High-precision double-optical-comb speed measurement method and speed measurement device

Abstract

The invention discloses a high-precision double-optical-comb speed measurement method and device. The method comprises the steps that a double-optical-comb system with a signal optical comb and a local oscillator optical comb is arranged; a target object is arranged in a distance measuring light path system, and the distance measuring light path system is debugged to enable signal light combs of a measuring arm and a reference arm to generate interference signals with local oscillator light combs; adjusting the center frequency of radio frequency spectrum comb teeth of the double optical combs to ensure that the radio frequency spectrum corresponding to the interference signal is in a non-aliasing interval; when the target object is in a moving state, collecting a non-aliasing interference signal of the ranging light path system, and calculating a to-be-measured non-fuzzy distance of the target object in real time based on the non-aliasing interference signal; and subtracting two adjacent groups of to-be-measured non-fuzzy distances of the target object, and calculating to obtain a speed value of the target object. Therefore, the influence of the actual repetition frequency difference change caused by the target motion of the measuring arm on the speed estimation can be corrected.

Description

Technical Field

[0001] The present invention relates to a high-precision dual optical frequency comb velocity measurement method and a velocity measurement device, and relates to the technical field of optical precision measurement. Background Art

[0002] High-precision velocity measurement has important applications in military weapons, aerospace, rail transit, etc. Among them, in the military field: carrier-based aircraft takeoff and landing positioning guidance requires real-time positioning of moving targets with speeds ranging from dozens of km / h to hundreds of km / h. The development of some military weapons, such as the identification of the trajectory and speed of a bullet during its movement, is the evaluation basis for reflecting the weapon's firing ability and firing state. In the aerospace field: in the space debris impact experiment, the speed of the space debris can reach 1000 km / h or even higher. In addition, in some application scenarios such as navigation and positioning target tracking, it is often necessary to obtain the position information and speed information of the current aircraft at the same time, and there are also high requirements for the real-time performance of speed and position measurement. In the rail transit field: there are also some high-speed motion scenarios, such as the detection of the train operation state, which requires real-time feedback calibration of the position information and speed information.

[0003] Currently, the commonly used velocity measurement methods include the magnetic induction coil method, the ultrasonic velocity measurement method, and the high-speed photography method, etc. Among them, the magnetic induction coil method uses the induced electromotive force generated after the target object passes through a constant magnetic field to obtain the velocity of the target object. The ultrasonic velocity measurement method uses the Doppler effect. When the sound source emitting ultrasonic waves and the detector receiving ultrasonic waves move relative to the object to be measured, the frequency of the received ultrasonic waves will change. The high-speed photography method uses a high-speed camera to directly record the change in the position of the object in a short time and infer the magnitude of the velocity. The above-mentioned existing methods have simple devices and can generally be used in scenarios with low accuracy requirements, such as vehicle violation detection, civilian navigation and positioning, etc.

[0004] For high-precision measurement requirements, optical means are often used to achieve them. Among them, the dual-frequency laser interferometer, as a mature product, can realize continuous tracking measurement of distance. Similarly, by measuring the optical beat frequency with the high coherence and Doppler frequency shift effect of the laser, the velocity of the target object can be obtained. In some scenarios, in order to obtain distance and velocity information at the same time, it is often necessary to combine multiple sensors for fusion measurement. For example, the global satellite navigation positioning system and laser Doppler velocimetry are fused. The high-precision velocity measurement characteristics of the laser can assist the positioning accuracy of navigation. However, this places certain requirements on the algorithm and the synchronization of the system, and also increases the complexity of the system.

[0005] Since the new optical frequency comb light source has the characteristic of frequency tracing, it has a wide range of applications in precision measurement. For example, the dual optical comb ranging technology can achieve micron-level accuracy and has the advantages of being able to disconnect and continue the light. Considering that speed measurement can be achieved by the distance differential method, the high-precision ranging advantage also helps to improve the accuracy of speed measurement. At present, there are two methods for measuring speed using dual optical combs: based on a microcavity dual optical comb as a light source, the continuous distance measurement value and high refresh rate are used to measure the bullet speed and the turntable speed. However, this method only measures the speed of the object perpendicular to the direction of light beam propagation, not the traditional speed measurement along the light beam direction; in addition, based on the dual optical comb system of electro-optical modulation, the principle of FWCW (frequency modulated continuous wave) can be used to achieve multi-channel parallel speed and distance measurement. However, this method is limited by the principle of FWCW, resulting in low speed measurement accuracy, and the speed measurement error for 10m / s is within 0.5m / s; based on the mode-locked fiber dual optical comb system, the envelope extraction method is used to measure the distance, and the speed measurement result is further obtained by using the difference of the distance. However, this method only measures low-speed moving targets of 0.5m / s, and does not conduct a systematic analysis of the situation of high-speed targets. Summary of the invention

[0006] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, in view of the above problems, the purpose of the present invention is to provide a high-precision dual-optical comb speed measurement method and speed measurement device, which can correct the influence of the actual repetition frequency difference change caused by the target movement of the measuring arm on the speed estimation.

