Displacement measurement system based on microwave interferometry and laser Doppler effect

Abstract

The present invention provides a displacement measurement system based on microwave interference and laser Doppler effect, including a laser generator, a detection unit and an acquisition card, and also including a static measurement unit and / or a dynamic measurement unit. The static measurement unit includes an attenuator and a static measurement branch. The two output ends of the laser generator are respectively connected to the input ends of the detection unit. The first output end of the detection unit is connected to the acquisition card through the dynamic measurement unit, and the second output end is connected to the acquisition card through the static measurement branch. The present invention uses microwave interference for measurement during static measurement, and measures based on the Doppler effect during dynamic measurement. Static measurement is combined with dynamic measurement, and the displacement measurement range and measurement accuracy can be guaranteed at the same time. The structure of the fusion of static displacement measurement and dynamic displacement is simple, and the present invention has a wide application range, high measurement accuracy and a large measurement range.

Description

Technical Field

[0001] The invention belongs to the field of displacement measurement, and in particular relates to a displacement measurement system based on microwave interference and laser Doppler effect. Background Art

[0002] At present, when displacement measurement is performed in a space with a high aspect ratio and limited space, ordinary light interference is mostly used. Due to the limited space size, it is difficult to separate the transmission and reception. Therefore, the probe is usually aimed at the object to be measured, and the reflected light from the probe and the surface of the object to be measured is used for interference measurement. In order to improve the contrast of interference, it is necessary to coat the end face of the probe to increase the reflectivity. For objects to be measured with different surface reflectivities, it is necessary to replace the probe with different reflectivities on the end face so that the reflectivity of the probe end face matches the reflectivity of the surface of the object to be measured, which brings great inconvenience to practical applications. In addition, when performing optical interference measurement, in order to reduce the interference of the external environment on the spatial light between the probe and the object to be measured, it is necessary to ensure that the distance between the probe and the object to be measured is close, which will result in a smaller free spectral range of interference, thereby resulting in a smaller measurement range of ordinary light interference. Summary of the invention

[0003] The invention provides a displacement measurement system based on microwave interference and laser Doppler effect, so as to solve the problems of low optical interference contrast and small measurement range of the current displacement measurement system.

[0004] According to a first aspect of an embodiment of the present invention, there is provided a displacement measurement system based on microwave interference and laser Doppler effect, comprising a laser generating device, a detection unit and an acquisition card, and further comprising a static measurement unit and / or a dynamic measurement unit, wherein the static measurement unit comprises an attenuator and a static measurement branch, wherein two output ends of the laser generating device are respectively connected to input ends of the detection unit, a first output end of the detection unit is connected to the acquisition card via the dynamic measurement unit, and a second output end is connected to the acquisition card via the static measurement branch;

[0005] The laser generating device transmits two incoherent lights with different wavelengths to the detection unit, the detection unit loads the same microwave signal into the two incoherent lights, and transmits the first incoherent light with the first wavelength loaded with the microwave signal to the probe in the detection unit. After receiving the first incoherent light emitted by the probe, the object to be measured transmits reflected light back to the probe, and the detection unit transmits the reflected light and the second incoherent light with the second wavelength loaded with the microwave signal as a combined beam to the static measurement branch and / or the dynamic measurement unit;

[0006] The attenuator adjusts the intensity of at least one of the reflected light and the second incoherent light;

[0007] The static measurement branch is used to adjust the delay difference between the reflected light and the second incoherent light, perform beat frequency detection on the reflected light and the second incoherent light after the light intensity and delay difference are adjusted, obtain a first beat frequency electrical signal, and restore the two microwave signals to generate microwave interference and generate a microwave interference electrical signal; determine the distance between the probe and the object to be measured according to the microwave interference electrical signal collected by the acquisition card, so as to calculate the displacement of the object to be measured in a static state;

[0008] When the object to be measured is in motion, based on the laser Doppler effect, a Doppler frequency shift is introduced into the reflected light, and the dynamic measurement unit is used to filter out the second incoherent light, and perform beat frequency detection on the reflected light and the incoherent light of the first wavelength provided by the laser generating device to obtain a second beat frequency electrical signal; based on the second beat frequency electrical signal collected by the acquisition card, the movement speed of the object to be measured is calculated, and the movement speed is integrated over time to calculate the displacement of the object to be measured in the motion state.

[0009] In an optional implementation, the attenuator adjusts the intensity of at least one of the reflected light and the second incoherent light to improve the consistency of the intensity of the reflected light and the second incoherent light, thereby increasing the contrast of the microwave interference;

[0010] When adjusting the delay difference between the reflected light and the second incoherent light, increasing the delay difference between the reflected light and the second incoherent light can improve the displacement measurement accuracy; reducing the delay difference between the reflected light and the second incoherent light can expand the displacement measurement range.

[0011] In another optional implementation, the detection unit includes a first coupler, an electro-optical modulator, a first wavelength division multiplexer, a circulator, a probe, and a second coupler; the two output ends of the laser generating device are respectively connected to the two input ends of the first coupler; the output end of the first coupler is connected to the first wavelength division multiplexer through the electro-optical modulator; the first output end of the first wavelength division multiplexer is connected to the first end of the circulator, the second output end is connected to the second input end of the second coupler; the second end of the circulator is connected to the probe, and the third end is connected to the first input end of the second coupler; the first output end of the second coupler serves as the first output end of the detection unit and is connected to the acquisition card through the dynamic measurement unit; the second output end of the second coupler serves as the second output end of the detection unit and is connected to the acquisition card through the static measurement branch;

[0012] The two incoherent lights with different wavelengths generated by the laser generating device are combined by the first coupler and then transmitted to the electro-optical modulator; the electro-optical modulator loads the microwave signal into the two incoherent lights; the first wavelength division multiplexer divides the two incoherent lights loaded with the microwave signal into two paths according to different wavelengths, wherein the first incoherent light with the first wavelength is transmitted to the first end of the circulator, and the second incoherent light with the second wavelength is transmitted to the second input end of the second coupler; the circulator transmits the first incoherent light to the probe through its second end, and after receiving the first incoherent light emitted by the probe, the object to be tested transmits the reflected light back to the probe to reach the circulator, and the reflected light is transmitted to the first input end of the second coupler through the third end of the circulator.

