LIDAR system with suppressed Doppler frequency shift

Abstract

LIDAR system with suppressed Doppler frequency shift A LIDAR system for reducing or suppressing frequency shifts caused by movement of objects in a scene relative to the LIDAR, comprising: a light source; an input aperture (101); a splitter (2) configured to split reflected light into a reference channel (4) and a first imaging channel (3); a first imaging light IQ receiver (5) configured to acquire a first interference signal; a reference light IQ receiver (6) configured to acquire a reference interference signal; an imaging oscillator (111) configured to be temporally coherent with the reflected light; and at least one mixer (12) connected to the first imaging light IQ (5) and the reference light IQ (6), configured to acquire a first intermodulation product having a higher frequency and an intermodulation product of interest scaled by its Doppler shift.

Description

Summary of the Invention

[0001] The object of the invention is a LIDAR system that is able to reduce or completely suppress the effect of the frequency shift caused by the movement of objects in the scene relative to the LIDAR, known as the Doppler frequency shift. [Background technology]

[0002] Light detection and ranging (LIDAR) devices generate distance maps to targets by shining a laser light at the target and measuring the reflected light with a sensor. Differences in the properties of the laser light, including the total number of round trips, phase or wavelength, can then be used to create a digital 3D representation of the target.

[0003] LIDAR is commonly used to create high-resolution maps and has applications in geodesy, geoinformation, archaeology, geography, geology, geomorphology, seismology, forestry, atmospheric physics, laser guidance, airborne laser swath mapping (ALSM), laser altimetry, etc. The technology is also used for control and navigation for some autonomous vehicles.

[0004] Some LIDARs use what is called coherent detection, in which the light reflected off the sample is mixed with a local oscillator that is coherent with the reflected light. This approach has several advantages, such as optical gain that allows single-photon sensitivity, and the change in the phase and wavelength of the light can be used to measure distance.

[0005] A common problem that appears when using this type of LIDAR is the frequency shift caused by the movement of objects in the scene relative to the device, an effect called Doppler frequency shift. Such frequency shifts may be large relative to the bandwidth of the signal used to measure the relevant properties of the objects, complicating the extraction of such relevant data. This problem becomes significant when the relative velocities of the objects are large, as is the case for vehicles, aircraft or satellites.

[0006] This frequency shift is variable, often unknown, and can lead to a very large broadening of the bandwidth of the detected signal. For ground vehicles, the relative speed can reach more than 300 km / h. This relative speed corresponds to a Doppler frequency shift of 54.0 MHz for an illumination of λ=1.55 μm. This variable frequency shift complicates the electronic readout and signal processing chains of systems that rely on coherent detection of the object signal.

[0007] Even if the signal chain may still be manageable for a small number of channels, it adds cost, size and complexity to the final LIDAR system, and is a major obstacle to practical implementation of multi-channel coherent LIDAR systems with a large number of inputs.

[0008] To solve the described problem, there are several approaches, one of which uses non-uniform sampling or other compressed sensing schemes to reduce the overall data rate of the signal.

[0009] In general, all developed approaches suffer from the same drawbacks of complex electronic readout circuitry and common signal processing chains, which make them expensive, large in size, typically difficult to implement, and difficult to scale to multi-channel architectures with a large number of channels.

[0010] The LIDAR system subject matter of the present invention describes a modification of a coherent LIDAR system utilizing one or more input apertures that is simple to implement, with the goal of reducing or completely eliminating the effect of frequency shifts caused by the movement of objects in the scene relative to the LIDAR, known as Doppler frequency shifts.

[0011] In the present invention, the reduction or elimination of frequency shift is achieved by measuring the Doppler shifted signal in a reference channel and then exploiting the mathematical properties of signal mixing in the time domain to shift the frequency of one or more imaging channels to cancel or reduce the Doppler shift.

[0012] Specifically, the Doppler frequency shift suppressed Light Detection and Ranging (LIDAR) system of the present invention comprises at least a light source configured to emit a first light toward an external object, the first light being diffusely or specularly reflected on the object and then received at least at an input aperture, thus resulting in a reflected light.

[0013] The reflected light may then be split with a splitter positioned at least following the input aperture, the splitter configured to split the reflected light into a reference channel and at least a first imaging channel.

[0014] A portion of the split reflected light is then directed through at least a first imaging channel to a first imaging light IQ (In-phase and Quadrature) receiver associated with the first imaging channel, the first imaging light IQ receiver configured to obtain a first interference signal including a first in-phase component and a first quadrature component.

[0015] Further, another portion of the reflected light is guided through a reference channel to a reference optical IQ receiver associated with the reference channel, the reference optical IQ receiver being configured to obtain a reference interference signal including a reference in-phase component and a reference quadrature component.

[0016] At least a local optical oscillator is associated with the first imaging light IQ receiver and the reference light IQ receiver and configured to be temporally coherent with the reflected light.

