Single-cavity double-optical-comb absolute distance measurement system and method based on repetition frequency scanning

Abstract

The invention relates to the technical field of ultrafast laser and light quantum, and provides a single-cavity double-optical-comb absolute distance measurement system and method based on repetition frequency scanning. The system comprises a single-cavity double-optical comb system which is used for simultaneously establishing clockwise and anticlockwise propagating mode-locked pulses in an annular cavity through a bidirectional pumping source and outputting a main oscillation optical comb and a local oscillation optical comb through a polarization maintaining optical fiber coupler; a first piezoelectric ceramic and a second piezoelectric ceramic are arranged in the annular cavity, and the first piezoelectric ceramic and the second piezoelectric ceramic are adjusted through a differential driving mode so as to lock and regulate the repetition frequency difference between the main oscillation optical comb and the local oscillation optical comb; the double-optical-comb distance measuring system is used for combining the main oscillation optical comb passing through the Michelson interferometer with the local oscillation optical comb not passing through the Michelson interferometer to generate a radio frequency beat frequency signal; and calculating the real-time absolute distance of the measured target according to the optical path difference of the radio frequency beat frequency signal and the repetition frequency difference of the main oscillation optical comb and the local oscillation optical comb.

Description

Technical Field

[0001] This invention relates to the fields of ultrafast laser and quantum optical technology, and in particular to a single-cavity dual-comb absolute distance measurement system and method based on repetitive frequency scanning. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] Optical frequency comb technology, as an important tool in modern precision measurement, has been widely used in distance measurement, frequency metrology, spectroscopy, and other fields due to its advantages such as extremely high frequency stability, ultra-narrow pulse width, and wide spectral range. Essentially, an optical frequency comb is a broadband light source with a comb-like spectral structure generated by a femtosecond mode-locked laser. In the frequency domain, it manifests as countless discrete, equally spaced spectral lines, which are the teeth of the optical frequency comb. The frequency of the nth tooth can be expressed as... In the formula The repetition frequency of the laser. This refers to the carrier envelope offset frequency. By precisely controlling these two parameters, the optical frequency comb can achieve precise measurements on sub-picosecond timescales and sub-micron spatial scales.

[0004] With the rapid development of micro-nano manufacturing and electronic integration technology, the demand for precision ranging technology is increasing. Optical frequency combs, relying on the aforementioned advantages, can achieve high-precision, wide-range absolute distance measurement. Dual-comb ranging technology is based on two sets of optical frequency combs with slightly different repetition frequencies. It obtains target distance information by measuring their interference signals in the time and frequency domains. Compared with traditional single-comb ranging or coherent detection, dual-comb ranging has significant advantages such as structural stability, no need for mechanical scanning, fast ranging speed, and high resolution.

[0005] Dual-comb ranging utilizes the repetition frequency difference between two optical frequency combs. By detecting the radio frequency beat frequency or time-domain cross-correlation signal between the two combs, optical time delay is measured, and thus the distance is calculated. This technology has the advantages of high resolution and fast measurement, but it suffers from distance ambiguity in practical applications.

[0006] Due to the periodicity of the phase, ranging has an ambiguity range. According to the Nyquist sampling theorem, the frequency of the sampling signal should be at least twice the frequency of the sampled signal. In two-beam ranging, the unambiguous distance... Typically related to the difference in repetition frequency between the two combs Related, and their correspondence is as follows:

[0007] in, At the speed of light, Let be the equivalent refractive index of light in the propagation medium. It can be seen that when high accuracy and a large ranging range are needed, a contradiction arises: improving resolution usually requires stable and relatively small refractive indexes. But small This will introduce a larger blur distance; while increasing It can reduce the blind zone but is not conducive to high-precision measurement.

[0008] In summary, existing technologies suffer from the problem that the fixed repetition frequency difference between the two optical combs makes it difficult to avoid ranging blind spots. Summary of the Invention

[0009] To address the technical problems mentioned above, this invention provides a single-cavity dual-comb absolute distance measurement system and method based on repetition frequency scanning. By achieving bidirectional mode-locked output in a single ring fiber laser and combining a differential-driven piezoelectric ceramic structure with an intelligent feedback algorithm, this invention achieves continuously adjustable and highly stable output of the repetition frequencies of the two optical combs, thereby significantly improving the environmental robustness and repeatability of the system while eliminating ambiguity.

[0010] To achieve the above objectives, the present invention adopts the following technical solution: The first aspect of the present invention provides a single-cavity dual-comb absolute distance measurement system based on repetitive frequency scanning.

[0011] A single-cavity dual-comb absolute distance measurement system based on repetition frequency scanning includes: a single-cavity dual-comb system and a dual-comb ranging system. A single-cavity dual-comb system is used to simultaneously establish clockwise and counterclockwise propagating mode-locked pulses in a ring cavity via a bidirectional pump source, and output a master oscillator comb and a local oscillator comb via a polarization-maintaining fiber coupler; the ring cavity is equipped with a first piezoelectric ceramic and a second piezoelectric ceramic, and the first and second piezoelectric ceramics are adjusted by differential driving mode to lock and control the repetition frequency difference between the master oscillator comb and the local oscillator comb; The dual-comb ranging system is used to combine the master optical comb that passes through the Michelson interferometer with the local optical comb that does not pass through the Michelson interferometer to generate a radio frequency beat frequency signal; based on the optical path difference of the radio frequency beat frequency signal and the repetition frequency difference between the master optical comb and the local optical comb, the real-time absolute distance of the target is calculated.