[0013] In another optional implementation, the laser generating device includes a first single-frequency laser and a second single-frequency laser, and the output ends of the first single-frequency laser and the second single-frequency laser respectively serve as two output ends of the laser generating device and are correspondingly connected to two input ends of the detection unit;

[0014] The first single-frequency laser is used to generate incoherent light of a first wavelength, and the second single-frequency laser is used to generate incoherent light of a second wavelength.

[0015] In another optional implementation, the attenuator is provided at at least one of the following positions: between the first output end of the laser generating device and the first input end of the first coupler, between the second output end of the laser generating device and the second input end of the first coupler, between the first output end of the first wavelength division multiplexer and the first end of the circulator, between the second end of the circulator and the probe, between the third end of the circulator and the first input end of the second coupler, and between the second output end of the first wavelength division multiplexer and the second input end of the second coupler;

[0016] The static measurement branch includes a dispersion module and a second photodetector, and the second output end of the detection unit is connected to the acquisition card through the dispersion module and the second photodetector in sequence;

[0017] The dispersion module adjusts the delay difference between the reflected light and the second incoherent light, and the second photodetector performs beat frequency detection on the reflected light and the second incoherent light after the light intensity and delay difference adjustment are completed to obtain a first beat frequency electrical signal, and restores the two microwave signals to generate microwave interference and generate a microwave interference electrical signal.

[0018] In another optional implementation, the dynamic measurement unit includes a second wavelength division multiplexer and a first photodetector, the input end of the second wavelength division multiplexer is connected to the first output end of the detection unit, the output end is connected to the first input end of the first photodetector, and the output end of the first photodetector is connected to the acquisition card; the laser generating device also includes a third coupler, the output end of the first single-frequency laser is connected to the input end of the third coupler, the first output end of the third coupler is connected to the input end of the detection unit, and the second output end is connected to the second input end of the first photodetector;

[0019] The second wavelength division multiplexer is used to filter out the second incoherent light and transmit the reflected light to the first photodetector. The first photodetector performs beat frequency detection on the reflected light and the incoherent light of the first wavelength provided by the laser generating device to obtain a second beat frequency electrical signal.

[0020] In another optional implementation, the light intensity of the incoherent light of the first wavelength generated by the laser generating device is expressed as: E1(t)=A1exp(jω1t); the light intensity of the incoherent light of the second wavelength generated by the laser generating device is expressed as: E2(t)=A2exp(jω2t); wherein A1, A2, ω1, ω2 are the amplitude and angular frequency of the two incoherent lights respectively;

[0021] The intensity of the optical signal after the electro-optic modulator performs microwave modulation on the two incoherent lights is expressed as: E M (t) = A1[1+M cos(ω M t)]exp(jω1t)+A2[1+M cos(ω M t)]exp(jω2t), where M is the microwave modulation coefficient, ω M is the angular frequency of microwave modulation;

[0022] The light intensity of the optical signal after the dispersion module adjusts the delay difference between the reflected light and the second incoherent light is expressed as:

[0023] E p (t) = αA1{1+M cos[ω M (t+τ0+τ)]}exp[jω1(t+τ0+τ)]+A2[1+M cos(ω M t)]exp(jω2t)

[0024] Where α is the output loss during measurement, τ0 is the initial delay difference, and τ is the delay difference caused by the distance between the probe and the object to be measured and the dispersion module;

[0025] The first beat frequency electrical signal is expressed as:

[0026] i p (t) = ηα 2 A1 2 M 2 cos[ω M (t+τ0+τ)]+ηA2 2 M 2 cos(ω M t)

[0027] Where η is the responsivity of the second photodetector;

[0028] The intensity of the microwave interference electrical signal is expressed as:

[0029] A p (ω M ) = η 2 α 4 A1 4 M 4 +η 2 A2 4 M 4 +2η 2 α 2 A1 2 A2 2 M 4 cos(ω M (τ0+τ));

[0030] The acquisition card converts the intensity of the acquired microwave interference electrical signal into a digital signal, and the microprocessor processes the digital signal to determine the distance between the probe and the object to be measured.

[0031] In another optional implementation, the reflected light and the incoherent light of the first wavelength of the laser generating device are expressed as:

[0032] E r (t) = αA1{1+M cos[(ω M +ω D )t]}exp[j(ω1+ω D )t]+A1exp(jω1t);

[0033] where ω D represents the Doppler shift;

[0034] The second beat frequency electrical signal is expressed as:

[0035] i r (t) = ηα 2 A1 2 cos(ω D t)+ηα 2 A1 2 M2 cos[(ω M +ω D )t];

[0036] The initial frequency of the second beat frequency electrical signal is:

[0037] The frequency after introducing Doppler shift is:

[0038] According to the relationship between frequency and the speed of the object to be measured: Calculate the velocity V of the object to be measured S , where V represents the speed of light in air.

[0039] In another optional implementation, the displacement measurement of the object to be measured in a static state and the displacement measurement in a moving state complement each other to ensure both the displacement measurement accuracy and the displacement measurement range.

[0040] In another optional implementation, the system is suitable for displacement measurement in a space with a high aspect ratio and limited space.

