Absolute distance measurement method and device based on optical frequency comb chirped pulse interferometry

Abstract

The present invention belongs to the field of laser ranging, and specifically relates to an absolute distance measurement method and device based on optical frequency comb chirped pulse interferometry. The method comprises: using an optical frequency comb to generate and split pulsed lasers; using one of the beams as signal light to generate reference light and measurement light, with a time delay between the two corresponding to the absolute distance to be measured; widening the other beam as local oscillator light, which interferes with the reference light and measurement light, respectively, to generate two interference pulses; widening the two interference pulses, and using a high-speed photodetector and a high-speed oscilloscope to collect information about the widened two interference pulses in real time; wherein the pulse width of the local oscillator light satisfies that the reference light and measurement light can interfere with the local oscillator light at any position; and subtracting the spectral phases of the two sets of chirped pulse interference fringe information to calculate the absolute distance to be measured. The present invention can achieve rapid absolute distance measurement along the entire path without blind spots.

Description

Technical Field

[0001] The present invention belongs to the field of laser ranging, and more specifically, relates to an absolute distance measurement method and device based on optical frequency comb chirped pulse interference. Background Art

[0002] In distance measurement schemes, chirped pulse interferometry (Chirped Pulse Interferometry) occurs when the reference pulse is stretched. In 1994, Minoshima et al. first employed Chirped Pulse Interferometry to achieve three-dimensional imaging of a target. In 2016, Minoshima's group, based on optical frequency comb Chirped Pulse Interferometry (CPI), used a single-mode fiber to stretch the reference pulse to the picosecond range, achieving absolute distance measurement over three meters.

[0003] However, in previous preliminary studies, due to the lack of in-depth exploration of the phase change mechanism after pulse broadening, additional calibration steps are required to match the wavelength shift corresponding to the widest fringe with the distance measurement. More urgently, since there is no guarantee that the measurement pulse and the reference pulse can "meet" at any position, there is still a very large blind spot in the measurement path, which greatly reduces the efficiency and performance of distance measurement and limits its future application prospects. Therefore, how to eliminate the blind spot in the measurement path based on optical frequency comb chirped pulse interferometry is a scientific problem that needs to be solved urgently.

[0004] In addition, distance measurement speed is an important measurement performance indicator. Many applications require rapid transient analysis of the position or movement of the target being measured. For example, flight trajectory monitoring of weapons and equipment, spindle vibration measurement of various machine tools, dynamic analysis of aircraft engine blades, and intracavity light field evolution of mode-locked lasers all require high-speed measurement to provide guarantees. However, due to the limitations of the frame rate of the CCD (Charge Coupled Device) camera or the mechanical scanning speed of the scanning stage, the single measurement time of the spectrum analyzer is in the millisecond range, which cannot meet the needs of fast measurement (single measurement time reaches microseconds or even nanoseconds). Therefore, how to break through the bottleneck of slow measurement speed and achieve fast real-time measurement for absolute distance measurement based on optical frequency comb chirped pulse interferometry is also a problem that needs to be solved. Summary of the Invention

[0005] In response to the defects of the existing technology and the need for improvement, the present invention provides an absolute distance measurement method and device based on optical frequency comb chirped pulse interferometry, the purpose of which is to achieve rapid absolute distance measurement without blind spots along the entire path.

[0006] To achieve the above object, according to one aspect of the present invention, a method for absolute distance measurement based on optical frequency comb chirped pulse interferometry is provided, comprising:

[0007] An optical frequency comb is used to generate pulsed laser light and split it into two beams. One of the beams is used as signal light, which is split into two beams and directed to a measuring mirror and a reference mirror, respectively. The measuring mirror and the reference mirror each reflect the light to the signal light splitting position, thereby obtaining a reference light and a measurement light. The difference between the distances from the measuring mirror and the reference mirror to the signal light splitting position is the absolute distance to be measured.

