Optical system, method, and device to increase lidar dynamic range

Abstract

To provide an improved lidar device, system and method.SOLUTION: A lidar device, system and method are provided that are for improving a dynamic range performance of a lidar sensor. A light detection and ranging sensor system comprises: a laser transmitter that is configured to transmit a laser beam to a target object; and a receiving optics device. The receiving optics device further comprises: a receiving lens that is configured to receive a returning beam from the target object and focus the returning beam from the target object on a detector; an optical lidar dynamic control lens that is installed on a section of the receiving lens, in which a part of the returning beam from the target object passes through the optical lidar dynamic control lens and the optical lidar dynamic control lens is configured to focus the returning beam from the target object to the detector; and the detector that is configured to receive the returning beam from the receiving optics device for measuring a measurement range between the sensor system and the target object.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The following relates generally to lidar sensors, and more particularly to devices, systems, and methods for improving the dynamic range performance of lidar sensors. [Background technology]

[0002] Lidar sensors work on the principles of Light Detection and Ranging (LIDAR) technology. Lidar technology provides remote sensing capabilities to interrogate target objects at great distances. Lidar sensors measure range by emitting a laser beam and measuring the time of flight (TOF) or phase change of the return beam that bounces off the target.

[0003] Lidar sensors are used to measure distances from targets and generate three-dimensional representations of targets, including the Earth's surface and physical structures. Other uses of lidar sensors include atmospheric studies, such as measuring wind speed, temperature, and particle concentrations at various altitudes; topographical surveys, such as generating highly accurate elevation data and landscape modeling; and meteorology. Developments in lidar technology and lidar sensors have expanded the use of lidar to new areas, including driverless cars, mining, wildlife conservation, and disaster management.

[0004] In space operations, lidar sensors have become indispensable in space missions to measure range or distance to generate 3D images of target objects. Lidar sensors have also been used in space exploration, such as mapping celestial bodies, natural satellites, and planetary surfaces. In navigation operations, lidar sensors have been used by space missions in spacecraft docking and rendezvous, satellite servicing, and space debris removal. Lidar sensors have also been used in landing operations on the Moon, Mars, and asteroids.

[0005] Conventional approaches to increasing lidar measurement range add complexity, volume, and mass to the lidar system and lidar sensor, and also require a larger number of components, thereby increasing damage risk and cost.

[0006] For space applications, lidar systems are required to meet measurement range requirements with minimal complexity and improved MVP (mass, volume, and power) performance.

[0007] A standard method for extending the lidar measurement range involves installing two separate lidar sensors, one of which is configured to operate for a long measurement range and the other lidar sensor to operate for a short measurement range. An alternative method is to install two laser emitters in one lidar sensor, one laser with a high emission pulse peak power and the other laser with a somewhat lower lidar emission pulse peak power compared to the first laser. Two lasers may also be installed in a lidar system with two receiving paths and two detectors.

[0008] Yet another standard method to extend the lidar measurement range is to install two sets of receivers in one lidar system, including one high-sensitivity receiver and another low-sensitivity sensor. Each receiver includes a receiving optics and a photodetector. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] U.S. Patent Application No. 20140078514 Summary of the Invention [Problem to be solved by the invention]

[0010] Therefore, there is a need for improved lidar devices, systems, and methods for improving the dynamic range performance of lidar sensors that overcome at least some of the disadvantages of existing systems and methods. [Means for solving the problem]

[0011] An optical detection and ranging ("LIDAR") dynamic control device is provided, the device including a receiver lens configured to receive a return beam from a target object and focus the return beam from the target object on a detector, and an optical LIDAR dynamic control lens mounted on a section of the receiver lens, where a portion of the return beam from the target object passes through the optical LIDAR dynamic control lens, and the optical LIDAR dynamic control lens is configured to focus the return beam from the target object on the detector.

[0012] The optical lidar dynamic control lens can be constructed as a freeform optics component.

[0013] The optical lidar dynamic control lens may include a continuous contour of the optical surface.

[0014] The design of the optical LIDAR dynamic control lens may be based on several parameters, including any two or more of the minimum measurement range required, the separation distance between the receiving aperture and the laser beam, the receiving aperture size, and the laser beam size.

[0015] The optical LIDAR dynamic control lens may include a lens array of multiple lenslets, each of which focuses a point source along the return beam onto a detector.

[0016] The subapertures of the multiple lenslets may provide sufficient area for collecting light.

[0017] The receiver lens may include a hole for receiving the optical lidar dynamic control lens.

[0018] The optical lidar dynamic control lens may overlap a section of the receiver lens.