[0041] The beneficial effects of the present invention are:

[0042] 1. When the static displacement detection is performed on the object to be measured, the present invention no longer relies on the reflected light of the probe end face, and there is no need to consider the matching problem between the reflectivity of the probe end face and the reflectivity of the surface of the object to be measured, so there is no need to replace the probe according to the different reflectivity of the surface of the object to be measured, so the application scope of the present invention is wider; when improving the microwave interference contrast, the present invention does not replace the probe that matches the reflectivity of the surface of the object to be measured, but uses an attenuator to adjust the light intensity of at least one of the reflected light and the second incoherent light to improve the light intensity consistency of the reflected light and the second incoherent light, so as to increase the contrast of microwave interference, and the method for improving the microwave interference contrast is simpler and the microwave interference contrast can be improved to a higher degree; in addition, the present invention can improve the displacement measurement accuracy by increasing the delay difference between the reflected light and the second incoherent light; reducing the delay difference between the reflected light and the second incoherent light can expand the free spectrum range of microwave interference and expand the displacement measurement range;

[0043] 2. When the present invention measures the dynamic displacement of the object to be measured, the object to be measured in motion introduces a Doppler frequency shift in the reflected light transmitted back by the object to be measured based on the laser Doppler effect. The reflected light of the first wavelength and the incoherent light provided by the laser generating device and not loaded with a microwave signal are subjected to beat frequency detection to obtain a second beat frequency electrical signal. The motion speed of the object to be measured can be calculated based on the second beat frequency electrical signal. The motion speed is integrated over time to calculate the displacement measurement of the object to be measured in motion. The present invention introduces a microwave modulation frequency into the reflected light so that the initial frequency of the second beat frequency electrical signal is non-zero. The Doppler frequency shift is then introduced into the reflected light. The motion speed of the object to be measured can be calculated based on the relationship between the initial frequency, the frequency after the Doppler frequency shift is introduced, and the motion speed of the object to be measured. The displacement of the object to be measured in motion can be calculated by integrating the motion speed over time. This measurement method does not involve interference problems, has a wide range of applications, and has high measurement accuracy and a large measurement range.

[0044] 3. The displacement measurement of the object to be measured in a static state and the displacement measurement in a moving state described in the present invention complement each other, and while expanding the displacement measurement range, the displacement measurement accuracy can be guaranteed; in addition, the present invention integrates static displacement measurement and dynamic displacement, and is very simple in structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is a block diagram of an embodiment of a displacement measurement system based on microwave interference and laser Doppler effect of the present invention;

[0046] Figure 2 It is a schematic structural diagram of an embodiment of a displacement measurement system based on microwave interference and laser Doppler effect of the present invention;

[0047] Figure 3 It is a schematic structural diagram of another embodiment of the displacement measurement system based on microwave interference and laser Doppler effect of the present invention;

[0048] Figure 4 A schematic structural diagram of another embodiment of the displacement measurement system based on microwave interference and laser Doppler effect of the present invention. DETAILED DESCRIPTION

[0049] In order to enable those skilled in the art to better understand the technical solutions in the embodiments of the present invention and to make the above-mentioned purposes, features and advantages of the embodiments of the present invention more obvious and understandable, the technical solutions in the embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings.

[0050] In the description of the present invention, unless otherwise specified and limited, it should be noted that the term "connection" should be understood in a broad sense. For example, it can be a mechanical connection or an electrical connection, or it can be the internal connection between two elements. It can be a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0051] See also Figure 1 , is a schematic diagram of an embodiment of a displacement measurement system based on microwave interference and laser Doppler effect of the present invention. The displacement measurement system based on microwave interference and laser Doppler effect may include a laser generator, a detection unit and an acquisition card, and also includes a static measurement unit and / or a dynamic measurement unit. The static measurement unit includes an attenuator and a static measurement branch. The two output ends of the laser generator are respectively connected to the input end of the detection unit. The first output end of the detection unit is connected to the acquisition card through the dynamic measurement unit, and the second output end is connected to the acquisition card through the static measurement branch. The laser generator transmits two incoherent lights with different wavelengths to the detection unit. The detection unit loads the same microwave signal into the two incoherent lights, and transmits the first incoherent light loaded with the first wavelength of the microwave signal to the probe in the detection unit. After receiving the first incoherent light emitted by the probe, the object to be measured transmits the reflected light back to the probe. The detection unit transmits the reflected light and the second incoherent light loaded with the second wavelength of the microwave signal to the static measurement branch and / or the dynamic measurement unit. The attenuator adjusts the light intensity of at least one of the reflected light and the second incoherent light; the static measurement branch is used to adjust the delay difference between the reflected light and the second incoherent light, perform beat frequency detection on the reflected light and the second incoherent light after the light intensity and delay difference adjustment are completed, obtain a first beat frequency electrical signal, and restore the two microwave signals to cause microwave interference to generate a microwave interference electrical signal; according to the microwave interference electrical signal collected by the acquisition card, determine the distance between the probe and the object to be measured, so as to calculate the displacement of the object to be measured in a static state.

[0052] When the object to be measured is in motion, based on the laser Doppler effect, a Doppler frequency shift is introduced into the reflected light, and the dynamic measurement unit is used to filter out the second incoherent light, and perform beat frequency detection on the reflected light and the incoherent light of the first wavelength provided by the laser generating device to obtain a second beat frequency electrical signal; based on the second beat frequency electrical signal collected by the acquisition card, the movement speed of the object to be measured is calculated, and the movement speed is integrated over time to calculate the displacement of the object to be measured in the motion state.

