A real-time absolute distance measurement system and method based on a hybrid electro-optic frequency comb

Abstract

The application discloses a kind of real-time absolute distance measurement system and method based on hybrid electro-optical frequency comb.The carrier comb module is modulated to emit the light beam of carrier comb, and the electro-optical frequency comb module is modulated to emit the light beam of electro-optical frequency comb and the light beam of local electro-optical frequency comb respectively, the light beam of electro-optical frequency comb and carrier comb is combined into the light beam of hybrid electro-optical frequency comb, and the light beam of hybrid electro-optical frequency comb and local electro-optical frequency comb is input to measurement optical path module to generate multi-heterodyne interference, and multi-heterodyne interference signal is output to signal processing module for analysis measurement.The application can construct a series of synthetic wavelengths from large to small at the same time, and is used for absolute distance measurement, to realize large-range high-precision real-time absolute distance measurement finally.

Description

Technical Field

[0001] This invention belongs to the field of laser absolute distance measurement technology, specifically an absolute distance measurement method, and more particularly a hybrid electro-optic frequency comb absolute distance measurement system and method. Background Technology

[0002] Laser absolute distance measurement technology is widely used in precision assembly, robot calibration and other fields. In these application scenarios, in addition to higher requirements for measurement accuracy and measurement range, real-time and high-speed measurement capabilities are also becoming a core requirement.

[0003] Achieving both long-range and high-precision real-time measurement is a common challenge in existing absolute distance measurement methods. For example, frequency scanning interferometry requires measuring phase changes during the scanning process, and the measurement result is only obtained after the scan is completed, making it suitable for measuring the absolute distance of static targets. Dispersive interferometry requires a spectrometer to distinguish interference fringes, and its unambiguous distance and real-time performance are limited by the spectrometer's performance, making it difficult to achieve large-scale and high-speed real-time measurement. Femtosecond pulse alignment time-of-flight method requires adjusting the optical comb repetition frequency to extend the unambiguous distance, limiting the measurement's real-time performance. Multiwavelength interferometry constructs a meter-scale synthetic wavelength chain by locking multiple lasers to an optical frequency comb, achieving high accuracy, but the unambiguous distance is still limited by the optical frequency comb repetition frequency. Multiheterodyne interferometry's unambiguous distance is limited by the modulation frequency, typically on the order of centimeters, and requires time-division measurement steps with adjusted repetition frequencies to extend it, limiting the improvement in real-time performance.

[0004] In summary, simultaneously constructing a chain of synthetic wavelengths from large to small and demodulating the fractional phase of each synthetic wavelength simultaneously to calculate the absolute distance in real time is the key to achieving long-distance, high-precision real-time absolute distance measurement. Summary of the Invention

[0005] To address the problems existing in the background art, this invention discloses a real-time absolute distance measurement system and method based on a hybrid electro-optic frequency comb. A carrier comb is mixed into the electro-optic frequency comb to generate a hybrid electro-optic frequency comb, which is used to simultaneously construct a synthetic wavelength chain from large to small. The absolute distance is then calculated in real time by combining phase synchronization demodulation technology with the transition calculation of the synthetic wavelength chain.

[0006] The method mainly includes the following steps:

[0007] I. A real-time absolute distance measurement system based on a hybrid electro-optic frequency comb:

[0008] It includes a carrier comb module, an electro-optic frequency comb module, a measurement optical path module, an optical fiber combiner, and a signal processing module;

[0009] The output of the carrier comb module and one output of the electro-optic frequency comb module are both connected to the two inputs of the fiber optic combiner. The output of the fiber optic combiner and the other output of the electro-optic frequency comb module are respectively input to the two inputs of the measurement optical path module after passing through the first collimator and the second collimator. The two outputs of the measurement optical path module are connected to the signal processing module. The moving part in the measurement optical path module is fixedly connected to the object / target under test.

[0010] The carrier comb module modulates and emits beam signals (laser) with different frequencies of carrier comb in the light intensity. The electro-optic frequency comb module modulates and emits beam signals with electro-optic frequency comb and frequency-shifted beam signals with local electro-optic frequency comb. The beam signals with electro-optic frequency comb and the beam signals with carrier comb are input together to the fiber optic combiner to form a beam signal with a hybrid electro-optic frequency comb. The beam signals with hybrid electro-optic frequency comb and the beam signals with local electro-optic frequency comb are input together to the measurement optical path module to generate multi-heterodyne interference, so that the multi-heterodyne interference signal with the motion information of the object / target under test is obtained. The measurement optical path module outputs the multi-heterodyne interference signal to the signal processing module for analytical measurement.

[0011] The carrier comb module includes multiple signal sources, an RF combiner, a low-pass filter, a laser driving circuit, and a carrier light source. The outputs of the multiple signal sources are connected to the input of the RF combiner. The output of the RF combiner is connected to the control terminal of the carrier light source after passing through the low-pass filter and the laser driving circuit. The output of the carrier light source contains beam signals with different frequencies of carrier comb in its light intensity and is connected to one input of the fiber optic combiner.

[0012] The electro-optic frequency comb module includes a seed light source, an optical fiber beam splitter, an acousto-optic frequency shifter, a first electro-optic phase modulator, and a second electro-optic phase modulator. The output end of the seed light source 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 first electro-optic phase modulator, and after modulation by the first electro-optic phase modulator, it outputs a beam signal with an electro-optic frequency comb. The other output end of the optical fiber beam splitter is connected to the acousto-optic frequency shifter and the second electro-optic phase modulator, and after modulation by the second electro-optic phase modulator, it outputs a beam signal with a local electro-optic frequency comb.