[0019] A light detection and ranging ("lidar") sensor system is provided that includes a laser emitter configured to emit a laser beam to a target object, a receiver optics device including a receiver lens configured to receive a return beam from the target object and focus the return beam on a detector, an optical lidar dynamic control lens mounted on a section of the receiver lens, where a portion of the return beam from the target object passes through the optical lidar dynamic control lens, the optical lidar dynamic control lens configured to focus the return beam from the target object on the detector, and a detector configured to receive the return beam from the receiver optics device to measure a measurement range between the lidar sensor system and the target object.

[0020] The optical lidar dynamic control lens may be constructed as a freeform optical system component.

[0021] The optical lidar dynamic control lens may include a continuous contour of the optical surface.

[0022] The design of the optical LIDAR dynamic control lens may be based on several parameters, including any two or more of the minimum measurement range required, the separation distance between the receiving aperture and the laser beam, the receiving aperture size, and the laser beam size.

[0023] The optical lidar dynamic control lens may include a lens array of multiple lenslets, each of which focuses a point source along the return beam onto a detector.

[0024] The subapertures of the multiple lenslets may provide sufficient area for collecting light.

[0025] The receiver lens may include a hole for receiving the optical lidar dynamic control lens.

[0026] The optical lidar dynamic control lens may overlap a section of the receiver lens.

[0027] Other aspects and features will become apparent to those of ordinary skill in the art upon review of the following description of several exemplary embodiments.

[0028] The drawings included herein are intended to illustrate various examples of the articles, methods, and apparatus herein. [Brief description of the drawings]

[0029] [Figure 1] FIG. 1 is a schematic diagram of a lidar system 100 in a monostatic optical configuration. [Diagram 2] FIG. 2 is a schematic diagram of a lidar system 200 in a bistatic optical configuration. [Diagram 3] 1 is a graphical plot of returned power versus measurement range for a monostatic optical system, a bistatic optical system, and a bistatic optical system according to the present disclosure. [Figure 4] FIG. 1 is a schematic diagram of a lidar system having an optical lidar dynamic control (OLDC) device, according to one embodiment. [Diagram 5] FIG. 1 is a schematic diagram illustrating the calculation of the power level of a return optical beam in a LIDAR system having an OLDC device, according to one embodiment. [Figure 6] 1 is a schematic diagram illustrating a comparison between a conventional circular lens and a freeform optics (FFO) lens, according to one embodiment. [Figure 7] FIG. 1 is a schematic diagram of an OLDC device on a receiving lens, according to one embodiment. [Figure 8A] FIG. 2 is a schematic diagram of one configuration for an OLDC device, according to one embodiment. [Figure 8B] FIG. 13 is a schematic diagram of another configuration for an OLDC device, according to one embodiment. [Figure 9]1 is a graphical plot of return power versus measurement range from a LIDAR with bistatic optics with an OLDC in accordance with one embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] Various devices or processes are described below to provide examples of each of the claimed embodiments. The embodiments described below do not limit any claimed embodiment, and any claimed embodiment may cover a process or device different from the process or device described below. The claimed embodiments are not limited to a device or process having all of the features of any one device or process described below, or to features common to multiple or all of the devices described below.

[0031] One or more systems described herein may be implemented as computer programs executing on programmable computers, each of which includes at least one processor, a data storage system (including volatile and non-volatile memory and / or storage elements), at least one input device, and at least one output device. For example, and without limitation, the programmable computer may be a programmable logic unit, a mainframe computer, a server, and a personal computer, a cloud-based program or system, a laptop, a personal data assistant, a mobile phone, a smartphone, or a tablet device.

[0032] Each program is desirably implemented in a high level procedural or object-oriented programming language and / or scripting language to communicate with a computer system. However, the programs may be implemented in assembly or machine language, if desired. In either case, the language may be a compiled or interpreted language. Each such computer program is desirably stored on a general purpose or special purpose programmable computer-readable storage medium or device for configuring and operating the computer when the storage medium or device is read by a computer to perform the procedures described herein.

[0033] A description of an embodiment having several components in communication with each other does not imply that all such components are required. On the contrary, a variety of optional components are described to illustrate a variety of possible embodiments of the present invention.

[0034] Additionally, although process steps, method steps, algorithms, or the like may be described (within this disclosure and / or in the claims) in a sequential order, such processes, methods, and algorithms may be configured to work in alternative orders. In other words, any sequence or order of steps that may be described does not necessarily indicate a requirement that the steps be performed in that order. Steps of processes described herein may be performed in any order that is practical. Additionally, some steps may be performed simultaneously.

[0035] It will be readily apparent that when a single device or article is described herein, two or more devices / articles (whether they cooperate or not) may be used in place of the single device / article. Similarly, when two or more devices or articles are described herein (whether they cooperate or not), it will be readily apparent that a single device / article may be used in place of the two or more devices or articles.

