A distance displacement measurement device and method for electro-optic frequency comb sparseness regulation

Abstract

The application discloses a kind of electric light frequency comb sparse regulation distance displacement measuring device and method.Sparse regulation light source module and heterodyne interference optical path are connected between optical path, signal processing module is respectively electrically connected with sparse regulation light source module, heterodyne interference optical path;Sparse regulation light source module emits light transmission to heterodyne interference optical path and carries out interference measurement, and heterodyne interference optical path exports measurement signal and reference signal to signal processing module;In signal processing module, absolute distance measurement submodule and relative displacement measurement submodule are respectively used for absolute distance measurement and relative displacement measurement data processing, simultaneously with the double-mode control unit that can be switched between absolute distance measurement mode and relative displacement measurement mode Work, sparse regulation unit sends electric signal to sparse regulation light source module under the control of double-mode control unit and carries out sparse regulation.The application can realize two kinds of measurement modes, has the advantages of two kinds of measurement methods, and can be widely applied in industrial equipment manufacturing and other fields.

Description

Technical Field

[0001] This invention belongs to the field of laser interferometry technology, and specifically relates to a distance displacement measurement and control method based on sparse modulation of an electro-optic frequency comb. Background Technology

[0002] Laser interferometry is mainly divided into two categories: absolute distance measurement and relative displacement measurement. Absolute distance measurement can directly obtain the true distance between two points in space, offering advantages such as recovery after light interruption and strong anti-interference capabilities. However, its resolution and real-time performance are generally inferior to relative displacement measurement. Relative displacement measurement measures the cumulative phase change of interference fringes as the target moves, thus obtaining the displacement of the target relative to an initial reference point. It boasts advantages such as nanometer-level high resolution and high-speed real-time measurement, but it relies on a precision guide rail and can only reflect displacement changes; light interruption will lead to measurement failure. Both measurement methods have their advantages and disadvantages, and their use alone has certain limitations.

[0003] In some measurement fields, it is necessary to combine two measurement technologies. For example, when using laser trackers for 3D measurement of large workpieces and high-precision assembly positioning, absolute distance measurement and relative displacement measurement need to be combined to achieve both wide-range, ambiguity-free distance measurement and high-precision displacement tracking. Existing technologies typically employ two separate measurement modules for absolute distance and relative displacement measurement, combining the measurement beams of the two modules before taking the final measurement. While this method allows for the application of both measurement methods and leverages their respective advantages, beam combining is susceptible to deformation of mechanical parts, leading to beam splitting and affecting measurement accuracy. Furthermore, the two sets of measurement modules increase the complexity of the system.

[0004] In summary, how to achieve absolute distance and relative displacement measurement within a single measurement system is a technical problem that needs to be solved. Summary of the Invention

[0005] To address the problems existing in the background art, this invention discloses an absolute distance and relative displacement measurement device and method using electro-optic frequency comb sparse control. This invention achieves absolute distance and relative displacement measurement using a single light source on a single system.

[0006] The technical solution adopted by this invention to solve its technical problem is:

[0007] I. A distance displacement measuring device with sparse modulation of electro-optic frequency comb:

[0008] The device includes a sparsely controlled light source module, a heterodyne interference optical path, and a signal processing module. The sparsely controlled light source module and the heterodyne interference optical path are optically connected, and the signal processing module is electrically connected to both the sparsely controlled light source module and the heterodyne interference optical path. The sparsely controlled light source module emits light that is transmitted to the heterodyne interference optical path for interferometric measurement. The heterodyne interference optical path outputs two electrical signals, a measurement signal and a reference signal, to the signal processing module. In the signal processing module, an absolute distance measurement submodule and a relative displacement measurement submodule are used for absolute distance measurement and relative displacement measurement data processing, respectively. It also has a dual-mode control unit that can switch between absolute distance measurement mode and relative displacement measurement mode. Under the control of the dual-mode control unit, the sparsely controlled unit emits electrical signals to the sparsely controlled light source module for sparse control.

[0009] The sparsely modulated light source module includes a continuous laser, an optical fiber beam splitter, an acousto-optic frequency shifter, a first electro-optic phase modulator, a second electro-optic phase modulator, an optical fiber combiner, and a modulation control module. The output end of the continuous laser is connected to the input end of the optical fiber beam splitter. One output end of the optical fiber beam splitter is connected to the input end of the first electro-optic phase modulator via the acousto-optic frequency shifter, and the other output end is connected to the input end of the second electro-optic phase modulator. The output ends of the first and second electro-optic phase modulators are connected to the optical fiber combiner. The acousto-optic frequency shifter and the two electro-optic phase modulators are all connected to the modulation control module. The optical fiber combiner is connected to the heterodyne interference optical path. The continuous laser emits a continuous laser beam, which is input to the optical fiber beam splitter and split into two continuous laser beams. The two continuous laser beams are each processed by an electro-optic phase modulator and output as two modulated laser beams with different phase modulations at different frequencies. The two modulated laser beams are input to the optical fiber combiner with slow-axis and fast-axis polarization states, respectively, and then combined to form a combined beam that is output to the heterodyne interference optical path. The modulation control module and the signal processing module are electrically connected.

[0010] The modulation control module includes a driver amplifier, a first broadband amplifier, a second broadband amplifier, a rubidium atomic clock, a power divider, a first adjustable signal source, and a second adjustable signal source. The rubidium atomic clock is connected to the input of the power divider, and the output of the power divider is connected to the driver amplifier, the first adjustable signal source, and the second adjustable signal source, respectively. The first adjustable signal source and the second adjustable signal source are connected to the first broadband amplifier and the second broadband amplifier, respectively. The driver amplifier, the first broadband amplifier, and the second broadband amplifier are connected to the acousto-optic frequency shifter, the first electro-optic phase modulator, and the second electro-optic phase modulator of the modulation module, respectively.

[0011] The heterodyne interference optical path includes a collimator, a beam splitter, a polarizing beam splitter, a reference corner cube prism, a measuring corner cube prism, a first analyzer, a second analyzer, a first photodetector, and a second photodetector. The combined laser beam output from the sparsely controlled light source module is collimated by a collimator aligned with the slow axis and the P-polarization state, then input to the beam splitter for reflection and transmission. The reflected beam from the beam splitter passes through the second analyzer and is then incident on the second photodetector to obtain a reference signal. The transmitted beam from the beam splitter is then input into the polarizing beam splitter according to the P-polarization state transmission and S-polarization state transmission. The law of vibrational reflection is used for transmission and reflection. The reflected beam from the polarizing beam splitter is input into the reference corner cube prism, undergoes internal retroreflection, and returns to the polarizing beam splitter to form the reference beam. The transmitted beam from the polarizing beam splitter is input into the measuring corner cube prism, undergoes internal retroreflection, and returns to the polarizing beam splitter to form the measuring beam. Both the reference beam and the measuring beam are emitted from the polarizing beam splitter, pass through the first analyzer, and then enter the first photodetector to obtain the measurement signal. The first photodetector and the second photodetector are both electrically connected to the signal processing module.

[0012] The signal processing module includes a signal preprocessing submodule, an absolute distance measurement submodule, a relative displacement measurement submodule, a dual-mode control unit, and a sparse control unit;

[0013] The signal preprocessing submodule includes a first amplification and filtering unit, a first analog-to-digital conversion unit, a second amplification and filtering unit, and a second analog-to-digital conversion unit. The output terminals of the first photodetector and the second photodetector are electrically connected to the first amplification and filtering unit and the second amplification and filtering unit, respectively. The two output terminals of the first amplification and filtering unit and the second amplification and filtering unit are respectively connected to the input terminals of the first analog-to-digital conversion unit and the second analog-to-digital conversion unit. The output terminals of the first analog-to-digital conversion unit and the second analog-to-digital conversion unit are simultaneously connected to the input terminals of the absolute distance measurement submodule and the relative displacement measurement submodule, respectively.

