Pulse compression LIDAR system

Abstract

This invention relates to a LIDAR system (100) intended for performing distance measurements suitable for implementing pulse compression effects. For this purpose, the transmission path (10) of the LIDAR system comprises two parallel transmission paths (13a, 13b), and at least one of the transmission paths includes a pulse compression modulator (14b). The detection path (20) of the LIDAR system includes a digital processing module (27) configured to calculate a correlation function between a measured detection signal and a reference detection signal. Double heterodyne detection and improvements to the comb pulse spectrum can optionally be used.

Description

Technical Field

[0001] This manual relates to pulse compression LIDAR systems. Background Technology

[0002] LIDAR systems (an acronym for Light Detection and Ranging) are widely used for distance measurement. The measurement sequence consists of emitting a radiation beam toward a target and collecting a portion of this radiation that has been retroreflected or backscattered by the target. The distance assessment that separates the target from the LIDAR system is then inferred from this. This assessment is performed by determining the length of time between the LIDAR system's radiation emission and the detection of the portion of this radiation that has been retroreflected or backscattered by the target. In practice, the radiation beam is emitted as a series of continuous pulses, and the detection signal of the portion of radiation retroreflected or backscattered by the target is accumulated, with each detection signal corresponding one-to-one with all the pulses in the series. In this way, the distance to the target can be measured even when the intensity of the radiation retroreflected or backscattered by the target is low. A trade-off is then made between a sufficient signal-to-noise ratio for the accumulated detection signal and the amount of energy used to perform the measurement. Furthermore, for LIDAR systems using atmospheric backscattering, spatial resolution along the pulse emission direction is an important issue. This resolution corresponds to an identified atmospheric slice of known thickness. The more detailed the resolution (in other words, the thickness of each atmospheric slice associated with the measured absorbance), the shorter each pulse will be. However, for pulse energies determined by operating conditions and desired measurement quality, shorter pulses—in other words, sharper spatial resolution—result in higher peak power values ​​per pulse.

[0003] Furthermore, the implementation of a LIDAR system using fiber optic connections offers significant advantages, particularly increased system robustness and the elimination of mechanisms for aligning the system's optical components relative to each other. However, the known phenomenon of stimulated Brillouin scattering (SBS) occurring in the fiber limits the peak power value that each transmitted pulse can have. Due to this peak power limitation, and when the target's backscattering capability is extremely low, it is necessary to increase the number of pulses transmitted per measurement to ensure that the detected signal has a sufficient signal-to-noise ratio. However, the measurement duration increases accordingly, and the axial resolution decreases.

[0004] Document US2020 / 049799 A1 describes a multi-heterodyne type LIDAR system architecture in which N phase modulators are used in parallel to generate N heterodyne detection beat frequencies with different frequencies.

[0005] Document US2021 / 055392 A1 describes a LIDAR system that utilizes the correlation between a measurement beam backscattered by a target and a reference beam not backscattered by the target. In other words, the LIDAR system in this document does not use dual-detection beams to apply signal correlation.

[0006] Documents US 7,342,651 B1 and US2019 / 383940 A1 describe other LIDAR systems that use dual-pulse or comb pulses.

[0007] Finally, document US2016 / 377721 A1 describes a LIDAR system with two separate laser sources.

[0008] Technical issues

[0009] In light of this, one objective of the present invention is to propose a new LIDAR system that at least partially overcomes these drawbacks.

[0010] Therefore, one of the objectives of this invention is to measure the distance to a target even when the target has low or extremely low backscattering or reflection capabilities, while improving the trade-off between the signal-to-noise ratio and the peak power consumed in each measurement.

[0011] A secondary objective of this invention is to propose a LIDAR system in which the transmission path can be implemented using optical fibers.

[0012] Finally, the general objective of this invention is to provide more accurate distance measurements than prior art LIDAR systems, especially when the duration of each measurement cycle is equal and the retroreflection or backscattering capability of the target is equal, particularly when the target consists of particles suspended in the atmosphere. Summary of the Invention

[0013] To achieve at least one of these or other objectives, a first aspect of the invention provides a LIDAR system comprising a transmission path and a detection path, the transmission path including a laser source and adapted to emit radiation pulses toward a target outside the LIDAR system. For the invention, the transmission path includes two transmission paths placed in parallel and arranged to simultaneously receive corresponding portions of radiation from the laser source at corresponding inputs of these transmission paths. Additionally, the two transmission paths are arranged at the output to superimpose the components of each pulse transmitted by the two transmission paths. At least one of the two transmission paths includes:

[0014] - A modulator called a pulse compression modulator, which may be of the acousto-optic modulator type; and

[0015] - A pulse compression controller, which is configured to control a pulse compression modulator in a manner that modulates the pulse components transmitted by the transmission path.

[0016] In this way, during the operation of the LIDAR system, at least two components of each pulse are...

[0017] It is generated simultaneously from radiation originating from the laser source.

[0018] Superimposed within the pulse during the duration of this pulse,

[0019] They have different corresponding spectra, and

[0020] At least one of the two components of the pulse is subjected to phase modulation or frequency modulation.

[0021] By known means, any radiation, especially pulsed radiation, has a periodic time field variation, and the frequency or phase modulation of this radiation consists of either a variation applied to its frequency or a variation applied to its phase, which are complements to those variations corresponding to the periodic field variation.

[0022] The detection path of the LIDAR system of the present invention includes at least one photodetector and is arranged to satisfy the following functions:

[0023] - A measurement path, specifically designed to detect radiation corresponding to each pulse emitted via the transmission path after it has been reflected or backscattered by the target, transmitting measurement and detection signals; and

[0024] - Reference path, which is dedicated to detecting radiation representing pulses emitted by the transmission path, transmits a reference detection signal.

[0025] Therefore, each detection in the measurement path and the reference path is used to determine the beat frequency for the distance between the target and the LiDAR system. Without heterodyne detection, these beat frequencies are generated by interference between pulse components from one of the two transmission paths and pulse components from the other, all of which are detected by the measurement path after being reflected or backscattered by the target and transmitted by the LiDAR system used for the reference path. When using heterodyne detection, for the pulse components received after being reflected or backscattered from the target on the measurement path, and for the pulse components transmitted by the LiDAR system used for the reference path, these beat frequencies caused by the association of the two transmission paths are replaced by beat frequencies caused by additional interference with the reference beam.

[0026] The detection path also includes a digital processing module, which is arranged to receive the measurement detection signal and the reference detection signal, and is configured to calculate the correlation function between these signals. In this way, the component of each modulated pulse is combined with the calculated correlation function to produce a pulse compression effect.

