A high-precision micro-displacement measurement device and method for FP cavity orthogonal detection

Abstract

The invention discloses a high-precision micro-displacement measurement device and method for F-P cavity orthogonal detection, comprising: a distributed feedback semiconductor laser, an electro-optic modulator, a first arbitrary waveform generator, an optical circulator, a low-fineness F-P interferometer, an erbium-doped fiber amplifier and an orthogonal detection system; the output end of the feedback semiconductor laser is connected to the input end of the electro-optic modulator; the output end of the electro-optic modulator is connected to the first input port of the optical circulator; the output end of the first arbitrary waveform generator is connected to the modulation port input end of the electro-optic modulator; the second port of the optical circulator is connected to the input end of the low-fineness F-P interferometer; the third port of the circulator is connected to the input end of the erbium-doped fiber amplifier; the output end of the erbium-doped fiber amplifier is connected to the orthogonal detection system. The invention has the significant advantages of high measurement accuracy and high sensitivity by eliminating absolute distance estimation.

Description

Technical Field

[0001] The invention belongs to the field of sensors, and in particular relates to a high-precision micro-displacement measurement device and method for FP cavity orthogonal detection. Background Art

[0002] With the rapid development of modern science and technology and production and life, precision measurement technology has become one of the important signs of high-end technology development in various countries. As one of the seven basic physical quantities, the measurement level of length determines the foundation of modern industrial development. It not only has a profound impact on human understanding of nature, but is also a key factor in promoting the progress of modern science. At present, the method of high-precision micro-displacement measurement mainly relies on optical measurement technology. This technology uses optical principles and precision optical components to achieve high-precision measurement, which has brought revolutionary changes to length measurement.

[0003] At present, the optical methods used for large-range, high-precision micro-displacement measurement mainly include traditional laser interferometers, grating interferometers, orthogonal demodulation interferometers, and FP interferometers. However, the main problem with traditional interferometers and grating interferometers is that their ranging sensitivity shows unevenness as the intensity of the interference light changes. In addition, due to the presence of noise in the actual system, the received signal often contains amplitude noise, and the traditional interferometer calculates the phase through intensity detection, and the system noise level limits its sensitivity.

[0004] In order to solve the above problems, people have proposed an orthogonal demodulation method that does not rely on changes in light intensity. The ranging sensitivity of this method does not change with position changes, that is, after adopting the orthogonal demodulation method, the ranging sensitivity remains uniform. At the same time, orthogonal demodulation greatly reduces the impact of system noise on the ranging system by normalizing the intensity information, thereby improving the stability of the system. In addition, since orthogonal reception normalizes the intensity information, the ranging system's tolerance to line loss changes is improved, thereby increasing the ranging range.

[0005] Nevertheless, these solutions are still essentially based on the Michelson interferometer, and all have a reference arm with a separated optical path. The measured value is actually the difference between the reference optical path and the measuring optical path. If you want to achieve nm or sub-nm measurement accuracy, you must ensure that the reference optical path is stable at the nm or sub-nm level, and the measurement accuracy depends on the stability of the instrument itself. The FP interferometer, on the other hand, does not have a separated reference arm and measuring arm. The reference optical path is completely placed inside the system measurement, eliminating the influence of the instability of the reference arm on the measurement accuracy. The FP interferometer can place the reference arm and the measuring arm on the same optical path to achieve self-compensation, and can also complete the detection through orthogonal reception.

[0006] However, in the current low-fineness FP interferometer, the two orthogonal terms of phase measurement are not completely equal in high-precision micro-displacement measurement (related to the absolute value of the distance to be measured), and direct orthogonal analysis cannot be performed. There are currently two methods reported internationally. One is to eliminate the impact of changes by using small disturbances in the distance, or to roughly estimate the test distance by other optical means. Both methods have great limitations in practical applications. Therefore, how to achieve orthogonal signal acquisition without relying on absolute distance estimation has become an urgent problem to be solved. Summary of the invention

[0007] In order to solve the above technical problems, the present invention proposes a high-precision micro-displacement measurement device and method for FP cavity orthogonal detection to solve the problems existing in the above prior art.