[0017] Finally, in one embodiment, the system comprises at least a mixer connected to the first imaging light IQ receiver and the reference light IQ receiver and configured to obtain a first intermodulation product having a higher frequency and a second intermodulation product of interest with its Doppler shift scaled or completely eliminated.

[0018] The above-mentioned system is one possible embodiment of the present invention. However, the system can include a reference aperture and several input apertures, or a reference channel and several imaging channels associated with one or more input apertures. Also, the system can include a single local optical oscillator associated with all the optical IQ receivers, or a reference local optical oscillator associated with the reference optical IQ receiver and an imaging local optical oscillator associated with the imaging optical IQ receiver, or a reference local optical oscillator associated with the reference optical IQ receiver and multiple imaging local optical oscillators each associated with one or more imaging optical IQ receivers.

[0019] The system may also comprise an optical amplitude modulator and / or an optical phase modulator applied to the imaging local optical oscillator such that the generation of intermodulation products occurs directly at the photodetector without the need for electronic mixing. [Brief description of the drawings]

[0020] In order to supplement the description and to assist towards a better understanding of the nature of the invention, a set of drawings is attached as an integral part of the description, in which, according to preferred examples of its practical embodiments, the following are represented, by way of illustrative and non-limiting character:

[0021] [Figure 1] FIG. 1 illustrates an exemplary LIDAR system for imaging an object in accordance with an embodiment of the present invention.

[0022] [Figure 1A] FIG. 1 illustrates the input aperture, optical IQ receiver, reference and imaging local optical oscillator scheme in one embodiment of the present invention.

[0023] [Figure 1B] FIG. 13 illustrates an alternative embodiment using a 2×4 MMI for an optical IQ receiver in accordance with an embodiment of the present invention.

[0024] [Diagram 2] FIG. 1 illustrates a scheme of a LIDAR system having a reference channel and an imaging channel in one embodiment of the present invention.

[0025] [Diagram 3] FIG. 1 illustrates a scheme for a LIDAR system having a reference channel and an array of imaging channels with directional information encoded in the relative phase between them in one embodiment of the present invention.

[0026] [Figure 4] FIG. 1 illustrates a scheme of a LIDAR system with multiple input apertures and an amplitude modulator for directly mixing a reference signal on the photodetector in one embodiment of the present invention.

[0027] [Diagram 5] FIG. 1 shows two versions of a Gilbert cell, one including a photodetector that allows direct multiplication of the differential photocurrent.

[0028] [Figure 6] FIG. 1 shows an integration scheme of a Gilbert cell using switched capacitors. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] Hereinafter, preferred embodiments of the present invention will be described with reference to FIGS.

[0030] The present invention relates to a LIDAR system, such as the LIDAR system (100) shown in FIG. 1, comprising at least a light source (102) configured to emit light (110) directed towards an external object (108). The light is reflected from the object (108) and the reflected light (112) is received at a receiver (104). More specifically, in a first embodiment of the invention, as will be described in more detail with reference to the figures below, the light is received at a reference input aperture (103) and an imaging input aperture (101). The light source (102) may represent a single light source or multiple light sources having different wavelengths. In some embodiments, the light source (102) comprises one or more laser light sources.

[0031] The LIDAR system (100) also includes a processor (106) configured to receive electrical signals from the light receiver (104) and perform one or more operations using the received electrical signals. For example, the processor (106) may use the received electrical signals to reconstruct a 3D image including the object (108). As described above, movement of the object (108) (identified by the upward arrow) while attempting to capture the reflected light (112) produces a frequency shift caused by the movement of the object (108) relative to the LIDAR system (100), an effect called a Doppler frequency shift.

[0032] 1A, the reference input aperture (103) enables the LIDAR system (100) to generate a reference interference signal between reflected light coming from the object (108) and a reference oscillator (113). This reference interference signal is then used to modulate an interference signal formed between reflected light (112) coming from the object (108) collected by the imaging input aperture (101) and the imaging oscillator (111).

[0033] In any given implementation, the reference input aperture (103) and one or more of the imaging input apertures (101) may overlap, for example as shown in the embodiment of FIG. 1A, as may the reference oscillator (113) and imaging oscillator (111).

[0034] According to some embodiments, the reference oscillator (113) and the imaging oscillator (111) exhibit a degree of temporal coherence with the reflected light (112) so that the interference signal formed can be processed at electrical frequencies.

[0035] In one example, shown in Figure 1A, the system comprises a single input aperture (101, 103). In this case, the system comprises a light source (102) that emits light toward an object (108). The light reflects off the object, and the reflected light (112) that enters the system by the input aperture (101, 103) is split by a splitting element (2), which may be a 1x2 splitter, into a first imaging channel (3) and a reference channel (4).