[0053] In this embodiment, the probe is spaced apart from the object to be measured, and the probe can be perpendicular to the object to be measured. The probe can be placed in a space with a high aspect ratio and limited to measure the displacement of the object to be measured in the space. The attenuator adjusts the light intensity of at least one of the reflected light and the second incoherent light to improve the light intensity consistency of the reflected light and the second incoherent light, thereby increasing the contrast of the microwave interference; when adjusting the delay difference between the reflected light and the second incoherent light, increasing the delay difference between the reflected light and the second incoherent light can improve the displacement measurement accuracy; reducing the delay difference between the reflected light and the second incoherent light can expand the displacement measurement range.

[0054] The present invention provides two displacement measurement methods for an object to be measured in a static state and in a moving state. When the static displacement of the object to be measured is measured, the present invention loads a microwave signal into two incoherent lights with different wavelengths, and divides the two incoherent lights loaded with the microwave signal into two paths according to the wavelength. The first path of incoherent light is transmitted to the object to be measured through a probe, and beat frequency detection is performed on the second path of incoherent light and the reflected light transmitted back after the object to be measured receives the first path of incoherent light. Since the second path of incoherent light and the reflected light both carry microwave signals, the two paths of microwave signals can be restored through beat frequency detection. In addition, the wavelengths of the second path of incoherent light and the reflected light are different and incoherent, so no optical interference occurs. However, there is a delay difference between the two paths of microwave signals, which leads to a phase difference, so microwave interference occurs and a microwave interference signal is generated. According to the collected microwave interference electrical signal, the distance between the probe and the object to be measured can be determined, so as to calculate the displacement of the object to be measured in a static state.

[0055] When the present invention performs static displacement detection on the object to be measured, it no longer relies on the reflected light of the probe end face, and there is no need to consider the matching problem of the reflectivity of the probe end face and the reflectivity of the surface of the object to be measured, so there is no need to replace the probe according to the different reflectivities of the surface of the object to be measured, so the application scope of the present invention is wider; when improving the microwave interference contrast, the present invention does not replace the probe that matches the reflectivity of the surface of the object to be measured, but uses an attenuator to adjust the light intensity of at least one of the reflected light and the second incoherent light to improve the light intensity consistency of the reflected light and the second incoherent light, so as to increase the contrast of microwave interference, and the method for improving the microwave interference contrast is simpler and the microwave interference contrast can be improved to a higher degree; in addition, the present invention can improve the displacement measurement accuracy by increasing the delay difference between the reflected light and the second incoherent light; reducing the delay difference between the reflected light and the second incoherent light can expand the free spectrum range of microwave interference and expand the displacement measurement range.

[0056] When the dynamic displacement of the object to be measured is measured, the object to be measured in the moving state introduces Doppler frequency shift in the reflected light transmitted back by the object to be measured based on the laser Doppler effect, and the reflected light of the same first wavelength and the incoherent light provided by the laser generating device without the microwave signal are beat-frequency detected to obtain a second beat-frequency electrical signal. According to the second beat-frequency electrical signal, the moving speed of the object to be measured can be calculated, and the moving speed is integrated in time to calculate the displacement measurement of the object to be measured in the moving state. The present invention introduces microwave modulation frequency in the reflected light so that the initial frequency of the second beat-frequency electrical signal is non-zero, and then introduces Doppler frequency shift in the reflected light. According to the relationship between the initial frequency, the frequency after the Doppler frequency shift is introduced, and the moving speed of the object to be measured, the moving speed of the object to be measured can be calculated. The moving speed can be integrated in time to calculate the displacement of the object to be measured in the moving state. This measurement method does not involve interference problems, has a wide range of applications, high measurement accuracy, and a large measurement range.

[0057] See also Figure 2 , is a schematic diagram of the structure of an embodiment of the displacement measurement system based on microwave interference and laser Doppler effect of the present invention. The displacement measurement system of this embodiment only includes a static measurement unit. In this embodiment, the laser generating device may include a first single-frequency laser and a second single-frequency laser. The output ends of the first single-frequency laser and the second single-frequency laser serve as the two output ends of the laser generating device, respectively, and are correspondingly connected to the two input ends of the detection unit; the first single-frequency laser is used to generate incoherent light of a first wavelength (for example, 1550.92nm), and the second single-frequency laser is used to generate incoherent light of a second wavelength (for example, 1550.12nm).

[0058] The detection unit includes a first coupler OC1, an electro-optical modulator EOM, a first wavelength division multiplexer DWDM, a circulator, a probe and a second coupler OC2. The two input ends of the first coupler OC1 serve as the two input ends of the detection unit. The two output ends of the laser generating device are respectively connected to the two input ends of the first coupler OC1. The output end of the first coupler OC1 is connected to the first wavelength division multiplexer DWDM through the electro-optical modulator EOM. The first output end of the first wavelength division multiplexer DWDM is connected to the first end of the circulator, and the second output end is connected to the second input end of the second coupler OC2. The second end of the circulator is connected to the probe, and the third end is connected to the first input end of the second coupler OC2. The first output end of the second coupler OC2 serves as the first output end of the detection unit and is connected to the acquisition card through the dynamic measurement unit. The second output end of the second coupler OC2 serves as the second output end of the detection unit and is connected to the acquisition card through the static measurement branch.

[0059] The two incoherent lights with different wavelengths generated by the laser generating device are combined by the first coupler OC1 and then transmitted to the electro-optical modulator EOM; the electro-optical modulator EOM loads the microwave signal into the two incoherent lights; the first wavelength division multiplexer DWDM divides the two incoherent lights loaded with the microwave signal into two paths according to different wavelengths, wherein the first incoherent light of the first wavelength is transmitted to the first end of the circulator, and the second incoherent light of the second wavelength is transmitted to the second input end of the second coupler OC2; the circulator transmits the first incoherent light to the probe through its second end, and after receiving the first incoherent light emitted by the probe, the object to be tested transmits the reflected light back to the probe to reach the circulator, and the reflected light is transmitted to the first input end of the second coupler OC2 through the third end of the circulator.

