Optical frequency scanning interferometry absolute distance measuring system and stable reference construction method thereof

Abstract

This invention provides an optical frequency scanning interferometric absolute ranging system and its stable reference construction method, including a measurement interferometer module, an auxiliary interferometer module, a frequency-stabilized laser reference module, and a laser synchronization control and signal calculation component. The measurement interferometer module generates a beat frequency interference signal related to the spatial distance to be measured. The auxiliary interferometer module generates a beat frequency interference signal related to the instantaneous optical frequencies of a first tunable laser and a second tunable laser, monitors the optical frequencies of the first tunable laser and the second tunable laser in real time, and corrects their sweep frequency nonlinearity error. A long fiber Bragg grating string is set on the measuring arm of the Mach-Zehnder interferometer in the auxiliary interferometer module. The frequency-stabilized laser reference module generates a beat frequency interference signal related to the optical path difference of the auxiliary interferometer module to compensate for the optical path drift of the auxiliary interferometer module. The laser synchronization control and signal calculation component calculates the distance to be measured based on the interference signals generated by the above three modules.

Description

Technical Field

[0001] This invention relates to the field of precision measurement technology, specifically to an absolute ranging system based on optical frequency scanning interferometry and a method for constructing a stable reference. Background Technology

[0002] High-precision, large-range absolute distance measurement plays a crucial role in cutting-edge scientific and industrial fields such as aerospace, large-scale equipment manufacturing, precision engineering, particle accelerator calibration, and geodesy. Among numerous ranging technologies, optical frequency scanning interferometry has become one of the ideal solutions for achieving absolute distance measurement due to its outstanding advantages, including high precision (down to the micrometer or even nanometer level), large range (tens of meters or more), high measurement speed, and non-contact measurement. It is currently a research hotspot.

[0003] The basic principle of optical frequency scanning interferometry is to calculate the absolute distance by precisely tuning the output frequency of a narrow-linewidth laser and detecting the beat frequency signals generated by the measuring interferometer and the reference interferometer. However, the measurement accuracy of this technique is heavily dependent on the linearity of the laser frequency scan. In practical applications, tunable lasers inevitably suffer from nonlinear scanning problems, which directly leads to errors in distance calculation and significantly reduces the system's resolution and accuracy.

[0004] To compensate for the nonlinearity of laser frequency scanning, an auxiliary interferometer is usually introduced to correct its nonlinearity.

[0005] Auxiliary interferometers typically consist of a long section of single-mode optical fiber. However, the refractive index and physical length of the fiber are highly susceptible to external environmental influences, causing optical path drift and resulting in instability of the measurement reference. This severely impacts the long-term stability and reliability of the entire ranging system in complex industrial environments. For example, CN118533069A discloses a method for high-precision calibration of the reference optical path in optical frequency scanning interferometric ranging. This method uses an optical frequency comb and a gas absorption cell to perform high-precision calibration of the auxiliary interferometer's optical path. However, this method has low measurement efficiency, and the gas absorption cell requires a tunable laser with a wide tuning range.

[0006] CN118131250A discloses a bidirectional optical frequency scanning interferometric absolute ranging system and a vibration error compensation method, including a measurement interferometer module, an auxiliary interferometer module, and a laser synchronous scanning control component. The stability of this ranging system depends entirely on the long-delay optical fiber. Because the long-delay optical fiber is greatly affected by the external environment, optical path drift occurs, making the measurement reference unstable. A drawback of the above method is that the auxiliary interferometer, which serves as the calibration reference, is itself unstable. Specifically, the refractive index and physical length of the single-mode optical fiber constituting the auxiliary interferometer are extremely sensitive to external environmental disturbances (such as temperature, stress, and vibration). This causes its reference optical path to drift with environmental changes, resulting in inaccurate measurement reference for the entire ranging system. The direct consequence of this problem is that the extremely high accuracy that the system can achieve under laboratory conditions is difficult to maintain in complex industrial environments over long periods. The long-term stability and environmental reliability of the system have become major bottlenecks restricting its widespread application.

[0007] Therefore, further research is needed on the construction of a stable reference for optical frequency scanning interferometric absolute ranging systems to meet the requirements of the field measurement environment for stability, efficiency, and accuracy. Summary of the Invention

[0008] This invention addresses the shortcomings of existing technologies by providing an optical frequency scanning interferometric absolute ranging system and its stable reference construction method. The absolute ranging system incorporates a long fiber Bragg grating string within an auxiliary interferometric module, capable of separating a portion of the laser wavelength that is related to the optical path difference of the auxiliary interferometric module. A frequency-stabilized laser reference module is introduced, generating a beat frequency interference signal related to the optical path difference of the auxiliary interferometric module, which serves as the system's reference standard. This real-time compensation for the optical path drift of the auxiliary interferometric module improves measurement reliability.