[0012] Furthermore, the single-cavity dual-comb system includes: a first pump source, a second pump source, a ring cavity, a master oscillator comb generation optical path, a local oscillator comb optical path, and a feedback module. The pump light generated by the first and second pump sources simultaneously establishes clockwise and counterclockwise propagating mode-locked pulses in the ring cavity; one mode-locked pulse enters the master oscillator comb generation optical path to generate the master oscillator comb; the other mode-locked pulse enters the local oscillator comb optical path to generate the local oscillator comb; the feedback module connects the first pump source, the second pump source, the ring cavity, the master oscillator comb generation optical path, and the local oscillator comb optical path, and is used to collect the repetition frequency signals of the master oscillator comb and the local oscillator comb, and adjust the first and second piezoelectric ceramics through differential driving mode to achieve linear scanning and locking of the repetition frequency difference between the master oscillator comb and the local oscillator comb.

[0013] Further, the ring cavity includes: a first polarization-maintaining wavelength division multiplexer, a second polarization-maintaining wavelength division multiplexer, a polarization-maintaining erbium-doped fiber, a saturable absorber, a first polarization-maintaining circulator, a second polarization-maintaining circulator, and a first polarization-maintaining fiber coupler. The clockwise optical path within the ring cavity is as follows: the pump light emitted from the first pump source is input into the polarization-maintaining erbium-doped fiber through the first polarization-maintaining wavelength division multiplexer to generate stimulated emission and produce a first signal light. The first signal light passes sequentially through the second polarization-maintaining wavelength division multiplexer and the first polarization-maintaining fiber coupler, then through the second polarization-maintaining circulator into a section of non-common transmission fiber, and then through the first polarization-maintaining circulator into a saturable absorber to generate a first mode-locked pulse. The first mode-locked pulse passes sequentially through the first polarization-maintaining wavelength division multiplexer, the polarization-maintaining erbium-doped fiber, and the second polarization-maintaining wavelength division multiplexer, and then through the first polarization-maintaining fiber coupler to output a stable first mode-locked pulse laser to the third polarization-maintaining fiber coupler. The counterclockwise optical path within the ring cavity is as follows: the pump light emitted from the second pump source is input into the polarization-maintaining erbium-doped fiber through the second polarization-maintaining wavelength division multiplexer to generate stimulated emission and produce a second signal light. The second signal light passes sequentially through the first polarization-maintaining wavelength division multiplexer and the saturable absorber to generate a second mode-locked pulse. The second mode-locked pulse passes sequentially through the first polarization-maintaining circulator, another section of non-common transmission fiber, and the second polarization-maintaining circulator before entering the first polarization-maintaining fiber coupler. The first polarization-maintaining fiber coupler outputs a stable second mode-locked pulse laser to the second polarization-maintaining fiber coupler. The first polarization-maintaining circulator and the second polarization-maintaining circulator are connected by two non-common transmission optical fibers, and the first piezoelectric ceramic and the second piezoelectric ceramic are respectively fixed on the two non-common transmission optical fibers.

[0014] Furthermore, the optical path generated by the master oscillator optical comb is the same as the optical path structure of the local oscillator optical comb.

[0015] Furthermore, the optical path generated by the master oscillator optical comb includes a second polarization-maintaining fiber coupler, a first photodetector, a first highly nonlinear fiber, a first frequency doubling module, and a third photodetector. After one mode-locked pulse enters the second polarization-maintaining fiber coupler, 1% enters the first photodetector, and 99% sequentially passes through the first highly nonlinear fiber and the first frequency doubling module to enter the third photodetector. The feedback module is connected to the first photodetector and is used to detect the repetition rate signal; the feedback module is also connected to the third photodetector and is used to detect the master oscillator optical comb.

[0016] Furthermore, the local oscillator optical comb optical path includes a third polarization-maintaining fiber coupler, a second photodetector, a second highly nonlinear fiber, a second frequency doubling module, and a fourth photodetector. Another mode-locked pulse enters the third polarization-maintaining fiber coupler, with 1% entering the second photodetector and 99% sequentially passing through the second highly nonlinear fiber and the second frequency doubling module before entering the fourth photodetector. The feedback module is connected to the second photodetector for detecting the repetition rate signal; the feedback module is also connected to the fourth photodetector for detecting the local oscillator optical comb.

[0017] Furthermore, the dual-comb ranging system includes a Michelson interferometer, a second beam splitter, a fifth photodetector, a low-pass filter, and a control module. The master optical comb is incident on the Michelson interferometer to generate an interference reference signal. The second beam splitter combines the interference reference signal with the local optical comb to obtain a radio frequency (RF) beat frequency signal. The RF beat frequency signal is then incident on the fifth photodetector, and after passing through the low-pass filter to reduce the bandwidth and remove noise, it enters the control module. The control module is used to calculate the real-time absolute distance of the target based on the optical path difference of the RF beat frequency signal and the repetition frequency difference between the master optical comb and the local optical comb. The formula is as follows:

[0018] in, The group velocity of the light pulse. To reference and measure the time delay between the interference signals, This represents the difference in repetition frequency between the master optical comb and the local optical comb. This indicates the repetition frequency of the master optical comb; The control module is connected to the feedback module.

