Techniques for compensating phase damage in LIDAR systems

Abstract

A method for compensating for phase impairments in a LiDAR (Light Detection and Ranging) system includes: transmitting a first light beam toward a target; receiving a second light beam from the target to generate a received light beam; and generating a digitally sampled target signal using a local oscillator (LO) beam, a first photodetector, and the received light beam. The method further includes generating a digitally sampled reference signal using a reference beam transmitted through an optical fiber delay device and a second photodetector, and using the digitally sampled reference signal to estimate one or more phase impairments in the LiDAR system to generate one or more estimated phase impairments. The method also includes performing a first correction on a first phase impairment introduced into the digitally sampled target signal by the LO beam; and performing a second correction on a second phase impairment introduced into the digitally sampled target signal by the received light beam.

Description

[0001] Related Applications

[0002] This application claims the benefit of U.S. Patent Application 16 / 994,325, filed April 19, 2021, pursuant to 35 U.S. SC §119(e), which claims priority and benefit to U.S. Provisional Application 63 / 087,432, filed October 5, 2020, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure relates to a light detection and ranging (LIDAR) system. Background Technology

[0004] Traditional frequency modulated continuous wave (FMCW) LiDAR systems include several potential phase impairments, such as laser phase noise, circuit phase noise, flicker noise injected into the laser by driving electronics, temperature / weather drift, and chirp rate shift. These impairments lead to a loss of detection probability, increase false alarms and range / velocity bias, and increase the error in the estimated target range / velocity. Summary of the Invention

[0005] This disclosure describes various embodiments of a LIDAR system and methods that add a reference channel to the system to simulate a target at a predetermined distance, estimate phase impairment based on the reference channel, and correct the signal based on the estimated phase impairment. Embodiments of the invention include functionality for estimating phase impairment and compensating for phase impairment in the echo signal. Such impairment includes, for example, impairment based on laser phase noise, circuit phase noise, flicker noise, drift due to temperature or weather, chirp rate shift, or other types of impairment, which may lead to a loss of detection probability, an increase in false alarms, and misestimation of range or velocity that may cause range / velocity deviation and range / velocity error.

[0006] According to one aspect, this disclosure relates to a method for correcting phase impairments in a LIDAR (Light Detection and Ranging) system. The method includes: sending a first light beam toward a target; receiving a second light beam from the target to generate a received beam; generating a digitally sampled target signal using an LO (Local Oscillator) beam, a first photodetector, and the received beam; and generating a digitally sampled reference signal using a reference beam transmitted through an optical fiber delay device and a second photodetector. The method further includes: using the digitally sampled reference signal to estimate one or more phase impairments in the LIDAR system to generate one or more estimated phase impairments. The method further includes: using the one or more estimated phase impairments to perform a first correction on a first phase impairment of the one or more phase impairments from the digitally sampled target signal, wherein the first phase impairment is introduced into the digitally sampled target signal by the LO beam. The method further includes: using the one or more estimated phase impairments to perform a second correction on a second phase impairment of the one or more phase impairments from the digitally sampled target signal, wherein the second phase impairment is introduced into the digitally sampled target signal by the received beam. The method further includes: processing the first correction and the second correction to generate a corrected target signal for transmission to a point cloud. In one embodiment, estimating the one or more phase impairments includes: using at least one of a zero-forcing estimator, an MMSE estimator, a maximum likelihood estimator, and a MAP estimator. In one embodiment, performing the first correction includes: using one or more filters shaped at least partially based on an estimate of the first phase impairment. In one embodiment, performing the second correction includes: using a smooth delay correction filter, wherein the smooth delay correction filter is used to delay the received beam through multiple digital delays and select an optimal delay. In one embodiment, selecting the optimal delay includes: performing an FFT (Fast Fourier Transform) of the digital delay and selecting the delay with the highest peak. In one embodiment, performing the second correction includes: using an iterative delay correction filter, wherein the iterative delay correction filter is used to repeatedly delay the reflected beam through different digital delays until peak convergence is achieved. In one embodiment, performing the second correction includes: using a deskip compensation correction filter. In one embodiment, the method further includes: generating multiple digitally sampled reference signals using reference beams transmitted through multiple different fiber delay devices, each fiber delay device being connected to a corresponding photodetector.

[0007] According to another aspect, this disclosure relates to a LIDAR (Optical Detection and Ranging) system. The system includes: a beam source for transmitting a first beam toward a target; a first detector for receiving an LO (Local Oscillator) beam and a received beam from the target, and generating a digitally sampled target signal; an optical fiber delay device having a known length and coupled to the beam source; a second detector coupled to the optical fiber delay device to generate a digitally sampled reference signal using a reference beam transmitted through the optical fiber delay device; a phase impairment estimator for estimating one or more phase impairments in the LIDAR system using the digitally sampled reference signal to generate one or more estimated phase impairments; a first phase impairment corrector for correcting a first phase impairment introduced into the digitally sampled target signal by the LO beam; and a second phase impairment corrector for correcting a second phase impairment introduced into the digitally sampled target signal by the received beam. In one embodiment, the system further includes a zero-forcing estimator, an MMSE estimator, a maximum likelihood estimator, or a MAP estimator for estimating the one or more phase impairments. In one embodiment, the first phase impairment corrector includes one or more filters shaped at least in part based on an estimate of the first phase impairment. In one embodiment, the second phase impairment corrector includes a smooth delay correction filter for delaying the received beam through multiple digital delays and selecting an optimal delay. In one embodiment, selecting the optimal delay includes performing an FFT (Fast Fourier Transform) on the digital delay and selecting the delay with the highest peak. In one embodiment, the second phase impairment corrector includes an iterative delay correction filter for repeatedly delaying the reflected beam through different digital delays until peak convergence is achieved. In one embodiment, the second phase impairment corrector includes a deskipation compensation correction filter. In one embodiment, the fiber delay device generates a delay proportional to the frequency of the received beam, such that reflections from targets at greater distances are delayed more, and reflections from targets at shorter distances are delayed less. In one embodiment, the system further includes multiple different fiber delay devices and photodetectors for generating multiple digitally sampled reference signals.