[0009] The first aspect of the present invention is to provide an optical frequency scanning interferometric absolute ranging system, including a measurement interferometry module, an auxiliary interferometry module, a frequency-stabilized laser reference module, and a laser synchronization control and signal processing component;

[0010] The measurement interferometry module is used to generate a beat frequency interference signal related to the spatial distance to be measured. The beat frequency signal is divided into an up-scan measurement interferometry signal and a down-scan measurement interferometry signal by a second wavelength division multiplexer to compensate for the influence of the Doppler effect.

[0011] The auxiliary interferometer module is used to generate beat frequency interference signals that are instantaneously related to the optical frequencies of the first and second tunable lasers, monitor the optical frequencies of the first and second tunable lasers in real time, and correct their sweep frequency nonlinearity errors. The auxiliary interferometer module includes a Mach-Zehnder interferometer, and a long fiber Bragg grating string is provided on the measuring arm of the Mach-Zehnder interferometer. The long fiber Bragg grating string is used to reflect a specific wavelength related to the optical path of the auxiliary interferometer module, and its grating pitch matches the wavelength of the first or second tunable laser.

[0012] The frequency-stabilized laser reference module is used to generate a beat frequency interference signal related to the optical path difference of the auxiliary interference module, in order to compensate for the optical path drift of the auxiliary interference module.

[0013] The laser synchronization control and signal calculation component is used to generate two radio frequency signals with opposite phases, synchronously driving the first tunable laser and the second tunable laser to generate optical frequency scanning lasers. It receives beat frequency interference signals generated by the measurement interference module, the auxiliary interference module, and the frequency-stabilized laser reference module in real time. Based on the phase of the upper and lower scan measurement interference signals generated by the measurement interference module, the phase of the upper and lower scan auxiliary interference signals generated by the auxiliary interference module, and the instantaneous frequency of the reference interference signal generated by the beat frequency interference of the wavelength-stabilized continuous wave emitted by the frequency-stabilized laser of the frequency-stabilized laser module and the reflected light from the long fiber Bragg grating string of the auxiliary interference module after beam combining, the distance to be measured is calculated.

[0014] Furthermore, the measurement interferometry module includes a Mach-Zehnder interferometer, a second circulator, an optical fiber collimator, a target corner cone, a second wavelength division multiplexer, a third photodetector, and a fourth photodetector.

[0015] The auxiliary interference module includes a Mach-Zehnder interferometer, a first wavelength division multiplexer, a first photodetector, and a second photodetector.

[0016] The frequency-stabilized laser reference module includes a frequency-stabilized laser, a first circulator, a third fiber beam splitter, and a fifth photodetector. The frequency-stabilized laser is used to generate a frequency-stable continuous-wave single-frequency laser with a wavelength approximately equal to the wavelength reflected by the long fiber Bragg grating string. The first circulator is used to separate the optical frequency signal reflected by the long fiber Bragg grating string that is related to its optical path change, and the reflected signal is close to the frequency of the frequency-stabilized laser.

[0017] Furthermore, the laser synchronization control and signal processing component includes a first tunable laser, a second tunable laser, an RF transceiver card, and a host computer;

[0018] The first tunable laser and the second tunable laser are used to generate optical frequency scanning lasers, and the two laser beams scan in opposite directions.

[0019] The radio frequency signal transceiver generates radio frequency signals to drive the first tunable laser and the second tunable laser to synchronously generate optical frequency scanning lasers. The optical frequencies of the two optical frequency scanning lasers are monotonically increasing and monotonically decreasing, respectively, and they receive beat frequency interference signals generated by the first to fifth photodetectors.

[0020] The host computer receives the beat frequency interference signal collected by the radio frequency signal transceiver card, compensates for the optical path change of the auxiliary interference module in real time, and calculates the distance to be measured.

[0021] Furthermore, the fifth photodetector is a balanced photodetector.

[0022] Furthermore, the first wavelength division multiplexer and the second wavelength division multiplexer are used to divide the beat frequency interference signal according to the spectral range.

[0023] Furthermore, the lasers from the first tunable laser and the second tunable laser are combined by the first fiber beam splitter and then split into two parts, which enter the measurement interference module and the auxiliary interference module, respectively.

[0024] Furthermore, the entire optical fiber path of the Mach-Zehnder interferometer is uniformly wound in a temperature-controlled, vibration-isolated optical fiber disk with near-zero tension.

[0025] A second aspect of the present invention is to provide a stable reference construction method for the optical frequency scanning interferometric absolute ranging system, comprising:

[0026] Step 1: The radio frequency transceiver generates two radio frequency signals with opposite phases, which synchronously drive the first tunable laser and the second tunable laser to generate optical frequency scanning lasers. The optical frequencies of the two optical frequency scanning lasers are monotonically increasing and monotonically decreasing, respectively. After being combined by the first fiber beam splitter, they are divided into two parts, which enter the measurement interference module and the auxiliary interference module, respectively.