[0014] The absolute distance measurement submodule includes a first fast Fourier transform unit, a second fast Fourier transform unit, a synthesized wavelength phase calculation unit, and an absolute distance calculation unit. Within the absolute distance measurement submodule, the output terminals of the first analog-to-digital converter unit and the second analog-to-digital converter unit are respectively connected to the input terminals of the first fast Fourier transform unit and the second fast Fourier transform unit. The output terminals of the first fast Fourier transform unit and the second fast Fourier transform unit are connected to the input terminal of the synthesized wavelength phase calculation unit. The output terminal of the synthesized wavelength phase calculation unit is connected to one of the input terminals of the adder via the absolute distance calculation unit.

[0015] The relative displacement measurement submodule includes a first orthogonal demodulation unit, a second orthogonal demodulation unit, a large-scale number counting unit, a relative displacement calculation unit, and an adder. Within the relative displacement measurement submodule, the outputs of the first analog-to-digital conversion unit and the second analog-to-digital conversion unit are connected to the inputs of the first and second orthogonal demodulation units, respectively. The outputs of the first and second orthogonal demodulation units are connected to the input of the large-scale number counting unit. The output of the large-scale number counting unit is connected to the other input of the adder via the relative displacement calculation unit. Simultaneously, the outputs of the first fast Fourier transform unit of the absolute distance measurement submodule and the first orthogonal demodulation unit of the relative displacement measurement submodule are both connected to the input of the dual-mode control unit. The output of the dual-mode control unit is connected to the large-scale number counting unit and the sparse control unit, respectively. The output of the sparse control unit is connected to the first and second adjustable signal sources of the sparse control light source module via a serial port.

[0016] II. A method for controlling the measurement of absolute distance and relative displacement using an electro-optic frequency comb with sparse modulation:

[0017] 1) The continuous laser is split into two continuous laser beams with a power ratio of 50:50 by the fiber beam splitter. One of the continuous laser beams is first frequency-shifted by an acousto-optic frequency shifter. The frequency-shifted continuous laser beam and the other continuous laser beam are respectively subjected to high-frequency sinusoidal phase modulation by a pair of frequency-adjustable first electro-optic phase modulators and second electro-optic phase modulators in the optical modulation module to generate a pair of laser beams with dual electro-optic frequency combs.

[0018] 2) A pair of laser beams with dual electro-optic frequency combs are combined by an optical fiber combiner and then input into a heterodyne interference optical path to obtain a reference signal and a measurement signal, respectively. The reference signal and the measurement signal are demodulated and processed to obtain the distance / displacement of the object under test, and then transmitted to the host computer via a network cable.

[0019] 3) The first and second electro-optic phase modulators in the optical modulation module are used to sparsely or non-sparsely modulate the repetition frequency of the electro-optic frequency comb in the laser passing through it, so that the comb tooth spacing of the reference and measurement signals of the multi-heterodyne interference varies sparsely, forming different working measurement modes, and switching between them is performed.

[0020] The frequency settings of the dual electro-optic frequency comb are as follows:

[0021] f S[i] (M)= f c +i* f1(M)

[0022] f L[i] (M)=( f c – f a )+i* f2(M)

[0023] Where M represents the measurement mode, M=0 represents the absolute distance measurement mode, and M=1 represents the relative displacement measurement mode; f1(M) and f2(M) represent the frequencies of the first and second electro-optic phase modulators, respectively; f S[i] (M) and f L[i] (M) represents the laser frequency of the comb tooth with index i in the signal electro-optic frequency comb and the local electro-optic frequency comb output by the second electro-optic phase modulator and the first electro-optic phase modulator, respectively. c f represents the frequency of a continuous laser. a The frequency of the acousto-optic frequency shifter is represented by i, which represents the order of the comb teeth in the dual electro-optic frequency comb, i=0,±1,±2,…,±Q, where Q represents the maximum order.

[0024] When measuring absolute distance and its mode, the comb tooth spacing is reduced so that the frequency band contains a large number of comb tooth signals of different frequencies, which meets the requirements of absolute distance for multi-wavelength phase acquisition.

[0025] When measuring relative displacement and its mode, the comb tooth spacing is increased to improve the maximum allowable Doppler frequency shift and meet the high signal bandwidth requirements of relative displacement measurement.

[0026] Step 3) specifically refers to:

[0027] When sparse control is not performed, absolute distance measurement is conducted in absolute distance measurement mode. A Fast Fourier Transform (FFT) is simultaneously performed on both the reference and measurement signals to obtain the phase difference of each frequency component. The phase of the synthesized wavelength constructed in the corresponding electro-optic frequency comb is then calculated, and the final absolute distance is determined based on the synthesized wavelength. L ADM ;

[0028] When performing sparse control, relative displacement measurement is performed in the relative displacement measurement mode. Phase demodulation is performed on the reference interference signal and the measurement interference signal to obtain two phase differences. After unpacking the two phase differences by counting their magnitudes, the two unpacked phase differences are combined with the wavelength of the comb teeth of the electro-optic frequency comb to obtain the two relative displacement values ​​R1 and R2 of the object under test. Finally, the relative displacement measurement result is obtained based on the two relative displacement values ​​R1 and R2.

[0029] Step 3) of the method includes:

[0030] The dual-mode control unit determines whether the object under test is stationary or moving based on the spectrum of the measurement signal output by the first fast Fourier transform unit, and then controls it accordingly.

[0031] When the object under test is stationary, the sparse modulation unit controls the repetition frequency of the electro-optic frequency comb to perform sparse modulation on the two continuous laser beams, so that the repetition frequency difference between the two electro-optic frequency combs in the pair of laser beams is adjusted to 100kHz. Then, it switches to the absolute distance measurement mode to obtain the absolute distance of the object under test as the initial absolute distance value. L ADM Then switch to relative displacement measurement mode to obtain the relative displacement of the object under test in real time as the real-time relative displacement value. R (t), and then the initial absolute distance value and the real-time relative displacement value are added together to obtain the distance measurement result of the object to be measured;

[0032] When the object under test is in motion, the first quadrature demodulation unit modulates the frequency components F1(1) and F in the measurement signal. -1 (1) Simultaneously perform phase demodulation. The second quadrature demodulation unit modulates the frequency components F1(1) and F in the reference signal. -1 (1) Simultaneously perform phase demodulation. The demodulation results of the first orthogonal demodulation unit and the second orthogonal demodulation unit are transmitted to the large and small number counting unit for subtraction to obtain the phase difference φ1(t) and φ2(t). During the movement of the object under test, the two phase differences will change continuously in the interval from 0 to 1. The large and small number counting unit simultaneously performs large and small number counting on the two phase differences φ1(t) and φ2(t) to obtain the unwrapped phase difference φ'1(t)=φ1(t)+k1 and φ'2(t)=φ2(t)+k2.

[0033] In the relative displacement calculation module, the two phase differences after unwrapping are multiplied by the wavelengths λ1=c / f of the comb teeth with serial numbers 1 and -1 in the corresponding signal electro-optic frequency comb. S[1] (1) and λ2=c / f S[-1] (1) The relative displacements of the target object to be measured are obtained as R1=[φ1(t)+k1]λ1 / 2 and R2=[φ2(t)+k2]λ2 / 2, where R1 and R2 represent the relative displacement results obtained by simultaneously measuring the comb teeth with serial numbers 1 and -1, respectively.

