LiDAR system with transmission optical power monitor

Abstract

A LiDAR transmitter with optical power monitoring includes a laser array positioned in a first plane that generates optical beams that propagate along optical paths. A first projection optical element positioned in the optical paths projects multiple optical beams that overlap at a common point. A second projection optical element projects light from the first projection optical element in a direction of transmission. A directing optical element positioned at a common point in the optical paths of the multiple beams generates an illuminated area at the second plane using light from each of the multiple beams. A monitor generates a detected signal in response to the collected light. A controller generates an electrical signal in response to the detected signal that controls the laser and achieves desired operation of the LiDAR system transmitter.

Description

Background Art

[0001] The headings of sections used in this specification are for organizational purposes only and are not to be construed in any way as limiting the subject matter described in this application.

[0002] (Cross - Reference to Related Applications) This application is a non - provisional application of U.S. Provisional Patent Application No. 63 / 112,735, filed on November 12, 2020, entitled "LiDAR System with Transmit Optical Power Monitor". The entire content of U.S. Provisional Patent Application No. 63 / 112,735 is incorporated herein by reference.

[0003] Introduction Autonomous, self - driving, and semi - autonomous vehicles use combinations of different sensors and technologies such as radar, image - recognition cameras, and sonar for detecting and locating surrounding objects. These sensors enable numerous improvements in driver safety, including collision warnings, automatic emergency braking, lane - departure warnings, lane - keeping assistance, adaptive cruise control, and pilot driving. Among these sensor technologies, Light Detection and Ranging (LiDAR) systems play an important role and enable real - time high - resolution 3D mapping of the surrounding environment.

[0004] Today, most LiDAR systems used for autonomous vehicles utilize a small number of lasers combined with several methods of mechanically scanning the environment. Some state-of-the-art LiDAR systems use a two-dimensional vertical-cavity surface-emitting laser (VCSEL) array as the illumination source and various types of solid-state detector arrays in the receiver. Future autonomous vehicles are highly likely to utilize solid-state semiconductor-based LiDAR systems with high reliability and a wide environmental operating range. These solid-state LiDAR systems are advantageous because they use solid-state technology with no moving parts. However, current state-of-the-art LiDAR systems have many practical limitations, and new systems and methods are needed to improve performance. [Overview of the project] [Means for solving the problem]