[0019] Furthermore, the Michelson interferometer includes: a first beam splitter, a first reflector, and a second reflector. After the master beam comb is incident on the first beam splitter, it is split into a reference beam and a measurement beam. The reference beam is reflected by the first reflector, and the measurement beam is reflected by the second reflector. After the two beams have traveled different optical paths, they return to the first beam splitter to generate an interference reference signal and are incident on the second beam splitter.

[0020] A second aspect of the present invention provides a method for measuring the absolute distance of a single-cavity dual-comb based on repetitive frequency scanning.

[0021] A method for measuring the absolute distance of a single-cavity dual-comb based on repetition frequency scanning, applied to the single-cavity dual-comb absolute distance measurement system based on repetition frequency scanning described in the first aspect, includes: The single-cavity dual-comb system is started, and mode-locked pulses propagating clockwise and counterclockwise are established simultaneously in the ring cavity through a bidirectional pump source. The main oscillator comb and the local oscillator comb are output through the polarization-maintaining fiber coupler. The first and second photodetectors detect the repetition frequency signals at the 1% output terminals of the second and third polarization-maintaining fiber couplers, respectively. The third and fourth photodetectors detect the frequency multiplication signals entering the first and second frequency multiplication modules at the 99% output terminals of the second and third polarization-maintaining fiber couplers, respectively. All detection signals are input to the feedback module. The feedback control module adjusts the first and second piezoelectric ceramics through differential drive mode to lock and control the repetition frequency of the master optical comb and the local optical comb, thereby achieving linear scanning and locking of the repetition frequency difference between the master optical comb and the local optical comb. The main optical comb passing through the Michelson interferometer and the local optical comb not passing through the Michelson interferometer are combined to generate a radio frequency beat frequency signal; the real-time absolute distance of the target is calculated based on the optical path difference of the radio frequency beat frequency signal and the repetition frequency difference between the main optical comb and the local optical comb. During the ranging process, the control module intelligently switches operating modes based on real-time measurement requirements and environmental feedback. By analyzing the radio frequency beat frequency signals corresponding to multiple sets of repetition frequency differences, it determines the target distance and achieves absolute ranging.

[0022] Furthermore, the operating mode also includes: High-precision locking mode with constant repetition frequency: When the absolute distance to the target is determined, and the target is in a relatively stationary or slightly moving state and requires long-term high-precision monitoring, the system automatically switches to the high-precision locking mode with constant repetition frequency; the control module locks the voltage of the first piezoelectric ceramic and the second piezoelectric ceramic through a PID algorithm and stops large-range scanning; based on the error signal output by the feedback module, the first piezoelectric ceramic and the second piezoelectric ceramic are adjusted in reverse to lock the repetition frequency difference at the optimal fixed value; Environmental drift common-mode suppression mode: When the feedback module detects that the first pump source and the second pump source change due to the change in ambient temperature, causing the repetition frequency of the master oscillator and the local oscillator to drift in the same direction and the repetition frequency difference to be relatively stable, the control module enters the common-mode drive state; applies a compensation voltage of the same polarity to the first piezoelectric ceramic and the second piezoelectric ceramic to counteract the change in physical cavity length caused by the environment; pulls the center frequency of the master oscillator and the local oscillator back to the set range, and keeps the repetition frequency difference constant; Loss-of-lock reset mode: When the repetition frequency of any optical comb is detected to jump instantaneously by more than 1MHz within 100ms, or the signal-to-noise ratio of the beat frequency signal drops sharply, it is determined that the mode-lock state is lost. A reset operation is performed on the first and second piezoelectric ceramics, and the driving voltage of the first and second piezoelectric ceramics is instantly reset to the preset intermediate bias point. The mode-lock is then attempted to be restored by mechanical impact. If the reset is ineffective, the control module starts the pump current scanning program, which scans within a range of 10mA near the mode-lock threshold current at a speed of 0.1mA / s to find a new mode-lock operating point. After mode-lock is restored, the system automatically re-executes the variable repetition frequency large-range scanning mode to reconfirm the absolute distance of the target.

[0023] Compared with the prior art, the beneficial effects of the present invention are: This invention provides a single-cavity dual-comb absolute distance measurement system and method based on repetition frequency scanning. The single-cavity dual-comb system employs a bidirectional pumped polarization-maintaining fiber ring laser structure, achieving linear scanning and locking of the repetition frequency difference between the two optical combs through dual piezoelectric ceramic differential driving. The dual-comb ranging system is based on time-of-flight ranging and a Michelson interferometer structure, calculating the target distance by acquiring beat frequency signals and combining them with the dynamic changes in the repetition frequency difference. This invention eliminates the ambiguity range of traditional dual-comb ranging through repetition frequency scanning. Combined with an intelligent multi-mode control strategy, it achieves wide dynamic range absolute distance measurement while maintaining nanometer-level measurement accuracy. Furthermore, the single-cavity structure improves the system's environmental robustness and repeatability, and reduces integration costs. Attached Figure Description

