Double-comb non-cooperative target ranging system based on single photon detection

Abstract

The invention discloses a double-comb non-cooperative target ranging system based on single photon detection, which is characterized in that an optical pulse output by a first optical frequency comb is divided into two paths of light through a first beam splitter, the first path of light is combined with one of two paths of light divided by a second optical frequency comb through a second beam splitter, and the combined light is transmitted to a first nonlinear frequency up-conversion module; a sum frequency light pulse in the wave band of 780 nm is generated and detected by a base avalanche diode photoelectric detector, and then a time-dependent single photon counter is triggered to start counting; the second path of light is output to a beam expanding collimator through the circulator and irradiates a target to be measured through spatial propagation, the beam expanding collimator collects diffuse reflection light and returns the diffuse reflection light to a third port of the circulator along the original path, and the diffuse reflection light and the other path of light split by the second optical frequency comb through the second beam splitter are combined and transmitted to a second nonlinear frequency up-conversion module; the up-conversion light after sum frequency conversion passes through the optical filter group and then is recorded by a stop end of the single photon counting module, multi-cycle accumulative statistics is carried out by the time correlation single photon counter, and finally a photon counting waveform is reconstructed and the flight time difference of the to-be-measured target is calculated by the computer.

Description

Technical Field

[0001] The present invention relates to the field of laser ranging, and in particular to a dual-comb non-cooperative target ranging system based on single-photon detection. Background Art

[0002] With the rapid development of fields such as aerospace and equipment manufacturing, the demand for large-size and high-precision geometric measurement and three-dimensional topography measurement in fields such as parts processing and large-component assembly is also continuously increasing. The ranging technology based on the laser principle has played a crucial role in high-precision large-scale industrial production and manufacturing. Among them, compared with the relative ranging method that can only achieve incremental measurement and the measurement cannot be interrupted, the absolute ranging method is more widely used in industrial sites. Among them, the emergence of femtosecond laser frequency combs has opened up a new situation in the field of precision metrology. On the one hand, it is a series of ultrashort pulses with a width of fs in the time domain, and in the frequency domain, it is manifested as a series of fine spectral lines with equal frequency intervals. The excellent time-frequency domain characteristics such as wide spectral range, narrow pulse width, and high repetition frequency stability provide new technical means for time-frequency measurement and absolute distance measurement. The dual-comb asynchronous optical sampling absolute distance measurement method is based on the "vernier effect" and can achieve the acquisition of high-frequency signals at a lower sampling rate, and can more truly reflect the waveform of high-frequency signals. This method combines the advantages of the time-of-flight method and the interference measurement method, and its accuracy is several orders of magnitude higher than that of the time-of-flight method, reaching the nanometer level, and has the advantages of high measurement accuracy, fast measurement speed (KHz), large non-ambiguous measurement range, and no dead zone, and has been further promoted in the fields of biological monitoring, spectral detection, and imaging. However, the dual-comb ranging has high requirements for the power of the returned light and also faces the problem of low signal-to-noise ratio. Therefore, for non-cooperative target ranging, improving the detection sensitivity is the development direction for realizing weak signal detection and carrying out radar applications.

[0003] Currently, in most industrial sites, the high-precision measurement of measuring instruments such as laser trackers and theodolites relies on the auxiliary measurement of cooperative targets and requires manual guidance, which reduces the measurement efficiency and has poor adaptability. The vision measurement method cannot directly obtain the depth information of the target and is often limited in non-cooperative target pose measurement. Therefore, proposing a direct large-size, fast, and high-precision dynamic measurement for non-cooperative surfaces is an urgent need in the industrial community for large-size high-precision measurement.