[0034] The final relative displacement calculation module determines the two relative displacements. R 1 and R If the deviation between the two values ​​is less than the preset deviation value, the relative displacement measurement is considered normal, and the average of the two values ​​is taken as the final result of the relative displacement measurement. R (t)=( R 1+ R 2) / 2.

[0035] Step 3) of the method further includes:

[0036] In relative displacement measurement mode, the strength of the measurement signal is continuously monitored and processed.

[0037] The dual-mode control unit determines whether abnormal interference such as light interruption has occurred based on the measurement signal strength output by the first quadrature demodulation unit.

[0038] When the measured signal strength suddenly drops to zero, a command is sent to the sparse control unit to automatically switch to the absolute distance measurement mode. After the spectrum of the measured signal output by the first fast Fourier transform unit returns to normal, the absolute distance measurement is performed. Then, a command is sent to the sparse control unit to automatically switch back to the relative displacement measurement mode. The sparse control unit sends serial port commands to the first and second adjustable signal sources through a serial port line to control the output signal frequency, thereby realizing the sparse control of the electro-optic frequency comb.

[0039] This invention sparsely modulates the repetition frequency of the electro-optic frequency comb of a laser, causing sparse variations in the comb tooth spacing of the multi-heterodyne interference signal. For absolute distance measurement, the comb tooth spacing is reduced to include a large number of comb tooth signals of different frequencies within the frequency band, obtaining the phase of the high- and low-order synthesized wavelengths to calculate the absolute distance. For relative displacement measurement, the comb tooth spacing is increased to raise the maximum allowable Doppler frequency shift, demodulating the phase of the moving target and performing a magnitude count to measure the relative displacement. The absolute distance and relative displacement measurements are automatically switched under the control of the mode control module. When the target is stationary, absolute distance measurement is performed first, then the system automatically switches to relative displacement measurement mode. When conditions such as light interruption are detected, the system automatically switches back to the absolute distance measurement module.

[0040] This invention enables two measurement modes, combining the advantages of both measurement methods, and can be widely applied in fields such as industrial equipment manufacturing.

[0041] The innovation of this invention lies in employing a sparse control method for an electro-optic frequency comb, which allows for sparse variation in the comb tooth spacing of the multiheterodyne interference signal. This generates a tightly spaced multiheterodyne interference signal that satisfies absolute distance measurement and a wide-spaced multiheterodyne interference signal that satisfies relative displacement measurement. A dual-mode control unit is designed, capable of automatically switching the measurement system between the two measurement modes based on the state of the multiheterodyne interference signal. When the target is stationary, absolute distance measurement is performed first, followed by automatic switching to relative displacement measurement mode to meet the needs of subsequent dynamic measurements. If light obstruction or a phase displacement measurement error is detected, the system automatically switches back to absolute distance measurement mode for re-measurement. Only one measurement system is used to achieve both measurement functions and can automatically switch between the two measurement modes, exhibiting excellent anti-interference capability and stability.

[0042] The beneficial effects of this invention are:

[0043] (1) The electro-optic frequency comb sparse control absolute distance and relative displacement ranging method in this invention, by sparsely controlling the electro-optic frequency comb, makes the comb tooth spacing of the multi heterodyne interference signal sparsely change, which can generate a multi heterodyne interference signal with tightly packed comb teeth that satisfies absolute distance measurement and a multi heterodyne interference signal with large frequency spacing that satisfies relative displacement measurement. Two measurement functions are realized by using a set of measurement system.

[0044] (2) The dual-mode control unit designed in this invention can automatically switch the measurement system between two measurement modes according to the state of the multiheterodyne interference signal. When the target is stationary, the absolute distance measurement is performed first, and then the system automatically switches to the relative displacement measurement mode to meet the needs of subsequent dynamic measurements. When light obstruction or relative displacement measurement error is detected, the system automatically switches back to the absolute distance measurement mode and performs the measurement again. The automatic switching between the two measurement modes improves the anti-interference capability and stability of the measurement system. Attached Figure Description

[0045] Figure 1 This is a schematic diagram of the principle of a dual-mode ranging device for absolute distance and relative displacement based on the sparse control of an electro-optic frequency comb.

[0046] Figure 2 This is a schematic diagram of the spectrum and measurement principle of multiheterodyne interference signals under two measurement modes: absolute distance and relative displacement, controlled by sparse modulation of electro-optic frequency comb.

[0047] Figure 3 This is a block diagram illustrating the principle of dual-mode ranging signal processing and dual-mode measurement control method for absolute distance and relative displacement.

[0048] In the diagram: 1. Continuous laser; 2. Fiber beam splitter; 3. Acousto-optic frequency shifter; 4. First electro-optic phase modulator; 5. Second electro-optic phase modulator; 6. Fiber beam combiner; 7. Collimator; 8. Beam splitter; 9. Polarizing beam splitter; 10. Reference corner cube prism; 11. Measuring corner cube prism; 12. Driver amplifier; 13. First broadband amplifier; 14. Second broadband amplifier; 15. Rubidium atomic clock; 16. Power divider; 17. First adjustable signal source; 18. Second adjustable signal source; 19. Signal processing module; 20. Host computer; 21. First analyzer; 22. Second analyzer; 23. First photodetector; 2 4. Second photodetector; 1901, First amplification and filtering unit; 1902, First analog-to-digital conversion unit; 1903, First fast Fourier transform unit; 1904, Second fast Fourier transform unit; 1905, Synthetic wavelength phase calculation unit; 1906, Absolute distance calculation unit; 1907, Dual-mode control unit; 1908, Sparse control unit; 1909, Second amplification and filtering unit; 1910, Second analog-to-digital conversion unit; 1911, First quadrature demodulation unit; 1912, Second quadrature demodulation unit; 1913, Large and small number counting unit; 1914, Relative displacement calculation unit; 1915, Adder. Detailed Implementation

[0049] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0050] like Figure 1 As shown, it includes a sparse control light source module, a heterodyne interference optical path and a signal processing module. The sparse control light source module and the heterodyne interference optical path are optically connected, and the signal processing module 19 is electrically connected to the sparse control light source module and the heterodyne interference optical path respectively.

[0051] The sparse control light source module emits light that is transmitted to the heterodyne interference optical path for interferometric measurement. The heterodyne interference optical path outputs two electrical signals, a measurement signal and a reference signal, to the signal processing module 19. In the signal processing module 19, the absolute distance measurement submodule and the relative displacement measurement submodule are used for absolute distance measurement and relative displacement measurement data processing, respectively. It also has a dual-mode control unit 1907 that can switch between absolute distance measurement mode and relative displacement measurement mode. The sparse control unit 1908 emits electrical signals to the sparse control light source module for sparse control under the control of the dual-mode control unit.

[0052] like Figure 1As shown, the sparsely modulated light source module includes a continuous laser 1, an optical fiber beam splitter 2, an acousto-optic frequency shifter 3, a first electro-optic phase modulator 4, a second electro-optic phase modulator 5, an optical fiber combiner 6, and a modulation control module. The output end of the continuous laser 1 is connected to the input end of the optical fiber beam splitter 2. The optical fiber beam splitter 2 has two output ends. One output end of the optical fiber beam splitter 2 is connected to the input end of the first electro-optic phase modulator 4 via the acousto-optic frequency shifter 3, and the other output end is connected to the input end of the second electro-optic phase modulator 5. The output ends of the first electro-optic phase modulator 4 and the second electro-optic phase modulator 5 are connected to the optical fiber combiner 6. Frequency converter 3 and the two electro-optic phase modulators are electrically connected to the modulation control module. Fiber optic combiner 6 is connected to the heterodyne interference optical path. Continuous laser 1 emits a continuous laser beam, which is input to fiber optic beam splitter 2 and split into two continuous laser beams. Each of the two continuous laser beams passes through its own electro-optic phase modulator and outputs two modulated laser beams with different phase modulations at different frequencies. The two modulated laser beams output from the first electro-optic phase modulator 4 and the second electro-optic phase modulator 5 are input to the fiber optic combiner 6 with slow-axis and fast-axis polarization states, respectively, and then combined to form a combined beam that is output to the heterodyne interference optical path. The modulation control module and signal processing module 19 are electrically connected. Signal processing module 19 is electrically connected to the host computer 20 via a network cable.