[0027] Due to this pulse compression effect, the signal-to-noise ratio (SNR) affecting the correlation function is improved with the same average power consumed in performing the measurement, compared to the result of accumulating the detection signal without pulse compression. This improvement provided by pulse compression can be achieved through coherent integration compared to the detection signal obtained from incoherent accumulation of continuous pulses. Therefore, the accuracy and resolution of each distance measurement are improved. In contrast, the LIDAR system of the present invention can reduce the time required to perform each measurement while maintaining the same SNR. Therefore, the measurement duration can be reduced, and / or the peak power value of each transmitted pulse can be reduced. Due to this latter possibility, the LIDAR system of the present invention can be used with targets having weak or very weak backscattering or reflection capabilities, even if the transmission path of the LIDAR system is implemented using fiber optic technology.

[0028] In terms of increasing the signal-to-noise ratio, or in terms of the spatial resolution of distance measurements, the gain is a factor that is essentially equal to the product of the spectral width of each pulse component modulated to produce a pulse compression effect and the duration of that pulse. This product can be greater than 500, preferably greater than 5000.

[0029] Because its transmission path has two parallel transmission paths, the LIDAR system of this invention is called a dual probe beam or DPB.

[0030] Within this transmission path, only one transmission path can be equipped with a pulse compression modulator with an associated pulse compression controller, or two transmission paths can be equipped with corresponding pulse compression modulators, wherein the pulse compression controller is associated with each modulator one-to-one. In the latter case, for the corresponding optical frequencies of the two pulse components transmitted by these transmission paths, the two transmission paths can generate time variations, preferably with opposite directions of change.

[0031] Each pulse compression controller can be adapted to control a gradual change in the optical frequency over the duration of the pulse, both during operation of the LIDAR system and for the pulse components transmitted through the transmission path to which this pulse compression controller belongs. Furthermore, this gradual change in the optical frequency can have a substantially constant rate of change over the duration of the pulse.

[0032] Within the detection path, the measurement path and the reference path can be separate and connected in parallel to individual inputs of the digital processing module. In this case, the detection path includes:

[0033] - A first detection path, the first detection path being dedicated to forming a measurement path and including a first photodetector, the first photodetector being arranged to receive radiation corresponding to the pulses emitted by the transmission path after they have been reflected or backscattered by the target, this first detection path transmitting a measurement detection signal; and

[0034] - A second detection path, separate from the first detection path and dedicated to forming a reference path, the second detection path including a second photodetector arranged to receive radiation representing pulses emitted by the transmission path, this second detection path transmitting a reference detection signal.

[0035] Then, the digital processing module is connected to the corresponding outputs of the first and second detection paths to receive the measurement detection signal and the reference detection signal.

[0036] Alternatively, when the LIDAR system is dedicated to measuring a sufficiently large distance for a measurement detection signal that will be temporally separated from the reference detection signal, the functions of both the measurement path and the reference path can be achieved through the same common detection path within the detection path due to the round-trip propagation delay of the pulse between the LIDAR system and the target. Those signals of the measurement detection signal are then separated from the reference detection signal by a time gate. This embodiment of the detection path is economical in terms of the components used. Furthermore, it eliminates the processing differences that may exist when the two measurement paths and the reference path are separated. In other words, in this case, the detection path includes:

[0037] - A photodetector shared by two functions, a measurement path and a reference path, the photodetector being designed to receive, during separate time windows, radiation corresponding one-to-one to the pulses emitted by the transmission path after they have been reflected or backscattered by the target, and radiation representing the pulses emitted by the transmission path, transmitting a detection signal during each time window; and

[0038] - A controller that assigns the detection signal transmitted by the shared photodetector as a measurement detection signal or a reference detection signal, depending on the time window.

[0039] According to a first possible improvement of the LIDAR system according to the invention, the system can be equipped with double heterodyne detection, or DHD. This double heterodyne detection improvement allows for an increase in the signal-to-noise ratio (SNR) of each path in the measurement and reference paths. For this purpose, the detection path can be optically coupled so that, on the one hand, it is simultaneous with the radiation corresponding one-to-one to the pulses emitted by the transmission path after they have been reflected or backscattered by the target, and on the other hand, it is simultaneous with the radiation representing the pulses emitted by the transmission path, while also receiving other portions of the radiation from the laser source. This first improvement provides the LIDAR system with higher sensitivity, particularly for applications where the target has very weak reflective or backscattering capabilities.

[0040] In this configuration, the digital processing module can be adapted to mix the components of the measurement detection signals originating from the two transmission paths to obtain the product-time signal of the measurement path, which is free from phase fluctuations of the laser source. Similarly, the digital processing module can also be adapted to mix the components of the reference detection signals originating from the two transmission paths to obtain the product-time signal of the reference path separately, which is also free from phase fluctuations of the laser source. The digital processing module can then calculate the correlation function between the corresponding product-time signals of the measurement path and the reference path. Therefore, the correlation function is unaffected by phase noise from the laser source and has an increased signal-to-noise ratio. Measurement results obtained based on this correlation function are more accurate.

[0041] According to a possible second improvement to the LIDAR system according to the invention, the system can be adapted such that each pulse has a spectrum consisting of several individual spectral components. In other words, each pulse can have a comb-like spectrum. Any number of individual spectral components can be present to form this comb. This second improvement allows for a further increase in the energy of the detection signal without reaching a predetermined threshold for stimulated Brillouin scattering of each spectral component of the comb. Therefore, the LIDAR system is even more suitable for applications where the target has very weak retroreflection or backscattering capabilities, or where its characteristics vary according to the spectral components.

[0042] The first improvement involving the use of double heterodyne detection can be applied without the second improvement, meaning that the spectrum of each pulse is not comb-shaped.

[0043] For embodiments combining the two improvements, the transmission path may further include:

[0044] - A first comb-generating modulator, the first comb-generating modulator being arranged to be effective for the component of each pulse transmitted by the two transmission paths; and

[0045] - A first comb controller, connected to control a first comb generating modulator, and configured to apply a first control signal consisting of a plurality of first equidistant spectral lines to the first comb generating modulator, the first spectral lines being separated by a first increment between any two lines that are spectral neighbors.

[0046] Meanwhile, the detection path can further include:

[0047] - A second comb-shaped generating modulator, the second comb-shaped generating modulator being arranged to be effective on the so-called other portions of radiation from the laser source on the one hand, simultaneously with detecting radiation corresponding to the pulses emitted by the transmission path after they have been reflected or backscattered by the target, and on the other hand, simultaneously with detecting radiation representing the pulses emitted by the transmission path; and.

[0048] - A second comb controller, connected to control a second comb generating modulator, and configured to apply a second control signal consisting of a plurality of second equidistant spectral lines to the second comb generating modulator, the second spectral lines being separated by a second increment between any two of the second lines that are spectral neighbors.