[0005] This specification also provides, for example, the following: (Item 1) A LiDAR (Light Detection and Ranging) transmitter with optical power monitoring, wherein the transmitter is a) A laser array positioned in a first plane, wherein the laser array generates a plurality of optical beams that propagate along an optical path in response to an electrical signal provided to an input, b) A first projection optical element, the first projection optical element being positioned within the optical path that projects the plurality of optical beams such that the plurality of optical beams overlap at least partially at common points, c) A second projection optical element, the second projection optical element being positioned in the optical path of the plurality of optical beams after the first projection optical element and projecting light from the first projection optical element in the direction of transmission, d) A directional optical element positioned at a common point in the optical paths of the plurality of beams, wherein the directional optical element generates an illumination region in a second plane that includes at least a portion of the light from each of the plurality of beams, e) A monitor positioned within the illumination area in the second plane for collecting at least a portion of the light from each of the plurality of beams, the monitor comprising a photodiode that generates a detected signal at its output in response to the collected light, f) A controller having an input connected to the output of the monitor and an output connected to the input of the laser array, wherein the controller controls the laser in response to the detected signal and generates an electrical signal to achieve the desired operation of the LiDAR system transmitter. A transmission device equipped with the following features. (Item 2) The laser array is a LiDAR transmitter as described in item 1, comprising a VCSEL array. (Item 3) The LiDAR transmitter according to item 1, wherein the laser array comprises a two-dimensional array, and at least two lasers in the array can be operated independently. (Item 4) The first and second planes are in the same plane, and the LiDAR transmitter is as described in item 1. (Item 5) The LiDAR transmitter described in item 1, wherein the first and second planes are positioned in different planes. (Item 6) The LiDAR transmission device described in item 1, wherein the directional optical element and the second projection optical element are the same optical element. (Item 7) The LiDAR transmitter according to item 1, wherein the directional optical element comprises a partially reflective element. (Item 8) The LiDAR transmitter according to item 1, wherein the directional optical element comprises a diffraction element. (Item 9) The directional optical element is a LiDAR transmitter as described in item 1, comprising a prism. (Item 10) The LiDAR transmitter described in item 1 comprises a holographic element as the directional optical element. (Item 11) The LiDAR transmitter according to item 1, wherein the directional optical element is both a partially reflective mirror and an optical filter. (Item 12) The LiDAR transmitter according to item 1, wherein the directional optical element comprises a flat optical element. (Item 13) The directional optical element is a transmissive element, as described in item 1, for the LiDAR transmission device. (Item 14) The LiDAR transmitter according to item 1, wherein the directional optical element has an optical coating on the second projection optical element. (Item 15) Achieving the desired operation of the LiDAR system transmitter is a LiDAR transmitter according to item 1, which includes achieving a predetermined performance metric. (Item 16) Achieving the desired operation of the LiDAR system transmitter is the LiDAR transmitter described in item 1, which includes achieving eye safety. (Item 17) Achieving the desired operation of the LiDAR system transmitter is the LiDAR transmitter described in item 1, which includes achieving functional safety. (Item 18) The monitor is a LiDAR transmitter as described in item 1, comprising a photodiode. (Item 19) The monitor is a LiDAR transmitter as described in item 1, comprising a sampling prism. (Item 20) The monitor is a LiDAR transmitter as described in item 1, comprising a light pipe optically coupled to a photodiode. (Item 21) The light pipe is located on the same substrate as the laser array, as described in item 20, in the LiDAR transmitter. (Item 22) The LiDAR transmitter according to item 1, wherein the monitor comprises a multi-wavelength monitor that provides wavelength information about the collected light. (Item 23) A method of optical detection and ranging (LiDAR) with optical power monitoring, wherein the method is: a) Generating multiple optical beams propagating along an optical path in a first plane, b) Projecting the plurality of optical beams such that they overlap at least partially at common points, c) Directing light from the common point, thereby generating an illumination region in a second plane that includes at least a portion of the light from each of the plurality of beams, d) Collecting at least a portion of the light from each of the plurality of beams in the plane described above, and generating a detected signal in response to the collected light, e) In response to the detected signal, control the generation of the plurality of optical beams and generate an electrical signal to achieve the desired operation of the LiDAR system transmitter. Methods that include... (Item 24) The first and second planes are in the same plane, as described in item 23. (Item 25) The method according to item 23, wherein the first and second planes are located in different planes. (Item 26) The method according to item 23, wherein directing light from the aforementioned common point includes diffracting the light. (Item 27) The method according to item 23, wherein directing light from the aforementioned common point includes reflecting and filtering the light. (Item 28) The method according to item 23, wherein directing light from the aforementioned common point includes transmitting the light. (Item 29) Achieving the desired operation of the LiDAR system transmitter is the method described in item 23, which includes achieving a predetermined performance metric. (Item 30) Achieving the desired operation of the LiDAR system transmitter is the method described in item 23, which includes achieving eye-safe operating conditions. (Item 31) The method according to item 23, wherein achieving the desired operation of the LiDAR system transmitter includes achieving functional safety. (Item 32) The method according to item 23, wherein generating the electrical signal in response to the detected signal includes generating multi-wavelength information about the collected light. In a preferred exemplary embodiment, this teaching, along with its further advantages, will be described more specifically in the following detailed description, together with the accompanying drawings. Those skilled in the art will understand that the drawings described below are for illustrative purposes only. The drawings are not necessarily to exact scale, and emphasis is placed, instead, generally to illustrate the principles of this teaching. The drawings are not intended to limit the scope of the applicant's teaching in any way. [Brief explanation of the drawing]

[0006] [Figure 1] Figure 1 illustrates an embodiment of a monitoring transmitter equipped with a reflective directional element for the LiDAR system of this teaching.

[0007] [Figure 2] Figure 2A shows a magnified view of part of the monitoring transmitter for the LiDAR system in Figure 1, with additional details. Figure 2B shows a cross-sectional view of the optical ray trace shown in Figure 2A.

[0008] [Figure 3] Figure 3A illustrates a portion of an embodiment of a monitoring transmitter equipped with a monitor having a light pipe for the LiDAR system of this teaching. Figure 3B illustrates a cross-sectional view of the optical ray trace shown in Figure 3A.

[0009] [Figure 4] Figure 4A shows part of an embodiment of a monitoring transmitter equipped with a transparent directional element for the LiDAR system of this teaching. Figure 4B shows a cross-sectional view of the optical ray trace shown in Figure 4A.