[0027] Step 2: The laser enters the measurement interferometer module to generate an up-scan measurement interferometer signal and a down-scan measurement interferometer signal. The laser enters the auxiliary interferometer module to generate an up-scan auxiliary interferometer signal and a down-scan auxiliary interferometer signal. The wavelength-stable continuous wave emitted by the frequency-stabilized laser in the frequency-stabilized laser reference module and the reflected light from the long fiber Bragg grating string from the auxiliary interferometer module undergo beat frequency interference after beam combining, generating a reference interferometer signal.

[0028] Step 3: The RF transceiver receives the beat frequency interference signals generated by the measurement interference module, the auxiliary interference module, and the frequency-stabilized laser reference module in real time. Based on the phase of the upper and lower scan measurement interference signals generated by the measurement interference module, the phase of the upper and lower scan auxiliary interference signals generated by the auxiliary interference module, and the instantaneous frequency of the reference interference signal generated by the beat frequency interference of the wavelength-stabilized continuous wave emitted by the frequency-stabilized laser of the frequency-stabilized laser module and the reflected light from the long fiber Bragg grating string of the auxiliary interference module, the distance to be measured is calculated.

[0029] Furthermore, step two specifically includes:

[0030] The laser incident on the measurement interferometer module is split into two parts by the second fiber beam splitter. One part serves as the reference arm of the Mach-Zehnder interferometer, and the other part is connected to the fiber collimator via the second circulator. After being reflected by the target corner cone mirror, it is coupled back into the fiber optical path through the fiber collimator. After passing through the second circulator, it serves as the measurement arm signal and is coupled with the reference arm signal through another second fiber beam splitter. The interference signals of different spectral ranges are then split by the second wavelength division multiplexer to generate the upper-scan measurement interference signal and the lower-scan measurement interference signal, which are received by the third photodetector and the fourth photodetector, respectively.

[0031] Among them, the phase φ of the formed up-scan measurement interference signal um (t) is in phase with the downscan measurement interference signal φ dm (t) is shown below:

[0032]

[0033] in, To measure the optical path length to be measured at the initial moment, To measure the change of the optical path length under test over time during the measurement process, and These represent the initial optical frequencies of the up-scanning laser and the down-scanning laser, respectively. and These represent the frequency changes of an upward-scanning laser and a downward-scanning laser over time, respectively, where c is the speed of light in a vacuum, and φ is the velocity of light. um (t) and φ dm (t) represent the phases of the upper-scan measurement interference signal and the lower-scan measurement interference signal, respectively;

[0034] The laser incident on the auxiliary interferometer module is split into two parts by the second fiber beam splitter. One part serves as the reference arm of the Mach-Zehnder interferometer, and the other part enters the measurement arm constructed by a long fiber Bragg grating string. The measurement arm signal and the reference arm signal are coupled through another second fiber beam splitter and the interference signals of different spectral ranges are separated by the first wavelength division multiplexer to generate the up-scan auxiliary interference signal and the down-scan auxiliary interference signal, which are received by the first photodetector and the second photodetector, respectively.

[0035] Among them, the phase φ of the formed up-scan auxiliary interference signal ur (t) is in phase with the downsweep auxiliary interference signal φ dr (t) is shown below:

[0036]

[0037] in, To measure the optical path length of the auxiliary interferometer module at the initial moment, To show the change in optical path length of the auxiliary interferometer module over time during the measurement process, and These represent the initial optical frequencies of the up-scanning laser and the down-scanning laser, respectively. and These represent the frequency changes of an upward-scanning laser and a downward-scanning laser over time, respectively, where c is the speed of light in a vacuum, and φ is the velocity of light. ur (t) and φ dr (t) represent the phases of the up-scan auxiliary interference signal and the down-scan auxiliary interference signal, respectively;

[0038] The wavelength of the frequency-scanning laser emitted from either the first or second tunable laser, matching the grating pitch of the long fiber Bragg grating string, is reflected. The reflected light from the long fiber Bragg grating string in the auxiliary interferometer module enters the frequency-stabilized laser reference module via the first circulator. It then interferes with the frequency-stabilized laser emitted from the frequency-stabilized laser by passing through the third fiber beam splitter, resulting in beat frequency interference. This interference is received by the fifth photodetector and converted into a reference interference signal. The fifth photodetector outputs the instantaneous frequency of the reference interference signal. as follows:

[0039]

[0040] in, λ is the wavelength of the emitted light from the frequency-stabilized laser, c is the speed of light in vacuum, and λ is the instantaneous wavelength of the reflected light from the long fiber Bragg grating string.

[0041] The frequency of the reference interference signal output by the frequency-stabilized laser reference module is related to the optical path length of the auxiliary interference module. As shown in the formula below:

[0042]

[0043] Where N is the number of gratings. Where is the wavelength of the frequency-stabilized laser, and f is the instantaneous frequency of the output signal of the frequency-stabilized laser reference module. The optical path length of the auxiliary interference module is given, and c is the speed of light in a vacuum.

[0044] Furthermore, the tuning range of the first tunable laser is 1527nm-1532nm, and the tuning range of the second tunable laser is 1535nm-1540nm.