[0036] According to some embodiments, at least two channels (e.g., the reference channel (4) and the first imaging channel (3)) are affected by object motion via Doppler frequency shift in substantially the same manner, but the non-Doppler information-bearing modulation remains different between them. This allows the signals of both channels to be combined in a manner that eliminates or greatly reduces the Doppler frequency shift while recovering the information-bearing modulation.

[0037] As shown in Figure 1A, the first imaging channel (3) is fed to a first imaging optical IQ receiver (5) and the reference channel (4) is fed to a reference optical IQ receiver (6). The first imaging optical IQ receiver (5) is associated with an imaging oscillator (111) and the reference optical IQ receiver (6) is associated with a reference oscillator (113). According to some embodiments, within the optical IQ receiver (5, 6), both oscillators (111, 113) are fed through a 90° hybrid that generates a phase shift between the in-phase (7, 9) and quadrature (8, 10) components of each channel.

[0038] In another embodiment, the IQ receivers (5, 6) are implemented by 2x4 MMI couplers designed to provide a phase shift between each of the four outputs (7, 8, 9, 10) and the two inputs (3, 4). In Fig. 1B an embodiment is shown in which the first imaging optical IQ receiver (5) is a 2x4 MMI coupler fed by the first imaging channel (3) and the imaging oscillator (111) and the reference optical IQ receiver (6) is a 2x4 MMI coupler fed by the reference channel (4) and the reference oscillator (113).

[0039] In one embodiment, the wavelength of the imaging oscillator (111) is swept according to a standard FMCW (Frequently Modulated Continuous Wave) scheme, while the reference oscillator (113) holds its wavelength stationary. According to some embodiments, the reflected light (112) has a component that is coherent with both components at the oscillators (111, 113). To this end, either the illumination originates from a combination of both components, or both components share a common origin with the illumination, ensuring mutual coherence.

[0040] According to some embodiments, a first imaging optical IQ receiver (5) is associated with the first imaging channel (3) and configured to obtain a first interference signal having a first in-phase component (7) and a first quadrature component (8). A reference optical IQ receiver (6) is associated with the reference channel (4) and configured to obtain a reference interference signal having a reference in-phase component (9) and a reference quadrature component (10).

[0041] Both interference signals will be affected by Doppler in substantially the same way (with small differences due to different wavelengths, in some embodiments), but only the first interference signal associated with the imaging oscillator (111) conveys information about the distance between the object (108) and the LIDAR system (100) at its interference frequency.

[0042] As can be seen in Fig. 2, mixing the first interfering signal with the reference signal in at least one mixer 121-124 (sometimes collectively identified as 12) results in the generation of two intermodulation products. For example, the mixing generates a first intermodulation product with a higher frequency that can be discarded and an output intermodulation product (16) with a lower frequency where the Doppler shift is significantly scaled, which provides the possibility to bring the ranging and amplitude information into the baseband, thus minimizing the sampling frequency and the readout complexity of the electronics.

[0043] For the sake of explanation, the first interference signal and the reference interference signal are derived for this implementation as described herein. The imaging input aperture (101) and the reference aperture (103) are assumed to be in substantially the same position, except for a possible relative phase shift if the imaging input aperture (101) is part of an array. When the scene is illuminated equally with two light sources having two wavelengths (with associated wave numbers and angular frequencies k1, k2 and ω1, ω2, respectively) and equal amplitude A, the optical signal at a distance x from the light source is:

number

[0044] Here, the first wavelength of the first light source of the LIDAR system is assumed to undergo a linear frequency modulation with a constant K. If the object reflecting the light emitted by the first light source is a single diffuse reflector, then the intensity reflectivity ρ j and the relative velocity v in the direction between the input opening (101) and the object. j and the distance x j and the reflected field of light collected at the input aperture (101) is:

number

[0045] where i is the refractive index of the input aperture when an array of apertures is present. The Doppler shift is calculated by subtracting 2k1v from the equation. j and 2k2v j This can be seen in the section on the frequency of reflected light.

[0046] In the calculation of the interference signal of the optical IQ receiver (5, 6), for simplicity, it is assumed that the two wavelength components of the reference oscillator and the imaging oscillator (111, 113) have a single amplitude.

number

number

[0047] After the imaging light IQ receiver (5) and the reference light IQ receiver (6) there is a first interference signal and a reference interference signal, respectively. 1.

number

number

[0048] Of these, the beating products, which are the result of differences in optical angular frequency, have a very high frequency, once detected, according to electrical standards. For example, if we assume that the wavelength of the light from the light source is 1.55 μm and the two wavelengths are 0.1 nm apart, the intermodulation products have a frequency of 12.5 GHz.

number

[0049] Conversely, the beating product, where the frequency of the local oscillator and the reflected light are equal, is demodulated to a lower frequency resulting from the frequency difference between the phase modulation frequencies of the emitted and received light, plus or minus a Doppler shift.