[0007] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention is:

[0008] In a first aspect, the present invention provides a high-precision dual-optical comb velocity measurement method, the method comprising:

[0009] A dual optical comb system having a signal optical comb and a local oscillator optical comb is provided;

[0010] The target object is placed in the ranging optical path system, and the ranging optical path system is adjusted so that the signal optical combs of the measuring arm and the reference arm generate interference signals with the local oscillator optical comb;

[0011] Adjust the center frequency of the RF spectrum teeth of the dual-optical comb to ensure that the RF spectrum corresponding to the interference signal is in the non-aliasing range;

[0012] When the target object is in motion, a non-aliasing interference signal in the distance measurement optical path system is collected, and an unambiguous distance to be measured of the target object is calculated in real time based on the non-aliasing interference signal;

[0013] The speed of the target object is calculated by subtracting two adjacent groups of unambiguous distances to be measured.

[0014] In some possible embodiments, the calculation formula for the non-ambiguous distance to be measured is as follows:

[0015]

[0016] In the formula, L' is the non-ambiguous distance to be measured, v g is the group velocity of the pulse, Δt is the time delay of the interference signals of the measurement arm and the reference arm, f r1 is the repetition frequency of the optical frequency comb of the signal, Δf r is the sub-frequency comb frequency interval.

[0017] In some possible embodiments, the calculation formula for the velocity value of the target object is as follows:

[0018]

[0019] In the formula, v is the velocity value of the target object, and ΔL is the difference between two adjacent groups of non-ambiguous distances to be measured of the target object.

[0020] In some possible embodiments, it further includes steps capable of realizing the distance measurement of the target object. The process is as follows: The non-ambiguous distance to be measured L' of the continuously measured target object is unwrapped with a period of v g / 2f r1 to obtain the distance measurement result of the target object. The calculation formula is as follows:

[0021] L = unwrap(L i ′, v g / 2f r1 );

[0022] In the formula, L is the distance measurement result of the target object, L i ′ is the non-ambiguous distance to be measured calculated from the i-th pair of measurement and reference signals, and unwrap is the unwrapping function.

[0023] In some possible embodiments, to ensure that the radio frequency spectra corresponding to the interference signals of the two arms are in the non-aliasing interval, it is implemented by using two band-pass filters. The band-pass filters are used to process the interference signals. Among them, the bandwidths of the two band-pass filters are both The center wavelength intervals differ by This parameter can ensure that the velocity measurement range is -Δf r v g / 2f r1 < v < Δf r v g / 2f r1 when the signal is not aliased.

[0024] In some possible embodiments, both the signal optical frequency comb and the local oscillator optical frequency comb are fiber mode-locked optical frequency combs, and both the signal optical frequency comb and the local oscillator optical frequency comb need to be re-frequency locked.

[0025] In a second aspect, the present invention also provides a speed measurement device for implementing the dual-optical-comb speed measurement method. The device includes:

[0026] A light source module, which uses two re-frequency locked optical frequency combs with a small re-frequency difference, including a signal optical frequency comb and a local oscillator optical frequency comb;

[0027] A speed measurement and ranging module, which measures a target object through a ranging optical path system, so that the signal optical frequency comb returned from the measurement arm and the reference arm interferes with the local oscillator optical frequency comb to generate an interference signal;

[0028] An anti-aliasing detection module, which is used to make the spectra of the interference signals of the two arms in a non-aliasing interval;

[0029] A data acquisition and processing module, which is used to process the acquired non-aliasing interference signals and output the speed information and / or distance information of the target object.

[0030] In some possible embodiments, the ranging optical path system adopts a spatial Michelson orthogonal polarization interference optical path or an all-fiber anti-blind-zone ranging optical path.

[0031] In some possible embodiments, the anti-aliasing detection module includes two band-pass filters with different central wavelengths, which are used to process the interference signals. The bandwidths of the two band-pass filters are both The central wavelength intervals differ by This parameter can ensure that the speed measurement range is -Δf r v g / 2f r1 < v < Δf r v g / 2f r1 When the signal is not aliased, where f r1 is the repetition frequency of the signal optical frequency comb, Δf r is the sub-frequency comb frequency interval, v is the speed of the target object, and v g is the group velocity of the pulse.

