Calibration of Transmitter and Receiver in 1D Scanning LIDAR

Abstract

Embodiments of the present disclosure relate to the calibration of transmitters and receivers in 1D scanning LIDAR. An optical detection and ranging (LIDAR) system is provided. The LIDAR system includes: a LIDAR transmitter configured with a first field of view and configured to transmit laser beams into the first field of view at a plurality of discrete transmission angles to scan the first field of view with the laser beams; a LIDAR receiver configured with a second field of view and configured to receive reflected laser beams from the second field of view and generate an electrical signal based on the received reflected laser beams; and a controller configured to move at least one of the first field of view or the second field of view based on misalignment to optimize the overlap of the first field of view and the second field of view.

Description

Technical Field

[0001] Embodiments of the present disclosure generally relate to devices and methods for a light detection and ranging (LIDAR) system. Background Art

[0002] Light detection and ranging (LIDAR) is a remote sensing method that uses light in the form of pulsed lasers to measure the range (variable distance) to one or more objects in a field of view. Specifically, light is transmitted towards the object. A single photodetector or an array of photodetectors receives the reflections from the object illuminated by the light and determines the time it takes for the reflections to reach the respective sensors in the photodetector array. This is also referred to as measuring the time of flight (TOF). LIDAR systems form depth measurements and perform distance measurements by mapping distances to objects based on time-of-flight calculations. Thus, time-of-flight calculations can create a distance map and a depth map, which can be used to generate an image.

[0003] A LIDAR transmitter can excite light as a narrow laser beam at different horizontal or vertical positions in the field of view. However, if the field of view of the receiver is not aligned with the field of view of the transmitter, errors may occur when detecting backscattered light. For example, this may result in areas or gaps in the field of view that cannot be read by the LIDAR system not being detected. This may in turn result in black spots in the image. Therefore, an improved device that performs transmitter and / or receiver calibration to reduce or prevent such misalignment may be desirable. Summary of the Invention

[0004] Embodiments provide an object scanning system and an operation method thereof. More specifically, embodiments provide alignment of a transmitter field of view and a receiver field of view.

[0005] According to one or more embodiments, a light detection and ranging (LIDAR) system includes: a LIDAR transmitter configured with a first field of view and configured to transmit laser beams into the first field of view at a plurality of discrete transmission angles to scan the first field of view with the laser beams; a LIDAR receiver configured with a second field of view and configured to receive reflected laser beams from the second field of view and generate an electrical signal based on the received reflected laser beams; and a controller configured to move at least one of the first field of view or the second field of view based on misalignment to optimize the overlap of the first field of view and the second field of view.

[0006] One or more embodiments provide a method for calibrating a Light Detection and Ranging (LIDAR) system. The method includes: configuring a LIDAR transmitter with a first field of view; configuring a LIDAR receiver with a second field of view; transmitting laser beams into the first field of view at a plurality of discrete transmission angles to scan the first field of view with the laser beams; receiving reflected laser beams from the second field of view; generating an electrical signal based on the received reflected laser beams; and moving at least one of the first field of view and the second field of view based on misalignment to optimize the overlap of the first field of view and the second field of view. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Embodiments are described herein with reference to the accompanying drawings.

[0008] Figure 1A is a schematic diagram of a horizontal LIDAR scanning system according to one or more embodiments;

[0009] Figure 1B is a schematic diagram of a vertical LIDAR scanning system according to one or more embodiments;

[0010] Figure 2 is a schematic block diagram of a LIDAR scanning system according to one or more embodiments;

[0011] Figure 3 is a top view of an overlapping TX field of view and RX field of view according to one or more embodiments;

[0012] Figure 4A and Figure 4B illustrate a transmitter-side compensation technique for aligning a TX FOV with an RX FOV according to one or more embodiments;

[0013] Figure 5A and Figure 5B illustrate a receiver-side compensation technique for aligning a TX FOV with an RX FOV according to one or more embodiments;

[0014] Figure 6 illustrate a receiver-side compensation technique for aligning a TX FOV with an RX FOV according to one or more embodiments;

[0015] Figure 7 illustrate a flow chart of a transmitter-side compensation technique for aligning a TX FOV with an RX FOV according to one or more embodiments;

[0016] Figure 8 illustrate a flow chart of a transmitter-side compensation technique for aligning a TX FOV with an RX FOV according to one or more embodiments;

[0017] Figure 9Illustrated is a flowchart of a receiver-side compensation method for aligning a TX FOV with an RX FOV according to one or more embodiments; and

[0018] Figure 10 Illustrated is a flowchart of a transmitter-side compensation technique for aligning a TX FOV with an RX FOV according to one or more embodiments. Detailed Description

[0019] Hereinafter, various embodiments will be described in detail with reference to the accompanying drawings. It should be noted that these embodiments are for illustrative purposes only and should not be construed as restrictive. For example, although an embodiment may be described as including multiple features or elements, this should not be construed as indicating that all such features or elements are required to implement the embodiment. Instead, in other embodiments, some of the features or elements may be omitted, or may be replaced by alternative features or elements. Additionally, other features or elements may be provided in addition to the features or elements explicitly shown and described, for example, conventional components of a sensor device.

[0020] Unless otherwise specifically indicated, features from different embodiments may be combined to form other embodiments. Changes or modifications described with respect to one embodiment may also apply to other embodiments. In some instances, well-known structures and devices are shown in block diagram form rather than in detail so as not to obscure the embodiments.

[0021] Unless otherwise specified, the connections or couplings between the elements shown in the drawings or described herein may be wired connections or wireless connections. Further, such connections or couplings may be direct connections or couplings without additional intermediate elements, or may be indirect connections or couplings with one or more additional intermediate elements, as long as the general purpose of the connection or coupling is substantially maintained (e.g., transmitting a certain signal or transmitting a certain information).

[0022] Embodiments relate to optical sensors and optical sensor systems and to obtaining information about optical sensors and optical sensor systems. A sensor may refer to a component that converts a physical quantity to be measured into an electrical signal (e.g., a current signal or a voltage signal). The physical quantity may include, for example, electromagnetic radiation such as visible light, infrared (IR) radiation, or other types of illumination signals, current, or voltage, but is not limited thereto. For example, an image sensor may be a silicon chip inside a camera that converts photons of light from a lens into a voltage. The larger the active area of the sensor, the more light can be collected to create an image.

[0023] As used herein, a sensor device can refer to a device that includes a sensor and other components (e.g., a bias circuit system, an analog-to-digital converter, or a filter). Although in other embodiments, multiple chips or off-chip components can be used to implement the sensor device, the sensor device can be integrated on a single chip.

[0024] In a light detection and ranging (LIDAR) system, a light source sends light pulses into a field of view (FOV), and the light is reflected from one or more objects by backscattering. Specifically, LIDAR is a direct time-of-flight (TOF) system, in which light pulses (e.g., a laser beam of infrared light) are emitted into the FOV, and a pixel array detects and measures the reflected beam. For example, a photodetector array receives the reflection from an object illuminated by the light.

[0025] Currently, a photodetector array can be used to measure the reflected light. The photodetector array can be a two-dimensional (2D) array, which consists of multiple rows and multiple columns of photodetectors (pixels) arranged in a grid-like pattern. Each pixel row or group of adjacent pixel rows can be read out as a measurement signal in the form of raw analog data. Each measurement signal can include data from a single pixel column or two or more pixel columns corresponding to a selected one or more pixel rows.

[0026] Then, the difference in the return time of each light pulse across multiple pixels of the pixel array can be used to create a digital 3D representation of the environment or generate other sensor data. For example, the light source can emit a single light pulse, and a time-to-digital converter (TDC) electrically coupled to the pixel array can start counting from the time of emitting the light pulse (corresponding to a start signal) until the time of receiving the reflected light pulse at the receiver (i.e., the pixel array) (which corresponds to a stop signal). Then, the "time of flight" of the light pulse is transformed into a distance. In another example, an analog-to-digital converter (ADC) can be electrically coupled to the pixel array (e.g., indirectly coupled through intermediate elements therebetween) for pulse detection and ToF measurement. For example, the ADC can be used to estimate the time interval between the start signal / stop signal using an appropriate algorithm.

[0027] Scanning such as wobble horizontal scanning (e.g., from left to right and right to left of the FOV) can illuminate the scene in a continuous scanning manner. Each time the light source excites the laser beam, a scan line is generated in the "field of view". By emitting continuous light pulses in different scan directions, an area called the field of view can be scanned, and the objects within this area can be detected and imaged. Thus, the field of view represents a scanning plane with a projection center. Raster scanning can also be used.