[0008] According to another aspect, this disclosure relates to a method for correcting phase impairments in a LIDAR (Optical Detection and Ranging) system. The method includes: generating a digitally sampled target signal using an LO beam (i.e., a local oscillator beam), a first photodetector, and a received beam reflected from a target; generating a digitally sampled reference signal using a reference beam transmitted through an optical fiber delay device and a second photodetector; estimating a first phase impairment introduced into the digitally sampled target signal by the LO beam; estimating a second phase impairment introduced into the digitally sampled target signal by the received beam; performing a first correction to correct the first phase impairment; and performing a second correction to correct the second phase impairment. In one embodiment, estimating the second phase impairment includes using at least one of a zero-forcing estimator, an MMSE estimator, a maximum likelihood estimator, and a MAP estimator. In one embodiment, performing the second correction includes using a smooth delay correction filter, wherein the smooth delay correction filter is used to delay the received beam through a plurality of digital delays and select an optimal delay; using an iterative delay correction filter, wherein the iterative delay correction filter is used to repeatedly delay the reflected beam through different digital delays until peak convergence is achieved; or using a deskip compensation correction filter. Attached Figure Description

[0009] To gain a more comprehensive understanding of the various examples, please now refer to the following detailed description taken in conjunction with the accompanying drawings, in which the same reference numerals correspond to the same elements.

[0010] Figure 1 An example LIDAR system is illustrated according to an embodiment of the present disclosure.

[0011] Figure 2 This illustrates how a time-frequency diagram of a LiDAR waveform is detected and processed according to embodiments of the present disclosure.

[0012] Figure 3 Examples of various rapid phase changes that can be detected by embodiments of this disclosure are provided.

[0013] Figure 4 Examples of various slow phase changes that can be detected by embodiments of this disclosure are provided.

[0014] Figure 5 Examples of various chirp rate offsets that can be detected by embodiments of this disclosure are provided.

[0015] Figure 6 This is a block diagram of an example LIDAR system with a reference arm according to an embodiment of the present disclosure.

[0016] Figure 7 A digital signal processing architecture according to embodiments of the present disclosure is described.

[0017] Figure 8 An example system for correcting damage from echo signals is described according to some embodiments of the present disclosure.

[0018] Figure 9 An example system for correcting phase impairment using multiple delays is described according to some embodiments of the present disclosure.

[0019] Figure 10 An example system for correcting phase impairment using an iterative delay correction filter, according to some embodiments of the present disclosure, is described.

[0020] Figure 11 An example system for correcting phase impairment using a deskipation compensation correction filter, according to some embodiments of the present disclosure, is described.

[0021] Figure 12 An example system for correcting phase damage using a combined damage corrector and a peak selector, according to some embodiments of the present disclosure, is described.

[0022] Figure 13 This is an example system for correcting phase impairment using multiple reference channels, according to some embodiments of the present disclosure.

[0023] Figure 14 This is a flowchart of an example method for compensating for phase impairments in a LIDAR system according to embodiments of the present disclosure. Detailed Implementation

[0024] This disclosure describes various examples of LIDAR systems and methods for compensating for phase impairment. According to some embodiments, the described LIDAR systems can be implemented in any sensing market, such as, but not limited to, transportation, manufacturing, metrology, medical, augmented reality, virtual reality, and security systems. According to some embodiments, the described LIDAR systems are implemented as part of the front end of a frequency modulated continuous wave (FMCW) device that assists automated driver assistance systems or autonomous vehicles in spatial perception.

[0025] Figure 1 An example of a LIDAR system 100 implemented according to this disclosure is illustrated. The LIDAR system 100 includes one or more of a plurality of components, but may include more than one of them. Figure 1 The components shown are fewer or additional. According to some embodiments, they can be implemented on a photonic chip. Figure 1The figure depicts one or more components. As shown, the LIDAR system 100 includes optical circuitry 101 implemented on a photonic chip. Optical circuitry 101 may include a combination of active and passive optical components. Active optical components may generate, amplify, and / or detect optical signals, etc. In some examples, active optical components include light beams of different wavelengths and include one or more optical amplifiers, one or more optical detectors, etc.

[0026] Free-space optics 115 may include one or more optical waveguides to carry optical signals and route and manipulate them to appropriate input / output ports of active optical circuitry. Free-space optics 115 may also include one or more optical components, such as taps, wavelength division multiplexers (WDMs), beam splitters / combiners, polarization beam splitters (PBSs), collimators, couplers, etc. In some examples, free-space optics 115 may include, for example, components for transforming polarization states and guiding received polarized light to an optical detector using a PBS. Free-space optics 115 may also include diffraction elements to deflect beams of different frequencies at different angles along an axis (e.g., the fast axis).

[0027] In some examples, the LIDAR system 100 includes an optical scanner 102 comprising one or more scanning mirrors rotatable along an axis orthogonal or substantially orthogonal to the fast axis of the diffraction element (e.g., the slow axis) to guide an optical signal to scan the environment according to a scanning pattern. For example, the scanning mirrors may be rotatable via one or more galvanometers. Objects in the target environment may scatter incident light into an echo beam or target echo signal. The optical scanner 102 also collects the echo beam or target echo signal, which may be returned to passive optical circuitry components of the optical circuitry 101. For example, the echo beam may be guided to an optical detector via a polarizing beam splitter. In addition to mirrors and galvanometers, the optical scanner 102 may also include components such as quarter-wave plates, lenses, anti-reflective coated windows, etc.

