CN118816705B - Correction method for phase modulation depth of laser frequency modulation interferometer - Google Patents
Correction method for phase modulation depth of laser frequency modulation interferometerInfo
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- CN118816705B CN118816705B CN202410849267.1A CN202410849267A CN118816705B CN 118816705 B CN118816705 B CN 118816705B CN 202410849267 A CN202410849267 A CN 202410849267A CN 118816705 B CN118816705 B CN 118816705B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B9/00—Measuring instruments characterised by the use of optical techniques
- G01B9/02—Interferometers
- G01B9/02055—Reduction or prevention of errors; Testing; Calibration
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B9/00—Measuring instruments characterised by the use of optical techniques
- G01B9/02—Interferometers
- G01B9/02001—Interferometers characterised by controlling or generating intrinsic radiation properties
- G01B9/0201—Interferometers characterised by controlling or generating intrinsic radiation properties using temporal phase variation
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B9/00—Measuring instruments characterised by the use of optical techniques
- G01B9/02—Interferometers
- G01B9/02015—Interferometers characterised by the beam path configuration
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Abstract
本发明公开了一种激光调频干涉仪相位调制深度的校正方法，涉及光纤干涉位移测量技术领域，包括：通过可调频激光器输出第一路调制激光和第二路调制激光；第一路调制激光通过分光棱镜后产生干涉，并通过第一光电探测器扫描输出，第二路调制激光通过气体吸收池的特定吸收谱线吸收特定波长激光，使用第二光电探测器进行探测，并通过解调模块进行解调输出，获取解调后激光光强信号两个峰值的扫描时间，以及测量镜相对位移与初始光程差获得干涉信号的干涉总光程差，通过扫描时间与干涉总光程差获取相位调制深度，并通过调制模块调节可调频激光器的电流幅度，通过调制模块控制电流输出可实现相位调制深度校正，降低了相位调制深度的校正难度。
This invention discloses a method for correcting the phase modulation depth of a laser frequency-modulated interferometer, relating to the field of fiber optic interferometric displacement measurement technology. The method includes: outputting a first modulated laser and a second modulated laser from a frequency-modulated laser; the first modulated laser generates interference after passing through a beam splitter and is scanned and output by a first photodetector; the second modulated laser absorbs a specific wavelength of laser light through a specific absorption spectral line in a gas absorption cell, is detected by a second photodetector, and demodulated by a demodulation module; the scanning time of the two peaks of the demodulated laser intensity signal is obtained, and the total optical path difference of the interference signal is obtained by measuring the relative displacement of the measuring mirror and the initial optical path difference; the phase modulation depth is obtained by the scanning time and the total optical path difference; and the current amplitude of the frequency-modulated laser is adjusted by a modulation module. Correcting the phase modulation depth by controlling the current output through the modulation module reduces the difficulty of phase modulation depth correction.
Description
Technical Field
The invention relates to the technical field of optical fiber interferometric displacement measurement, in particular to a method for correcting the phase modulation depth of a laser frequency modulation interferometer.
Background
Precision displacement measurement is a key technology in the advanced manufacturing field, and the precision of the precision measurement directly influences the quality of production and manufacturing. Among the numerous displacement measuring instruments, the laser interferometer provides the top level accuracy of the displacement measurement. High-precision displacement interferometers such as single-frequency interferometers, double-frequency interferometers and the like are developed in succession for decades, and the development of the high-precision tip manufacturing industry is greatly promoted. Modern high-end equipment manufacturing now places more stringent requirements on interferometers, such as small size, ease of installation, and high robustness, for which fiber optic Sinusoidal Frequency Modulation Interferometers (SFMI) provide a near perfect solution.
The Michelson laser interference displacement sensor is the most classical optical interference displacement measurement method, and through long-term research and development, the technology is mature and reliable, and the resolution after circuit subdivision can reach 1nm. However, the measurement accuracy is directly related to the stability of the wavelength of the light source, so that the requirements on the environment where the light source and the light path are located are high, and the measurement range is greatly limited due to the existence of sine errors.