[0053] like Figure 1 As shown, the modulation control module includes a driver amplifier 12, a first broadband amplifier 13, a second broadband amplifier 14, a rubidium atomic clock 15, a power divider 16, a first adjustable signal source 17, and a second adjustable signal source 18. The input terminals of the rubidium atomic clock 15 and the power divider 16 are connected. The output terminals of the power divider 16 are electrically connected to the driver amplifier 12, the first adjustable signal source 17, and the second adjustable signal source 18, respectively. The first adjustable signal source 17 and the second adjustable signal source 18 are electrically connected to the first broadband amplifier 13 and the second broadband amplifier 14, respectively. The driver amplifier 12, the first broadband amplifier 13, and the second broadband amplifier 14 are electrically connected to the acousto-optic frequency shifter 3, the first electro-optic phase modulator 4, and the second electro-optic phase modulator 5 of the modulation module for modulation.

[0054] like Figure 1As shown, the heterodyne interference optical path includes a collimator 7, a beam splitter 8, a polarizing beam splitter 9, a reference corner cube prism 10, a measuring corner cube prism 11, a first analyzer 21, a second analyzer 22, a first photodetector 23, and a second photodetector 24. The combined laser beam output from the sparsely controlled light source module is input to the beam splitter 8 via the collimator 7, which is aligned with the slow axis and the P-polarization state, and is reflected and transmitted at a power ratio of 3:7. The reflected beam output from the beam splitter 8 is then incident on the second photodetector 24 after passing through the second analyzer 22 to obtain a reference signal. The transmitted beam output from the beam splitter 8 is then input into the polarizing beam splitter 9 according to the P-polarization state. The transmission and reflection are carried out according to the law of S-polarization state reflection. The reflected beam output from the polarization beam splitter 9 is input to the reference corner cube prism 10. After internal retroreflection, it returns to the polarization beam splitter 9 and is reflected to form the reference beam. The transmitted beam output from the polarization beam splitter 9 is input to the measuring corner cube prism 11. After internal retroreflection, it returns to the polarization beam splitter 9 and is transmitted to form the measuring beam. The reference beam and the measuring beam are both emitted from the polarization beam splitter 9 by beam combining. After passing through the first analyzer 21, they are incident on the first photodetector 23 to obtain the measurement signal. The first photodetector 23 and the second photodetector 24 are both electrically connected to the signal processing module 19.

[0055] The reference corner cube prism 10 is fixedly arranged relative to the polarizing beam splitter 9, etc. The measuring corner cube prism 11 is fixedly connected to the external object to be measured, and moves with the object to be measured relative to the reference corner cube prism 10 and the polarizing beam splitter 9, etc.

[0056] The output of the first electro-optic phase modulator 4 and the second electro-optic phase modulator 5 respectively output a local electro-optic frequency comb and a signal electro-optic frequency comb, collectively referred to as dual electro-optic frequency combs, which enter the orthogonal fiber combiner 6 with slow-axis and fast-axis polarization states, respectively. The output of the orthogonal fiber combiner 6 is connected to the input of the collimator 7. The local electro-optic frequency comb and the signal electro-optic frequency comb are output from collimator 7 in s-polarization and p-polarization states, respectively, and incident on beam splitter 8. The two electro-optic frequency combs are transmitted and reflected at a power ratio of 3:1. The reflected two electro-optic frequency combs are then incident on second photodetector 24 after passing through second analyzer 22 to obtain a reference signal. The transmitted two electro-optic frequency combs from beam splitter 8 are then incident on polarization beam splitter 9 for transmission and reflection, with the signal frequency comb being transmitted and the local frequency comb being reflected. The reflected local frequency comb and the transmitted signal frequency comb from polarization beam splitter 9 are incident on reference corner cube prism 10 and measuring corner cube prism 11, respectively, and then reflected back to polarization beam splitter 9. After reflection and transmission again, they converge, pass through a reflector, and then through first analyzer 21 to first photodetector 23 to obtain a measurement signal. The reference corner cube prism 10 is attached to the side of polarization beam splitter 9 with optical adhesive, and the measuring corner cube prism 11 is mounted on a movable target to be measured.

[0057] like Figure 1As shown, the signal processing module 19 includes a signal preprocessing submodule, an absolute distance measurement submodule, a relative displacement measurement submodule, a dual-mode control unit 1907, and a sparse control unit 1908. The signal preprocessing submodule includes a first amplification and filtering unit 1901, a first analog-to-digital converter (ADC) unit 1902, a second amplification and filtering unit 1909, and a second ADC unit 1910. The output terminals of the first photodetector 23 and the second photodetector 24 are electrically connected to the first amplification and filtering unit 1901 and the second amplification and filtering unit 1909 of the signal preprocessing submodule, respectively. The two output terminals of the first amplification and filtering unit 1901 and the second amplification and filtering unit 1909 are respectively connected to the input terminals of the first ADC unit 1902 and the second ADC unit 1910. Analog-to-digital conversion processing is performed by the first ADC unit 1902 and the second ADC unit 1910. The output terminals of the first ADC unit 1902 and the second ADC unit 1910 are simultaneously connected to the input terminals of the absolute distance measurement submodule and the relative displacement measurement submodule, respectively.

[0058] The absolute distance measurement submodule includes a first fast Fourier transform unit 1903, a second fast Fourier transform unit 1904, a synthesized wavelength phase calculation unit 1905, and an absolute distance calculation unit 1906. Within the absolute distance measurement submodule, the output terminals of the first analog-to-digital converter unit 1902 and the second analog-to-digital converter unit 1910 are respectively connected to the input terminals of the first fast Fourier transform unit 1903 and the second fast Fourier transform unit 1904. The output terminals of the first fast Fourier transform unit 1903 and the second fast Fourier transform unit 1904 are connected to the input terminal of the synthesized wavelength phase calculation unit 1905. The output terminal of the synthesized wavelength phase calculation unit 1905 is connected to one of the input terminals of the adder 1915 via the absolute distance calculation unit 1906.

[0059] The relative displacement measurement submodule includes a first orthogonal demodulation unit 1911, a second orthogonal demodulation unit 1912, a large-small number counting unit 1913, a relative displacement calculation unit 1914, and an adder 1915. Within the relative displacement measurement submodule, the output terminals of the first analog-to-digital conversion unit 1902 and the second analog-to-digital conversion unit 1910 are respectively connected to the input terminals of the first orthogonal demodulation unit 1911 and the second orthogonal demodulation unit 1912. The output terminals of the first orthogonal demodulation unit 1911 and the second orthogonal demodulation unit 1912 are connected to the input terminal of the large-small number counting unit 1913. The output terminal of the large-small number counting unit 1913 is connected to another input terminal of the adder 1915 via the relative displacement calculation unit 1914. The adder 1915 adds the data output by the absolute distance calculation unit 1906 and the relative displacement calculation unit 1914 to obtain distance / displacement information, which is then transmitted to the host computer 20 via a network cable.