[0013] The measurement optical path module includes a first polarizing beam splitter, a target mirror, a reference mirror, a second polarizing beam splitter, a first photodetector, and a second photodetector. A beam signal with a hybrid electro-optic frequency comb is incident on the first polarizing beam splitter and undergoes reflection and transmission. The beam signal reflected by the first polarizing beam splitter is incident on the second polarizing beam splitter and undergoes reflection. The beam signal transmitted through the first polarizing beam splitter is reflected back to the first polarizing beam splitter by the target mirror and undergoes retransmission. A beam signal with a local electro-optic frequency comb is incident on the second polarizing beam splitter and undergoes reflection and transmission. The beam signal reflected by the second polarizing beam splitter is incident on the first polarizing beam splitter and undergoes reflection and transmission. The beam signal transmitted through the second polarizing beam splitter is reflected back to the second polarizing beam splitter by the reference mirror and is transmitted again. The beam signal with a hybrid electro-optic frequency comb that is transmitted again through the first polarizing beam splitter and the beam signal with a local electro-optic frequency comb that is reflected through the first polarizing beam splitter are combined to form a measurement beam, which is then incident on the first photodetector and detected and received. The beam signal with a hybrid electro-optic frequency comb that is transmitted through the second polarizing beam splitter and the beam signal with a local electro-optic frequency comb that is reflected again through the second polarizing beam splitter are combined to form a reference beam, which is then incident on the second photodetector and detected and received.

[0014] The reference mirror is fixed in position, and the target mirror is fixed on the object / target to be tested and moves with the object / target to be tested.

[0015] II. A method for measuring real-time absolute distance in a real-time absolute distance measurement system, the method specifically comprising:

[0016] 1) Hybrid electro-optic frequency comb generation

[0017] Seed laser and carrier laser are generated separately. The seed laser is split to generate a beam signal with an electro-optic frequency comb and a beam signal with a local electro-optic frequency comb. The carrier laser generates a beam signal with a carrier comb. The beam signal with an electro-optic frequency comb and the beam signal with a carrier comb are combined to form a beam signal with a hybrid electro-optic frequency comb.

[0018] 2) The beam signal with a hybrid electro-optic frequency comb and the beam signal with a local electro-optic frequency comb undergo multi-heterodyne interference during optical path propagation in the measurement optical path module. Two mixed signals S1(t) and S2(t) with multi-heterodyne interference measurement signal and reference signal are obtained by the photodetector.

[0019] Among them, the beam signal with hybrid electro-optic frequency comb constructs a synthetic wavelength chain from large to small when the optical path propagation in the measurement optical path module undergoes multiple heterodyne interference. The synthetic wavelength chain from large to small includes first-order synthetic wavelength, second-order synthetic wavelength and millimeter-level synthetic wavelength, so that the hybrid electro-optic frequency comb can be used to perform real-time, fast, accurate and efficient absolute distance measurement on the target mirror and the object / target to be measured on it.

[0020] A series of synthetic wavelengths of different sizes, ordered from largest to smallest, constitute a synthetic wavelength chain.

[0021] 3) The two mixed signals obtained in step 2) containing the absolute distance and phase information of the object / target under test are input to the signal processing module, and the signal processing module analyzes and obtains the accurate value of the absolute distance of the object / target under test.

[0022] Step 1) specifically refers to:

[0023] Two seed lasers are emitted from a seed light source. One seed laser is subjected to high-frequency electro-optic phase modulation by a first electro-optic phase modulator to obtain a beam signal with an electro-optic frequency comb. The other seed laser is subjected to frequency shifting and high-frequency electro-optic phase modulation by an acousto-optic frequency shifter and a second electro-optic phase modulator to generate a beam signal with a local electro-optic frequency comb. Multiple signal sources each generate sinusoidal signals. The sinusoidal signals generated by the multiple signal sources are added together by an RF combiner to obtain a multi-frequency signal. The multi-frequency signal is input to a low-pass filter and a laser driving circuit and is used to modulate the current of a carrier light source, so that the light intensity of the carrier light source changes with the multi-frequency signal (intensity modulation). That is, the light intensity has the same frequency components as the multi-frequency signal, so that the carrier light source generates a beam signal with a carrier comb with different frequencies. The beam signal with the electro-optic frequency comb and the beam signal with the carrier comb are combined by an optical fiber combiner, that is, the electro-optic frequency comb and the carrier comb are combined to obtain a beam signal with a hybrid electro-optic frequency comb.

[0024] A carrier comb output from a carrier source is a laser whose intensity contains a comb-like frequency component, where the carrier refers to the frequency component of the intensity. An electro-optic frequency comb refers to a laser whose spectrum exhibits comb-like characteristics after the seed laser undergoes electro-optic phase modulation. A local electro-optic frequency comb refers to a laser whose spectrum exhibits comb-like characteristics and has a certain frequency shift compared to the electro-optic frequency comb after the seed laser undergoes acousto-optic modulation and electro-optic phase modulation. "Local" here means that the local electro-optic frequency comb resides within the measurement optical path module and is not transmitted to the external measurement target mirror.

[0025] The carrier comb and the electro-optic frequency comb have different wavelengths. The carrier comb light intensity contains the same comb-shaped frequency components as the multi-frequency signal, while the electro-optic frequency comb spectrum has a comb-shaped distribution with electro-optic phase modulation frequencies as intervals.

[0026] The frequency distributions of the beam signal with an electro-optic frequency comb and the beam signal with a carrier comb are pre-set so that when the beam signal with the hybrid electro-optic frequency comb undergoes multi-heterodyne interference during optical path propagation in the measurement optical path module, it constructs a composite wavelength chain from largest to smallest that satisfies the following formula: The wavelength distribution in the beam signal satisfies the following formula from largest to smallest composite wavelength chain:

[0027] The large synthesized wavelength is formed by constructing different frequency components of the carrier comb, as shown in the following formula:

[0028] λ s[i] =c / f p (i)

[0029] Where i represents the sequence number of different frequency carriers, i =1 , 2 ,..M p , M p f represents the maximum sequence number of carriers at different frequencies. p (i) represents the carrier frequency, λ s[i] This represents the first-order synthesized wavelength constructed by the carrier with index i in the carrier comb;

[0030] A larger second-order synthesized wavelength is constructed from the first-order synthesized wavelength, as shown in the following formula:

[0031] λ ss[i1,i2] =(λ s[i1] *λ s[i2] ) / (λ s[i1] -λ s[i2] )

[0032] Where i1 and i2 represent 1 to M p The sequence number of the first-stage synthesized wavelength of different frequency carriers, λ ss[i1,i2] This represents the second-level synthesized wavelength constructed from the first-level synthesized wavelengths of the carrier combs with serial numbers i1 and i2;

[0033] + by electro-optic frequency comb j and- j Different comb teeth of different orders are used to construct millimeter-scale small synthesized wavelengths, as shown in the following formula:

[0034] Λ s[j] =c / (2j*f E )

[0035] Where j = ±1, ±2… M E Indicates the serial number of different comb teeth of the electro-optic frequency comb. M E f represents the largest sequence number of the comb teeth in the electro-optic frequency comb. E Λ represents the modulation frequency of the electro-optic frequency comb.s[j] Indicates the comb tooth sequence number is j comb teeth and - j The synthesized wavelength between the comb teeth.

[0036] In step 2), the beam signal with the hybrid electro-optic frequency comb is split into two beams after entering the measurement optical path module:

[0037] After being reflected by the target mirror, the beam returns and is combined with the beam signal with the local electro-optic frequency comb. The beam is then converted by the first photodetector to obtain a mixed measurement signal S1(t) that includes the carrier comb measurement light intensity signal and the electro-optic frequency comb multi-heterodyne interference measurement signal.

[0038] Another beam signal, after being reflected by two polarizing beam splitters, is combined with the beam signal with a local electro-optic frequency comb reflected by the reference mirror. The beam is then converted by a second photodetector to obtain a reference mixed signal S2(t) that includes the carrier comb reference light intensity signal and the electro-optic frequency comb multi-heterodyne interference reference signal.

[0039] The measured mixed signal S1(t) and the reference mixed signal S2(t) are represented as follows:

[0040] S1(t) = ∑ 3 i=1 A m (i)sin[2πf p (i)t+ψ m (i)] + ∑ 5 j=1 B m (j)sin[2πf d (j)t+φ m (j)]

[0041] S2(t)=∑ 3 i=1 A r (i)sin[2πf p (i)t+ψ r (i)] + ∑ 5 j=1 B r (j)sin[2πf d (j)t+φ r (j)]

[0042] in, i This indicates the sequence number of the different frequency carriers in the carrier comb. j The number f indicates the sequence number of the different frequency comb teeth in the electro-optic frequency comb. p (i) indicates that the carrier comb is indexed as... i The frequency of the carrier frequency, f d (j) indicates that the sequence number of the multiheterodyne interference signal is...j The frequency of the comb tooth components, A m (i) with A r (i) represent the amplitudes of the carrier frequency with index i in the measured light intensity signal and the reference light intensity signal, respectively. m (j) and B r (j) represent the amplitudes of the comb components with index j in the multiheterodyne interferometric measurement signal and the multiheterodyne interferometric reference signal, respectively. m (i) and ψ r (i) represent the phases of the carrier frequencies with index i in the measured light intensity signal and the reference light intensity signal, respectively, φ m (j) and φ r (j) represent the phases of the comb components with index j in the multiheterodyne interferometric measurement signal and the multiheterodyne interferometric reference signal, respectively. t Indicates time.

[0043] Among them, the carrier comb does not interfere with the local electro-optic frequency comb, while the electro-optic frequency comb and the local electro-optic frequency comb undergo multi-heterodyne interference, which is generated at the photodetector.

[0044] Step 3) specifically refers to:

[0045] 31) First, the fractional phase of each synthesized wavelength in the synthesized wavelength chain is demodulated in parallel by the signal processing module;

[0046] 32) Combining the known synthesized wavelengths in the synthesized wavelength chain with the fractional phases obtained in step 31), the large-number phases of each synthesized wavelength in the synthesized wavelength chain are obtained by solving the system of equations:

[0047] L=λ ss[i1,i2] [N SS (i1,i2) + ε SS [i1,i2)] / 2, i1,i2=1,2,…M p

[0048] L=λ s[i] [N S (i) + ε S [(i)] / 2, i=1,2,…M p

[0049] L=Λ s[j] [N Λ (j) + ε Λ [(j)] / 2, j=1,2,…M E

[0050] in, L For the unknown distance to be measured, ε SS (i1,i2),ε S (i), εΛ (j) represents the fractional phase of the second-order composite wavelength, the first-order composite wavelength, and the millimeter-level composite wavelength, respectively, N. SS (i1,i2),N S (i), N Λ (j) represent the large-number phases of the second-order synthesized wavelength, the first-order synthesized wavelength, and the millimeter-level synthesized wavelength, respectively; the synthesized wavelength (λ) ss[i1,i2] , λ s[i] Λ s[j] ) and the corresponding fractional phase (ε) SS (i1,i2),ε S (i), ε Λ (j) are all known variables, and the synthesized wavelength corresponds to a large number of phases (N). SS (i1,i2),N S (i), N Λ (j) is an unknown integer.

[0051] SS represents the second-order synthesized wavelength, and S represents the first-order synthesized wavelength. In practice, according to the synthesized wavelength transition theory, the major phase values ​​are obtained by recursively solving the above equations.

[0052] 33) Based on the largest index M among the obtained millimeter-level synthesized wavelengths E The large-number phase is used to finally obtain the accurate value of the absolute distance between the measured object / target using the following formula:

[0053] L ADM =Λ s[ME] [N Λ (M E ) + ε Λ (M E )] / 2

[0054] Among them, L ADM Indicates the final absolute distance measurement result, Λ s[ME] Indicates that the serial number is M E Millimeter-scale synthesized wavelength, M E N represents the largest index among the millimeter-scale synthesized wavelengths. Λ (M E ) and ε Λ (M E ) respectively represent the sequence number M E The large-number phase and small-number phase corresponding to the millimeter-level synthesized wavelength.

