Dual dynamic sideband multi-heterodyne interference absolute distance measurement device and method

Abstract

The present invention discloses a dual dynamic sideband multi-heterodyne interference absolute distance measurement device and method. A pair of frequency-adjustable electro-optical phase modulators are used to modulate the laser to generate a pair of laser sidebands with different frequency intervals. The two electro-optical phase modulators are driven by a pair of adjustable clock sources with a specific frequency difference; the frequencies of the two laser sidebands are determined by the two adjustable clock sources, and the two adjustable clock sources are controlled to perform fast dynamic frequency hopping, and the frequencies of the two laser sidebands will change rapidly and dynamically accordingly, i.e., dual dynamic sidebands. The frequency difference between the two adjustable clock sources remains unchanged before and after the frequency hopping, and the heterodyne frequency difference between the same-order sidebands of the dual dynamic sidebands remains unchanged. Each dynamic frequency hopping can simultaneously generate multiple variable synthetic wavelengths whose sizes are determined by the adjustable clock source; the dual dynamic sidebands combine heterodyne interference with multi-wavelength interference to measure the distance to be measured. The present invention solves the problem that it is difficult to continuously and accurately construct a synthetic wavelength chain from large to small in absolute distance measurement, and can be widely used in the field of long-length absolute distance measurement.

Description

Technical Field

[0001] The invention relates to an interference absolute distance measurement device and method belonging to the technical field of laser interference measurement, in particular to a dual dynamic sideband multi-heterodyne interference absolute distance measurement device and method. Background Art

[0002] The multi-wavelength interferometry based on synthetic wavelength is widely used in the field of absolute distance interferometry due to its advantages such as flexible synthetic wavelength construction and high measurement accuracy. The key technologies of multi-wavelength interferometry include constructing synthetic wavelengths through multiple different laser wavelengths and separating and high-precision phase discrimination of the corresponding phases of each synthetic wavelength.

[0003] The multi-wavelength interferometry method locked to a femtosecond optical frequency comb utilizes the advantages of the femtosecond optical frequency comb having comb-like frequency characteristics and all comb tooth frequencies can be traced back to a high-stability microwave frequency reference. The tunable laser bias frequency is locked to the femtosecond optical frequency comb to produce a high-power, high-stability multi-wavelength light source, which solves the problem of low comb tooth power of the optical frequency comb. However, when the synthetic wavelength is constructed in time-sharing by locking to different comb teeth, frequent locking and unlocking are required, resulting in low measurement efficiency. The measurement efficiency can be improved when multiple tunable lasers are simultaneously bias-locked to different comb teeth to simultaneously construct synthetic wavelengths, but the number of constructed synthetic wavelengths is limited and a multi-channel bias frequency locking system and a multi-wavelength separation optical path are required, resulting in a complex system structure and high cost. The size of the synthetic wavelength is inversely proportional to the size of the multi-wavelength frequency difference. The multi-wavelength frequency difference locked to the femtosecond optical frequency comb is an integer multiple of the optical frequency comb repetition frequency. The maximum synthetic wavelength constructed is limited by the size of the optical frequency comb repetition frequency. Usually, only a meter-level synthetic wavelength can be constructed, which is difficult to meet the requirements of large-length absolute distance measurement.

[0004] Compared with the multi-wavelength interferometry method locked to a femtosecond optical frequency comb, the multi-heterodyne interferometry absolute distance measurement method based on the electro-optical frequency comb uses electro-optical modulation of continuous laser to generate a comb-shaped multi-wavelength light source for absolute distance measurement. It does not require a complex bias frequency locking system, and the multi-heterodyne interference method allows each wavelength interference signal to be distinguished from the spectrum, which simplifies the signal processing system and has the advantages of high measurement efficiency and relatively simple system structure. Among them, the cavity-enhanced dual electro-optical frequency comb multi-heterodyne interferometry method uses a fixed frequency dual-phase modulator with a small frequency difference and a Fabry-Perot cavity to perform multiple sinusoidal phase modulations on the single-frequency laser to widen the width of the electro-optical frequency comb, which plays a role in compressing the minimum synthetic wavelength and improving the measurement accuracy. However, the maximum synthetic wavelength is only tens of millimeters, and the initial value of the distance to be measured needs to be obtained in advance by other methods. In addition, the signal is collected to the computer using a data acquisition card and then phase demodulation is achieved through offline software processing, which limits the improvement of measurement efficiency and accuracy. The triple electro-optic frequency comb multi-heterodyne interferometry method uses three sets of cascaded fixed-frequency intensity modulators and phase modulators for multiple modulations to generate three electro-optic frequency combs with a small frequency difference. Two of the electro-optic frequency combs are used as measurement light sources at the same time to construct a synthetic wavelength of hundreds of meters, solving the problem of small measurement range of the dual electro-optic frequency comb multi-heterodyne interferometry method. However, the driving signals of each modulator need to be phase matched, which increases the hardware requirements. In addition, the numerous modulators and supporting driving circuits increase the complexity and cost of the system.

[0005] Therefore, how to continuously construct multi-level synthetic wavelengths from large to small, and how to achieve high-speed and high-precision demodulation of multi-wavelength phases are key technical issues that need to be solved. Summary of the invention

[0006] In order to solve the problems existing in the background technology, the present invention discloses a dual dynamic sideband multi-heterodyne interference absolute distance measurement device and method, which solves the problem that it is difficult to continuously construct multi-level synthetic wavelengths from large to small in the multi-heterodyne interference absolute distance measurement method.

[0007] The technical solution adopted by the present invention to solve its technical problem is:

[0008] 1. A dual dynamic sideband multi-heterodyne interference absolute distance measurement device:

[0009] The device includes a single-frequency laser, an optical fiber beam splitter, an acousto-optic frequency shifter, a first electro-optic phase modulator, a second electro-optic phase modulator, an orthogonal optical fiber combiner, a collimator, a beam splitter, a polarization beam splitter, a reference corner cube, a measuring corner cube, a driver amplifier, a first broadband amplifier, a second broadband amplifier, a fixed clock source, a first adjustable clock source, a second adjustable clock source, an atomic clock, a computer, a signal processing module, a first photodetector, a second photodetector, a first polarizer and a second polarizer;

[0010] The output end of the single-frequency laser is connected to the input end of the optical fiber beam splitter, the two output ends of the optical fiber beam splitter are respectively connected to the input ends of the acousto-optic frequency shifter and the second electro-optic phase modulator, the output end of the acousto-optic frequency shifter is connected to the input end of the first electro-optic phase modulator, the output end of the first electro-optic phase modulator and the output end of the second electro-optic phase modulator are connected to the two input ends of the orthogonal optical fiber combiner, and the output end of the orthogonal optical fiber combiner is connected to the input end of the collimator; the atomic clock is respectively connected to the input ends of the fixed clock source, the first adjustable clock source and the second adjustable clock source; the output end of the fixed clock source is connected to the input end of the driving amplifier, and the output end of the driving amplifier is connected to the control end of the acousto-optic frequency shifter; the output ends of the first adjustable clock source and the second adjustable clock source are respectively connected to the input ends of the first broadband amplifier and the second broadband amplifier, and the output ends of the first broadband amplifier and the second broadband amplifier are respectively connected to the output end of the first electro-optic phase modulator and the control end of the second electro-optic phase modulator;

[0011] The output end of the collimator outputs spatial light which is incident on a heterodyne interference optical path consisting of a beam splitter, a polarization beam splitter, a reference corner cube, a measuring corner cube, a first photodetector, a second photodetector, a first analyzer and a second analyzer, and two interference signals are collected by the first photodetector and the second photodetector in the heterodyne interference optical path.