[0008] Another beam of light is stretched to the nanosecond level to serve as local oscillator light; interfering with the reference light and the measurement light to generate two interference pulses; the two interference pulses are stretched respectively, and chirped pulse interference fringe information of the two stretched interference pulses is collected in real time using a high-speed photodetector and a high-speed oscilloscope; wherein the pulse width of the local oscillator light satisfies that the reference light and the measurement light can interfere with the local oscillator light at any position;

[0009] The spectral phases of the two sets of chirped pulse interference fringe information are subtracted, and the result of the subtraction is used as the product of the optical frequency and the time delay between the measurement light and the reference light to calculate the delay time, and the absolute distance to be measured is calculated from the delay time.

[0010] Furthermore, the polarization directions of the reference light and the measurement light are set to be different to achieve beam splitting.

[0011] Furthermore, the pulse width of the local oscillator light is T r / 2, where T r =1 / f rep , which represents the time interval between two adjacent pulses.

[0012] Furthermore, the absolute distance to be measured is calculated as follows:

[0013] The spectral phase Φ of the chirped pulse interference fringes of the reference light and the local oscillator light is ref,LO (ω) is expressed as:

[0014]

[0015] The spectral phase Φ of the chirped pulse interference fringes between the measurement light and the local oscillator light is meas,LO (ω) is expressed as:

[0016]

[0017] Calculate the spectral phase difference, ΔΦ=Φ meas,LO (ω)-Φ ret,LO (ω) = τω;

[0018] Calculate the measured distance using the following formula:

[0019] Where c is the speed of light in vacuum, ng is the group refractive index of air, β1, β2, and β3 are the group velocity dispersion coefficients of different orders, ω c is the central angular frequency of the optical frequency comb, z is the length of the first dispersion fiber, Φ r is the initial phase difference between the reference light and the local oscillator light, and τ is the time delay between the measurement light and the reference light.

[0020] The present invention also provides an absolute distance measurement device based on optical frequency comb chirped pulse interferometry, which is used to perform an absolute distance measurement method based on optical frequency comb chirped pulse interferometry as described above, comprising: an optical frequency comb, a fiber coupler, a first dispersive optical fiber, a first 1 / 2 wave plate, a first polarization beam splitter, a first 1 / 4 wave plate, a second 1 / 4 wave plate, a measuring mirror, a reference mirror, a second 1 / 2 wave plate, a third 1 / 2 wave plate, a beam combiner, a second polarization beam splitter, a second dispersive optical fiber, a third dispersive optical fiber, a first high-speed photodetector, a second high-speed photodetector, a high-speed oscilloscope, and a processor;

[0021] The optical frequency comb is used to emit pulsed laser light for ranging;

[0022] The optical fiber coupler is used to split the pulsed laser light, with one part used as signal light and the other part being broadened by the first dispersion optical fiber and used as local oscillator light;

[0023] A Michelson interferometer is formed by the first polarization beam splitter, the measuring mirror, and the reference mirror, and is used to generate reference light and measurement light. The distance difference between the measuring mirror and the reference mirror to the first polarization beam splitter is the absolute distance to be measured, and there is a time delay between the measurement light and the reference light corresponding to the absolute distance to be measured. The first 1 / 2 wave plate is arranged at the front end of the first polarization beam splitter, the first 1 / 4 wave plate and the second 1 / 4 wave plate are respectively arranged on the two arms of the Michelson interferometer, and the second 1 / 2 wave plate is arranged at the output end of the first polarization beam splitter for outputting reference light and measurement light. The combination of the first 1 / 2 wave plate, the first 1 / 4 wave plate, the second 1 / 4 wave plate, and the second 1 / 2 wave plate is used to enable the Michelson interferometer to output reference light and measurement light with different polarization directions.

[0024] The third half-wave plate is used to generate local oscillator light with two different polarization directions, so that after the beam combiner combines the local oscillator light output by the third half-wave plate with the reference light and the measurement light, the second polarization beam splitter separates the light pulses after the interference of the two signal lights with the local oscillator light, thereby obtaining two interference pulses;

[0025] The second dispersive optical fiber and the third dispersive optical fiber are respectively used to broaden the two interfering pulses; the first high-speed photodetector, the second high-speed photodetector and the high-speed oscilloscope are used to collaboratively acquire chirped pulse interference fringe information of the two interfering pulses after broadening in real time; the processor is used to calculate the absolute distance to be measured based on the two sets of chirped pulse interference fringe information;

[0026] The dispersion parameter and length of the first dispersive optical fiber satisfy the following requirements: the reference light and the measurement light can interfere with the local oscillator light obtained by broadening the first dispersive optical fiber at any position.