[0008] To achieve the above object, the present invention provides a high-precision micro-displacement measurement device with FP cavity orthogonal detection, comprising: a distributed feedback semiconductor laser, an electro-optic modulator, a first arbitrary waveform generator, an optical circulator, a low-fineness FP type interferometer, an erbium-doped fiber amplifier and an orthogonal detection system;

[0009] The output end of the feedback semiconductor laser is connected to the input end of the electro-optic modulator;

[0010] The output end of the electro-optic modulator is connected to the first input port of the optical circulator;

[0011] The output end of the first arbitrary waveform generator is connected to the modulation port input end of the electro-optic modulator;

[0012] The second port of the optical circulator is connected to the input end of the low-fineness FP type interferometer;

[0013] The third port of the circulator is connected to the input end of the erbium-doped fiber amplifier;

[0014] The output end of the erbium-doped fiber amplifier is connected to an orthogonal detection system.

[0015] Preferably, the orthogonal detection system comprises a photodetector, an electrical amplifier, a first electrical bandpass filter, a second electrical bandpass filter, a first electrical mixer, a second electrical mixer, a second arbitrary waveform generator, a first low-pass filter, a second low-pass filter and an orthogonal demodulation system;

[0016] The photoelectric detector input end is connected to the output end of the erbium-doped fiber amplifier;

[0017] The output end of the photodetector is connected to the input end of the electric amplifier;

[0018] The first output terminal of the electric amplifier is connected to the input terminal of the first electric bandpass filter;

[0019] The second output terminal of the electrical amplifier is connected to the input terminal of the second electrical bandpass filter;

[0020] The output end of the electrical bandpass filter is connected to the input end of the first electrical mixer;

[0021] The output end of the electrical bandpass filter is connected to the input end of the second electrical mixer;

[0022] The output terminal of the first electrical mixer is connected to the input terminal of the first low-pass filter;

[0023] The output terminal of the second electrical mixer is connected to the input terminal of the second low-pass filter;

[0024] The first output terminal of the arbitrary waveform generator is connected to the local oscillator signal input terminal of the first electrical mixer;

[0025] The second output terminal of the arbitrary waveform generator is connected to the local oscillator signal input terminal of the second electrical mixer;

[0026] The output end of the first low-pass filter is connected to the first input end of the orthogonal demodulation system;

[0027] The output end of the second low-pass filter is connected to the second input end of the orthogonal demodulation system.

[0028] The present invention also provides a high-precision micro-displacement measurement method for FP cavity orthogonal detection, comprising the following steps:

[0029] A laser beam is emitted by a distributed feedback semiconductor laser;

[0030] The first arbitrary waveform generator provides a modulation signal, and the wavelength of the laser beam is modulated by an electro-optical modulator based on the modulation signal;

[0031] Based on the optical circulator, the modulated laser beam is subjected to laser interference through a low-fineness FP-type interferometer to obtain an interference laser signal;

[0032] Amplifying the interference laser signal by an erbium-doped fiber amplifier to obtain an amplified laser signal;

[0033] The orthogonal detection system analyzes the amplified laser signal to obtain micro displacement.

[0034] Preferably, the method for analyzing the amplified laser signal includes:

[0035] converting the amplified laser signal into an electrical signal through a photodetector;

[0036] amplifying the power of the electrical signal by an electrical amplifier;

[0037] Selecting the components with the first and second frequencies from the amplified power electrical signal through an electrical bandpass filter;

[0038] The amplitudes of the one-fold and two-fold frequency components are extracted using a multiplication operation in an electrical mixer;

[0039] The amplitude is filtered out by a low-pass filter to remove the sum frequency term, thereby obtaining an orthogonal DC signal;

[0040] The orthogonal DC signal is analyzed to obtain the micro displacement.