[0032] In some possible embodiments, both the signal optical frequency comb and the local oscillator optical frequency comb are fiber mode-locked optical frequency combs.

[0033] Due to the above technical solutions adopted by the present invention, it has the following characteristics:

[0034] 1. Based on the dual-optical-comb ranging principle, the present invention proposes a dual-optical-comb speed measurement method, which can correct the influence of the actual re-frequency difference change caused by the target movement of the measurement arm on the speed estimation.

[0035] 2. The present invention is provided with a band - pass filter with dual wavelengths, which can solve the problem of spectral aliasing of interference signals caused by the movement of the target object.

[0036] 3. The speed measurement accuracy of the present invention depends on the accuracy of dual - optical - comb ranging and the accuracy of repetition - frequency locking. At high speeds, compared with the accuracy of traditional speed - measurement methods, it is improved, and high - precision simultaneous measurement of speed and distance can be achieved.

[0037] In summary, the present invention can be widely applied to ranging and speed - measurement scenarios such as high - speed moving target tracking, carrier - based aircraft take - off and landing guidance, and shell trajectory measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] By reading the following detailed description of the preferred embodiments, various other advantages and benefits will become clear to those of ordinary skill in the art. The drawings are only for the purpose of showing the preferred embodiments and are not considered as limiting the present invention. Throughout the drawings, the same reference numerals are used to represent the same components. In the drawings:

[0039] Figure 1 is a schematic diagram of the principle of dual - optical - comb ranging according to an embodiment of the present invention. Among them, (a) is a schematic diagram of the dual - optical - comb ranging device, and (b) is a schematic diagram of the result of multi - longitudinal - mode heterodyne interference of the local - oscillator light and the signal - light comb teeth.

[0040] Figure 2 is a schematic diagram of the interference signal collected in the speed - measurement scenario according to an embodiment of the present invention.

[0041] Figure 3 is a schematic diagram of the structure of the dual - optical - comb speed - measurement device according to an embodiment of the present invention.

[0042] Figure 4 is a structural diagram of the speed - measurement and ranging module according to an embodiment of the present invention. Among them, (a) uses a spatial Michelson orthogonal polarization interference optical path as the ranging optical path, and (b) uses an all - fiber blind - area - eliminating ranging optical path;

[0043] Figure 5 is a radio - frequency - optical - frequency relationship diagram of the anti - aliasing interference signals at different speeds according to an embodiment of the present invention. Among them, (a), (b), and (c) are schematic diagrams of the radio - frequency - optical - frequency relationships of two band - pass filters corresponding to different speed intervals respectively.

[0044] Figure 6 is a schematic diagram of the specific application of the dual - optical - comb speed - measurement device according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0045] It should be understood that the terms used herein are for the purpose of describing particular example embodiments only and are not intended to be limiting. Unless the context clearly dictates otherwise, the singular forms "a", "an", and "the" as used herein may also include the plural forms. The terms "comprising", "including", "containing", and "having" are inclusive and thus specify the presence of stated features, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and / or combinations thereof. Method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order described or illustrated, unless an execution order is explicitly stated. It should also be understood that additional or alternative steps may be used.

[0046] Although the terms first, second, third, etc. may be used herein to describe multiple elements, components, regions, layers, and / or sections, these elements, components, regions, layers, and / or sections should not be limited by these terms. These terms may be used only to distinguish one element, component, region, layer, or section from another. Unless the context clearly indicates otherwise, terms such as "first", "second", and other numerical terms when used herein do not imply an order or sequence. Thus, a first element, component, region, layer, or section discussed below may be referred to as a second element, component, region, layer, or section without departing from the teachings of example embodiments.

[0047] For ease of description, spatial relative relationship terms may be used herein to describe the relationship of one element or feature shown in the figures to another element or feature, such as "inside", "outside", "inner side", "outer side", "below", "above", etc. Such spatial relative relationship terms are intended to include different orientations of the device in use or operation in addition to the orientation depicted in the figures.

[0048] Since some current optical frequency comb - based velocity measurement methods only measure low - speed moving targets and do not systematically analyze the situation of high - speed targets. The high - precision dual - optical - comb velocity measurement method and velocity measurement device provided by the present invention include: setting up a dual - optical - comb system with a signal optical comb and a local oscillator optical comb; placing the target object in the ranging optical path system, and debugging the ranging optical path system so that the signal optical combs of the measurement arm and the reference arm and the local oscillator optical comb generate interference signals; adjusting the center frequency of the radio - frequency spectral teeth of the dual - optical combs to ensure that the radio - frequency spectrum corresponding to the interference signal is in the non - aliasing interval; when the target object is in a moving state, collecting the non - aliasing interference signals of the ranging optical path system, and calculating the to - be - measured unambiguous distance of the target object in real - time based on the non - aliasing interference signals; taking the difference between two adjacent sets of to - be - measured unambiguous distances of the target object to calculate the speed value of the target object. Therefore, the present invention can correct the influence on speed estimation caused by the change of the actual repetition - frequency difference due to the target movement in the measurement arm.