[0012] In the heterodyne interference optical path, the output spatial light of the collimator is first incident on the beam splitter prism to be transmitted and reflected, the reflected light of the beam splitter prism is incident on the first photodetector after passing through the first polarizer to obtain a detection interference signal, the transmitted light of the beam splitter prism is then incident on a point of the reference corner cube prism to be transmitted and reflected, the reflected light at one point of the reference corner cube prism is reflected at another point of the reference corner cube prism after reverse reflection inside the reference corner cube prism, the transmitted light at one point of the reference corner cube prism is reverse reflected by the measuring corner cube prism and returns to another point of the reference corner cube prism to be transmitted, the reflected light at another point of the reference corner cube prism is combined with the transmitted light, passes through a reflector, and then passes through a second polarizer to be incident on the second photodetector to obtain a measurement interference signal.

[0013] The measuring corner cube prism and the object to be measured are fixed together.

[0014] It also includes a dual dynamic sideband control and signal processing module, which specifically includes a computer and a signal processing module that are interconnected, and the atomic clock is connected to the input end of the signal processing module; the output end of the computer is connected to the input end of the first adjustable clock source and the second adjustable clock source, the output end of the first photodetector and the second photodetector is connected to the input end of the signal processing module, and the phase output end of the signal processing module is connected to the computer, and the computer is respectively connected to the first adjustable clock source and the second adjustable clock source.

[0015] 2. A dual dynamic sideband multi-heterodyne interference absolute distance measurement method, the method comprising the following steps:

[0016] 1) The single-frequency laser outputs a single-frequency laser and is divided into two laser beams, one of which is obtained by frequency shifting by an acousto-optic modulator (AOM), and the other laser beam and the frequency-shifted laser are subjected to high-frequency sinusoidal phase modulation by a pair of frequency-adjustable high-frequency electro-optic phase modulators (EOPM), generating a pair of dual dynamic sidebands with different frequency intervals and dynamic adjustment.

[0017] 2) Different frequencies are f M[i] (k) and f R[i] The dual dynamic sidebands of (k) are respectively formed into a measuring light and a reference light for multi-heterodyne interference absolute distance measurement through a first beam splitter prism, and the interference signal of the measuring light and the reference light is detected by a photoelectric detector through multi-heterodyne interference to obtain a measuring interference signal and a monitoring interference signal respectively;

[0018] Specifically, step 2) is: different frequencies are f M[i] (k) and f R[i] The dual dynamic sidebands of (k) are combined into an orthogonal laser beam in space through an orthogonal fiber combiner and collimator with a frequency of f. M[i] (k) and f R[i] The dynamic sidebands of (k) are P polarization state and S polarization state, and the frequency is f M[i] (k) and f R[i] The dynamic sidebands of (k) are used as the measurement light and reference light for multi-heterodyne interference absolute distance measurement, and are divided into a reflected beam and a transmitted beam by a beam splitter prism. Both of them contain a frequency of f M[i] (k) and f R[i] The dual dynamic sidebands of (k) are used to monitor drift and measure absolute distance respectively, wherein the reflected laser is detected by a photodetector to obtain a monitoring interference signal of multi-heterodyne interference between the measuring light and the reference light, wherein the dual dynamic sidebands in the transmitted laser are separated into measuring light and reference light by a polarization beam splitter prism, which are respectively reflected back to the polarization beam splitter prism by a measuring corner cube prism and a reference corner cube prism and combined, and detected by a photodetector to obtain a measuring interference signal of multi-heterodyne interference between the measuring light and the reference light.

[0019] 3) The initial frequency difference of the modulation frequency of a pair of electro-optic phase modulators is f c , controlling the modulation frequencies of a pair of electro-optic phase modulators to dynamically hop with the same frequency hopping amount, and obtaining a measured interference signal and a monitored interference signal after each frequency hopping by measuring with a photoelectric detector, obtaining a primary synthetic wavelength according to the interference signal processing, obtaining a secondary synthetic wavelength according to the primary synthetic wavelength, and processing to obtain a synthetic wavelength phase difference between the primary synthetic wavelength and the secondary synthetic wavelength;

[0020] Specifically, step 3): the measuring light constructs a primary synthetic wavelength between the polarization beam splitter prism and the measuring corner cube prism in the measuring path, and processes the measuring interference signal and the monitoring interference signal obtained in step 2) to obtain a synthetic wavelength phase difference of the primary synthetic wavelength; if the dual dynamic sideband has been dynamically frequency-hopped, a secondary synthetic wavelength is constructed according to the primary synthetic wavelength before and after the dynamic frequency hopping, and the synthetic wavelength phase difference of the primary synthetic wavelength is processed to obtain a synthetic wavelength phase difference of the secondary synthetic wavelength;

[0021] Then, the computer sends an instruction to control the first adjustable clock source 16 and the second adjustable clock source 17 to perform dynamic frequency hopping with the same frequency hopping amount. The initial frequency difference is f c , change the output signal frequency, drive the high-frequency electro-optical phase modulator EOPM in step 1) after amplification, and change the frequency interval of the dual dynamic sidebands. Among them, the frequency interval of the reference light and the measurement light dynamic sidebands is equal to the frequency of the output signals of the first adjustable clock source 16 and the second adjustable clock source 17 respectively.

[0022] 4) Sending instructions through the computer to control the dual dynamic sidebands to cyclically execute steps 1) to 3), and a total of P dynamic frequency hopping is performed. During each dynamic frequency hopping, 2Q dynamic sidebands participate in the measurement at the same time and can simultaneously construct Q secondary synthetic wavelengths Λ ss[1] (k),Λ ss[2] (k),Λ ss[3] (k), ... ss[Q] (k), P times of dynamic frequency hopping constructs PQ secondary synthetic wavelengths, and each secondary synthetic wavelength Λ is obtained through step 3). ss[j] (k) corresponds to the synthetic wavelength phase The PQ secondary synthetic wavelengths are recorded as Q×P matrix to obtain the secondary synthetic wavelength matrix Λ ss ;

[0023] Secondary synthetic wavelength matrix Λ ss It is expressed as follows:

[0024]

[0025] 5) After completing the P times of dual dynamic sideband frequency hopping in step 4), the dual dynamic sideband frequency is controlled to jump back to the initial value k=0, and the minimum secondary synthetic wavelength Λ in the secondary synthetic wavelength matrix is ​​used. ss[Q] (P) corresponds to the final synthetic wavelength transition result L ss[Q] (P) is used as the initial value of the synthetic wavelength transition of the first-order synthetic wavelength, and the first-order synthetic wavelength transition is further performed step by step to obtain the first-order synthetic wavelength Λ of each order laser sideband after P dynamic frequency hopping. s[j] (k) The corresponding synthetic wavelength transition result L s[j] , the first-order synthetic wavelength Λ after each dynamic frequency hopping s[j](k) The corresponding synthetic wavelength transition result L s[j] The final absolute distance is obtained by weighted averaging, which can improve the measurement accuracy.

[0026] like Figure 1 The figure shows the frequency relationship of the dual dynamic sidebands and the schematic diagram of the synthetic wavelength construction, wherein the short line with a circle at the top represents the measurement light, the short line with a triangle at the top represents the reference light, the solid line represents the laser sideband before frequency hopping, and the dotted line represents the laser sideband after frequency hopping.