[0045] The beneficial effects of this invention are as follows:

[0046] This invention uses a long fiber Bragg grating string to construct an auxiliary interferometer and introduces a frequency-stabilized laser to monitor the optical path of the auxiliary interferometer in real time, making the system reference more stable. Compared with other reference construction methods, the stable reference construction method described in this invention has high solution efficiency, low cost, good stability, low requirements for the tuning range of the tunable laser, and a compact structure that is easy to integrate. It is suitable for absolute ranging scenarios in industrial environments where high reliability and accuracy are required. Attached Figure Description

[0047] Figure 1 This is a schematic diagram of the optical frequency scanning interferometric absolute ranging system described in this invention;

[0048] Figure 2 This is a schematic diagram of the optical frequency scanning interferometric absolute ranging system described in this invention;

[0049] Figure 3 This is a flowchart of the stable reference construction method described in this invention.

[0050] Wherein, 101-1: first tunable laser; 101-2: second tunable laser; 101-3: frequency-stabilized laser;

[0051] 102-1: First fiber optic beam splitter; 102-2: Second fiber optic beam splitter; 102-3: Third fiber optic beam splitter;

[0052] 103-1: First fiber optic circulator; 103-2: Second fiber optic circulator;

[0053] 104: Long fiber Bragg grating string; 105: Fiber collimator; 106: Target corner cone;

[0054] 107-1: First wavelength division multiplexer; 107-2: Second wavelength division multiplexer; 108-1: First photodetector;

[0055] 108-2: Second photodetector; 108-3: Third photodetector; 108-4: Fourth photodetector;

[0056] 108-5: Fifth photodetector; 109: RF transceiver card; 110: Measurement interferometry module;

[0057] 111: Auxiliary interference module; 112: Frequency-stabilized laser reference module; 113: Host computer. Detailed Implementation

[0058] To make the objectives, technical solutions, beneficial effects, and significant advancements of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings provided in the examples of the present invention. Obviously, all the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0059] In the description of this application, unless otherwise expressly specified and limited, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance; the term "multiple" refers to two or more; unless otherwise specified or explained, the terms "connected," "fixed," etc., should be interpreted broadly. For example, "connected" can be a fixed connection, a detachable connection, an integral connection, or an electrical connection; "connected" can be a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0060] like Figure 1-2 As shown, an optical frequency scanning interferometric absolute ranging system includes a measurement interferometry module 110, an auxiliary interferometry module 111, a frequency-stabilized laser reference module 112, and a laser synchronization control and signal processing component.

[0061] The measurement interferometry module 110 is used to generate a beat frequency interference signal related to the spatial distance to be measured, compensating for the Doppler effect. The measurement interferometry module 110 includes a Mach-Zehnder interferometer, a second circulator 103-2, an optical fiber collimator 105, a target corner cone 106, a second wavelength division multiplexer 107-2, a third photodetector 108-3, and a fourth photodetector 108-4. The Mach-Zehnder interferometer includes two second optical fiber beam splitters 102, and a measuring arm and a reference arm located between the two beam splitters. The second wavelength division multiplexer 107-2 is used to divide the beat frequency interference signal according to the spectral range.

[0062] The auxiliary interferometer module 111 is used to generate beat frequency interference signals that are instantaneously related to the optical frequencies of the first tunable laser 101-1 and the second tunable laser 101-2, monitor the optical frequencies of the first tunable laser 101-1 and the second tunable laser 101-2 in real time, and correct their sweep frequency nonlinearity errors. The auxiliary interferometer module 111 includes a Mach-Zehnder interferometer, a first wavelength division multiplexer 107-1, a first photodetector 108-1, and a second photodetector 108-2. The Mach-Zehnder interferometer includes two second fiber beam splitters 102, a long fiber Bragg grating string 104, and a measuring arm and a reference arm located between the two beam splitters. The long fiber Bragg grating string 104 is disposed on the measuring arm and is used to reflect specific wavelengths related to the optical path of the auxiliary interferometer module; its grating pitch matches the wavelength of the first / second tunable laser. When the frequency-scanning laser passes through the auxiliary interferometer module, part of the wavelength is reflected by the long fiber Bragg grating string and enters the frequency-stabilized laser reference module through a circulator. The first wavelength division multiplexer 107-1 is used to divide the beat frequency interference signal according to the spectral range.

[0063] The frequency-stabilized laser reference module 112 is used to generate a beat frequency interference signal related to the optical path difference of the auxiliary interference module 111, and to compensate for the optical path drift of the auxiliary interference module. The frequency-stabilized laser reference module 112 includes a frequency-stabilized laser 101-3, a first circulator 103-1, a third fiber beam splitter 102-3, and a fifth photodetector 108-5.