[0024] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0025] Figure 1 This is a structural diagram of a single-cavity dual-comb absolute distance measurement system based on repetitive frequency scanning, as shown in an embodiment of the present invention. Figure 2 This is a structural diagram of the frequency multiplier module shown in an embodiment of the present invention; Figure 3 This is a schematic diagram of the repetition rate locked master oscillator optical comb and local oscillator optical comb shown in an embodiment of the present invention; Figure 4 This is a schematic diagram of a beat frequency signal filtered by a low-pass filter, as shown in an embodiment of the present invention; The components include: 1. First 976nm pump source; 2. Second 976nm pump source; 3. First polarization-maintaining wavelength division multiplexer; 4. Second polarization-maintaining wavelength division multiplexer; 5. Polarization-maintaining erbium-doped fiber; 6. Saturable absorber; 7. First polarization-maintaining circulator; 8. Second polarization-maintaining circulator; 9. First polarization-maintaining fiber coupler; 10. First piezoelectric ceramic; 11. Second piezoelectric ceramic; 12. Second polarization-maintaining fiber coupler; 13. First highly nonlinear fiber; 14. First frequency doubling module; 15. Third polarization-maintaining fiber coupler; and 16. Second highly nonlinear fiber. 17. Second frequency doubling module; 18. First photodetector; 19. Second photodetector; 20. Feedback module; 21. Third photodetector; 22. Fourth photodetector; 23. First beam splitter; 24. First reflector; 25. Second reflector; 26. Second beam splitter; 27. Fifth photodetector; 28. Low-pass filter; 29. ​​Control module; L1. First collimating lens; L2. First focusing lens; PPLN. Periodically polarized lithium niobate crystal; L3. Second collimating lens; L4. Second focusing lens. Detailed Implementation

[0026] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0027] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0028] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0029] As described in the background section, existing technologies suffer from a fixed difference in the repetition frequency of the two optical combs, making it difficult to avoid blind spots in ranging. Furthermore, existing technologies also have the following shortcomings: if the two optical combs originate from different cavities, factors such as temperature drift and mechanical vibration can cause differences in their frequency instability; and the integration and low-cost implementation of the system still face technical bottlenecks that need to be overcome. To address at least one of the above technical problems, this invention provides a single-cavity dual-optical-comb absolute distance measurement system and method based on repetition frequency scanning. The following describes the solution in detail through several embodiments.

[0030] Figure 1This is a structural diagram of a single-cavity dual-comb absolute distance measurement system based on repetition frequency scanning, as shown in an embodiment of the present invention; refer to Figure 1 The single-cavity dual-comb absolute distance measurement system based on repetitive frequency scanning includes: a single-cavity dual-comb system I and a dual-comb ranging system II.

[0031] like Figure 1 As shown, the single-cavity dual-comb system I is a polarization-maintaining fiber ring laser structure based on bidirectional pumping, including: a first 976nm pump source 1, a second 976nm pump source 2, a first polarization-maintaining wavelength division multiplexer (WDM) 3, a second polarization-maintaining wavelength division multiplexer 4, a polarization-maintaining erbium-doped fiber (EDF) 5, a saturable absorber (SA) 6, a first polarization-maintaining circulator (CIR) 7, a second polarization-maintaining circulator 8, and a first polarization-maintaining fiber coupler 9. The bidirectional pumping structure can simultaneously establish clockwise and counterclockwise propagating mode-locked pulse sequences in the ring cavity. The clockwise transmission optical path is as follows: the pump light emitted from the first 976nm pump source 1 is input into the polarization-maintaining erbium-doped fiber 5 through the first polarization-maintaining wavelength division multiplexer 3, where stimulated emission occurs, generating a first signal light. The first signal light passes sequentially through the second polarization-maintaining wavelength division multiplexer 4 and the first polarization-maintaining fiber coupler 9, and is then input from port ① of the second polarization-maintaining circulator 8 and output from port ② of the second polarization-maintaining circulator 8. The signal light then passes through a section of non-common transmission fiber, input from port ③ of the first polarization-maintaining circulator 7, and output from port ① of the first polarization-maintaining circulator 7. It then passes through the saturable absorber 6 to generate a first mode-locked pulse. The first mode-locked pulse passes sequentially through the first polarization-maintaining wavelength division multiplexer 3, the polarization-maintaining erbium-doped fiber 5, and the second polarization-maintaining wavelength division multiplexer 4, and is then output as a stable first mode-locked laser pulse through the first polarization-maintaining fiber coupler 9 to the third polarization-maintaining fiber coupler 15 for subsequent use. The counterclockwise transmission optical path is as follows: the pump light emitted by the second 976nm pump source 2 is input into the polarization-maintaining erbium-doped fiber 5 through the second polarization-maintaining wavelength division multiplexer 4 to undergo stimulated emission and generate a second signal light. The second signal light passes through the first polarization-maintaining wavelength division multiplexer 3 and the saturable absorber 6 in sequence to generate a second mode-locked pulse. The second mode-locked pulse is then input from port ① of the first polarization-maintaining circulator 7 and output from port ② of the first polarization-maintaining circulator 7. Then, the signal light passes through another non-common transmission fiber and is input from port ③ of the second polarization-maintaining circulator 8 and output from port ① of the second polarization-maintaining circulator 8. Finally, the stable second mode-locked pulse laser is output to the second polarization-maintaining fiber coupler 12 via the first polarization-maintaining fiber coupler 9 for subsequent use.