[0010] [Figure 5] Figure 5 illustrates a block diagram of a LiDAR system, including a monitoring transmitter, according to one embodiment of this teaching. [Modes for carrying out the invention]

[0011] Description of various embodiments This teaching will be described in more detail herewith reference to exemplary embodiments thereof, such as those shown in the accompanying drawings. While this teaching will be described in conjunction with various embodiments and examples, it is not intended to be limited to such embodiments. Rather, this teaching includes various alternatives, modifications, and equivalents, as will be understood by those skilled in the art. Those skilled in the art who have access to the teachings herein will recognize additional implementations, modifications, and embodiments, and other fields of use, which fall within the scope of this disclosure as described herein.

[0012] Any reference in this specification to “one embodiment” or “a particular embodiment” means that certain features, structures, or characteristics described in relation to an embodiment are included in at least one embodiment of this teaching. Expressions of the phrase “in one embodiment” in various places in this specification do not necessarily all refer to the same embodiment.

[0013] It should be understood that the individual steps of the method in this instruction may be performed in any order and / or simultaneously, as long as this instruction remains operational. Furthermore, it should be understood that the apparatus and method in this instruction may include any number or all of the embodiments described, as long as this instruction remains operational.

[0014] This instruction relates generally to light detection and ranging (LiDAR), a remote sensing method that uses laser light to measure the distance (range) to an object. LiDAR systems generally measure the distance to various objects or targets that reflect and / or scatter light. Autonomous vehicles use LiDAR systems to generate highly accurate 3D maps of their surroundings with high resolution. The systems and methods described herein aim to provide a solid-state pulsed time-of-flight (TOF) LiDAR system that maintains a long measurement range and low cost while also having a high level of reliability.

[0015] Some embodiments of the LiDAR systems described herein utilize a laser transmitter, which includes a laser array. In some specific embodiments, the laser array comprises vertical-cavity surface-emitting laser (VCSEL) devices. These may include top-emitting VCSELs, bottom-emitting VCSELs, and various types of high-power VCSELs. The VCSEL array may be monolithic. All laser emitters may share a common substrate, which may include a semiconductor or ceramic substrate.

[0016] In various embodiments, individual lasers and / or groups of lasers using one or more transmitter arrays can be individually controlled. Each individual emitter within the transmitter array can be emitted independently. The optical beam emitted by each laser emitter corresponds to a 3D projection angle that limits the scope to only a portion of the overall system field of view. One embodiment of such a LiDAR system is described in U.S. Patent Publication 2017 / 0307736A1, which has been assigned to the assignee and is incorporated herein by reference. In addition, the number of pulses emitted by individual lasers or groups of lasers can be controlled based on desired performance objectives of the LiDAR system. The duration and timing of this sequence can also be controlled to achieve various performance objectives.

[0017] Some embodiments of the LiDAR systems described herein also utilize detectors and / or groups of detectors in a detector array that can be individually controlled. See, for example, U.S. Provisional Application No. 62 / 859,349, entitled "Eye-Safe Long-Range Solid-State LiDAR System," which has been assigned to the assignee and is incorporated herein by reference. This independent control of individual lasers and / or groups of lasers in a transmitter array and / or detectors and / or groups of detectors in a detector array provides a variety of desirable operating characteristics, including control of the system field of view, optical power level, and scanning pattern.

[0018] The optical power level emitted by the LiDAR system transmitter is a critical parameter considered among the numerous performance metrics of the LiDAR system. These include, for example, distance, field of view, resolution, speed, frame rate, and eye safety, among other performance metrics. Therefore, a system and method for monitoring the transmission power for the LiDAR system is desirable. The monitoring system should be compact, low-cost, and produce the desired accuracy and precision of the monitored parameters.

[0019] One feature of the LiDAR system described in this instruction is the inclusion of direct monitoring of optical performance within the LiDAR transmission module. Monitoring of optical performance within the LiDAR module can be important for various reasons. For example, incorporating optical power monitoring inside the illuminator assembly can improve calibration, performance, and reliability monitoring. Lasers degrade over time, and therefore, monitoring the laser output power within the projector assembly itself can be useful. For example, by monitoring the light as it is emitted from the projector, rather than simply relying on the optical signal received after the light has been reflected from an external object, it is possible to monitor the generated power more accurately and quickly. It is also possible to monitor the temperature adjacent to the VCSEL laser. Such features are useful for improving reliability and performance. Optional monitoring of both temperature and power can be used not only for diagnostics but also to control the laser during operation to improve the system's performance and / or lifespan.