[0027] Furthermore, it also includes a power amplifier, which is arranged between the optical fiber coupler and the first 1 / 2 wave plate and is used to amplify the optical power.

[0028] Furthermore, the pulse width of the local oscillator light is T r / 2, where T r =1 / f rep , which represents the time interval between two adjacent pulses.

[0029] Furthermore, the processor calculates the absolute distance to be measured in the following manner:

[0030] The spectral phase Φ of the chirped pulse interference fringes of the reference light and the local oscillator light is ref,LO (ω) is expressed as:

[0031]

[0032] The spectral phase Φ of the chirped pulse interference fringes between the measurement light and the local oscillator light is meas,LO (ω) is expressed as:

[0033]

[0034] Calculate the spectral phase difference, ΔΦ=Φ meas,LO (ω)-Φ ref,LO (ω) = τω;

[0035] Calculate the measured distance using the following formula:

[0036] Where c is the speed of light in vacuum, n g is the group refractive index of air, β1, β2, and β3 are the group velocity dispersion coefficients of different orders, ω c is the central angular frequency of the optical frequency comb, z is the length of the first dispersion fiber, Φ r is the initial phase difference between the reference light and the local oscillator light, and τ is the time delay between the measurement light and the reference light.

[0037] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects:

[0038] This method uses dispersive fiber to significantly broaden a second pulsed laser beam to the nanosecond level, serving as the local oscillator (LO) light. This ensures that the probe pulse (i.e., signal light) and the LO pulse (i.e., LO light) always meet, eliminating the blind spot problem and enabling absolute distance measurement along the entire path. A high-speed oscilloscope is used to collect interference fringe information, minimizing single-shot measurement time and enabling rapid measurement. These two technologies work together to achieve rapid, absolute distance measurement along the entire path. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 A flowchart of an absolute distance measurement method based on optical frequency comb chirped pulse interferometry provided by an embodiment of the present invention;

[0040] Figure 2 A schematic diagram of chirped pulse interference fringe information of two interfering pulses provided in an embodiment of the present invention;

[0041] Figure 3 A comparison diagram of interference fringes collected by a spectrometer and an oscilloscope provided in an embodiment of the present invention;

[0042] Figure 4 A diagram showing the relationship between optical frequency and time provided in an embodiment of the present invention;

[0043] Figure 5 A schematic diagram of the phase difference between two interference fringes provided by an embodiment of the present invention;

[0044] Figure 6 A schematic diagram of an absolute distance measurement device based on optical frequency comb chirped pulse interferometry provided by an embodiment of the present invention.

[0045] Throughout the drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0046] 1 is a hydrogen clock, 2 is an optical frequency comb, 3 is a power amplifier, 4 is a fiber coupler, 5 is the first collimator, 6 is the first 1 / 2 wave plate, 7 is the first polarization beam splitter, 8 is the first 1 / 4 wave plate, 9 is a measuring mirror, 10 is the second 1 / 4 wave plate, 11 is a reference mirror, 12 is the second 1 / 2 wave plate, 13 is the first dispersive fiber, 14 is the second collimator, 15 is the third 1 / 2 wave plate, 16 is a beam combiner, 17 is the second polarization beam splitter, 18 is a reflector, 19 is the third collimator, 20 is the second dispersive fiber, 21 is the first photodetector, 22 is the fourth collimator, 23 is the third dispersive fiber, 24 is the second photodetector, and 25 is an oscilloscope. DETAILED DESCRIPTION

[0047] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0048] Example 1

[0049] An absolute distance measurement method based on optical frequency comb chirped pulse interferometry, such as Figure 1 Shown, including:

[0050] An optical frequency comb is used to generate pulsed laser light and split it into two beams. One of the beams is used as signal light, which is split into two beams and directed to a measuring mirror and a reference mirror, respectively. The measuring mirror and the reference mirror each reflect the light to the signal light splitting position, thereby obtaining a reference light and a measurement light. The difference between the distances from the measuring mirror and the reference mirror to the signal light splitting position is the absolute distance to be measured.