[0027] In the above 3), after each k-th dynamic frequency hopping, the laser frequencies of the measurement light and the reference light in the dual dynamic sideband are set to f M[i] (k) and f R[i] (k):

[0028] f M[i] (k) = f o +i·f r1 (k)

[0029] f R[i] (k)=(f o -f a )+i·f r2 (k)

[0030] Among them, f o represents the frequency of single-frequency laser, f a represents the shift frequency of the acousto-optic frequency shifter, f r1 (k) and f r2 (k) respectively represent the modulation frequencies of a pair of electro-optic phase modulators in the kth dynamic frequency hopping, which are equal to the output signal frequencies of the first adjustable clock source 16 and the second adjustable clock source 17, respectively; k represents the serial number of the modulation frequency of the electro-optic phase modulator, k = 0, 1, 2, 3 ... P, k = 0 represents the initial modulation frequency, k ≥ 1 represents the modulation frequency of the kth dynamic frequency hopping, P represents the total number of dynamic frequency hopping; i represents the order of the laser sideband generated by the modulation, i = 0, ±1, ±2, ... ±Q, Q represents the maximum order; f M[i] (k) and f R[i] (k) represents the laser frequency of the i-th order laser sideband in the measurement light and the reference light after the k-th dynamic frequency hopping, respectively. The subscript M represents the measurement light (Measurement), and the subscript R represents the reference light (Reference).

[0031] In the above 3), the first-order synthetic wavelength Λ is constructed by using the symmetrical positive and negative sidebands in the measurement light according to the measurement interference signal. s[j] (k), the formula is as follows:

[0032]

[0033] Among them, Λ s[j] (k) represents the first-order synthetic wavelength of the j-order laser sideband under the k-th dynamic frequency hopping, the subscript s represents the first order, λ M[j] (k), λ M[-j] (k) respectively represent the laser wavelengths of the j-th order laser sideband and the -j-th order laser sideband in the measurement light, c represents the vacuum light speed; the laser sidebands within ±Q orders are used to construct the synthetic wavelength, j = 1, 2, 3...Q;

[0034] From the above formula, it can be seen that the first-order synthetic wavelength Λ s[j] (k) is determined by the measured light modulation frequency f r1 (k) is determined jointly with the order j.

[0035] The following relationship is established between the kth (k ≥ 1) frequency hopping amount and the modulation frequency of a pair of electro-optical phase modulators:

[0036] Δf r (k) = f r1 (k)-f r1 (k-1) = f r2 (k)-f r2 (k-1)

[0037] Then, after each k-th dynamic frequency hopping, the k-th primary synthetic wavelength and the k-1-th primary synthetic wavelength are used to construct the secondary synthetic wavelength. The formula is as follows:

[0038]

[0039] Among them, Λ ss[j] (k) represents the secondary synthetic wavelength of the j-order laser sideband under the k-th dynamic frequency hopping, the subscript ss represents the secondary, Δf r (k) indicates that the modulation frequencies of the two electro-optical phase modulators are equal to the kth frequency hopping amount of the output signal frequencies of the first adjustable clock source 16 and the second adjustable clock source 17, that is, the frequency difference between before and after the frequency hopping.

[0040] It can be seen that the size of the secondary synthetic wavelength is determined by the frequency hopping amount Δf r (k) determines, that is, the synthesized wavelength is rapidly adjustable; when the laser sidebands within ±Q orders are used to construct the secondary synthetic wavelength, Q secondary synthetic wavelengths can be constructed simultaneously each time the dual dynamic sidebands perform frequency hopping, and the size of the secondary synthetic wavelength is inversely proportional to the laser sideband order.

[0041] The smaller the frequency hopping amount, the larger the secondary synthesized wavelength, and vice versa. By controlling the frequency hopping amount, the secondary synthesized wavelength can be continuously constructed from the km level to the mm level.

[0042] In addition, the frequency hopping of the dynamic sideband is traced back to the atomic clock, ensuring the stability and traceability of the constructed secondary synthetic wavelength.

[0043] In the above 3), the frequency spectrum components of the measured interference signal and the monitored interference signal are:

[0044] F i (k) = f M[i] (k)-f R[i] (k) = f a +i·[f r1 (k)-f r2 (k)]

[0045] Among them, F i (k) represents the frequency difference between the i-th order laser sideband in the measurement light and the i-th order laser sideband in the reference light under the k-th frequency hopping.

[0046] In dual dynamic sideband frequency hopping, the frequency hopping amounts of the two modulation frequencies are equal, so that the frequency difference of the same-order sidebands after each frequency hopping is still equal to the initial frequency difference f c , the frequency of the interference signal spectrum component remains unchanged after each frequency hopping, so the spectrum component is simplified to F i (k) = f a +i·f c In this way, the spectrum components remain unchanged after frequency hopping, which is beneficial to the phase demodulation of the interference signal.

[0047] In the above 3), the measurement and monitoring interference signals are amplified, filtered and down-mixed, and the two signals after down-mixing are processed by a field programmable gate array signal processor (FPGA), and the phase difference of the same-order sideband signal in the measurement interference signal and the monitoring interference signal is obtained according to the following formula:

[0048]

[0049] in, Indicates that the frequency of the measured interference signal under the kth dynamic frequency hopping is equal to F i (k) The phase of the interference signal corresponding to the i-th order laser sideband, Indicates that the frequency of the monitoring interference signal under the kth dynamic frequency hopping is equal to F i (k) The phase of the interference signal corresponding to the i-th order laser sideband, represents the phase difference between the i-th order laser sideband in the measured interference signal and the monitored interference signal;

[0050] Then solve the first-order synthetic wavelength Λ according to the following formula s[j] (k) Synthetic wavelength phase difference With the secondary synthetic wavelength Λ ss[j] (k) Synthetic wavelength phase difference It is expressed as follows:

[0051]

[0052] in, represents the synthetic wavelength phase difference of the first-order synthetic wavelength constructed by the ±j-order laser sidebands in the measurement light under the k-th dynamic frequency hopping, It represents the synthetic wavelength phase difference of the secondary synthetic wavelength constructed by the ±j-order laser sidebands in the measurement light under the k-th dynamic frequency hopping.

[0053] In the above 3), the frequency hopping amount is controlled so that the secondary synthesized wavelength is gradually reduced as the frequency hopping number k increases, and at the same time, the secondary synthesized wavelength is gradually reduced as the dynamic sideband order number j increases during each frequency hopping. ss In the figure, the elements in each column decrease from top to bottom, and the elements in each row decrease from left to right. The secondary synthetic wavelength Λ in the upper left corner ss[1] (1) Maximum, with the largest measurement range, the secondary synthetic wavelength Λ in the lower right corner ss[Q] (P) is the smallest, with higher measurement accuracy.

[0054] In the above 4), a double-loop method is used to synthesize the secondary wavelength matrix Λ ss Perform calculations for synthetic wavelength "column transition" and "row transition" to achieve the transition from Λ ss[1] (1) to Λ ss[Q] (P) Synthetic wavelength transition:

[0055] "Column transition" means that the synthetic wavelength is transitioned from the 1st column to the Pth column column by column, and "row transition" is performed in each column of the synthetic wavelength transition of "column transition", and "row transition" means that the synthetic wavelength chain is transitioned from the 1st row to the Qth row in each column row by row;

[0056] For each column and row of the secondary synthetic wavelength, a synthetic wavelength transition is performed through the secondary synthetic wavelength of the current column and row according to the transition to the current synthetic wavelength transition initial value;

[0057] The synthetic wavelength transition is processed according to the synthetic wavelength transition theory according to the following formula:

[0058]

[0059] Among them, int[] means rounding to the nearest integer, L in Indicates the current synthetic wavelength transition initial value, L out represents the result of synthetic wavelength transition, Λ and ε represent the phase difference between the secondary synthetic wavelength of the current column and the current row and the corresponding synthetic wavelength;

[0060] Finally, the secondary synthetic wavelength matrix Λ is completed ssAll secondary synthetic wavelengths Λ ss[j] (k) to obtain the secondary final synthetic wavelength transition result, that is, the secondary synthetic wavelength Λ of the Pth column and the Qth row ss[Q] (P) The synthetic wavelength transition result L ss[Q] (P).