[0028] Figure 1Ais a schematic diagram of a LIDAR scanning system 100a according to one or more embodiments. The LIDAR scanning system 100a is an optical scanning device that includes: a transmitter that includes an illumination unit 10, transmitter optics 11, and a one-dimensional (1D) MEMS mirror 12 (1D MEMS scanner); and a receiver that includes main optics 14 and an optical receiver 15. The optical receiver 15 in the illustration is a 2D photodetector array 15. The receiver may also include receiver circuitry, such as data acquisition / readout circuitry and data processing circuitry, as will be further described according to Figure 2 As described above with respect to LIDAR technology, the LIDAR scanning system 100a uses pulse modulation to measure the distance to a 3D object by measuring the absolute time it takes for a light pulse to travel from a source to a 3D scene and back after reflection.

[0029] Return Figure 1A , the photodetector array 15 is arranged in such a way that the expected field of view is vertically mapped onto the vertical extent of the photodetector array 15. The received light beam will hit only a particular row or a group of rows of the detector array depending on the vertical angle of the received light beam. The expected field of view is also horizontally mapped onto the horizontal extent of the 2D photodetector array.

[0030] Specifically, the transmitter field of view may include a plurality of discrete transmission angle regions originating from the transmitter (e.g., MEMS mirror 12). The center of each discrete angle region represents the transmission angle / direction of the emitted laser beam. The MEMS mirror 12 may have a discrete number of transmission positions (i.e., rotation angles), each transmission position corresponding to one or more of the discrete transmission angle regions of the transmitted light. The excitation of the light source can be timed to coincide with a particular transmission position or a particular transmission angle region of the MEMS mirror 12. Thus, each transmission position represents the transmission direction of the emitted laser beam, and the transmission direction can be adjusted by adjusting the timing of the excitation light source to coincide with the transmission position of the MEMS mirror 12.

[0031] In the case of horizontal scanning, each discrete transmission angle can be mapped to a transmission position of the MEMS mirror 12 and one or more pixel columns of the photodetector array 15. Thus, the light transmitted at a particular transmission angle region should be incident on one or more corresponding mapped pixel columns of the photodetector array 15. Thus, each light source (i.e., each laser channel) has a transmission timing that is mapped to a particular transmission angle region or transmission position and is also mapped to one or more pixel columns of the photodetector array 15.

[0032] Each light source is also mapped to a row or a group of rows of pixels of the photodetector array 15. Thus, individual pixels can be activated based on the light source and its excitation, which is consistent with a specific transmission angle region. As a result, each pixel of the photodetector array 15 is mapped to a light source and a specific transmission angle region, where the specific transmission angle region is mapped to a specific transmission position of the MEMS mirror 12.

[0033] There can be a mapping for each light source and each pixel. Each mapping can be stored, for example, in the form of a look-up table in the memory of the system controller 23 (see Figure 2 ). The calibration transmitter and / or receiver can include: updating the mapping information stored in one or more look-up tables.

[0034] In this example, the illumination unit 10 includes three light sources (e.g., laser diodes or light emitting diodes), which are linearly aligned in a single bar formation and are configured to transmit light for scanning the field of view of an object. The light sources can be excited as a single unit (i.e., as a single laser diode at the same time), or as separate laser diodes at different timings.

[0035] Although light having another wavelength can also be used, the light emitted by the light sources is typically infrared light. As can be seen from the Figure 1A embodiment, the shape of the light emitted by the light sources spreads in a direction perpendicular to the transmission direction to form a light beam having a rectangle perpendicular to the transmission direction. The illumination light transmitted from the light sources is directed towards the transmitter optics 11, which is configured to focus each laser onto the MEMS mirror 12 that scans in one dimension. The transmitter optics 11 can be, for example, a lens or a prism.

[0036] When reflected by the MEMS mirror 12, the light from the light sources is vertically aligned to form a one-dimensional vertical scan line SL of infrared light or a vertical bar of infrared light for each emitted laser beam. Each light source of the illumination unit 10 contributes to a different vertical region of the vertical scan line SL. Thus, the light sources can be activated and deactivated simultaneously to obtain a light pulse having multiple vertical segments, where each vertical segment corresponds to a respective light source. However, each vertical region or segment of the vertical scan line SL can also be independently activated or deactivated by turning on or off a corresponding one of the light sources of the illumination unit 10. Thus, a part or the entire vertical scan line SL of light can be output from the system 100 into the field of view.

[0037] It should also be noted that the horizontal width of each laser beam corresponds to the discrete angular region where the laser beam is projected into the field of view in the horizontal direction. The width of each beam can correspond to the width of one pixel column of the photodetector array 15. However, more preferably, the width of each beam (and thus the discrete angular region in which the laser beam is projected) is less than the width of one pixel column.

[0038] Thus, the transmitter of system 100 is an optical device configured to generate a laser beam based on laser pulses, the laser beam having a rectangle extending in a direction perpendicular to the transmission direction of the laser beam. As can be seen from Figure 1A each light source in the light source is associated with a different vertical region in the field of view such that each light source illuminates only a vertical scan line into the vertical region associated with the light source. For example, the first light source illuminates into the first vertical region, while the second light source illuminates into a second vertical region different from the first vertical region.

[0039] In addition, although three laser sources are shown, it should be appreciated that the number of laser sources is not limited thereto. For example, the vertical scan line SL can be generated by a single laser source, two laser sources, or more than three laser sources.

[0040] The MEMS mirror 12 is a mechanically movable mirror (i.e., a MEMS micromirror) integrated on a semiconductor chip (not shown). The MEMS mirror 12 according to this embodiment is configured to rotate about a single scan axis and can be said to have only one scanning degree of freedom. Different from a 2D-MEMS mirror (2D MEMS scanner), in a 1D MEMS mirror, the single scan axis is fixed to a non-rotating substrate and thus maintains its spatial orientation during the swinging of the MEMS mirror. Due to this single scan axis of rotation, the MEMS mirror 12 is referred to as a 1D MEMS mirror or a 1D MEMS scanner.

[0041] The MEMS mirror 12 is configured to swing "side-to-side" about a single scan axis 13 such that the light reflected from the MEMS mirror 12 (i.e., the vertical scan line of light) swings back and forth in the horizontal scan direction. The scan period or the swing period is defined, for example, by a single complete swing from the first edge (e.g., the left side) of the field of view to the second edge (e.g., the right side) of the field of view and then back to the first edge. The mirror period of the MEMS mirror 12 corresponds to the scan period.

[0042] Thus, by changing the angle of the MEMS mirror 12 about its scan axis 13, the field of view is scanned in the horizontal direction by vertical stripes of light. For example, the MEMS mirror 12 can be configured to swing between + / - 15 degrees along the horizontal scan direction to deflect light within + / - 30 degrees (i.e., 60 degrees) of the horizontal scan range that constitutes the field of view. Thus, the field of view can be scanned line by line by the rotation of the MEMS mirror 12 by the degree of its movement. One such sequence of the degree of movement (e.g., from -15 degrees to +15 degrees and vice versa) is referred to as a single scan. Thus, for each scan cycle, two consecutive scans are used. The processing unit can use multiple scans to generate a distance map, a depth map, and a 3D image. The horizontal resolution of the depth map and the image depends on the magnitude of the incremental step of the rotation angle of the MEMS mirror 12 taken between two scans.

[0043] Each laser beam has divergence in the horizontal direction. Specifically, the width of each laser beam can have a Gaussian shape, where the laser beam has a peak intensity at its center and the intensity drops off at the respective sides. Thus, while each laser beam extends longitudinally in the vertical direction, its width can also cover a discrete angular range (i.e., an angular region) in the horizontal direction. Thus, the angular region used herein refers to a region that includes a plurality of discrete angles. When the transmitter excites laser beams into the field of view at different positions (i.e., based on the position of the MEMS mirror 12), different angular regions in the horizontal direction of the field of view are sampled.

[0044] When two angular regions overlap, the overlapping angular region can correspond to beams excited by the same laser diode at different times. "The same laser diode" can refer to multiple light sources that are configured to simultaneously excite light to generate a laser beam (i.e., an entire or partial scan line) whose width completely occupies the angular region within the entire longitudinal extent of the beam produced by all the light sources. Alternatively, "the same laser diode" can refer to a single light source that is configured to generate a laser beam (i.e., a partial scan line) whose width completely occupies the angular region within the entire longitudinal extent of the beam produced only by that light source. Thus, multiple beams are beams generated by the same laser diode, and the beam width of each laser beam completely occupies the angular region of the field of view within the entire longitudinal extent of the laser beam.

[0045] Although the transmissive mirror has been described in the context of a MEMS mirror, it should be appreciated that other 1D mirrors or even 2D mirrors with two orthogonal axes of rotation can also be used. Additionally, the degree of rotation is not limited to + / - 15 degrees, and the field of view can be increased or decreased depending on the application. Thus, the one-dimensional scanning mirror is configured to swing about a single scanning axis and direct laser beams at different directions into the field of view. Accordingly, the transmission technique includes: transmitting a light beam from a transmissive mirror that swings about a single scanning axis into the field of view such that as the transmissive mirror swings about the single scanning axis, the light beam is projected into the field of view as a vertical scan line SL that horizontally traverses the field of view.