[0032] In this embodiment, the polarization-maintaining erbium-doped fiber 5 is approximately 0.8m long and exhibits anomalous dispersion; the modulation depth of the saturable absorber 6 is approximately 20%, and the relaxation time is approximately 2ps; the first polarization-maintaining circulator 7, the second polarization-maintaining circulator 8, and two bridging transmission fibers form a non-common optical path, with the bridging fibers being PM1550 fibers; the first polarization-maintaining fiber coupler 9 has 2×2 ports and a splitting ratio of 50 / 50, serving as the output end to achieve bidirectional clockwise and counterclockwise output. After passing through the second polarization-maintaining fiber coupler 12 and the third polarization-maintaining fiber coupler 15 respectively, the 1% output end is incident on the first photodetector (PD) 18 and the second photodetector 19 to detect the repetition rate signal and input the data into the feedback module 20. The 99% output end is broadened into a supercontinuum spectrum by passing through the first high nonlinear fiber (HNLF) 13 and the second high nonlinear fiber 16 with the same parameters. Then, it is frequency-doubled by the same first frequency doubling module 14 and the second frequency doubling module 17 to double the long-wavelength component to the short-wavelength end. The frequency-doubled signal is detected by the third photodetector 21 and the fourth photodetector 22 and input into the feedback module 20 for f-2f self-reference to realize the carrier envelope offset frequency. The detection and locking are performed. A first piezoelectric ceramic (PZT) 10 and a second piezoelectric ceramic 11 are fixed on two non-common transmission optical fibers to control the repetition frequency of mode-locked pulses in two directions. and Locking and control are performed. The system's feedback module 20 acquires the two output repetition frequency signals in real time, and adjusts the first piezoelectric ceramic 10 and the second piezoelectric ceramic 11 through differential drive mode to achieve control over the repetition frequency difference. Linear scanning and locking, such as Figure 3 As shown, the final output is obtained by dual optical combs.

[0033] In some embodiments, the second polarization-maintaining fiber coupler 12 and the third polarization-maintaining fiber coupler 15 have the same structure, both having 1×2 ports and a splitting ratio of 1 / 99.

[0034] In some embodiments, the first highly nonlinear fiber 13 and the second highly nonlinear fiber 16 have the same length, approximately 0.5 m, and the nonlinear coefficient γ is approximately... .

[0035] In some embodiments, the structures of the first frequency multiplier module 14 and the second frequency multiplier module 17 are as follows: Figure 2 As shown, it includes: a first collimating lens L1, a first focusing lens L2, a periodically polarized lithium niobate crystal PPLN, a second collimating lens L3, and a second focusing lens L4.

[0036] In some embodiments, the maximum tensile stroke of the first piezoelectric ceramic 10 and the second piezoelectric ceramic 11 is 20 μm, and the control frequency is ≥10 kHz.

[0037] In this embodiment, the dual-comb ranging system II is based on the time-of-flight (TOF) ranging method, and the optical path is a typical Michelson interferometer structure. For example... Figure 1 As shown, the system includes: a first beam splitter 23, a second beam splitter 26, a first reflector (R) 24, a second reflector (M) 25, a fifth photodetector 27, a low-pass filter (LPF) 28, and a control module 29. The first beam splitter 23, together with the first and second reflectors 24 and 25, constitutes a Michelson interferometer. The master oscillator optical comb (comb 1) is incident on the first beam splitter 23 and split into a reference beam and a measurement beam. The reference beam is reflected by the first reflector 24, and the measurement beam is reflected by the second reflector 25. After traveling different optical paths, the two beams return to the first beam splitter 23, generating an interference reference signal which is then incident on the second beam splitter 26. The local oscillator optical comb (comb 2) is incident on the second beam splitter 26, and together with the interference beam returning from the master oscillator optical comb, they are combined and incident on the fifth photodetector 27, forming a cross-heterodyne interference signal band with a relatively wide frequency range, i.e., a radio frequency beat frequency signal. In the time domain, this cross-heterodyne signal exhibits a series of periodic interference peaks. The beat frequency signal bandwidth is then filtered to [a specific value] by low-pass filter 28. Filter out noise outside of DC and bandwidth, such as Figure 4 As shown. The beat frequency signal contains optical path difference information. The absolute distance to the target can be obtained by signal acquisition and phase calculation via control module 30. The measured absolute distance D satisfies the following relationship:

[0038] in, The group velocity of the light pulse. To reference and measure the time delay between the interference signals, the beat frequency signal can be measured by the photodetector 27 and then sent to the control module 29 for Fast Fourier Transform (FFT). During the ranging process, the control module 29 adjusts the driving of the first piezoelectric ceramic 10 and the second piezoelectric ceramic 11 to adjust the repetition frequency difference between the master oscillator optical comb (optical comb 1) and the local oscillator optical comb (optical comb 2). Continuous variation within a certain range enables movement of the blind zone (ambiguity distance) in the frequency domain. This is achieved through multiple sets of... The corresponding beat frequency signal analysis can uniquely determine the target distance, thus achieving absolute ranging.

[0039] This invention utilizes the ability of the first piezoelectric ceramic 10 and the second piezoelectric ceramic 11, which are located in a non-common optical path, to independently control the repetition frequency of the clockwise (CW) and counterclockwise (CCW) optical combs. The control module 29 intelligently switches between the following four operating modes based on real-time measurement requirements and environmental feedback: (1) Variable repetition rate wide-range scanning mode Variable repetition rate wide-range scanning mode is the operating mode when the system starts up or when the target position changes drastically. This mode is used when the system is in the initial ranging phase, or when the detected target distance exceeds the current unambiguous range. When the control module 29 applies a differential scanning voltage to the first piezoelectric ceramic 10 and the second piezoelectric ceramic 11, for example, applying a positive voltage signal to the first piezoelectric ceramic 10 to make it elongate (decrease) Simultaneously, a reverse voltage signal is applied to the second piezoelectric ceramic 11 to cause it to contract (increase). This differential drive causes a difference in the repetition frequency of the two optical combs. Achieve the maximum range of linear changes in a short time (e.g., from) Scan to During this process, the system continuously collects multiple sets of different data. and the corresponding beat frequency signal delay Using these dynamically changing data sets, control module 29 uses the Time-of-Flight (TOF) formula:

[0040] Perform joint solution by analyzing real-time data sets ( and The analysis yields the real-time absolute distance D of the measured target, effectively eliminating the interference of ambiguity range in traditional dual-comb ranging.