[0041] Preferably, the method for determining the first harmonic frequency and the second harmonic frequency includes:

[0042] The response of the low-fineness FP cavity is approximately a sinusoidal curve, expressed as:

[0043] I=K+P cosφ

[0044] When the wavelength of the incident light changes sinusoidally, the phase introduced by the wavelength change will also change, expressed as:

[0045] φ(t)=φ0+ΔφsinΩt

[0046] Combining the above two equations, we get:

[0047] I=K+P[cosφ0·cos(ΔφsinΩt)-sinφ0·sin(ΔφsinΩt)]

[0048] Through the Bessel function expansion combination, it can be known that the magnitude of the amplitude of the first harmonic frequency and the second harmonic frequency component is orthogonal to φ0, so the first harmonic frequency and the second harmonic frequency are selected;

[0049] Where K represents bias, P represents amplitude, φ represents the additional phase introduced by the distance to be measured, Ω represents the frequency of the modulated signal, φ0 represents the additional phase introduced by the central wavelength, Δφ represents the maximum value of the additional phase change, and t represents time.

[0050] Preferably, the expression of the orthogonal DC signal is:

[0051]

[0052] In the formula, P represents the amplitude, A represents the amplitude of the local oscillator signal, and J n represents the nth-order coefficient of the Bessel function, Δφ represents the maximum value of the additional phase change, and φ0 represents the additional phase introduced by the central wavelength.

[0053] Preferably, the orthogonal DC signal is processed by a new orthogonal signal solution method based on distance calibration to obtain an additional phase introduced by the central wavelength, and the micro-displacement is calculated based on the additional phase value.

[0054] Preferably, the calculation expression of the micro displacement is:

[0055]

[0056] Where φ0 represents the additional phase introduced by the center wavelength, and λ0 represents the center wavelength.

[0057] Compared with the prior art, the present invention has the following advantages and technical effects:

[0058] The invention discloses a high-precision micro-displacement measuring device for FP cavity orthogonal detection, comprising: a distributed feedback semiconductor laser, an electro-optic modulator, a first arbitrary waveform generator, an optical circulator, a low-fineness FP interferometer, an erbium-doped fiber amplifier and an orthogonal detection system; the output end of the feedback semiconductor laser is connected to the input end of the electro-optic modulator; the output end of the electro-optic modulator is connected to the first input port of the optical circulator; the output end of the first arbitrary waveform generator is connected to the modulation port input end of the electro-optic modulator; the second port of the optical circulator is connected to the input end of the low-fineness FP interferometer; the third port of the circulator is connected to the input end of the erbium-doped fiber amplifier; the output end of the erbium-doped fiber amplifier is connected to the orthogonal detection system. The invention provides a new method for low-precision FP cavity orthogonal detection based on a distance calibration algorithm to solve the existing absolute distance estimation problem. Through this distance measurement principle, a certain distance is calibrated once, and after the constant is determined, the measurement accuracy within a large working range can be met, and the low-fineness FP interferometer orthogonal detection based on distance calibration is realized, thereby completing high-precision micro-displacement measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0060] Figure 1 is a schematic diagram of a device according to an embodiment of the present invention;

[0061] Figure 2 is a flow chart of a method according to an embodiment of the present invention;

[0062] Figure 3 A Bessel function waveform diagram according to an embodiment of the present invention;

[0063] Among them: 1. distributed feedback semiconductor laser; 2. electro-optic modulator; 3. first arbitrary waveform generator; 4. optical circulator; 5. low-fineness FP type interferometer; 6. erbium-doped fiber amplifier; 7. photodetector; 8. electric amplifier; 9. first electric bandpass filter; 10. second electric bandpass filter; 11. first electric mixer; 12. second electric mixer; 13. second arbitrary waveform generator; 14. first low-pass filter; 15. second low-pass filter; 16. orthogonal demodulation system. DETAILED DESCRIPTION