[0064] The frequency-stabilized laser 101-3 is used to generate a frequency-stable continuous-wave single-frequency laser with a wavelength almost equal to the wavelength reflected by the long fiber Bragg grating string. The first circulator 103-1 is used to separate the optical frequency signal reflected by the long fiber Bragg grating string 104, which is related to its optical path change; the reflected signal has a frequency close to that of the frequency-stabilized laser 101-3. The third fiber beam splitter 102-3 is used to perform beat frequency interference on the combined beam of reflected light from the frequency-stabilized laser 101-3 and the long fiber Bragg grating string, generating a beat frequency signal, which is then received by the fifth photodetector 108-5.

[0065] The laser synchronization control and signal processing component includes a first tunable laser 101-1, a second tunable laser 101-2, an RF transceiver 109, and a host computer 113. The first tunable laser 101-1 and the second tunable laser 101-2 generate optical frequency scanning lasers, and the two laser beams scan in opposite directions. The RF transceiver 109 generates RF signals to drive the first tunable laser 101-1 and the second tunable laser 101-2 to synchronously generate optical frequency scanning lasers. The optical frequencies of the two optical frequency scanning lasers are monotonically increasing and monotonically decreasing, respectively, and the system receives beat frequency interference signals generated by the first to fifth photodetectors. The host computer receives the beat frequency interference signals collected by the RF transceiver 109, compensates for optical path changes in the auxiliary interference module in real time, calculates the distance to be measured, and displays the output. Furthermore, the input terminal of the RF transceiver card 109 is electrically connected to the first to fifth photodetectors, and the output terminal of the RF transceiver card is electrically connected to the host computer 113.

[0066] Furthermore, the fifth photodetector 108-5 is a balanced photodetector.

[0067] The optical frequency scanning interferometric absolute ranging system further includes a first fiber beam splitter 102-1, which is used to combine the lasers from the first tunable laser 101-1 and the second tunable laser 101-2 and then split them into two parts, which enter the measurement interferometric module 110 and the auxiliary interferometric module 111 respectively; the splitting ratio of the first fiber beam splitter 102-1 is 50:50.

[0068] like Figure 3 As shown, the stable reference construction method for the absolute ranging system based on optical frequency scanning interferometry includes:

[0069] Step 1: The radio frequency transceiver 109 generates two radio frequency signals with opposite phases, which synchronously drive the first tunable laser 101-1 and the second tunable laser 101-2 to generate optical frequency scanning lasers. The optical frequencies of the two optical frequency scanning lasers are monotonically increasing and monotonically decreasing, respectively. After being combined by the first fiber beam splitter 102-1, they are divided into two parts, which enter the measurement interference module 110 and the auxiliary interference module 111, respectively.

[0070] Step 2: The laser enters the measurement interference module 110 to generate an up-scan measurement interference signal and a down-scan measurement interference signal. The laser enters the auxiliary interference module 111 to generate an up-scan auxiliary interference signal and a down-scan auxiliary interference signal. The wavelength-stable continuous wave emitted by the frequency-stabilized laser of the frequency-stabilized laser reference module beats with the reflected light from the long fiber Bragg grating string from the auxiliary interference module 111, generating a reference interference signal.

[0071] Specifically, it includes:

[0072] The laser incident on the measurement interferometer module 110 is split into two parts by the second fiber beam splitter 102-2. One part serves as the reference arm of the Mach-Zehnder interferometer, and the other part is connected to the fiber collimator 105 via the second circulator 103-2. After being reflected by the target corner cone mirror 106, it is coupled into the fiber optical path again through the fiber collimator 105. After passing through the second circulator 103-2, it serves as the measurement arm signal and is coupled with the reference arm signal through another second fiber beam splitter 102-2. The interference signals of different spectral ranges are split by the second wavelength division multiplexer 107-2 to generate the upper-scan measurement interference signal and the lower-scan measurement interference signal. These signals are received by the third photodetector 108-3 and the fourth photodetector 108-4, respectively, and are collected by the radio frequency transceiver card 109.

[0073] Among them, the phase φ of the formed up-scan measurement interference signal um (t) is in phase with the downscan measurement interference signal φ dm (t) is shown in the following formula:

[0074] ;

[0075] in, To measure the optical path length to be measured at the initial moment, To measure the change of the optical path length under test over time during the measurement process, and These represent the initial optical frequencies of the up-scanning laser and the down-scanning laser, respectively. and These represent the frequency changes of an upward-scanning laser and a downward-scanning laser over time, respectively, where c is the speed of light in a vacuum, and φ is the velocity of light. um (t) and φ dm (t) represents the phase of the upper-scan measurement interference signal and the phase of the lower-scan measurement interference signal, respectively. After the upper-scan laser and the lower-scan laser form a beat frequency interference, they are separated by a second wavelength division multiplexer according to the spectral range.