[0036] The following relates generally to lidar sensors, and more particularly to devices, systems, and methods for improving the dynamic range performance of lidar sensors.

[0037] The systems and methods of the present disclosure may increase the return optical signal level for any type of lidar, such as a lidar that measures range by measuring the time of flight (TOF) or phase change of the return beam bounced by a target. In some cases, the present disclosure may be applied in heterodyne lidar or photon counting lidar.

[0038] A lidar sensor generally includes various components that are responsible for transmitting, receiving, and processing the optical signals used in the lidar measurements. The main components of a lidar sensor are: (a) a laser beam generator for generating a beam of light directed toward a target, the light may correspond to different wavelengths based on the nature of the target and the type of incident light; (b) delivery optics, which are various lenses and mirrors that shape and direct the laser beam toward the target; (c) a scanning mechanism, which may be a mirror or prism that moves in a predetermined pattern to scan the laser beam over the target area; (d) receiving optics, which are various lenses or mirrors that collect the reflected light from the target object and direct it towards the detector, the size and design of these optics can affect the amount of light collected and the resolution of the measurement result; and (e) a photodetector, which is a device for converting the received light into an electrical signal or data for measuring range and mapping the target object, where the sensitivity of the detector to the wavelength of the laser light and the strength of the return signal can affect the performance of the LIDAR system; and (f) an optical filter, which is a component for blocking light beams of unnecessary wavelengths to improve the accuracy of the measurement results; (g) Beam splitters and dichroic mirrors, which are components for separating or combining beams of different wavelengths.

[0039] The receiving optics in a lidar sensor collects different return light beams from a target object given different measurement ranges of the target, especially for diffusive targets that scatter the incident light in many directions.

[0040] The maximum measurement range of a lidar sensor refers to the farthest distance at which the lidar sensor can effectively detect and accurately measure a target object.

[0041] The maximum measurement range is determined by the lidar equation:

[0042]

number

[0043] In the equation, P is the peak power of the lidar return signal, i.e., the highest power level of the reflected laser pulse detected by the lidar sensor. The lidar sensor measures the power level and time of the return signal to determine the distance and mapping of diffuse targets. Diffuse targets return a light beam at a lower power level compared to a light beam returned from a specular target. P is measured in watts (W).

[0044] ρ is the reflectivity of a diffuse target. Reflectivity refers to the proportion of the laser light reflected from a target object relative to the incident laser light. Although the reflected light may propagate in all directions, only a portion of the reflected light may be received by the lidar sensor.

[0045] P t P refers to the threshold of the LIDAR receiver. The LIDAR receiver threshold is the minimum power level of the returning light beam that can be detected by the LIDAR receiver. The LIDAR receiver can be dynamically adjusted based on the operating conditions to avoid ambient light and accurately detect the returning light beam.t is measured in watts (W).

[0046] P0 is the peak power of the lidar fire pulse. The peak power of the lidar fire pulse is the maximum power output of the laser pulse when it is first emitted from the lidar sensor. The maximum measurement range and resolution of the lidar sensor are directly related to the peak power of the lidar fire pulse. P0 is measured in watts (W). The maximum measurement range R is proportional to the square root of the peak power of the lidar fire pulse for a diffuse target. Higher lidar peak power generally provides higher resolution. However, the exact and detailed relationship between lidar peak power and resolution depends on the specific design.

[0047] A is the area of ​​the receiving optical aperture, i.e., the area of ​​the detector or receiving optical lens that captures the reflected optical signal from the target.

[0048] R is the measurement range or distance between the lidar sensor and the target object. The return power level of the light beam is proportional to the inverse root square of the distance between the sensor and the target object.

[0049] To increase the measurement range of the lidar sensor, the peak power (P0) of the lidar emission pulse may be increased. However, this increment may lead to heating of the laser and other components of the lidar sensor. Therefore, additional measures may be required to manage the heat and operation of the system.

[0050] Furthermore, to increase the measurement range of the lidar sensor, the area (A) of the receiving optical aperture may be increased. However, this increases the size and weight of the lidar sensor, which may make it difficult to transport and deploy. Furthermore, a larger area (A) of the receiving optical aperture may introduce optical aberrations, thereby reducing the quality of the measurement results.

[0051] An optical solution for a lidar sensor system is disclosed herein. The lidar sensor system includes an optical solution that manages a "very high" dynamic range by controlling the amount of return light beam onto the lidar detector depending on the target measurement range. As a result, the ranging performance of the lidar sensor system is improved with a simpler and less complex lidar sensor system.