[0004] At present, multiple teams have combined single-photon detection devices and time-correlated single-photon counting (TCSPC) technology to achieve ultra-sensitive optical ranging at the few / single-photon level. Such single-photon ranging technology is mainly based on the pulse time-of-flight method. Its advantage is that it can achieve long-distance (>50 km) and non-cooperative target distance measurement, and is widely used in low-light imaging, satellite altimetry, and remote sensing mapping. Limited by the time jitter (10 ps - 0.1 ns) of the light source and the response time of the detector, the measurement accuracy is limited, only at the mm-cm level. Summary of the Invention

[0005] The present invention provides a dual-comb non-cooperative target ranging system based on single-photon detection. The present invention utilizes a pair of femtosecond optical frequency combs with stable repetition frequencies, broad spectra, and a small repetition frequency difference, combines time-correlated single-photon counting technology with dual-comb nonlinear asynchronous optical sampling technology, and realizes fast and high-precision absolute ranging of non-cooperative targets of different material types in daylight environments through single-photon level optical heterodyne detection; the present invention solves the limitations of low signal-to-noise ratio, low precision, and difficulty in measurement for non-cooperative targets based on optical frequency combs, as described in detail below:

[0006] A dual-comb non-cooperative target ranging system based on single-photon detection, the system includes: an asynchronous optical sampling method measurement module, which is used to achieve complete sampling of high-frequency signal waveforms with a low-bandwidth electronic receiving device, and further measure the absolute distance using the time-of-flight method, including:

[0007] The optical pulse output by the first optical frequency comb is split into two paths of light by the first beam splitter. One path is combined with one of the two paths of light split by the second optical frequency comb through the second beam splitter and transmitted to the first nonlinear frequency up-conversion module to generate a sum-frequency optical pulse in the 780 nm band, which is detected by a base avalanche diode photodetector, and then triggers the time-correlated single-photon counter to start counting;

[0008] The other path passes through the circulator and outputs to the beam expander-collimator, and is irradiated onto the target to be measured through space propagation. The beam expander-collimator collects the diffuse reflection light and returns it along the original path to the third port of the circulator, and is combined with the other path of light split by the second optical frequency comb through the second beam splitter and transmitted to the second nonlinear frequency up-conversion module;

[0009] The up-converted light after sum-frequency conversion is recorded at the "stop" end of the single-photon counting module through the filter group, and is accumulated and statistically analyzed by the time-correlated single-photon counter for multiple cycles. Finally, the photon counting waveform is reconstructed by a computer and the time-of-flight difference of the target to be measured is calculated.

[0010] Among them, the repetition frequencies of the first optical frequency comb and the second optical frequency comb are finely tuned using a piezoelectric ceramic and coarsely tuned using a temperature control system.

[0011] Among them, the optical pulses output by the second optical frequency comb complete the complete sampling and reproduction of the optical pulses output by the first optical frequency comb within one sampling interval, completing the asynchronous optical sampling process; at this time, the first nonlinear frequency up-conversion module or the second first nonlinear frequency up-conversion module directly outputs the upper envelope of the sum-frequency signal. Compared with the original signal pulse, the pulse width of this upper envelope signal is stretched by M times.

[0012] Among them, the reference path asynchronous optical sampling signal output by the base avalanche diode photodetector is used as the trigger signal, and the counting starts when the trigger signal enters the time measurement unit in the time-correlated single photon counter;

[0013] The output signal of the single photon avalanche photodetector is used as the stop signal, and the entire sampling period is divided into several time units, and each time unit has a counting storage unit; the time-correlated single photon counter calculates the time difference between the detection moment and the start of timing, and increments the count of the counting storage unit corresponding to the time difference by one. After cumulative measurement over multiple cycles, the stronger the optical signal, the more counts in the corresponding counting storage unit, and the photon count histogram formed by accumulation is the same as the waveform of the echo beam.

[0014] Among them, in multiple non-cooperative target measurement scenarios, multiple Gaussian peaks are resolved from the photon distribution histogram statistically obtained by the time-correlated single photon counter, and the dual-comb non-cooperative target ranging system has the ability to measure multiple targets simultaneously.