[0051] Another beam of light is stretched to the nanosecond level to serve as the local oscillator (LO) light. This light interferes with the reference light and the measurement light to generate two interference pulses. The two interference pulses are stretched separately, and chirped pulse interference fringe information of the stretched pulses is collected in real time using a high-speed photodetector and a high-speed oscilloscope. The pulse width of the LO light satisfies the requirement that the reference light and the measurement light can interfere with the LO light at any position in the spectrum.

[0052] The spectral phase difference in the two sets of chirped pulse interference fringe information is taken as the product of the optical frequency and the time delay between the measurement light and the reference light to calculate the delay time, and the absolute distance to be measured is calculated from the delay time.

[0053] This embodiment employs a dispersive optical fiber to significantly broaden a second pulsed laser beam to the nanosecond level, serving as the local oscillator (LO) light. This ensures that the probe pulse (i.e., signal light) and the LO pulse (i.e., LO light) always coincide, eliminating the blind spot issue and enabling absolute distance measurement along the entire path. Furthermore, this embodiment employs a high-speed oscilloscope to acquire interference fringe information, minimizing single measurement times and enabling rapid measurement.

[0054] As a preferred embodiment of the present invention, the polarization directions of the reference light and the measurement light are set to be different to achieve beam splitting.

[0055] The pulse width of the local oscillator light is greater than or equal to T r / 2 can solve the problem of blind spots and can be used as a preferred embodiment of the present invention. The pulse width of the local oscillator light is T r / 2where T r =1 / frep , represents the time interval between two adjacent pulses. This setting can effectively ensure that the reference light and the measurement light can interfere with the local oscillator light at any position in the spectrum. The pulse width of the two interfering pulses after broadening is T r / 2, where T r =1 / f rep , which represents the time interval between two adjacent pulses.

[0056] Finally, regarding the calculation of the absolute distance to be measured, the following explanation is given:

[0057] Assuming the third-order Taylor approximation of the spectral phase is taken into account, the spectral phase of the chirped pulse interference fringes between the reference light and the local oscillator light can be calculated as:

[0058]

[0059] In formula (1), β1, β2, and β3 are the group velocity dispersion coefficients of different orders, ω c is the central angular frequency of the optical frequency comb, z is the length of the first dispersion fiber, Φ r is the initial phase difference between the reference light and the local oscillator light.

[0060] Similarly, the spectral phase of the chirped pulse interference fringes between the measurement light and the local oscillator light is:

[0061]

[0062] In formula (2), τ is the time delay between the measurement light and the reference light.

[0063] By taking the difference between the spectral phases in formulas (1) and (2), we can obtain:

[0064] ΔΦ=Φ meas,LO (ω)-Φ ref,LO (ω)=τω(3

[0065] The measured distance L is:

[0066]

[0067] In formula (4), c is the speed of light in vacuum, n g is the group refractive index of air.

[0068] Combining formulas (3) and (4), we can obtain the measured absolute distance.

[0069] like Figure 2As shown in the figure, the upper left and upper right figures correspond to the chirped pulse interference fringes between the reference light and the local oscillator light, and the chirped pulse interference fringes between the measurement light and the local oscillator light, respectively. Hilbert transforms are performed on these two fringes to obtain the corresponding phase curves, which are plotted in the lower left figure. Subtracting the two phase curves yields the relationship between the phase difference and frequency, corresponding to the slope in the lower right figure. Its slope, dΔΦ / dω, is the delay time τ to be calculated. Combined with formula (4), the measured distance L can be calculated.

[0070] In addition, regarding the broadening of the two interfering pulse lights, the following explanation is given:

[0071] Another two dispersion optical fibers are used to respectively widen the pulse width of the interference pulse between the reference light and the local oscillator light and the interference pulse between the measurement light and the local oscillator light.

[0072] When an ultrashort pulse passes through a dispersive fiber, pulse broadening occurs due to the different phase velocities of different frequency components. The corresponding relationship between optical frequency and time is:

[0073]

[0074]

[0075] Precisely matching optical frequency with time enables rapid measurement.