[0064] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0065] It should be noted that the steps shown in the flowcharts of the accompanying drawings can be executed in a computer system such as a set of computer executable instructions, and that, although a logical order is shown in the flowcharts, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0066] Embodiment 1

[0067] like Figure 1 As shown, in this embodiment, a high-precision micro-displacement measuring device with FP cavity orthogonal detection is provided, including: a distributed feedback semiconductor laser 1, an electro-optical modulator 2, a first arbitrary waveform generator 3, an optical circulator 4, a low-fineness FP type interferometer 5, an erbium-doped fiber amplifier 6, a photodetector 7, an electrical amplifier 8, two electrical bandpass filters, respectively denoted as a first electrical bandpass filter 9 and a second electrical bandpass filter 10, two electrical mixers, respectively denoted as a first electrical mixer 11 and a second electrical mixer 12, a second arbitrary waveform generator 13, two low-pass filters, respectively denoted as a first low-pass filter 14 and a second low-pass filter 15, and an orthogonal demodulation system 16.

[0068] The output end of the distributed feedback semiconductor laser 1 is connected to the input end of the electro-optic modulator 2;

[0069] The output end of the electro-optic modulator 2 is connected to the first input port of the optical circulator 4;

[0070] The output end of the first arbitrary waveform generator 3 is connected to the modulation port input end of the electro-optic modulator 2;

[0071] The second port of the optical circulator 4 is connected to the input end of the low-fineness FP type interferometer 5;

[0072] The third port of the circulator 4 is connected to the input end of the erbium-doped fiber amplifier 6;

[0073] The output end of the erbium-doped fiber amplifier 6 is connected to the input end of the photodetector 7;

[0074] The output end of the photodetector 7 is connected to the input end of the electric amplifier 8;

[0075] The first output terminal of the electric amplifier 8 is connected to the input terminal of the first electric band pass filter 9;

[0076] The second output terminal of the electric amplifier 8 is connected to the input terminal of the second electric band pass filter 10;

[0077] The output end of the first electrical bandpass filter 9 is connected to the input end of the first electrical mixer 11;

[0078] The output end of the second electrical bandpass filter 10 is connected to the input end of the second electrical mixer 12;

[0079] The output end of the first electrical mixer 11 is connected to the input end of the first low-pass filter 14;

[0080] The output end of the second electrical mixer 12 is connected to the input end of the second low-pass filter 15;

[0081] The first output terminal of the second arbitrary waveform generator 13 is connected to the local oscillator signal input terminal of the first electrical mixer 11;

[0082] The second output terminal of the second arbitrary waveform generator 13 is connected to the local oscillator signal input terminal of the second electrical mixer 12;

[0083] An output end of the first low-pass filter 14 is connected to a first input end of the orthogonal demodulation system 16;

[0084] An output end of the second low-pass filter 15 is connected to a second input end of the orthogonal demodulation system 16 .

[0085] like Figure 2 As shown, this embodiment provides a high-precision micro-displacement measurement method for FP cavity orthogonal detection, including the following steps:

[0086] Step 1: Turn on the distributed feedback semiconductor laser 1, so that the semiconductor laser emits a laser with a wavelength of λ and a frequency of f;

[0087] Step 2: The output laser beam enters the electro-optic modulator 2 for wavelength modulation; a microwave signal source with a frequency of Ω is provided as a modulation signal through the first arbitrary waveform generator 3, and enters the modulation port of the electro-optic modulator 2 for modulation with the laser;

[0088] Step 3: The modulated laser enters from the first port of the circulator 4, and enters the low-finesse FP interferometer 5 through the second port of the circulator 4 for laser interference. The response of the ideal low-finesse FP cavity is approximately a sine curve, which is set as:

[0089] I=K+P cosφ (1)