[0015] The beneficial effects of the technical solution provided by the present invention are as follows:

[0016] 1. The present invention uses the dual-comb asynchronous optical sampling method to improve the accuracy of absolute distance measurement. The measurement speed corresponds to the dual-comb repetition frequency difference, improving the dynamic measurement ability and greatly expanding the non-ambiguity range of ranging;

[0017] 2. The present invention combines the Si-based single photon detector and the time-correlated single photon counting technology, and overcomes the low signal-to-noise ratio problem in the traditional non-cooperative target measurement method with the ultra-high sensitivity of photon-level signals. Through single photon-level optical heterodyne detection, fast and high-precision absolute ranging under daylight environment and weak echo conditions is realized;

[0018] 3. The present invention can be widely applied to high-precision target detection in dynamic environments such as lidar, rendezvous and docking of space non-cooperative targets, and positioning monitoring of the deployment of large space structures. Description of the Drawings

[0019] Figure 1 It is a schematic structural diagram of a dual-comb non-cooperative target ranging system based on single photon detection;

[0020] Figure 2It is the schematic diagram of time - related single - photon counting detection;

[0021] Figure 3 It is the histogram of photon - counting distribution;

[0022] Figure 4 It is the histogram of photon - counting distribution for multi - target measurement.

[0023] In the attached drawings, the list of components represented by each label is as follows:

[0024] 1 - asynchronous optical sampling method measurement module; 11 - first optical frequency comb;

[0025] 12 - second optical frequency comb; 13 - first beam splitter;

[0026] 14 - second beam splitter; 15 - circulator;

[0027] 16 - beam expander and collimator; 17 - target to be measured;

[0028] 18 - first non - linear frequency up - conversion module; 19 - Si avalanche photodetector;

[0029] 110 - second non - linear frequency up - conversion module; 111 - filter bank;

[0030] 112 - single - photon avalanche photodetector; 113 - time - related single - photon counter;

[0031] 114 - computer;

[0032] 2 - first or second non - linear frequency up - conversion module; 21 - first fiber collimator;

[0033] 22 - second fiber collimator; 23 - polarization beam splitting cube;

[0034] 24 - focusing lens; 25 - non - linear crystal. Detailed implementation mode

[0035] To make the objectives, technical solutions and advantages of the present invention clearer, the following further describes the implementation modes of the present invention in detail.

[0036] As Figure 1 shown, a dual - comb non - cooperative target ranging system based on single - photon detection, the system includes:

[0037] Asynchronous optical sampling method measurement module 1, which is used to achieve complete sampling of high-frequency signal waveforms with a low-bandwidth electronic receiving device, and further measure the absolute distance using the time-of-flight method. It includes: a first optical frequency comb 11, a second optical frequency comb 12, a first beam splitter 13, a second beam splitter 14, a circulator 15, a beam expander collimator 16, a target to be measured 17, a first non-linear frequency up-conversion module 18, an Si-based avalanche diode photodetector 19, a second non-linear frequency up-conversion module 110, a filter group 111, a single-photon avalanche photodetector 112, a time-correlated single-photon counter 113, and a computer 114.

[0038] Among them, the optical pulse output by the first optical frequency comb 11 is split into two paths of light by the first beam splitter 13. One of the paths is combined with the two paths of light obtained by splitting the second optical frequency comb 12 by the second beam splitter 14, and one of the paths is combined and transmitted to the first non-linear frequency up-conversion module 18 to generate a sum-frequency optical pulse in the 780 nm band, which is detected by the Si-based avalanche diode photodetector 19, and then triggers the time-correlated single-photon counter 113 to start counting; the other path of the optical pulse output by the first optical frequency comb 11 after passing through the first beam splitter 13 passes through the circulator 15 and is output to the beam expander collimator 16, and propagates through space and irradiates the target to be measured 17. The beam expander collimator 16 collects the diffuse reflection light and returns it along the original path to the three-port of the circulator 15, and is further combined with the other path of light obtained by splitting the second optical frequency comb 12 by the second beam splitter 14 and transmitted to the second non-linear frequency up-conversion module 110. The up-converted light after sum-frequency conversion passes through the filter group 111 and is recorded by the "stop" end of the single-photon counting module 112, and is further multi-period cumulatively counted by the time-correlated single-photon counter 113. Finally, the computer 114 reconstructs the photon counting waveform and calculates the time-of-flight difference of the target to be measured.