[0076] The laser incident on the auxiliary interferometer module 111 is split into two parts by the second fiber beam splitter 102-2. One part serves as the reference arm of the Mach-Zehnder interferometer, and the other part enters the measurement arm constructed by the long fiber Bragg grating string 104. The measurement arm signal and the reference arm signal are coupled through another second fiber beam splitter 102-2 and the interference signals of different spectral ranges are split by the first wavelength division multiplexer 107-1 to generate the up-scan auxiliary interference signal and the down-scan auxiliary interference signal. These signals are received by the first photodetector 108-1 and the second photodetector 108-2, respectively, and are acquired by the radio frequency transceiver card 109.

[0077] In this process, since the grating pitch of the long fiber Bragg grating string only matches the wavelength band of the first tunable laser 101-1 and does not interact with the second tunable laser 101-2, the wavelength in the frequency-scanning laser emitted by the first tunable laser 101-1 that matches the grating pitch of the long fiber Bragg grating string is reflected. The relationship between the reflected light wavelength λ and the grating pitch Λ is shown in the following formula:

[0078] ;

[0079] in, The refractive index of the optical fiber. The wavelength of the reflected light from the long fiber Bragg grating string. The grating pitch is denoted by .

[0080] Among them, the phase φ of the formed up-scan auxiliary interference signal ur (t) is in phase with the downsweep auxiliary interference signal φ dr (t) is shown in the following formula:

[0081] ;

[0082] in, To measure the optical path length of the auxiliary interferometer module at the initial moment, To show the change in optical path length of the auxiliary interferometer module over time during the measurement process, and These represent the initial optical frequencies of the up-scanning laser and the down-scanning laser, respectively. and These represent the frequency changes of an upward-scanning laser and a downward-scanning laser over time, respectively, where c is the speed of light in a vacuum, and φ is the velocity of light. ur (t) and φ dr (t) represent the phases of the upper-scan auxiliary interference signal and the lower-scan auxiliary interference signal, respectively. After the upper-scan laser and the lower-scan laser form a beat frequency interference, they are separated by the first wavelength division multiplexer 107-1 according to the spectral range.

[0083] The reflected light from the long fiber Bragg grating string 104 enters the frequency-stabilized laser reference module through the first circulator 103-1. It then interacts with the frequency-stabilized laser emitted from the frequency-stabilized laser 101-3. This interaction occurs through the third fiber beam splitter 102-3, resulting in beat frequency interference. The interference is received by the fifth photodetector 108-5 and converted into an electrical signal. The instantaneous frequency f of the electrical signal output by the fifth photodetector 108-5 is... As shown in the formula below:

[0084] ;

[0085] in, λ is the wavelength of the emitted light from the frequency-stabilized laser, c is the speed of light in vacuum, and λ is the instantaneous wavelength of the reflected light from the long fiber Bragg grating string.

[0086] The frequency of the reference interference signal output by the frequency-stabilized laser reference module 112 is related to the optical path length of the auxiliary interference module. As shown in the formula below:

[0087] ;

[0088] Where N is the number of gratings. Where is the wavelength of the frequency-stabilized laser, and f is the instantaneous frequency of the output signal of the frequency-stabilized laser reference module. The optical path length of the auxiliary interference module is given, and c is the speed of light in a vacuum.

[0089] Step 3: The RF transceiver 109 collects the beat frequency interference signals generated by the first to fifth photodetectors and sends them to the host computer for calculation, specifically including:

[0090] Based on the phase φ of the up-scan measurement interference signal generated by the measurement interference module 110 um (t) is in phase with the downscan measurement interference signal φ dm (t), the phase φ of the up-scan auxiliary interference signal generated by the auxiliary interference module 111 ur (t) is in phase with the downsweep auxiliary interference signal φ dr (t), and the instantaneous frequency of the reference interference signal formed by the frequency-stabilized laser module 112. Calculate the distance to the target. As shown in the formula below:

[0091] .

[0092] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style of the specification is merely for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in the embodiments can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A light-frequency scanning interferometric absolute ranging system, characterized in that, It includes a measurement interferometry module (110), an auxiliary interferometry module (111), a frequency-stabilized laser reference module (112), and a laser synchronization control and signal processing component; The measurement interferometer module (110) is used to generate a beat frequency interference signal related to the spatial distance to be measured. The beat frequency signal is divided into an upper sweep measurement interferometer signal and a lower sweep measurement interferometer signal by a second wavelength division multiplexer (107-2) to compensate for the influence of the Doppler effect. The auxiliary interference module (111) is used to generate beat frequency interference signals that are instantaneously related to the optical frequencies of the first tunable laser (101-1) and the second tunable laser (101-2), monitor the optical frequencies of the first tunable laser (101-1) and the second tunable laser (101-2) in real time, and correct their sweep frequency nonlinearity error; wherein, the auxiliary interference module (111) includes a Mach-Zehnder interferometer, and a long fiber Bragg grating string (104) is provided on the measuring arm of the Mach-Zehnder interferometer. The long fiber Bragg grating string (104) is used to reflect a specific wavelength related to the optical path of the auxiliary interference module, and its grating pitch is matched with the wavelength of the first tunable laser (101-1) or the second tunable laser (101-2); The frequency-stabilized laser reference module (112) is used to generate a beat frequency interference signal related to the optical path difference of the auxiliary interference module to compensate for the optical path drift of the auxiliary interference module; The laser synchronization control and signal calculation component is used to generate two radio frequency signals with opposite phases, synchronously driving the first tunable laser (101-1) and the second tunable laser (101-2) to generate optical frequency scanning lasers. It receives beat frequency interference signals generated by the measurement interference module (110), the auxiliary interference module (111), and the frequency-stabilized laser reference module (112) in real time. Based on the phase of the upper and lower scan measurement interference signals generated by the measurement interference module (110), the phase of the upper and lower scan auxiliary interference signals generated by the auxiliary interference module (111), and the instantaneous frequency of the reference interference signal generated by the wavelength-stabilized laser emitted by the frequency-stabilized laser of the frequency-stabilized laser reference module (112) and the reflected light from the long fiber Bragg grating string from the auxiliary interference module (111) through beam combining to generate beat frequency interference, the distance to be measured is calculated.