[0028] To control and support the optical circuitry 101 and the optical scanner 102, the LIDAR system 100 includes a LIDAR control system 110. The LIDAR control system 110 may include processing means for the LIDAR system 100. In some examples, the processing means may be one or more general-purpose processing means, such as a microprocessor, a central processing unit, etc. More specifically, the processing means may be a Complex Instruction Set Computing (CISC) microprocessor, a Reduced Instruction Set Computer (RISC) microprocessor, a Very Long Instruction Word (VLIW) microprocessor, or a processor implementing other instruction sets, or a processor implementing combinations of instruction sets. The processing means may also be one or more special-purpose processing means, such as an Application-Specific Integrated Circuit (ASIC), a Field-Programmable Gate Array (FPGA), a Digital Signal Processor (DSP), a network processor, etc.

[0029] In some examples, the LIDAR control system 110 may include a signal processing unit 112, such as a DSP. The LIDAR control system 110 is configured to output digital control signals to control the optical driver 103. In some examples, the digital control signals may be converted into analog signals by a signal conversion unit 106. For example, the signal conversion unit 106 may include a digital-to-analog converter. The optical driver 103 can then provide drive signals to the active optical components of the optical circuit 101 to drive light sources such as lasers and amplifiers. In some examples, several optical drivers 103 and signal conversion units 106 may be provided to drive multiple light sources.

[0030] The LIDAR control system 110 is also configured to output digital control signals for the optical scanner 102. The motion control system 105 can control the galvanometer of the optical scanner 102 based on the control signals received from the LIDAR control system 110. For example, a digital-to-analog converter (DAC) can convert coordinate routing information from the LIDAR control system 110 into signals that can be interpreted by the galvanometer in the optical scanner 102. In some examples, the motion control system 105 can also return information to the LIDAR control system 110 relating to the position or operation of components of the optical scanner 102. For example, an DAC can further convert information about the galvanometer position into signals that can be interpreted by the LIDAR control system 110.

[0031] The LIDAR control system 110 is also configured to analyze incoming digital signals. In this regard, the LIDAR system 100 includes an optical receiver 104 for measuring one or more beams received by the optical circuitry 101. For example, a reference beam receiver may measure the amplitude of a reference beam from an active optical component, and an analog-to-digital converter converts the signal from the reference receiver into a signal interpretable by the LIDAR control system 110. A target receiver measures an optical signal carrying information related to the range and velocity of the target, in the form of a beat-modulated optical signal. The reflected beam may be mixed with a signal from a local oscillator. The optical receiver 104 may include a high-speed analog-to-digital converter to convert the signal from the target receiver into a signal interpretable by the LIDAR control system 110. In some examples, the signal from the optical receiver 104 may be signal-conditioned by a signal conditioning unit 107 before being received by the LIDAR control system 110. For example, the signal from the optical receiver 104 may be provided to an operational amplifier to amplify the echo signal, and the amplified signal may be provided to the LIDAR control system 110.

[0032] In some applications, the LIDAR system 100 may additionally include one or more imaging devices 108 configured to capture images of the environment, a Global Positioning System 109 configured to provide the system's geographic location, or other sensor inputs. The LIDAR system 100 may also include an image processing system 114. The image processing system 114 may be configured to receive images and geographic locations, and to transmit the images and locations, or related information, to the LIDAR control system 110 or other systems connected to the LIDAR system 100.

[0033] In some example operations, the LIDAR system 100 is configured to use a non-degenerate light source to simultaneously measure range and velocity across two dimensions. This capability allows for real-time, remote measurement of the range, velocity, azimuth, and elevation of the surrounding environment.

[0034] In some examples, the scanning process begins with an optical driver 103 and a LIDAR control system 110. The LIDAR control system 110 instructs the optical driver 103 to independently modulate one or more beams, and these modulated signals are propagated through passive optical circuitry to a collimator. The collimator guides the light at an optical scanning system used to scan the environment on a pre-programmed pattern defined by a motion control system 105. The optical circuitry 101 may also include a polarizing waveplate (PWP) to change the polarization of the light as it leaves the optical circuitry 101. In some examples, the polarizing waveplate may be a quarter-wave plate or a half-wave plate. A portion of the polarized light may also be reflected back to the optical circuitry 101. For example, the lens or collimation system used in the LIDAR system 100 may have natural reflective properties or a reflective coating to reflect a portion of the light back to the optical circuitry 101.

[0035] The optical signal reflected from the environment is transmitted to the receiver via optical circuit 101. Since the polarization of the light has been transformed, it can be reflected together with a portion of the polarized light reflected back to optical circuit 101 by a polarization beamsplitter. Therefore, the reflected light does not return to the same fiber or waveguide as the light source, but is reflected to a separate optical receiver. These signals interfere with each other and generate a combined signal. The individual beams of signal returning from the target produce time-shifted waveforms. The time phase difference between the two waveforms generates a beat frequency measured on the optical receiver (photodetector). The combined signal can then be reflected back to optical receiver 104.