[0041] (2) High-precision locking mode with constant repetition frequency Once the absolute distance to the target is determined through the scanning mode, and the target is in a relatively stationary or slightly moving state requiring long-term high-precision monitoring, the system will automatically switch to this mode to improve measurement accuracy and stability. The control module 29 uses a PID algorithm to lock the voltage of the first piezoelectric ceramic 10 and the second piezoelectric ceramic 11. At this point, a large-range scan is no longer performed; instead, based on the error signal from the feedback module 20, a small reverse adjustment is made to the first piezoelectric ceramic 10 and the second piezoelectric ceramic 11. It is locked at an optimal fixed value. This control mode can eliminate dynamic errors during the scanning process, reduce random noise by using long-term integral averaging, and achieve nanometer-level measurement resolution.

[0042] (3) Environmental drift common mode suppression mode This addresses the potential impact of ambient temperature variations or mechanical vibrations on single-cavity lasers. When the feedback module detects a slow overall change in the laser cavity length due to ambient temperature drift, it... and They drift in the same direction at the same time (common mode drift), but When relatively stable, the control module 29 enters the common-mode drive state. A compensation voltage of the same polarity is applied to the first piezoelectric ceramic 10 and the second piezoelectric ceramic 11 (e.g., simultaneous elongation or simultaneous contraction) to counteract changes in the physical cavity length caused by the environment, pulling the center frequencies of the two optical combs back to the set range without changing the repetition rate difference between them. This mode maintains distance measurement without interruption (i.e., keeps the distance measured). Under the premise of constant stability, the long-term drift of the laser is corrected, which greatly enhances the environmental robustness of the system.

[0043] This invention, through environmental drift common-mode suppression, can effectively compensate for the effects of environmental temperature changes and mechanical vibrations on the laser cavity length, maintain the stability of the repetition frequency difference, and significantly improve the measurement repeatability of the system in complex environments.

[0044] (4) Unlock Reset Mode When the photodetector detects the repetition rate of any optical comb or If a momentary jump (>1MHz) occurs within 100ms or the signal-to-noise ratio of the beat frequency signal drops sharply, it is determined that the mode-locked state has been lost. At this time, a rapid reset of the first piezoelectric ceramic 10 and the second piezoelectric ceramic 11 is executed. First, the driving voltages of the first piezoelectric ceramic 10 and the second piezoelectric ceramic 11 are instantaneously reset to a preset intermediate bias point, attempting to restore mode-locking using the mechanical impact of the first piezoelectric ceramic 10 and the second piezoelectric ceramic 11. If the reset of the first piezoelectric ceramic 10 and the second piezoelectric ceramic 11 is ineffective, the control module 29 starts a pump current scanning program, scanning at a speed of 0.1mA / s within 10mA of the mode-locking threshold current to find a new mode-locking operating point. After mode-locking is restored, the "variable repetition rate wide-range scanning mode" is automatically re-executed to reconfirm the absolute distance and prevent counting errors during the loss of lock.

[0045] The single-cavity dual-comb absolute distance measurement system based on repetition frequency scanning of this invention achieves wide-range absolute distance measurement while maintaining nanometer-level high precision by realizing differential control of the repetition frequency in the single-cavity dual-comb structure, significantly eliminating measurement ambiguity. Simultaneously, the single-cavity structure simplifies the system's optical path design, reduces the number of core components used, lowers system integration difficulty and manufacturing costs, and the intelligent control strategy of dual piezoelectric ceramics eliminates the need for additional hardware, further optimizing the system's cost-effectiveness.

[0046] As another embodiment, the present invention provides a single-cavity dual-comb absolute distance measurement method based on repetition frequency scanning, applied to the above-mentioned single-cavity dual-comb absolute distance measurement system based on repetition frequency scanning, comprising: The single-cavity dual-comb system is started, and mode-locked pulses propagating clockwise and counterclockwise are established simultaneously in the ring cavity through a bidirectional pump source. The main oscillator comb and the local oscillator comb are output through the polarization-maintaining fiber coupler. The first and second photodetectors detect the repetition frequency signals at the 1% output terminals of the second and third polarization-maintaining fiber couplers, respectively. The third and fourth photodetectors detect the frequency multiplication signals entering the first and second frequency multiplication modules at the 99% output terminals of the second and third polarization-maintaining fiber couplers, respectively. All detection signals are input to the feedback module. The feedback control module adjusts the first and second piezoelectric ceramics through differential drive mode to lock and control the repetition frequency of the master optical comb and the local optical comb, thereby achieving linear scanning and locking of the repetition frequency difference between the master optical comb and the local optical comb. The main optical comb passing through the Michelson interferometer and the local optical comb not passing through the Michelson interferometer are combined to generate a radio frequency beat frequency signal; the real-time absolute distance of the target is calculated based on the optical path difference of the radio frequency beat frequency signal and the repetition frequency difference between the main optical comb and the local optical comb. During the ranging process, the control module intelligently switches operating modes based on real-time measurement requirements and environmental feedback. By analyzing the radio frequency beat frequency signals corresponding to multiple sets of repetition frequency differences, it determines the target distance and achieves absolute ranging.