[0061] For the secondary synthetic wavelength matrix Λ ss The secondary synthetic wavelength of the first column and first row is Λ ss[1] (1) Directly obtain the measured distance result L according to the following formula 1 :

[0062]

[0063] The measured distance result L 1 as the synthetic wavelength transition initial value at the secondary synthetic wavelength in column 1, row 1;

[0064] For the first row of each column starting from the second column, the result of the synthetic wavelength transition of the Qth row of the previous column is used as the initial value of the synthetic wavelength transition; for each column starting from the second row, the result of the synthetic wavelength transition of the previous row of the current column is used as the initial value of the synthetic wavelength transition. In this way, in each column, starting from the second row, the result of the synthetic wavelength transition of the previous row is used as the initial value of the synthetic wavelength transition, and the synthetic wavelength transition is performed row by row downward.

[0065] In the above 5), the primary synthetic wavelength Λ after each dynamic frequency hopping is s[j] (k) The corresponding synthetic wavelength transition result L s[j] The final absolute distance is obtained by weighted average. The calculation process is as follows:

[0066]

[0067] Among them, L ADM This is the final result of the absolute distance measurement using dual dynamic sideband multi-heterodyne interferometry.

[0068] The first-order synthetic wavelength is inversely proportional to the dynamic sideband order number j, and gradually decreases with the increase of j. When the phase detection accuracy is the same, the measurement accuracy will be improved step by step.

[0069] During the measurement process, the secondary synthesized wavelength is larger than the primary synthesized wavelength, and as the secondary and primary synthesized wavelengths continue to shrink, the measurement accuracy continues to improve, and ultimately large-length absolute distance measurement with micron-level accuracy within a kilometer-level measurement range can be achieved.

[0070] In the above 5), the first-order synthetic wavelength transition is further performed step by step, and the first-order synthetic wavelength Λ is obtained according to the synthetic wavelength transition theory. s[j](0) The corresponding synthetic wavelength transition result L s[j] , specifically:

[0071]

[0072] Among them, int[] means rounding to the nearest integer, L ss[Q] (P) represents the final transition result of the secondary synthetic wavelength, L s[j] Represents the j-th order first-order synthetic wavelength transition result.

[0073] The present invention uses a pair of frequency-adjustable electro-optical phase modulators to modulate the laser to generate a pair of laser sidebands with different frequency intervals. The two electro-optical phase modulators are driven by a pair of adjustable clock sources with a specific frequency difference; the frequencies of the two laser sidebands are determined by the two adjustable clock sources, and the two adjustable clock sources are controlled to perform fast dynamic frequency hopping, and the frequencies of the two laser sidebands will change rapidly and dynamically, that is, dual dynamic sidebands; the frequency difference of the two adjustable clock sources remains unchanged before and after the frequency hopping, and the heterodyne frequency difference between the same-order sidebands of the dual dynamic sidebands remains unchanged; each dynamic frequency hopping can simultaneously generate multiple variable synthetic wavelengths whose sizes are determined by the adjustable clock source; the dual dynamic sidebands combine heterodyne interference and multi-wavelength interference to measure the distance to be measured.

[0074] Compared with the background technology, the present invention has the following beneficial effects:

[0075] (1) The variable synthetic wavelength construction method of dual dynamic sidebands in the present invention generates dual dynamic sidebands by modulating a pair of frequency-adjustable phase modulators. Multiple levels of synthetic wavelengths can be simultaneously constructed with only a single frequency hop. The synthetic wavelengths cover the order of kilometers to millimeters, solving the problem of difficulty in continuously and accurately constructing a synthetic wavelength chain from large to small in long-length absolute distance measurement.

[0076] (2) The present invention constructs a synthetic wavelength through dual dynamic sidebands and has the ability to construct a synthetic wavelength by fast frequency hopping. The constructed synthetic wavelength is directly traceable to the atomic clock and has excellent stability. In addition, only a single laser is needed as a light source, and no femtosecond optical frequency comb is needed as a laser frequency reference. No bias frequency locking system is needed, and the locking capability of the bias frequency locking system is not limited. No Fabry-Perot cavity or cascaded multiple modulators are needed, and the system structure is more concise.

[0077] (3) The frequency difference before and after the dual dynamic sideband frequency hopping of the present invention remains unchanged, and the corresponding multi-heterodyne frequency also remains unchanged, which is beneficial to signal processing; a multi-channel phase demodulation method based on FPGA is used to extract multi-wavelength phase, which has the advantages of good real-time performance and high precision.

[0078] In summary, the present invention solves the problems in the multi-heterodyne interference absolute distance measurement method that it is difficult to continuously and accurately construct multi-level synthetic wavelengths from large to small, and the phase detection real-time performance and accuracy are not high enough, and can be widely used in the field of multi-heterodyne interference absolute distance measurement technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0079] Figure 1 It is a schematic diagram of the relationship between laser frequencies before and after dual dynamic sideband frequency hopping and the construction of synthetic wavelength.

[0080] Figure 2 It is a principle block diagram of a device of an embodiment of the method of the present invention.

[0081] In the figure: 1. single-frequency laser, 2. optical fiber beam splitter, 3. acousto-optic frequency shifter, 4. first electro-optic phase modulator, 5. second electro-optic phase modulator, 6. orthogonal optical fiber combiner, 7. collimator, 8. beam splitter, 9. polarization beam splitter, 10. reference corner cube, 11. measuring corner cube, 12. driver amplifier, 13. first broadband amplifier, 14. second broadband amplifier, 15. fixed clock source, 16. first adjustable clock source, 17. second adjustable clock source, 18. atomic clock, 19. computer, 20. signal processing module, 21. first photodetector, 22. second photodetector, 23. first polarizer, 24. second polarizer. DETAILED DESCRIPTION

[0082] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0083] like Figure 2 As shown, the device includes a single-frequency 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 orthogonal optical fiber combiner 6, a collimator 7, a beam splitter 8, a polarization beam splitter 9, a reference corner cube 10, a measuring corner cube 11, a driving amplifier 12, a first broadband amplifier 13, a second broadband amplifier 14, a fixed clock source 15, a first adjustable clock source 16, a second adjustable clock source 17, an atomic clock 18, a computer 19, a signal processing module 20, a first photodetector 21, a second photodetector 22, a first polarizer 23, and a second polarizer 24.

[0084] The output end of the single-frequency laser 1 is connected to the input end of the optical fiber splitter 2, the two output ends of the optical fiber 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 end of the first electro-optic phase modulator 4 and the output end of the second electro-optic phase modulator 5 are connected to the two input ends of the orthogonal optical fiber combiner 6, and the output end of the orthogonal optical fiber combiner 6 is connected to the input end of the collimator 7.