The optical fiber sinusoidal frequency modulation interferometer is based on the PGC technology, has high sensitivity and excellent precision, and is widely applied to the fields of vibration measurement, displacement sensing and the like. However, the phase modulation depth of the sinusoidal frequency modulation interferometer can be changed along with the change of the position of the measurement target, and the linear measurement range of displacement/vibration is often only a few to tens of micrometers, so that the calculation amount of the conventional phase modulation depth correction algorithm is extremely large, and the occupied hardware resources are excessive, which greatly limits the application of the sinusoidal frequency modulation interferometer.
Disclosure of Invention
The invention aims to overcome the defects of the prior art, and provides a correction method for the phase modulation depth of a laser frequency modulation interferometer, so as to solve the problems that the phase modulation depth of the sinusoidal frequency modulation interferometer in the prior art can be changed along with the change of the position of a measurement target, the linear measurement range of displacement/vibration is often only a few to tens of micrometers, the calculated amount of the conventional phase modulation depth correction algorithm is extremely large, and the occupied hardware resources are excessive, so that the application of the sinusoidal frequency modulation interferometer is greatly limited.
The invention specifically provides a method for correcting the phase modulation depth of a laser frequency modulation interferometer, which comprises the following steps:
Outputting a first path of modulated laser and a second path of modulated laser by a tunable laser of a laser tunable interferometer;
dividing the first path of modulated laser into two beams through a beam splitting prism, respectively transmitting the two beams of laser to a reflecting mirror and a measuring mirror, taking the laser transmitted to the reflecting mirror as a reference beam, taking the laser transmitted to the measuring mirror as a measuring beam, generating interference when the reference beam and the measuring beam are reflected back, detecting the laser generated by the interference by using a first photoelectric detector, and demodulating a signal detected by using a demodulation module to obtain an interference signal;
The second path of modulated laser is input into a gas absorption tank, the second path of modulated laser with specific wavelength is received through two specific absorption spectral lines in the gas absorption tank, the second path of modulated laser with specific wavelength is detected by using a second photoelectric detector, and a signal detected by the second photoelectric detector is input into a demodulation module for demodulation, so that a modulated laser light intensity signal is obtained;
Acquiring scanning time corresponding to two peaks of the modulated laser light intensity signal, acquiring an optical path from a beam splitting prism to a measuring mirror, and acquiring an initial optical path difference between the beam splitting prism and an optical path of a reflecting mirror, and acquiring an interference total optical path difference of an interference signal based on the sum of the relative displacement of the measuring mirror and the initial optical path difference;
And acquiring phase modulation depth through the scanning time and the interference total optical path difference, adjusting the current amplitude of the tunable laser through a modulation module when the phase modulation depth reaches an ideal value, and carrying out phase modulation depth correction through the relation between the current amplitude and the laser frequency.
Preferably, the demodulating module demodulates the signal detected by the first photodetector to obtain an interference signal, and includes the following steps:
extracting a current signal phase value of the tunable laser by using Hilbert transformation, wherein the specific expression is as follows:
Wherein, I (t) is a current signal, t is a time variable, Hilbert transform, I (t), j is the imaginary unit,Is I (t) after Hilbert transformation,Is thatUnwrap [ ] represents the phase-wise expansion;
the specific expression of the interference signal is as follows:
preferably, the step of obtaining the initial optical path difference between the optical path from the beam splitter prism to the measuring mirror and the optical path from the beam splitter prism to the reflecting mirror includes the following steps:
according to the dual-wavelength interference theory, the initial optical path difference is obtained, and the specific expression is:
Wherein l 0 is an initial optical path difference, t 1 and t 2 are two different time points corresponding to two signal peaks detected by the second detector, and λ 1 and λ 2 are laser wavelengths corresponding to two signal peaks detected by the second photodetector.