[0049] Exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided so that the present invention can be more thoroughly understood and the scope of the present invention can be completely conveyed to those skilled in the art.

[0050] As Figure 1 shown in (a), the signal optical comb and the local oscillator optical comb respectively emit two pulse sequences with different repetition frequencies. After the pulse sequence emitted by the signal optical comb is split by the non - polarization beam splitter BS1, a pair of pulses with a certain time interval is reflected back, and then combined and interfered with the local oscillator optical comb at the non - polarization beam splitter BS2, passed through the band - pass filter BPF, and detected by the photodetector PD. Finally, after passing through the electrical low - pass filter LPF, a pair of pulses in the electrical radio - frequency domain is obtained. The pulses in the radio - frequency domain are the result of the multi - longitudinal - mode heterodyne interference of the local oscillator light and the signal optical - comb teeth in the optical - frequency domain. As Figure 1 shown in (b), where f r1 is the repetition frequency of the signal optical comb, f r2 is the repetition frequency of the local oscillator optical comb, and the frequency interval of the obtained sub - frequency comb is Δf r , which is the repetition - frequency difference between the signal light and the local oscillator light. Among them, the to - be - measured unambiguous distance L' is defined as the interval between the mirror corresponding to the measured target object and the mirror corresponding to the reference arm, and can be calculated by the following formula:

[0051]

[0052] where v g is the group velocity of the pulse, and Δt is the time delay of the interference signals of the measurement arm and the reference arm.

[0053] Since the refresh rate of dual-comb ranging depends on the repetition rate difference, for scenarios where the target object is in motion, based on the high refresh rate feature of the dual-comb, the speed to be measured can be obtained by taking the difference in distances. The basic principle of dual-comb speed measurement is described below. According to the principle of dual-comb interference, the interference signal for speed measurement is expressed as follows:

[0054]

[0055]

[0056] L M = L m0 + vt(3);

[0057] In the formula, A(i) represents the intensity of the i-th sub-frequency comb tooth, the number of teeth is 2m + 1, f RF (i) represents the corresponding tooth frequency, f LO (i) and f s (i) represent the optical frequencies of the local oscillator optical comb and the signal optical comb corresponding to the beat frequency teeth, L LO and L R represent the distances corresponding to the reference arms of the local oscillator light and the signal light, L M represents the real-time distance corresponding to the measurement arm of the signal light, which contains information about the movement of the target object. Among them, L m0 represents the position of the target object at the initial moment of movement, v represents the speed of the target object, I R and I M are the interference signals of the sub-frequency comb measurement arm and the reference arm returning pulses collected. The non-ambiguous distance L' to be measured = L M - L R .

[0058] When the target object is in motion, the distance between the measurement arm and the reference arm is constantly changing. Therefore, the distances between several pairs of interference signals as shown in Figure 2 are also constantly changing. After derivation, different from the interference signal of the reference arm, the moving target changes the center frequency and repetition rate difference of the interference signal of the measurement arm. Among them, the center frequency is:

[0059]

[0060] Among them, f s (0) represents the tooth frequency of the optical frequency comb with the serial number 0 (i.e., the carrier of the central tooth of the optical comb spectrum), f RF (0) represents the tooth frequency of the sub-frequency comb with the serial number 0 (sub-frequency comb carrier).

[0061] The repetition rate difference is:

[0062]

[0063] It can be seen that due to the moving object, the measured pulse interference signal corresponds to a new repetition frequency difference Δf r ′, which is related to the velocity and is constantly changing.

[0064] According to formulas (4) and (5), for a high-speed moving object, the change brought by the center frequency may cause the interference signal to be located at 0 frequency or around f r1 / 2, that is, it may cause spectral aliasing of the interference signal, affecting the solution of dual-comb ranging. In addition, when calculating the velocity, the repetition frequency difference corresponding to the interference signal of the measurement arm needs to be used, and the new repetition frequency difference is related to the velocity, which affects the measurement accuracy of the velocity. To solve these two problems, the velocity measurement method and device of the present invention will be described in detail below.

[0065] Since the distance of the target object is constantly changing, the specific velocity calculation method is to use the change amount of the distance between two adjacent measurements and the time interval between the two times to obtain the velocity. However, for the interference signal of the measurement arm, its actual time interval has changed and is no longer 1 / Δf r , but 1 / Δf r ′, and the following equation holds:

[0066]

[0067] It can be obtained that:

[0068]

[0069] In the formula, ΔL is the change amount of the distance corresponding to two adjacent ranging results.