[0060] Meanwhile, the outputs of the first Fast Fourier Transform unit 1903 of the absolute distance measurement submodule and the first quadrature demodulation unit 1911 of the relative displacement measurement submodule are both connected to the input of the dual-mode control unit 1907. The output of the dual-mode control unit 1907 is connected to the large and small number counting unit 1913 and the sparse control unit 1908, respectively. The output of the sparse control unit 1908 is connected to the first adjustable signal source 17 and the second adjustable signal source 18 of the sparse control light source module through a serial port.

[0061] In a specific implementation, the power divider 16 also has an output terminal connected to the first analog-to-digital converter 1902 and the second analog-to-digital converter 1910 in the signal processing module 19. This allows the clock signal output from the rubidium atomic clock 15 to be multiplied by the power divider 16 and then input to the first analog-to-digital converter 1902 and the second analog-to-digital converter 1910, thereby controlling the entire signal processing sampling frequency of the signal processing module 19.

[0062] In a specific implementation, the output end of the continuous laser 1 is connected to the input end of the fiber beam splitter 2. The two output ends of the fiber beam splitter 2 are respectively connected to the input ends of the acousto-optic frequency shifter 3 and the second electro-optic phase modulator 5. The output end of the acousto-optic frequency shifter 3 is connected to the input end of the first electro-optic phase modulator 4. The output ends of the first electro-optic phase modulator 4 and the second electro-optic phase modulator 5 are connected to the two input ends of the fiber beam combiner 6. The output end of the orthogonal fiber beam combiner 6 is connected to the input end of the collimator 7.

[0063] The acousto-optic frequency shifter 3 is used to shift the frequency of the beam passing through it, changing the original frequency; the second electro-optic phase modulator 5 and the first electro-optic phase modulator 4 are used to modulate the two beams at different frequencies to form a laser with comb teeth containing different frequency intervals, i.e., an electro-optic frequency comb.

[0064] More specifically, the output of collimator 7 is spatial light, which is incident on beam splitter 8 and undergoes transmission and reflection. The reflected light from beam splitter 8 passes through second analyzer 22 and then enters second photodetector 24 to obtain a reference signal. The transmitted light from beam splitter 8 then enters polarizing beam splitter 9 and undergoes transmission and reflection. The reflected light from polarizing beam splitter 9 enters reference corner cube prism 10, undergoes retroreflection inside reference corner cube prism 10, and then undergoes reflection at another point on polarizing beam splitter 9. The transmitted light from polarizing beam splitter 9 enters measuring corner cube prism 11, undergoes retroreflection, and then undergoes transmission at another point on polarizing beam splitter 9. The reflected light and transmitted light at the other point on polarizing beam splitter 9 are combined, pass through a reflector, and then through first analyzer 21 to enter first photodetector 23 to obtain a measurement signal containing information about the movement of the object under test.

[0065] More specifically, the output of the rubidium atomic clock 15 is connected to the input of the power divider 16. The clock signal output from the rubidium atomic clock 15 is sent to the power divider 16 for equal power distribution. The four outputs of the power divider are connected to the driver amplifier 12, the first adjustable signal source 17, the second adjustable signal source 18, and the signal processing module 19, respectively, providing a reference clock for these four circuit modules. The output of the driver amplifier 12 is connected to the control terminal of the acousto-optic frequency shifter 3. The outputs of the first adjustable signal source 17 and the second adjustable signal source 18 are connected to the inputs of the first broadband amplifier 13 and the second broadband amplifier 14, respectively. The outputs of the first broadband amplifier 13 and the second broadband amplifier 14 are connected to the modulation terminals of the first electro-optic phase modulator 4 and the second electro-optic phase modulator 5, respectively. The outputs of the first photodetector 23 and the second photodetector 24 are connected to the input of the signal processing module 19, which is electrically connected to the host computer 20 via a network cable.

[0066] The absolute distance measurement submodule, relative displacement measurement submodule, dual-mode control unit 1907 and sparse control unit 1908 in the signal processing module 19 operate at high speed within the FPGA chip.

[0067] The specific measurement process of this invention includes the following:

[0068] 1) such as Figure 1 As shown, in the sparsely modulated light source module, the continuous laser 1 is split into two continuously modulated laser beams with a power ratio of 50:50 by the fiber beam splitter. One of the continuous laser beams is first frequency-shifted by the acousto-optic frequency shifter 3. The frequency-shifted continuous laser beam and the other unshifted continuous laser beam are respectively subjected to high-frequency sinusoidal phase modulation by a pair of frequency-tunable first electro-optic phase modulators 4 and second electro-optic phase modulators 5 in the optical modulation module, generating a pair of laser beams with dual electro-optic frequency comb waveforms.

[0069] A pair of laser beams have dual electro-optic frequency comb waveforms with different comb tooth spacing and sparsely adjustable frequency.

[0070] 2) A pair of laser beams with dual electro-optic frequency comb frequency domain waveforms are combined by fiber optic combiner 6 and input into the heterodyne interference optical path to obtain reference signal and measurement signal respectively. The reference signal and measurement signal are input into signal processing module 19 for signal demodulation and calculation to obtain the distance / displacement of the object / target under test, and then transmitted to host computer 20 through network cable.

[0071] 3) The first electro-optic phase modulator 4 and the second electro-optic phase modulator 5 in the optical modulation module are used to sparsely or non-sparsely modulate the repetition frequency of the comb frequency waveform with electro-optic frequency in the laser that passes through it. This makes the comb tooth spacing of the reference and measurement signals of the multi-heterodyne interference sparsely change, forming different working measurement modes, and switching between them. This allows the heterodyne interference optical path to generate a multi-heterodyne interference signal with tightly packed comb teeth that satisfies absolute distance measurement and a multi-heterodyne interference signal with large frequency spacing that satisfies relative displacement measurement. This enables a single measurement system to achieve both absolute distance and relative displacement measurement functions, and has good anti-interference ability and stability.

[0072] like Figure 2 As shown, in the absolute distance measurement mode, sparse modulation is not used in the first electro-optic phase modulator 4 and the second electro-optic phase modulator 5; in the relative displacement measurement mode, sparse modulation is used in the first electro-optic phase modulator 4 and the second electro-optic phase modulator 5. Sparse modulation means that the modulation frequency difference between the first electro-optic phase modulator 4 and the second electro-optic phase modulator 5 is set to about 10MHz, and vice versa, it is 100kHz.

[0073] The laser frequency settings for each tooth in the dual electro-optic frequency comb of a pair of laser beams are as follows:

[0074] f S[i] (M)= f c +i* f1(M)

[0075] f L[i] (M)=( f c – f a )+i* f2(M)

[0076] Where M represents the measurement mode, M=0 represents the absolute distance measurement mode, and M=1 represents the relative displacement measurement mode; f1(M) and f2(M) represent the frequencies of the first electro-optic phase modulator 4 and the second electro-optic phase modulator 5, respectively; f S[i] (M) and f L[i] (M) represents the laser frequency of the comb tooth with serial number i in the signal electro-optic frequency comb and the local electro-optic frequency comb output by the second electro-optic phase modulator 5 and the first electro-optic phase modulator 4, respectively. c f represents the frequency of continuous laser 1. a The frequency of the acousto-optic frequency shifter 3 is represented by i, which represents the order of the comb teeth in the dual electro-optic frequency comb, i=0,±1,±2,…,±Q, where Q represents the maximum order.

[0077] A pair of sparsely modulated laser beams with dual electro-optic frequency comb waveforms are subjected to multiheterodyne interference after passing through a heterodyne interference optical path to obtain a reference signal and a measurement signal for multiheterodyne interference. The reference signal and the measurement signal have the same comb-shaped frequency distribution relationship, and the magnitudes of various frequency components satisfy the following relationship:

[0078] F i (M)= f a +i*[f1(M)-f2(M)]= f a +i*f d (M)

[0079] f d (M) = f1(M) - f2(M)

[0080] Among them, F i (M) represents the magnitude of the laser frequency component of the comb tooth with serial number i under measurement mode M, f d (M) represents the frequency interval between adjacent frequency components in the measured signal and the reference interferometric signal.