[0050] According to some embodiments, at typical speeds of ground vehicles, the Doppler shift is equal to or lower than 100 MHz, so that the higher frequency mixing terms (including the difference in optical angular frequency) can be suppressed by low pass filters. Thus, as shown in Figure 2, a first set of low pass filters (13) can be associated with the optical IQ receivers (5, 6) to filter the first in-phase component (7), the first quadrature component (8), the reference in-phase component (9) and the reference quadrature component (10).

[0051] The low frequency component of the interference signal is given by: 3.

number

number

[0052] Depth and velocity information is encoded in the frequency (and phase) of both photocurrents. By focusing only on the frequency information, the frequencies of I1(t) and I2(t) are ascertained.

number

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[0053] These two frequency shift components scale differently with line speed. The modulation constant K directly affects the frequency resulting from the range. However, the Doppler shift remains independent and is determined by the scene characteristics. Since the Doppler shift can go up to frequencies of tens of MHz, it usually necessitates the use of faster capture electronics, which can add to the cost of the system. Also, these video frequencies can be problematic when scaling up scene detection with multiple parallel imaging channels (3).

[0054] However, the differences between these two frequencies are as follows:

number

[0055] According to some embodiments, if the two wavelengths of light emitted from the two light sources are selected to be close to each other (e.g., 1.55 μm wavelengths with 0.1 nm separation), the difference in Doppler frequency shift is significantly reduced (v j (If the velocity is 50 m / s, it will be 2 kHz.)

[0056] However, it is noteworthy that both wavelengths can be equal. In this case, the Doppler shift may be completely suppressed, but the frequency shift due to FMCW is maintained. This approach simplifies the optical system and the associated electro-optical circuitry.

[0057] If both wavelengths are equal, the Doppler shift may be completely suppressed and the signal frequency may move to baseband. This lower Doppler frequency can significantly reduce line speed, data throughput, and hardware complexity in systems where a large number of input apertures (101) are desired. If the Doppler frequency is maintained, then to measure the Doppler shift, it should be decoupled from the FMCW modulation. One exemplary way to achieve this is to vary K in the FMCW frequency sweep over time (e.g., alternating its sign) and compare the resulting shift in electrical frequency between both modulation slopes.

[0058] One exemplary method for subtracting the frequencies obtained in the optical IQ receiver (5, 6) above is to multiply one current by the complex conjugate of the other. Standard frequency mixing techniques can be applied. This can be done in the digital or analog domain, and potentially based on an interfering signal, as shown below.

number

[0059] In one embodiment, this can be implemented using one or more mixers 121-124 connected to the first imaging light IQ (5) and reference light IQ (6) outputs or to the first low pass filter set (13) output as shown in Figure 2. Each of the four multiplication terms above is a first intermodulation product with a difference in frequency (low frequency) Δf and a Doppler frequency

number

[0060] By combining the four multiplication terms, the terms related to the addition of Doppler frequencies are cancelled, leaving only the low frequency intermodulation products whose frequencies contain depth information (as per Δf above) as the output intermodulation products (16).

[0061] According to some embodiments, the higher frequency components of each of the multiplication terms are filtered using a second set of low pass filters (23) such that only the low frequency intermodulation products are retained. These low frequency intermodulation products contain depth information of their frequency (as above Δf) as output intermodulation products (16). According to some embodiments, the output intermodulation products (16) are amplified using one or more non-linear amplifiers (25).

[0062] In the embodiment shown in FIG. 2, one or more mixers 121-124 mix a first quadrature component (8) with a reference in-phase component (9) to produce a multiplication term (l 1q *l 2i ), which mixes the first in-phase component (7) with the reference in-phase component (9) to give a multiplication term (l 1i *l 2i ) is included.

[0063] In alternative demodulation techniques, it is possible to handle the individual components of the interference signal, namely the first in-phase component (7), the first quadrature component (8) and the derivative of the reference interference signal provided by a time differentiation module (15) which generates a time derivative of a reference in-phase component (90) and a time derivative of a reference quadrature component (91), and it is also possible to apply FM demodulation techniques which perform baseband conversion and demodulation simultaneously.

[0064] This can be particularly useful in embodiments where both the imaging oscillator and the reference oscillator are the same, since in that situation the frequency difference of the multiplicative term expressed above can be used to extract depth information that is frequency encoded in the amplitude of the time-differentiated signal by using time differentiation.

[0065] For example, in the case where the imaging oscillator and the reference oscillator are the same, the possible operations of one or more mixers (121)-(124) are as follows.

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[0066] Similar to the direct frequency mixing approach, in this case one can generate the four multiplication terms above and combine them leaving only the DC component, or alternatively one can use a second set of low pass filters (23) to filter the higher frequency components of each of the multiplication terms, retaining only the DC component, whose amplitude contains the depth and Doppler information.