[0070] Since the accuracy of dual-comb ranging can reach the micron level, which is relatively high compared to other distance measurement methods, this high-precision feature is transmitted to the estimation of the velocity. In addition, since the differential distance method is used to measure the velocity, the advantage of this method is that the relative accuracy of the measured velocity is independent of the absolute value of the velocity. In the case of high-speed motion, sufficient velocity measurement accuracy can also be obtained: for example, when the ranging accuracy is 10 μm at a single point, for a velocity measurement of 100 m / s and a repetition frequency difference of 2 kHz, a velocity accuracy result of 0.02 m / s can be obtained at a single point, and its relative velocity measurement accuracy can reach 0.02%, which is better than the common laser Doppler velocimetry method. In addition, the ranging distance of the dual-comb is limited by the unambiguous range (the distance interval between adjacent pulses of the signal light, v g / 2f r1) Limitation: When the speed is relatively high, for example, for a pulse repetition frequency of 100 MHz, a pulse repetition frequency difference of 2 kHz, and a speed of 1000 m / s, the change in distance between two adjacent measurements is 0.5 m, approaching the non-ambiguity range of dual-comb ranging. However, due to the continuous movement of the target object, it is possible to track based on the change in dual-comb ranging to obtain the true distance result beyond the non-ambiguity range; it is also possible to obtain an integer multiple of the distance beyond the non-ambiguity range through other auxiliary rough measurement methods.

[0071] Based on the above dual-comb ranging and velocity measurement principles, as Figure 3 shown, the high-precision dual-comb velocity measurement device provided in this embodiment includes a light source module 1, a velocity and distance measurement module 2, an anti-aliasing detection module 3, and a data acquisition and processing module 4, where:

[0072] The light source module 1, namely two optical frequency combs with a small pulse repetition frequency difference, includes a signal optical frequency comb and a local oscillator optical frequency comb;

[0073] The velocity and distance measurement module 2 sets up a ranging optical path system and a target object 5 to enable the signal optical frequency comb and the local oscillator optical frequency comb to generate an interference signal for velocity measurement and ranging;

[0074] The anti-aliasing detection module 3, due to the different interference signal spectra of the measurement arm and the reference arm caused by the velocity change, its function is to make the interference signal spectra of both arms in the non-aliasing interval;

[0075] The data acquisition and processing module 4 is used to collect the non-aliasing interference signal and process it, and output the distance information and / or velocity information of the target object 5.

[0076] In a preferred embodiment of the present invention, the light source module 1 includes two optical frequency comb light sources with a small pulse repetition frequency difference. Among them, the optical frequency comb light source can adopt a fiber mode-locked optical frequency comb, and both optical frequency combs need to be locked in pulse repetition frequency.

[0077] In a preferred embodiment of the present invention, the ranging optical path system can adopt a spatial Michelson orthogonal polarization interference optical path or an all-fiber blind-zone elimination ranging optical path, as shown in Figure 4 (a) and Figure 4 (b) respectively.

[0078] Since the interval between the reference and measurement interference signals continuously changes during the movement of the dual-comb target object, the main purpose of this module is to eliminate the blind-zone range in dual-comb ranging. The spatial optical path is as shown in Figure 4As shown in (a), the pulse emitted by the signal light is divided into two orthogonally polarized signals after passing through the polarization beam splitter PBS, and then passes through the quarter-wave plates Q1 and Q2. The pulses returned after passing through the reference optical path and the measurement optical path are divided into two paths after passing through the polarization beam splitter PBS and the non-polarizing beam splitter BS. Then, the signal emitted by the local oscillator light also passes through the non-polarizing beam splitter BS and is divided into two paths, which are respectively combined with the pulses of the signal light, and then interfere with the signal optical comb after passing through the polarizer P1 and the polarizer P2. The optical fiber optical path is as Figure 4 As shown in (b), the light emitted by the signal optical comb is divided into two paths by the fiber coupler CP1. One path passes through the circulator CIRC and the collimator COL and is emitted onto the moving target object 5, and then the reflected pulse enters the fiber coupler CP4; the local oscillator optical signal is divided into two paths by the fiber coupler CP3. One path is combined and interfered with the other reference light divided by the fiber coupler CP1 through the fiber coupler CP2, and the other path is combined and interfered with the signal light.

