the central angular frequency ω of the laser0It is related. This means that by changing the angular frequency modulation rate α of the laser, the beat frequency of the interference signal can be changed without affecting the measurement of the initial phase (i.e., the optical path difference).
Based on the theory, the method for expanding the interference measurement range of the frequency modulated continuous wave laser provided by the invention changes the laser frequency modulation degree of the frequency modulated continuous wave laser light source by measuring the beat frequency of the current interference signal, wherein the beat frequency is linear modulation, so that the beat frequency of the interference signal is always in the frequency range capable of effectively demodulating the phase, the initial phase and the change of the interference signal can be accurately measured, and the interference measurement range of the frequency modulated continuous wave laser is greatly expanded.
When the beat frequency is less than 3 multiplied by the modulation frequency, the slope of the modulation straight line of the laser driving signal is increased according to the 2/3 geometric progression, and the linear modulation data table is updated until the beat frequency is more than 3 multiplied by the modulation frequency.
When the beat frequency > is 10 × modulation frequency, the slope of the interpolation line is reduced to k according to the proportional series of 2/3, and the linear modulation data table is updated until the beat frequency <10 × modulation frequency.
The laser driving circuit and the interferometer signal processing circuit both adopt digital circuits, the laser driving signal is obtained by reading a data table by a microprocessor and converting the data table by a DA circuit, and the modulation degree of the laser frequency emitted by the laser is in direct proportion to the modulation degree of the laser driving signal; the data table is composed of an average value and linear modulation data, the linear modulation data is obtained by interpolation of a straight line with the slope of k, and the interference signal is a digital signal which is converted into an electric signal through a photoelectric detector and then is converted through an AD circuit.
Example (b): a method for expanding the measuring range of frequency modulation continuous wave laser interferometry comprises the following steps:
step 1: for a frequency modulation continuous wave interference modulation and demodulation system of a digital semiconductor laser, a laser driving signal is obtained by reading a data table by a microprocessor and converting the data table by a DA circuit, the data comprises an average value and linear modulation data, and the linear modulation data is obtained by interpolating according to a straight line with the slope of k. The interference signal is a digital signal obtained by converting an optical signal into an electric signal by a photoelectric detector and then converting the electric signal by an AD circuit, and the beat frequency of the interference signal can be calculated by measuring the position of a minimum value point (or a maximum value point) of the waveform of the interference signal in each modulation period on a time axis. Referring to fig. 1, the driving signal in the present embodiment is a sawtooth waveform.
When the beat frequency is less than 3 multiplied by the modulation frequency, the slope of the interpolation straight line is increased to be k according to the proportional series of 2/3, and the linear modulation data table is updated until the beat frequency is more than 3 multiplied by the modulation frequency.
Therefore, the beat frequency of the frequency modulation continuous wave interference is always in the frequency range of 3 to 10 times of the modulation frequency, and a good condition is provided for high-precision identification of the initial phase.
Note that: maximum value k of kmaxDetermined by the laser threshold current and operating current and the modulation frequency, if k increases to a maximum value kmaxTime, beat frequency<The OPD corresponding to 3 × modulation frequency is called "dead zone before residual", and the "dead zone before residual" should be avoided when measuring the displacement.