[0046] Upon striking one or more objects, the transmitted vertical light bar is reflected by backscattering as a reflected vertical line towards the LIDAR scanning system 100a, where a second optical component 14 (e.g., a lens or a prism) receives the reflected light. The second optical component 14 directs the reflected light onto a photodetector array 15 that receives the reflected light as a received line RL and is configured to generate an electrical measurement signal. The electrical measurement signal can be used to generate a 3D map of the environment and / or other object data based on the reflected light (e.g., via TOF calculations and processing).

[0047] The received line RL is shown as a vertical column of light that extends along one of the pixel columns in the longitudinal direction of the pixel columns. The received line has three vertical regions that correspond to the vertical regions of the Figure 1A shown vertical scan line SL. As the vertical scan line SL horizontally traverses the field of view, the vertical column of light RL incident on the 2D photodetector array 15 also horizontally traverses the 2D photodetector array 15. When the reception direction of the reflected light beam RL changes, the reflected light beam RL moves from a first edge of the photodetector array 15 to a second edge of the photodetector array 15. The reception direction of the reflected light beam RL corresponds to the transmission direction of the scan line SL. Thus, the LIDAR transmitter can excite light as a narrow laser pulse at different positions in the field of view, where each excitation position corresponds to a pixel column of the photodetector array 15.

[0048] The photodetector array 15 can be any type of photodetector among multiple photodetector types; including avalanche photodiodes (APDs), phototubes, and / or other photodiode devices. An imaging sensor such as a charge-coupled device (CCD) can be a photodetector. In the examples provided herein, the photodetector array 15 is a two-dimensional (2D) APD array that includes an APD pixel array. The activation of the photodiodes can be synchronized with the light pulses emitted by the illumination unit 10.

[0049] The photodetector array 15 receives the reflected light pulses as the received line RL and generates an electrical signal in response thereto. Since the time at which each light pulse is transmitted from the illumination unit 10 is known and since light travels at a known speed, the time-of-flight calculation using the electrical signal can determine the distance of the object from the photodetector array 15. A depth map can be drawn of the distance information.

[0050] In one example, for each distance measurement, a processing circuitry such as a microcontroller, a field programmable logic array (FPGA), or a processor triggers a laser pulse from each light source in the light source of the illumination unit 10 and also turns on a timer in a time-to-digital converter (TDC) integrated circuit (IC). The laser pulse is propagated through the transmission optics, reflected by the target field, and captured by one or more receiving photodiodes of the photodetector array 15. Each receiving photodiode emits a short electrical pulse, which is read out by an analog readout circuit. Each signal read out from the analog readout circuit can be amplified by an electrical signal amplifier.

[0051] A comparator IC identifies the pulse and sends a digital signal to the TDC to stop the timer. The TDC uses the clock frequency to calibrate each measurement. The TDC sends serial data of the differential time between the start digital signal and the stop digital signal to the processing circuitry, which filters out any error readings, averages multiple time measurements, and calculates the distance to the target at a specific field location. By emitting successive light pulses in different directions established by the MEMS mirror 12, an area (i.e., the field of view) can be scanned, a three-dimensional image can be generated, and objects within the area can be detected.

[0052] The signal processing chain of the receiver can also include an ADC for each photodiode or for a group of photodiodes. The ADC is configured to convert the analog electrical signal from the photodiode or group of photodiodes into a digital signal for further data processing.

[0053] Alternatively, instead of using the TDC approach, an ADC can be used for signal detection and ToF measurement. For example, each ADC can be used to detect the analog electrical signal from one or more photodiodes to estimate the time interval between the start signal (i.e., corresponding to the timing of the emitted light pulse) and the stop signal (i.e., corresponding to the timing of receiving the analog electrical signal at the ADC) using an appropriate algorithm.

[0054] When a laser energy pulse serving as a vertical scan line SL enters the field of view from the surface of the MEMS mirror 12, the reflected pulse appears when the laser illuminates an object in the field of view. These reflected pulses arrive at the photodetector array 15 as vertical columns of light. The width of these reflected pulses is, for example, one photodetector pixel, and its length vertically spans at least partially along the pixel columns of the photodetector array 15 in the longitudinal direction. That is, all the photodetector pixels in the pixel column or a part of the photodetector pixels in the pixel column can receive the light bar. For example, in one instance, all the light sources of the illumination unit 10 can be used to generate the scan line SL / receiving line RL. In this case, the receiving line RL can extend along the entire pixel column in the longitudinal direction. In another instance, only a subset of the light sources can be used to generate the scan line SL / receiving line RL. In this case, the receiving line can extend only along a part of the pixel column in the longitudinal direction.

[0055] In some instances, two or more pixel columns can receive light from the same light bar. For example, when a part of the received light bar impinges on the area between two photodetector pixels, two pixel columns can receive light. In this case, two pixel columns can be partially illuminated by a single light bar in the width direction.

[0056] On the other hand, as described above, if the illumination unit 10 generates partial vertical scan lines SL, only a part of the pixel columns of the photodetector array 15 can be illuminated in the longitudinal direction.

[0057] The photodetector array 15 is configured to generate a measurement signal (electrical signal) for generating a 3D map of the environment based on the reflected light (e.g., via TOF calculation and processing). For example, as described above, the photodetector array 15 can be a 2D array of photodiodes or other light detection components capable of detecting and measuring light and thereby generating an electrical signal.

[0058] Although not shown, the LIDAR scanning system 100a can also include a digital micromirror device (DMD) and auxiliary optics (e.g., a lens, a total internal reflection (TIR) prism, or a beam splitter), which are configured to first receive the reflected light through the main optics 14 and then redirect the received reflected light toward the photodetector array 15. For example, the DMD first receives the reflected light pulse from the main optics and deflects the received reflected light onto the photodetector array 15 through the auxiliary optics (e.g., a lens, a total internal reflection (TIR) prism, or a beam splitter). In this case, as described above, the photodetector array 15 can still receive vertical columns of light.

[0059] Figure 1BSchematic diagram of a vertical LIDAR scanning system 100b according to one or more embodiments. Specifically, the LIDAR scanning system 100b is similar to the LIDAR scanning system 100a, except that the scanning direction is rotated by 90°, such that the scan line SL and the reception line RL move in the vertical direction (i.e., from top to bottom or from bottom to top). Thus, the scan line is a horizontal scan line SL, which is projected into the field of view, and when the transmission mirror swings around a single scan axis, the horizontal scan line SL moves vertically across the field of view. Further, when the horizontal scan line SL moves vertically across the field of view, the horizontal column RL of light incident on the 2D photodetector array 15 also moves vertically across the 2D photodetector array 15.

[0060] Further, each transmission position of the transmitter can correspond to a pixel row of the photodetector array 15. For example, in such a setup, the reflected pulses arrive at the photodetector array 15 as a horizontal row of light, the width of which can be, for example, the width of one photodetector pixel, and the length of which can horizontally span at least partially along the pixel row of the photodetector array 15 in the longitudinal direction. That is, all the photodetector pixels in the pixel row or a part of the photodetector pixels in the pixel row can receive the light bar. For example, in one instance, all the light sources of the illumination unit 10 can be used to generate the scan line SL / reception line RL. In this case, the reception line RL can extend along the entire pixel row in the longitudinal direction. In another instance, only a subset of the light sources can be used to generate the scan line SL / reception line RL. In this case, the reception line can extend only along a part of the pixel row in the longitudinal direction.

[0061] In some instances, two or more pixel rows can receive light from the same light bar. For example, when a part of the received light bar impinges on the area between two photodetector pixels, two pixel rows can receive the light. In this case, two pixel rows can be partially illuminated by a single light bar in the width direction.

[0062] On the other hand, as described above, if only a part of the horizontal scan line SL is generated by the illumination unit 10, only a part of the pixel rows of the photodetector array 15 can be illuminated in the longitudinal direction.

[0063] Each laser beam has divergence in the vertical direction. Specifically, the width of each laser beam can have a Gaussian shape, where the laser beam has a peak intensity at its center and the intensity decreases at the sides. Thus, while each laser beam extends longitudinally in the horizontal direction, its width can also cover a discrete angular range (i.e., an angular region) in the vertical direction. Therefore, the angular region as used herein refers to a region that includes a plurality of discrete angles. When the transmitter excites the laser beam into the field of view at different positions (i.e., based on the position of the MEMS mirror 12), different angular regions in the vertical direction of the field of view are sampled.