[0067] To separate the Doppler and depth information, one can vary the K of the FMCW frequency sweep over time, e.g., alternating its sign, and compare the resulting shift in the DC component between both modulation slopes.

[0068] The drawback of direct FM demodulation is that this DC value is multiplied by the reflectivity of the object (ρ j) and frequency shift are mixed. According to some embodiments, this can be addressed by demodulating the amplitudes separately.

number

[0069] Alternatively, if the imaging oscillator and the reference oscillator are the same, the object reflectivity can also be obtained from the multiplication term between the signal component before time differentiation and the reference component (e.g., as provided by the first mixer (121) and the second mixer (122) from FIG. 2).

[0070] For use of a direct FM demodulation approach, Fig. 2 shows one or more mixers (121)-(124) including a time differentiation module (15), a third mixer (123) designed to mix the first in-phase component (7) with the time differentiated reference quadrature component (91), and a fourth mixer (124) designed to mix the first quadrature component (8) with the time differentiated reference quadrature component (91). Thus, in the embodiment of Fig. 2, a demodulation scheme is provided that includes both frequency demodulation and amplitude demodulation simultaneously.

[0071] FIG. 3 shows an implementation in which multiple imaging channels (3) are combined with a common reference channel (4) obtained from reflected light (112) coming from the same scene but mixed with another light source (one of a different wavelength, but coherent with at least a portion of the power collected from the scene).

[0072] The advantage of the scheme shown in Fig. 3 is that the different imaging channels (3) maintain their relative phase differences (contained in the IQ data) in the electrical domain after demodulation, which allows coherent combination of the demodulated signals coming from said imaging channels (3) in order to recover the different directions.

[0073] It is possible to use different construction schemes for the various mixers (collectively designated 12 in FIG. 3). For example, the mixers may be implemented in the analog domain, based on circuits relying on translinear techniques. One of these circuits may be the Gilbert cell, an example of which is depicted in FIG. 5. This circuit has the advantage of operating in all four quadrants of the interference signal. According to some embodiments, considering that the input to the cell is differential and voltage-based, the photocurrent coming from the optical IQ receiver (5, 6) described above) is amplified to a voltage by a transimpedance amplifier (14) and may be derived in the analog domain, if appropriate.

[0074] To simplify the Gilbert cell, it may be possible to use a balanced differential pair of photocurrents as both the source of the input signal and the current bias. This would reduce the need for intermediate transimpedance amplifiers, making the cell more amenable to duplication for large scale integration. According to some embodiments, the imaging oscillator (111) mixed with the different imaging channels (3) can be generated and distributed as voltage signals onto the detector array (e.g., imaging channels) from a single imaging input aperture (101) without significant scalability issues.

[0075] To simplify the cell readout, an integrated scheme with switched capacitors and multiplexed video output can be applied, for example as shown in Figure 6. Such switched capacitor readout can be configured similarly to a normal image sensor: for example, the switched capacitors can be organized by column, and a multiplexing scheme can be used to route the analog values ​​to the appropriate ADC circuitry.

[0076] Finally, it is also possible to modulate the amplitude of the optical local oscillator going to each of the imaging channels to provide the desired mixing function. In this way, no electronic mixing is required after photodetection, providing advantages in terms of system complexity. According to some embodiments, as shown in FIG. 4, an optical modulator (17) is used to modulate the amplitude of the optical local oscillator. In one embodiment, the optical modulator (17) is an optical amplitude modulator, whether based on electro-optic absorption, Mach-Zehnder interferometer or otherwise.

[0077] If the amplitude modulation leaves some phase modulation, a phase modulator can be added in series to ensure constant phase behavior and avoid undesired frequency shifts in the reference channel. Amplitude modulation can also be obtained via different methods, e.g. optical amplifiers, modulation of the laser current, etc.

[0078] In some embodiments, the first in-phase component (7), the first quadrature component (8), the reference in-phase component (9) and the reference quadrature component (10) are multiplied with different versions of the signal and shifted 90° with respect to each other to directly achieve the desired mathematical result. To physically achieve this, a distribution of the reference signals modulated separately to each output mixer (12) may be used. Considering the fact that the modulation applied to these two channels is also orthogonal in the electrical domain, in some embodiments it is possible to add them together in a modulated signal, as shown in FIG. 4.

[0079] According to some embodiments, products between the first in-phase component (7) and the first quadrature component (8), or between the reference in-phase component (9) and the reference quadrature component (10), generate high-frequency intermodulation products that can be filtered.

[0080] According to some embodiments, to separate the amplitude and distance information, the modulation signal applied to the optical modulator (17) can be switched between different modes (with or without time differentiation) to alternatively recover the depth information and / or the signal amplitude. This time domain multiplexing may be suitable for implementation by an integrator synchronized with the switching of the demodulation signal, but can also be replaced by other multiplexing schemes (frequency domain multiplexing, code multiplexing, etc.). The switching of the demodulation signal in both the imaging channel and the reference channel can be performed using a switch (27).