[0079] In a preferred embodiment of the present invention, the anti-aliasing detection module 3 includes two band-pass filters BPF1 and BPF2 with different central wavelengths. The central wavelength of the band-pass filter BPF1 is selected at the central position of the optical comb spectrum, and the central wavelength of the band-pass filter BPF2 is different from the central wavelength of the band-pass filter BPF1. The purpose of the anti-aliasing detection module 3 is that during the movement of the target object 5, the radio frequency spectrum of the interference signal will change, resulting in the radio frequency spectrum position of the pulse in the measurement arm being at 0 frequency or f r1 / 2 vicinity. By selecting the central wavelengths of 2 different band-pass filters, it can be ensured that the radio frequency spectrum of the interference signal corresponding to one of the band-pass filters is in the non-aliasing interval.

[0080] Further, in order to illustrate the selection process of the bandwidth and central wavelength of the band-pass filter in the anti-aliasing detection module 3, taking a group of common optical frequency comb ranging parameters as an example, assuming that the repetition frequency of the optical frequency comb is 100 MHz, the repetition frequency difference is 2 kHz, and the central frequency in the optical frequency domain is 1.92×10 14 Hz, then when the speed is 10 m / s, the change amount of the central frequency in the radio frequency domain is 6.4 MHz, the repetition frequency difference is 1996.67 Hz, when the speed is 500 m / s, the central frequency change amount is 320 MHz, the repetition frequency difference is 1833.33 Hz, and when the speed is -1000 m / s, the central frequency change amount is 640 MHz, the repetition frequency difference is 2333.33 Hz. From the above parameters, it can be seen that for high-speed moving objects, the change amounts of the central frequency and the repetition frequency difference are far beyond the stationary state, so anti-aliasing design is required. The specific parameters are that the bandwidths of the two band-pass filters are both The central wavelength interval difference is This parameter can ensure that the speed measurement range is -Δfr v g / 2f r1 < v < Δf r v g / 2f r1 When the signal is not aliased. The following specifically explains three cases, namely when the speed of the target object is approximately 0, much greater than 0, and much less than 0.

[0081] As Figure 5 shown, the solid line shows the relationship polyline between the optical frequency and radio frequency of the interference signal corresponding to the reference target, and the dashed line shows the relationship between the optical frequency and radio frequency of the interference signal corresponding to the moving target. Assume that first, the central wavelength corresponding to the band-pass filter BPF2 is selected to satisfy that the spectrum of the corresponding reference target is located within the non-aliasing interval (the intersection area of the gray box and the solid line does not pass through the 0 frequency or f r1 / 2); then, since the moving target changes the central frequency and pulse repetition frequency difference of the radio frequency spectrum, the slope and the left and right positions of the corresponding dashed polyline change relative to the original solid line. The following is divided into three cases: When the speed of the target object is approximately 0, the moving range of the central frequency of the radio frequency spectrum is much larger than the change in the slope. Figure 5 (a) shows the case where the band-pass filter BPF1 is in the non-aliasing interval of the dashed polyline, while the band-pass filter BPF2 is in the aliasing interval of the dashed polyline; when the speed of the target object is much less than 0, the changes in both the central frequency and slope of the radio frequency spectrum are relatively large, and the non-aliasing interval of the dashed line becomes smaller relative to the solid line. Since the bandwidth of the two filters is , it can ensure that when the speed -Δf r v g / 2f r1 < v < 0, one of the band-pass filters BPF1 / BPF2 is in the non-aliasing interval. One such case is as Figure 5 (b) shows, where the band-pass filter BPF1 is in the non-aliasing interval of the dashed polyline, while the band-pass filter BPF2 is in the aliasing interval; when the speed of the target object is much greater than 0, the range of the non-aliasing interval becomes larger relative to the interval of the reference target. When the speed 0 < v < Δf r v g / 2f r1 < v, at least one of the band-pass filters BPF1 / BPF2 is in the non-aliasing interval. One such case is as Figure 5 (c) shows.

[0082] In a preferred embodiment of the present invention, the main function of the data acquisition and processing module 4 is to collect the non-aliasing interference signal and calculate the distance and speed. The specific implementation method can collect data using devices such as a data acquisition card or an oscilloscope, and then use software such as MATLAB to perform subsequent processing on the data; it can also use a hardware system such as an FPGA to perform real-time processing on the collected data, which will not be elaborated here.

[0083] The high-precision dual optical frequency comb velocity measurement device and ranging and velocity measurement method of the present invention will be described in detail below through specific embodiments.

[0084] As Figure 3 、 Figure 6 shown, the high-precision dual optical frequency comb velocity measurement device provided in this embodiment includes:

[0085] The light source module 1 uses a signal optical frequency comb and a local oscillator optical frequency comb as two dual optical frequency comb systems with a small repetition frequency difference.