[0064] It should be appreciated that although some embodiments are described with reference to the horizontal LIDAR scanning system 100a, any embodiment can be equally applicable to both the horizontal LIDAR scanning system 100a and the vertical LIDAR scanning system 100b. In this sense, the concept of calibrating the transmitter and / or receiver in the horizontal direction with reference to the scanning system 100a can be interchanged with the concept of calibrating the transmitter and / or receiver in the vertical direction with reference to the scanning system 100b, and vice versa.

[0065] Figure 2 is a schematic block diagram of a LIDAR scanning system 200 according to one or more embodiments. Specifically, Figure 2 shows additional features of the LIDAR scanning system 200, which includes example processing and control system components such as a MEMS driver, a receiver circuit, and a system controller.

[0066] The LIDAR scanning system 200 includes a transmitter unit 21, which is responsible for the transmitter path of the system 200; and a receiver unit 22, which is responsible for the receiver path of the system 200. The system also includes a system controller 23, which is configured to control the components of the transmitter unit 21 and the receiver unit 22, and to receive the raw data from the receiver unit 22 and perform processing thereon (e.g., via digital signal processing) for generating object data (e.g., point cloud data). Thus, the system controller 23 includes at least one processor and / or processing circuitry (e.g., comparators, TDCs, ADCs, FPGAs, and digital signal processors (DSPs)) for processing data in a signal processing chain, as well as control circuitry (such as a microcontroller or an FPGA) that is configured to generate control signals. The control circuitry can also be incorporated as part of the processing circuitry. The LIDAR scanning system 200 may also include a sensor 26, such as a temperature sensor, which provides sensor information to the system controller 23.

[0067] The transmitter unit 21 includes an illumination unit 10, a MEMS mirror 12, and a MEMS driver 25 configured to drive the MEMS mirror 12. Specifically, the MEMS driver 25 actuates and senses the rotational position of the mirror and provides position information of the mirror (e.g., the tilt angle or the rotation angle about the axis of rotation) to the system controller 23. Based on this position information, the laser source of the illumination unit 10 is triggered by the system controller 23, and the photodiodes are activated to sense and thus measure the reflected light signal. The controller 23 may refer to the relevant mapping information stored in a look-up table for determining the timing for: exciting a specific light source and activating a specific photodiode, and transmitting control signals to the illumination unit 10 and thus to the photodetector array 15. Thus, higher position sensing accuracy of the MEMS mirror results in more accurate and precise control of other components of the LIDAR system.

[0068] Specifically, the system controller 23 is configured to control the illumination unit 10 and the MEMS mirror 12 to implement a calibrated scanning technique. The laser beam is excited from the illumination unit 10 in coordination with the rotational (angular) position of the MEMS mirror 12 to transmit the laser beam into the field of view based on, for example, a desired time interval and / or a desired transmission direction.

[0069] As pointed out above, each laser beam covers a discrete angular region of the field of view. The system controller 23 determines the discrete mirror positions for each laser beam transmission and synchronizes the laser beam transmission with the discrete mirror positions. Thus, each discrete mirror position corresponds to a discrete transmission direction and thus to the angular region covered by the width of the transmitted laser beam. Further, each transmission position of the transmitter may correspond to a pixel column of the photodetector array 15. Thus, the system controller 23 also determines which photodiodes to activate and which to deactivate based on the corresponding light source and the discrete angular region sampled by the corresponding light source.

[0070] The receiver unit 22 includes a photodetector array 15 and a receiver circuit 24 including an analog readout circuit. As described in more detail below, each row of the photodetector array 15 can be selectively coupled to and decoupled from the receiver circuit 24 by an analog multiplexer. The pixels, rows, or columns that can be coupled to the receiver circuit 24 may be referred to as "activated" (enabled), while the pixels, rows, or columns that are not coupled to the receiver circuit 24 may be referred to as "deactivated" (disabled).

[0071] The analog readout circuit includes N analog output channels (e.g., 32 channels), which are configured to read out the measurement signals received from the selected pixels of the coupled rows of the photodetector array 15. Further, more than one pixel can be selected from the coupled rows, multiple rows can be simultaneously coupled to the output channels, and one or more pixels can be selected from each coupled row.

[0072] The analog readout circuit can include a multiplexer that is configured to selectively couple the received pixels to the plurality of analog output channels to activate the coupled pixels while decoupling the non-received pixels from the plurality of analog output channels to deactivate the decoupled pixels. The received pixels are the pixels that are expected to receive the reflected laser beam based on the discrete transmission directions of the corresponding transmitted laser beams. In contrast, the non-received pixels are the pixels that are not expected to receive the reflected laser beam based on the discrete transmission directions of the corresponding transmitted laser beams.

[0073] Thus, the receiver circuit 24 can receive an analog electrical signal from the photodetectors of the photodetector array 15 and transmit the electrical signal as raw analog data to the analog-to-digital converter (ADC). Before the ADC receives the electrical signal, the electrical signal can pass through an amplifier (e.g., a transimpedance amplifier (TIA)) that converts the electrical signal from, for example, current to voltage. The ADC is configured to convert the raw analog data into raw digital data for further processing. The amplifier and / or the ADC can be incorporated in the system controller 23 or the receiver circuit 24, or can be inserted as a separate circuit between the receiver circuit 24 and the system controller 23.

[0074] The receiver circuit 24 can also receive a trigger control signal from the system controller 23, and the system controller 23 triggers the activation of one or more photodetectors. The receiver circuit 24 can also receive a gain setting control signal that is used to control the gain of one or more photodetectors.

[0075] The system controller 23 includes signal processing circuitry that receives the raw digital data and the serial data of the differential time between the start digital signal and the stop digital signal generated by the ADC, and uses the received data to calculate the time-of-flight information for each field position in the field of view, generate object data (e.g., point cloud data), and generate a 3D point cloud.

[0076] Specifically, the signal processing circuitry of the system controller 23 can be configured to detect an object based on the electrical signals generated by the photodetectors of the photodetector array 15. Based on this detection, the signal processing circuitry can determine the estimated position of the object in the field of view, the direction to the object, and / or the angular position of the mirror 12 corresponding to the position or direction of the object. The system controller 23 can control the transmission of one or more laser beams based on the estimated position of the object while implementing the calibration scan techniques described herein.

[0077] As described above, the MEMS mirror 12 is configured to swing between two extreme positions (e.g., + / - 15 degrees) in the horizontal scan direction or the vertical scan direction to deflect light within + / - 30 degrees (i.e., 60 degrees) of the full scan range that constitutes the field of view. The receiver (specifically, the photodetector array 15) also has a field of view from which it can receive and detect light, and more specifically, receive and detect backscattered light. Thus, the transmitter (TX) 21 and the receiver (RX) 22 each have their own field of view (i.e., TX FOV and RX FOV, respectively), and only the overlapping portion of the fields of view is used to detect information and generate image data. The misalignment of the TX FOV and the RX FOV reduces the overlapping area.

[0078] As a result, transmitter and / or receiver calibration is used to maximize the overlapping area of the fields of view. Based on this calibration, the correct receiver columns / pixels are activated to match the FOV.

[0079] Several conditions are used for calibration. First, the transmitter 21 and the receiver 22 are mounted on top of each other to maximize the overlapping area of their respective FOVs. Second, the actual operating FOV of the transmitter 21 is set to be less than the entire FOV of the transmitter 21. For example, for a maximum mirror tilt of + / - 15 degrees, the maximum FOV of the transmitter 21 can be 60 degrees. Thus, as an example, the operating TX FOV of the transmitter 21 can be set to 40 degrees. When aligning the operating TX FOV with the RX FOV, setting the actual operating TX FOV to be less than the entire (maximum) TX FOV allows a certain degree of calibration freedom (e.g., + / - 10 degrees).

[0080] Figure 3 is a top view of the overlapping TX and RX fields of view according to one or more embodiments. The left figure shows the fields of view before calibration, and the right figure shows the fields of view after calibration.

[0081] The field of view includes the full TX FOV 31, the operating TX FOV 32, and the RX FOV 33. The overlapping area 34 is the area where the operating TX FOV 32 overlaps with the RX FOV 33.

[0082] As can be seen from the left figure, the misalignment angle β between the transmitter 21 and the receiver 22 reduces the overlapping region 34. Specifically, this misalignment results in a misalignment angle β between the discrete transmission angle TX0° of the transmitter 21 and the discrete reception angle RX0° of the receiver 22, and this discrete reception angle RX0° corresponds to a pixel column. For example, the discrete transmission angle TX° can be 0° (i.e., the mirror tilt angle is 0°), and the discrete reception angle RX° can also be 0°, which is mapped to the central pixel column of the photodetector array 15. When the misalignment angle β is greater than 0°, misalignment exists.

[0083] In contrast, as can be seen from the right figure, the TX FOV 32 has been moved to align with the RX FOV 33, thereby maximizing the overlapping region 34. In this case, the misalignment angle β is 0°. In an alternative, it should be appreciated that the RX FOV 33 can be moved to align with the TX FOV 32 to reduce or eliminate misalignment.