[0049] Then, the difference between the first increment and the second increment is greater than the spectral width used to obtain the pulse compression effect. Additionally, the digital processing module is configured to add or average the detection signal contributions associated with different pairs of optical paths, each pair of optical paths being formed by a first optical path generated by a first comb generating modulator and a second optical path generated by a second comb generating modulator.

[0050] Similarly, when combining the two improvements, the correlation function can be recalculated between the corresponding product-time signals of the measurement path and the reference path, free from the influence of phase noise from the laser source. In this case, the product-time signal of the measurement path can be obtained by mixing two comb-shaped spectral components, respectively derived from the two transmission paths and already reflected or backscattered by the target, and the product-time signal of the reference path can also be obtained by mixing two comb-shaped spectral components, respectively derived from the two transmission paths, but representing part of the radiation of the pulse emitted by the transmission paths. For this purpose, each mixing is performed in a manner that eliminates the influence of phase fluctuations from the laser source.

[0051] Furthermore, the second improvement can also be applied without the first improvement. According to the second improvement, the spectrum of each pulse is comb-shaped, meaning that double heterodyne detection is not used. In this case, the transmission path can further include:

[0052] - A first comb generating modulator, which is arranged in one of the two transmission paths to be effective for the radiated portion transmitted through that transmission path;

[0053] - A first comb controller, connected to control a first comb generating modulator, and configured to apply a first control signal consisting of a plurality of first equidistant spectral lines to the first comb generating modulator, the first spectral lines being separated by a first increment between any two of the first lines that are spectral neighbors.

[0054] - A second comb-shaped generating modulator, the second comb-shaped generating modulator being arranged in the other of the two transmission paths to be effective for the radiated portion transmitted through this other transmission path; and

[0055] - A second comb controller, connected to control a second comb generating modulator, and configured to apply a second control signal consisting of a plurality of second equidistant spectral lines to the second comb generating modulator, the second spectral lines being separated by a second increment between any two of the second lines that are spectral neighbors.

[0056] As described above, the difference between the first increment and the second increment is still greater than the spectral width used to obtain the pulse compression effect, and the digital processing module is configured to add or average the detection signal contributions associated with different pairs of optical paths, each pair of optical paths being formed by the first optical path generated by the first comb generating modulator and the second optical path generated by the second comb generating modulator.

[0057] When the second improvement is used with or without the first improvement, the first and second comb-generating modulators can belong to the electro-optic modulator type. Attached Figure Description

[0058] The features and advantages of the invention will become more apparent from the following detailed description of some non-limiting exemplary embodiments, with reference to the accompanying drawings, in which:

[0059] [ Figure 1a [This is a block diagram of the first LIDAR system according to the present invention, without optional improvements such as double heterodyne detection or comb pulse spectrum;]

[0060] [ Figure 1b ] is composed of [ Figure 1a The first LIDAR system's detection path serves as the input radiation spectrum.

[0061] [ Figure 2a ] corresponds to [ Figure 1a [Illustration of a second LIDAR system according to the present invention, wherein the second LIDAR system implements an improvement in double heterodyne detection without having an improvement in comb pulse spectrum;]

[0062] [ Figure 2b ] corresponds to [ Figure 1b] is based on [ Figure 2a A schematic diagram of the second LIDAR system;

[0063] [ Figure 2c ] shows what can be used for [ Figure 2a Details of the digital processing module in the second LIDAR system;

[0064] [ Figure 3a ] corresponds to [ Figure 1a [Illustration] is a schematic diagram of a third LIDAR system according to the present invention, which implements two improvements: double heterodyne detection and comb pulse spectrum.

[0065] [ Figure 3b ] corresponds to [ Figure 2b ] is based on [ Figure 3a A schematic diagram of the third LiDAR system;

[0066] [ Figure 3c ] is with [ Figure 3a The spectrum diagram of the detection signal of the third LIDAR system;

[0067] [ Figure 3d ] corresponds to [ Figure 2c ] is based on [ Figure 3a A schematic diagram of the third LiDAR system;

[0068] [ Figure 4a ] corresponds to [ Figure 1a [Illustration of a fourth LIDAR system according to the present invention, which implements an improved comb pulse spectrum without the improvement of double heterodyne detection; and]

[0069] [ Figure 4b ] corresponds to [ Figure 1b ] is based on [ Figure 4a A schematic diagram of the fourth LIDAR system. Detailed Implementation

[0070] In these figures, all elements are represented only symbolically. Furthermore, the same reference numerals used in different figures indicate the same elements or elements having the same function.

[0071] For all embodiments of the invention described below, reference numeral 100 denotes a LIDAR system according to the invention, and reference numerals 10 and 20 denote its transmission path and its detection path, respectively. Transmission path 10 includes the following components: a laser source 11, a first coupler 12, a first transmission path 13a, a second transmission path 13b, a second coupler 16, an optical amplifier 17, an amplitude splitter / beam splitter 18, an optical circulator 21, and a transmitting optics 22 designated OPT. All these components of transmission path 10 can be implemented using fiber optic technology. In this case, the laser source 11 can be designed to produce radiation of approximately 1560 nm (nanometers), couplers 12 and 16 can be “Y” evanescent field couplers, and the optical amplifier 17 can be of the EDFA type (“Erbium-doped fiber amplifier”). Beam splitter 18 can have an output intensity ratio of 95% to 5%, for example, 95% of its intensity output is dedicated to the transmission path 10 toward the emitting optics 22 via optical circulator 21, and 5% of its intensity output is dedicated to transmitting a portion of the radiation generated by the transmission path 10 to the reference path 23b of the detection path 20.

[0072] Transmission path 10 is a dual-probe beam (DPB): it is adapted to transmit a radiation pulse I toward a target T outside the LIDAR system 100, the radiation pulse having at least two spectral components with correspondingly different optical frequency values. For this purpose, the first transmission path 13a may include a first modulator 14a and a first electrical signal generator 15a. Similarly, the second transmission path 13b may include a second modulator 14b and a second electrical signal generator 15b. The two modulators 14a and 14b may each be acousto-optic modulators, and are therefore designated MAO1 and MAO2, respectively. The electrical signal generators 15a and 15b may each have arbitrary waveform generator types, and are therefore designated AWG1 and AWG2, respectively. The electrical output of generator 15a (and correspondingly 15b) is connected to the modulation input of modulator 14a (and correspondingly 14b), such that a portion of the radiation from laser source 11 and transmitted via transmission path 13a (and correspondingly 13b) is modified by modulator 14a (and correspondingly 14b) according to the electrical signal generated by generator 15a (and correspondingly 15b). Transmission paths 13a and 13b are arranged in parallel between couplers 12 and 16, and these couplers are selected such that each transmission path transmits approximately half the energy of the radiation generated by laser source 11.