[0052] Referring now to FIG. 1, a lidar system 100 in a monostatic optical configuration is shown therein.

[0053] In a monostatic optical configuration, the laser projector and the incident beam receiver share the same optical path. Therefore, the outgoing and returning laser beams from the lidar system are coaxial. Lens 120 is part of the receiving optics. Laser 110 emits the outgoing laser beam from the lidar system. For illustrative purposes, three targets 1, 2, and 3 are shown. The targets are placed at various distances on the path, i.e., target 1 is placed closer to the receiving optics, target 2 is placed farther away than target 1, and target 3 is placed farthest compared to both target 1 and target 2.

[0054] When the outgoing laser beam hits a target object, the light is reflected, refracted, or scattered depending on the characteristics of the target and the wavelength of the laser beam. The returning laser beam is received by a lens that focuses the returning laser beam onto a detector 130. The laser spot on the target is imaged onto the receiving detector, regardless of the target measurement range.

[0055] Referring now to FIG. 2, a lidar system 200 in a bistatic optical configuration is shown therein.

[0056] In a bistatic optical configuration, the laser projector and the incident beam receiver are physically separated and do not share the same optical path. Therefore, the outgoing and returning laser beams from the lidar system are not coaxial and follow different paths. Lens 220 is part of the receiving optics. Laser 210 emits the outgoing laser beam from the lidar system. For illustrative purposes, three target objects 1, 2, and 3 are shown. The target objects are placed at various distances on the path, i.e., target object 1 is placed closer to the receiving optics, target object 2 is placed farther away than target object 1, and target object 3 is placed at the farthest distance compared to both target object 1 and target object 2.

[0057] When the outgoing laser beam hits a target object, the light is reflected, refracted, or scattered depending on the target characteristics and the wavelength of the laser beam. The returning laser beam is received by a lens that focuses the returning laser beam onto a detector 230. The laser spot on the target is imaged onto the receiving detector, regardless of the target measurement range.

[0058] In a bistatic lidar system, the power level of the returning laser beam from targets at short distances (target object 1 and target object 2) is reduced. This occurs because the image spots 240a and 240b of the laser spot on the target object are shifted away from the detector due to triangulation effects. As a result, the image spots of the laser beam are only partially on the detector compared to a monostatic system, leading to power loss. Furthermore, the image spots 240a and 240b are not in focus and are larger than the detector on the focal plane where the detector is located compared to a monostatic system, leading to further power loss. The APD (Avalanche Photodiode) detectors in lidar systems are usually very small (less than 200 μm) to be fast enough for pulse detection.

[0059] Referring now to FIG. 3, there is shown a graphical plot 300 of returned power versus measurement range for a monostatic optical system, a bistatic optical system, and a bistatic optical system according to an embodiment of the present disclosure.

[0060] In a monostatic lidar system 302, the power level of the return light, when plotted on a logarithmic scale, shows a linear decrease as the distance between the target object and the lidar system increases. The power drop is from 10 W to 10 W for distances from 1 m to 10,000 m. -7 Up to W.

[0061] The graphical plot 300 is provided for illustration purposes with a specific lidar peak power, area of ​​the receiving aperture, and target reflectivity. According to one embodiment, a straight line on a logarithmic scale is fit for a diffusive target. Most common targets can be modeled as diffusive targets from the so-called lidar equation. There is no general equation for other types of targets such as retroreflectors. From 10 W to 10-7 W, the reduction in return pulse power is a factor of 10E-8, which is 1 / (R ∧ 2), i.e., (1 / 10000 ∧2 )=10E-8. In a bistatic lidar system 304, the power level of the return light remains substantially constant when the distance between the lidar system and the target is between about 1 m and over 100 m. Curve 302 for the monostatic case is mathematically correct under the assumption that the image spot is on the APD, which in this test is smaller than the APD, and all of the return light collected by the lens is received by the APD. Curves 304 and 306 below 100 m are approximated for illustration purposes. Above 100 m, the triangulation effect is small, and curves 304 and 306 nearly overlap with curve 302.

[0062] This occurs because the location of image spot 240c is formed on the detector. However, a sharp drop in the power level of the return beam is observed for distances less than 100 m. This occurs because image spots 240a and 240b are not formed on the detector. The shift of image spots 240a and 240b is determined by the characteristics of the circular focusing lens 220. As the distance between the lidar system and the target object approaches zero, a large shift occurs. In this graph, the power level of the return light beam is observed below the lidar receiver threshold level for distances less than 30 m to 40 m. As a result, the bistatic lidar system cannot report distance measurements for distances below 30 m to 40 m. Because the power level of the return laser beam falls off with the distance between the lidar sensor and the target object, the spot size of the incident laser, and the inverse square root of the target measurement range, conventional circular optics do not provide the degree of freedom to manage the return power level over the entire measurement range.