[0060] The attenuator VOA of the present invention can be arranged at at least one of the following positions: between the first output end of the laser generating device and the first input end of the first coupler OC1, between the second output end of the laser generating device and the second input end of the first coupler OC1, between the first output end of the first wavelength division multiplexer DWDM and the first end of the circulator, between the second end of the circulator and the probe, between the third end of the circulator and the first input end of the second coupler OC2, between the second output end of the first wavelength division multiplexer DWDM and the second input end of the second coupler OC2. In this embodiment, the attenuator VOA is arranged between the first output end of the laser generating device and the first input end of the first coupler OC1.

[0061] The static measurement branch may include a dispersion module DCM and a second photodetector PD2, and the second output end of the detection unit (i.e., the second output end of the second coupler OC2) is connected to the acquisition card via the dispersion module DCM and the second photodetector PD2 in sequence; the dispersion module DCM adjusts the delay difference between the reflected light and the second incoherent light, and the second photodetector PD2 performs beat frequency detection on the reflected light and the second incoherent light after the light intensity and delay difference adjustment are completed to obtain a first beat frequency electrical signal, and restores the two microwave signals to generate microwave interference and generate a microwave interference electrical signal.

[0062] In this embodiment, when performing static displacement measurement, the intensity of the incoherent light of the first wavelength (for example, 1550.92nm) generated by the laser generating device can be expressed as: E1(t)=A1exp(jω1t); the intensity of the incoherent light of the second wavelength (for example, 1550.12nm) generated by the laser generating device can be expressed as: E2(t)=A2exp(jω2t); wherein A1, A2, ω1, ω2 are the amplitude and angular frequency of the two incoherent lights, respectively. The incoherent light of 1550.12nm is attenuated by the attenuator VOA, so that when the incoherent light of 1550.12nm and the incoherent light of 1550.92nm enter the second coupler OC2, the light intensity of the two incoherent lights is kept as consistent as possible to enhance the contrast of microwave interference, wherein the attenuator VOA needs to take into account the losses of the electro-optic intensity modulator, the measurement path (i.e., the path from the first output end of the first coupler to the first input end of the second coupler), and the reference path (the path from the second output end of the first coupler to the second input end of the second coupler).

[0063] The incoherent light of 1550.12nm and 1550.92nm is combined and transmitted from the first coupler OC1 to the electro-optic modulator EOM for microwave modulation, and the microwave signal is loaded into the two incoherent lights. The intensity of the optical signal after the electro-optic modulator performs microwave modulation on the two incoherent lights can be expressed as: E M (t) = A1[1+M cos(ω M t)]exp(jω1t)+A2[1+M cos(ω M t)]exp(jω2t), where M is the microwave modulation coefficient, ω M is the angular frequency of microwave modulation. The microwave modulated optical signal is transmitted to the first wavelength division multiplexer DWDM, which divides the microwave modulated optical signal into two paths according to the wavelength. The first incoherent light of 1550.92nm is transmitted to the circulator as the measurement light, and the second incoherent light of 1550.12nm is directly transmitted to the second coupler OC2 as the reference light. The circulator transmits the incoherent light of 1550.92nm to the probe. After receiving the light emitted by the probe, the object to be measured transmits the reflected light back to the probe, and the reflected light is transmitted to the second coupler OC2 via the probe and the circulator in turn. The second coupler OC2 transmits the reflected light and the second incoherent light beam to the dispersion module DCM, which adjusts the delay difference. The intensity of the optical signal after the dispersion module adjusts the delay difference between the reflected light and the second incoherent light can be expressed as:

[0064] E p (t) = αA1{1+M cos[ω M(t+τ0+τ)]}exp[jω1(t+τ0+τ)]+A2[1+M cos(ω M t)]exp(jω2t)

[0065] Where α is the output loss during measurement, τ0 is the initial delay difference, and τ is the delay difference caused by the distance between the probe and the object to be measured and the dispersion module.

[0066] The reflected light and the second incoherent light after the delay difference adjustment by the attenuator and the dispersion module are detected by the second photodetector to obtain the first beat frequency electrical signal, and the two microwave signals are restored to generate microwave interference and microwave interference electrical signal. The first beat frequency electrical signal can be expressed as:

[0067] i p (t) = ηα 2 A1 2 M 2 cos[ω M (t+τ0+τ)]+ηA2 2 M 2 cos(ω M t)

[0068] Where η is the responsivity of the second photodetector;

[0069] The intensity of the microwave interference electrical signal can be expressed as:

[0070] A p (ω M ) = η 2 α 4 A1 4 M 4 +η 2 A2 4 M 4 +2η 2 α 2 A1 2 A2 2 M 4 cos(ω M (τ0+τ));

[0071] The acquisition card converts the intensity of the acquired microwave interference electrical signal into a digital signal, and the microprocessor processes the digital signal to determine the distance between the probe and the object to be measured.

[0072] It can be seen from the above embodiments that the present invention no longer relies on the reflected light of the probe end face when performing static displacement detection on the object to be measured, and there is no need to consider the matching problem of the probe end face reflectivity and the surface reflectivity of the object to be measured, so there is no need to replace the probe according to the different surface reflectivities of the object to be measured, so the application scope of the present invention is wider; when improving the microwave interference contrast, the present invention does not replace the probe that matches the surface reflectivity of the object to be measured, but uses an attenuator to adjust the light intensity of at least one of the reflected light and the second incoherent light to improve the light intensity consistency of the reflected light and the second incoherent light, so as to increase the contrast of microwave interference, and the method for improving the microwave interference contrast is simpler and the microwave interference contrast can be improved to a higher degree; in addition, the present invention can improve the displacement measurement accuracy by increasing the delay difference between the reflected light and the second incoherent light; reducing the delay difference between the reflected light and the second incoherent light can expand the free spectrum range of microwave interference and expand the displacement measurement range.