[0073] Electrical signal generators 15a and 15b can be programmed to divide radiation from laser source 11 into continuous pulses, such that each pulse I leaving optical amplifier 17 consists of two components of a synchronization pulse, one transmitted by transmission path 13a and the other by transmission path 13b.

[0074] Generator 15a can be further programmed to transmit a first sinusoidal electrical signal during each time window corresponding to pulse I, the first sinusoidal electrical signal causing, for example, an optical frequency increase of 100 MHz (megahertz) for the component pulse transmitted by transmission path 13a.

[0075] Simultaneously, generator 15b can be further programmed to transmit a second electrical signal that causes optical frequency modulation in response to the pulse component transmitted by transmission path 13b. Specifically, this second electrical signal can be sinusoidal, with its frequency continuously increasing during each time window corresponding to pulse I, for example, from 105 MHz at the start of the pulse to 125 MHz at the end of the pulse. Therefore, according to the incremental change from 105 MHz to 125 MHz during each pulse I, the optical frequency of the pulse component transmitted by transmission path 13b increases relative to the radiation received by transmission path 13b as input. The rate of change of this optical frequency over time can be substantially constant throughout the duration of each pulse I.

[0076] Detection path 20 shares optics 22, optical circulator 21, and beam splitter 18 with transmission path 10. The detection path further includes two detection paths 23a and 23b, and a digital processing module 27, denoted as NUM. Detection path 23a is designed to form a measurement path: its optical input is connected to the output of circulator 21 dedicated to detection path 20. The measurement path sequentially includes a photodetector 24a, denoted as DETECT.1, an amplifier 25a, denoted as AMPL.1, and a filter 26a, denoted as FILT.1. Therefore, measurement path 23a receives pulse I portions RI that have been reflected or backscattered by target T as input, and these pulse portions RI are detected by photodetector 24a. Photodetector 24a then generates a measurement detection signal, which is amplified, filtered, and then transmitted to the first input of digital processing module 27. In parallel, detection path 23b is designed to form a reference path: its optical input is connected to the output of beam splitter 18 dedicated to detection path 20. The reference path includes, in sequence, a photodetector 24b, denoted as DETECT.2, an amplifier 25b, denoted as AMPL.2, and a filter 26b, denoted as FILT.2. Therefore, reference path 23b receives a portion of pulse I emitted by LIDAR system 100 toward target T as input, and these portions of pulse I are detected by photodetector 24b. Photodetector 24b then generates a reference detection signal, which is amplified, filtered, and then transmitted to another input of digital processing module 27. For the values ​​referenced in this specification, filters 26a and 26b, as analog low-pass filters, can have a cutoff frequency of approximately 150MHz to 200MHz to eliminate aliasing.

[0077] With optical probe beam (DPB) Figure 1a The LIDAR system 100 does not use double heterodyne detection and reportedly has direct detection. The signals transmitted separately by measurement path 23a and reference path 23b each consist of the superposition of two components of a pulse portion RI, which has the same propagation delay relative to the emission from laser source 11. Therefore, the superposition of these two components in each of measurement path 23a and reference path 23b is insensitive to phase fluctuations of laser source 11. Such phase fluctuations of laser source 11 present in each component of the pulse portion RI then automatically disappear when they beat in a photodetector, which generates a signal with an instantaneous phase equal to the phase difference between the two spectral components.

[0078] During the operation of LIDAR system 100, digital processing module 27 calculates the correlation function between the measurement detection signal output via measurement path 23a and the reference detection signal output via reference path 23b. In practice, this correlation signal is calculated for several consecutively transmitted pulses I, and then the power of all the correlation signals is summed, representing their squared modulus. The measured distance to target T is equal to half the time shift, which corresponds to the maximum value of the accumulated correlation power function. In practice, this time shift of the maximum value equals the round-trip time of the radiation between LIDAR system 100 and target T.

[0079] In the operation just described, modulator 14b and digital processing module 27 together produce a pulse compression effect. For this reason, in the general part of this specification, modulator 14b and generator 15b have been referred to as pulse compression modulator and pulse compression controller, respectively. Due to this pulse compression effect, for the same value of the accumulated energy of pulse I used to perform distance measurement, the result of the correlation function passed by module 27 presents an increased signal-to-noise ratio. This increase in signal-to-noise ratio compared to a LIDAR system without pulse compression occurs in the factor B·T, where B is the modulation spectral width controlled by generator 15b and T is the duration of each pulse I. In the described example, B is equal to 125MHz - 105MHz = 20MHz, and T can be equal to 1ms (milliseconds), resulting in a pulse compression factor equal to 20,000. This results in an improvement in distance resolution provided by LIDAR system 100, which is equivalent to using ultrashort pulses with a single duration of approximately 80ns (nanoseconds). According to another perspective, for the same signal-to-noise ratio, pulse compression allows for a reduction in the total energy of pulses I emitted to perform distance measurements. This reduction allows the peak power of each pulse I to remain below the stimulated Brillouin scattering threshold relative to the transmission path 10, and / or allows for a reduction in the number of pulses I required to perform distance measurements. In the latter alternative, pulse compression allows for a reduction in the time required to perform distance measurements.

[0080] [ Figure 1a The LIDAR system 100 has the components just described, but lacks improvements in double heterodyne detection and comb pulse spectrum. Figure 1b The spectrum of the radiation received by measurement path 23a and reference path 23b as inputs is shown. These two radiation components have the same or substantially the same spectrum because, on the one hand, there is a radiation propagation delay between the target T and the transmitting optics 22 when the target T is stationary relative to the LIDAR system 100, and on the other hand, the radiation received by measurement path 23a is distinguishable only from the radiation received by reference path 23b due to the amplitude difference between the two radiation components; the radiation received by the measurement path is much weaker than that received by the reference path due to additional atmospheric propagation. Each of these radiation components consists of a superposition of: a pulse component transmitted by transmission path 13a, denoted as CIa and spectrally offset by 100 MHz relative to the radiation from laser source 11 in the considered example; and a pulse component transmitted by transmission path 13b, denoted as CIb and occupying a spectral band offset by 105 MHz to 125 MHz relative to the radiation from laser source 11. Figure 1bIn the diagram, the horizontal axis represents the optical frequency value of f, the vertical axis represents the spectral intensity value of I(f), and reference numeral 11 indicates the spectral position of the laser emission from source 11. For each of measurement path 23a and reference path 23b, the detection signal transmitted to digital processing module 27 corresponds to the interference between pulse components CIa and CIb.