[0085] The atomic clock 18 is connected to the input ends of the fixed clock source 15, the first adjustable clock source 16 and the second adjustable clock source 17 respectively; the output end of the fixed clock source 15 is connected to the input end of the driving amplifier 12, and the output end of the driving amplifier 12 is connected to the control end of the acousto-optic frequency shifter 3; the output ends of the first adjustable clock source 16 and the second adjustable clock source 17 are connected to the input ends of the first broadband amplifier 13 and the second broadband amplifier 14 respectively, and the output ends of the first broadband amplifier 13 and the second broadband amplifier 14 are connected to the output end of the first electro-optical phase modulator 4 and the control end of the second electro-optical phase modulator 5 respectively.

[0086] The output end of the collimator 7 outputs spatial light which is incident on a heterodyne interference optical path consisting of a beam splitter prism 8, a polarization beam splitter prism 9, a reference corner cube prism 10, a measuring corner cube prism 11, a first photodetector 21, a second photodetector 22, a first polarizer 23 and a second polarizer 24. The first photodetector 21 and the second photodetector 22 in the heterodyne interference optical path collect two interference signals of reference and measurement.

[0087] In the heterodyne interference optical path, the output spatial light of the collimator 7 is first incident on the beam splitter 8 to undergo transmission and reflection, the reflected light of the beam splitter 8 is incident on the first photodetector 21 after passing through the first polarizer 23 to obtain a detection interference signal, the transmitted light of the beam splitter 8 is then incident on a point of the reference corner cube prism 10 to undergo transmission and reflection, the reflected light at a point of the reference corner cube prism 10 is reflected at another point of the reference corner cube prism 10 after being reversely reflected inside the reference corner cube prism 10, the transmitted light at a point of the reference corner cube prism 10 is reversely reflected by the measuring corner cube prism 11 and returns to another point of the reference corner cube prism 10 to undergo transmission, the reflected light at another point of the reference corner cube prism 10 is combined with the transmitted light, passes through a reflector, and then passes through the second polarizer 24 to be incident on the second photodetector 22 to obtain a measurement interference signal.

[0088] The measuring corner cube prism 11 and the object to be measured are fixed together.

[0089] It also includes a dual dynamic sideband control and signal processing module, which specifically includes a computer 19 and a signal processing module 20 connected to each other, and the atomic clock 18 is connected to the input end of the signal processing module 20;

[0090] The output end of the computer 19 is connected to the input end of the first adjustable clock source 16 and the second adjustable clock source 17, the output end of the first photodetector 21 and the second photodetector 22 are connected to the input end of the signal processing module 20, the phase output end of the signal processing module 20 is connected to the computer 19, and the computer 19 is respectively connected to the first adjustable clock source 16 and the second adjustable clock source 17.

[0091] Among them, a dual dynamic sideband generation module is composed of a single-frequency laser 1, a 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 orthogonal fiber combiner 6, a driver amplifier 12, a first broadband amplifier 13, a second broadband amplifier 14, a fixed clock source 15, a first adjustable clock source 16, a second adjustable clock source 17 and an atomic clock 18; a heterodyne interference optical path is composed of a beam splitter prism 8, a polarization beam splitter prism 9, a reference corner cube prism 10, a measuring corner cube prism 11, a first photodetector 21, a second photodetector 22, a first polarizer 23 and a second polarizer 24; and a dual dynamic sideband control and signal processing module is composed of a computer 19 and a signal processing module 20.

[0092] like Figure 2 As shown, the laser output by the single-frequency laser 1 is divided into two laser beams with a power ratio of 75:25 by the optical fiber beam splitter 2, wherein the laser beam with a power ratio of 25% is first frequency-shifted by the acousto-optic frequency shifter 3, and the laser beam with a power ratio of 75% and the frequency-shifted laser beam are respectively subjected to high-frequency sinusoidal phase modulation by a pair of frequency-adjustable first electro-optic phase modulators 4 and second electro-optic phase modulators 5, to generate a pair of dual dynamic sidebands with different frequency intervals and dynamically adjustable. The frequencies of the dual dynamic sidebands are respectively expressed as follows:

[0093] f M[i] (k) = f o +i·f r1 (k) (1)

[0094] f R[i] (k)=(f o -f a )+i·f r2 (k) (2)

[0095] Among them, f o represents the laser frequency of single-frequency laser 1, f a represents the frequency shift of the acousto-optic frequency shifter 3, f r1 (k) and f r2 (k) represents the modulation frequency of the first electro-optical phase modulator 4 and the second electro-optical phase modulator 5 respectively, k represents the serial number of the modulation frequency (k=0, 1, 2, 3...P), k=0 represents the initial modulation frequency, k≥1 represents the modulation frequency of the kth dynamic frequency hopping, P=2 represents the total number of dynamic frequency hopping; i represents the order of the laser sideband generated by the modulation (i=0, ±1, ±2,...±Q), and Q represents the maximum order.

[0096] In the dual dynamic sideband generation module, the driving signal of the acousto-optic frequency shifter 3 is generated by a fixed clock source 15 traced back to an atomic clock 18 and is power-amplified by a driving amplifier 12. The driving signals of the first electro-optic phase modulator 4 and the second electro-optic phase modulator 5 are generated by a first adjustable clock source 16 and a second adjustable clock source 17 traced back to an atomic clock 18 and are power-amplified by a first broadband amplifier 13 and a second broadband amplifier 14. The modulation frequency of the first electro-optic phase modulator 4 and the second electro-optic phase modulator 5 is equal to the output signal frequency of the first adjustable clock source 16 and the second adjustable clock source 17. The output signal frequency of the first adjustable clock source 16 and the second adjustable clock source 17 is controlled by a control instruction sent by a computer 19, that is, the frequency hopping control of the dual dynamic sideband can be realized by the computer 19. The frequency is f M[i] (k) and f R[i] The measuring light and the reference light composed of the double dynamic sidebands of (k) are combined into a beam of orthogonal linear polarized light by the orthogonal fiber combiner 6, and the output of the collimator 7 is spatial light, wherein the measuring light and the reference light are in P polarization state and S polarization state respectively, and are incident on a heterodyne interference optical path composed of a beam splitter prism 8, a polarization beam splitter prism 9, a reference corner cube prism 10, a measuring corner cube prism 11, a first photodetector 21, a second photodetector 22, a first polarizer 23 and a second polarizer 24.

[0097] like Figure 1 As shown, when absolute distance measurement is performed in a heterodyne interference optical path, the symmetrical positive and negative order sidebands in the measurement light are used to construct a first-order synthetic wavelength Λ s[j] (k), the formula is as follows:

[0098]

[0099] Among them, λ M[j] (k) = c / f M[j] (k), λ M[-j] (k) = c / f M[-j] (k) respectively represent the laser wavelengths of the j-th and -j-th order laser sidebands in the measurement light, and c represents the vacuum light speed; it is assumed that the laser sidebands within ±Q (Q=5) orders are used to construct the synthetic wavelength, that is, j=1,2,3...Q;

[0100] Obviously, the first-order synthetic wavelength Λ s[j] (k) is determined by the measured light modulation frequency f r1 (k) is determined together with the order j. As the order increases, the first-order synthetic wavelength will shrink and the corresponding measurement accuracy will improve.