[0063] Referring now to FIG. 4, a lidar system having an optical lidar dynamic control (OLDC) device is shown therein, according to one embodiment.

[0064] The OLDC device 450 may be either attached to the main receiving lens 420 as part of the receiving optics or mounted separately. As used herein, the term "circular" generally refers to the shape in which the lens is cut. For example, the two lenses in FIG. 6 are both cut in a circle but have different surface profiles. The terms "spherical", "aspherical" and "cylindrical" are used to describe the lens surface profile. In one embodiment, the receiving lens 420 is a spherical lens or an aspherical lens (we used both in a practical implementation). A cylindrical lens has a surface shape similar to a cylinder. A cylindrical lens may be cut in a rectangle. A cylindrical lens may be cut in a circle. In one embodiment, the receiving lens 420 may act as the main receiving lens. The receiving lens 420 may also be referred to herein as a lenslet (or lenslet 420).

[0065] In one embodiment, the OLDC device 450 covers a section of the receiving lens 420. Preferably, most of the area of ​​the receiving lens 420 is unaffected for collecting returning light beams from distant targets and focuses the returning light beam 440c onto the detector 430. For returning light beams from closer targets, the OLDC device 450 modifies the direction of the returning light beam to focus the light beam onto the detector 430.

[0066] 4, the return laser beams (1i and 2i) from closer targets, i.e., target object 1 and target object 2, are formed on the receiving lens 420, and image spots 440a and 440b are focused outside the detector 430. The return laser beams (1ii and 2ii) are formed on the OLDC device 450. As a result, the image spot 440c is focused on the detector 430, despite returning from a different target object distance.

[0067] Referring now to FIG. 5, a calculation of the power level of a return optical beam on a LIDAR system having an OLDC device (e.g., OLDC device 450 of FIG. 4) is shown therein, according to one embodiment.

[0068] P1 and P2 refer to the drop in optical power at two optical sub-apertures s1 and s2 on the OLDC device after the returning laser beam hits two target objects (target object 1 and target object 2).

[0069] The laser return powers P1 and P2 are a function of many parameters, including the emitted laser power P0, the laser spots on the object (a1 and a2), the object BDRFs (bidirectional reflectance functions) BDRF1 and BDRF2, the measurement ranges of objects R1 and R2, the horizontal distances d1 and d2, and the solid angles ω1 and ω2 subtended by s1 and s2.

[0070] According to one embodiment, P1 and P2 may be presented as functions of other parameters as P1 = f(P0, R1, d1, a1, s1, BDRF1, ω1), and P2 = f(P0, R2, d2, a2, s2, BDRF2, ω2).

[0071] According to an embodiment, assuming sub-apertures s1 and s2 in the OLDC image and laser spots a1 and a2 on the focal plane as the imaged spots of a3 and a4, the relationship between the laser spots and the imaged spots can be related by defining an imaging transfer function H. The imaging transfer function H transfers the laser spot in the object space to the imaged spot on the imaging plane of the optical system. The imaging transfer function H depends on the surface shape and material properties of the optical system of the sub-aperture. If the imaging transfer functions of the sub-apertures s1 and s2 are H1 and H2, a3 and a4 can be expressed as a3=H1(a1) and a4=H2(a2). If the detector surface ad is placed on the focal plane at (x0 and y0), the powers P3 and P4 received by the detector from the laser spots a1 and a2 can be expressed as P1 and P2 times the 2D convolution functions between the ad spot and the a3 spot and between the ad spot and the a4 spot, respectively, as P3=P1×∬ad(x-x0,y-y0)*a3(x,y)dxdy and P4=P2×∬ad(x-x0,y-y0)*a4(x,y)dxdy, where the function ad is 1 if the position is inside the detector and 0 if the position is outside the detector.

[0072] Referring now to FIG. 6, a comparison between a conventional spherical lens 602 and a freeform optics (FFO) lens 604 is shown therein, according to one embodiment.

[0073] Conventional optics, such as spherical lens 602, include translational or rotational symmetry. In this case where the optimization design is constrained by many parameters, conventional optics do not provide enough degrees of freedom. Conventional optics may not keep the return light focused on a small detector as the laser spot on the target object moves along the measurement range direction. In recent years, advances in design, manufacturing, and testing have allowed freeform optics (FFOs), such as those implemented in FFO lens 604, to emerge as a practical method to achieve performance that cannot be provided by conventional optics. OLDCs can be designed and manufactured as FFO components to achieve optimized performance.