[0081] [ Figure 2a The LIDAR system 100 corresponds to [ Figure 1a The LIDAR system is supplemented to implement double heterodyne detection (DHD). Double heterodyne detection has the effect of increasing the signal-to-noise ratio in each of the measurement path 23a and the reference path 23b, but when the distance to the target T becomes equivalent to or greater than half the coherence length of the laser source 11, the mixing of signals between the two paths may be degraded due to phase fluctuations of the laser source 11. For this purpose, a portion of the radiation generated by the laser source 11 is collected at its output by a beam splitter 40, collecting only a small portion of the radiation. This collected portion of radiation, commonly referred to in the technical terms of those skilled in the art as the local oscillator signal, is then split into two parts so that it can be transmitted in parallel with the optical inputs of the measurement path 23a and the reference path 23b. For example, the beam splitter 40 may be coupled by an evanescent field. A beam splitter (indicated by reference numeral 41) dividing the intensity in a 50%-50% ratio is used to divide the portion of radiation collected from the laser source 11 into two sub-beams. Another beamsplitter 42a, used for performing beam combining, is arranged to superimpose one of the two sub-beams from beamsplitter 11 with the pulse portion RI after it has been reflected or backscattered by the target T. Yet another beamsplitter 42b, also used for performing beam combining, is arranged to superimpose another of the two sub-beams from beamsplitter 41 with the radiating portion from beamsplitter 18, which represents the pulse I emitted by the LIDAR system 100 toward the target T. With this arrangement, photodetector 24a performs heterodyne detection of the pulse portion RI, and photodetector 24b independently performs heterodyne detection of the emitted pulse I.

[0082] [ Figure 2b ] shows for [ Figure 2a The LIDAR system 100 receives the spectrum of the radiation portion from the measurement path 23a and reference path 23b as inputs. For the same reasons indicated above, these two radiation portions still have the same spectrum or substantially the same spectrum. However, this spectrum is now composed of the superposition of pulse components CIa and CIb with additional monochromatic components corresponding to the emission from the laser source 11 and again indicated by reference numeral 11 in the spectrum diagram. The relative positions of the three components 11, CIa, and CIb are indicated, and these relative positions correspond to those already present in […]. Figure 1b The instructions in ]

[0083] [ Figure 2c The figure symbolically illustrates the main signal processing steps performed in digital processing module 27. Reference numeral 270 indicates the digitization of signals transmitted by measurement path 23a and reference path 23b, respectively, performed at the input of module 27. Then, the measurement detection signal from measurement path 23a and the reference detection signal from reference path 23b are independently subjected to Fourier transforms, denoted as TF and denoted by reference numeral 271. Reference numeral 272 indicates a digital spectrum filter. The two filters 272, denoted as FILT.aa and FILT.ab, are bandpass filters, and are selected at the positive frequencies of components CIa and CIb, respectively, because these two components appear in […]. Figure 2b [In the figure]. For example, the spectral window of filter FILT.aa is 97MHz to 103MHz, and the spectral window of filter FILT.ab is 103MHz to 128MHz. Reference numeral 273 denotes the inverse Fourier transform, which is performed in parallel on the signal passed by filter 272 and is represented as TF. -1 For the measurement detection signal, mixer 274, denoted as MIX.a, calculates the complex conjugate product of the filtered components CIa and CIb for each moment of the measurement detection signal. Therefore, there is no phase fluctuation of the laser source 11 in the product time signal obtained for measurement path 23a. The reference detection signal is processed in parallel in the same manner. Filters FILT.ba and FILT.bb have the same spectral windows as filters FILT.aa and FILT.ab, respectively, and mixer 274, denoted as MIX.b, this time calculates the complex conjugate product of the filtered components Cla and CIb for each moment of the reference detection signal. Therefore, similarly, there is no phase fluctuation of the laser source 11 in the product time signal obtained for reference path 23b. Then, module 275, denoted as CORR., calculates the correlation function between the two product time signals from measurement path 23a and reference path 23b, respectively. The techniques described herein are suitable for non-real-time processing, but equivalent operations can be performed in real time using other digital filtering techniques known to those skilled in the art, such as by using FIR (Finite Impulse Response) or IIR (“Infinite Impulse Response”) filters.

[0084] [ Figure 3a The LIDAR system 100 corresponds to [ Figure 2aThe LIDAR system 100 is further supplemented to also utilize the improved comb spectrum of pulse I. For this purpose, two additional modulators are added to the LIDAR system 100: a first additional modulator 51 on the radiation path between beamsplitters 40 and 41, and a second additional modulator 53 on the radiation path between beamsplitters 40 and 41. In other words, the second additional modulator 53 is inserted to be effective for the local oscillator signal. The two additional modulators 51 and 53 may be of electro-optical type and are designated MEO1 and MEO2, respectively. Each of modulators 51 and 53 is associated with an electrical signal generator whose electrical output is connected to the modulation input of the modulator: the electrical output of generator 52 (correspondingly 54) is connected to the modulation input of modulator 51 (correspondingly 53). The two generators 52 and 54 may be of AWG type and are therefore designated AWG1' and AWG2', respectively. The generators are programmed to generate electrical signals, each consisting of the sum of several sinusoidal components. Therefore, modulator 51 transforms the radiation transmitted from laser source 11 to the two transmission paths 13a and 13b into a superposition of several monochromatic or quasi-monochromatic spectral components, such that the spectrum of this radiation has a comb shape. Therefore, modulator 51 is referred to as a first comb-generating modulator in the general part of this specification, and generator 52 is referred to as a first comb controller. For example, an electrical signal applied by generator 52 to modulator 51 may cause the radiation transmitted to the two transmission paths 13a and 13b to consist of five monochromatic spectral components spaced 2.00 GHz (gigahertz) apart in terms of optical frequency. Those skilled in the art describe this spectral composition as a frequency micro-comb.

[0085] Within transmission path 13a, modulator 14a applies an offset of +100MHz to the entire microcomb of each pulse I generated by modulator 51.

[0086] Meanwhile, within the transmission path 13b, the modulator 14b applies modulation to the entire microcomb of each pulse I generated by the modulator 51 according to an optical frequency increment ranging from +105MHz to +125MHz.

[0087] Depend on[ Figure 3a The spectrum of pulse I emitted by the LIDAR system 100 and detected by reference path 23b is composed of [ Figure 3b The diagram is indicated by brackets represented by the letter I. The spectral composition consists of five spectral patterns, each corresponding to […]. Figure 2b The spectral patterns in [ ] are identical and spaced 2000 MHz apart between adjacent patterns. All frequency deviations shown in this figure are expressed in megahertz. This spectral composition is still substantially the same as that of the pulse portion RI, which has been reflected or backscattered by the target T and detected by measurement path 23a.