[0020] Another feature of this teaching is that the power monitoring element is configured to monitor light reflected from or directed from various optical devices within the LiDAR transmitter, which provide other functions. The reflected or directed light detected within the transmitter can be used not only for passive monitoring purposes, but also to provide additional active control of the lasers and detectors within the transmitter.

[0021] Some embodiments of the performance monitors for LiDAR system transmitters described in this teaching monitor one or more parameters of the light generated by the LiDAR system transmitter itself. For example, the light generated by the transmitter can be monitored with respect to laser wavelength, optical power, pulse timing, and pulse frequency. The wavelength of the generated light can be detected by using a power monitor that includes a receiver, which instead has a more complex set of optics that enables the detection of wavelength and optical power, rather than simply a photodiode.

[0022] In LiDAR designs using multiple wavelengths, it may be desirable to monitor the absolute or relative wavelengths, especially when the wavelengths are close to their absolute values, to ensure that system parameters are as intended. Various known methods exist for monitoring either the absolute wavelength of light generated by a laser or the relative offset between light generated by lasers of different wavelengths. For example, etalon-based devices can be used as wavelength monitors.

[0023] Embodiments of the systems and methods of this teaching that utilize multi-wavelength power monitoring can also improve system robustness to detect whether a failure is caused by laser degradation or deviation in the optical performance metric. Multi-wavelength power monitoring can also provide redundancy in case one set of wavelengths fails within the transmitter. A partial or complete failure of one set of wavelengths in the transmitter during operation would still allow for the ability of the system to partially operate using the other sets of wavelengths within the transmitter, provided that the optical monitoring for each wavelength is independent.

[0024] Another feature of the system and method of this teaching is that multi-element, multi-wavelength optical power monitoring can be realized. One or more directional elements can be positioned to direct light to one or more monitors so that the collective and individual power from one or more laser elements at one or more wavelengths can be monitored. For example, in one embodiment, the multiple reflective elements may be partial mirrors. In other embodiments, the multiple reflective elements may be configured to project beams. In some embodiments, the monitors include photodetectors, each sensitive to one specific wavelength band of light. This configuration allows for independent monitoring of optical power at one or more wavelengths, which improves the system capability. Multi-wavelength power monitoring according to this teaching can be configured to monitor with respect to multiple parameters, including absolute and / or relative wavelengths, such as laser wavelength, optical power, pulse timing, and pulse frequency.

[0025] As demonstrated in this instruction, multi-wavelength power monitoring also improves the robustness of LiDAR systems to detect whether a failure is caused by laser degradation or deviations in optical performance. Multi-wavelength power monitoring is useful, for example, to provide redundancy if one set of wavelengths generated by the transmitter is faulty. A partial or complete failure in the generation of one set of wavelengths by the transmitter would still allow the LiDAR system to operate partially using other sets of wavelengths, provided that the system is configured to have independent optical monitoring for each wavelength band.

[0026] It is known that degradation in the performance of an optical transmitter can be determined by monitoring the laser output power of the optical transmitter and then comparing the measured optical power to an expected baseline value. The degradation in the performance of the optical transmitter may be caused by the laser itself, or by various aspects of the opticmechanical assembly, or both. The degradation in the performance of the optical transmitter can then be analyzed. For example, U.S. Patent Application Publication US2016 / 0025842A1, titled "System and Method for Monitoring Optical Subsystem Performance in Cloud LiDAR Systems," describes the benefits of laser output power monitoring for LiDAR systems designed for cloud measurement.

[0027] The measurement of optical signals generated by a LiDAR transmitter can also be used within passive monitoring systems. In addition, optical signals from a LiDAR transmitter can be used for active control of the laser bias current driving a semiconductor laser. The laser diode operates over a range of operating bias currents. Many types of semiconductor laser diode systems operate in a closed-loop configuration, where the photodiode current received from a monitor photodiode is used as input to a bias control feedback loop. The output power of the semiconductor laser can be maintained near a constant value primarily by monitoring and maintaining the monitor photodiode current, which is a linear function of the incident power. This condition enables the system to respond to environmental changes such as temperature and mechanical movement to achieve improved output power stability. Furthermore, monitoring the optical power and controlling the laser bias in response to the monitored optical power can be used to adapt to the degradation of laser efficiency over its lifetime without loss of optical power at the system level.