[0036] The analog signal from the optical receiver 104 is converted into a digital signal using an ADC. The digital signal is then sent to the LIDAR control system 110. The signal processing unit 112 can then receive and interpret the digital signals. In some embodiments, the signal processing unit 112 also receives position data from the motion control system 105 and a galvanometer (not shown), as well as image data from the image processing system 114. Then, as the optical scanner 102 scans additional points, the signal processing unit 112 can use information related to the range and velocity of points in the environment to generate a 3D point cloud. The signal processing unit 112 can also overlay the 3D point cloud data with the image data to determine the velocity and distance of objects in the surrounding area. The system also processes satellite-based navigation and positioning data to provide accurate global positioning.

[0037] Figure 2 This is a time-frequency graph 200 of an FMCW scan signal 201 that can be used by a LIDAR system such as System 100 to scan a target environment, according to some embodiments. In one example, the scan waveform 201 labeled fFM(t) is a sawtooth waveform (sawtooth "chirp") with a chirped bandwidth ΔfC and a chirped period TC. The slope of the sawtooth is given as k = (ΔfC / TC). Figure 2A target echo signal 202 according to some embodiments is also depicted. The target echo signal 202, denoted as fFM(t-Δt), is a delayed version of the scan signal 201, where Δt is the round-trip time relative to the target illuminated by the scan signal 201. The round-trip time is given as Δt = 2R / v, where R is the target range and v is the speed of the beam, i.e., the speed of light c. Therefore, the target range R can be calculated as R = c(Δt / 2). When the echo signal 202 is optically mixed with the scan signal, a range-related difference frequency (“beat frequency”) ΔfR(t) is generated. The beat frequency ΔfR(t) is linearly related to the time delay Δt by the slope k of the sawtooth. That is, ΔfR(t) = kΔt. Since the target range R is proportional to Δt, the target range R can be calculated as R = (c / 2)(ΔfR(t) / k). In other words, the range R is linearly related to the beat frequency ΔfR(t). The beat frequency ΔfR(t) can be generated as an analog signal, for example, in the optical receiver 104 of system 100. Then, the beat frequency can be digitized by an analog-to-digital converter (ADC), for example in a signal conditioning unit such as signal conditioning unit 107 in LIDAR system 100. The digitized beat frequency signal can then be digitally processed, for example in a signal processing unit such as signal processing unit 112 in system 100. It should be noted that if the target has a velocity relative to LIDAR system 100, the target echo signal 202 will typically also include a frequency shift (Doppler shift). The Doppler shift can be determined separately and can be used to correct the frequency of the echo signal; therefore, for simplicity and ease of interpretation, in Figure 2 Doppler offset is not shown. It should also be noted that the sampling frequency of the ADC will determine the highest beat frequency that the system can process without aliasing. Generally, the highest frequency that can be processed is half the sampling frequency (i.e., the "Nyquist limit"). In one example, and not limited to, if the ADC sampling frequency is 1 GHz, the highest beat frequency (ΔfRmax) that can be processed without aliasing is 500 MHz. This limit further determines the maximum range of the system as Rmax = (c / 2)(ΔfRmax / k), which can be adjusted by changing the chirp slope k. In one example, although the data samples from the ADC can be continuous, the subsequent digital processing described below can be divided into "time periods" that can be associated with some periodicity in the LIDAR system 100. In one example, but not limited to, the time period can correspond to a predetermined number of chirp periods T, or the number of full rotations of the optical scanner in azimuth.

[0038] Figure 3This is a diagram illustrating various rapid phase changes or phase impairments that can be detected by embodiments of the present invention. In this example embodiment, the change in the scan signal Tx is shown at 301, and the change in the echo signal Rx is shown at 303. Figure 3 As shown, the LIDAR system described through embodiments of the present invention can use, for example... Figure 1 The components described herein are used to detect changes in laser phase noise, circuit phase noise, and flicker noise.

[0039] Figure 4 Examples of various slow phase changes that can be detected by embodiments of the invention are shown. In this example embodiment, a change in the scan signal Tx is shown at 401, and a change in the echo signal Rx is shown at 403. Figure 4 As shown, the LIDAR system described through embodiments of the present invention can use, for example... Figure 1 The components described in the text are used to detect changes in temperature, etc.

[0040] Figure 5 Various chirp rate shifts that can be detected by embodiments of the present invention are illustrated. In this example embodiment, the change in the scan signal Tx is shown at 501, and the change in the echo signal Rx is shown at 503. Figure 5 As shown, the LIDAR system described through embodiments of the present invention can use, for example... Figure 1 The components described herein are used to detect laser calibration and / or offsets caused by component degradation over time.

[0041] Figure 6 This is a block diagram of an example LIDAR system with reference arm 627 according to an embodiment of the present disclosure. Figure 6As shown, according to some embodiments, one or more reference arms 627 can be added to a LIDAR system to generate a digital sampling reference signal 626, which can be used to estimate phase impairments in the transmitted signal described herein. In this way, reference arms 627 create a digital sampling reference signal 626 corresponding to a target (e.g., target 607) with a known delay, wherein the digital sampling reference signal 626 has phase impairments similar to those of the received signal from the target. The digital sampling reference signal 626 can be used to estimate phase impairments for subsequent correction. For example, in one example embodiment, the system includes a beam source 601, such as an FMCW laser source. A target arm 605 includes multiple optical components (e.g., lenses or filters) through which a scan signal 603 can be transmitted to the target 607. An echo signal 609 can be reflected from the target 607 and directed to a photodetector 611. In this embodiment, a local oscillator signal 613, which is part of the scan signal 603, is directed to the photodetector 611 before being transmitted to the target 607. Then, the digitally sampled target signal 616 is transmitted from the photodetector 611 to the target ADC 615, and then to the DSP 617.