[0074] To achieve nearly constant return power in the near measurement range, the continuous contour of the optical surface provided by the freeform optics (FFO) is necessary for the design of the OLDC. Various algorithms are developed to design the FFO optics. According to one embodiment, for the optical lidar dynamic control (OLDC), the design desirably depends on several parameters including the required minimum measurement range, the separation between the receiving aperture and the laser beam, the receiving aperture size, and the laser beam size.

[0075] In one embodiment, the dimensions of the primary receiving lens are determined by the maximum measurement range requirement, such that R is equal to the maximum range Rmax when P=Pt. For a given P0 and Pt, the dimensions of the primary receiving lens are determined by A (area of ​​a circular lens). In one embodiment, the area of ​​the FFO lens should not exceed a few percent, such as less than 5-10% of the area of ​​the primary receiving lens, because the return light reflected from distant targets will not be focused by the FFO lens onto the detector. Since the FFO lens works on the reflected light from close targets, a small size to design (e.g., less than 5% of the area of ​​the primary receiving lens) may be sufficient. In general, the optimal FFO lens size and location will depend on the specific requirements for each sensor, but the design principles of the FFO remain the same.

[0076] 7, there is shown a side perspective view 700 of a primary receive lens 702 having an OLDC device 704 thereon, according to one embodiment. The OLDC device 704 may be the OLDC device 450 of FIG.

[0077] In one embodiment, the OLDC device 704 is an array of cylindrical lenses mounted within the primary receiving lens 702. The OLDC can be an array of cylindrical lenses or freeform optics. Additionally, the OLDC can be an array of spherical or aspheric lenses, but spherical or aspheric lenses may not work optimally since the collected light that falls on the detector may be weak. The OLDC itself does not include any part of the primary receiving lens when it is attached to the primary receiving lens, and its design must take into account the optical power of the primary receiving lens to ultimately provide the required functionality.

[0078] According to one embodiment, the OLDC device 704 refers to a lens array or lenses that includes multiple small spherical lenses. Each of the small spherical lenses focuses the point source onto the detector along a line connecting the laser beam spot and the center of the detector. This situation is only true if each spherical lens is small, such as less than 200 μm in diameter. Otherwise there would not be enough space for all the spherical lenses to image onto the detector the laser spots that are generated in different locations when the target measurement range changes. In this case, the aperture of each lens is 0.1 mm (or 0.0314 mm) in diameter. 2 ) aperture is very small and the collected light falling on the detector is too small to be practically useful. In a practical design, each sub-aperture of the OLDC has a sufficient area to collect enough light. The design objective is to have sufficient and nearly constant return power (curve 304) falling on the detector shown in FIG. 2 as the finite size laser spot moves along the measurement range direction. As the laser spot moves along the measurement range direction, the power on the detector is kept nearly constant because the finite imaged spot moves in and out of the detector (e.g., 200 μm diameter).

[0079] 8A and 8B, there are shown two configurations 800, 850 for an OLDC device, such as OLDC device 450 of FIG 4 or OLDC device 704 of FIG 7, according to one embodiment. Each configuration includes a laser beam 808.

[0080] In a first configuration 800 shown in Figure 8A, the OLDC device is placed in an area where there is no primary receiving lens, i.e., where there is a hole on the primary receiving lens for the OLDC. In one embodiment, the OLDC device is placed outside the primary receiving lens.

[0081] In a second configuration 850 shown in FIG. 8B, the OLDC device (e.g., 704 in FIG. 7) is mounted on the primary receiving lens (702 in FIG. 7). In this configuration, the optical transfer function of the OLDC device should be designed to include the optical transfer function of the primary receiving lens at its location to achieve that function. An explanation of the work of freeform optics (FFO) in design according to one embodiment is provided. As shown in FIG. 8A and FIG. 8B, we explore a concept involving a more symmetrical optical system, namely an array of spherical lenslets including spherical lenslet 1 802 and spherical lenslet 2 804, or an array of aspheric lenslets as a way to receive reflected light from target 1 808 and target 2 810 to detector 806. In a spherical or aspheric lens, the focal point is along the line connecting the light source and its center. Two lenslets 802, 804 are shown in FIG. 8A. A cone of light from target 1 808 hits detector 806 with its central ray passing through the center of circular lenslet 1 802 in FIG. 8A. A cone of light from target 2 810 hits detector 806 with its central ray passing through the center of lenslet 2 804. However, the cone of light from target 2 810 would not hit detector 806 if the center of the light cone passed through the center of lenslet 1 802. To receive reflected light from all points between target 1 808 and target 2 810, many lenslets would be needed to replace lenslet 1 802 and lenslet 2 804, which may cause the area of ​​each lenslet to be small (e.g., a diameter of less than a few hundred microns). Because the light received by detector 806 is proportional to the area of ​​each lenslet, the amount of light received does not create a sufficient electrical signal.