[0086] The velocity measurement and ranging module 2 uses a ranging optical path system including a polarization beam splitter PBS, quarter-wave plates Q1-Q2, a non-polarizing beam splitter BS1, and a reference target as a corner cube or a mirror, and a corresponding corner cube or mirror is also placed at the target object 5. Among them, the entire ranging optical path system in this embodiment uses an orthogonal polarization optical path to separate the pulses returned by the measurement arm and the reference arm. The specific transmission process is as follows: The signal optical frequency comb is split by the polarization beam splitter PBS, and a part of the emitted light is emitted to the reference target through the quarter-wave plate Q1 as the reference light, and the other part of the light is emitted to the target object 5 through the quarter-wave plate Q2 as the measurement light. After the reference light and the measurement light return, they are combined by the polarization beam splitter PBS and then split by the non-polarizing beam splitter BS1; the local oscillator optical frequency comb is also split by the non-polarizing beam splitter BS1.

[0087] The anti-aliasing detection module 3 includes band-pass filters BPF1-BPF2 with different central wavelengths, non-polarizing beam splitters BS2-BS3, and polarizers P1-P4. Among them, after the signal light and the local oscillator light passing through the velocity measurement and ranging module 2 are split by the non-polarizing beam splitter BS1, they respectively enter different band-pass filters BPF1-BPF2 for filtering, and then are split by the non-polarizing beam splitters BS2 / BS3, and finally after passing through the polarizers P1-P4, the reference light and the measurement light of the signal optical frequency comb respectively interfere with the local oscillator optical frequency comb.

[0088] The data acquisition and processing module 4 includes photodetectors PD1-PD4, which respectively correspond to different interference signals. The photodetectors PD1-PD4 correspond to the band-pass filter BPF1 + reference arm signal, the band-pass filter BPF1 + measurement arm signal, the band-pass filter BPF2 + reference arm signal, and the band-pass filter BPF2 + measurement arm signal.

[0089] This embodiment also provides a high-precision dual optical frequency comb velocity measurement method, including:

[0090] S1. According to the repetition frequencies of the two optical frequency combs, set appropriate repetition frequency differences and the parameters of the band-pass filters, and adjust the center frequencies of the radio frequency spectral teeth of the two optical frequency combs. In this embodiment, it is assumed that when the target object is stationary, the radio frequency spectrum corresponding to the band-pass filter BPF2 is in the non-aliasing interval.

[0091] S2. When the moving object is in a moving state, collect the interference signals through the photodetectors PD1 - PD4, and observe the spectra of these four groups of interference signals, which are divided into three cases:

[0092] (1) If the interference signals of the photodetectors PD1 - PD4 are all in the non - aliasing frequency range of the spectrum, then the four groups of interference signals can be subjected to FFT transformation, and then the phase of the spectrum is obtained. After phase unwrapping, the corresponding slopes t1 - t4 are calculated. Then, using the signals I1 - I2 corresponding to the photodetectors PD1 - PD2, and according to L s1 ' = v g (t2 - t1)Δf r / 2f r1 the measured non - ambiguous distance L s1 ' is obtained. Using the signals I3 - I4 corresponding to the photodetectors PD3 - PD4, and according to L s2 ' = v g (t4 - t3)Δf r / 2f r1 the distance L s2 ' is obtained. Then, take the average to get L'=(L s1 '+L s2 ) / 2.

[0093] (2) If the interference signals of the photodetectors PD1 and PD4 are in the aliasing frequency range of the spectrum, and PD2 and PD3 are in the non - aliasing range, only for these two groups of signals I2, I3, after phase unwrapping, the corresponding slopes t2, t3 are calculated, and according to L' = v g (t2 - t3)Δf r / 2f r1 the measured non - ambiguous distance L' is obtained.

[0094] (3) If the interference signals of the photodetector PD1 and the photodetector PD2 are in the aliasing frequency range of the spectrum, and the photodetectors PD3 and PD4 are in the non - aliasing range, only for these two groups of signals I3, I4, after phase unwrapping, the corresponding slopes t3, t4 are calculated, and according to L' = v g (t4 - t3)Δf r / 2f r1 the distance L' is obtained.

[0095] S3. Based on the movement of the target object 5, several measured non - ambiguous distance L i ' values are obtained. The difference between adjacent two groups of distances L i ' is calculated to get ΔL, and then substituted into formula (7) to obtain the corresponding instantaneous velocity value.

[0096] S4. For the velocity satisfying - Δf r vg / 2f r1 <v < Δf r v g / 2f r1 When, there is |ΔL| < v g / 2f r1 , then the distance values obtained from continuous measurements can be unwrapped with v g / 2f r1 as the period to obtain a ranging result beyond the non-ambiguity range, and then the distance measurement result of the target object is obtained: L = unwrap(L i ', v g / 2f r1 ), where, unwrap represents the unwrapping function, and L i ′ is the non-ambiguous distance to be measured calculated from the i-th pair of measurement and reference signals.