[0088] Modulator 53 transforms the radiation portion transmitted from laser source 11 to measurement path 23a and reference path 23b into two identical superpositions of several monochromatic or quasi-monochromatic spectral components, such that the spectrum of these radiation portions again has a comb shape. Modulator 53 has been referred to as the second comb generating modulator in the general part of this specification, and generator 54 is referred to as the second comb controller. For [ Figure 3a In an exemplary embodiment of the invention, the electrical signal applied by the generator 54 to the modulator 53 causes the comb of radiation transmitted to the two measurement paths 23a and the reference path 23b to consist of five monochromatic spectral components spaced 1.97 GHz apart in terms of optical frequency.

[0089] Under these conditions, for the spectrum of the radiation received as input by measurement path 23a and reference path 23b, double heterodyne detection using a microcomb is added to [ Figure 3b The diagram shows the five components represented by the letter R.

[0090] For each heterodyne detection performed in measurement path 23a or reference path 23b, each monochromatic component R is interfered with by modulators 51 and 14a, and with its nearest monochromatic component CIa, generates detection signal components of 40MHz, 70MHz, 100MHz, 130MHz, and 160MHz (representing 100MHz+k·30MHz), where k is an index used to identify comb components with values ​​-2, -1, 0, +1, and +2. Simultaneously, each monochromatic component R is further interfered with by modulators 51 and 14b, and with its nearest modulation component CIb, generating five additional detection signal components extending between 105MHz+k·30MHz and 125MHz+k·30MHz, respectively, where k is the same index as before. Figure 3c The spectrum diagram below, represented by MS, corresponds to the measurement detection signal thus transmitted from measurement path 23a to digital processing module 27, while [ Figure 3c The diagram above, represented by REF in the same figure, shows the reference detection signal simultaneously transmitted from reference path 23b to module 27. In this diagram, the horizontal axis identification is represented by f. 外差(heterodyne) Furthermore, the frequency value of the heterodyne detection signal is expressed in megahertz, and the vertical axis identification is represented as I(f 外差And the corresponding spectral intensity expressed in decibels. Due to the interruption experienced by pulse I during its propagation between the transmitting optics 22 and the target T, the measured detection signal (lower figure) has lower coherence than the reference detection signal (upper figure): a higher noise level and a less thin peak. In the described example, other spectral components of the measured detection signal (correspondingly the reference detection signal) generated by interference between the comb teeth associated with different values ​​of index k are eliminated by filter 26a (and correspondingly 26b). The inventors further point out that the […] were obtained experimentally. Figure 3c The spectrum of [ ]. This is why they contain some parasitic lines that are not directly generated by the use of this invention.

[0091] For a series of continuously emitted pulses I, such as one hundred consecutive pulses I, the digital processing module 27 independently stores the measurement detection signal and the reference detection signal. (The rest of the text appears to be incomplete and requires further context.) Figure 3a The LIDAR system related to [ Figure 3d The processing steps performed by module 27 of [] are as follows: Figure 2a The LIDAR system related to [ Figure 2c The processing steps shown are of the same type. Module 27 first calculates the spectrum of the measured detection signal by applying a Fourier transform relative to time (reference numeral 271), and then filters the component centered at 100MHz+k·30MHz (reference numeral 272) (filters FILT.aa-1 to FILT.aaM) within this spectrum, as well as the components included in 105MHz+k·30MHz and 125MHz+k·30MHz (filters FILT.ab-1 to FILT.abM), where k is again the index introduced above, with values ​​of -2, -1, 0, +1, and +2 for M equal to 5. Then an inverse Fourier transform (reference numeral 273) is applied to each filtered component, and then for each value of k, the time signal of the filtered component CIa is individually multiplied by the complex conjugate of the time signal of the filtered component CIb (reference numeral 274). Thus, M product time signals are obtained for measurement path 23a, where M is again the number of monochromatic spectral components in the miniature comb of each pulse I. For reference path 23b, M product-time signals are obtained independently and in parallel using filters FILT.ba-1 to FILT.baM and FILT.bb-1 to FILT.bbM in the same manner. Module 275 then calculates the cross-correlation square matrix M x M, where the correlation functions in columns k and rows k' of this matrix are correlated with the product-time signals of the measurement path 23a for component k of the microcomb and the reference path 23b for component k' of the microcomb. Thus, the distance M from the target T is obtained by the corresponding maximum value of all correlation functions.2 One assessment, and these M 2 A weighted average of distance assessments provides measurements with reduced noise. Specifically, the weighting can consider M... 2 The change in signal-to-noise ratio that can be evaluated.

[0092] In the alternative operation, the components from filters FILT aa-1 to FILT.aaM can be spectrally superimposed by digitally removing a k·30MHz offset, and then added together or averaged, as with the components from filters FILT ab-1 to FILT.abM. The same process is performed independently for the reference detection signal: the components from filters FILT.ba-1 to FILT.baM are spectrally superimposed by digitally removing a k·30MHz offset, and then added together or averaged; similarly, the components from filters FILT.bb-1 to FILT.bbM are superimposed and then added together or averaged in the same manner. Then, [the process can be implemented from the starting point with...] Figure 2c The operation is the same as that described in [ ]. This operation involves using two mixers 274MIX.a and MIX.b to eliminate phase fluctuations in the laser source 11. The result of the correlation function then exhibits a very narrow peak, the reduction in width of which is due to the combination of pulse compression effect and the coherent superposition effect of the micro-comb spectral components. As mentioned above, the temporal location of this peak is equal to the round-trip propagation duration of pulse I between the emitting optics 22 and the target T. This correlation function calculation can be performed in a particularly economical manner, especially by using a dedicated electronic module.

[0093] Optionally, the spectrum obtained for the measured detection signal (and correspondingly the reference detection signal) can be frequency-shifted overall, thus becoming centered relative to zero frequency. Then, each reconstructed detection signal (both the measured and reference detection signals) centered at zero frequency has a moment when its instantaneous frequency change is canceled out. The difference between the frequency cancellation moment obtained for the reconstructed measured detection signal and the frequency cancellation moment obtained for the reconstructed reference detection signal corresponds to the round-trip propagation duration of pulse I between the transmitting optics 22 and the target T.