[0042] As depicted in this embodiment, the reference arm 627 receives a signal portion 619 of the scan signal 603, which can be provided directly to the photodetector 621, or it can be provided to the photodetector 621 after transmission through a delay device 623 having a known length and / or delay. According to some embodiments, the signal portion 619 is received by the photodetector 621 while the scan signal 603 is simultaneously transmitted through the optical components of the target arm 605. According to some embodiments, the signal portion 619 is received by the photodetector 621 after the scan signal 603 has been transmitted through the optical components of the target arm 605. According to some embodiments, the delay device 623 can be a fiber optic delay device, etc. In one embodiment, the delay device 623 may include a fiber optic coil of a known length that can create a virtual target (e.g., a fiber optic target) at a known distance.

[0043] In some scenarios, the distance to a virtual target can be predetermined. The optical signal at the output of the reference delay has the same characteristics as... Figure 2 The target echo signal 202 described herein has the same characteristics. According to some embodiments, it is to be consistent with... Figure 2 In a manner similar to that described herein, the virtual target described here can generate an echo signal 609 as a delayed version of the scan signal 603. When the echo signal 609 is optically mixed with the scan signal 603, a difference frequency (“reference beat frequency”) related to a reference range is generated. According to some embodiments, it can then be used, for example, as described here. Figure 1The process described herein is used to digitize and adjust the reference beat frequency. This digitally sampled reference signal 626 has the same phase impairment characteristics as the received signal from the target. A phase impairment estimator (based at least in part on the digitally sampled reference signal 626 generated by reference arm 627) and a phase impairment corrector described by embodiments of this disclosure (discussed in more detail below) can compensate for phase impairment in the signal transmitted toward the target (i.e., the "target" signal) and the signal received from the target (i.e., the "received" signal).

[0044] Then, the reference arm signal 626 is transmitted from the photodetector 621 to the reference ADC 625, and then to the DSP 617. For example... Figure 6 As shown, embodiments of the present invention can generate point cloud data 629 based on the transmission and reception of various signals including echo signal 609, LO signal 613, digital sampling target signal 616 and digital sampling reference signal 626.

[0045] As described above, the phase impairment on the digitally sampled target signal 616 comprises two components: impairment introduced from the LO signal 613 and impairment introduced by the echo signal 609. These two impairments are corrected in various ways through the embodiments described herein, as discussed in more detail below. For example, Figure 14 The techniques used to correct two types of phase impairment are described, and Figure 7-8 This disclosure describes techniques for correcting phase impairment introduced from the LO signal 613 according to embodiments of the present disclosure, and... Figure 9-12 This disclosure describes a technique for correcting phase impairment introduced from echo signal 609 according to embodiments of the present disclosure.

[0046] Figure 7 A digital signal processing architecture according to an embodiment of the present invention is described. In one embodiment, Figure 7 The signal processing architecture described in [the document] can correspond to [the specific architecture]. Figure 1 Components within the signal processor 112 shown. For example... Figure 7 As shown, according to some embodiments, the digital signal processing architecture includes a phase impairment estimator 703 and a phase impairment corrector 707, as well as one or more reference ADCs 701 and target ADCs 705. Figure 7 As shown, the digital signal processing architecture also includes a time-domain filter 709, a time-frequency domain transformer 711 (e.g., FFT), a frequency-domain filter 713, and a peak selection component 715. The phase impairments processed by this architecture include various phase impairments (including those mentioned above). Figure 7 As shown, according to some embodiments, a digital signal processing architecture can generate and process data such as point cloud data 717. Figure 7In some scenarios, the corrections can be performed before one or more digital signal processor processes (such as those performed by time-domain filter 709, time-frequency domain converter 711, frequency-domain filter 713, and peak selection component 715).

[0047] According to some embodiments, the phase impairment estimator 703 can use several different methods to estimate phase impairment. For example, in some embodiments, the phase impairment estimator 703 can use "zero-forcing" estimation, in which the reference phase passes through a filter having a frequency response equal to the inverse frequency response of the reference arm described in the embodiments. In some embodiments, the phase impairment estimator 703 can use least mean square estimation (MMSE), in which noise enhancement caused by zero-forcing estimation can be mitigated around frequencies where the frequency response of the reference arm is typically weak. In some embodiments, the phase impairment estimator 703 can use maximum likelihood / MAP estimation, which can be based at least in part on statistical data related to phase impairment collected over a time period.

[0048] According to some embodiments, the phase impairment corrector 707 can use several different methods to correct phase impairment in the echo signal. Phase impairment in the echo signal consists of impairments introduced from the LO signal and the echo signal. For example, in some embodiments, the phase impairment corrector 707 can compensate for phase impairment components introduced by both the LO signal and the echo signal path, which will be described in more detail below.

[0049] Figure 8 Example systems for correcting impairments introduced from LO signals are described according to some embodiments of the present disclosure. In some embodiments, as disclosed herein, a phase impairment estimator 801 can estimate phase impairments, and these impairments can be corrected using a correction filter 807 having filter taps shaped based on the estimated phase impairments. In one embodiment, the shape of the filter taps can be calculated based on the phase impairment estimator 801 using a filter tap calculation module 803.

[0050] In some embodiments, filter taps may be shaped to cancel or equalize phase noise impairment and / or mitigate noise enhancement due to inaccurate estimation. In some scenarios, if an instantaneous estimate of the phase impairment is unavailable, embodiments may utilize matched filter tap 805 shaped based on the average power spectral density (PSD) of the phase impairment. In some scenarios, if an instantaneous estimate of the phase impairment is unavailable, embodiments may use a matched filter for correction, which may have different taps and / or shapes at different frequencies to account for variations in the phase impairment bandwidth across frequencies.