[0081] In the embodiment, under the absolute distance measurement mode, f d (0) = 100 kHz, in relative displacement measurement mode, f d (1) = 10MHz. Taking 1560nm measurement light as an example, for f d (1) For a frequency interval of 10MHz, the maximum allowable Doppler frequency shift is 5MHz, which corresponds to a maximum moving speed of 3.9m / s.

[0082] The sparse control unit 1908 controls the signal frequencies of the first adjustable signal source 17 and the second adjustable signal source 18 through serial port commands, thereby realizing the sparse control of the electro-optic frequency comb.

[0083] Figure 3 The diagram shown is a block diagram illustrating the principle of dual-mode ranging signal processing and dual-mode measurement control method for absolute distance and relative displacement. Figure 1 Further explanation of the signal processing module 19. The measurement signal and reference signal output by the first photodetector 23 and the second photodetector 24 are respectively amplified and filtered by the first amplification and filtering unit 1901 and the second amplification and filtering unit 1909, respectively, and then converted to digital by the first analog-to-digital converter unit 1902 and the second analog-to-digital converter unit 1910, and then transmitted to the FPGA field-programmable logic array chip for signal processing.

[0084] In the measurement optical path, a sparsely controlled electro-optic frequency comb is used for multi-heterodyne interferometry measurement. During the measurement, a series of virtual synthetic wavelengths of different sizes are constructed using the electro-optic frequency comb to obtain the measurement signal and reference signal of multi-heterodyne interferometry. The measurement signal and reference signal are transmitted to the signal processing module. After being processed by the preprocessing module, the signal is transmitted to the FPGA chip for the measurement of absolute distance and relative displacement.

[0085] Step 3) specifically refers to:

[0086] When sparse control is not performed, the signal processing module 19 measures the absolute distance of the object under test in absolute distance measurement mode. In absolute distance measurement mode, the reference signal and the measurement signal are simultaneously subjected to Fast Fourier Transform (FFT) to obtain the phase difference of each frequency component, and then the phase of the synthesized wavelength constructed in the corresponding electro-optic frequency comb is calculated. Finally, the absolute distance is calculated based on the synthesized wavelength. L ADM ;

[0087] Specifically, in absolute distance measurement mode (when the target is stationary), the sequence number in the signal electro-optic frequency comb is ± j The laser frequency components are used to construct the synthetic wavelength λ s (j)=c / [f S[j] (0)-f S[-j] (0)], j=0,1,2,…,Q; The absolute distance to the measuring corner cube prism 11 is measured via the heterodyne interference optical path. In the FPGA, the first fast Fourier transform unit 1903 and the second fast Fourier transform unit 1904 simultaneously perform fast Fourier transform (FFT) on the measurement signal and reference signal output from the heterodyne interference optical path, and then the synthesized wavelength phase calculation unit 1905 calculates all synthesized wavelengths λ. s (j) fractional phase e j (Range within 0 to 1), in absolute distance calculation unit 1907, based on the fractional phase e of the synthesized wavelength... j The relationship between L and the distance to be measured is L=[e j +N j ]*λ s We can construct a system of equations using (j) / 2, where N j To determine the large number phases (which are unknown integers) corresponding to the synthesized wavelength, further calculate the large number phases N. j Finally, the absolute distance measurement result L was obtained. ADM =[e Q +N Q ]λ s (Q) / 2.

[0088] When sparse control is performed, the signal processing module 19 measures the relative displacement of the object under test in the relative displacement measurement mode. In the relative displacement measurement mode, the reference interference signal and the measurement interference signal are demodulated to obtain two phase differences. The two phase differences are then unwrapped by counting the magnitudes of the two phase differences. The two unwrapped phase differences are combined with the wavelength of the comb teeth of the electro-optic frequency comb in the continuous laser output by the continuous laser 1 to obtain the two relative displacement values ​​R1 and R2 of the object under test. Then, the final result of the relative displacement measurement is obtained based on the two relative displacement values ​​R1 and R2.

[0089] Specifically, when sparse modulation is performed, the signal processing module 19 measures the relative displacement of the object under test in a relative displacement measurement mode. In this mode, the object under test is allowed to move. In the FPGA, the first quadrature demodulation unit 1911 modulates the frequency components F1(1) and F in the measurement signal. -1 (1) Simultaneously perform phase demodulation. The second quadrature demodulation unit 1912 modulates the frequency components F1(1) and F in the reference signal. -1 (1) Simultaneously perform phase demodulation. The demodulation results of the first quadrature demodulation unit 1911 and the second quadrature demodulation unit 1912 are transmitted to the large and small number counting unit 1913 for subtraction to obtain the phase difference φ1(t) and φ2(t). During the movement of the object under test, the two phase differences will change continuously in the interval from 0 to 1 (1 represents 360 degrees). The large and small number counting unit 1913 simultaneously performs large and small number counting on the two phase differences φ1(t) and φ2(t) to obtain the unwrapped phase difference φ'1(t) = φ1(t) + k1 and φ'2(t) = φ2(t) + k2; where k1 and k2 represent the number of positive cycles (360°) of the cumulative change of the two phase differences φ1(t) and φ2(t), respectively.

[0090] In the relative displacement calculation module 1914, the two phase differences after unwrapping are multiplied by the wavelengths λ1=c / f of the comb teeth with serial numbers 1 and -1 in the corresponding signal electro-optic frequency comb. S[1] (1) and λ2=c / f S[-1] (1) The relative displacements of the target object to be measured are obtained as R1=[φ1(t)+k1]λ1 / 2 and R2=[φ2(t)+k2]λ2 / 2, where R1 and R2 represent the relative displacement results obtained by simultaneously measuring the comb teeth with serial numbers 1 and -1, respectively.

[0091] Finally, the relative displacement calculation module 1914 determines that if the deviation between the two relative displacements R1 and R2 is less than the preset deviation value, such as 0.1 micrometers, then the relative displacement measurement is considered normal, and the average of the two is taken as the final result of the relative displacement measurement, R(t)=(R1+R2) / 2. Otherwise, it is considered that external interference has occurred, and an alarm message is given.

[0092] In specific implementation, the signal processing module 19 is also equipped with a dual-mode control unit 1907. The dual-mode control unit 1907 determines whether the object under test is stationary or moving based on the measurement signal spectrum output by the first fast Fourier transform unit 1903, and then controls it accordingly.