[0082] However, as shown in FIG. 8B, if the lenslets 802, 804 are replaced by a less symmetrical optical system, for example an array of cylindrical lenses 814, more design freedom is possible. This also allows for more light to be obtained on the detector 806. With a cylindrical lens 814, it focuses the light in a line along its length. The lens 814 can have a much larger height (out of the page) to collect more light from a larger surface. In FIG. 8B, the light reflected between target 1 808 and target 2 810 is focused in a line with a dimension slightly longer than the detector 806. Furthermore, the width of the line, controlled by the radius of the cylindrical lens 814, is also slightly wider than the detector 806. As a result, the detector 806 receives sufficient light from the targets at any position from target 1 808 to target 2 810. In the FFO design, the smooth contour of the surface can be considered for a surface that includes multiple cylindrical lenses 814. One of the cylindrical lenses 814 may provide an optimized length and width of the image line covering the detector 806 depending on the distance of one target section between target 1 808 and target 2 810.

[0083] Note that the above description assumes that there is no primary receiving lens. If the FFO is mounted over the primary receiving lens, then the surface of the FFO, in addition to its optical functions described above, must include optical power to counteract the optical focusing power from the primary circular lens.

[0084] Freeform optics (FFOs) may be difficult to design, manufacture, and verify using conventional techniques, since they do not have translational or rotational symmetry. According to one embodiment, an array of conventional optical components may be used as a segment that approximates the functionality of a freeform optics-based OLDC device. According to one embodiment, an array of cylindrical lenses is used for this purpose, each cylindrical lens focusing light from a laser spot within a certain measurement range (e.g., 1m-2m, 2m-10m, 10m-100m) onto a detector with several overlapping imaging spots. The cylindrical lenses may be designed with various parameters (curvature and size) to keep the collected return power approximately constant in a close measurement range, as expected from a freeform optics-based OLDC device.

[0085] One cylindrical lens may be designed to collect reflected light from one measurement range section (e.g., 1 m to 2 m). In one embodiment, the shape and size of the lens are designed to create a line that overlaps with the detector. The line width of the line is desirably slightly larger than the size of the detector (e.g., 200 μm). The length of the line may be long enough to cover the detector to minimize optical losses. Multiple cylindrical lenses may be used for different measurement range sections. The total area occupied by the cylindrical lens array is desirably kept to no more than a few percent of the total area of ​​the primary receiving lens to minimize the impact on the maximum measurement range of the lidar.

[0086] Referring now to FIG. 9 , a graphical plot of return power versus measurement range from a LIDAR with bistatic optics and an OLDC is shown therein, in accordance with one embodiment.

[0087] Curves 902, 904 and 906 are all recorded for a diffusive target at a measurement range of up to 2000 meters. A diffusive target reflects light in all directions, which is a good estimate for most common objects. It can be easily modeled without the need for specific details. Curve 902 in a log-log scale represents the measurement range versus the returned power for a lidar with monostatic optics. In this case, the returned power from a diffusive target is inversely proportional to the range square of the measurement range. The returned power is above the detector threshold (shown by curve 906) over a measurement range of 1 km. At 1 meter, the returned optical power is the inverse square of the ratio (1000m / 1m) 2 or a million times higher than the returned optical power at 1000 m from the detection threshold. This variation is usually beyond the dynamic range of the detector electronics, which can cause problems for the lidar to work at close measurement ranges or to report accurate ranging results.

[0088] Curve 906 is the return power from the bistatic optical system. The third line shows that the bistatic optical system collects a similar amount of light as the monostatic optical system at the far measurement range. However, at the near measurement range, the triangulation effect (parallax effect) causes the return image spot to fall off the detector. Therefore, the bistatic lidar can have the same maximum measurement range of 1 km, but it cannot detect objects at less than 15 m. Curve 904 shows the return power from the bistatic optical system with OLDC. In this case, the designed OLDC keeps the return power almost constant from 1 m to 20 m, and it keeps the return power within 20 db from 1 m to 1000 m, compared to 60 db for the monostatic optical system.

[0089] Compared to designs that use dual laser emitters (high and low power) or a split return beam directed onto two detectors, the OLDC device controls the amount of return light that falls on the lidar detector depending on the target measurement range.

[0090] The OLDC device provides a bistatic lidar system that has smaller mass, size, and power consumption while maintaining performance.

[0091] The OLDC device can be implemented in a bistatic lidar architecture that overcomes the short measurement range weaknesses of the bistatic optical path while maintaining the backscattering robustness of the bistatic optical path.