Preferably, the specific expression of the interference total optical path difference is l=l 0 +l (t), wherein l (t) is the relative displacement of the measuring mirror.
Preferably, the phase modulation depth is obtained through the scanning time and the interference total optical path difference, and when the phase modulation depth reaches an ideal value, the current amplitude of the tunable laser is adjusted through the modulation module, and the phase modulation depth correction is performed through the relation between the current amplitude and the laser frequency, comprising the following steps:
Obtaining according to a phase modulation depth expression:
C=2πl(t)Δν(t)/c=2.63
wherein, C is the ideal value of the phase modulation depth, C is the speed of light, and Deltav is the frequency modulation depth;
The frequency modulation depth Δv is subjected to linear conversion, and the current modulation depth Δi is obtained, specifically expressed as:
ΔI=kiνΔν
Where k iv is a constant, calibration is performed by offline acquisition.
Preferably, before the second path of modulated laser light with a specific wavelength is detected by using the second photodetector, the working temperature of the tunable laser is adjusted by the modulation module, and the wavelength of the laser output by the tunable laser is scanned linearly.
Preferably, when the operating temperature of the tunable laser is adjusted by the modulation module and the wavelength of the laser output by the tunable laser is linearly scanned, P10 and P11 in H13C14 are selected as two absorption lines, and the wavelength corresponding to the two absorption lines is used as the measurement wavelength.
Preferably, before the first path of modulated laser is split into two beams by the beam splitting prism, the method further includes the following steps:
Inputting the first path of modulated laser into an optical fiber circulator along a single-mode fiber;
and the laser is input into a collimator for condensation through the optical fiber circulator, and the condensed laser is input into a beam splitting prism.
Preferably, the reference beam and the measuring beam interfere when passing through a single mode optical fiber when they are reflected back.
Compared with the prior art, the invention has the following remarkable advantages:
According to the invention, two paths of modulated laser are output through the tunable laser, one path of modulated laser passes through the beam splitting prism to generate interference, the first photoelectric detector scans and outputs the other path of modulated laser, the specific absorption spectrum line of the gas absorption tank absorbs the specific wavelength laser, the second photoelectric detector is used for detection, demodulation module demodulates and outputs the modulated laser light intensity signal, the scanning time of two peaks of the demodulated laser light intensity signal and the relative displacement and initial optical path difference of the measuring mirror are obtained, the interference total optical path difference of the interference signal is obtained, the phase modulation depth is obtained through the scanning time and the interference total optical path difference, the current amplitude of the tunable laser is regulated through the modulation module, the phase modulation depth correction can be realized through the control of the current output by the modulation module, the phase modulation depth is obtained through the additional path of the scanning time and the interference total optical path difference, the frequency modulation amplitude can be linearly converted into the current modulation amplitude, the phase modulation depth correction can be realized through the control of the modulation module, the calculation amount of the phase modulation depth correction algorithm is extremely large and the occupation of hardware resources is excessively high when the linear measurement range of displacement/vibration is extremely small, and the phase modulation depth correction effect is reduced.
Drawings
Fig. 1 is a schematic structural diagram provided in an embodiment of the present invention.
The device comprises a 1-tunable laser, a 2-optical fiber circulator, a 3-single mode fiber, a 4-collimator, a 5-reflecting mirror, a 6-measuring mirror, a 7-beam splitting prism, an 8-first photoelectric detector, a 9-gas absorption cell, a 10-second photoelectric detector, an 11-demodulation module, a 12-upper computer and a 13-modulation module.
Detailed Description
The following description of the embodiments of the present invention, taken in conjunction with the accompanying drawings, will clearly and completely describe the embodiments of the present invention, and it is evident that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the present invention without making any inventive effort, shall fall within the scope of the present invention.