[0055] Based on engineering experience, the synthesized wavelength λ constructed by the carrier comb ss[i1,i2] It can reach hundreds of meters or more, and the corresponding non-fuzzy measurement distance (range) can easily cover 100m; the relative accuracy of the fractional phase of the synthesized wavelength can usually reach 0.001, and the accuracy requirements of each synthesized wavelength are met.

[0056] For a minimum synthesized wavelength in the millimeter range, the corresponding absolute distance measurement accuracy can reach the micrometer level.

[0057] In this invention, the carrier comb and electro-optic frequency comb enable the simultaneous construction of multi-level synthesized wavelengths and the synchronous demodulation of corresponding phases. This allows the fractional phases of all synthesized wavelengths to be obtained at the same time. By combining the known synthesized wavelengths, the absolute distance can be calculated by solving the equations simultaneously. Ultimately, this enables real-time measurement of absolute distance with micron-level precision within a long measurement range of hundreds of meters.

[0058] This invention involves generating an electro-optic frequency comb through high-frequency electro-optic phase modulation of a seed light source. This comb is then combined with a carrier comb generated by low-frequency multi-carrier intensity modulation of a carrier light source via fiber optic bundling to obtain a hybrid electro-optic frequency comb. The carrier comb constructs a series of large composite wavelengths (including first-order and second-order composite wavelengths) on the order of meters and above, while the electro-optic frequency comb constructs a series of small composite wavelengths on the order of millimeters. The hybrid electro-optic frequency comb is used to measure the absolute distance to a target mirror via a measurement optical path. The reflected light is photoelectrically converted into a carrier comb intensity signal and an electro-optic frequency comb multi-heterodyne interference signal by a photodetector. The two signals are synchronously demodulated to obtain the phase information of the large and small composite wavelengths, respectively. The absolute distance is then calculated in real-time using composite wavelength transition calculation.

[0059] This invention can simultaneously construct a series of synthetic wavelengths from large to small, and use them for absolute distance measurement, ultimately achieving large-scale, high-precision real-time absolute distance measurement.

[0060] The beneficial effects of this invention are:

[0061] The real-time absolute distance measurement method based on a hybrid electro-optic frequency comb proposed in this invention uses a hybrid electro-optic frequency comb to simultaneously construct a chain of synthetic wavelengths from large to small. Combined with phase parallel demodulation technology, it realizes the simultaneous measurement of each synthetic wavelength and the real-time calculation of the absolute distance, and finally achieves real-time measurement of the absolute distance over a wide range with high precision. Attached Figure Description

[0062] Figure 1 This is a block diagram illustrating the principle of a real-time absolute distance measurement method based on a hybrid electro-optic frequency comb.

[0063] Figure 2 This is a schematic diagram illustrating the frequency relationship of a hybrid electro-optic frequency comb and the construction of a synthetic wavelength chain.

[0064] In the diagram: 1. First signal source, 2. Second signal source, 3. Third signal source, 4. RF combiner, 5. Low-pass filter, 6. Laser drive circuit, 7. Carrier light source, 8. Fiber optic combiner, 9. First collimator, 10. Second collimator, 11. Seed light source, 12. Fiber optic splitter, 13. Acousto-optic frequency shifter, 14. First electro-optic phase modulator, 15. Second electro-optic phase modulator, 16. First polarization beam splitter, 17. Target mirror, 18. Reference mirror, 19. Second polarization beam splitter, 20. First photodetector, 21. Second photodetector, 22. Signal processing module, 23. Computer. Detailed Implementation

[0065] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0066] like Figure 1 As shown, the system includes a carrier comb module, an electro-optic frequency comb module, a measurement optical path module, an optical fiber combiner 8, a first collimator 9, a second collimator 10, and a signal processing module 22.

[0067] The output of the carrier comb module and one output of the electro-optic frequency comb module are both connected to the two inputs of the fiber optic combiner 8. The output of the fiber optic combiner 8 and the other output of the electro-optic frequency comb module are respectively input to the two inputs of the measurement optical path module via the first collimator 9 and the second collimator 10. The two outputs of the measurement optical path module are connected to the inputs of the signal processing module 22. The moving part in the measurement optical path module is fixedly connected to the object / target under test. In a specific implementation, the first collimator 9 and the second collimator 10 can also be part of the measurement optical path module.

[0068] The carrier comb module emits beam signals (lasers) with different frequencies in light intensity after modulation. The electro-optic frequency comb module emits electro-optic frequency comb beam signals with comb-shaped spectra and local electro-optic frequency comb beam signals with different frequency intervals after frequency shifting. The beam signals with electro-optic frequency combs and the beam signals with carrier combs are input together to the fiber optic combiner 8 to form a beam signal with a hybrid electro-optic frequency comb. The beam signals with hybrid electro-optic frequency combs and the beam signals with local electro-optic frequency combs are input together to the measurement optical path module to generate multi-heterodyne interference, thereby detecting and obtaining multi-heterodyne interference signals with the movement information of the object / target under test. The measurement optical path module outputs the multi-heterodyne interference measurement signal and reference signal to the signal processing module 22 for analytical measurement.

[0069] The carrier comb module includes multiple signal sources 1-3, an RF combiner 4, a low-pass filter 5, a laser driving circuit 6, and a carrier light source 7. The outputs of the multiple signal sources are connected to the input of the RF combiner 4. The output of the RF combiner 4 is connected to the control terminal of the carrier light source 7 after passing through the low-pass filter 5 and the laser driving circuit 6 in sequence. The output of the carrier light source 7 serves as the output of the carrier comb module, outputting beam signals with different frequencies of carrier comb in the light intensity and connecting to one input of the fiber optic combiner 8.

[0070] Multiple signal sources emit electrical signals of different frequencies to the radio frequency combiner 4. After being combined, the signals are then processed by the low-pass filter 5 and input to the laser drive circuit 6 to generate a current modulation signal. The current modulation signal is input to the carrier light source 7 to excite the output light beam signal containing carriers of different frequencies, i.e., the carrier comb.