[0094] [ Figure 4a The LIDAR system 100 incorporates improvements to the comb spectrum of pulse I, but without improvements to double heterodyne detection. Therefore, it is a direct detection system and obtains information from […]. Figure 1aThe embodiment obtained is described above. The comb generating modulator 51 is now inserted in series with the pulse compression modulator 14b into the transmission path 13b. Two comb generating modulators 51 and 53 are associated with their respective comb controllers: modulator 51 is associated with generator 52 to generate a comb spectrum, for example, with an increment of 2.00 GHz; and modulator 53 is associated with generator 54 to generate another comb spectrum with a different increment, for example, equal to 1.97 GHz. The pulse compression modulator 14b can be the same as the modulator in the foregoing embodiment, wherein controller 15b is used to control modulation according to optical frequency increments varying from 105 MHz to 125 MHz.

[0095] and[ Figure 1a Like the LiDAR system, Figure 4a The results of the correlation function of the LIDAR system are not sensitive to the phase fluctuations of the laser source 11.

[0096] for[ Figure 4a ] in the embodiment, [ Figure 4b The diagram corresponds to [] Figure 3b The figure shows that, according to the elimination of double heterodyne detection, all spectral components correspond to pulse I. Component CIa corresponds to the microcomb generated in transmission path 13a, where the optical frequency increment is equal to 1.97 GHz, and component CIb is the component generated in transmission path 13b. The latter is generated by convolution of the microcomb with an optical frequency increment equal to 2.00 GHz with pulse compression modulation generated by modulator 14b. The measurement (and corresponding reference) detection signal transmitted by filter 26a (and correspondingly 26b) is a coherent superposition of each monochromatic component CIb with the interference of the modulation component CIa that is closest to it in the spectrum.

[0097] Although the operation of the digital processing module 27 has been described for the most complex cases, the corresponding [ Figure 3a The embodiments described herein are applicable to other embodiments, but those skilled in the art will be able to apply them without demonstrating inventive activity. Specifically, the final step of averaging the distance assessment, or the step of adding or averaging the spectral components corresponding to different values ​​of index k, is omitted when the improvement on the comb spectrum of each pulse I is not implemented.

[0098] It should be understood that the invention can be reproduced by modifying minor aspects of the embodiments already described in detail above while retaining at least some of the enumerated advantages. Specifically, the following modifications can be applied:

[0099] - Instead of at least one of the electro-optic modulators 51 and 53, a DPMZ-type component for "dual parallel Mach-Zehnder" is used, as described in the paper "Tunable Frequency Shifter Based on LiNbO3 I / Q Modulators" by Alexandre Mottet et al., Photline Technologies, ZI Les Tilleroyes-Trépillot, 16 Rue Auguste Juchoux, Besançon, France 25000;

[0100] - When using double heterodyne detection and improvements to the comb shape of the pulse spectrum, the detection signal can be filtered to select a mixture of the following: a first line from the radiation comb, after the pulse has been reflected or backscattered by the target, the radiation corresponding to the pulse; and a mixture of a second line from the pulse sparse emitted toward the target, the first and second lines being associated with different values ​​of index k.

[0101] - Using two simultaneous modulations, for each pulse, the two simultaneous modulations are applied separately to the two pulse components transmitted by the two transmission paths 13a and 13b, one modulation being performed in transmission path 13a and the other modulation being performed in transmission path 13b. For example, the modulation performed in transmission path 13a can modify the optical frequency of the radiation according to an increment gradually increasing from 90MHz to 100MHz during each pulse, and simultaneously, the other modulation performed in transmission path 13b can modify the optical frequency according to another increment gradually decreasing from 120MHz to 110MHz during each pulse;

[0102] -Using modulation forms other than linear variations of the optical frequency, including phase modulation instead of optical frequency modulation; and

[0103] - Only a single detection path in detection path 20 is used to provide a detection signal to digital processing module 27. When the target is far enough that the start of the measurement detection signal does not overlap with the end of the reference detection signal, this single detection path is assigned to each pulse that is first transmitted to the reference path function and then to the measurement path function.

[0104] Finally, all the values ​​cited are for illustrative purposes only and are subject to change.

Claims

1. A LIDAR system (100) comprising a transmission path (10) and a detection path (20), the transmission path (10) comprising a laser source (11) and adapted to emit radiation pulses (I) toward a target (T) outside the LIDAR system. The LIDAR system (100) is characterized in that the transmission path (10) includes two transmission paths (13a, 13b), which are placed in parallel and arranged to simultaneously receive corresponding portions of radiation from the laser source (11) at their respective inputs, and are arranged to superimpose the components of each pulse (I) transmitted by the two transmission paths at the output. At least one of the two transmission paths (13a, 13b) includes: - Modulator, which is called pulse compression modulator (14b). as well as - A pulse compression controller (15b) is connected to control the pulse compression modulator (14b) in a manner that modulates the pulse components transmitted by the transmission path. Such that during the operation of the LIDAR system (100), at least two components of each pulse (I) Simultaneously generated from radiation originating from the laser source (11), Superimposed within the duration of the pulse (I), They have different corresponding spectra, and At least one of the two components of the pulse (I) is subjected to phase modulation or frequency modulation. Furthermore, the detection path (20) includes at least one photodetector (24a, 24b) and is arranged to satisfy the following functions: - Measurement path (23a), which is dedicated to detecting radiation corresponding to the pulse (I) emitted by the transmission path (10) after it has been reflected or backscattered by the target (T), and transmitting measurement detection signals; and - Reference path (23b), which is dedicated to detecting radiation representing a pulse (I) emitted by the transmission path (10), and transmitting a reference detection signal; and The detection path (20) further includes a digital processing module (27), which is arranged to receive the measured detection signal and the reference detection signal, and is configured to calculate the correlation function between the measured detection signal and the reference detection signal. This results in a pulse compression effect when at least one component of each modulated pulse (I) is combined with the calculated correlation function.

2. The LIDAR system (100) according to claim 1, characterized in that, Each pulse compression controller (14b) is adapted to control the gradual change of optical frequency during the operation of the LIDAR system and for pulse components transmitted by the transmission path (13b) to which the pulse compression controller belongs, within the duration of the pulse (I).

3. The LIDAR system (100) according to claim 2, characterized in that, Each pulse compression controller (14b) is further adjusted so that the gradual change of the optical frequency has a substantially constant rate of change over the duration of the pulse (I).

4. The LIDAR system (100) according to any one of claims 1 to 3, characterized in that, The detection path (20) includes: - A first detection path, dedicated to forming the measurement path (23a), comprising a first photodetector (24a) arranged to receive radiation corresponding to the pulse (I) emitted by the transmission path (10) after it has been reflected or backscattered by the target (T), and to transmit the measurement detection signal; and - A second detection path, separate from the first detection path and dedicated to forming the reference path (23b), the second detection path including a second photodetector (24b), the second photodetector being arranged to receive radiation representing a pulse (I) emitted by the transmission path (10) and to transmit the reference detection signal. The digital processing module (27) is connected to the corresponding outputs of the first detection path and the second detection path to receive the measurement detection signal and the reference detection signal.