[0090] Where K represents the bias, P represents the amplitude, and φ represents the additional phase introduced by the distance to be measured, satisfying: x is the distance to be measured, n is the refractive index, and λ is the wavelength of the laser incident on the FP cavity. When the wavelength λ of the incident light changes in a sinusoidal manner, the phase introduced by the wavelength change will also change, and its change law is also sinusoidal, expressed as:

[0091] φ(t)=φ0+ΔφsinΩt (2)

[0092] Where Ω is the frequency of the modulation signal, represents the additional phase introduced by the central wavelength. λ0 is the central wavelength, Δλ is the maximum change in wavelength, and Δφ is the maximum value of the additional phase change;

[0093] Step 4: The laser light interfered in the low-fineness FP interferometer is output from the third port of the circulator 4 and enters the erbium-doped fiber amplifier 6 for amplification;

[0094] Step 5: The photodetector 7 converts the received optical signal amplified by the erbium-doped fiber amplifier into an electrical signal. The output end of the photodetector is connected to the input end of the electrical amplifier 8, which is used to amplify the power of the electrical signal. Substituting equation (2) into equation (1) yields:

[0095] I=K+P[cosφ0·cos(ΔφsinΩt)-sinφ0·sin(ΔφsinΩt)] (3)

[0096] Using Bessel function to expand equation (3) we get:

[0097] I=K+PJ0(Δφ)cosφ0-2PJ1(Δφ)sinφ0sinΩt+2PJ2(Δφ)cosφ0cos2Ωt+··

[0098] =I DC (φ0)+I Ω (φ0)+I 2Ω (φ0)+… (4)

[0099] in:

[0100]

[0101] It can be seen from the above formula that the magnitudes of the Ω and 2Ω components are orthogonal to φ0, J n represents the nth order coefficient of the Bessel function. The output end of the electric amplifier 8 is connected to the input end of the first electric band pass filter 9 and the second electric band pass filter 10, the first electric band pass filter 9 is used to select the component with a frequency of Ω, and the second electric band pass filter 10 is used to select the component of 2Ω;

[0102] Step 6: The output end of the first electric bandpass filter 9 is connected to the input end of the first electric mixer 11, and the output end of the second electric bandpass filter 10 is connected to the second electric mixer 12. The filtered electric signal enters the RF port of the electric mixer. Consider using the multiplication operation in the electric mixer to extract the amplitudes of Ω and 2Ω. Assume that the two local oscillator signals LO with equal amplitudes are:

[0103]

[0104] Among them, A represents the amplitude of the local oscillator signal, Ω and 2Ω represent the frequencies of the two local oscillator signals, and φ1 and φ2 represent the initial phases of the two local oscillator signals. The signal output by the system is used as the RF signal of the mixer and multiplied by the two local oscillator signals to obtain:

[0105]

[0106] After simplifying the product-sum-difference formula, when the LO frequency of the local oscillator signal is the same as the RF frequency and the phase difference is zero, a DC signal can be obtained;

[0107] Step 7: Provide a signal with a frequency of Ω through an output port of the second arbitrary waveform generator 13 as the local oscillation signal of the first electrical mixer 11, and input it to the local oscillation signal port of the mixer; provide a signal with a frequency of 2Ω through another output port as the local oscillation signal of the second electrical mixer 12, and input it to the local oscillation signal port of the mixer;

[0108] Step 8: The output end of the first electric mixer 11 is connected to the input end of the first low-pass filter 14, and the output end of the second electric mixer 12 is connected to the second low-pass filter 15. After filtering out the sum frequency term with the low-pass filter, a DC signal is obtained:

[0109]

[0110] By comparison, it can be found that the amplitude information extracted by the mixer contains the coefficient A, that is, the DC term obtained by equation (8) is not strictly the magnitude of the amplitude of the Ω and 2Ω components. Nevertheless, according to the idea of ​​orthogonal demodulation, the intensity coefficient has been offset during data processing and has no effect on the ranging result;