[0081] According to some embodiments, FIG. 4 illustrates a combination of the two implementation options described above for the single wavelength case: Doppler frequency demodulation with amplitude modulation of an optical reference signal and time multiplexed amplitude / frequency demodulation. [Other possible items] [Item 1] 1. A light detection and ranging (LIDAR) system with suppressed Doppler frequency shift, the system comprising: at least one light source (102) configured to emit a first light; At least one imaging input aperture (101) configured to receive input reflected light reflected by a moving object (108) illuminated by the light source (102), and one imaging channel (3) associated with the at least one imaging input aperture (101); At least one reference aperture (103) configured to receive a reference reflected light reflected by the moving object illuminated by the light source (102), and one reference channel (4) associated with the at least one reference aperture (103); At least one imaging oscillator (111); at least one first imaging light receiver (5) associated with the imaging input aperture (101) and the imaging oscillator (111), configured to obtain an interference signal between the input reflected light and the imaging oscillator (111); A reference oscillator (113); a reference light receiver (6) associated with the reference aperture (101) and the reference oscillator (113), configured to obtain a reference interference signal between the reference reflected light and the reference oscillator (113); at least one mixer (12) connected to the at least one first imaging light receiver (5) and the reference light receiver (6), configured to generate intermodulation products (16) between the interference signal and the reference interference signal so as to cancel or reduce a Doppler frequency shift caused by the moving object (108); A light detection and ranging (LIDAR) system comprising: [Item 2] 2. The LIDAR system of claim 1, wherein the at least one first imaging optical receiver (5) is an optical IQ receiver configured to acquire an interference signal between the input reflected light and the imaging oscillator (111) including a first in-phase component (7) and a first quadrature component (8), and the reference optical receiver (6) is an optical IQ receiver configured to acquire a reference interference signal including a reference in-phase component (9) and a reference quadrature component (10). [Item 3] 3. The LIDAR system of item 2, further comprising a time differentiation module (15) associated with the reference light receiver (6) and intended to time differentiate the reference in-phase component (9) and the reference quadrature component (10). [Item 4] The at least one mixer (12) comprises: a first mixer (121) intended to mix said first quadrature component (8) and said reference in-phase component (9); a second mixer (122) intended to mix said first in-phase component (7) and said reference in-phase component (9); 3. The LIDAR system according to item 2, comprising: [Item 5] The at least one mixer (12) comprises: a first mixer (121) intended to mix said first quadrature component (8) and said reference quadrature component (10); a second mixer (122) intended to mix the first in-phase component (7) and the reference quadrature component (10); 3. The LIDAR system according to item 2, comprising: [Item 6] The at least one mixer (12) comprises: a third mixer (123) intended to mix said first in-phase component (7) and said time-differentiated reference quadrature component (91); a fourth mixer (124) intended to mix said first quadrature component (8) with said time-differentiated reference quadrature component (91); 3. The LIDAR system according to item 2, comprising: [Item 7] The at least one mixer (12) comprises: a third mixer (123) intended to mix said first in-phase component (7) and said time-differentiated reference in-phase component (90); a fourth mixer (124) intended to mix said first quadrature component (8) with said time-differentiated reference in-phase component (90); 3. The LIDAR system according to item 2, comprising: [Item 8] 8. The LIDAR system of any one of items 4 to 7, further comprising a low pass filter (23) associated with each mixer (12). [Item 9] 2. The LIDAR system of claim 1, wherein the reference oscillator (113) shares a common origin with the imaging oscillator (111). [Item 10] 2. The LIDAR system of claim 1, wherein the reference aperture (103) is the same as the input aperture (101), and the reference channel (4) and the imaging channel (3) are derived therefrom by a splitter (2). [Item 11] 2. The LIDAR system of item 1, wherein the wavelength of the reference oscillator (113) remains stationary and the wavelength of the first optical oscillator (111) is swept according to a standard FMCW (Frequency Modulated Continuous Wave) scheme. [Item 12] 2. The LIDAR system of claim 1, further comprising one or more low-pass filters (13) associated with the optical receivers (5, 6) configured to filter the interference signal and the reference interference signal. [Item 13] 3. The LIDAR system of claim 2, further comprising a transimpedance amplifier (14) arranged following the reference light receiver (6) and the first imaging light receiver (5), configured to amplify the reference in-phase component (9), the reference quadrature component (10), the first in-phase component (7), and the first quadrature component (8). [Item 14] 8. The LIDAR system of any one of items 1 or 4 to 7, wherein the mixer (12) is a Gilbert cell. [Item 15] at least one light source (102) configured to emit a first light; At least one imaging input aperture (101) configured to receive input reflected light reflected by a moving object (108) illuminated by the light source (102), and one imaging channel (3) associated with the at least one imaging input aperture (101); At least one reference aperture (103) configured to receive a reference reflected light reflected by the moving object illuminated by the light source, and one reference channel (4) associated with the at least one reference aperture (103); At least one imaging oscillator (111); at least one first imaging light receiver (5) associated with the imaging input aperture (101) and the imaging oscillator (111), configured to obtain an interference signal between the input reflected light and the imaging oscillator (111); The reference oscillator (113); a reference light receiver (6) associated with the reference aperture (101) and the reference oscillator (113), configured to obtain a reference interference signal between the reference reflected light and the reference oscillator (113); an optical modulator (17) connected to the at least one imaging oscillator (111) configured to apply amplitude or phase modulation to the imaging oscillator (111) with a signal derived from the reference channel (4) such that intermodulation products (16) between the interference signal and the reference interference signal appear at the output of the at least one first imaging optical receiver (5) to cancel or reduce a Doppler frequency shift due to the moving object; A LIDAR system equipped with [Item 16] Item 16. The LIDAR system of item 15, wherein the at least one first imaging optical receiver (5) is an optical IQ receiver configured to acquire an interference signal between the input reflected light and the imaging oscillator (111) including a first in-phase component (7) and a first quadrature component (8), and the reference optical receiver (6) is an optical IQ receiver configured to acquire a reference interference signal including a reference in-phase component (9) and a reference quadrature component (10). [Item 17] Item 16. The LIDAR system of item 15, wherein the reference oscillator (113) shares a common origin with the imaging oscillator (111). [Item 18] 16. The LIDAR system of item 15, wherein the reference aperture (103) is the same as the input aperture (101), and the reference channel (4) and the imaging channel (3) are derived therefrom by a splitter (2). [Item 19] Item 16. The LIDAR system of item 15, wherein the wavelength of the reference oscillator (113) remains stationary and the wavelength of the first optical oscillator (111) is swept according to a standard FMCW (Frequency Modulated Continuous Wave) scheme. [Item 20] Item 16. The LIDAR system of item 15, further comprising one or more low-pass filters (13) associated with the optical receivers (5, 6) configured to filter the interference signal and the reference interference signal. [Item 21] Item 17. The LIDAR system according to item 16, further comprising a transimpedance amplifier (14) arranged following the reference light receiver (6) and the first imaging light receiver (5) intended to amplify the reference in-phase component (9), the reference quadrature component (10), the first in-phase component (7) and the first quadrature component (8). [Item 22] A method for suppressing Doppler frequency shift in a LIDAR system using a system according to any one of the preceding paragraphs, comprising: Emitting a first light (110) directed toward a moving object (108); receiving reflected light (112) coming from the moving object (108); obtaining a first interference signal between the reflected light (112) and an imaging oscillator (111); obtaining a reference interference signal between the reflected light (112) and a reference oscillator (113); obtaining an intermodulation product (16) between the interference signal and the reference interference signal so as to cancel or reduce the Doppler frequency shift due to the moving object (108); The method comprises the steps of:

Claims

1. 1. A Doppler frequency shift suppressed light detection and ranging (LIDAR) system, the system comprising: at least one light source configured to emit a first light; At least one imaging input aperture configured to receive input reflected light reflected by a moving object illuminated by the light source, and an imaging channel associated with the at least one imaging input aperture; At least one reference aperture configured to receive a reference reflected light reflected by the moving object illuminated by the light source, and a reference channel associated with the at least one reference aperture; at least one imaging oscillator; at least one first imaging light receiver associated with the imaging input aperture and the at least one imaging oscillator configured to obtain an interference signal between the input reflected light and the at least one imaging oscillator; a reference oscillator, wherein the at least one imaging oscillator is separately modulated with respect to the reference oscillator; a reference light receiver associated with the reference aperture and the reference oscillator, configured to obtain a reference interference signal between the reference reflected light and the reference oscillator; at least one mixer coupled to the at least one first imaging light receiver and the reference light receiver, configured to generate intermodulation products between the interference signal and the reference interference signal so as to cancel or reduce the Doppler frequency shift due to the moving object; 1. A light detection and ranging (LIDAR) system comprising:

2. 2. The LIDAR system of claim 1, wherein the at least one first imaging optical receiver is an optical IQ receiver configured to acquire an interference signal between the input reflected light and the at least one imaging oscillator including a first in-phase component and a first quadrature component, and the reference optical receiver is an optical IQ receiver configured to acquire a reference interference signal including a reference in-phase component and a reference quadrature component.

3. 3. The LIDAR system of claim 2, further comprising a time differentiation module associated with the reference light receiver and intended to time differentiate the reference in-phase component and the reference quadrature component.