[0028] In various embodiments, the transmitter optical signal can be monitored with respect to a number of parameters, including, among other things, laser wavelength, optical power, pulse timing, pulse frequency, and pulse duration. The laser wavelength can be detected not simply by photodiodes or other optical detectors, but by a power monitor, which is an optical system that enables the detection of wavelength and optical power. In LiDAR system designs where multiple wavelengths are used, it may be desirable to monitor their absolute or relative values ​​to ensure that the system parameters are as intended, especially when the wavelengths are close to their absolute values. Various methods for monitoring either absolute wavelengths or relative offsets between lasers of different wavelengths are known in the art. For example, etalon-based devices can be used as wavelength monitors.

[0029] Some LiDAR systems are desirable to have calibration performed early in their life (BOL) to provide a reference point throughout the system's lifetime operation. Calibration refers to the initial characterization of the device's laser bias, temperature, and output power, followed by subsequent adjustments of the laser bias and output power as a function of temperature to meet the required performance specifications, with suitable tolerances in the BOL. Often, this process is performed as part of the manufacturing process for the LiDAR system. Performance parameters such as laser bias and measured optical power acquired during the calibration process will often be stored in the LiDAR system memory as a function of temperature to serve as a reference point for use in various operations. Various monitors in this teaching can provide measured optical power for some of these calibration processes.

[0030] During operation of the LiDAR system, the actual temperature is monitored and, in conjunction with a reference value stored in memory in a lookup table, can be used to determine the optical laser bias setpoint. Alternatively, in combination with an optical power monitor, the actual values ​​of output power, laser bias, and temperature during operation are compared with reference values ​​in the lookup table to identify any significant changes or degradations in the system, which can indicate potential reliability issues. In various practical implementations of the system, upon detecting such changes, the LiDAR system can then communicate with other overall monitoring systems in the vehicle to identify potential inspection or repair needs.

[0031] Figure 1 illustrates an embodiment of a monitoring transmitter 100 comprising a reflective directional element 110 for the LiDAR system of this teaching. The monitoring transmitter 100 uses a 2D VCSEL array 102 for a laser source combined with a set of optics to project a laser beam along the transmission direction 104. A monitor photodiode (MPD) 106 is shown mounted on the same substrate 108 as the VCSEL array 102. The monitor photodiode 106 or VCSEL 102 may also be mounted on a separate carrier or in a separate package. In some embodiments, the monitor photodiode 106 and the VCSEL array 102 are nominally coplanar. In some embodiments, the monitor photodiode 106 and the VCSEL array 102 have normal projections to their respective surfaces having the same orientation. In some embodiments, this orientation is the same orientation as the transmission direction 104. A directional element 110, located between the first lens 112 and the second lens 114, directs a portion of the optical beam generated by the VCSEL array 102 back to the monitor photodiode 106. In some embodiments, the directional element 110 includes a partial mirror located between the first lens 112 and the second lens 114 that reflects a portion of the optical beam generated by the VCSEL array 102 back to the monitor photodiode 106. The first lens 112, the second lens 114, and the directional element 110 can be mounted in or on a common housing 116 fixed to a substrate 108. In some embodiments, the direction of transmission is along the optical axes of the first lens 112 and / or the second lens 114.

[0032] The monitoring transmitter 100 is described as using lenses 112, 114 to project light from the optical beam generated by the VCSEL array 102. However, those skilled in the art will understand that a number of other projection optical elements can also be used. A number of known implementations of projection elements can be used in the monitoring transmitter 100 of this teaching. In various embodiments, these projection elements play a role in shaping the optical beam and projecting it toward a target to achieve, for example, a desired field of view, target range, resolution, etc. These projection elements may be configured such that the directional elements generate a common point for the optical beams within the transmitter-occupied area, enabling the illumination area to be generated on the monitor plane, so that light from each of the optical beams can be monitored.

[0033] Those skilled in the art will understand that some embodiments of this teaching do not require all optical beams generated from the VCSEL array 102 to appear within the illumination area. Instead, in some embodiments, only a subset of optical beams sharing a common point for the optical beams is provided within the illumination area and sampled by the monitor. The relative positions of the projection element, the VCSEL array 102, and the directional element play a role in determining the desired subset of optical beams that share a common point and are therefore provided within the illumination area.