[0101] In the embodiment, the initial frequency difference of the modulation frequencies of the two electro-optic phase modulators is f c=1kHz, the modulation frequencies of the two electro-optical phase modulators are controlled to perform dynamic frequency hopping with the same frequency hopping amount. The relationship between the kth (k≥1) frequency hopping amount and the two modulation frequencies can be expressed as follows:

[0102] Δf r (k) = f r1 (k)-f r1 (k-1) = f r2 (k)-f r2 (k-1) (4)

[0103] After the kth dynamic frequency hopping, the kth primary synthetic wavelength and the k-1th primary synthetic wavelength are used to construct the secondary synthetic wavelength. The formula is as follows:

[0104]

[0105] Among them, the size of the secondary synthetic wavelength is determined by the frequency hopping amount Δf r (k) determines, that is, the synthesized wavelength is fast and adjustable; when the laser sideband within ±Q orders is used to construct the secondary synthetic wavelength, Q secondary synthetic wavelengths can be constructed simultaneously each time the dual dynamic sidebands perform frequency hopping, and the size of the secondary synthetic wavelength is inversely proportional to the laser sideband order; the smaller the frequency hopping amount, the larger the secondary synthetic wavelength, and vice versa, the larger the frequency hopping amount, the smaller the secondary synthetic wavelength. At the same time, the frequency hopping amount of the dynamic sideband is traced back to the atomic clock, ensuring the stability and traceability of the constructed secondary synthetic wavelength.

[0106] When the dual dynamic sideband is used for multi-heterodyne interferometry, the spectral components of the monitoring interference signal and the measuring interference signal obtained by the first photodetector 21 and the second photodetector 22 can be expressed as follows:

[0107]

[0108] Since the frequency hopping amounts of the two modulation frequencies are equal during dual dynamic sideband frequency hopping, the frequency difference of the same-order sidebands after each frequency hopping is still equal to the initial frequency difference f c , that is, f r1 (k)-f r2 (k) = f c , corresponding to the frequency of the interference signal spectrum component remains unchanged after each frequency hopping, that is, F i (k) = f a +i·f c , the unchanged spectrum components after frequency hopping are beneficial to the phase demodulation of the interference signal. Taking the 4th-order laser sideband as an example, the frequency difference between the 4th-order laser sideband in the measurement light and the reference light before and after frequency hopping is F 4 (k) = f a +4f c In the embodiment, the frequency shift frequency f a =60MHz, the original interference signal spectrum appears in the form of fa =60MHz as the center frequency and the frequency interval is equal to the frequency difference f c =1kHz comb distribution, the spectrum coverage is 60MHz±5kHz.

[0109] In the signal processing module 20, the interference signal is amplified, filtered and shifted to a frequency of f d =59.99MHz down-mixing, after down-mixing, each spectrum component can be expressed as F' i =(f a -f d )+i·f c The spectrum coverage range is 10±5kHz. The down-mixed signal is transmitted to the field programmable gate array signal processor (FPGA) after analog-to-digital conversion. In the FPGA, 2Q parallel phase demodulation is performed on both signals, and the phase difference of each same-order sideband signal in the measured interference signal and the monitored interference signal is obtained.

[0110] FPGA will obtain the phase difference The phase difference array is transmitted to the computer 19 in the form of an array for absolute distance calculation. In the computer 19, the phase difference array is used by the LabVIEW program Calculate the first-order synthetic wavelength Λ s[j] (k) and the secondary synthetic wavelength Λ ss[j] (k) Synthetic wavelength phase difference π and φ ss[j] (k) = φ s[j] (k)-φ s[j] (k-1), and its relationship with the distance to be measured L can be expressed as follows:

[0111]

[0112] Among them, mod(x) 1 Represents the decimal part of the value x (greater than or equal to 0 and less than 1).

[0113] The computer 19 sends instructions to control the first adjustable clock source 16 and the second adjustable clock source 17 to perform P times of dynamic frequency hopping. After each frequency hopping, the signal processing module 20 solves and records the corresponding synthetic wavelength phase difference φ s[j] (k),φ ss[j] (k), combining the first-level synthetic wavelength and the second-level synthetic wavelength to perform synthetic wavelength chain transition, the process of solving the absolute distance is as follows:

[0114] Each time the frequency hop occurs, 2Q dynamic sidebands are simultaneously involved in the measurement, and Q secondary synthetic wavelengths Λ can be constructed simultaneously ss[j](k), that is, a total of PQ secondary synthetic wavelengths can be generated. For the sake of convenience, these PQ secondary synthetic wavelengths are recorded in the form of a Q×P matrix, as shown below:

[0115]

[0116] The frequency hopping amount is controlled so that the secondary synthesized wavelength is gradually reduced as the frequency hopping number k increases. At the same time, the secondary synthesized wavelength is gradually reduced as the dynamic sideband order number j increases during each frequency hopping. Then, in the secondary synthesized wavelength matrix Λ ss In the figure, the elements in each column decrease from top to bottom, and the elements in each row decrease from left to right. The secondary synthetic wavelength Λ ss[1] (1) Maximum, with the largest measurement range, the secondary synthetic wavelength Λ in the lower right corner ss[Q] (P) is minimum, in the secondary synthetic wavelength matrix Λ ss The absolute distance measurement accuracy is the highest.

[0117] In order to achieve ss[1] (1) to Λ ss[Q] (P) synthetic wavelength chain transition, adopts double cycle mode to calculate synthetic wavelength "column transition" and "row transition", "column transition" refers to the column-by-column synthetic wavelength chain transition from the 1st column to the Pth column, and "row transition" refers to the row-by-row synthetic wavelength chain transition from the 1st row to the Qth row in each column.

[0118] Λ ss In the first column of the matrix, the synthetic wavelength Λ is taken from the first row ss[1] (1) Directly measured distance result Λ ss[1] (1) φ ss[1] (1) / 2 is used as the initial value of the synthetic wavelength transition of this column; starting from the second column, the synthetic wavelength transition result L of the Qth row of the previous column is taken. ss[Q] (k-1) is used as the initial value of the synthetic wavelength transition of the first row of the column. In each column, starting from the second row, the synthetic wavelength transition result L of the previous row is used. ss[j-1] (k) is used as the initial value of the synthetic wavelength transition, and the synthetic wavelength transition is performed row by row downward, and finally the secondary synthetic wavelength Λ ss[j] The synthetic wavelength transition of (k) corresponds to the absolute distance measurement result expressed as L ss[j] (k). The synthetic wavelength transition is performed according to the synthetic wavelength transition theory, and the formula is as follows:

[0119]

[0120] In the formula, int[] means rounding to the nearest integer, L in represents the transition initial value, L outrepresents the transition result, Λ and ε represent the synthetic wavelength and corresponding phase difference of the transition.

[0121] After completing P times of dual dynamic sideband frequency hopping, the computer 19 sends instructions to control the first adjustable clock source 16 and the second adjustable clock source 17 to jump the dual dynamic sideband frequency back to the initial value (k=0). ss[Q] (P) corresponds to the measurement result L ss[Q] (P) as the first-order synthetic wavelength Λ s[j] The transition initial value of (0) is further subjected to the first-order synthetic wavelength transition step by step to obtain the first-order synthetic wavelength Λ s[j] (k) corresponds to the absolute distance measurement result L s[j] , the calculation process is as follows:

[0122]

[0123] In order to further improve the measurement accuracy, the measurement results of each order of the first-order synthetic wavelength are weighted averaged. The calculation process is as follows:

[0124]

[0125] Among them, L ADM This is the final result of the dual dynamic sideband multi-heterodyne interference absolute distance measurement.