[0084] To mitigate misalignment, the TX FOV 32 or the RX FOV 33 can be configured to be slightly larger than the other FOV (e.g., up to 10%) to compensate for misalignment in the worst case. However, from the perspective of system performance, the RX FOV 33 should be kept as small as possible to limit ambient light and noise. Therefore, it can be preferred that the TX FOV 32 is larger than the RX FOV 33. This can be achieved by modifying the tilt range of the MEMS mirror 12. Since the RX FOV 33 is smaller than the TX FOV 32 in one or both of the horizontal and vertical directions, part or all of the RX FOV 33 can be surrounded by the TX FOV 32. In other words, the RX FOV 33 can completely overlap with the TX FOV 32 in the horizontal direction, vertical direction, or both.

[0085] Figure 4A and Figure 4B Illustrated is a transmitter-side compensation technique for aligning the TX FOV with the RX FOV according to one or more embodiments. In both figures, the left figure illustrates the misalignment before auto-calibration, and the right figure illustrates the result after auto-calibration, where auto-calibration is performed by moving the TX FOV. Additionally, both figures illustrate the projection of the received line RL onto a portion of the photodetector array 15. The received line includes eight segments, each segment corresponding to a different laser channel (i.e., a different light source). Therefore, eight light sources are used in this example. The eight light sources are configured to transmit corresponding light beams at discrete transmission angles TX°, resulting in the received line RL being incident on the photodetector array 15.

[0086] Additionally, both figures identify the target pixel column 15T mapped to the discrete angle TX°. In this case, each laser beam (i.e., each laser source) is vertically mapped to two adjacent pixels of the target pixel column 15T. The target pixel column 15T defines the reception angle RX° corresponding to the discrete transmission angle TX°.

[0087] In Figure 4A there is an alignment angle β between the discrete transmission angle TX° and the reception angle RX°. As a result, there is an alignment offset d in the horizontal direction, and only a part of the reception line RL intended for the target pixel column 15T actually impinges on the target pixel column 15T.

[0088] As Figure 4A demonstrated on the right side of , a timing offset is applied to each light source such that the transmission time of the laser relative to the position of the MEMS mirror 12 is adjusted to be consistent with the target pixel column 15T, particularly with the target pixel corresponding to the light source. As described above, the mapping information of each light source itself is stored in the corresponding lookup table. Due to the horizontal misalignment, the timing offset is applied to the horizontal mapping information stored in the corresponding lookup table. Calibration is performed separately for each light source.

[0089] For each light source, the system controller 23 determines the position where the corresponding light beam impinges on the photodetector array 15, determines the misalignment offset d relative to the target pixel column 15T for each light source, determines the adjusted timing offset for each light source based on the misalignment offset d, and updates the mapping information in the corresponding lookup table based on the determined timing offset. Since the misalignment offset d of each light source may be different, the timing offset of each light source may also be different.

[0090] Determining the position where the corresponding light beam impinges on the photodetector array 15 can be performed by activating all the pixels of the photodetector array 15 and detecting the pixels on which the corresponding light beam impinges.

[0091] Once the transmitter 21 has been calibrated, the transmission angle TX° and the receiver angle RX° are aligned, and the reception line RL is substantially projected onto the target pixel column 15T. Therefore, for the corresponding discrete transmission angle, a single pixel column can be enabled. That is, the timing offset can be configured such that for each discrete transmission angle, the corresponding reception line RL impinges on a single pixel column. In this way, the readout of the detector can be simplified. Furthermore, high accuracy of calibration (i.e., high resolution of offset compensation) can be achieved.

[0092] In Figure 4B the calibration technique applied is similar to the calibration technique applied to Figure 4A However, in Figure 4BIn the case of misalignment, the reasons are different. Here, deformation caused by components (such as lenses) of the transmitter 21 may result in misalignment.

[0093] The deformation can be corrected in a similar manner as described above in conjunction with Figure 4A Specifically, for each light source, the system controller 23 determines the position where the corresponding light beam is incident on the photodetector array 15, determines the misalignment offset d relative to the target pixel column 15T for each light source, determines the timing offset to be adjusted for each light source according to the misalignment offset d, and updates the mapping information in the corresponding look-up table based on the determined timing offset. Since the misalignment offset d for each light source may be different, the timing offset for each light source may also be different.

[0094] Figure 5A and Figure 5B Figs. illustrate receiver-side compensation techniques for aligning the TX FOV with the RX FOV according to one or more embodiments. In both figures, the left figure shows the misalignment before auto-calibration, while the right figure shows the result after auto-calibration, where auto-calibration is performed by moving the RX FOV. Additionally, both figures illustrate the projection of the received line RL onto a portion of the photodetector array 15. The received line includes eight segments, each corresponding to a different laser channel (i.e., a different light source). Thus, eight light sources are used in this example. The eight light sources are configured to transmit corresponding light beams at discrete transmission angles TX°, resulting in the received line RL being incident on the photodetector array 15.

[0095] In Figure 4A and Figure 4B the timing offset of each light source is adjusted to align with the target pixel column 15T. This results in the movement of the projection of the received line on the target pixel column 15T. In contrast, in Figure 5A and Figure 5B for the receiver-side compensation technique, the timing of the laser transmission remains unchanged. Instead, the activation of the target pixels at the receiver is changed to follow the expected position of the received line RL. In other words, for each light source, the assignment of the target pixels corresponding to the discrete transmission angle TX° is modified.

[0096] Specifically, for each light source, the system controller 23 determines the position where the corresponding light beam is incident on the photodetector array 15, identifies one or more pixels at that position, and updates the mapping information in the corresponding look-up table for the detector readout circuit based on the identified pixels.

[0097] Determining the position where the corresponding beam impinges on the photodetector array 15 can be performed by activating all the pixels of the photodetector array 15 and detecting the pixels on which the corresponding beam impinges. Thus, the misalignment at the receiver 22 is compensated by selecting the RX pixel with the strongest responsiveness for each TX laser channel.

[0098] The system includes Mk laser channels, Ni detector columns, and Oj detector rows. For each laser channel k, detector pixels ij with the highest intensity for each discrete transmission angle are defined.

[0099] For example, in Figure 5A the left figure, column n is initially set as the target pixel column 15T for all light sources 1 - 8. Thus, before auto - calibration, for a given discrete transmission angle, all laser channels are read by the same column n. After auto - calibration, each laser channel has an assigned pixel column and pixel row (i.e., an assigned target pixel) that has the highest intensity for the given discrete transmission angle. Calibration is performed for each discrete angle, and thus the mapping information in the corresponding look - up table for the detector read - out circuit is updated. Thus, in Figure 5A the right figure, pixel column n is assigned to light sources 1 and 2 for the given discrete transmission angle, pixel column n + 1 is assigned to light sources 3 and 4 for the given discrete transmission angle, pixel column n + 2 is assigned to light sources 5 and 6 for the given discrete transmission angle, and pixel column n + 3 is assigned to light sources 7 and 8 for the given discrete transmission angle.

[0100] Similar receiver - side compensation techniques are used to compensate for Figure 5B the left figure. Before auto - calibration in the presence of distortion effects, all laser channels are configured to be read by the same pixel column n. However, after auto - calibration in the presence of distortion effects, each laser channel has an assigned pixel column and pixel row (i.e., an assigned target pixel) that has the highest intensity for the given discrete transmission angle. Calibration is performed for each discrete angle, and thus the mapping information in the corresponding look - up table for the detector read - out circuit is updated. Thus, in Figure 5B the right figure, pixel column n is assigned to light sources 1 and 8 for the given discrete transmission angle, pixel column n - 1 is assigned to light sources 2 and 7 for the given discrete transmission angle, and pixel column n - 2 is assigned to light sources 3 to 6 for the given discrete transmission angle.

[0101] Figure 6 Illustrates receiver - side compensation techniques for aligning the TX FOV with the RX FOV according to one or more embodiments. Specifically, Figure 6 the receiver - side compensation techniques shown in Figure 5A and Figure 5BAn extension of the described compensation technique, and for activation / deactivation of pixels or columns, different distances are also taken into account as a factor.

[0102] In this case, the mapping of the photodetector array 15 can be changed for different distances. For example, until the first transmission distance d1 (i.e., the distance from d1 is zero), pixel column a is enabled; for distances greater than distance d1 until distance d2, pixel column b is enabled; for distances greater than distance d2 until distance d3, pixel column c is enabled; for distances greater than distance d3, pixel column d is enabled. Thus, certain pixel columns can be enabled (activated) or disabled (deactivated) based on the time of flight. As a result, different overlapping regions of the TX FOV and RX FOV are defined according to different distances. Therefore, each mapping for the corresponding pixels can be defined according to the light source, the discrete transmission angle, and the distance or range of distances.