[0034] In the monitoring transmitter 100 embodiment shown in Figure 1, the directional element 110 is illustrated to be tilted toward the monitor photodiode 106. In other embodiments, the reflective mirror is not tilted toward the photodiode. Instead, the orientation of the directional element 110 may be such that the normal to the surface of the directional element 110 is parallel to the optical axis of the lens system in order to maintain rotational symmetry. This orientation may be advantageous in some cases for ease of assembly / manufacturing. Also, although the directional element 110 is shown as a separate optical element in Figure 1, it should be understood that in some embodiments, one or more of the two lenses 112, 114 or one or more of the surfaces of some other optical element in the transmitter path may function to provide the required reflection or direction.

[0035] In some embodiments, the optical component, including one or more of the first lens 112, the second lens 114, and the directional element 110, has an optical coating on its surface that is designed to control reflectivity. In embodiments where monitoring is not required, the optical reflectivity is often set as low as possible to maximize output power in the transmission direction 104 from the transmitter 100. In some embodiments, the optical coating on the directional element 110 may have a reflectivity of up to 5%. In some embodiments, the directional element 110 is not a separate discrete element, but rather an optical coating or set of coatings on one or more of the optical lens surfaces, and the reflectivity of the coating is selected to optimize the measured optical signal.

[0036] A feature of this teaching is that the directional element 110 can be positioned in the path of the optical beam generated by the lasers at a common point such that all lasers in the transmitter array have a portion of the light that can be reflected. See, for example, U.S. Patent No. 10,514,444, which describes a LiDAR transmitter including multiple lenses to achieve small-angle divergence of the transmitted optical beam. U.S. Patent No. 10,514,444 has been assigned to the assignee and is incorporated herein by reference.

[0037] In some embodiments, the directional element 110 is a diffractive optical system element. In other embodiments, the directional element 110 is both a partially reflective mirror and an optical filter, which blocks a portion of the visible spectrum. In one specific embodiment, the directional element is a prism. In some embodiments, the directional element is a holographic element. Numerous known lens configurations can be utilized to achieve the desired lens optical power, size, and relative position of the first lens 112 and the second lens 114 and the laser array 102.

[0038] In some embodiments, the monitor photodiode 106 is fabricated monolithically with the VCSEL array 102. The monitor photodiode 106 can be fabricated in a number of configurations. For example, in some embodiments, the monitor photodiode 106 is a single photodiode, which receives light from all individual lasers in the 2D array. In other embodiments, more than one photodiode is used, and the outputs of multiple photodiodes are combined in some way to provide a common signal output at a point in the signal chain.

[0039] In some embodiments, the monitor photodiode 106 includes an optical element positioned to receive light propagating from the monitor photodiode 106. For example, the monitor photodiode 106 may include an optical guide or prism positioned to receive light and configured to direct the collected light to the photodiode. The optical element can capture all the light in the monitoring aperture or only a portion of the light from different spatial regions of the monitoring aperture and then direct that light to one or more photodiodes. For example, the optical element may be a light pipe, as described herein.

[0040] Figure 2A illustrates an enlarged view 200 with some additional details of the monitoring transmitter 100 for the LiDAR system of Figure 1. Figure 2A shows an optical ray trace schematic 202 illustrating light emitted from the VCSEL array 102, passing through lens 1 112 and then reflecting back from the partially reflective mirror 110 toward the monitor photodiode 106 and the VCSEL array 102. The monitor photodiode 106 is shown as a photodiode positioned coplanar 204 with the VCSEL array 102. The optical beams illustrated in the ray trace schematic 202 are shown passing through a directional element 110, where they propagate to a second lens (not shown) and then exit the LiDAR transmitter 100 and be redirected toward the direction of transmission 104.

[0041] Figure 2B illustrates a cross-sectional view 250 of the optical ray trace 202 shown in Figure 2A. Referring to Figures 1, 2A, and 2B, the cross-sectional view 250 shows an illuminated area 256 encompassing reflections from the directional element 110 from different lasers in the VCSEL array 102. The illuminated area 256 for each beam is mapped and illustrated across the area 252 of the monitor photodiode 106 and the area 254 of the VCSEL array 102. This is because the directional element 110 projects light from the common point of the optical beams generated by the VCSELs, and therefore the illuminated area 256 contains at least some light from all beams. That is, the location of the directional element 110 and the inclination angle of the mirror are selected so that all reflected areas are close to and overlap with the monitor photodiode 106, regardless of the location of any particular VCSEL element in the VCSEL array 102. This ensures that the power emitted from all lasers in the VCSEL array 102 can be monitored. The location of the monitor photodiode 106 is often constrained by other electronic components within the LiDAR system.