[0051] In some embodiments, the correction filter 807 may receive the echo signal, as well as inputs provided by the filter tap calculation module 803 calculated by the phase impairment estimator 801 and / or the matched filter tap 805 matched to the average PSD. Based on these inputs, the correction filter 807 may generate a compensated echo signal.

[0052] According to some embodiments, the systems and components described herein can correct for impairments in the echo signal introduced by a received signal from a target. In some scenarios, the received signal may have a delay equal to the target delay. In some embodiments, correcting phase impairments from the received signal includes compensating for the delay before running a correction filter. The methods used in various embodiments may include, but are not limited to, brute-force delayed correction filters using multiple delays, iterative delayed correction filters, and deskip compensation correction filters. In one embodiment, the phase impairment estimator 801 and the filter tap calculation module may correspond to... Figure 1 The components within the signal processor 112 described herein, wherein the matched filter tap 805 and the correction filter 807 may correspond to Figure 1 Components within the optical circuit 101.

[0053] Figure 9 Example systems for correcting phase impairment using multiple delays are depicted according to some embodiments of the present disclosure. In some embodiments, the phase impairment corrector may be configured with a smoothing delay correction filter that can delay the received beam using multiple digital delays and select an optimal delay. Selecting the optimal delay may include, for example, performing an FFT of digital delays and selecting the delay with the highest peak. Figure 9 As shown, the technique may involve, but is not limited to, the use of a phase impairment estimator 901, a computed filter tap 903, one or more correction filters 909-911, a time-domain filter 915, a time-frequency domain transformer 917 (e.g., FFT), a frequency-domain filter 919, and a peak selection component 921.

[0054] In some embodiments, the target arm signal is transmitted through N different delays 905-907, and correction filters 909-911 can be applied to each possible target delay 905-907. Once multiple delays have been applied to the target arm signal, an optimal delay 913 can be selected. In some embodiments, the optimal match can be defined based on, for example, but not limited to, the strongest peak, higher SNR, or other metrics used for signal detection. In one embodiment, selecting the optimal delay includes performing a Fast Fourier Transform (FFT) on multiple delayed beams and selecting the delay with the highest peak. In one embodiment, Figure 9 The components described in the document can correspond to Figure 1 The components within the signal processor 112 or optical circuit 101 described herein.

[0055] Figure 10 An example system for correcting phase impairment using an iterative delay correction filter, according to some embodiments of this disclosure, is described. For example... Figure 10 As shown, this technique may involve, but is not limited to, the use of a phase impairment estimator 1001, a computed filter tap 1003, one or more correction filters 1007, a time-domain filter 1009, a time-frequency domain transformer 1011 (e.g., FFT), a frequency-domain filter 1013, and a peak selection component 1015. In some embodiments, the target arm signal may be transmitted through a delay 1005, and then through the correction filter 1007 and other signal processing components. After peak selection 1015, the signal may return to delay 1005, and processing iterates between the optimal delay and peak frequency until convergence is achieved. In some embodiments, the initialization of delay 1005 may be based on, for example, neighboring points in the current frame and / or points from previous frames. In one embodiment, Figure 10 The components described in the document can correspond to Figure 1 The components within the signal processor 112 or optical circuit 101 described herein.

[0056] Figure 11 Example systems for correcting phase impairment using a deskipation compensation correction filter, according to some embodiments of this disclosure, are described. For example... Figure 11 As shown, this technique may involve, but is not limited to, the use of a phase impairment estimator 1101, a computed filter tap 1103, one or more correction filters 1107, a time-domain filter 1109, a time-frequency domain transformer 1111 (e.g., FFT), a frequency-domain filter 1113, and a peak selection component 1115. In some embodiments, the target arm signal can be transmitted through a deskip filter 1105 to apply different delays based on the signal frequency. Embodiments may utilize the fact that the frequency of the peak is linearly related to the delay.

[0057] In some embodiments, the deskipation filter 1105 can offset phase impairment estimation based on the frequency of the peak. In some embodiments, the deskipation filter 1105 can be used to apply a group delay to the signal, which can be proportional to the frequency components of the target arm signal. In some embodiments, when there is no Doppler offset on the echo signal (Rx), one or more deskipation filters can be used to apply the correct group delay. In scenarios where Doppler offset is present, some embodiments of this disclosure can detect performance loss due to Doppler offset. In one embodiment, Figure 11 The components described in the document can correspond to Figure 1 The components within the signal processor 112 or optical circuit 101 described herein.

[0058] Figure 12 An example system for correcting phase damage using a combined damage corrector and peak selector 1213, according to some embodiments of this disclosure, is described. Figure 12 As shown, this technique may involve, but is not limited to, the use of a phase impairment estimator 1203, a joint impairment corrector and peak selector 1213, a time-domain filter 1207, a time-frequency domain transformer 1209 (e.g., FFT), a frequency-domain filter 1211, and one or more reference ADCs 1201 and target ADCs 1205. Embodiments of the invention can generate point cloud data 1215 from the architecture described herein. In some embodiments, the phase impairment corrector may be integrated as part of the peak selector to achieve a joint optimal estimate of the peaks, rather than pre-correcting phase impairment. In one embodiment, Figure 12 The components described in the document can correspond to Figure 1 The components within the signal processor 112 or optical circuit 101 described herein.

[0059] Figure 13 These are example systems for correcting phase impairment using multiple reference channels, according to some embodiments of this disclosure. Figure 13 As shown, the LIDAR system includes a beam source 1301, such as an FMWC laser source. The target arm includes multiple optical components 1305, through which a scan signal 1303 can be transmitted to the target 1307. An echo signal 1309 can be reflected from the target 1307 and guided to a photodetector 1311. In this embodiment, the LO signal 1313 is guided to the photodetector 1311 before being transmitted to the target 1307. The target arm signal is then transmitted from the photodetector 1311 to the target ADC 1315, and then to the DSP 1317.