[0076] The interference light pulses are then detected by a first photodetector and a second photodetector, preferably a high-speed photodetector with a bandwidth of 50 GHz. The interference signal is then measured and stored by a high-speed oscilloscope with a bandwidth of 40 GHz and a sampling rate of 80 GS / s.

[0077] Directly detecting interference fringes with a spectrometer is limited by the spectrometer's resolution, resulting in slow measurement speeds. High-speed oscilloscopes have high sampling rates, so it's preferable to use them to detect interference fringes to address this issue.

[0078] like Figure 3 The above picture is the interference fringes collected by the spectrometer, such as Figure 3 The image below shows interference fringes captured by a high-speed oscilloscope. The two images have similar shapes, and the optical frequency and time correspond. By changing the position of the measuring mirror, the fringes shift, and the corresponding optical frequency and time also change. By repeatedly changing the position of the measuring mirror, the relationship between optical frequency and time is obtained.

[0079] like Figure 4 As shown in the figure, the dots correspond to the measured data, and the solid line is the fitting line. Figure 4It can be seen that time and light frequency satisfy a linear relationship, which can be expressed as t = k·v + b, where k corresponds to the slope and b corresponds to the bias.

[0080] The method of obtaining interference fringes using a high-speed oscilloscope is similar to that of using a spectrometer. Both methods first obtain the phase through Hilbert transform, and then subtract the two phase curves. The difference is that the final result is a curve of phase difference and time, such as Figure 5 As shown in the figure, the slope dΔΦ / dt can be obtained from the figure. Substituting it into formula (6), the delay time τ can be calculated. Substituting τ into formula (4) can solve the measured distance L.

[0081]

[0082] This embodiment is based on the time stretching principle to achieve high-precision mapping of the optical frequency domain and time domain, and adopts a high-speed photoelectric detection unit to quickly detect spectral interference fringes in real time, thereby solving the problem of slow speed measurement and achieving fast distance measurement.

[0083] Example 2

[0084] An absolute distance measurement device based on optical frequency comb chirped pulse interferometry, such as Figure 6 As shown, a method for absolute distance measurement based on optical frequency comb chirped pulse interferometry as described in Example 1 is used to perform the method, comprising: an optical frequency comb 2, a fiber coupler 4, a first dispersive fiber 13, a first 1 / 2 wave plate 6, a first polarization beam splitter 7, a first 1 / 4 wave plate 8, a second 1 / 4 wave plate 10, a measuring mirror 9, a reference mirror 11, a second 1 / 2 wave plate 12, a third 1 / 2 wave plate 15, a combiner 16, a second polarization beam splitter 17, a second dispersive fiber 20, a third dispersive fiber 23, a first high-speed photodetector 21, a second high-speed photodetector 24, a high-speed oscilloscope 25, and a processor.

[0085] Among them, the optical frequency comb is used to emit continuous pulse laser for distance measurement; the fiber coupler is used to split the pulse laser, one part of which is used as signal light, and the other part is broadened by the first dispersion fiber and used as local oscillator light; a Michelson interferometer composed of a first polarization beam splitter, a measuring mirror and a reference mirror is used to generate reference light and measurement light, the distance difference between the measuring mirror and the reference mirror to the first polarization beam splitter is the absolute distance to be measured, and there is a time delay between the measurement light and the reference light corresponding to the absolute distance to be measured; the first 1 / 2 wave plate is arranged at the front end of the first polarization beam splitter, the first 1 / 4 wave plate and the second 1 / 4 wave plate are respectively arranged on the two arms of the Michelson interferometer, and the second 1 / 2 wave plate is arranged at the output end of the first polarization beam splitter for outputting reference light and measurement light, and the first 1 / 2 wave plate, the first 1 / 4 wave plate, the second 1 / 4 wave plate and the second 1 / 2 wave plate are combined to make The Michelson interferometer outputs reference light and measurement light with different polarization directions; the third 1 / 2 wave plate is used to generate local oscillator lights with two different polarization directions, so that after the local oscillator light output by the third 1 / 2 wave plate is combined with the reference light and the measurement light by the beam combiner, the second polarization beam splitter separates the light pulses after the two signal lights interfere with the local oscillator light to obtain two interference pulses; the second dispersive optical fiber and the third dispersive optical fiber are respectively used to widen the two interference pulses; the first high-speed photodetector, the second high-speed photodetector and the high-speed oscilloscope are used to cooperate in real-time acquisition of chirped pulse interference fringe information of the two widened interference pulses; the processor is used to calculate the absolute distance to be measured based on the two sets of chirped pulse interference fringe information; the dispersion parameter and length of the first dispersive optical fiber satisfy: the reference light and the measurement light can interfere with the local oscillator light obtained by widening the first dispersive optical fiber at any position.