[0039] Among them, the first or second non-linear frequency up-conversion module 2 is used to convert the 1550 nm optical pulses from the first optical frequency comb 11 and the second optical frequency comb 12 into sum-frequency optical pulses of 780 nm through sum-frequency effect, and finally received by the Si-based avalanche diode photodetector 19 and the single-photon avalanche photodetector 112. The first or second non-linear frequency up-conversion module 2 includes: a first fiber collimator 21, a second fiber collimator 22, a polarization beam splitting cube 23, a focusing lens 24, and a non-linear crystal 25. Further, the repetition frequencies of the first optical frequency comb 11 and the second optical frequency comb 12 are finely tuned by a piezoelectric ceramic and coarsely tuned by a temperature control system. The repetition frequency of the first optical frequency comb 11 is fr, and the difference from the repetition frequency of the second optical frequency comb 12 is Δfr. In the non-linear frequency up-conversion module 2, the optical pulses output by the first optical frequency comb 11 and the optical pulses output by the second optical frequency comb 12 are combined by the polarization beam splitting cube 23 and focused on the center of the non-linear crystal 25 based on the type-II phase matching principle through the focusing lens 24, and then sum-frequency optical pulses are output.

[0040] From the perspective of the relative time sequence of pulse propagation, the optical pulses output by the second optical frequency comb 12 complete the complete sampling and reproduction of the optical pulses output by the first optical frequency comb 11 within one sampling interval, which completes the asynchronous optical sampling process. At this time, the non-linear frequency up-conversion module can directly output the upper envelope of the sum-frequency signal. Compared with the original signal pulse, the pulse width of this signal is stretched by M times:

[0041] M = f r / △f r (1)

[0042] Further, the reference path asynchronous optical sampling signal output by the Si-based avalanche diode photodetector 19 is used as a trigger signal, and the counting starts when the trigger signal enters the time measurement unit in the time-correlated single-photon counter 113; the output signal of the single-photon avalanche photodetector 112 is used as a stop signal. Suppose the entire sampling period is divided into several time units bins, and there is a counting storage unit in each time unit bin. There are no photons in some periods, and one photon will be detected in some periods.

[0043] Such as Figure 2As shown in the figure, when a single-photon avalanche photodetector 112 detects a photon, the time difference between the detection moment and the start of timing is calculated, and the count of the count storage unit corresponding to the time difference is incremented by one. Since the stronger the light intensity, the greater the probability of being detected, after cumulative measurements over multiple cycles, the stronger the optical signal, the more counts in the count storage unit corresponding to that moment. Therefore, the photon count histogram formed by accumulation is the same as the waveform of the echo beam. Even if the echo optical power is very weak, the time-correlated single-photon counting technique can still reconstruct the waveform diagram of the echo beam through the photon count histogram, as Figure 3 shown.

[0044] Further, by using a Gaussian function to fit and reconstruct the peak of the waveform, and taking the time τ corresponding to the maximum value of the fitting curve as the flight time difference of the stretched pulse after asynchronous optical sampling, the computer 114 calculates the target distance according to the following formula:

[0045]

[0046] where c is the speed of light in vacuum, n is the refractive index of air, τ is the flight time difference of the stretched pulse, f r is the repetition frequency of the first optical frequency comb, and Δf r is the repetition frequency difference between the first optical frequency comb and the second optical frequency comb.

[0047] Figure 4 shows the photon distribution histograms statistically obtained by the time-correlated single-photon counter in multiple non-cooperative target measurement scenarios, demonstrating that the proposed dual-comb non-cooperative target ranging system based on single-photon detection has the ability to measure multiple targets simultaneously.