As shown in fig. 1, the laser frequency modulation interferometer structure comprises a tunable laser 1, an optical fiber circulator 2, a single-mode optical fiber 3, a collimator 4, a reflecting mirror 5, a measuring mirror 6, a beam splitting prism 7, a first photoelectric detector 8, a demodulation module 11, an upper computer 12 and a modulation module 13. For correcting the phase modulation depth, a gas absorption cell 9 and a second photodetector 10 are added.
The tunable laser device comprises a tunable laser 1, a collimator 4, a beam splitting prism 7, a demodulation module 13, a demodulation module 11, a gas absorption tank 9, a modulation module 13, an upper computer 12, a demodulation module 11 and a current modulation and modulation device 1, wherein the tunable laser 1 is used for outputting a first path of modulated laser and a second path of modulated laser, the input end of the fiber loop 2 is connected with the tunable laser 1, the output end of the fiber loop 2 is connected with the collimator 4, the fiber loop 2 is used for inputting the first path of modulated laser into the collimator 4, the beam splitting prism 7 is connected with the collimator 4 and is used for splitting the modulated laser converged by the collimator 4 into two beams of laser, interference is generated, the laser is input into the fiber loop 2 after interference, the input end of the first photoelectric detector 8 is connected with the fiber loop 2, the demodulation module 11 is connected with the upper computer 12, the input end of the gas absorption tank 9 is connected with the tunable laser 1, two specific absorption spectral lines are arranged in the gas absorption tank 9 and are used for receiving the second path of modulated laser with specific wavelength, the input end of the second photoelectric detector 10 is connected with the gas absorption tank 9, the output end of the demodulation module 11 is connected with the upper computer 12, the modulation module 12 is used for recording modulated laser signals, and the output end of the tunable laser is connected with the tunable laser 1, and the current for outputting the modulated current for carrying out the modulation and the depth of the tunable laser 1.
A single-mode fiber 3 is arranged between the optical fiber circulator 2 and the collimator 4, and the single-mode fiber 3 is used for interfering two laser beams. The two laser beams include laser light reflected to the reflecting mirror 5 via the beam splitting prism 7 and laser light transmitted to the measuring mirror 6 via the beam splitting prism 7.
Based on the laser frequency modulation interferometer structure and the added correction structure, the correction method of the phase modulation depth of the laser frequency modulation interferometer provided by the invention realizes the initialization setting of the current modulation depth of the working point of the laser sinusoidal frequency modulation interferometer by utilizing the theoretical relation between the current modulation depth and the absolute distance, and comprises the following steps:
step S1, outputting a first path of modulated laser and a second path of modulated laser by a tunable laser 1 of a laser tunable interferometer
Step S2, the first path of modulated laser is divided into two beams through a beam splitting prism 7, the two beams of laser are respectively transmitted to a reflecting mirror 5 and a measuring mirror 6, the laser transmitted to the reflecting mirror 5 is used as a reference beam, the laser transmitted to the measuring mirror 6 is used as a measuring beam, interference is generated when the reference beam and the measuring beam are reflected back, the laser generated by the interference is detected by using a first photoelectric detector 8, and a signal detected by the first photoelectric detector 8 is demodulated by using a demodulation module 11, so that an interference signal is obtained.
Before the first path of modulated laser is split into two beams by the beam splitting prism, the method further comprises the following steps:
inputting the first path of modulation into the optical fiber circulator 2 along the single-mode optical fiber 3;
the laser light is condensed by the collimator 4 through the fiber circulator 2, and the condensed laser light is inputted to the beam-splitting prism 7.
Wherein the signal detected by the first photodetector is demodulated by a demodulation module, obtaining an interference signal comprising the steps of:
The phase value of the current signal of the tunable laser is extracted by Hilbert transformation, and the specific expression is as follows:
Wherein, I (t) is a current signal, t is a time variable, Hilbert transform for I (t) is obtainedIs of the phase angle of (a)J is the unit of an imaginary number,For I (t) after Hilbert transform, unwrap [ ] represents the phase-wise expansion.