[0042] In some configurations, it is not possible to place the monitor photodiode 106 immediately next to the VCSEL array 102. Instead, for easier manufacturing, the monitor photodiode 106 may need to be at a certain distance from the VCSEL array 102, but still close enough to be within the illuminated area of ​​the reflected optical beam. Therefore, the inclination and position of the directional element 110 must be appropriately selected so that light from multiple elements in the array 102 overlaps at the monitor photodiode 106.

[0043] Figure 3A illustrates a portion 300 of an embodiment of a monitoring transmitter having a light pipe 304 for the LiDAR system of this teaching. The embodiments shown in Figures 2A and 3A share many features. The VCSEL array 302 and the monitor photodiode 304 are positioned in the same plane 306. A first lens 308 directs a light beam from the array 302 toward a directional element 310, which may be a partially reflective mirror, and then toward a second lens (not shown) along the direction of transmission out of the transmitter 312. Figure 3A shows a schematic optical ray trace 305 illustrating the light emitted from the VCSEL array 302, passing through lens 1 308 and then reflected back toward the light pipe 304 and VCSEL array 302 from the partially reflective mirror 310.

[0044] Figure 3B illustrates a cross-sectional view 350 of the optical ray trace 202 shown in Figure 3A. Referring to Figures 1, 3A, and 3B, the cross-sectional view 350 shows an illuminated area 352 encompassing reflections from the directional element 310 from different lasers within the VCSEL array 302. The illuminated area 352 for each beam is mapped and illustrated across the area 354 of the monitor area, which includes the collection area of ​​the light pipe 358, and the area 356 of the VCELS array occupied area. The light pipe 358 is shown connected to a remotely located monitor photodiode 360. The illuminated area 352 includes light from each of the optical beams generated by the VCSEL array 302, as the directional element 310 directs light from the common point of the optical beams generated by the VCSEL array 302 to the monitor 304 located in the monitor plane.

[0045] In this embodiment, monitor 304 includes a light pipe 358. The light pipe is a device that acts as a waveguide, retaining light internally through total internal reflection as light propagates along the length of the light pipe. The light pipe 358 can be made of glass or plastic, or it can be a hollow waveguide with an internal mirror surface. Typically, the dimensions of the cross-section of the light pipe 358 perpendicular to the axis of propagation are much smaller than the propagation distance. The light pipe 358 can be constructed with fixed or flexible bends to direct the light as desired, provided that the bending radius is large enough to maintain total internal reflection. A common embodiment of a light pipe is an optical fiber cable.

[0046] In the light pipe configuration, as in the embodiment of Figure 2, instead of the reflected light being directly measured by a photodiode located within the illuminated area, a light pipe 358 is used to capture the light and provide the collected light to a photodiode (not shown). Thus, the light pipe 358 captures a portion of the light from the illuminated area and redirects it to a monitor photodiode (not shown) that is physically away from the VCSEL array 302 and outside the illuminated area.

[0047] Embodiments of a monitoring transmitter using a light pipe have additional components, which can increase costs. For example, a light pipe may incorporate various optical elements, including lenses and mirrors. However, light pipe embodiments have several potential advantages compared to other embodiments that do not use a light pipe. One advantage of a light pipe is that the size of the monitor photodiode for the active area is often limited in physical size, which limits the optical signal that can be generated. In particular, when the actual pulse shape, which is often nanosecond duration, needs to be measured, the photodiode active area should be small to have a good dynamic response. In this case, the light pipe can be designed with a larger collection area, allowing the measured light to be densely / focused onto a smaller photodiode active area, thereby improving the SNR. Since the light pipe is purely a passive optical component, it can be positioned above the elements, which can be physically close to the VCSEL array 302, such as electrically driven components. Placing the light pipe closer to the VCSEL can also improve the optical efficiency of the monitoring function.

[0048] Another potential advantage of using light pipes is the ability to locate monitor photodiodes relatively far from the VCSEL array and VCSEL drive circuitry. This feature is important because when monitor diodes are placed physically close to those components, the drive current / voltage used to operate the VCSELs can electrically couple and become a source of noise in the optical monitor circuit. It is highly desirable to keep the noise level as low as possible within the optical monitor circuitry in order to provide high SNR and any misreadings.

