CN114264238A - Interferometric displacement measurement system and method based on frequency multiplication principle - Google Patents
Interferometric displacement measurement system and method based on frequency multiplication principle Download PDFInfo
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- CN114264238A CN114264238A CN202111593146.8A CN202111593146A CN114264238A CN 114264238 A CN114264238 A CN 114264238A CN 202111593146 A CN202111593146 A CN 202111593146A CN 114264238 A CN114264238 A CN 114264238A
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Abstract
The invention relates to an interference displacement measuring system and method based on frequency multiplication principle, wherein laser emitted by a fiber laser is divided into two paths by a fiber coupler; inputting the first path of laser to an optical fiber beam combiner; the second path of laser is output to the optical fiber probe through the first port of each optical fiber circulator and the second port of each optical fiber circulator, the optical fiber probe emits received optical signals to a measured object, and light reflected by the measured object is input to the optical fiber beam combiner through the optical fiber probe, the second port of the optical fiber circulator, the third port of the optical fiber circulator and the optical fiber filter in sequence; the optical fiber beam combiner combines the first path of laser and the filtered light into a beam and inputs the beam to the frequency doubling crystal, and the frequency doubling crystal performs frequency doubling on the input light and then inputs the beam to the data processing device through the photoelectric detector and the signal acquisition device in sequence. The measuring system adopts the frequency doubling crystal to adjust the frequency of the signal light, can increase the number of interference fringes and improve the time resolution and the measuring precision of low-speed measurement.
Description
Technical Field
The invention relates to the technical field of high-time-resolution precision displacement measurement, in particular to an interference displacement measurement system and method based on a frequency doubling principle.
Background
Laser interferometry is a widely used precision measurement method. At present, a laser displacement interferometer based on a Doppler frequency shift technology is commonly adopted, when the laser displacement interferometer with the wavelength of 1550nm is used for low-speed measurement, the number of generated interference fringes is rare, the motion speed of an object and the number of the interference fringes have a linear relation, and the measurement time resolution is low due to the fact that the number of the interference fringes is too small, and the measurement precision is influenced. The invention provides an interference displacement measurement system and method based on a frequency multiplication principle, aiming at solving the problem of low measurement precision in low-speed measurement.
Disclosure of Invention
The invention aims to provide an interference displacement measurement system and method based on a frequency doubling principle.
In order to achieve the purpose, the invention provides the following scheme:
an interference displacement measuring system based on frequency multiplication principle comprises an optical fiber laser, an optical fiber coupler, at least one optical fiber circulator, an optical fiber probe, an optical fiber filter, an optical fiber beam combiner, a frequency multiplication crystal, a photoelectric detector, a signal acquisition device and a data processing device;
laser emitted by the optical fiber laser is divided into two paths by the optical fiber coupler;
inputting the first path of laser to the optical fiber beam combiner;
the second path of laser is received by the first port of each optical fiber circulator and then is output to the optical fiber probe by the second port of each optical fiber circulator, the optical fiber probe emits a received optical signal to a measured object, light reflected by the measured object is input to the second port of each optical fiber circulator through the optical fiber probe, and the third port of each optical fiber circulator filters the input light through the optical fiber filter and then inputs the filtered light to the optical fiber beam combiner;
the optical fiber beam combiner combines the first path of laser and the filtered light into one beam and inputs the beam to the frequency doubling crystal, the frequency doubling crystal performs frequency doubling on the input light and inputs the beam to the signal acquisition device through the photoelectric detector, and the signal acquisition device inputs the acquired signal to the data processing device;
and the data processing device is used for carrying out Fourier transform on the input signal to obtain the linear relation between the laser offset frequency and the time, and further obtain the movement displacement of the measured object.
Optionally, signal light output by the optical fiber coupler is input to the first port of the optical fiber circulator after passing through the first optical fiber amplifier; and light output by the optical fiber filter is input to the optical fiber beam combiner after passing through the second optical fiber amplifier.
Optionally, the first optical fiber amplifier and/or the second optical fiber amplifier are erbium-doped optical fiber amplifiers.
Optionally, the signal acquisition device adopts an oscilloscope.
Optionally, the center wavelength of the optical fiber laser is 1550nm, the output power is 10mw, and the laser spectral line width is less than 100 KHZ.
Optionally, the optical fiber filter uses a narrow-band filter with a center wavelength of 1550 nm.