[0071] The electro-optic frequency comb module includes a seed light source 11, an optical fiber beam splitter 12, an acousto-optic frequency shifter 13, a first electro-optic phase modulator 14, and a second electro-optic phase modulator 15. The output end of the seed light source 11 is connected to the input end of the optical fiber beam splitter 12. One output end of the optical fiber beam splitter 12 is connected to the first electro-optic phase modulator 14, and the beam signal with an electro-optic frequency comb is output after being modulated by the first electro-optic phase modulator 14. The other output end of the optical fiber beam splitter 12 is connected to the acousto-optic frequency shifter 13 and the second electro-optic phase modulator 15, and the beam signal with a local electro-optic frequency comb is output after being modulated by the second electro-optic phase modulator 15.

[0072] The measurement optical path module includes a first collimator 9, a second collimator 10, a first polarizing beam splitter 16, a target mirror 17, a reference mirror 18, a second polarizing beam splitter 19, a first photodetector 20, and a second photodetector 21. The beam signal output from the first collimator 9, which has a hybrid electro-optic frequency comb, is incident on the first polarizing beam splitter 16 and undergoes reflection and transmission. The beam signal transmitted through the first polarizing beam splitter 16 is reflected back to the first polarizing beam splitter 16 by the target mirror 17 and undergoes retransmission. The beam signal reflected by the first polarizing beam splitter 16 is then incident on the second polarizing beam splitter 19 and undergoes reflection. The beam signal output from the second collimator 10, which has a local electro-optic frequency comb, is incident on the second polarizing beam splitter 19 and undergoes reflection and transmission. The second polarizing beam splitter 19 transmits... The beam signal is reflected by the reference mirror 18 and returned to the second polarizing beam splitter 19 for retransmission. The beam signal reflected by the second polarizing beam splitter 19 is incident on the first polarizing beam splitter 16 and reflected. The beam signal with a hybrid electro-optic frequency comb that is retransmitted by the first polarizing beam splitter 16 and the beam signal with a local electro-optic frequency comb that is reflected by the first polarizing beam splitter 16 are combined to form a measurement beam, which is then incident on the first photodetector 20 for detection and reception. The beam signal with a hybrid electro-optic frequency comb that is transmitted by the second polarizing beam splitter 19 and the beam signal with a local electro-optic frequency comb that is reflected by the second polarizing beam splitter 19 are combined to form a reference beam, which is then incident on the second photodetector 21 for detection and reception.

[0073] The reference mirror 18 is fixed in position, and the target mirror 17 is fixed on the object / target to be tested and moves with the object / target to be tested.

[0074] In practice, three signal sources can be set up, namely, a first signal source 1, a second signal source 2, and a third signal source 3, with different signal frequencies emitted by the first signal source 1, the second signal source 2, and the third signal source 3.

[0075] It also includes a computer 23, the output of the signal processing module 22 is connected to the computer 23, and the computer 23 is used to read the calculation data in the signal processing module 22 and send configuration parameters.

[0076] In the embodiments of the present invention, the carrier comb takes three carrier frequencies as an example, the carrier light source wavelength is 808nm, and the seed light source is a frequency-stabilized continuous laser with a wavelength of 780nm.

[0077] The specific implementation is as follows:

[0078] like Figure 1 As shown, the first signal source 1, the second signal source 2, and the third signal source 3 output three sinusoidal signals with different frequencies, each frequency equal to f. p (1), f p (2), f p(3) The signal is added by the radio frequency combiner 4, and then filtered by the low-pass filter 5 to remove harmonics and other interference components. It is then transmitted to the laser drive circuit 6 to modulate the carrier light source 7 with current, so that the carrier of its output laser contains different frequency components, generating a carrier comb. The first signal source 1, the second signal source 2, and the third signal source 3 are all traced to the same high-stability reference clock. The seed light source 11 is split into two paths by the fiber beam splitter 12. One path is subjected to high-frequency electro-optic phase modulation by the first electro-optic phase modulator 14 to output an electro-optic frequency comb, which is then combined with the carrier comb by the fiber beam combiner 8 to obtain a hybrid electro-optic frequency comb. The other seed laser output from the fiber beam splitter 12 is frequency-shifted by the acousto-optic frequency shifter 13 and then subjected to electro-optic phase modulation by the second electro-optic phase modulator 15 to generate a local electro-optic frequency comb.

[0079] The hybrid electro-optic frequency comb and the local electro-optic frequency comb are collimated and output through the first collimator 9 and the second collimator 10, respectively. The hybrid electro-optic frequency comb is split into two laser beams, one transmitted and one reflected, by the first polarizing beam splitter 16. The transmitted portion is incident on the target mirror 17 and returns, ultimately reaching the first photodetector 20. The reflected portion is reflected by the second polarizing beam splitter 19 and ultimately reaches the second photodetector 21. The local electro-optic frequency comb is split into two laser beams, one transmitted and one reflected, by the second polarizing beam splitter 19. The transmitted portion is incident on the reference mirror 18 and returns, ultimately reaching the second photodetector 21. The reflected portion is reflected by the first polarizing beam splitter 16 and ultimately reaches the first photodetector 20. The electro-optic frequency comb in the hybrid electro-optic frequency comb interferes with the local electro-optic frequency comb on the first photodetector 20 and the second photodetector 21. This interference is photoelectrically converted into a multiheterodyne interferometry measurement signal by the first photodetector 20 and into a multiheterodyne interferometry reference signal by the second photodetector 21. In the hybrid electro-optic frequency comb, the carrier comb does not interfere with the first photodetector 20 and the second photodetector 21, directly generating the carrier comb measured light intensity signal and the carrier comb reference light intensity signal. That is, the signal output by the first photodetector 20 includes the carrier comb measured light intensity signal and the multi-heterodyne interferometry measurement signal, and the signal output by the second photodetector 21 includes the carrier comb reference light intensity signal and the multi-heterodyne interferometry reference signal.