[0048] In summary, the embodiment of the present invention designs a dual-comb non-cooperative target ranging system based on single-photon detection. This system can achieve ultra-high sensitivity, high speed, and high-precision measurement for non-cooperative targets, and has the advantages of simple structure and easy integration. This technology has broad application prospects in high-precision space ranging fields such as position monitoring of large flexible structures in space, rendezvous and docking of non-cooperative targets in space, etc. In addition, single-photon dual-comb asynchronous optical sampling is an ultrafast technology that plays an important role in ultrafast detection, imaging, and ultrafast ranging of single spectra, and has the potential for further development.

[0049] For the models of each device in the embodiment of the present invention, except for those with special descriptions, the models of other devices are not limited, as long as they can perform the above functions.

[0050] Those skilled in the art can understand that the drawings are only schematic diagrams of a preferred embodiment. The serial numbers of the above embodiments of the present invention are only for description and do not represent the advantages or disadvantages of the embodiments.

[0051] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A dual-comb non-cooperative target ranging system based on single-photon detection, the system comprising: An asynchronous optical sampling method measurement module, characterized in that the module is used to achieve complete sampling of a high-frequency signal waveform with a low-bandwidth electronic receiving device, and further measure the absolute distance using the time-of-flight method, including: The optical pulses output by the first optical frequency comb are split into two paths of light by the first beam splitter. One path is combined with one of the two paths of light obtained by splitting the second optical frequency comb by the second beam splitter and transmitted to the first non-linear frequency up-conversion module to generate sum-frequency optical pulses in the 780 nm band, which are detected by a Ge avalanche diode photodetector, and then trigger the time-correlated single-photon counter to start counting; The other path passes through the circulator and outputs to the beam expander-collimator, and is irradiated onto the target to be measured through spatial propagation. The beam expander-collimator collects the diffuse reflection light and returns it along the original path to the third port of the circulator, and is combined with the other path of light obtained by splitting the second optical frequency comb by the second beam splitter and transmitted to the second non-linear frequency up-conversion module; The up-converted light after sum-frequency conversion passes through the filter bank and is recorded by the "stop" end of the single-photon counting module, and is accumulated and statistically analyzed by the time-correlated single-photon counter for multiple periods. Finally, the computer reconstructs the photon counting waveform and calculates the time-of-flight difference of the target to be measured.

2. The dual-comb non-cooperative target ranging system based on single-photon detection according to claim 1, characterized in that, The repetition frequencies of the first optical frequency comb and the second optical frequency comb are finely tuned using a piezoelectric ceramic and coarsely tuned using a temperature control system.

3. A dual-comb non-cooperative target ranging system based on single-photon detection according to claim 1, characterized in that The optical pulses output by the second optical frequency comb complete the complete sampling and reproduction of the optical pulses output by the first optical frequency comb within one sampling interval, and complete the asynchronous optical sampling process; At this time, the first non-linear frequency up-conversion module or the second first non-linear frequency up-conversion module directly outputs the upper envelope of the sum-frequency signal. Compared with the original signal pulse, the pulse width of this upper envelope signal is stretched by M times.

4. A dual-comb non-cooperative target ranging system based on single-photon detection according to claim 1, characterized in that, Taking the reference path asynchronous optical sampling signal output by the Ge avalanche diode photodetector as the trigger signal, start counting when the trigger signal enters the time measurement unit in the time-correlated single-photon counter; Taking the output signal of the single-photon avalanche photodetector as the stop signal, dividing the entire sampling period into several time units, and each time unit has a counting storage unit; the time-correlated single-photon counter calculates the time difference between the detection moment and the start of timing, and increments the count of the counting storage unit corresponding to the time difference by one. After cumulative measurement for multiple periods, the stronger the optical signal, the more the count of the corresponding counting storage unit, and the photon counting histogram formed by accumulation is the same as the waveform of the echo beam.

5. The dual-comb non-cooperative target ranging system based on single-photon detection according to claim 1, characterized in that, In multiple non-cooperative target measurement scenarios, multiple Gaussian peaks are resolved from the photon distribution histogram statistically obtained by the time-correlated single-photon counter, and the dual-comb non-cooperative target ranging system has the ability to simultaneously measure multiple targets.

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