[0126] In the embodiment, a total of P=2 dynamic frequency hopping (Δf r (1) = 0.75 MHz, Δf r (2) = 75MHz), a total of ten secondary synthetic wavelengths from 200m to 0.4m are constructed, and the corresponding measurement range is half of the synthetic wavelength, that is, the maximum measurement range can reach 100m. Assume that the phase difference φ of the synthetic wavelength in the signal processing module 20 is s[j] (k),φ ss[j] (k) The relative accuracy of demodulation is 0.1% and 0.2% respectively, then Λ ss[1] (1) = 200m, the corresponding distance measurement accuracy is 0.2m, the secondary synthesis wavelength decreases to ±5th order with the order, and the minimum secondary synthesis wavelength is Λ ss[5] (2) = 0.4m, the corresponding distance measurement accuracy is improved to 0.4mm. The initial value of the measured light modulation frequency is f r1 (0) = 18.75GHz, the first-order synthetic wavelength constructed by the ±1 to ±5 order dynamic sidebands covers 8.0mm to 1.6mm, and the corresponding distance measurement accuracy is 4.0μm to 0.8μm, that is, the distance measurement accuracy of each first-order synthetic wavelength is in the micron level. By weighted averaging the distance measurement results of each first-order synthetic wavelength, the distance measurement accuracy can be further improved. In summary, after the transition of the synthetic wavelength chain, the absolute distance measurement with micron-level accuracy can be finally achieved within a large length range of 100m.

[0127] In summary, the variable synthetic wavelength construction method of the dual dynamic sideband in the present invention generates dual dynamic sidebands through a pair of frequency-adjustable phase modulators, and can simultaneously construct multi-level synthetic wavelengths with only a single frequency hopping. The synthetic wavelength covers the order of kilometers to millimeters, solving the problem that it is difficult to continuously and accurately construct multi-level synthetic wavelengths from large to small in the measurement of long absolute distances. The present invention constructs synthetic wavelengths through dual dynamic sidebands, has the ability to construct synthetic wavelengths by fast frequency hopping, and the constructed synthetic wavelength is directly traced back to the atomic clock, and has excellent stability; and only a single laser is required as a light source, no femtosecond optical frequency comb is required as a laser frequency reference, no offset frequency locking system is required, and the locking capability of the offset frequency locking system is limited, no Fabry-Perot cavity or cascaded multiple modulators are required, and the system structure is more concise. The multi-wavelength phase synchronization extraction based on FPGA is adopted, which has the advantages of good real-time performance and high phase discrimination accuracy. The above specific embodiments are used to explain the present invention, rather than to limit the present invention. Within the spirit of the present invention and the protection scope of the claims, any modifications and changes made to the present invention fall within the protection scope of the present invention.

Claims

1. A dual dynamic sideband multi-heterodyne interferometer absolute distance measurement device, characterized in that: The device comprises a single-frequency 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 orthogonal optical fiber combiner (6), a collimator (7), a beam splitter (8), a polarization beam splitter (9), a reference corner cube prism (10), a measuring corner cube prism (11), a driving amplifier (12), a first broadband amplifier (13), a second broadband amplifier (14), a fixed clock source (15), a first adjustable clock source (16), a second adjustable clock source (17), an atomic clock (18), a computer (19), a signal processing module (20), a first photodetector (21), a second photodetector (22), a first polarization analyzer (23) and a second polarization analyzer (24); The output end of the single-frequency laser (1) is connected to the input end of the optical fiber beam splitter (2), the two output ends of the optical 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 end of the first electro-optic phase modulator (4) and the output end of the second electro-optic phase modulator (5) are connected to the two input ends of the orthogonal optical fiber combiner (6), and the output end of the orthogonal optical fiber combiner (6) is connected to the input end of the collimator (7); the atomic clock (18) is respectively connected to the fixed clock source (15), the first The input ends of the adjustable clock source (16) and the second adjustable clock source (17); the output end of the fixed clock source (15) is connected to the input end of the driving amplifier (12), and the output end of the driving amplifier (12) is connected to the control end of the acousto-optic frequency shifter (3); the output ends of the first adjustable clock source (16) and the second adjustable clock source (17) are respectively connected to the input ends of the first broadband amplifier (13) and the second broadband amplifier (14), and the output ends of the first broadband amplifier (13) and the second broadband amplifier (14) are respectively connected to the output end of the first electro-optic phase modulator (4) and the control end of the second electro-optic phase modulator (5); The output end of the collimator (7) outputs spatial light that is incident on a heterodyne interference optical path composed of a beam splitter prism (8), a polarization beam splitter prism (9), a reference corner cube prism (10), a measuring corner cube prism (11), a first photodetector (21), a second photodetector (22), a first polarizer (23) and a second polarizer (24), and two interference signals are collected via the first photodetector (21) and the second photodetector (22) in the heterodyne interference optical path.

2. The dual dynamic sideband multi-heterodyne interference absolute distance measurement device according to claim 1, characterized in that: In the heterodyne interference optical path, the output spatial light of the collimator (7) is first incident on the beam splitter (8) to be transmitted and reflected, the reflected light of the beam splitter (8) is incident on the first photodetector (21) after passing through the first analyzer (23) to obtain a detection interference signal, the transmitted light of the beam splitter (8) is then incident on a point of the reference corner cube prism (10) to be transmitted and reflected, the reflected light of the point of the reference corner cube prism (10) is reflected at another point of the reference corner cube prism (10) after being reversely reflected inside the reference corner cube prism (10), the transmitted light of the point of the reference corner cube prism (10) is reversely reflected by the measuring corner cube prism (11) and then returns to another point of the reference corner cube prism (10) to be transmitted, the reflected light of the other point of the reference corner cube prism (10) and the transmitted light are combined and then passed through a reflector and then through a second analyzer (24) to be incident on the second photodetector (22) to obtain a measurement interference signal.

3. The dual dynamic sideband multi-heterodyne interference absolute distance measurement device according to claim 1, characterized in that: The invention also comprises a dual dynamic sideband control and signal processing module, which specifically comprises a computer (19) and a signal processing module (20) which are connected to each other, wherein the atomic clock (18) is connected to the input end of the signal processing module (20); the output end of the computer (19) is connected to the input ends of the first adjustable clock source (16) and the second adjustable clock source (17); the output ends of the first photodetector (21) and the second photodetector (22) are connected to the input end of the signal processing module (20); the phase output end of the signal processing module (20) is connected to the computer (19); and the computer (19) is respectively connected to the first adjustable clock source (16) and the second adjustable clock source (17).