[0080] The measurement mixed signal S1(t) output by the first photodetector 20 and the reference mixed signal S2(t) output by the second photodetector 21 can be represented as follows:

[0081] S1(t) = ∑ 3 i=1 A m (i)sin[2πf p (i)t+ψ m (i)] + ∑ 5 j=1 B m(j)sin[2πf d (j)t+φ m (j)]

[0082] S2(t)=∑ 3 i=1 A r (i)sin[2πf p (i)t+ψ r (i)] + ∑ 5 j=1 B r (j)sin[2πf d (j)t+φ r (j)]

[0083] in, i This indicates the sequence number of the different frequency carriers in the carrier comb. j The number f indicates the sequence number of the different frequency comb teeth in the electro-optic frequency comb. p (i) indicates that the carrier comb is indexed as... i The frequency of the carrier frequency, f d (j) indicates that the sequence number of the multiheterodyne interference signal is... j The frequency of the comb tooth components, A m (i) with A r (i) represent the amplitudes of the carrier frequency with index i in the measured light intensity signal and the reference light intensity signal, respectively. m (j) and B r (j) represent the amplitudes of the comb components with index j in the multiheterodyne interferometric measurement signal and the multiheterodyne interferometric reference signal, respectively. m (i) and ψ r (i) represent the phases of the carrier frequencies with index i in the measured light intensity signal and the reference light intensity signal, respectively, φ m (j) and φ r (j) represent the phases of the comb components with index j in the multiheterodyne interferometric measurement signal and the multiheterodyne interferometric reference signal, respectively. t Indicates time.

[0084] like Figure 2 The diagram shows the frequency relationships and composite wavelength construction of a hybrid electro-optic frequency comb. The dashed box on the left shows the frequency domain diagram of the hybrid electro-optic frequency comb, which consists of a carrier comb and an electro-optic frequency comb. The right side shows the construction diagram of each composite wavelength. The carrier comb forms a large composite wavelength chain, corresponding to... Figure 2 The upper half of the medium-synthesized wavelength chain consists of an electro-optic frequency comb forming a smaller synthesized wavelength chain, corresponding to... Figure 2 The lower half of the synthesized wavelength chain is then used to simultaneously construct the wavelength chain from both large and small sizes. For example... Figure 2 As shown in the mid-carrier comb spectrum diagram, in the embodiment, f p(1) = 241MHz, f p (2) = 242MHz, f p (3) = 271 MHz, and the constructed first-order synthesis wavelengths are: λ s[i] =c / f p (1) = 1.244813m, λ s[2] =c / f p (2) = 1.239669m, λ s[3] =c / f p (3) = 1.107011m. Let λ be one of the λ values. s[1] With λ s[3] To construct a larger second-order synthesis wavelength, λ ss[1,3] =λ s[1] *λ s[3] / (λ s[1] -λ s[3] ) = 10m. Take λ as an example. s[1] With λ s[3] To construct a larger second-order synthesis wavelength, λ ss[1,2] =λ s[1] *λ s[2] / (λ s[1] -λ s[2] =300m.

[0085] In summary, the carrier comb in this embodiment can construct synthesized wavelengths of different sizes, such as 300m, 10m, and 1m. In this embodiment, the modulation frequency f of the electro-optic frequency comb... E =10GHz, by constructing millimeter-scale small synthesized wavelengths using different comb teeth, a series of small synthesized wavelengths can be obtained: Λ s[1] =c / (2f E )=15mm、Λ s[2] =c / (4f E )=7.5mm、Λ s[3] =c / (6f E )=5mm、Λ s[4] =c / (8f E )=3.75mm、Λ s[5] =c / (10f E =3mm. That is, a series of small synthesized wavelengths on the order of millimeters can be constructed by using an electro-optic frequency comb.

[0086] In summary, the four large synthesized wavelengths λ constructed using a carrier comb are... ss[1,2] , λ ss[1,3] , λ s[i] ( i =1,2,3) and 5 small synthesized wavelengths Λ constructed by the electro-optic frequency comb. s[j] ( j=1,2,3,4,5), a synthetic wavelength chain ranging from hundreds of meters to millimeters can be constructed, while simultaneously performing absolute distance measurements. Measurement and reference mixed signals S1(t) and S2(t) are obtained via the first photodetector 20 and the second photodetector 21. The measurement and reference mixed signals are transmitted to the signal processing module 22 for signal processing. The signal processing module 22 includes four stages: signal preprocessing, phase demodulation, synthetic wavelength phase difference calculation, and absolute distance calculation. The preprocessing stage amplifies, filters, and performs digital-to-analog conversion on the two mixed signals, and then transmits them to a field-programmable gate array (FPGA) signal processor for phase demodulation to obtain the phase ψ. m (i), ψ r (i), φ m (j) and φ r (j).

[0087] Then calculate the fractional phase corresponding to each synthesized wavelength, and the carrier comb synthesized wavelength λ. s[i] The corresponding fractional phase is ε S (i)=[ψ m (i)-ψ r (i)] / (2π), carrier comb synthesized wavelength λ ss[1,3] With λ ss[1,2] The corresponding fractional phases are ε SS (1,3)= ε S (1)-ε S (3) with ε SS (1,2)= ε S (1)-ε S (2) Electro-optic frequency combing to synthesize wavelength λ s[i] The corresponding fractional phase is ε Λ (j)={[φ m (j)-φ r (j)]-[φ m (-j)-φ r (-j)]} / (2π). In the absolute distance calculation stage, based on the synthesized wavelengths and fractional phases, the following system of equations is established simultaneously:

[0088] L=λ ss[1,2] [N SS (1,2)+ ε SS [(1,2)] / 2

[0089] L=λ ss[1,3] [N SS (1,3) + ε SS [(1,3)] / 2

[0090] L=λ s[i] [N S (i) + ε S[(i)] / 2, i=1,2,3

[0091] L=Λ s[j] [N Λ (j) + ε Λ [(j)] / 2, j=1,2,3,4,5

[0092] In practical applications, when the distance to be measured L At half of the maximum synthesis wavelength (λ) ss[1,2] When the value is within 150m ( / 2=150m), the corresponding N is... SS When (1,2)=0, the estimated value ε of the distance to be measured can be obtained by calculating using the first formula in the system of equations. SS (1,2)λ ss[1,2] / 2, According to the synthetic wavelength transition theory, the major phase values ​​can be obtained by recursion, and finally the accurate value of the absolute distance can be obtained:

[0093] L ADM =Λ s[5] [N Λ (5) + ε Λ (5)] / 2

[0094] Based on engineering experience, the relative accuracy of the fractional phase can typically reach 0.001, corresponding to the accuracy requirements of the transition for each synthesized wavelength. For the minimum synthesized wavelength Λ s[5] =3mm, corresponding to an absolute distance measurement accuracy of 1.5 micrometers.