The specific expression of the interference signal is as follows:
And S3, inputting a second path of modulated laser into the gas absorption tank 9, receiving the second path of modulated laser with specific wavelength through two specific absorption spectral lines in the gas absorption tank 9, detecting the second path of modulated laser with specific wavelength by using the second photoelectric detector 10, inputting a signal detected by the second photoelectric detector 10 into the demodulation module 11 for demodulation, obtaining a modulated laser light intensity signal, and transmitting the modulated laser light intensity signal to the upper computer 12 for recording.
When the second photodetector 10 is used to detect the second path of modulated laser light with a specific wavelength, the working temperature of the laser is adjusted by the modulation module 13, and the laser output laser light is subjected to wavelength linear scanning, wherein the tunable laser performs frequency scanning by adjusting the temperature of the laser diode.
When the temperature of the laser diode is adjusted to perform frequency scanning, a wavelength corresponding to the P10 and P11 absorption lines of H13C14 is selected as a measurement wavelength.
Step S5, obtaining scanning time corresponding to two peaks of the obtained modulated laser light intensity signal by the upper computer 12, obtaining the optical path from the beam splitting prism 7 to the measuring mirror 6, and obtaining the initial optical path difference between the optical path from the beam splitting prism 7 to the reflecting mirror 5, and obtaining the interference total optical path difference of the interference signal based on the sum of the relative displacement of the measuring mirror 6 and the initial optical path difference.
Wherein, and the initial optical path difference between the optical path of the beam splitting prism 7 to the measuring mirror 6 and the optical path of the beam splitting prism 7 to the reflecting mirror 5, comprising the following steps:
according to the dual-wavelength interference theory, the initial optical path difference is obtained, and the specific expression is:
Wherein l 0 is the initial optical path difference, t 1 and t 2 are two different time points corresponding to two signal peaks detected by the second detector, and λ 1 and λ 2 are laser wavelengths corresponding to two signal peaks detected by the second photodetector 10.
The specific expression of the interference total optical path difference is l=l 0 +l (t), wherein l (t) is the relative displacement.
And S6, acquiring phase modulation depth through scanning time and interference total optical path difference, regulating current amplitude of the tunable laser 1 through a modulation module 13 when the phase modulation depth reaches an ideal value, and carrying out phase modulation depth correction through the relation between the current amplitude and laser frequency.
When the total interference optical path difference reaches a threshold value, the laser injects current modulation amplitude, and according to the linear conversion relation between the frequency modulation amplitude and the current modulation, the modulation module 13 controls the modulation current output to perform phase modulation depth correction, and the method comprises the following steps:
the method comprises the following steps of obtaining according to a phase modulation depth calculation formula:
C=2πl(t)Δν(t)/c=2.63
Wherein, C is the ideal value of the phase modulation depth, C is the speed of light, and Deltav is the frequency modulation depth.
The frequency modulation depth Δv is subjected to linear conversion, and the current modulation depth Δi is obtained, specifically expressed as:
ΔI=kiνΔν
Where k iv is a constant, calibration is performed by offline acquisition.
The present invention has been described in further detail with reference to specific preferred embodiments, and it should be understood by those skilled in the art that the present invention may be embodied with several simple deductions or substitutions without departing from the spirit of the invention.
Claims (9)
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| CN110701998A (en) * | 2019-10-28 | 2020-01-17 | 哈尔滨工业大学 | Nonlinear Error Correction Method of Fiber Michelson Interferometer |
| CN110702210A (en) * | 2019-10-28 | 2020-01-17 | 哈尔滨工业大学 | Nonlinear error correction method for optical fiber Michelson interference vibration meter |
| CN117192560B (en) * | 2023-08-02 | 2024-04-09 | 哈尔滨工业大学 | Micro-probe laser frequency modulation interferometry ranging method and system |
| CN117740047B (en) * | 2023-12-22 | 2025-08-05 | 中国科学院电工研究所 | A method and system for extracting and correcting phase modulation depth and eliminating nonlinear influencing factors in PGC-Atan demodulation method |
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