[0103] Figure 7 The flowchart of the transmitter-side compensation technique 700 for aligning the TX FOV with the RX FOV according to one or more embodiments is illustrated.

[0104] The transmitter-side compensation method 700 includes: pointing the LIDAR system at a flat and uniform reference target such as a white wall that is greater than the LIDAR FOV (i.e., greater than the entire FOV) (operation 705); and enabling the transmitter to emit a laser beam at an angle X (operation 710). The method 700 also includes: in response to the measured light, reading out all receiver pixel columns and identifying the pixel column Y with the highest intensity (operation 715). In the case where it is determined that two or more adjacent pixel columns have intensities greater than a predetermined threshold, operation 715 also includes: in response to the measured light, identifying the second pixel column Z with the second highest intensity.

[0105] The method 700 also includes: determining the misalignment angle β, which is defined as β = X - angle1(Y) (operation 720). Here, X is an angle in the FOV that the transmitter is illuminating (i.e., the angle at which the laser beam is emitted), and angle1(Y) is the specific angle in the FOV that the pixel column Y points to (i.e., corresponds to) (i.e., the receiving angle to which the pixel column Y is mapped).

[0106] In the case of identifying two pixel columns, the misalignment angle β is defined as β = X – (angle 2(Z) + (angle 1(Y) – angle 2(Z)) * amplitude(Z) / amplitude(Y)). In this text, X is the specific angle at which the transmitter is illuminating (i.e., the angle at which the laser beam is sent), and angle 1(Y) is the specific angle to which pixel column Y points (i.e., corresponds) in the FOV (i.e., the receiving angle to which pixel column Y is mapped), angle 2(Z) is the specific angle to which pixel column Z points (i.e., corresponds) in the FOV (i.e., the receiving angle to which pixel column Z is mapped), amplitude(Y) is the amplitude of the optical signal detected by pixel column Y (i.e., the amplitude of the electrical signal generated by pixel column Y), and amplitude(Z) is the amplitude of the optical signal detected by pixel column Z (i.e., the amplitude of the electrical signal generated by pixel column Z).

[0107] The method 700 further includes: for each light source, applying a correction factor (e.g., timing offset) in the TX look-up table (operation 725); and checking whether a discrete transmission angle X is read at the target pixel column (i.e., whether the discrete transmission angle is consistent with the receiver angle) (operation 730). This check can be performed by sending the laser beam again at angle X and monitoring the response at pixel column Y or at pixel columns Y and Z. If one or more pixel columns do not match the transmission angle X, the process returns to operation 710. On the other hand, if one or more pixel columns match the transmission angle X, it is found that the LIDAR system is calibrated (operation 735).

[0108] It will also be appreciated that the compensation method 700 can be performed in real time during the operation of the LIDAR system, and calibration is not limited to being performed in a calibration mode or in front of a white wall. In other words, in a real environment with non-uniform objects, additional signal processing can be used to perform calibration in the operating mode.

[0109] Figure 8 A flowchart of a transmitter-side compensation technique 800 for aligning the TX FOV with the RX FOV according to one or more embodiments is illustrated. Specifically, the transmitter-side compensation method corresponds to the compensation technique described in conjunction with Figures 4A to 4B the compensation technique described.

[0110] The transmitter-side compensation method 800 includes: pointing the LIDAR system at a flat and uniform reference target such as a white wall that is larger than the LIDAR FOV (i.e., larger than the entire FOV) (operation 805); and enabling the transmitter to transmit a laser beam at angle X (operation 810). The method 800 further includes: in response to the measured light, reading out all receiver pixel columns and identifying the pixel column Y with the highest intensity (operation 815). In the case where two or more adjacent pixel columns have intensities greater than a predetermined threshold, operation 815 further includes: in response to the measured light, identifying a second pixel column Z with the second highest intensity. The method 800 further includes: determining an alignment offset d, which is defined as d = X - angle1(Y) (operation 820). In the case of identifying two pixel columns, the misalignment angle β is defined as d = X - (angle2(Z)+(angle1(Y) - angle2(Z)) * amplitude(Z) / amplitude(Y)).

[0111] The method 800 further includes: for each light source, applying a correction factor (e.g., timing offset) from the TX look-up table (operation 825); and checking whether the discrete transmission angle X is read at the target pixel column (i.e., whether the discrete transmission angle is consistent with the receiver angle) (operation 830). This check can be performed by transmitting the laser beam again at angle X and monitoring the response at pixel column Y or pixel columns Y and Z. If one or more pixel columns do not match the transmission angle X, the process returns to operation 810. On the other hand, if one or more pixel columns match the transmission angle X, it is found that the LIDAR system is calibrated (operation 835).

[0112] It will also be appreciated that the compensation method 800 can be performed in real time during the operation of the LIDAR system, and the calibration is not limited to being performed in a calibration mode or in front of a white wall. In other words, in a real environment with non-uniform objects, additional signal processing can be used to perform calibration in the operating mode.

[0113] Figure 9 A flowchart of a receiver-side compensation method 900 for aligning the TX FOV with the RX FOV according to one or more embodiments is illustrated. Specifically, the receiver-side compensation method corresponds to the compensation techniques described in conjunction with Figure 5A and Figure 5B as described.

[0114] The receiver-side compensation method 900 includes: pointing the LIDAR system at a flat and uniform reference target such as a white wall that is larger than the LIDAR FOV (i.e., larger than the entire FOV) (operation 905); and enabling the transmitter to emit a laser beam at angle X and enabling laser channel n (operation 910). The method 900 further includes: in response to the measured light, reading all receiver pixel rows associated with the pixel column corresponding to angle X and identifying the (one or more) pixel rows Y with the highest intensity; and assigning the (one or more) identified pixel rows to laser channel n (operation 915). Thus, laser channel n has been calibrated. The compensation method 900 further includes: determining whether all laser channels have been calibrated (operation 920). If not, the process is repeated for laser channel n+1, and so on, until all laser channels have been calibrated (operation 925).

[0115] It will also be appreciated that the compensation method 900 can be performed in real time during the operation of the LIDAR system, and the calibration is not limited to being performed in a calibration mode or in front of a white wall. In other words, in a real environment with non-uniform objects, additional signal processing can be used to perform the calibration in the operating mode.

[0116] Figure 10 The flowchart of a transmitter-side compensation technique 1000 for aligning the TX FOV with the RX FOV according to one or more embodiments is illustrated.

[0117] The transmitter-side compensation method 1000 includes: pointing the LIDAR system at a flat and uniform reference target such as a white wall that is larger than the LIDAR FOV (i.e., larger than the entire FOV) (operation 1005); and enabling the transmitter to transmit a laser beam at angle X and enabling laser channel n (operation 1010). The method 1000 further includes: in response to the measured light, reading all receiver pixel rows and pixel columns associated with laser channel n and identifying the pixel column Y with the highest intensity (operation 1015). In the case where two or more adjacent pixel columns have intensities greater than a pre-determined threshold, operation 1015 further includes: in response to the measured light, identifying a second pixel column Z with the second highest intensity.

[0118] The method 1000 further includes: determining an alignment offset d, which is defined as d = X - angle1(Y) (operation 1020). In the case of identifying two pixel columns, the misalignment angle β is defined as d = X - (angle2(Z) + (angle1(Y) - angle2(Z)) * amplitude(Z) / amplitude(Y)).

[0119] The method 1000 further includes: for each light source, applying a correction factor (e.g., timing offset) from the TX look-up table (operation 1025); and checking whether a discrete transmission angle X is read at the target pixel column (i.e., whether the discrete transmission angle coincides with the receiver angle) (operation 1030). This check can be performed by sending the laser beam again at angle X and monitoring the response at pixel column Y or at pixel columns Y and Z. If one or more pixel columns do not match the transmission angle X, the process returns to operation 1010. On the other hand, if one or more pixel columns match the transmission angle X, it is found that the laser channel n is calibrated. The compensation method 1000 further includes: determining whether all laser channels are calibrated (operation 1035). If not, the process is repeated for laser channel n+1, and so on, until all laser channels are calibrated (operation 1040).

[0120] It should also be appreciated that the compensation method 800 can be performed in real time during the operation of the LIDAR system, and calibration is not limited to being performed in a calibration mode or in front of a white wall. In other words, in a real environment with non-uniform objects, additional signal processing can be used to perform calibration in the operating mode.

[0121] Although the embodiments described herein relate to a MEMS device having a mirror, it should be understood that other implementations may include optical devices other than MEMS mirror devices. Additionally, although some aspects have been described in the context of an apparatus, it is evident that these aspects also represent a description of the corresponding method, where a block or device corresponds to a method step or a feature of a method step. Similarly, each aspect described in the context of a method step also represents a description of the corresponding block or item or feature of the corresponding apparatus. Some or all of the method steps may be performed by (or using) a hardware device (e.g., a microprocessor, a programmable computer, or an electronic circuit). In some embodiments, a certain or certain method steps may be performed by such a device.