[0060] exist Figure 13 In the illustrated embodiment, a portion 1319 of the scan signal 1303 is directed to a plurality of reference arms. In some embodiments, each reference arm may include a photodetector and an optical fiber delay of a known length. For example, a reference arm may include a photodetector 1321, an optical fiber delay 1323, and a reference ADC 1325. Similarly, the Nth reference arm may include its own photodetector 1327, optical fiber delay 1329, and ADC 1331.

[0061] In some embodiments, multiple reference channels with different reference arm delays can be added to improve the estimation of phase impairment. In some embodiments, the system can generate point cloud data 1333 based on the transmission and reception of various signals, including signals from the target environment and LO signals. In one embodiment, Figure 9 The components described in the document can correspond to Figure 1 The components within the signal processor 112 or optical circuit 101 described herein.

[0062] Figure 14 This is a flowchart of an example method for compensating for phase impairments within a LiDAR system according to embodiments of the present disclosure. The method begins at operation 1401 by sending a beam of light toward a target. The beam may include, for example, an FMWC beam.

[0063] At operation 1403, the reflected beam is received from the target to generate the received beam.

[0064] At operation 1405, the LO beam, photodetector, and receiving beam are used to generate a digitally sampled target signal.

[0065] At operation 1407, a digital sampling reference signal is generated using a reference beam transmitted through an optical fiber delay device and a photodetector. In some embodiments, multiple digital sampling reference signals are generated using reference beams transmitted through multiple different optical fiber delay devices. In some embodiments, each optical fiber delay device may be connected to a corresponding photodetector. In some embodiments, the optical fiber delay device generates a delay proportional to the frequency of the received beam, such that reflections from targets at greater distances are delayed more, while reflections from targets at shorter distances are delayed less.

[0066] At operation 1409, a digitally sampled reference signal is used to estimate one or more phase impairments in the LIDAR system. This produces one or more estimated phase impairments. In some embodiments, estimating the phase impairments includes using a zero-forcing estimator, an MMSE estimator, a maximum likelihood estimator, or a MAP estimator.

[0067] At operation 1411, a first correction is performed. This first correction is performed on a first phase impairment corresponding to the LO bundle. In other words, the first correction corrects the phase impairment introduced from the LO bundle into the digitally sampled target signal. In some embodiments, performing the first correction includes using one or more filters shaped at least in part based on an estimate of the first phase impairment. The filter may be, for example, a matched filter tap discussed above.

[0068] At operation 1413, a second correction is performed. This second correction addresses a second phase impairment corresponding to the received beam. In other words, the second correction corrects the phase impairment introduced from the received beam into the digitally sampled target signal. In some embodiments, performing the second correction may include using a smooth delay correction filter that delays the received beam through multiple digital delays and selects an optimal delay. In some embodiments, the optimal delay may be selected by performing a Fast Fourier Transform (FFT) on the digital delay and selecting the delay with the highest peak. In alternative embodiments, the second correction may include using an iterative delay correction filter that repeatedly delays the reflected beam through different digital delays until peak convergence is achieved. In other embodiments, the second correction may include using a deskipation compensation correction filter.

[0069] At operation 1415, the corrected target signal is generated by processing the first and second corrections. Once the corrected target signal is generated, it can be sent to the point cloud.

[0070] In some embodiments, it can be used Figure 1 The signal processing unit 112, signal conversion unit 106, or signal conditioning unit 107 described above are used to perform the various operations and methods described in this application. Various optical components, fiber optic delayers, and other structural components can be implemented as... Figure 1 The optical circuit 101 described herein.

[0071] The foregoing description sets forth numerous specific details, such as examples of specific systems, components, methods, etc., to provide a thorough understanding of several examples in this disclosure. However, it will be apparent to those skilled in the art that at least some examples of this disclosure can be implemented without these specific details. In other instances, well-known components or methods have not been described in detail or presented in the form of simple block diagrams to avoid unnecessarily obscuring this disclosure. Therefore, the specific details set forth are merely exemplary. Specific examples may differ from these exemplary details and are still contemplated within the scope of this disclosure.

[0072] Any reference to "an embodiment" or "example" throughout this specification means that a particular feature, structure, or characteristic described in connection with the example is included in at least one example. Therefore, the phrases "in an example" or "in the example" appearing in various places throughout this specification do not necessarily refer to the same example.

[0073] The term "coupling" and its derivatives are used to describe the interaction of two or more elements. These coupled elements may or may not be in direct physical or electrical contact with each other.

[0074] Although this document shows and describes the operations of the methods in a specific order, the order of the operations of each method can be changed so that some operations can be performed in reverse order, or so that some operations can be performed at least partially concurrently with other operations. Instructions or sub-operations of different operations can be performed intermittently or alternately.

[0075] The above description of the illustrated implementations of the invention (including those described in the abstract) is not intended to exhaustively or limit the invention to the precise forms disclosed. While specific implementations and examples of the invention have been described herein for illustrative purposes, various equivalent modifications can be made within the scope of the invention, as will be appreciated by those skilled in the art. The terms “example” or “exemplary” are used herein to mean used as an example, instance, or illustration. Any aspect or design described herein as “example” or “exemplary” is not necessarily to be construed as being more preferred or advantageous than other aspects or designs. Rather, the use of the terms “example” or “exemplary” is intended to present concepts in a concrete manner. As used herein, the term “or” means inclusive “or” rather than exclusive “or.” That is, unless otherwise specified or the context clearly indicates, “X includes A or B” means any natural inclusion arrangement. That is, if X includes A; X includes B; or X includes both A and B, then “X includes A or B” is satisfied under any of the above instances. Furthermore, the terms “a” and “an” as used in this application and the appended claims should generally be interpreted as meaning “one or more” unless otherwise specified or clearly indicated from the context as singular. Additionally, the terms “first,” “second,” “third,” “fourth,” etc., as used herein refer to labels used to distinguish between different elements and do not necessarily have a meaning according to the order of their numerical names.