4. A dual dynamic sideband multi-heterodyne interference absolute distance measurement method, characterized in that: The method comprises the following steps: 1) The single-frequency laser outputs a single-frequency laser and is divided into two laser beams, one of which is obtained by frequency shifting by an acousto-optic modulator (AOM), and the other laser beam and the frequency-shifted laser are subjected to high-frequency sinusoidal phase modulation by a pair of frequency-adjustable electro-optic phase modulators (EOPM), generating a pair of dual dynamic sidebands with different frequency intervals and dynamic adjustment. 2) The dual dynamic sidebands of different frequencies form the measuring light and the reference light respectively, and the interference signals of the measuring light and the reference light are detected by multi-heterodyne interference, and the measuring interference signal and the monitoring interference signal are obtained respectively; 3) controlling the modulation frequencies of a pair of electro-optic phase modulators to perform dynamic frequency hopping with the same frequency hopping amount, and measuring and obtaining a measured interference signal and a monitored interference signal after each frequency hopping, obtaining a primary synthetic wavelength according to the interference signal processing, obtaining a secondary synthetic wavelength according to the primary synthetic wavelength, and processing and obtaining a synthetic wavelength phase difference between the primary synthetic wavelength and the secondary synthetic wavelength; 4) Control the dual dynamic sidebands to cyclically execute step 1) to step 4), and perform P dynamic frequency hopping times in total. During each dynamic frequency hopping, 2Q dynamic sidebands simultaneously participate in the measurement and can simultaneously construct Q secondary synthetic wavelengths. P dynamic frequency hopping times construct PQ secondary synthetic wavelengths in total. These PQ secondary synthetic wavelengths are recorded as a Q×P matrix to obtain a secondary synthetic wavelength matrix Λ ss ; 5) After completing the P times of dynamic frequency hopping in step 4), the dual dynamic sideband frequency is controlled to jump back to the initial value k=0, with the minimum secondary synthetic wavelength Λ in the secondary synthetic wavelength matrix ss[Q] (P) corresponds to the final synthetic wavelength transition result L ss[Q] (P) is used as the initial value of the synthetic wavelength transition of the first-order synthetic wavelength, and the first-order synthetic wavelength transition is further performed step by step to obtain the first-order synthetic wavelength Λ of each order laser sideband s[j] (k) The corresponding synthetic wavelength transition result L s[j] , the first-order synthetic wavelength Λ after each order of dynamic frequency hopping s[j] (k) The corresponding synthetic wavelength transition result L s[j] The weighted average is performed to obtain the final absolute distance.

5. The dual dynamic sideband multi-heterodyne interference absolute distance measurement method according to claim 4, characterized in that: In the above 3), after each k-th dynamic frequency hopping, the laser frequencies of the measurement light and the reference light in the dual dynamic sideband are set to f M[i] (k) and f R[i] (k): f M[i] (k)=f o +i·f r1 (k) f R[i] (k)=(f o -f a )+i·f r2 (k) Among them, f o represents the frequency of single-frequency laser, f a represents the shift frequency of the acousto-optic frequency shifter, f r1 (k) and f r2 (k) respectively represent the modulation frequencies of a pair of electro-optic phase modulators in the kth dynamic frequency hopping, k represents the modulation frequency sequence of the electro-optic phase modulator, k = 0, 1, 2, 3 ... P, P represents the total number of dynamic frequency hopping; i represents the order of the laser sideband generated by the modulation, i = 0, ±1, ±2, ... ±Q, Q represents the maximum order; f M[i] (k) and f R[i] (k) represents the laser frequency of the i-th order laser sideband in the measurement light and the reference light after the k-th dynamic frequency hopping; f M[j] (k) and f M[-j] (k) respectively denote the laser frequencies of the j-th and -j-th order laser sidebands in the measurement light after the k-th dynamic frequency hopping.

6. The dual dynamic sideband multi-heterodyne interference absolute distance measurement method according to claim 5, characterized in that: In the above 3), the first-order synthetic wavelength Λ is constructed by using the symmetrical positive and negative sidebands in the measurement light. s[j] (k), the formula is as follows: Among them, Λ s[j] (k) represents the first-order synthetic wavelength of the j-order laser sideband under the k-th dynamic frequency hopping, the subscript s represents the first order, λ M[j] (k), λ M[-j] (k) respectively represent the laser wavelengths of the j-th order laser sideband and the -j-th order laser sideband in the measurement light, c represents the vacuum light speed; the laser sidebands within ±Q orders are used to construct the synthetic wavelength, j = 1, 2, 3...Q; The following relationship is established between the kth frequency hopping amount and the modulation frequency of a pair of electro-optical phase modulators: Δf r (k)=f r1 (k)-f r1 (k-1)=f r2 (k)-f r2 (k-1) Then, after each k-th dynamic frequency hopping, the k-th primary synthetic wavelength and the k-1-th primary synthetic wavelength are used to construct the secondary synthetic wavelength. The formula is as follows: Among them, Λ ss[j] (k) represents the secondary synthetic wavelength of the j-order laser sideband under the k-th dynamic frequency hopping, the subscript ss represents the secondary, Δf r (k) represents the kth frequency hopping amount of the modulation frequency of the two electro-optic phase modulators.

7. The dual dynamic sideband multi-heterodyne interference absolute distance measurement method according to claim 4, characterized in that: In the above 3), the measurement and monitoring interference signals are amplified, filtered and down-mixed, and the two signals after down-mixing are processed by a field programmable gate array signal processor (FPGA), and the phase difference of the same-order sideband signal in the measurement interference signal and the monitoring interference signal is obtained according to the following formula: in, Indicates that the frequency of the measured interference signal under the kth dynamic frequency hopping is equal to F i (k) is the phase of the interference signal, Indicates that the frequency of the monitoring interference signal under the kth dynamic frequency hopping is equal to F i (k) is the phase of the interference signal, represents the phase difference between the i-th order laser sideband in the measured interference signal and the monitored interference signal; Then solve the first-order synthetic wavelength Λ according to the following formula s[j] (k) Synthetic wavelength phase difference With the secondary synthetic wavelength Λ ss[j] (k) Synthetic wavelength phase difference It is expressed as follows: f ss[j] (k)=φ ss[j] (k)-φ ss[j] (k-1) in, represents the synthetic wavelength phase difference of the first-order synthetic wavelength constructed by the ±j-order laser sidebands in the measurement light under the k-th dynamic frequency hopping, It represents the synthetic wavelength phase difference of the secondary synthetic wavelength constructed by the ±j-order laser sidebands in the measurement light under the k-th dynamic frequency hopping.

8. The dual dynamic sideband multi-heterodyne interference absolute distance measurement method according to claim 4, characterized in that: In the above 3), the frequency hopping amount is controlled each time so that the secondary synthesized wavelength is gradually reduced as the frequency hopping number k increases. At the same time, the secondary synthesized wavelength is gradually reduced as the dynamic sideband order number j increases during each frequency hopping.

9. The dual dynamic sideband multi-heterodyne interference absolute distance measurement method according to claim 4, characterized in that: In the above 4), a double-loop method is used to synthesize the secondary wavelength matrix Λ ss Perform calculations for the "column transition" and "row transition" of synthetic wavelengths to achieve the transition from Λ ss[1] (1) to Λ ss[Q] (P) Synthetic wavelength transition: "Column transition" refers to the transition of synthetic wavelengths from the 1st column to the Pth column, and "row transition" refers to the transition of synthetic wavelength chains from the 1st row to the Qth row in each column. For each column and row of the secondary synthetic wavelength, a synthetic wavelength transition is performed according to the current synthetic wavelength transition initial value; The synthetic wavelength transition is processed according to the following formula: Among them, int[] means rounding to the nearest integer, L in Indicates the current synthetic wavelength transition initial value, L out represents the result of synthetic wavelength transition, Λ and ε represent the phase difference between the secondary synthetic wavelength of the current column and the current row and the corresponding synthetic wavelength; Finally, the secondary synthetic wavelength matrix Λ is completed ss All secondary synthetic wavelengths Λ ss[j] (k) to obtain the final secondary synthetic wavelength transition result, that is, the secondary synthetic wavelength Λ of the Pth column and the Qth row ss[Q] (P) The synthetic wavelength transition result L ss[Q] (P).

10. The dual dynamic sideband multi-heterodyne interference absolute distance measurement method according to claim 4, characterized in that: In the above 5), the primary synthetic wavelength Λ after each dynamic frequency hopping is s[j] (k) The corresponding synthetic wavelength transition result L s[j] The final absolute distance is obtained by weighted average. The calculation process is as follows: Among them, L ADM This is the final result of the absolute distance measurement using dual dynamic sideband multi-heterodyne interferometry.

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