5. The LIDAR system (100) according to any one of claims 1 to 3, characterized in that, The detection path (20) includes: - A photodetector shared by two functions of the measurement path (23a) and the reference path (23b), the photodetector being designed to receive, during separate time windows, radiation corresponding one-to-one with the pulse (I) emitted by the transmission path (10) after it has been reflected or backscattered by the target (T), and to receive radiation representing the pulse emitted by the transmission path, transmitting a detection signal during each time window; and - A controller that assigns the detection signal transmitted by the shared photodetector as a measurement detection signal or a reference detection signal, depending on the time window.

6. The LIDAR system (100) according to any one of claims 1 to 3, characterized in that, The detection path (20) is optically coupled to receive, on the one hand, radiation corresponding to the pulse (I) emitted by the transmission path (10) after it has been reflected or backscattered by the target (T), and on the other hand, radiation representing the pulse emitted by the transmission path, additionally receiving other portions of the radiation from the laser source (11).

7. The LIDAR system (100) according to claim 6, characterized in that, The digital processing module (27) is adapted, on the one hand, to mix the components of the measurement detection signals respectively from the two transmission paths (13a, 13b) to obtain the product time signal of the measurement path (23a), the product time signal having no phase fluctuation of the laser source (11), and on the other hand, to mix the components of the reference detection signals respectively from the two transmission paths to obtain the product time signal of the reference path (23b) separately, the product time signal having no phase fluctuation of the laser source, and the digital processing module is adapted to calculate the correlation function between the corresponding product time signals of the measurement path and the reference path.

8. The LIDAR system (100) according to claim 6, characterized in that, The transmission path (10) further includes: - A first comb-shaped modulator (51), the first comb-shaped modulator being arranged to be effective for the component of each pulse (I) transmitted by the two transmission paths (13a, 13b); and - A first comb controller (52), connected to control the first comb generating modulator (51), and configured to apply a first control signal consisting of a plurality of first equidistant spectral lines to the first comb generating modulator, the first equidistant spectral lines being separated by a first increment between any two of the first lines that are spectral neighbors. The detection path (20) further includes: - A second comb-shaped generating modulator (53), the second comb-shaped generating modulator being arranged to be effective on the other part of the radiation from the laser source (11) simultaneously with the detection of radiation corresponding to the pulse (I) emitted by the transmission path (10) after it has been backscattered or reflected by the target (T), and simultaneously with the detection of radiation representing the pulse emitted by the transmission path; and - A second comb controller (54), connected to control the second comb generating modulator (53), and configured to apply a second control signal consisting of a plurality of second equidistant spectral lines to the second comb generating modulator, the second equidistant spectral lines being separated by a second increment between any two of the second lines that are spectral neighbors. The difference between the first increment and the second increment is greater than the spectral width used to obtain the pulse compression effect. Furthermore, the digital processing module (27) is configured to add or average the detection signal contributions associated with different pairs of optical paths, each pair of optical paths being formed by the first optical path generated by the first comb generating modulator (51) and the second optical path generated by the second comb generating modulator (53).

9. The LIDAR system (100) according to claim 6, characterized in that, The transmission path (10) further includes: - A first comb-shaped modulator (51), the first comb-shaped modulator being arranged to be effective for the component of each pulse (I) transmitted by the two transmission paths (13a, 13b); and - A first comb controller (52), connected to control the first comb generating modulator (51), and configured to apply a first control signal consisting of a plurality of first equidistant spectral lines to the first comb generating modulator, the first equidistant spectral lines being separated by a first increment between any two of the first lines that are spectral neighbors. The detection path (20) further includes: - A second comb-shaped generating modulator (53), the second comb-shaped generating modulator being arranged to be effective on the other part of the radiation from the laser source (11) simultaneously with the detection of radiation corresponding to the pulse (I) emitted by the transmission path (10) after it has been backscattered or reflected by the target (T), and simultaneously with the detection of radiation representing the pulse emitted by the transmission path; and - A second comb controller (54), connected to control the second comb generating modulator (53), and configured to apply a second control signal consisting of a plurality of second equidistant spectral lines to the second comb generating modulator, the second equidistant spectral lines being separated by a second increment between any two of the second lines that are spectral neighbors. The difference between the first increment and the second increment is greater than the spectral width used to obtain the pulse compression effect. Furthermore, the digital processing module (27) is configured to calculate the correlation function between the corresponding product time signals of the measurement path (23a) and the reference path (23b), the product time signal of the measurement path being a mixture of two comb spectral components originating from the two transmission paths (13a, 13b) and having been reflected or backscattered by the target (T), and the product time signal of the reference path being a mixture of two comb spectral components originating from the two transmission paths but representing part of the radiation of the pulse (I) emitted by the transmission path (10), each mixture being performed in a manner to eliminate the phase fluctuation effect of the laser source (11).

10. The LIDAR system (100) according to any one of claims 1 to 3, characterized in that, The transmission path (10) further includes: - A first comb-shaped generating modulator (51) is arranged in one of the two transmission paths (13a, 13b) to be effective for the radiated portion transmitted by the transmission path; - A first comb controller (52) is connected to control the first comb generating modulator and is configured to apply a first control signal consisting of a plurality of first equidistant spectral lines to the first comb generating modulator, the first equidistant spectral lines being separated by a first increment between any two of the first lines that are spectral neighbors. - A second comb-shaped generating modulator (53), the second comb-shaped generating modulator being arranged in another of the two transmission paths (13a, 13b) to be effective for the radiated portion transmitted by said other transmission path; and - A second comb controller (54), connected to control the second comb generating modulator, and configured to apply a second control signal consisting of a plurality of second equidistant spectral lines to the second comb generating modulator, the second equidistant spectral lines being separated by a second increment between any two of the second lines that are spectral neighbors. The difference between the first increment and the second increment is greater than the spectral width used to obtain the pulse compression effect. Furthermore, the digital processing module (27) is configured to add or average the detection signal contributions associated with different pairs of optical paths, each pair of optical paths being formed by the first optical path generated by the first comb generating modulator (51) and the second optical path generated by the second comb generating modulator (53).

11. The LIDAR system (100) according to claim 8, characterized in that, The first and second comb-shaped generating modulators (51, 53) belong to the electro-optic modulator type.

12. The LIDAR system (100) according to any one of claims 1 to 3, characterized in that, The product of the spectral width of each pulse component modulated to produce the pulse compression effect and the duration of the pulse is greater than 500.

13. The LIDAR system (100) according to any one of claims 1 to 3, characterized in that, The product of the spectral width of each pulse component modulated to produce the pulse compression effect and the duration of the pulse is greater than 5000.

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