Claims (1)
1. A method for expanding the measuring range of frequency modulation continuous wave laser interferometry is characterized in that: the beat frequency of the interference signal is always in the frequency range capable of effectively phase discrimination by measuring the beat frequency of the current interference signal and changing the laser frequency modulation degree of the frequency modulation continuous wave laser light source, so that the initial phase and the change of the interference signal can be accurately measured, and the interference measurement range of the frequency modulation continuous wave laser is greatly expanded;
when the beat frequency is less than 3 multiplied by the modulation frequency, increasing the slope of a laser driving signal modulation straight line according to an 2/3 geometric progression, and updating a linear modulation data table until the beat frequency is more than 3 multiplied by the modulation frequency;
when the beat frequency > is 10 × modulation frequency, the slope of the laser drive signal modulation straight line is decreased in accordance with the 2/3 geometric progression, and the linear modulation data table is updated until the beat frequency <10 × modulation frequency.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201910648286.7A CN110375864B (en) | 2019-07-18 | 2019-07-18 | Method for expanding frequency modulation continuous wave laser interference measurement range |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201910648286.7A CN110375864B (en) | 2019-07-18 | 2019-07-18 | Method for expanding frequency modulation continuous wave laser interference measurement range |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CN110375864A CN110375864A (en) | 2019-10-25 |
| CN110375864B true CN110375864B (en) | 2021-07-02 |
Family
ID=68253775
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN201910648286.7A Active CN110375864B (en) | 2019-07-18 | 2019-07-18 | Method for expanding frequency modulation continuous wave laser interference measurement range |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN110375864B (en) |
Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN109557547A (en) * | 2018-12-27 | 2019-04-02 | 武汉万集信息技术有限公司 | Laser radar, range measurement and/or method for determining speed and storage medium |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB0421520D0 (en) * | 2004-09-28 | 2004-10-27 | Qinetiq Ltd | Frequency modulated continuous wave (FMCW) radar having improved frquency sweep linearity |
| GB0506209D0 (en) * | 2005-03-29 | 2005-05-04 | Qinetiq Ltd | Coherent frequency modulated continuous wave radar |
| CN105006736A (en) * | 2015-05-08 | 2015-10-28 | 上海交通大学 | Frequency modulated continuous wave (FMCW) frequency sweep non-leaner calibration system based on closed loop control and FMCW frequency sweep non-leaner calibration method based on closed loop control |
| CN108050941A (en) * | 2017-12-25 | 2018-05-18 | 西安工业大学 | A kind of CW with frequency modulation laser interference optical fiber displacement sensor and its displacement detecting method |
| CN108444381B (en) * | 2018-05-15 | 2020-02-14 | 西安工业大学 | Correction method for eliminating nonlinearity of frequency modulation interference signal of semiconductor laser |
-
2019
- 2019-07-18 CN CN201910648286.7A patent/CN110375864B/en active Active
Patent Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN109557547A (en) * | 2018-12-27 | 2019-04-02 | 武汉万集信息技术有限公司 | Laser radar, range measurement and/or method for determining speed and storage medium |
Non-Patent Citations (1)
| Title |
|---|
| 频率调制连续波激光雷达技术基础与研究进展;卢炤宇 等;《光电工程》;20190701;第46卷(第7期);正文第1-2部分及图1-2 * |
Also Published As
| Publication number | Publication date |
|---|---|
| CN110375864A (en) | 2019-10-25 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| Norgia et al. | Self-mixing instrument for simultaneous distance and speed measurement | |
| EP2000810B1 (en) | Determination of sine wave period | |
| CN108594254B (en) | Method for improving ranging precision of TOF laser imaging radar | |
| CN106405570A (en) | Laser distance measurement method and device | |
| JP2019045200A (en) | Optical distance measuring device and method | |
| Duan et al. | Absolute distance measurement based on multiple self-mixing interferometry | |
| WO2020131337A1 (en) | Lidar system that is configured to compute ranges with differing range resolutions | |
| TW200916731A (en) | Distance/speed meter, and distance/speed measuring method | |
| CN105785385A (en) | Laser ranging method and device based on synchronous sampling and multiple phase measurement | |
| CN110375864B (en) | Method for expanding frequency modulation continuous wave laser interference measurement range | |
| CN110146012B (en) | Semiconductor laser nonlinear frequency modulation pre-correction method | |
| Kokuyama et al. | Simple digital phase-measuring algorithm for low-noise heterodyne interferometry | |
| US20240142584A1 (en) | Lidar time-of-flight signal processing | |
| CN203535223U (en) | A laser phase range-measuring circuit | |
| US10634563B2 (en) | Phase measurement device and instrument in which phase measurement device is applied | |
| WO2019205847A1 (en) | Displacement measuring system for sensor device and displacement measuring method | |
| CN108241144B (en) | FMCW radar waveform modulation method and device | |
| CN109870677B (en) | Frequency modulation continuous wave interference signal amplitude normalization method | |
| JP5735483B2 (en) | System for demodulating a signal | |
| WO2022250775A1 (en) | Long range coherent lidar | |
| Liu et al. | Rotational speed measurement using self-mixing interferometry | |
| CN109506684B (en) | Wavelength correction method and system for fast scanning laser demodulation FBG sensor | |
| CN108761487B (en) | Large-bandwidth laser wind-finding radar system | |
| JP2012184967A (en) | Wavelength scanning interferometer | |
| JP2012522449A5 (en) |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PB01 | Publication | ||
| PB01 | Publication | ||
| SE01 | Entry into force of request for substantive examination | ||
| SE01 | Entry into force of request for substantive examination | ||
| GR01 | Patent grant | ||
| GR01 | Patent grant |