[0086] As a preferred embodiment, the device further includes a power amplifier 3, which is arranged between the optical fiber coupler and the first 1 / 2 wave plate and is used to amplify the optical power.

[0087] That is, the working method of the device of this embodiment is as follows: first, the hydrogen clock signal is connected to the optical frequency comb as a reference, and the pulse light emitted by the optical frequency comb is amplified by the power amplifier. The amplified light is divided into two parts by the fiber coupler. One part is used as signal light and input into the Michelson interferometer composed of the first polarization beam splitter, the measuring mirror and the reference mirror. The light reflected back by the measuring mirror is the measuring light, and the light reflected back by the reference mirror is the reference light. A 1 / 4 wave plate is placed in each arm of the Michelson interferometer so that the measuring light and the reference light are combined by the first polarization beam splitter. The other part of the light is broadened by the first dispersive optical fiber and used as the local oscillator light. By reasonably designing the dispersion parameters and length of the dispersive optical fiber, the pulse width (the full width at half maximum of the pulse) of the optical pulse emitted by the local oscillator light is close to 1 / (2×f rep ), ensuring that the signal light can meet the local oscillator light at any position, where f repis the repetition frequency of the optical frequency comb. The signal light (including the measurement light and the reference light) and the local oscillator light are combined at the beam combiner to cause interference. The interference light pulses are distinguished by the second polarization beam splitter. The reflected light corresponds to the interference light pulse of the reference light and part of the local oscillator light, and the transmitted light corresponds to the interference light pulse of the measurement light and part of the local oscillator light. The second dispersive fiber and the third dispersive fiber are then used to widen the pulse width of the reflected light pulse and the transmitted light pulse to close to T r / 2, where T r =1 / f re , is the time interval between two adjacent pulses. The interference light pulses are then detected by the first photodetector and the second photodetector respectively, and then the interference signal is measured and stored by a high-speed oscilloscope.

[0088] It should be noted that in this embodiment, the central wavelength of the above-mentioned optical frequency comb is 1560nm, the repetition frequency is 250MHz, and the output power is 30mW; the power amplifier uses an erbium-doped fiber amplifier with a gain of 10dB, which amplifies the light to 230mW; and a first high-speed photodetector and a second high-speed photodetector with a bandwidth of 50GHz are also provided at the front end of the high-speed oscilloscope; the bandwidth of the high-speed oscilloscope is 40GHz, and the sampling rate is 80GS / s.

[0089] As a preferred embodiment, the pulse width of the local oscillation light is T r / 2, where T r =1 / f rep , which represents the time interval between two adjacent pulses.

[0090] Furthermore, the processor calculates the absolute distance to be measured as follows:

[0091] The spectral phase Φ of the chirped pulse interference fringes of the reference light and the local oscillator light is ref,LO (ω) is expressed as:

[0092]

[0093] The spectral phase Φ of the chirped pulse interference fringes between the measurement light and the local oscillator light is meas,LO (ω) is expressed as:

[0094]

[0095] Calculate the spectral phase difference, ΔΦ=Φ meas,LO (ω)-Φ ref,LO (ω) = τω;

[0096] Calculate the measured distance using the following formula:

[0097] Where c is the speed of light in vacuum, n gis the group refractive index of air, β1, β2, and β3 are the group velocity dispersion coefficients of different orders, ω c is the central angular frequency of the optical frequency comb, z is the length of the first dispersion fiber, Φ r is the initial phase difference between the reference light and the local oscillator light, and τ is the time delay between the measurement light and the reference light.