[0097] Each embodiment in this specification is described in a progressive manner. The same or similar parts among the embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In the description of this specification, the descriptions with reference to terms such as "a preferred embodiment", "furthermore", "specifically", "in this embodiment", etc. mean that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the embodiments of this specification. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0098] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high-precision dual optical frequency comb velocity measurement method, characterized in that, The method includes: A dual optical comb system having a signal optical comb and a local oscillator optical comb is provided; The target object is placed in the ranging optical path system, and the ranging optical path system is adjusted so that the signal optical combs of the measuring arm and the reference arm generate interference signals with the local oscillator optical comb; Adjust the center frequency of the RF spectrum teeth of the dual-optical comb to ensure that the RF spectrum corresponding to the interference signal is in the non-aliasing range; When the target object is in motion, a non-aliasing interference signal in the distance measurement optical path system is collected, and an unambiguous distance to be measured of the target object is calculated in real time based on the non-aliasing interference signal; The speed of the target object is calculated by subtracting two adjacent groups of unambiguous distances to be measured.

2. The dual-comb velocimetry method according to claim 1, wherein The calculation formula of the unambiguous distance to be measured is: where L' is the non-ambiguous distance to be measured, v g is the group velocity of the pulse, Δt is the time delay of the interference signal between the measurement arm and the reference arm, f r1 is the repetition frequency of the signal optical comb, Δf r is the sub-frequency comb frequency interval.

3. The dual-comb velocimetry method according to claim 2, wherein, The calculation formula of the velocity value of the target object is: Where v is the velocity of the target object, and ΔL is the difference between two adjacent groups of unambiguous distances to be measured of the target object.

4. The dual-comb velocimetry method according to claim 2, wherein It also includes steps capable of achieving distance measurement of the target object. The process is as follows: The unambiguous distance L' of the continuously measured target object is unwrapped with a period of v g / 2f r1 to obtain the distance measurement result of the target object. The calculation formula is as follows: L = unwrap(L i ′, v g / 2f r1 ); where L is the distance measurement result of the target object, L i ′ is the unambiguous distance to be measured calculated from the i-th pair of measurement and reference signals, and unwrap is the unwrapping function.

5. The dual-comb velocimetry method according to claim 2, wherein To ensure that the radio frequency spectra corresponding to the interference signals of the two arms are in the non-aliasing interval, two band-pass filters are used to implement this. The band-pass filters are used to process the interference signals. Among them, the bandwidths of the two band-pass filters are both The difference in the center wavelength intervals is This parameter can ensure that the velocity measurement range is -Δf r v g / 2f r1 <v<Δf r v g / 2f r1 and the signals are not aliased when 6. The dual-comb velocimetry method according to claim 1, characterized in that The signal light comb and the local oscillator light comb both use fiber mode-locked optical frequency combs, and both the signal light comb and the local oscillator light comb need to be repetition-frequency locked.

7. A speed measurement device for implementing the dual optical frequency comb speed measurement method according to any one of claims 1 to 6, characterized in that, The device includes: The light source module uses two frequency-locked optical frequency combs with a small repetition frequency difference, including a signal optical comb and a local oscillator optical comb; A speed and distance measurement module measures the target object through a distance measurement optical path system, so that the signal light comb returned from the measuring arm and the reference arm generates an interference signal with the local oscillator light comb; An anti-aliasing detection module is used to make the spectrum of the two-arm interference signal in a non-aliasing range; The data acquisition and processing module is used to process the acquired non-aliasing interference signal and output the speed information and / or distance information of the target object.

8. The speed measuring device according to claim 7, wherein, The distance measuring optical path system adopts a spatial Michelson orthogonal polarization interference optical path or an all-fiber blind zone elimination distance measuring optical path.

9. The speed measuring device according to claim 7, characterized in that The anti-aliasing detection module includes two band-pass filters with different central wavelengths for processing the interference signal. The bandwidths of the two band-pass filters are both The difference in the central wavelength intervals is This parameter can ensure that the velocity measurement range is -Δf r v g / 2f r1 <v<Δf r v g / 2f r1 When the signal is not aliased, where f r1 is the repetition frequency of the signal optical comb, Δf r is the sub-frequency comb frequency interval, v is the velocity of the target object, and v g is the group velocity of the pulse.

10. The speed measurement device according to claim 7, characterized in that The signal optical comb and the local oscillator optical comb both adopt optical fiber mode-locked optical frequency combs.

Images