[0073] See also Figure 3 , is a schematic diagram of another embodiment of the displacement measurement system based on microwave interference and laser Doppler effect of the present invention. The displacement measurement system of this embodiment only includes a dynamic measurement unit, wherein Figure 3 The detection unit of the embodiment shown is Figure 2 The detection unit structure of the embodiment shown is the same, the dynamic measurement unit includes a second wavelength division multiplexer WDM and a first photodetector PD1, the input end of the second wavelength division multiplexer WDM is connected to the first output end of the detection unit (i.e., the first output end of the second coupler OC2), the output end is connected to the first input end of the first photodetector PD1, and the output end of the first photodetector PD1 is connected to the acquisition card. Figure 2 Compared with the laser generating device in the illustrated embodiment, the laser generating device in this embodiment can also be a third coupler OC3, the output end of the first single-frequency laser is connected to the input end of the third coupler OC3, the first output end of the third coupler OC3 is connected to the input end of the detection unit (i.e., the second input end of the first coupler OC1), and the second output end is connected to the second input end of the first photodetector PD1. The second wavelength division multiplexer WDM is used to filter out the second incoherent light and transmit the reflected light to the first photodetector PD1, and the first photodetector PD1 performs beat frequency detection on the reflected light and the incoherent light of the first wavelength provided by the laser generating device to obtain a second beat frequency electrical signal.

[0074] The two incoherent lights with different wavelengths generated by the laser generating device are combined by the first coupler OC1 and then transmitted to the electro-optical modulator EOM; the electro-optical modulator EOM loads the microwave signal into the two incoherent lights; the first wavelength division multiplexer DWDM divides the two incoherent lights loaded with the microwave signal into two paths according to different wavelengths, wherein the first incoherent light with a first wavelength (for example, 1550.92nm) is transmitted to the first end of the circulator, and the second incoherent light with a second wavelength (for example, 1550.12nm) is transmitted to the second input end of the second coupler OC2; the circulator transmits the first incoherent light to the probe through its second end, and after receiving the first incoherent light emitted by the probe, the object to be tested transmits the reflected light back to the probe to reach the circulator, and the reflected light is transmitted to the first input end of the second coupler OC2 through the third end of the circulator.

[0075] When the object to be measured is in motion, based on the laser Doppler effect, an additional Doppler frequency shift is added to the reflected light, and the dynamic measurement unit is used to filter out the second incoherent light (wavelength is 1550.12nm), and perform beat frequency detection on the reflected light (wavelength is 1550.92nm) and the incoherent light of the first wavelength (wavelength is 1550.92nm) provided by the laser generating device to obtain a second beat frequency electrical signal; according to the second beat frequency electrical signal collected by the acquisition card, the movement speed of the object to be measured is calculated, and the movement speed is integrated over time to calculate the displacement of the object to be measured in the motion state.

[0076] In this embodiment, when performing static displacement measurement, the light intensity of the incoherent light of the first wavelength (e.g., 1550.92nm) generated by the laser generating device can be expressed as: E1(t)=A1exp(jω1t); the light intensity of the incoherent light of the second wavelength (e.g., 1550.12nm) generated by the laser generating device can be expressed as: E2(t)=A2exp(jω2t); wherein A1, A2, ω1, ω2 are the amplitude and angular frequency of the two incoherent lights respectively. The reflected light and the incoherent light of the first wavelength of the laser generating device can be expressed as: E r (t) = αA1{1+M cos[(ω M +ω D )t]}exp[j(ω1+ω D )t]+A1exp(jω1t); where ω D represents the Doppler shift;

[0077] The second beat frequency electrical signal can be expressed as:

[0078] i r (t) = ηα 2 A1 2cos(ω D t)+ηα 2 A1 2 M 2 cos[(ω M +ω D )t];

[0079] The initial frequency of the second beat frequency electrical signal is:

[0080] The frequency after introducing Doppler shift is:

[0081] According to the relationship between frequency and the speed of the object to be measured: Calculate the velocity V of the object to be measured S , where V represents the propagation speed of light in air. The acquisition card converts the intensity of the acquired second beat frequency electrical signal into a digital signal, and the microprocessor processes the digital signal to obtain the movement speed of the object to be measured, and integrates it over time to obtain the displacement of the object to be measured.

[0082] As can be seen from the above embodiments, when the present invention performs dynamic displacement measurement on the object to be measured, the object to be measured in the moving state introduces Doppler frequency shift in the reflected light transmitted back by the object to be measured based on the laser Doppler effect, and the reflected light of the same first wavelength and the incoherent light provided by the laser generating device without the microwave signal are beat-frequency detected to obtain a second beat-frequency electrical signal. According to the second beat-frequency electrical signal, the moving speed of the object to be measured can be calculated, and the moving speed is integrated in time to calculate the displacement measurement of the object to be measured in the moving state. The present invention introduces microwave modulation frequency into the reflected light so that the initial frequency of the second beat-frequency electrical signal is non-zero, and then introduces Doppler frequency shift into the reflected light. According to the relationship between the initial frequency, the frequency after the Doppler frequency shift is introduced, and the moving speed of the object to be measured, the moving speed of the object to be measured can be calculated. The moving speed of the object to be measured can be calculated by integrating the moving speed in time. This measurement method does not involve interference problems, has a wide range of applications, high measurement accuracy, and a large measurement range.