[0093] When the object under test is stationary, a command is sent to the sparse control unit 1908 to control the repetition frequency of the electro-optic frequency comb for sparse control. The first electro-optic phase modulator 4 and the second electro-optic phase modulator 5 are used to control the electro-optic frequency comb of the two continuous laser beams for sparse control, so that the repetition frequency difference of the optical spectrum waveform of the two electro-optic frequency combs in a pair of laser beams is adjusted to 100kHz. Then, the signal processing module 19 is switched to the absolute distance measurement mode M=0 to obtain the absolute distance between the object under test and the target under test as the initial absolute distance value. L ADM Then switch to relative displacement measurement mode M=1 to measure displacement changes in real time and obtain the relative displacement of the object under test as the real-time relative displacement value. R (t), then the initial absolute distance value is added to the real-time relative displacement value to obtain the distance measurement result of the object under test, which is the final distance measurement result. L ( t )= L ADM + R (t), where L ADM This represents the initial absolute distance value. R (t) represents the real-time relative displacement value at time t;

[0094] When the object / target under test is in motion, the first quadrature demodulation unit 1911 modulates the frequency components F1(1) and F in the measurement signal. -1 (1) Simultaneously perform phase demodulation. The second quadrature demodulation unit 1912 modulates the frequency components F1(1) and F in the reference signal. -1 (1) Simultaneously perform phase demodulation. The demodulation results of the first quadrature demodulation unit 1911 and the second quadrature demodulation unit 1912 are transmitted to the large and small number counting unit 1913 for subtraction to obtain the phase difference φ1(t) and φ2(t). During the movement of the object under test, the two phase differences will change continuously in the interval from 0 to 1 (1 represents 360 degrees). The large and small number counting unit 1913 simultaneously performs large and small number counting on the two phase differences φ1(t) and φ2(t) to obtain the unwrapped phase difference φ'1(t) = φ1(t) + k1 and φ'2(t) = φ2(t) + k2; where k1 and k2 represent the number of positive cycles (360°) of the cumulative change of the two phase differences φ1(t) and φ2(t), respectively.

[0095] In the relative displacement calculation module 1914, the two phase differences after unwrapping are multiplied by the wavelengths λ1=c / f of the comb teeth with serial numbers 1 and -1 in the corresponding signal electro-optic frequency comb. S[1] (1) and λ2=c / f S[-1] (1) The relative displacements of the target object to be measured are obtained as R1=[φ'1(t)+k1]λ1 / 2 and R2=[φ'2(t)+k2]λ2 / 2, where R1 and R2 represent the relative displacement results obtained by simultaneously measuring the comb teeth with serial numbers 1 and -1, respectively.

[0096] The final relative displacement calculation module 1914 determines the two relative displacements. R 1 and R If the deviation between the two values ​​is less than the preset deviation value, for example, 0.1 micrometers, the relative displacement measurement is considered normal, and the average of the two values ​​is taken as the final result of the relative displacement measurement. R (t)=( R 1+ R 2) / 2, otherwise it is considered that there is external interference and an alarm message is given.

[0097] In relative displacement measurement mode, the dual-mode control unit continuously monitors and processes the measurement signal strength.

[0098] The dual-mode control unit 1907 determines whether abnormal interference such as light interruption occurs based on the measurement signal strength output by the first quadrature demodulation unit 1911.

[0099] When the measured signal strength suddenly drops to zero, it is assumed that the electro-optic frequency comb incident on the measuring corner prism 11 is experiencing external interference due to obstruction. At this time, a command is sent to the sparse control unit 1908 to automatically switch to the absolute distance measurement mode. After the spectrum of the measured signal output by the first fast Fourier transform unit 1903 returns to normal, the absolute distance measurement is performed. Then, a command is sent to the sparse control unit 1908 to automatically switch back to the relative displacement measurement mode. The sparse control unit 1908 sends serial port commands to the first adjustable signal source 17 and the second adjustable signal source 18 through a serial port line to control the output signal frequency, thereby realizing the sparse control of the electro-optic frequency comb.

[0100] The signal processing module 19 also transmits measurement results and other data to the host computer 20 via network cable for display and storage. At the same time, the host computer 20 can send frequency information and other configuration parameters to the signal processing module 19.

[0101] In summary, the electro-optic frequency comb sparse control method for absolute distance and relative displacement ranging in this invention, by sparsely controlling the electro-optic frequency comb, allows for sparse variations in the comb tooth spacing of the multiheterodyne interference signal. This generates a tightly spaced multiheterodyne interference signal that satisfies absolute distance measurement and a wide-spaced multiheterodyne interference signal that satisfies relative displacement measurement. A single measurement system can achieve both measurement functions. The mode control module designed in this invention can automatically switch the measurement system between the two measurement modes based on the state of the multiheterodyne interference signal. When the target is stationary, absolute distance measurement is performed first, and then the system automatically switches to the relative displacement measurement mode to meet the needs of subsequent dynamic measurements. If light obstruction or a relative displacement measurement error is detected, the system automatically switches back to the absolute distance measurement mode and re-measures. This automatic switching between the two measurement modes improves the anti-interference capability and stability of the measurement system.

[0102] The above specific embodiments are used to explain and illustrate the present invention, but not to limit the present invention. Any modifications and changes made to the present invention within the spirit and scope of the claims shall fall within the protection scope of the present invention.

Claims

1. A distance displacement measuring device with sparse control of electro-optic frequency comb, characterized in that: It includes a sparse control light source module, a heterodyne interference optical path and a signal processing module. The sparse control light source module and the heterodyne interference optical path are optically connected, and the signal processing module is electrically connected to the sparse control light source module and the heterodyne interference optical path respectively. The sparse control light source module emits light that is transmitted to the heterodyne interference optical path for interferometric measurement. The heterodyne interference optical path outputs two electrical signals, a measurement signal and a reference signal, to the signal processing module. In the signal processing module, the absolute distance measurement submodule and the relative displacement measurement submodule are used for absolute distance measurement and relative displacement measurement data processing, respectively. It also has a dual-mode control unit that can switch between absolute distance measurement mode and relative displacement measurement mode. Under the control of the dual-mode control unit, the sparse control unit emits an electrical signal to the sparse control light source module for sparse control. The signal processing module includes a signal preprocessing submodule, an absolute distance measurement submodule, a relative displacement measurement submodule, a dual-mode control unit, and a sparse control unit; In the signal preprocessing submodule, the output terminals of the two photodetectors are electrically connected to the two amplification and filtering units, respectively. The two output terminals of the two amplification and filtering units are connected to the input terminals of the two analog-to-digital conversion units, respectively. The output terminals of the two analog-to-digital conversion units are simultaneously connected to the input terminals of the absolute distance measurement submodule and the relative displacement measurement submodule, respectively. In the absolute distance measurement submodule, the outputs of the two analog-to-digital conversion units are connected to the inputs of the two fast Fourier transform units, and the outputs of the two fast Fourier transform units are connected to one input of the adder via the synthesized wavelength phase calculation unit and the absolute distance calculation unit. In the relative displacement measurement submodule, the outputs of the two analog-to-digital conversion units are connected to the inputs of the two quadrature demodulation units, respectively. The outputs of the two quadrature demodulation units are connected to the other input of the adder via the large-to-small number counting unit and the relative displacement calculation unit. Meanwhile, the outputs of a fast Fourier transform unit and a quadrature demodulation unit are connected to the large-to-small number counting unit and the sparse control unit, respectively, via the dual-mode control unit. The output of the sparse control unit is connected to two adjustable signal sources.

2. The distance displacement measuring device with sparse control of electro-optic frequency comb according to claim 1, characterized in that: The sparsely modulated light source module includes a continuous laser, an optical fiber beam splitter, an acousto-optic frequency shifter, a first electro-optic phase modulator, a second electro-optic phase modulator, an optical fiber combiner, and a modulation control module. The output of the continuous laser is connected to the input of the fiber optic beam splitter. One output of the fiber optic beam splitter is connected to the input of the first electro-optic phase modulator via an acousto-optic frequency shifter, and the other output is connected to the input of the second electro-optic phase modulator. The outputs of the first and second electro-optic phase modulators are connected to the fiber optic combiner. The acousto-optic frequency shifter and the two electro-optic phase modulators are all connected to the modulation control module. The fiber optic combiner is connected to the heterodyne interference optical path. The continuous laser emits a continuous laser beam, which is input to the fiber optic beam splitter and split into two continuous laser beams. The two continuous laser beams are each converted into two modulated laser beams with different phase modulations at different frequencies after passing through their respective electro-optic phase modulators. The two modulated laser beams are input to the fiber optic combiner with slow-axis and fast-axis polarization states, respectively, and then combined to form a combined beam that is output to the heterodyne interference optical path. The modulation control module and the signal processing module are electrically connected.