2. The optical frequency scanning interferometric absolute ranging system according to claim 1, characterized in that, The measurement interferometer module (110) includes a Mach-Zehnder interferometer, a second circulator (103-2), an optical fiber collimator (105), a target corner cone (106), a second wavelength division multiplexer (107-2), a third photodetector (108-3), and a fourth photodetector (108-4). The auxiliary interference module (111) includes a Mach-Zehnder interferometer, a first wavelength division multiplexer (107-1), a first photodetector (108-1), and a second photodetector (108-2). The frequency-stabilized laser reference module (112) includes a frequency-stabilized laser (101-3), a first circulator (103-1), a third fiber beam splitter (102-3), and a fifth photodetector (108-5). The frequency-stabilized laser (101-3) is used to generate a frequency-stabilized continuous wave single-frequency laser with a wavelength approximately equal to the wavelength reflected by the long fiber Bragg grating string. The first circulator (103-1) is used to separate the optical frequency signal reflected by the long fiber Bragg grating string (104) and related to its optical path change. The reflected signal is close to the frequency of the frequency-stabilized laser (101-3).

3. The optical frequency scanning interferometric absolute ranging system according to claim 1 or 2, characterized in that, The laser synchronization control and signal processing component includes a first tunable laser (101-1), a second tunable laser (101-2), an RF transceiver card (109), and a host computer (113). The first tunable laser (101-1) and the second tunable laser (101-2) are used to generate optical frequency scanning lasers, and the two laser beams have opposite frequency scanning directions; The radio frequency signal transceiver (109) generates radio frequency signals to drive the first tunable laser (101-1) and the second tunable laser (101-2) to synchronously generate optical frequency scanning lasers. The optical frequencies of the two optical frequency scanning lasers are monotonically increasing and monotonically decreasing, respectively, and receive beat frequency interference signals generated by the first to fifth photodetectors. The host computer receives the beat frequency interference signal collected by the radio frequency signal transceiver card (109), compensates for the optical path change of the auxiliary interference module in real time, and calculates the distance to be measured.

4. The optical frequency scanning interferometric absolute ranging system according to claim 2, characterized in that, The fifth photodetector (108-5) is a balanced photodetector.

5. The optical frequency scanning interferometric absolute ranging system according to claim 2, characterized in that, The first wavelength division multiplexer (107-1) and the second wavelength division multiplexer (107-2) are used to divide the beat frequency interference signal according to the spectral range.

6. The optical frequency scanning interferometric absolute ranging system according to claim 2, characterized in that, The lasers from the first tunable laser (101-1) and the second tunable laser (101-2) are combined by the first fiber beam splitter (102-1) and then split into two parts, which enter the measurement interference module (110) and the auxiliary interference module (111) respectively.

7. The optical frequency scanning interferometric absolute ranging system according to claim 2, characterized in that, The fiber optic paths of the Mach-Zehnder interferometers of the measurement interferometer module (110) and the auxiliary interferometer module (111) are uniformly wound in a temperature-controlled, vibration-isolated fiber optic disk with near-zero tension.

8. The stable reference construction method for the optical frequency scanning interferometric absolute ranging system according to claim 2, characterized in that... include: Step 1: The radio frequency transceiver (109) generates two radio frequency signals with opposite phases, which synchronously drive the first tunable laser (101-1) and the second tunable laser (101-2) to generate optical frequency scanning lasers. The optical frequencies of the two optical frequency scanning lasers are monotonically increasing and monotonically decreasing, respectively. After being combined by the first fiber beam splitter (102-1), they are divided into two parts and enter the measurement interference module (110) and the auxiliary interference module (111), respectively. Step 2: The laser enters the measurement interference module (110) to generate an up-scan measurement interference signal and a down-scan measurement interference signal. The laser enters the auxiliary interference module (111) to generate an up-scan auxiliary interference signal and a down-scan auxiliary interference signal. The wavelength-stable continuous wave emitted by the frequency-stabilized laser of the frequency-stabilized laser reference module and the reflected light from the long fiber Bragg grating string from the auxiliary interference module (111) undergo beat frequency interference after beam combining to generate a reference interference signal. Step 3: The radio frequency transceiver (109) receives the beat frequency interference signals generated by the measurement interference module (110), the auxiliary interference module (111), and the frequency-stabilized laser reference module (112) in real time. Based on the phase of the upper and lower scan measurement interference signals generated by the measurement interference module (110), the phase of the upper and lower scan auxiliary interference signals generated by the auxiliary interference module (111), and the instantaneous frequency of the reference interference signal generated by the wavelength-stabilized laser emitted by the frequency-stabilized laser of the frequency-stabilized laser reference module (112) and the reflected light from the long fiber Bragg grating string of the auxiliary interference module (111) after beam combining, the distance to be measured is calculated.