[0083] See also Figure 4 , is a schematic diagram of another embodiment of the displacement measurement system based on microwave interference and laser Doppler effect of the present invention. This embodiment includes both a static measurement unit and a dynamic measurement unit. Figure 4 In the embodiment shown, the laser generating device and the detection unit are respectively Figure 3 In the embodiment shown, the laser generating device and the detection unit have the same structure, and the static detection unit is Figure 2 In the embodiment shown, the static detection unit has the same structure as the dynamic detection unit. Figure 3The structure of the dynamic detection unit in the illustrated embodiment is the same. In this embodiment, the structure and working principle of the laser generating device, the detection unit, the static detection unit and the dynamic detection unit are not described in detail. Since in the static measurement of the displacement of the object to be measured, when the delay difference between the reflected light and the second incoherent light is adjusted, increasing the delay difference between the reflected light and the second incoherent light can improve the displacement measurement accuracy, and correspondingly narrow the displacement measurement range. The displacement measurement of the object to be measured in a static state and the displacement measurement in a moving state of the present invention complement each other, and while expanding the displacement measurement range, the displacement measurement accuracy can be guaranteed; in addition, the present invention integrates static displacement measurement and dynamic displacement, and is very simple in structure. It should be noted that the above-mentioned first wavelength division multiplexer can be a dense wavelength division multiplexer, and the present invention is particularly suitable for displacement measurement in a space with a high aspect ratio.

[0084] Those skilled in the art will readily appreciate other embodiments of the present invention after considering the specification and practicing the invention disclosed herein. This application is intended to cover any variations, uses or adaptations of the present invention that follow the general principles of the present invention and include common knowledge or customary techniques in the art that are not disclosed by the present invention. The specification and examples are to be considered exemplary only, and the true scope and spirit of the present invention are indicated by the following claims.

[0085] It will be appreciated that the invention is not limited to the precise construction that has been described above and shown in the drawings and that various modifications and changes may be made without departing from its scope. The scope of the invention is governed solely by the appended claims.

Claims

1. A displacement measurement system based on microwave interference and laser Doppler effect, characterized in that: It includes a laser generating device, a detection unit and an acquisition card, and also includes a static measurement unit and / or a dynamic measurement unit. The static measurement unit includes an attenuator and a static measurement branch. The two output ends of the laser generating device are respectively connected to the input end of the detection unit. The first output end of the detection unit is connected to the acquisition card through the dynamic measurement unit, and the second output end is connected to the acquisition card through the static measurement branch. The laser generating device transmits two incoherent lights with different wavelengths to the detection unit, the detection unit loads the same microwave signal into the two incoherent lights, and transmits the first incoherent light with the first wavelength loaded with the microwave signal to the probe in the detection unit. After receiving the first incoherent light emitted by the probe, the object to be measured transmits reflected light back to the probe, and the detection unit transmits the reflected light and the second incoherent light with the second wavelength loaded with the microwave signal as a combined beam to the static measurement branch and / or the dynamic measurement unit; The attenuator adjusts the intensity of at least one of the reflected light and the second incoherent light; The static measurement branch is used to adjust the delay difference between the reflected light and the second incoherent light, perform beat frequency detection on the reflected light and the second incoherent light after the light intensity and delay difference are adjusted, obtain a first beat frequency electrical signal, and restore the two microwave signals to generate microwave interference and generate a microwave interference electrical signal; determine the distance between the probe and the object to be measured according to the microwave interference electrical signal collected by the acquisition card, so as to calculate the displacement of the object to be measured in a static state; When the object to be measured is in motion, based on the laser Doppler effect, a Doppler frequency shift is introduced into the reflected light, and the dynamic measurement unit is used to filter out the second incoherent light, and perform beat frequency detection on the reflected light and the incoherent light of the first wavelength provided by the laser generating device to obtain a second beat frequency electrical signal; based on the second beat frequency electrical signal collected by the acquisition card, the movement speed of the object to be measured is calculated, and the movement speed is integrated over time to calculate the displacement of the object to be measured in the motion state.

2. The displacement measurement system based on microwave interference and laser Doppler effect according to claim 1, characterized in that: The attenuator adjusts the light intensity of at least one of the reflected light and the second incoherent light to improve the light intensity consistency of the reflected light and the second incoherent light, thereby increasing the contrast of the microwave interference; When adjusting the delay difference between the reflected light and the second incoherent light, increasing the delay difference between the reflected light and the second incoherent light can improve the displacement measurement accuracy; reducing the delay difference between the reflected light and the second incoherent light can expand the displacement measurement range.

3. The displacement measurement system based on microwave interference and laser Doppler effect according to claim 1, characterized in that: The detection unit includes a first coupler, an electro-optic modulator, a first wavelength division multiplexer, a circulator, a probe, and a second coupler. The two output ends of the laser generating device are respectively connected to the two input ends of the first coupler. The output end of the first coupler is connected to the first wavelength division multiplexer through the electro-optic modulator. The first output end of the first wavelength division multiplexer is connected to the first end of the circulator, and the second output end is connected to the second input end of the second coupler. The second end of the circulator is connected to the probe, and the third end is connected to the first input end of the second coupler. The first output end of the second coupler serves as the first output end of the detection unit and is connected to the acquisition card through the dynamic measurement unit. The second output end of the second coupler serves as the second output end of the detection unit and is connected to the acquisition card through the static measurement branch. The two incoherent lights with different wavelengths generated by the laser generating device are combined by the first coupler and then transmitted to the electro-optical modulator; The electro-optic modulator loads the microwave signal into the two incoherent lights; the first wavelength division multiplexer divides the two incoherent lights loaded with the microwave signal into two paths according to different wavelengths, wherein the first incoherent light of the first wavelength is transmitted to the first end of the circulator, and the second incoherent light of the second wavelength is transmitted to the second input end of the second coupler; the circulator transmits the first incoherent light to the probe through its second end, and after receiving the first incoherent light emitted by the probe, the object to be tested transmits the reflected light back to the probe to reach the circulator, and the reflected light is transmitted to the first input end of the second coupler through the third end of the circulator.