Claims

1. A method for correcting phase impairment in a LIDAR system, wherein LIDAR refers to optical detection and ranging, the method comprising: Send the first beam toward the target; A second beam is received from the target to generate a received beam; The LO beam, i.e., the local oscillator beam, the first photodetector, and the received beam are used to generate a digitally sampled target signal; A digital sampling reference signal is generated using a reference beam that is sent through an optical fiber delay device and a second photodetector; The digitally sampled reference signal is used to estimate one or more phase defects in the LIDAR system to produce one or more estimated phase defects. The first phase impairment of the first phase impairment of the one or more estimated phase impairments from the digitally sampled target signal is corrected using the one or more estimated phase impairments, wherein the first phase impairment is introduced into the digitally sampled target signal by the LO beam; A second correction is performed on a second phase impairment of one or more estimated phase impairments from the digitally sampled target signal, wherein the second phase impairment is introduced into the digitally sampled target signal by the received beam; and The first correction and the second correction are processed to generate a corrected target signal for transmission to the point cloud.

2. The method according to claim 1, wherein, The estimation of one or more phase defects includes: Use at least one of the following: zero-forcing estimator, MMSE estimator, maximum likelihood estimator, and MAP estimator.

3. The method according to claim 1, wherein, Performing the first correction includes: Use one or more filters shaped at least in part based on the estimation of the first phase impairment.

4. The method according to claim 1, wherein, Performing the second correction includes: A smooth delay correction filter is used, wherein the smooth delay correction filter is used to delay the received beam through multiple digital delays and select the optimal delay.

5. The method according to claim 4, wherein, Selecting the optimal delay includes: Perform an FFT (Fast Fourier Transform) on the multiple digital delays and select the delay with the highest peak.

6. The method according to claim 1, wherein, Performing the second correction includes: An iterative delay correction filter is used, wherein the iterative delay correction filter is used to repeatedly delay the received beam with different digital delays until peak convergence is reached.

7. The method according to claim 1, wherein, Performing the second correction includes: Use a deskip compensation correction filter.

8. The method according to claim 1, further comprising: Multiple digital sampling reference signals are generated by sending a reference bundle through multiple different fiber delay devices, each of which is connected to a corresponding photodetector.

9. A LIDAR system, namely a light detection and ranging system, comprising: A beam source, used to send the first beam of light toward the target; The first detector is used to receive the LO beam, i.e., the local oscillator beam, and the received beam from the target, and to generate a digitally sampled target signal; An optical fiber delay device having a known length and coupled to the beam source; A second detector, coupled to the fiber delay device, generates a digital sampling reference signal using a reference beam transmitted through the fiber delay device. A phase impairment estimator is used to estimate one or more phase impairments in the LIDAR system using the digitally sampled reference signal to produce one or more estimated phase impairments. A first phase impairment corrector is used to correct the first phase impairment introduced into the digitally sampled target signal by the LO beam; as well as A second phase damage corrector is used to correct a second phase damage introduced into the digitally sampled target signal by the received beam.

10. The system of claim 9 further includes at least one of a zero-forcing estimator, an MMSE estimator, a maximum likelihood estimator, and a MAP estimator for estimating the one or more phase impairments.

11. The system according to claim 9, wherein, The first phase impairment corrector includes one or more filters shaped at least in part based on an estimate of the first phase impairment.

12. The system according to claim 9, wherein, The second phase damage corrector includes a smooth delay correction filter, which is used to delay the received beam through multiple digital delays and select the optimal delay.

13. The system according to claim 12, wherein, Selecting the optimal delay includes: Perform an FFT (Fast Fourier Transform) on the multiple digital delays and select the delay with the highest peak.

14. The system according to claim 9, wherein, The second phase impairment corrector includes an iterative delay correction filter, which is used to repeatedly delay the received beam with different digital delays until peak convergence is achieved.

15. The system according to claim 9, wherein, The second phase impairment corrector includes a deskipation compensation correction filter.

16. The system according to claim 9, wherein, The fiber optic delay device generates a delay proportional to the frequency of the received beam, such that reflections from targets at greater distances are delayed more, and reflections from targets at shorter distances are delayed less.

17. The system according to claim 9, further comprising: Multiple different fiber delay devices and photodetectors are used to generate multiple digital sampling reference signals.

18. A method for correcting phase impairment in a LIDAR system, wherein LIDAR refers to optical detection and ranging, the method comprising: The LO beam (local oscillator beam), the first photodetector, and the received beam reflected from the target are used to generate a digitally sampled target signal. A digital sampling reference signal is generated using a reference beam that is sent through an optical fiber delay device and a second photodetector; Estimate the first phase impairment introduced into the digitally sampled target signal by the LO beam; Estimate the second phase impairment introduced into the digitally sampled target signal by the received beam; Perform a first correction to correct the first phase impairment; and A second correction is performed using a smooth delay correction filter to correct the second phase impairment. The smooth delay correction filter is used to delay the received beam through multiple digital delays and select the optimal delay.

19. The method according to claim 18, wherein, The estimation of the second phase impairment includes: Use at least one of the following: zero-forcing estimator, MMSE estimator, maximum likelihood estimator, and MAP estimator.

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