The invention also provides an interference displacement measuring method based on the frequency multiplication principle, which comprises the following steps:
acquiring a signal acquired by a signal acquisition device;
carrying out Fourier transform on the signals acquired by the signal acquisition device to obtain a linear relation between the laser offset frequency and the time;
and calculating the movement displacement of the measured object according to the linear relation between the laser offset frequency and the time.
According to the specific embodiment provided by the invention, the invention discloses the following technical effects:
the invention provides an interference displacement measuring system based on a frequency multiplication principle, which comprises an optical fiber laser, an optical fiber coupler, at least one optical fiber circulator, an optical fiber probe, an optical fiber filter, an optical fiber beam combiner, a frequency multiplication crystal, a photoelectric detector, a signal acquisition device and a data processing device, wherein the optical fiber coupler is arranged on the optical fiber; the laser emitted by the optical fiber laser is divided into two paths by the optical fiber coupler; inputting the first path of laser to the optical fiber beam combiner; the second path of laser is received by the first port of each optical fiber circulator and then is output to the optical fiber probe by the second port of each optical fiber circulator, the optical fiber probe emits a received optical signal to a measured object, light reflected by the measured object is input to the second port of each optical fiber circulator through the optical fiber probe, and the third port of each optical fiber circulator filters the input light through the optical fiber filter and then inputs the filtered light to the optical fiber beam combiner; the optical fiber beam combiner combines the first path of laser and the filtered light into one beam and inputs the beam to the frequency doubling crystal, the frequency doubling crystal performs frequency doubling on the input light and inputs the beam to the signal acquisition device through the photoelectric detector, and the signal acquisition device inputs the acquired signal to the data processing device; and the data processing device is used for carrying out Fourier transform on the input signal to obtain the linear relation between the laser offset frequency and the time, and further obtain the movement displacement of the measured object. The measuring system adopts the frequency doubling crystal to adjust the frequency of the signal light, so that the number of interference fringes can be increased, and the time resolution and the measuring precision of low-speed measurement are improved.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.
Fig. 1 is a structural diagram of an interferometric displacement measuring system based on a frequency doubling principle according to embodiment 1 of the present invention;
fig. 2 is a flowchart of an interferometric displacement measurement method based on a frequency doubling principle according to embodiment 2 of the present invention.
Description of the symbols:
1: a fiber laser; 2: a fiber coupler; 3: a first fiber amplifier; 4: a fiber optic circulator; 5: a fiber optic probe; 6: an object to be measured; 7: an optical fiber filter; 8: a second fiber amplifier; 9: an optical fiber combiner; 10: frequency doubling crystals; 11; a photodetector; 12: a signal acquisition device; 13: a data processing apparatus.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The invention aims to provide an interference displacement measurement system based on a frequency doubling principle, which adopts a frequency doubling crystal to adjust the frequency of signal light, can increase the number of interference fringes, improves the time resolution of measurement and further improves the displacement measurement precision.
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in further detail below.
Example 1
Referring to fig. 1, the present embodiment provides an interferometric displacement measuring system based on frequency doubling principle, which includes a fiber laser 1, a fiber coupler 2, at least one fiber circulator 4, a fiber probe 5, a fiber filter 7, a fiber combiner 9, a frequency doubling crystal 10, a photodetector 11, a signal acquisition device 12, and a data processing device 13;
the laser emitted by the optical fiber laser 1 is divided into two paths by the optical fiber coupler 2;
the central wavelength of the optical fiber laser 1 is 1550nm, the output power is 10mw, and the laser spectral line width is less than 100 KHZ.
The first path of laser is input to the optical fiber beam combiner 9; the second path of laser is received by a first port of each optical fiber circulator 4, and is output to the optical fiber probe 5 by a second port of each optical fiber circulator 4, the optical fiber probe 5 emits a received optical signal to a measured object 6, light reflected by the measured object 6 is input to the second port of each optical fiber circulator 4 by the optical fiber probe 5, and the input light is filtered by a third port of each optical fiber circulator 4 by the optical fiber filter 7 and is input to the optical fiber beam combiner 9;
for the optical fiber probe 5, a dual-core optical fiber probe 5 may be adopted, the second port of the optical fiber circulator 4 enters the optical signal into the dual-core optical fiber probe 5, one tail fiber of the dual-core optical fiber probe 5 irradiates the surface of the object to be measured 6, and the light reflected from the surface of the object enters the other tail fiber of the dual-core optical fiber probe 5. The number of the optical fiber cores of the optical fiber probe 5 is not limited to the double core, and can be set as required.