[0095] In summary, the hybrid electro-optic frequency comb used in this embodiment can simultaneously construct a synthetic wavelength chain covering 300m to 3mm, corresponding to an unambiguous distance of 150m and a measurement accuracy of 1.5 micrometers. Furthermore, all synthetic wavelengths are constructed simultaneously, and their corresponding phases are demodulated synchronously, ultimately enabling real-time measurement of absolute distances with micrometer-level accuracy over a long measurement range of hundreds of meters.

[0096] 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 real-time absolute distance measurement system based on a hybrid electro-optic frequency comb, characterized in that: It includes a carrier comb module, an electro-optic frequency comb module, a measurement optical path module, an optical fiber combiner (8), and a signal processing module (22); the output end of the carrier comb module and one output end of the electro-optic frequency comb module are both connected to the two input ends of the optical fiber combiner (8), the output end of the optical fiber combiner (8) and the other output end of the electro-optic frequency comb module are respectively input to the measurement optical path module after passing through two collimators, the output end of the measurement optical path module is connected to the signal processing module (22), and the moving part in the measurement optical path module is fixedly connected to the object / target under test; The carrier comb module is modulated to emit beam signals with different frequencies of carrier comb in light intensity. The electro-optic frequency comb module is modulated to emit beam signals of electro-optic frequency comb and beam signals of local electro-optic frequency comb after frequency shift. The beam signals with electro-optic frequency comb and the beam signals with carrier comb are input into the fiber optic combiner (8) to form a beam signal with a hybrid electro-optic frequency comb. The beam signal is then input into the measurement optical path module along with the beam signal of the local electro-optic frequency comb to generate multi-heterodyne interference, so that the multi-heterodyne interference signal of the object / target under test can be detected. Finally, the signal processing module (22) performs analytical measurement.

2. The real-time absolute distance measurement system based on a hybrid electro-optic frequency comb according to claim 1, characterized in that: The carrier comb module includes multiple signal sources, an RF combiner (4), a low-pass filter (5), a laser driving circuit (6), and a carrier light source (7). The output ends of the multiple signal sources are connected to the input end of the RF combiner (4). The output end of the RF combiner (4) is connected to the control end of the carrier light source (7) after passing through the low-pass filter (5) and the laser driving circuit (6) in sequence. The output end of the carrier light source (7) outputs beam signals with different frequencies of carrier comb in the light intensity and is connected to one input end of the fiber optic combiner (8).

3. The real-time absolute distance measurement system based on a hybrid electro-optic frequency comb according to claim 1, characterized in that: The electro-optic frequency comb module includes a seed light source (11), an optical fiber beam splitter (12), an acousto-optic frequency shifter (13), a first electro-optic phase modulator (14), and a second electro-optic phase modulator (15). The output end of the seed light source (11) is connected to the input end of the optical fiber beam splitter (12). One output end of the optical fiber beam splitter (12) is connected to the first electro-optic phase modulator (14), and outputs a beam signal with an electro-optic frequency comb after being modulated by the first electro-optic phase modulator (14). The other output end of the optical fiber beam splitter (12) is connected to the acousto-optic frequency shifter (13) and the second electro-optic phase modulator (15), and outputs a beam signal with a local electro-optic frequency comb after being modulated by the second electro-optic phase modulator (15).

4. The real-time absolute distance measurement system based on a hybrid electro-optic frequency comb according to claim 1, characterized in that: The measurement optical path module includes a target mirror (17), a reference mirror (18), two polarization beam splitters (16, 19), and two photodetectors (20, 21). A hybrid electro-optic frequency comb beam is incident on the first polarization beam splitter (16) for reflection and transmission. The reflected beam is then incident on the second polarization beam splitter (19) for reflection. After transmission, the beam is reflected back to the first polarization beam splitter (16) by the target mirror (17) and transmitted again. A local electro-optic frequency comb beam is incident on the second polarization beam splitter (19) for reflection. After transmission, the beam reflected by the second polarizing beam splitter (19) is incident on the first polarizing beam splitter (16) for reflection. The two beams after reflection and retransmission by the first polarizing beam splitter (16) are combined and then incident on the first photodetector (20). After transmission by the second polarizing beam splitter (19), the beam is reflected by the reference mirror (18) and returns to the second polarizing beam splitter (19) for retransmission. The two beams after transmission and rereflection by the second polarizing beam splitter (19) are combined and then incident on the second photodetector (21).

5. A real-time absolute distance measurement system based on a hybrid electro-optic frequency comb according to claim 4, characterized in that: The reference mirror (18) is fixed in position, and the target mirror (17) is fixed on the object to be tested / target to be tested and moves with the object to be tested / target to be tested.