4. The at least one mixer comprises: a first mixer intended to mix said first quadrature component with said reference in-phase component; a second mixer intended to mix said first in-phase component with said reference in-phase component; 3. The LIDAR system of claim 2, comprising:

5. The at least one mixer comprises: a first mixer intended to mix said first quadrature component with said reference quadrature component; a second mixer intended to mix the first in-phase component and the reference quadrature component; 3. The LIDAR system of claim 2, comprising:

6. The at least one mixer comprises: a third mixer intended to mix the first in-phase component with the time-differentiated reference quadrature component; a fourth mixer intended to mix the first quadrature component with the time-differentiated reference quadrature component; 3. The LIDAR system of claim 2, comprising:

7. The at least one mixer comprises: a third mixer intended to mix said first in-phase component with said time-differentiated reference in-phase component; a fourth mixer intended to mix said first quadrature component with said reference in-phase component time-differentiated; 3. The LIDAR system of claim 2, comprising:

8. 8. The LIDAR system of claim 4, further comprising a low pass filter associated with each mixer.

9. 10. The LIDAR system of claim 1, wherein the reference oscillator and the at least one imaging oscillator share a common origin.

10. 2. The LIDAR system of claim 1, wherein the reference aperture is the same as the imaging input aperture, and the reference channel and the imaging channel are derived therefrom by a splitter.

11. 10. The LIDAR system of claim 1, wherein the wavelength of the reference oscillator remains stationary and the wavelength of the at least one imaging oscillator is swept according to a standard FMCW (Frequency Modulated Continuous Wave) scheme.

12. 10. The LIDAR system of claim 1, further comprising: one or more low pass filters associated with the first imaging light receiver and the reference light receiver configured to filter the interference signal and the reference interference signal.

13. 3. The LIDAR system of claim 2, further comprising a transimpedance amplifier disposed following the reference light receiver and the first imaging light receiver configured to amplify the reference in-phase component, the reference quadrature component, the first in-phase component, and the first quadrature component.

14. 8. The LIDAR system of claim 1, wherein the mixer is a Gilbert cell.

15. at least one light source configured to emit a first light; At least one imaging input aperture configured to receive input reflected light reflected by a moving object illuminated by the light source, and an imaging channel associated with the at least one imaging input aperture; At least one reference aperture configured to receive a reference reflected light reflected by the moving object illuminated by the light source, and a reference channel associated with the at least one reference aperture; at least one imaging oscillator; at least one first imaging light receiver associated with the imaging input aperture and the at least one imaging oscillator configured to obtain an interference signal between the input reflected light and the at least one imaging oscillator; A reference oscillator; a reference light receiver associated with the reference aperture and the reference oscillator, configured to obtain a reference interference signal between the reference reflected light and the reference oscillator; an optical modulator connected to the at least one imaging oscillator configured to apply amplitude or phase modulation to the at least one imaging oscillator with a signal derived from the reference channel such that intermodulation products between the interference signal and the reference interference signal appear at an output of the at least one first imaging optical receiver so as to cancel or reduce a Doppler frequency shift due to the moving object; A LIDAR system comprising:

16. 16. The LIDAR system of claim 15, wherein the at least one first imaging optical receiver is an optical IQ receiver configured to acquire an interference signal between the input reflected light and the at least one imaging oscillator comprised of a first in-phase component and a first quadrature component, and the reference optical receiver is an optical IQ receiver configured to acquire a reference interference signal comprised of a reference in-phase component and a reference quadrature component.

17. 16. The LIDAR system of claim 15, wherein the reference oscillator and the at least one imaging oscillator share a common origin.

18. 16. The LIDAR system of claim 15, wherein the reference aperture is the same as the imaging input aperture, and the reference channel and the imaging channel are derived therefrom by a splitter.

19. 16. The LIDAR system of claim 15, wherein the wavelength of the reference oscillator remains stationary and the wavelength of the at least one imaging oscillator is swept according to a standard FMCW (Frequency Modulated Continuous Wave) technique.

20. 16. The LIDAR system of claim 15, further comprising one or more low pass filters associated with the first imaging light receiver and the reference light receiver configured to filter the interference signal and the reference interference signal.

21. 17. The LIDAR system of claim 16, further comprising a transimpedance amplifier arranged following the reference light receiver and the first imaging light receiver intended to amplify the reference in-phase component, the reference quadrature component, the first in-phase component and the first quadrature component.

22. 22. A method for suppressing Doppler frequency shift in a LIDAR system using a LIDAR system according to any one of claims 1 to 21, comprising the steps of: Emitting a first light directed toward a moving object; receiving reflected light coming from the moving object; obtaining a first interference signal between the reflected light and an imaging oscillator; obtaining a reference interference signal between the reflected light and a reference oscillator; obtaining an intermodulation product between the first interference signal and the reference interference signal so as to cancel or reduce the Doppler frequency shift due to the moving object; A method comprising:

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