[0122] In accordance with the requirements of certain implementations, the embodiments provided herein may be implemented in hardware or software. The implementation may be performed using a digital storage medium (e.g., a floppy disk, a DVD, a Blu-ray, a CD, a ROM, a PROM, an EPROM, an EEPROM, or a FLASH memory) storing an electronically readable control signal that cooperates (or is capable of cooperating) with a programmable computer system to perform the corresponding method. Thus, the digital storage medium may be a computer-readable medium.

[0123] The instructions may be executed by one or more processors such as one or more central processing units (CPUs), digital signal processors (DSPs), general purpose microprocessors, application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), or other equivalent integrated or discrete logic circuitry. Thus, as used herein, the term "processor" or "processing circuitry" refers to any of the foregoing structures or any other structure suitable for implementing the techniques described herein. Additionally, in some aspects, the functions described herein may be provided within dedicated hardware and / or software modules. Further, the techniques may be fully implemented in one or more circuits or logic elements.

[0124] The above-described exemplary embodiments are merely illustrative embodiments. It should be understood that modifications and variations to the arrangements and details described herein will be apparent to other those skilled in the art. Thus, the intention is to be limited only by the scope of the subsequent claims, rather than by the specific details presented in the description and explanation of the embodiments herein.

Claims

1. A light detection and ranging LIDAR system, comprising: A LIDAR transmitter configured with a first field of view and configured to transmit laser beams into the first field of view at a plurality of discrete transmission angles to scan the first field of view with the laser beams; A LIDAR receiver configured with a second field of view and configured to receive reflected laser beams from the second field of view and generate an electrical signal based on the received reflected laser beams; A controller configured to move at least one of the first field of view or the second field of view based on misalignment to optimize the overlap between the first field of view and the second field of view; and A memory configured to store mapping information, wherein the controller is configured to: detect the misalignment between the first field of view and the second field of view; and move at least one of the first field of view or the second field of view based on the detected misalignment to optimize the overlap between the first field of view and the second field of view, wherein the LIDAR transmitter includes: A light source configured to generate the laser beams at a plurality of transmission times; and A scanning mirror configured to swing around a single scanning axis such that the laser beams are received from the light source and projected into the first field of view, wherein as the scanning mirror swings around the single scanning axis, the laser beams move across the first field of view; wherein the LIDAR receiver includes: A two-dimensional 2D photodetector array including a plurality of pixels arranged in a plurality of pixel rows and a plurality of pixel columns, wherein each pixel is configured to generate an electrical signal based on the received light; wherein the mapping information maps the plurality of transmission times to different target pixels among the plurality of pixels, wherein each transmission time is mapped to at least one target pixel and corresponds to a different discrete transmission angle among the plurality of discrete transmission angles, wherein the controller is configured to: Select a discrete transmission angle; Trigger the light source at a transmission time to generate a laser beam whose transmission direction corresponds to the selected discrete transmission angle; Enable the plurality of pixels of the 2D photodetector array during a measurement window corresponding to the transmission time; Evaluate the intensity of each pixel among the plurality of pixels based on the electrical signals generated by the plurality of pixels; Select at least one first pixel having the highest intensity from among the plurality of pixels as the at least one target pixel; and Update the mapping information to link the at least one target pixel to the selected discrete transmission angle.

2. The LIDAR system according to claim 1, wherein the first field of view is larger than the second field of view, and the controller is configured to move at least one of the first field of view or the second field of view such that the second field of view is completely overlapped by the first field of view in at least one of the horizontal direction or the vertical direction.

3. The LIDAR system according to claim 1, wherein the first field of view is greater than the second field of view, and the controller is configured to: move at least one of the first field of view or the second field of view such that the second field of view is completely overlapped by the first field of view in both the horizontal and vertical directions.

4. The LIDAR system according to claim 1, wherein the controller is configured to: compare the expected position where the reflected laser beam is expected to be incident on the LIDAR receiver with the actual position where the reflected laser beam is incident on the LIDAR receiver, wherein the expected position is mapped to a discrete transmission angle, and the laser beam associated with the reflected laser beam is transmitted at the discrete transmission angle; calculate a correction factor based on the difference between the expected position and the actual position; and move at least one of the first field of view or the second field of view based on the correction factor.

5. The LIDAR system according to claim 1, wherein the controller is configured to: detect the area of the LIDAR receiver on which the reflected laser beam is incident; link the detected area to a discrete transmission angle, and the laser beam associated with the reflected laser beam is transmitted at the discrete transmission angle such that the detected area is activated when subsequent laser beams are transmitted at the discrete transmission angle.

6. The LIDAR system according to claim 5, wherein the controller is configured to: detect the misalignment angle between the first field of view and the second field of view; calculate a correction factor based on the detected misalignment angle; and move at least one of the first field of view or the second field of view based on the correction factor.

7. The LIDAR system according to claim 5, wherein the controller is configured to: detect the misalignment offset between the first field of view and the second field of view; calculate a correction factor based on the detected misalignment offset; and move at least one of the first field of view or the second field of view based on the correction factor.

8. The LIDAR system according to claim 1, wherein the controller is configured to: compare the first position information of at least one target pixel where the reflected laser beam is expected to be incident with the second position information of at least one received pixel among the plurality of pixels where the reflected laser beam is incident; calculate a correction factor based on the difference between the first position information and the second position information; and update the mapping information based on the correction factor.

9. The LIDAR system according to claim 1, wherein the controller is configured to: select at least one second pixel having the second highest intensity from among the plurality of pixels as the at least one target pixel; and update the mapping information to link the at least one target pixel to the selected discrete transmission angle.

10. An optical detection and ranging LIDAR system, comprising: A LIDAR transmitter configured with a first field of view and configured to transmit laser beams into the first field of view at a plurality of discrete transmission angles to scan the first field of view with the laser beams; A LIDAR receiver configured with a second field of view and configured to receive reflected laser beams from the second field of view and generate an electrical signal based on the received reflected laser beams; A controller configured to move at least one of the first field of view or the second field of view based on misalignment to optimize the overlap of the first field of view and the second field of view; And A memory configured to store mapping information, wherein the controller is configured to: detect the misalignment between the first field of view and the second field of view; And move at least one of the first field of view or the second field of view based on the detected misalignment to optimize the overlap of the first field of view and the second field of view, wherein the LIDAR transmitter includes: A light source configured to generate the laser beams at a plurality of transmission times; and A scanning mirror configured to swing about a single scanning axis such that the laser beams are received from the light source and projected into the first field of view, wherein as the scanning mirror swings about the single scanning axis, the laser beams move across the first field of view; wherein the LIDAR receiver includes: A two-dimensional 2D photodetector array including a plurality of pixels arranged in a plurality of pixel rows and a plurality of pixel columns, wherein each pixel is configured to generate an electrical signal based on received light; wherein the mapping information maps the plurality of transmission times to different target pixels among the plurality of pixels, wherein each transmission time is mapped to at least one target pixel and corresponds to a different discrete transmission angle among the plurality of discrete transmission angles, wherein the controller is configured to: Compare first position information of at least one target pixel where the reflected laser beam is expected to be incident with second position information of at least one received pixel among the plurality of pixels where the reflected laser beam is incident; Calculate a correction factor based on a difference between the first position information and the second position information; and Update the mapping information based on the correction factor, wherein the correction factor is a time offset applied to at least one of the plurality of transmission times to generate at least one updated transmission time, and the controller is configured to use the at least one updated transmission time to update the mapping information.

11. The LIDAR system according to claim 10, wherein for each transmission time, the controller is configured to synchronize the at least one target pixel with the transmission time based on the mapping information.