6. A real-time absolute distance measurement method applied to any one of the real-time absolute distance measurement systems described in claims 1-5, characterized in that: The method is specifically as follows: 1) Hybrid electro-optic frequency comb generation Seed laser and carrier laser are generated separately. The seed laser is split to generate a beam signal with an electro-optic frequency comb and a beam signal with a local electro-optic frequency comb. The carrier laser generates a beam signal with a carrier comb. The beam signal with an electro-optic frequency comb and the beam signal with a carrier comb are combined to form a beam signal with a hybrid electro-optic frequency comb. 2) The beam signal with a hybrid electro-optic frequency comb and the beam signal with a local electro-optic frequency comb undergo multi-heterodyne interference during optical path propagation in the measurement optical path module. Two mixed signals S1(t) and S2(t) with multi-heterodyne interference measurement signal and reference signal are obtained by the photodetector. Among them, the beam signal with hybrid electro-optic frequency comb propagates in the measurement optical path module to form a chain of synthesized wavelengths from large to small. The chain of synthesized wavelengths from large to small includes first-order synthesized wavelengths, second-order synthesized wavelengths and millimeter-level synthesized wavelengths. 3) The two mixed signals obtained in step 2) are input to the signal processing module (22), and the signal processing module (22) analyzes and obtains the accurate value of the absolute distance of the object to be measured / target to be measured.

7. The real-time absolute distance measurement method according to claim 6, characterized in that: Step 1) specifically involves: the seed light source (11) emitting two seed lasers, performing high-frequency electro-optic phase modulation on one seed laser to obtain a beam signal with an electro-optic frequency comb; and using an acousto-optic frequency shifter (13) and a second electro-optic phase modulator (15) to perform frequency shifting and high-frequency electro-optic phase modulation on the other seed laser to generate a beam signal with a local electro-optic frequency comb. Multiple signal sources generate sinusoidal signals, and the sinusoidal signals are added together to obtain a multi-frequency signal. The multi-frequency signal is input and current modulated on the carrier light source (7) so that the carrier light source (7) generates a beam signal with a carrier comb of different frequencies. The beam signal with an electro-optic frequency comb and the beam signal with a carrier comb are combined to obtain a beam signal with a hybrid electro-optic frequency comb.

8. The real-time absolute distance measurement method according to claim 6, characterized in that: The frequency distributions of the beam signal with an electro-optic frequency comb and the beam signal with a carrier comb are preset so that when the beam signal with the hybrid electro-optic frequency comb undergoes multi-heterodyne interference during optical path propagation in the measurement optical path module, a synthetic wavelength chain from large to small is formed that satisfies the following formula.

9. The real-time absolute distance measurement method according to claim 6, characterized in that: In step 2), the beam signal with the hybrid electro-optic frequency comb enters the measurement optical path module and is split into two beams: one beam is reflected by the target mirror (17) and returns, and is combined with the local electro-optic frequency comb beam signal and then photoelectrically converted to obtain the measurement hybrid signal S1(t) of the multi-heterodyne interference measurement signal; the other beam is reflected by two polarizing beam splitters (16, 19) and is combined with the local electro-optic frequency comb beam signal reflected by the reference mirror (18), and then photoelectrically converted to obtain the reference hybrid signal S2(t) of the multi-heterodyne interference reference signal; the two hybrid signals are represented as follows: S1(t)=∑ 3 i=1 A m (i)sin[2πf p (i)t+ψ m (i)] + ∑ 5 j=1 B m (j)sin[2πf d (j)t+φ m (j)] S2(t)=∑ 3 i=1 A r (i)sin[2πf p (i)t+ψ r (i)] + ∑ 5 j=1 B r (j)sin[2πf d (j)t+φ r (j)] in, i and j Indicates the sequence number of the frequency carrier and frequency comb, f p (i) represents the first in the carrier comb i carrier frequency, f d (j) represents the first multiheterodyne interference signal. j Comb tooth component frequency, A m (i) with A r (i) represents the amplitude of the i-th carrier frequency in the measured and reference light intensity signals, B m (j) and B r (j) represents the amplitude of the j-th comb component in the multiheterodyne interferometry measurement and reference signal, ψ m (i) and ψ r (i) represents the phase of the i-th carrier frequency in the measured and reference light intensity signals, φ m (j) and φ r (j) represents the phase of the j-th comb component in the multiheterodyne interferometry and reference signal. t Indicates time.

10. The real-time absolute distance measurement method according to claim 6, characterized in that: Step 3) specifically refers to: 31) First, the fractional phase of each synthesized wavelength in the synthesized wavelength chain is demodulated in parallel by the signal processing module (22); 32) Combining the synthetic wavelengths in the synthetic wavelength chain with the fractional phases obtained in step 31), the large-number phases of each synthetic wavelength in the synthetic wavelength chain are obtained by solving the system of equations: L=λ ss[i1,i2] [N SS (i1,i2) + e SS (i1,i2)] / 2, i1,i2=1,2,…M p L=λ s[i] [N S (i) + ε S (i)] / 2, i=1,2,…M p L=Λ s[j] [N Λ (j) + e Λ (j)] / 2, j=1,2,…M E in, L For the unknown distance to be measured, ε SS (i1,i2),ε S (i), ε Λ (j) represents the fractional phase of the second-order composite wavelength, the first-order composite wavelength, and the millimeter-level composite wavelength, respectively, N. SS (i1,i2),N S (i), N Λ (j) represent the large number phases of the second-order synthesized wavelength, the first-order synthesized wavelength, and the millimeter-level synthesized wavelength, respectively; M p λ represents the maximum sequence number of carriers at different frequencies. s[i] λ represents the first-order synthesized wavelength constructed from carrier number i in the carrier comb; ss[i1,i2] This represents the second-level synthesized wavelength constructed from the first-level synthesized wavelengths of carrier combs numbered i1 and i2; Λ s[j] Indicates the comb tooth sequence number is j comb teeth and - j The synthesized wavelength between the comb teeth; 33) Based on the largest index M among the obtained millimeter-level synthesized wavelengths E The large-number phase is used to obtain the accurate value of the absolute distance between the object and the target being measured using the following formula: L ADM =L s[ME] [N Λ (M E ) + e Λ (M E )] / 2 Among them, L ADM Indicates the final absolute distance measurement result, Λ s[ME] Indicates that the serial number is M E Millimeter-scale synthesized wavelength, M E N represents the largest index among the millimeter-scale synthesized wavelengths. Λ (M E ) and ε Λ (M E ) respectively represent the sequence number M E The large-number phase and small-number phase corresponding to the millimeter-level synthesized wavelength.

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