[0098] The related technical description is the same as that of Example 1 and will not be repeated here.

[0099] In general, the main implementation of this measurement device involves referencing an optical frequency comb to a hydrogen clock signal. The pulsed light emitted by the optical frequency comb is amplified by a power amplifier and then split into two parts by a fiber coupler. One part, serving as the signal light, enters a Michelson interferometer to generate measurement light and reference light. The light reflected by the measurement mirror is the measurement light, and the light reflected by the reference mirror is the reference light. The other part, after being broadened by a first dispersive fiber, becomes the local oscillator light. The signal light (including the measurement light and reference light) and the local oscillator light are combined in a beam splitter, causing interference. After being separated by a second polarization beam splitter, the reflected light corresponds to the reference light and a portion of the local oscillator light, while the transmitted light corresponds to the measurement light and a portion of the local oscillator light. The interference light pulses separated by the second polarization beam splitter are then pulse-width-broadened using a second dispersive fiber and a third dispersive fiber, respectively. The pulses then reach the first and second photodetectors, respectively. After the photodetectors detect the interference light pulses, a high-speed oscilloscope measures and stores the interference signal. The device in this embodiment uses dispersive fiber to significantly broaden another pulsed laser beam to the nanosecond level, serving as the local oscillator light. This ensures that the probe pulse (i.e., signal light) and the local oscillator pulse (i.e., local oscillator light) always meet, eliminating the blind spot problem and enabling full-path absolute distance measurement. A high-speed oscilloscope is used to collect interference fringe information, resulting in a short single measurement time and enabling rapid measurement. This present invention offers the advantages of eliminating blind spots, ensuring full-path measurement, and achieving rapid measurement for absolute distance measurement.

[0100] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An absolute distance measurement method based on optical frequency comb chirped pulse interferometry, characterized in that: include: Use an optical frequency comb to generate pulsed laser light and split it into beams; One of the beams is used as signal light, which is split into two beams and guided to a measuring mirror and a reference mirror respectively. The measuring mirror and the reference mirror respectively reflect the light to the signal light splitting position to obtain reference light and measurement light, wherein the distance difference between the measuring mirror and the reference mirror to the signal light splitting position is the absolute distance to be measured; Another beam of light is stretched to the nanosecond level to serve as local oscillator light; the light interferes with the reference light and the measurement light to generate two interference pulses; the two interference pulses are stretched, and chirped pulse interference fringe information of the two stretched interference pulses is collected in real time using a high-speed photodetector and a high-speed oscilloscope; wherein the pulse width of the local oscillator light satisfies that the reference light and the measurement light can interfere with the local oscillator light at any position; The spectral phases of the two sets of chirped pulse interference fringe information are subtracted, and the result of the subtraction is used as the product of the optical frequency and the time delay between the measurement light and the reference light to calculate the delay time, and the absolute distance to be measured is calculated from the delay time.

2. The absolute distance measurement method according to claim 1, characterized in that: The polarization directions of the reference light and the measurement light are set to be different to achieve beam splitting.

3. The absolute distance measurement method according to claim 1, wherein: The pulse width of the local oscillator light is T r / 2, where T r =1 / f rep , which represents the time interval between two adjacent pulses.

4. The absolute distance measurement method according to any one of claims 1 to 3, characterized in that: The absolute distance to be measured is calculated as follows: The spectral phase Φ of the chirped pulse interference fringes of the reference light and the local oscillator light is ref,LO (ω) is expressed as: The spectral phase Φ of the chirped pulse interference fringes between the measurement light and the local oscillator light is meas,LO (ω) is expressed as: Calculate the spectral phase difference, ΔΦ=Φ meas,LO (ω)-Φ ref,LO (ω) = τω; Calculate the measured distance using the following formula: Where c is the speed of light in vacuum, n g is the group refractive index of air, β1, β2, and β3 are the group velocity dispersion coefficients of different orders, ω c is the central angular frequency of the optical frequency comb, z is the length of the first dispersion fiber, Φ r is the initial phase difference between the reference light and the local oscillator light, and τ is the time delay between the measurement light and the reference light.