For the filter, a narrow band filter having a center wavelength of 1550nm may be used.
As the fiber circulator 4, a three-port circulator is used, and light input from the first port is output from the second port and light input from the second port is output from the third port. In fig. 1, I denotes a first port of the optical fiber circulator 4, II denotes a second port of the optical fiber circulator 4, and III denotes a third port of the optical fiber circulator 4.
In order to improve the accuracy of displacement measurement, a plurality of optical fiber circulators 4 may be provided, light output by the optical fiber coupler 2 enters the first ports of different optical fiber circulators 4, is output by the second ports of different optical fiber circulators 4 and irradiates on the object to be measured 6 through the optical fiber probe 5, and light reflected by the object to be measured 6 is input to the second ports of different optical fiber circulators 4 through the optical fiber probe 5 and is output to the optical fiber filter 7 through the third ports of different optical fiber circulators 4.
The optical fiber combiner 9 combines the first path of laser light and the filtered light into one beam and inputs the beam to the frequency doubling crystal 10, the frequency doubling crystal 10 performs frequency doubling on the input light and inputs the beam to the signal acquisition device 12 through the photoelectric detector 11, and the signal acquisition device 12 inputs the acquired signal to the data processing device 13; the signal acquisition device 12 may be an oscilloscope, and the oscilloscope is used to acquire the signal processed by the photodetector 11 and record the waveform, or any other acquisition device, which is set according to the requirement.
The data processing device 13 is configured to perform fourier transform on the input signal, convert the time domain signal into a frequency domain signal, obtain a linear relationship between the laser offset frequency and time, and further obtain the movement displacement of the object 6 to be measured. The data processing device 13 may be a computer.
The frequency doubling crystal 10 is a PPLN, which is an abbreviation of "periodic Poled Lithium Niobate" in english, and is called Periodically Poled Lithium Niobate, and is a highly efficient wavelength conversion nonlinear optical crystal. The signal light with the central wavelength of 1550nm can be frequency doubled to 775nm frequency doubled light by the frequency doubling crystal 10; by utilizing the characteristics of high nonlinearity and periodic reversal of lithium niobate, the signal light with the center wavelength of 1550nm is subjected to frequency doubling, the number of interference fringes is increased, and the time resolution and the measurement precision are improved.
In order to ensure that the light intensity irradiated on a moving object to be detected is larger, and simultaneously, considering that the light intensity of light reflected by the moving object to be detected is weakened after being filtered by the optical fiber filter 7, and the collection precision of light intensity information is influenced, a first optical fiber amplifier 3 is arranged between the optical fiber coupler 2 and the optical fiber circulator 4, and a second optical fiber amplifier 8 is arranged between the optical fiber filter 7 and the optical fiber beam combiner 9, namely, signal light output by the optical fiber coupler 2 is input to a first port of the optical fiber circulator 4 after passing through the first optical fiber amplifier 3; the light output by the optical fiber filter 7 is input to the optical fiber combiner 9 after passing through the second optical fiber amplifier 8.
Further, the first Fiber Amplifier 3 and/or the second Fiber Amplifier 8 are Erbium-doped Fiber amplifiers (EDFAs), which are active Optical devices that amplify signal light and can ensure the amplification accuracy.
Principle of the measurement system of the present embodiment: a beam of laser is irradiated on the surface of a moving object to be measured, reflected light generates Doppler frequency shift under the action of Doppler effect, and interference signals with light source phase information are generated by interfering the reflected light and homologous reference light, so that precise displacement measurement of the moving object with high speed is realized. Meanwhile, the measuring system adopts the frequency doubling crystal 10 to adjust the frequency of the signal light, so that the number of interference fringes can be increased, and the time resolution and the measuring precision of low-speed measurement are improved.