12. An optical detection and ranging LIDAR system, comprising: A LIDAR transmitter configured with a first field of view and configured to transmit laser beams into the first field of view at a plurality of discrete transmission angles to scan the first field of view with the laser beams; A LIDAR receiver configured with a second field of view and configured to receive a reflected laser beam from the second field of view and generate an electrical signal based on the received reflected laser beam; A controller configured to move at least one of the first field of view or the second field of view based on misalignment to optimize the overlap of the first field of view and the second field of view; And A memory configured to store mapping information, wherein the controller is configured to: detect the misalignment between the first field of view and the second field of view; And move at least one of the first field of view or the second field of view based on the detected misalignment to optimize the overlap of the first field of view and the second field of view, wherein the LIDAR transmitter includes: A light source configured to generate the laser beam at a plurality of transmission times; and A scanning mirror configured to swing around a single scanning axis such that the laser beam is received from the light source and projected into the first field of view, wherein as the scanning mirror swings around the single scanning axis, the laser beam moves across the first field of view; wherein the LIDAR receiver includes: A two-dimensional (2D) photodetector array including a plurality of pixels arranged in a plurality of pixel rows and a plurality of pixel columns, wherein each pixel is configured to generate an electrical signal based on received light; wherein the mapping information maps the plurality of transmission times to different target pixels among the plurality of pixels, wherein each transmission time is mapped to at least one target pixel and corresponds to a different discrete transmission angle among the plurality of discrete transmission angles, wherein the controller is configured to: Select a discrete transmission angle; For the selected discrete transmission angle, select a first detection range and a second detection range; Trigger the light source at a transmission time to generate a laser beam whose transmission direction corresponds to the selected discrete transmission angle; Enable the plurality of pixels of the 2D photodetector array during a measurement window corresponding to the transmission time; Evaluate the intensity of each pixel among the plurality of pixels based on the electrical signals generated by the plurality of pixels; For the first detection range, select at least one first pixel having the highest first intensity from among the plurality of pixels as at least one first target pixel; For the first detection range, update the mapping information to link the at least one first target pixel to the selected discrete transmission angle; For the second detection range, select at least one second pixel having the highest second intensity from among the plurality of pixels as at least one second target pixel; and For the second detection range, update the mapping information to link the at least one second target pixel to the selected discrete transmission angle.

13. An optical detection and ranging (LIDAR) system, comprising: A LIDAR transmitter configured with a first field of view and configured to send a laser beam into the first field of view at a plurality of discrete transmission angles to scan the first field of view with the laser beam; A LIDAR receiver, the LIDAR receiver being configured with a second field of view and being configured to receive a reflected laser beam from the second field of view and generate an electrical signal based on the received reflected laser beam; A controller configured to move at least one of the first field of view or the second field of view based on misalignment to optimize the overlap between the first field of view and the second field of view; And A memory configured to store mapping information, wherein the controller is configured to: detect the misalignment between the first field of view and the second field of view; And move at least one of the first field of view or the second field of view based on the detected misalignment to optimize the overlap between the first field of view and the second field of view, wherein the LIDAR transmitter includes: A light source configured to generate the laser beam at a plurality of transmission times; and A scanning mirror configured to swing around a single scanning axis such that the laser beam is received from the light source and projected into the first field of view, wherein as the scanning mirror swings around the single scanning axis, the laser beam moves across the first field of view; wherein the LIDAR receiver includes: A two-dimensional 2D photodetector array including a plurality of pixels arranged in a plurality of pixel rows and a plurality of pixel columns, wherein each pixel is configured to generate an electrical signal based on received light; wherein the mapping information maps the plurality of transmission times to different target pixels among the plurality of pixels, wherein each transmission time is mapped to at least one target pixel and corresponds to a different discrete transmission angle among the plurality of discrete transmission angles, wherein the controller is configured to: Compare first position information of at least one target pixel where the reflected laser beam is expected to be incident with second position information of at least one received pixel among the plurality of pixels where the reflected laser beam is incident; Calculate a correction factor based on a difference between the first position information and the second position information; and Update the mapping information based on the correction factor, wherein the controller is further configured to: Select a discrete transmission angle; Trigger the light source at a transmission time to generate a laser beam whose transmission direction corresponds to the selected discrete transmission angle; Enable the plurality of pixels of the 2D photodetector array during a measurement window corresponding to the transmission time; Evaluate the intensity of each pixel among the plurality of pixels based on the electrical signals generated by the plurality of pixels; Identify at least one pixel having the highest intensity among the plurality of pixels as the at least one received pixel; Calculate the correction factor based on the difference between the first position information and the second position information; and Update the mapping information based on the correction factor.

14. The LIDAR system according to claim 13, wherein the correction factor is a time offset applied to the transmission time to generate an updated transmission time, and the controller is configured to use the updated transmission time to update the mapping information.

15. An optical detection and ranging LIDAR system, comprising: A LIDAR transmitter configured with a first field of view and configured to transmit laser beams into the first field of view at a plurality of discrete transmission angles to scan the first field of view with the laser beams; A LIDAR receiver configured with a second field of view and configured to receive reflected laser beams from the second field of view and generate an electrical signal based on the received reflected laser beams; A controller configured to move at least one of the first field of view or the second field of view based on misalignment to optimize the overlap of the first field of view and the second field of view; And A memory configured to store mapping information, wherein the controller is configured to: detect the misalignment between the first field of view and the second field of view; And move at least one of the first field of view or the second field of view based on the detected misalignment to optimize the overlap of the first field of view and the second field of view, wherein the LIDAR transmitter includes: A light source configured to generate the laser beams at a plurality of transmission times; and A scanning mirror configured to swing around a single scanning axis such that the laser beams are received from the light source and projected into the first field of view, wherein as the scanning mirror swings around the single scanning axis, the laser beams move across the first field of view; wherein the LIDAR receiver includes: A two-dimensional 2D photodetector array including a plurality of pixels arranged in a plurality of pixel rows and a plurality of pixel columns, wherein each pixel is configured to generate an electrical signal based on received light; wherein the mapping information maps the plurality of transmission times to different target pixels among the plurality of pixels, wherein each transmission time is mapped to at least one target pixel and corresponds to a different discrete transmission angle among the plurality of discrete transmission angles, wherein the controller is configured to: Compare first position information of at least one target pixel where the reflected laser beam is expected to be incident with second position information of at least one received pixel among the plurality of pixels where the reflected laser beam is incident; Calculate a correction factor based on a difference between the first position information and the second position information; and Update the mapping information based on the correction factor, wherein the controller is further configured to: Select a discrete transmission angle; For the selected discrete transmission angle, select a first detection range and a second detection range; Trigger the light source at a transmission time to generate a laser beam whose transmission direction corresponds to the selected discrete transmission angle; Enable the plurality of pixels of the 2D photodetector array during a measurement window corresponding to the transmission time; Based on the electrical signals generated by the plurality of pixels, evaluate a first intensity of each pixel among the plurality of pixels for the first detection range and evaluate a second intensity of each pixel among the plurality of pixels for the second detection range; For the first detection range, at least one first pixel having the highest first intensity among the plurality of pixels is identified as the at least one received pixel, and for the second detection range, at least one second pixel having the highest second intensity among the plurality of pixels is identified as the at least one received pixel; calculate the correction factor based on the difference between the first position information and the second position information; and update the mapping information based on the correction factor.

16. A method for calibrating a light detection and ranging LIDAR system, the method comprises: configuring a LIDAR transmitter with a first field of view; configuring a LIDAR receiver with a second field of view; transmitting laser beams into the first field of view at a plurality of discrete transmission angles so as to scan the first field of view with the laser beams; receiving reflected laser beams from the second field of view; generating an electrical signal based on the received reflected laser beams; moving at least one of the first field of view or the second field of view based on misalignment so as to optimize the overlap between the first field of view and the second field of view; select a discrete transmission angle; trigger a light source at a transmission time to generate a laser beam whose transmission direction corresponds to the selected discrete transmission angle; enable the plurality of pixels of a 2D photodetector array during a measurement window corresponding to the transmission time; evaluate the intensity of each of the plurality of pixels based on the electrical signals generated by the plurality of pixels; select at least one first pixel having the highest intensity from among the plurality of pixels as the at least one target pixel; and update mapping information to link the at least one target pixel to the selected discrete transmission angle, wherein the mapping information maps different discrete transmission angles to different target pixels among the plurality of pixels.

17. The method according to claim 16, further comprises: detect the misalignment between the first field of view and the second field of view based on the electrical signal; and move at least one of the first field of view or the second field of view based on the detected misalignment so as to optimize the overlap between the first field of view and the second field of view.

18. The method according to claim 17, further comprises: compare the expected position where a reflected laser beam is expected to be incident on the LIDAR receiver with the actual position where the reflected laser beam is incident on the LIDAR receiver, wherein the expected position is mapped to a discrete transmission angle, and the laser beam associated with the reflected laser beam is transmitted at the discrete transmission angle; calculate a correction factor based on the difference between the expected position and the actual position; and move at least one of the first field of view or the second field of view based on the correction factor.

19. The method according to claim 17, further comprises: detect the area of the LIDAR receiver on which the reflected laser beam is incident; and Link the detected region to a discrete transmission angle, and transmit the laser beam associated with the reflected laser beam at the discrete transmission angle such that the detected region is activated when subsequent laser beams are transmitted at the discrete transmission angle.

20. The method according to claim 17, wherein detecting the misalignment comprises: detecting an angle of misalignment between the first field of view and the second field of view, the method further comprising: calculating a correction factor based on the detected angle of misalignment; and moving at least one of the first field of view or the second field of view based on the correction factor.

21. The method according to claim 17, wherein detecting the misalignment comprises: detecting a misalignment offset between the first field of view and the second field of view, the method further comprising: calculating a correction factor based on the detected misalignment offset; and moving at least one of the first field of view or the second field of view based on the correction factor.

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