5. An absolute distance measurement device based on optical frequency comb chirped pulse interferometry, characterized in that: Used to perform the absolute distance measurement method based on optical frequency comb chirped pulse interferometry as claimed in claim 1, comprising: an optical frequency comb, a fiber coupler, a first dispersive fiber, a first 1 / 2 wave plate, a first polarization beam splitter, a first 1 / 4 wave plate, a second 1 / 4 wave plate, a measuring mirror, a reference mirror, a second 1 / 2 wave plate, a third 1 / 2 wave plate, a beam combiner, a second polarization beam splitter, a second dispersive fiber, a third dispersive fiber, a first high-speed photodetector, a second high-speed photodetector, a high-speed oscilloscope, and a processor; The optical frequency comb is used to emit pulsed laser light for ranging; The optical fiber coupler is used to split the pulsed laser light, with one part used as signal light and the other part being broadened by the first dispersion optical fiber and used as local oscillator light; A Michelson interferometer is formed by the first polarization beam splitter, the measuring mirror, and the reference mirror, and is used to generate reference light and measurement light. The distance difference between the measuring mirror and the reference mirror to the first polarization beam splitter is the absolute distance to be measured, and there is a time delay between the measurement light and the reference light corresponding to the absolute distance to be measured. The first 1 / 2 wave plate is arranged at the front end of the first polarization beam splitter, the first 1 / 4 wave plate and the second 1 / 4 wave plate are respectively arranged on the two arms of the Michelson interferometer, and the second 1 / 2 wave plate is arranged at the output end of the first polarization beam splitter for outputting reference light and measurement light. The combination of the first 1 / 2 wave plate, the first 1 / 4 wave plate, the second 1 / 4 wave plate, and the second 1 / 2 wave plate is used to enable the Michelson interferometer to output reference light and measurement light with different polarization directions. The third half-wave plate is used to generate local oscillator light with two different polarization directions, so that after the beam combiner combines the local oscillator light output by the third half-wave plate with the reference light and the measurement light, the second polarization beam splitter separates the light pulses after the interference of the two signal lights with the local oscillator light, thereby obtaining two interference pulses; The second dispersive optical fiber and the third dispersive optical fiber are respectively used to broaden the two interfering pulses; the first high-speed photodetector, the second high-speed photodetector and the high-speed oscilloscope are used to collaboratively acquire chirped pulse interference fringe information of the two interfering pulses after broadening in real time; the processor is used to calculate the absolute distance to be measured based on the two sets of chirped pulse interference fringe information; The dispersion parameter and length of the first dispersive optical fiber satisfy the following requirements: the reference light and the measurement light can interfere with the local oscillator light obtained by broadening the first dispersive optical fiber at any position.

6. The absolute distance measuring device according to claim 5, characterized in that It also includes a power amplifier, which is arranged between the optical fiber coupler and the first 1 / 2 wave plate and is used to amplify the optical power.

7. The absolute distance measuring device according to claim 6, characterized in that: The pulse width of the local oscillator light is T r / 2, where T r =1 / f rep , which represents the time interval between two adjacent pulses.

8. The absolute distance measuring device according to any one of claims 5 to 7, characterized in that: The processor calculates the absolute distance to be measured in the following manner: The spectral phase Φ of the chirped pulse interference fringes between the reference light and the local oscillator light is ref,LO (ω) is expressed as: The spectral phase Φ of the chirped pulse interference fringes between the measurement light and the local oscillator light is meas,LO (ω) is expressed as: Calculate the spectral phase difference, ΔΦ=Φ meas,LO (ω)-Φ ref,LO (ω) = τω; Calculate the measured distance using the following formula: Where c is the speed of light in vacuum, n g is the group refractive index of air, β1, β2, and β3 are the group velocity dispersion coefficients of different orders, ω c is the central angular frequency of the optical frequency comb, z is the length of the first dispersion fiber, Φ r is the initial phase difference between the reference light and the local oscillator light, and τ is the time delay between the measurement light and the reference light.

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