[0111] Step 9: The two orthogonal signals output by the first low-pass filter 14 and the second low-pass filter 15 enter the orthogonal demodulation system 16. A new orthogonal signal resolution method based on distance calibration low-fineness FP cavity orthogonal detection is proposed. A calibration process is added, that is, when the distance x is known, the modulation depth Δλ of the wavelength is adjusted at the same time, so that Δφ is a constant and J1(Δφ)=J2(Δφ) can be guaranteed. Then the distance resolution will be very simple. And through I Ω,rms , I 2Ω,rms The sum of the squares of the two terms gives us the constant In actual measurement, although the distance x cannot be known in advance, by changing the modulation depth of wavelength modulation, I Ω,rms， I 2Ω,rms The sum of the squares of the two terms is equal to the constant value obtained during calibration, which ensures that J1(Δφ)=J2(Δφ). Then, through orthogonal operation, the measured value is obtained. The specific solution process is as follows: The waveform of the Bessel function is as follows: Figure 3 As shown, when x is constant, by changing the modulation depth Δλ of the laser, the variable Δφ of the Bessel function can be changed to select different points. In our solution process, we hope that J1(Δφ)=J2(Δφ), so that the magnitude of the amplitude of the Ω and 2Ω components in equation (8) is orthogonal to φ0, as shown in Figure 3 As shown. In general, we hope that the value of Δφ is slightly larger. On the one hand, when Δφ is larger, J1(Δφ)=J2(Δφ) changes slowly, and the instability of distance will have less impact on it; on the other hand, when the minimum modulation index Δλ of the laser is constant, the larger Δφ makes the measurement range larger. After comprehensive consideration, the present invention selects Δφ=15.634. At this time, J1(Δφ) and J2(Δφ) are roughly equal, about 0.150. In terms of working distance, assuming that the distance range of the micro-displacement measurement is from 1cm to 1m, the wavelength of the detection light is 1530nm, Δφ=15.634, according to the formula The wavelength modulation depth can be obtained to be approximately 0.291nm~2.91pm, corresponding to the change of the optical frequency of 36.38GHz~363.8MHz. Such a modulation depth is relatively easy to achieve. The calibration algorithm proposed in this application calibrates a certain distance once, and after determining the constant, the measurement accuracy within a large working range can be met.

[0112] Step 10: When the calibration constant is determined, during the test, no matter where the distance x is, the modulation depth Δλ of the wavelength is adjusted so that the modulus of the responses of the two detectors is equal to the calibration value. According to the response of the orthogonal detector:

[0113]

[0114] The phase value can be analyzed. When the distance changes, the corresponding φ0 value will also change. The micro-displacement D can be calculated by the following formula.

[0115]

[0116] The above are only preferred specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A high-precision micro-displacement measurement device for FP cavity orthogonal detection, characterized in that: include: Distributed feedback semiconductor laser, electro-optic modulator, first arbitrary waveform generator, optical circulator, low-fineness FP-type interferometer, erbium-doped fiber amplifier and orthogonal detection system; The output end of the feedback semiconductor laser is connected to the input end of the electro-optic modulator; The output end of the electro-optic modulator is connected to the first input port of the optical circulator; The output end of the first arbitrary waveform generator is connected to the modulation port input end of the electro-optic modulator; The second port of the optical circulator is connected to the input end of the low-fineness FP type interferometer; The third port of the circulator is connected to the input end of the erbium-doped fiber amplifier; The output end of the erbium-doped fiber amplifier is connected to an orthogonal detection system; The orthogonal detection system includes a photodetector, an electrical amplifier, a first electrical bandpass filter, a second electrical bandpass filter, a first electrical mixer, a second electrical mixer, a second arbitrary waveform generator, a first low-pass filter, a second low-pass filter and an orthogonal demodulation system; The photoelectric detector input end is connected to the output end of the erbium-doped fiber amplifier; The output end of the photodetector is connected to the input end of the electric amplifier; The first output terminal of the electric amplifier is connected to the input terminal of the first electric bandpass filter; The second output terminal of the electrical amplifier is connected to the input terminal of the second electrical bandpass filter; The output end of the electrical bandpass filter is connected to the input end of the first electrical mixer; The output end of the electrical bandpass filter is connected to the input end of the second electrical mixer; The output terminal of the first electrical mixer is connected to the input terminal of the first low-pass filter; The output terminal of the second electrical mixer is connected to the input terminal of the second low-pass filter; The first output terminal of the arbitrary waveform generator is connected to the local oscillator signal input terminal of the first electrical mixer; The second output terminal of the arbitrary waveform generator is connected to the local oscillator signal input terminal of the second electrical mixer; The output end of the first low-pass filter is connected to the first input end of the orthogonal demodulation system; The output end of the second low-pass filter is connected to the second input end of the orthogonal demodulation system.