The structures of the measurement system are described from the perspective of the connection relationship:
the optical fiber laser 1 is connected with the input end of an optical fiber coupler 2 through an optical fiber, one output end of the optical fiber coupler 2 is connected with one input end of an optical fiber combiner 9 through an optical fiber, the other output end of the optical fiber coupler 2 is connected with the input end of an optical fiber amplifier through an optical fiber, the output end of the optical fiber amplifier is connected with a first port of an optical fiber circulator 4 through an optical fiber, a second port of the optical fiber circulator 4 is connected with one end of a double-core optical fiber probe 5, a third port of the optical fiber circulator 4 is connected with an optical fiber filter 7 through an optical fiber, the optical fiber filter 7 is connected with the input end of the optical fiber amplifier through an optical fiber, the output end of the optical fiber amplifier is connected with the other input end of the optical fiber combiner 9, the output end of the optical fiber combiner 9 is connected with a frequency doubling crystal 10 through an optical fiber, the frequency doubling crystal 10 is connected with a photoelectric detector 11 and a signal acquisition device 12, the data processing means 13 are in turn connected.
In the embodiment, in order to solve the problems of low time resolution and low measurement precision when the existing laser displacement interferometer performs low-speed measurement, the frequency doubling crystal 10 is arranged in the measurement system, and the frequency doubling crystal 10 is used for performing frequency doubling processing on input light, so that the number of interference fringes is increased, and the time resolution and the measurement precision are improved; meanwhile, the EDFA amplifying device is adopted to amplify the optical signals, so that the intensity of the optical signals is improved, the collected light intensity information is more accurate, and the accuracy of displacement measurement can be improved.
Example 2
As shown in fig. 2, the present embodiment provides an interferometric displacement measurement method based on frequency doubling principle, which includes:
step S1: acquiring signals acquired by the signal acquisition device 12;
step S2: performing fourier transform on the signal acquired by the signal acquisition device 12 to obtain a linear relation between the laser offset frequency and time;
step S3: and calculating the movement displacement of the object to be measured 6 according to the linear relation between the laser offset frequency and the time.
The principles and embodiments of the present invention have been described herein using specific examples, which are provided only to help understand the method and the core concept of the present invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, the specific embodiments and the application range may be changed. In view of the above, the present disclosure should not be construed as limiting the invention.
Claims (7)
1. An interference displacement measurement system based on a frequency multiplication principle is characterized by comprising an optical fiber laser, an optical fiber coupler, at least one optical fiber circulator, an optical fiber probe, an optical fiber filter, an optical fiber beam combiner, a frequency multiplication crystal, a photoelectric detector, a signal acquisition device and a data processing device;
laser emitted by the optical fiber laser is divided into two paths by the optical fiber coupler;
inputting the first path of laser to the optical fiber beam combiner;
the second path of laser is received by the first port of each optical fiber circulator and then is output to the optical fiber probe by the second port of each optical fiber circulator, the optical fiber probe emits a received optical signal to a measured object, light reflected by the measured object is input to the second port of each optical fiber circulator through the optical fiber probe, and the third port of each optical fiber circulator filters the input light through the optical fiber filter and then inputs the filtered light to the optical fiber beam combiner;
the optical fiber beam combiner combines the first path of laser and the filtered light into one beam and inputs the beam to the frequency doubling crystal, the frequency doubling crystal performs frequency doubling on the input light and inputs the beam to the signal acquisition device through the photoelectric detector, and the signal acquisition device inputs the acquired signal to the data processing device;
and the data processing device is used for carrying out Fourier transform on the input signal to obtain the linear relation between the laser offset frequency and the time, and further obtain the movement displacement of the measured object.
2. The system of claim 1, wherein the signal light output from the fiber coupler is input to the first port of the fiber circulator after passing through the first fiber amplifier; and light output by the optical fiber filter is input to the optical fiber beam combiner after passing through the second optical fiber amplifier.
3. The system of claim 2, wherein the first fiber amplifier and/or the second fiber amplifier is an erbium doped fiber amplifier.
4. The system of claim 1, wherein the signal acquisition device employs an oscilloscope.
5. The system of claim 1, wherein the fiber laser has a center wavelength of 1550nm, an output power of 10mw, and a laser line width of less than 100 KHZ.
6. The system of claim 1, wherein the fiber filter is a narrow band filter having a center wavelength of 1550 nm.
7. A method for testing an interferometric displacement measuring system based on frequency multiplication principle according to any one of claims 1 to 6, comprising:
acquiring a signal acquired by a signal acquisition device;
carrying out Fourier transform on the signals acquired by the signal acquisition device to obtain a linear relation between the laser offset frequency and the time;
and calculating the movement displacement of the measured object according to the linear relation between the laser offset frequency and the time.
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2021
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| JPH0943344A (en) * | 1995-08-03 | 1997-02-14 | Mitsubishi Electric Corp | Fm-cw radar |
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