9. The stable reference construction method according to claim 8, characterized in that, Step two specifically includes: The laser incident on the measurement interferometer module (110) is split into two parts by the second fiber beam splitter 102-2. One part serves as the reference arm of the Mach-Zehnder interferometer, and the other part is connected to the fiber collimator (105) via the second circulator (103-2). After being reflected by the target corner cone (106), it is coupled into the fiber optical path again through the fiber collimator (105). After passing through the second circulator (103-2), it serves as the measurement arm signal and is coupled with the reference arm signal through another second fiber beam splitter (102-2). The interference signals of different spectral ranges are split by the second wavelength division multiplexer (107-2) to generate the upper-scan measurement interference signal and the lower-scan measurement interference signal, which are received by the third photodetector (108-3) and the fourth photodetector (108-4), respectively. Among them, the phase φ of the formed up-scan measurement interference signal um (t) is in phase with the downscan measurement interference signal φ dm (t) is shown below: ； in, To measure the optical path length to be measured at the initial moment, To measure the change of the optical path length under test over time during the measurement process, and These represent the initial optical frequencies of the up-scanning laser and the down-scanning laser, respectively. and These represent the frequency changes of an upward-scanning laser and a downward-scanning laser over time, respectively, where c is the speed of light in a vacuum, and φ is the velocity of light. um (t) and φ dm (t) represent the phases of the upper-scan measurement interference signal and the lower-scan measurement interference signal, respectively; The laser incident on the auxiliary interferometer module (111) is split into two parts by the second fiber beam splitter (102-2). One part serves as the reference arm of the Mach-Zehnder interferometer, and the other part enters the measurement arm constructed by the long fiber Bragg grating string (104). The measurement arm signal and the reference arm signal are coupled through another second fiber beam splitter (102-2) and the interference signals of different spectral ranges are split by the first wavelength division multiplexer (107-1) to generate the up-scan auxiliary interference signal and the down-scan auxiliary interference signal, which are received by the first photodetector (108-1) and the second photodetector (108-2) respectively. Among them, the phase φ of the formed up-scan auxiliary interference signal ur (t) is in phase with the downsweep auxiliary interference signal φ dr (t) is shown below: ； in, To measure the optical path length of the auxiliary interferometer module at the initial moment, To show the change in optical path length of the auxiliary interferometer module over time during the measurement process, and These represent the initial optical frequencies of the up-scanning laser and the down-scanning laser, respectively. and These represent the frequency changes of an upward-scanning laser and a downward-scanning laser over time, respectively, where c is the speed of light in a vacuum, and φ is the velocity of light. ur (t) and φ dr (t) represent the phases of the up-scan auxiliary interference signal and the down-scan auxiliary interference signal, respectively; The wavelength of the frequency-scanning laser emitted from the first tunable laser (101-1) or the second tunable laser (101-2) that matches the grating pitch of the long fiber Bragg grating string (104) is reflected. The reflected light from the long fiber Bragg grating string (104) from the auxiliary interference module (111) enters the frequency-stabilized laser reference module via the first circulator (103-1). It undergoes beat frequency interference with the frequency-stabilized laser emitted from the frequency-stabilized laser (101-3) after being combined by the third fiber beam splitter (102-3). The interference is received by the fifth photodetector (108-5) and converted into a reference interference signal. The fifth photodetector outputs the instantaneous frequency of the reference interference signal. as follows: ； in, λ is the wavelength of the emitted light from the frequency-stabilized laser, c is the speed of light in vacuum, and λ is the instantaneous wavelength of the reflected light from the long fiber Bragg grating string. The frequency of the reference interference signal output by the frequency-stabilized laser reference module (112) is related to the optical path length of the auxiliary interference module. As shown in the formula below: ； Where N is the number of gratings. λ is the wavelength of the frequency-stabilized laser, f is the instantaneous frequency of the output signal of the frequency-stabilized laser reference module, and c is the speed of light in vacuum.

10. The stable reference construction method according to claim 8, characterized in that, The tuning range of the first tunable laser (101-1) is 1527nm-1532nm, and the tuning range of the second tunable laser (101-2) is 1535nm-1540nm.

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