[0092] The disclosed system uses a lidar operating in a bistatic optical configuration. An example of such a scanning bistatic lidar is U.S. Patent Application Publication No. 20140078514, Wide-Angle Bistatic Scanning (WABS) lidar.

[0093] The systems and methods of the present disclosure may be applicable to lidars that need to have a short minimum measurement range (e.g., 1 meter) to a very long measurement range (e.g., 1 kilometer). The systems and methods of the present disclosure may be implemented in space applications such as landing lidars and rendezvous and docking lidars.

[0094] Although the above description provides examples of one or more devices, methods, or systems, it will be appreciated that other devices, methods, or systems are within the scope of the claims as interpreted by one of ordinary skill in the art. [Explanation of symbols]

[0095] 100 Lidar System 110 Laser 120 Lens 130 Detector 200 Rider System 210 Laser 220 Lens 230 Detector 240a Image Spot 240b Image Spot 240c Image Spot 300 Graphical Plots 302 Monostatic Lidar System, Curved 304 Bistatic Lidar System, Curved 306 curve 400 Optical system 410 Laser 420 Lens 430 Detector 440a Image Spot 440b Image Spot 440c Image Spot 450 Optical Lidar Dynamic Control (OLDC) Device 500 Optical system 602 Conventional spherical lens 604 Freeform Optical System (FFO) Lens 700 Main receiving lens, side perspective view 702 Main receiving lens 704 OLDC device 800 Configuration 802 Spherical Small Lens 804 Spherical Small Lens 806 Detector 808 Target 810 Target 814 Cylindrical Lens 850 Configuration 902 curve 904 curve 906 curve

Claims

1. 1. An optical light detection and ranging ("lidar") dynamic control device, comprising: a receiving lens configured to receive the return beam from the target object and focus the return beam from the target object onto a detector; an optical lidar dynamic control lens disposed over a section of the receiving lens; Including, A device wherein a portion of the return beam from the target object passes through the optical LIDAR dynamic control lens, the optical LIDAR dynamic control lens being configured to focus the return beam from the target object onto the detector.

2. 10. The device of claim 1 , wherein the optical lidar dynamic control lens is configured as a freeform optical component.

3. 10. The device of claim 1 , wherein the optical lidar dynamic control lens comprises a continuous contour of an optical surface.

4. 10. The device of claim 1 , wherein a design of the optical LIDAR dynamic control lens is based on multiple parameters including any two or more of a required minimum measurement range, a separation distance between a receiving aperture and a laser beam, a receiving aperture size, and a laser beam size.

5. 2. The device of claim 1, wherein the optical LIDAR dynamic control lens comprises a lens array of a plurality of lenslets, each of the plurality of lenslets focusing a point source along the return beam onto the detector.

6. The device of claim 5 , wherein each sub-aperture of the plurality of lenslets provides a sufficient area for collecting light.

7. The device of claim 1 , wherein the receiver lens includes a hole for receiving the optical lidar dynamic control lens.

8. The device of claim 1 , wherein the optical LIDAR dynamic control lens overlaps the section of the receiver lens.

9. 1. A light detection and ranging (lidar) sensor system, comprising: a laser transmitter configured to transmit a laser beam to a target object; A light receiving optical system device; The light receiving optical system device includes: a receiving lens configured to receive the return beam from the target object and focus the return beam onto a detector; an optical lidar dynamic control lens mounted on a section of the receiving lens, a portion of the return beam from the target object passing through the optical lidar dynamic control lens, the optical lidar dynamic control lens configured to focus the return beam from the target object onto the detector; a detector configured to receive the return beam from the receiving optics to measure a measurement range between the lidar sensor system and the target object; A sensor system comprising:

10. 10. The sensor system of claim 9, wherein the optical LIDAR dynamic control lens is configured as a freeform optical component.

11. 10. The sensor system of claim 9, wherein the optical LIDAR dynamic control lens includes a continuous contour of an optical surface.

12. 10. The sensor system of claim 9, wherein a design of the optical LIDAR dynamic control lens is based on multiple parameters including any two or more of a required minimum measurement range, a separation distance between a receiving aperture and a laser beam, a receiving aperture size, and a laser beam size.

13. 10. The sensor system of claim 9, wherein the optical LIDAR dynamic control lens includes a lens array of a plurality of lenslets, each of the plurality of lenslets focusing a point source along the return beam onto the detector.

14. The sensor system of claim 13 , wherein each sub-aperture of the plurality of lenslets provides a sufficient area for collecting light.

15. The sensor system of claim 9 , wherein the receiver lens includes a hole for receiving the optical lidar dynamic control lens.

16. The sensor system of claim 9 , wherein the optical LIDAR dynamic control lens overlaps the section of the receiver lens.

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