3. The distance displacement measuring device with sparse control of electro-optic frequency comb according to claim 2, characterized in that: The modulation control module includes a driver amplifier, a first broadband amplifier, a second broadband amplifier, a rubidium atomic clock, a power divider, a first adjustable signal source, and a second adjustable signal source. The rubidium atomic clock is connected to the input of the power divider, and the output of the power divider is connected to the driver amplifier, the first adjustable signal source, and the second adjustable signal source, respectively. The first adjustable signal source and the second adjustable signal source are connected to the first broadband amplifier and the second broadband amplifier, respectively. The driver amplifier, the first broadband amplifier, and the second broadband amplifier are connected to the acousto-optic frequency shifter, the first electro-optic phase modulator, and the second electro-optic phase modulator of the modulation module, respectively.

4. The distance displacement measuring device with sparse control of electro-optic frequency comb according to claim 1, characterized in that: The heterodyne interference optical path includes a collimator, a beam splitter, a polarizing beam splitter, a reference corner cube prism, a measuring corner cube prism, a first analyzer, a second analyzer, a first photodetector, and a second photodetector. The combined laser beam output from the sparsely controlled light source module is collimated to the slow axis and P-polarized state by a collimator and input to a beam splitter for reflection and transmission. The reflected beam from the beam splitter is then passed through a second analyzer and incident on a second photodetector to obtain a reference signal. The transmitted beam from the beam splitter is then input into a polarizing beam splitter for transmission and reflection according to the rule of P-polarized state transmission and S-polarized state reflection. The reflected beam from the polarizing beam splitter is input into a reference pyramidal prism, undergoes internal retroreflection, and returns to the polarizing beam splitter for reflection to form a reference beam. The transmitted beam from the polarizing beam splitter is input into a measuring pyramidal prism, undergoes internal retroreflection, and returns to the polarizing beam splitter for transmission to form a measuring beam. Both the reference beam and the measuring beam exit from the polarizing beam splitter, pass through a first analyzer, and are then incident on a first photodetector to obtain a measuring signal. Both the first and second photodetectors are electrically connected to the signal processing module.

5. A method for measuring absolute distance and relative displacement using electro-optic frequency comb sparse modulation applied to any of the distance and displacement measuring devices described in claims 1-4, characterized in that: The method includes the following: 1) The continuous laser is split into two continuous laser beams with a power ratio of 50:50 by the fiber beam splitter. One of the continuous laser beams is first frequency-shifted by an acousto-optic frequency shifter. The frequency-shifted continuous laser beam and the other continuous laser beam are respectively subjected to high-frequency sinusoidal phase modulation by a pair of frequency-adjustable first electro-optic phase modulators and second electro-optic phase modulators in the optical modulation module to generate a pair of laser beams with dual electro-optic frequency combs. 2) A pair of laser beams with dual electro-optic frequency combs are combined by an optical fiber combiner and then input into a heterodyne interference optical path to obtain a reference signal and a measurement signal, respectively. The reference signal and the measurement signal are demodulated and processed to obtain the distance / displacement of the object under test, and then transmitted to the host computer via a network cable. 3) The first and second electro-optic phase modulators in the optical modulation module are used to sparsely or non-sparsely modulate the repetition frequency of the electro-optic frequency comb in the laser that passes through it, so that the comb tooth spacing of the reference and measurement signals of the multi-heterodyne interference changes sparsely, forming different working measurement modes, and switching between them.

6. The method for measuring absolute distance and relative displacement according to claim 5, characterized in that: The frequency settings of the dual electro-optic frequency comb are as follows: f S[i] (M)= f c +i* f1(M) f L[i] (M)=( f c – f a )+i* f2(M) Where M represents the measurement mode, M=0 represents the absolute distance measurement mode, and M=1 represents the relative displacement measurement mode; f1(M) and f2(M) represent the frequencies of the first and second electro-optic phase modulators, respectively; f S[i] (M) and f L[i] (M) represents the laser frequency of the comb tooth with index i in the signal electro-optic frequency comb and the local electro-optic frequency comb output by the second electro-optic phase modulator and the first electro-optic phase modulator, respectively. c f represents the frequency of a continuous laser. a The frequency of the acousto-optic frequency shifter is represented by i, which represents the order of the comb teeth in the dual electro-optic frequency comb, i=0,±1,±2,…,±Q, where Q represents the maximum order.

7. The method for measuring absolute distance and relative displacement according to claim 5, characterized in that: Step 3) specifically refers to: When sparse control is not performed, absolute distance measurement is conducted in absolute distance measurement mode. A Fast Fourier Transform (FFT) is simultaneously performed on both the reference and measurement signals to obtain the phase difference of each frequency component. The phase of the synthesized wavelength constructed in the corresponding electro-optic frequency comb is then calculated, and the final absolute distance is determined based on the synthesized wavelength. L ADM ; When performing sparse control, relative displacement measurement is performed in the relative displacement measurement mode. Phase demodulation is performed on the reference interference signal and the measurement interference signal to obtain two phase differences. After unpacking the two phase differences by counting their magnitudes, the two unpacked phase differences are combined with the wavelength of the comb teeth of the electro-optic frequency comb to obtain the two relative displacement values ​​R1 and R2 of the object under test. Finally, the relative displacement measurement result is obtained based on the two relative displacement values ​​R1 and R2.

8. The method for measuring absolute distance and relative displacement according to claim 5, characterized in that: In step 3), the dual-mode control unit determines whether the object under test is stationary or moving based on the spectrum of the reference signal and the measurement signal, and then controls it accordingly. When stationary, the sparse modulation unit controls the sparse modulation of the electro-optic frequency comb repetition frequency of the two continuous laser beams and switches to the absolute distance measurement mode to obtain the initial absolute distance value. L ADM Then switch to relative displacement measurement mode to obtain real-time relative displacement values. R (t), and then add them together to get the distance measurement result of the object to be measured; When in motion, the frequency components F1(1) and F in the measurement signal and reference signal are respectively demodulated by two quadrature demodulation units. -1 (1) Simultaneously perform phase demodulation of two signals and transmit the phase demodulation results to the large and small number counting unit to obtain two phase differences φ1(t) and φ2(t) after subtraction. During the movement of the object under test, the large and small number counting unit simultaneously counts the two phase differences to obtain the two phase differences after unwrapping. In the relative displacement calculation module, the two phase differences after unpacking are multiplied by the wavelengths of the comb teeth numbered 1 and -1 in the corresponding electro-optic frequency comb, and then the two relative displacements of the object under test are obtained based on the wavelengths. R 1 and R 2; When the final determination is that the deviation between the two relative displacements is less than the preset deviation value, the relative displacement measurement is normal, and the average of the two values ​​is taken as the result.

9. The method for measuring absolute distance and relative displacement according to claim 5, characterized in that: In relative displacement measurement mode, the strength of the measurement signal is continuously monitored and processed. The dual-mode control unit determines whether abnormal interference such as light outage has occurred based on the measured signal strength output by the first quadrature demodulation unit. When the measured signal strength suddenly drops to zero, a command is sent to the sparse control unit to automatically switch to the absolute distance measurement mode. After the spectrum of the measured signal output by the first fast Fourier transform unit returns to normal, the absolute distance measurement is performed. Then, a command is sent to the sparse control unit to automatically switch back to the relative displacement measurement mode. The sparse control unit sends serial port commands to the first and second adjustable signal sources through a serial port line to control the output signal frequency, thereby realizing the sparse control of the electro-optic frequency comb.

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