[0047] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A single cavity dual optical comb absolute distance measurement system based on repetition frequency scanning, characterized in that, The application relates to a single-cavity double-comb system and a double-comb distance measuring system. The single-cavity double-comb system is used for simultaneously establishing clockwise and counterclockwise propagation mode-locked pulses in a ring cavity through bidirectional pumping sources, and outputs a master light comb and a local light comb through a polarization maintaining fiber coupler; the ring cavity is provided with a first piezoelectric ceramic and a second piezoelectric ceramic, and the first piezoelectric ceramic and the second piezoelectric ceramic are adjusted through a differential driving mode to realize locking and control of the repetition frequency difference between the master light comb and the local light comb; the double-comb distance measuring system is used for combining the master light comb passing through a Michelson interferometer and the local light comb not passing through the Michelson interferometer to generate a radio frequency beat signal; the real-time absolute distance of a measured target is calculated according to the optical path difference of the radio frequency beat signal and the repetition frequency difference between the master light comb and the local light comb. The single-cavity double-comb system comprises a first pumping source, a second pumping source, a ring cavity, a master light comb generating light path, a local light comb light path and a feedback module; the pumping light generated by the first pumping source and the second pumping source simultaneously establishes clockwise and counterclockwise propagation mode-locked pulses in the ring cavity; one mode-locked pulse enters the master light comb generating light path to generate a master light comb; the other mode-locked pulse enters the local light comb light path to generate a local light comb; the feedback module is connected with the first pumping source, the second pumping source, the ring cavity, the master light comb generating light path and the local light comb light path, and is used for collecting the repetition frequency signals of the master light comb and the local light comb, and adjusting the first piezoelectric ceramic and the second piezoelectric ceramic through a differential driving mode to realize linear scanning and locking of the repetition frequency difference between the master light comb and the local light comb. The ring cavity comprises a first polarization maintaining wavelength division multiplexer, a second polarization maintaining wavelength division multiplexer, a polarization maintaining erbium-doped optical fiber, a saturable absorber, a first polarization maintaining ring, a second polarization maintaining ring and a first polarization maintaining fiber coupler; 2. The repetition rate-scan-based single-cavity dual-comb absolute distance measurement system of claim 1, wherein, The clockwise transmission light path in the ring cavity is that the pumping light emitted by the first pumping source passes through the first polarization maintaining wavelength division multiplexer and is input into the polarization maintaining erbium-doped optical fiber to generate first signal light through stimulated radiation; the first signal light passes through the second polarization maintaining wavelength division multiplexer and the first polarization maintaining fiber coupler in sequence, then enters the first polarization maintaining ring, and then enters the saturable absorber through the first polarization maintaining ring after passing through a section of non-common transmission optical fiber to generate first mode-locked pulses; the first mode-locked pulses pass through the first polarization maintaining wavelength division multiplexer, the polarization maintaining erbium-doped optical fiber and the second polarization maintaining wavelength division multiplexer in sequence, and then are output to the third polarization maintaining fiber coupler through the first polarization maintaining fiber coupler; 3. The repetition rate-scan-based single-cavity dual-comb absolute distance measurement system of claim 2, wherein, The counterclockwise transmission light path in the ring cavity is that the pumping light emitted by the second pumping source passes through the second polarization maintaining wavelength division multiplexer and is input into the polarization maintaining erbium-doped optical fiber to generate second signal light through stimulated radiation; the second signal light passes through the first polarization maintaining wavelength division multiplexer and the saturable absorber in sequence to generate second mode-locked pulses; the second mode-locked pulses pass through the first polarization maintaining ring, another section of non-common transmission optical fiber and the second polarization maintaining ring in sequence, and then enter the first polarization maintaining fiber coupler; the first polarization maintaining fiber coupler outputs stable second mode-locked pulse laser to the second polarization maintaining fiber coupler. ​ ​ The first polarization maintaining optical circulator and the second polarization maintaining optical circulator are connected by two non-common transmission optical fibers, and the first piezoelectric ceramic and the second piezoelectric ceramic are fixed on the two non-common transmission optical fibers respectively.

4. The repetition rate-scan-based single-cavity dual-comb absolute distance measurement system of claim 2, wherein, The main oscillator light comb generation light path is the same as the local oscillator light comb light path structure.

5. The repetition rate-scan-based single-cavity dual-optical-comb absolute distance measurement system of claim 4, wherein, The main oscillator light comb generation light path comprises a second polarization maintaining fiber coupler, a first photodetector, a first high nonlinear fiber, a first frequency doubling module and a third photodetector, one way of the mode-locked pulse enters the second polarization maintaining fiber coupler, 1% enters the first photodetector, and 99% enters the third photodetector in turn through the first high nonlinear fiber and the first frequency doubling module, the feedback module is connected with the first photodetector and is used for detecting the repetition frequency signal, and the feedback module is also connected with the third photodetector and is used for detecting the main oscillator light comb.

6. The repetition rate-scan-based single-cavity dual-optical-comb absolute distance measurement system of claim 4, wherein, The local oscillator light comb light path comprises a third polarization maintaining fiber coupler, a second photodetector, a second high nonlinear fiber, a second frequency doubling module and a fourth photodetector, the other way of the mode-locked pulse enters the third polarization maintaining fiber coupler, 1% enters the second photodetector, and 99% enters the fourth photodetector in turn through the second high nonlinear fiber and the second frequency doubling module, the feedback module is connected with the second photodetector and is used for detecting the repetition frequency signal, and the feedback module is also connected with the fourth photodetector and is used for detecting the local oscillator light comb.