4. The displacement measurement system based on microwave interference and laser Doppler effect according to any one of claims 1 to 3, characterized in that: The laser generating device comprises a first single-frequency laser and a second single-frequency laser, wherein the output ends of the first single-frequency laser and the second single-frequency laser respectively serve as two output ends of the laser generating device and are correspondingly connected to two input ends of the detection unit; The first single-frequency laser is used to generate incoherent light of a first wavelength, and the second single-frequency laser is used to generate incoherent light of a second wavelength.

5. The displacement measurement system based on microwave interference and laser Doppler effect according to claim 4, characterized in that: The attenuator is provided at at least one of the following positions: between the first output end of the laser generating device and the first input end of the first coupler, between the second output end of the laser generating device and the second input end of the first coupler, between the first output end of the first wavelength division multiplexer and the first end of the circulator, between the second end of the circulator and the probe, between the third end of the circulator and the first input end of the second coupler, and between the second output end of the first wavelength division multiplexer and the second input end of the second coupler; The static measurement branch includes a dispersion module and a second photodetector, and the second output end of the detection unit is connected to the acquisition card through the dispersion module and the second photodetector in sequence; The dispersion module adjusts the delay difference between the reflected light and the second incoherent light, and the second photodetector performs beat frequency detection on the reflected light and the second incoherent light after the light intensity and delay difference adjustment are completed to obtain a first beat frequency electrical signal, and restores the two microwave signals to generate microwave interference and generate a microwave interference electrical signal.

6. The displacement measurement system based on microwave interference and laser Doppler effect according to claim 4, characterized in that: The dynamic measurement unit includes a second wavelength division multiplexer and a first photodetector, wherein the input end of the second wavelength division multiplexer is connected to the first output end of the detection unit, the output end is connected to the first input end of the first photodetector, and the output end of the first photodetector is connected to the acquisition card; the laser generating device also includes a third coupler, the output end of the first single-frequency laser is connected to the input end of the third coupler, the first output end of the third coupler is connected to the input end of the detection unit, and the second output end is connected to the second input end of the first photodetector; The second wavelength division multiplexer is used to filter out the second incoherent light and transmit the reflected light to the first photodetector. The first photodetector performs beat frequency detection on the reflected light and the incoherent light of the first wavelength provided by the laser generating device to obtain a second beat frequency electrical signal.

7. The displacement measurement system based on microwave interference and laser Doppler effect according to claim 5, characterized in that: The light intensity of the incoherent light of the first wavelength generated by the laser generating device is expressed as: E1(t)=A1exp(jω1t); the light intensity of the incoherent light of the second wavelength generated by the laser generating device is expressed as: E2(t)=A2exp(jω2t); wherein A1, A2, ω1, ω2 are the amplitudes and angular frequencies of the two incoherent lights respectively; The intensity of the optical signal after the electro-optic modulator performs microwave modulation on the two incoherent lights is expressed as: E M (t) = A1[1+Mcos(ω M t)]exp(jω1t)+A2[1+Mcos(ω M t)]exp(jω2t), where M is the microwave modulation coefficient, ω M is the angular frequency of microwave modulation; The light intensity of the optical signal after the dispersion module adjusts the delay difference between the reflected light and the second incoherent light is expressed as: E p (t)=αA1{1+Mcos[ω M (t+τ0+τ)]}exp[jω1(t+τ0+τ)]+A2[1+Mcos(ω M t)]exp(jω2t) Where α is the output loss during measurement, τ0 is the initial delay difference, and τ is the delay difference caused by the distance between the probe and the object to be measured and the dispersion module; The first beat frequency electrical signal is expressed as: I p (t)=ηα 2 A1 2 M 2 cos[ω M (t+τ0+τ)]+ηA2 2 M 2 cos(ω M t) Where η is the responsivity of the second photodetector; The intensity of the microwave interference electrical signal is expressed as: A p (oh M )=η 2 a 4 A1 4 M 4 +n 2 A2 4 M 4 +2nd 2 a 2 A1 2 A2 2 M 4 cos(ω M (τ0+τ)); The acquisition card converts the intensity of the acquired microwave interference electrical signal into a digital signal, and the microprocessor processes the digital signal to determine the distance between the probe and the object to be measured.

8. The displacement measurement system based on microwave interference and laser Doppler effect according to claim 7, characterized in that: The reflected light and the incoherent light of the first wavelength of the laser generating device are expressed as: r (t) = αA1{1+Mcos[(ω M +ω D )t]}exp[j(ω1+ω D )t]+A1exp(jω1t); where ω D represents the Doppler shift; The second beat frequency electrical signal is expressed as: I r (t)=ηα 2 A1 2 cos(ω D t)+ηα 2 A1 2 M 2 cos[(ω M +oh D )t]; The initial frequency of the second beat frequency electrical signal is: The frequency after introducing Doppler shift is: According to the relationship between frequency and the speed of the object to be measured: Calculate the velocity V of the object to be measured S , where V represents the speed of light in air.

9. The displacement measurement system based on microwave interference and laser Doppler effect according to claim 1, characterized in that: The displacement measurement of the object to be measured in a static state and the displacement measurement in a moving state complement each other to ensure both the displacement measurement accuracy and the displacement measurement range.

10. The displacement measurement system based on microwave interference and laser Doppler effect according to claim 1, characterized in that: The system is suitable for displacement measurement in a space with a high aspect ratio and limited space.

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