2. A high-precision micro-displacement measurement method using FP cavity orthogonal detection, characterized in that: The following steps are involved: A laser beam is emitted by a distributed feedback semiconductor laser; The first arbitrary waveform generator provides a modulation signal, and the wavelength of the laser beam is modulated by an electro-optical modulator based on the modulation signal; Based on the optical circulator, the modulated laser beam is subjected to laser interference through a low-fineness FP-type interferometer to obtain an interference laser signal; Amplifying the interference laser signal by an erbium-doped fiber amplifier to obtain an amplified laser signal; The orthogonal detection system analyzes the amplified laser signal to obtain micro displacement; The method for analyzing the amplified laser signal includes: converting the amplified laser signal into an electrical signal through a photodetector; amplifying the power of the electrical signal by an electrical amplifier; Selecting the components with the first and second frequencies from the amplified power electrical signal through an electrical bandpass filter; The amplitudes of the one-fold and two-fold frequency components are extracted using a multiplication operation in an electrical mixer; The amplitude is filtered out by a low-pass filter to remove the sum frequency term, thereby obtaining an orthogonal DC signal; The orthogonal DC signal is analyzed to obtain the micro displacement.

3. The high-precision micro-displacement measurement method of FP cavity orthogonal detection according to claim 2 is characterized in that: Methods for determining the first and second harmonic frequencies include: The response of the low-fineness FP cavity is approximately a sinusoidal curve, expressed as: I=K+P cosφ When the wavelength of the incident light changes sinusoidally, the phase introduced by the wavelength change will also change, expressed as: φ(t)=φ0+ΔφsinΩt Combining the above two equations, we get: I=K+P[cosφ0·cos(ΔφsinΩt)-sinφ0·sin(ΔφsinΩt)] Through the Bessel function expansion, it can be known that the magnitudes of the first harmonic frequency and the second harmonic frequency components are orthogonal to φ0, so the first harmonic frequency and the second harmonic frequency are selected; Where K represents bias, P represents amplitude, φ represents the additional phase introduced by the distance to be measured, Ω represents the frequency of the modulated signal, φ0 represents the additional phase introduced by the central wavelength, Δφ represents the maximum value of the additional phase change, and t represents time.

4. The high-precision micro-displacement measurement method of FP cavity orthogonal detection according to claim 2 is characterized in that: The expression of the orthogonal DC signal is: In the formula, P represents the amplitude, A represents the amplitude of the local oscillator signal, and J n represents the nth-order coefficient of the Bessel function, Δφ represents the maximum value of the additional phase change, and φ0 represents the additional phase introduced by the central wavelength.

5. The high-precision micro-displacement measurement method of FP cavity orthogonal detection according to claim 2 is characterized in that: The orthogonal direct current signal is processed by a new orthogonal signal solution method based on distance calibration to obtain an additional phase introduced by the central wavelength, and the micro-displacement is calculated based on the additional phase value.

6. The high-precision micro-displacement measurement method of FP cavity orthogonal detection according to claim 5 is characterized in that: The calculation expression of the micro displacement is: Where φ0 represents the additional phase introduced by the center wavelength, and λ0 represents the center wavelength.

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