7. The repetition rate-scan-based single-cavity dual optical comb absolute distance measurement system of claim 2, wherein, The double optical comb distance measurement system comprises a Michelson interferometer, a second beam splitter, a fifth photodetector, a low-pass filter and a control module, the main oscillator light comb is incident on the Michelson interferometer to generate an interference reference signal, the second beam splitter combines the interference reference signal with the local oscillator light comb to obtain a radio frequency beat signal, the radio frequency beat signal is incident on the fifth photodetector, then the bandwidth of the radio frequency beat signal is reduced through the low-pass filter, and after filtering out noise, the radio frequency beat signal enters the control module, and the control module is used for calculating the real-time absolute distance of the measured target according to the optical path difference of the radio frequency beat signal and the repetition frequency difference between the main oscillator light comb and the local oscillator light comb; the formula is as follows: wherein, is a group velocity of the light pulse, is a time delay between the reference and measurement interference signals, denotes a repetition frequency difference of the master and slave optical combs, denotes a repetition frequency of the master optical comb; The control module is connected with the feedback module.

8. The repetition rate-scan-based single-cavity dual optical comb absolute distance measurement system of claim 7, wherein, The Michelson interferometer comprises a first beam splitter, a first reflector and a second reflector, the main oscillator light comb is divided into reference light and measurement light after being incident on the first beam splitter, the reference light is reflected by the first reflector, the measurement light is reflected by the second reflector, and the two beams of light return to the first beam splitter after transmitting different optical paths to generate an interference reference signal and are incident on the second beam splitter.

9. A single cavity dual comb absolute distance measurement method based on repetition frequency scanning, characterized in that, The application is applied to the single-cavity double optical comb absolute distance measurement system based on repetition frequency scanning in any one of claims 1-8, comprising: The single-cavity double optical comb system is started, the mode-locked pulses propagating clockwise and counterclockwise in the ring cavity are established by the bidirectional pump source, and the main oscillator light comb and the local oscillator light comb are output through the polarization maintaining fiber coupler. The first photodetector and the second photodetector detect the repetition frequency signals at the output ends of the second polarization maintaining fiber coupler and the third polarization maintaining fiber coupler, respectively, and the third photodetector and the fourth photodetector detect the frequency multiplication signals at the output ends of the second polarization maintaining fiber coupler and the third polarization maintaining fiber coupler, which enter the first frequency multiplication module and the second frequency multiplication module, respectively, and all the detected signals are input into the feedback module; the feedback control module adjusts the first piezoelectric ceramic and the second piezoelectric ceramic through a differential driving mode, so as to realize the locking and regulation of the repetition frequencies of the master light comb and the local light comb, and further realize the linear scanning and locking of the repetition frequency difference between the master light comb and the local light comb; The master light comb passing through the Michelson interferometer is combined with the local light comb not passing through the Michelson interferometer to generate a radio frequency beat signal; and the real-time absolute distance of the measured target is calculated according to the optical path difference of the radio frequency beat signal and the repetition frequency difference between the master light comb and the local light comb; During the distance measurement process, the control module intelligently switches the working condition mode according to the real-time measurement requirements and environmental feedback, determines the target distance through analysis of a plurality of groups of radio frequency beat signals corresponding to the repetition frequency difference, and realizes absolute distance measurement.

10. The repetition frequency swept single-cavity dual-comb absolute distance measurement method of claim 9, wherein, The working condition mode further includes: A fixed repetition frequency high-precision locking mode: when the absolute distance of the target is determined and the target is in a relatively static or micro-motion state and needs to be monitored for a long time with high precision, the system is automatically switched to the fixed repetition frequency high-precision locking mode; the control module locks the voltages of the first piezoelectric ceramic and the second piezoelectric ceramic through a PID algorithm, and stops large-scale scanning; based on the error signal output by the feedback module, the first piezoelectric ceramic and the second piezoelectric ceramic are adjusted in the opposite direction, and the repetition frequency difference is locked at an optimal fixed value; An environmental drift common mode rejection mode: when the feedback module detects that the first pump source and the second pump source change due to environmental temperature drift, causing the repetition frequencies of the master light comb and the local light comb to drift in the same direction and the repetition frequency difference to be relatively stable, the control module enters a common mode driving state; the same polarity compensation voltage is applied to the first piezoelectric ceramic and the second piezoelectric ceramic to offset the physical cavity length change caused by the environment; the center frequencies of the master light comb and the local light comb are pulled back to a set range, and the repetition frequency difference is kept constant; A lock loss reset mode: when it is detected that the repetition frequency of any light comb instantaneously jumps by more than 1MHz within 100ms or the signal-to-noise ratio of the beat signal sharply decreases, it is determined that the mode locking state is lost; the first piezoelectric ceramic and the second piezoelectric ceramic are reset, the driving voltages of the first piezoelectric ceramic and the second piezoelectric ceramic are instantaneously reset to a preset intermediate bias point, and mechanical impact is used to attempt to restore the mode locking; if the reset is invalid, the control module starts a pump current scanning program to scan in a range of 10mA near the mode locking threshold current at a speed of 0.1mA / s, and finds a new mode locking working point; after the mode locking is restored, the system automatically re-executes the variable repetition frequency large-scale scanning mode to reconfirm the absolute distance of the target.

Images