[0049] Figure 4A shows a portion 400 of an embodiment of a monitoring transmitter comprising a transparent directional element 410 for a LiDAR system of this teaching. A VCSEL array 402 generates multiple optical beams directed to first and second lenses 404, 406. In this embodiment, the light is not reflected back toward the VCSEL array 402. The light collides onto the directional element 410, which is a transparent element, in this embodiment being a mounting plate. In this configuration, the directional element 410 transmits or passes the light toward a monitor 408 at the common point of the paths of the optical beams. For example, in some embodiments, the monitor 408 is a microprism. The directional element 410 resides at a position with the common point of the paths of the optical beams generated by the laser array, defining an illumination area containing light from each laser. Therefore, the directional element 410 allows light from each of the optical beams generated by the lasers to pass through so that all the lasers in the VCSEL array 402 have a portion of the light supplied to the illumination area and the light can be sampled by a monitor 408 installed within the illumination area. A small portion of the transmitted light within the illumination area is reflected by the monitor 408, primarily in a direction perpendicular to the optical axis of the transmitter, using small microprisms, which may be diffractive optical elements.

[0050] The microprism of monitor 408 is shown mounted on a directional element 410, which is a mounting plate that is a transparent optical window in some embodiments and an optical filter in other embodiments. In some configurations, the directional element 410 is an optical element within the LiDAR transmitter that would be required even without monitor 408. Thus, the directional element 410 provides two functions, one of which is to fix the microprism of monitor 408, and the other is to be optical by nature. In some configurations, the directional element 410 protects the LiDAR system from the external environment. The microprism in monitor 410 is shown coupled to an optical fiber 412 having a core large enough to maintain the required optical signal level. The optical fiber 412 then directs the light to a monitor photodiode (not shown in the schematic diagram).

[0051] Figure 4B illustrates a cross-sectional view 450 of the optical ray trace shown in Figure 4A. The cross-sectional view 450 shows an illumination region 452 encompassing illumination from all the different lasers in the VCSEL array 402 in the plane of the directional element 410. The illumination region 452, including light from each beam, is mapped and illustrated over the collection area 454 of the sample prism area. The directional element 410 is positioned in the path of the optical beams generated by the lasers at a common point such that all lasers in the transmitter array have a portion of the light that can be sampled by the monitor 408, which includes a microprism.

[0052] The embodiment of the monitoring transmitter with a sampling prism, shown in Figure 4A, has several advantages. One feature of this embodiment is that by removing the reflecting plate from within the lens system, the manufacturing and assembly of the lens system are simplified, and the rotational symmetry of the lens system is maintained.

[0053] The embodiment of the monitored transmitter with optical fiber 412, shown in Figure 4A, also has several advantages. One feature of this embodiment is that fiber 412 allows the monitor photodiode to be installed physically away from the VCSEL array 402 and the VCSEL drive network. In some embodiments, the monitor photodiode is not even on the same circuit board as the VCSEL array 402 drive network. This configuration primarily eliminates the possibility that the VCSEL array 402 drive circuit could introduce any undesirable noise or spurious signals present in the optical monitor signal. Eliminating the physical constraints associated with the monitor photodiode being on the same circuit board as the VCSEL array 402 also enables great flexibility in the size and type of the optical monitor, which can be advantageous for several reasons, including reducing the size and / or complexity of the transmitter or manufacturing process.

[0054] Another feature of the monitored transmitter in this teaching is that the common point, from which light is directed to form an illuminated area, can be located at various points within the optical transmitter. The common point can be determined by the position of the projection element and the laser device. For example, the common point can be located before the last optical lens surface in the transmitter optical system. Alternatively, or in addition, the common point can be located after the last optical lens surface in the transmitter optical system. In some embodiments, the optical monitor can be mounted on an optical window, which is the last optical element in the transmitter path and protects the LiDAR system from the external environment. In other embodiments, the optical monitor can be mounted on one of the optical lens surfaces. In yet another embodiment, the optical monitor can be mounted on an optical filter element, which blocks a portion of the visible spectrum.

[0055] It should be understood that the monitored transmitters described in this instruction are described in relation to a specific configuration. These embodiments are illustrative only and are not intended to limit the scope of this instruction. It should be understood that various aspects of different embodiments may be used in different combinations to achieve the advantages of the methods and systems described in this instruction.

[0056] Figure 5 illustrates a block diagram of an embodiment of the LiDAR system 500, including a supervising transmitter, according to this teaching. The LiDAR system 500 has six main components: (1) controller and interface electronics 502, (2) transmission electronics 504 including a laser driver, (3) laser array 506, (4) receiving and time-of-flight calculation electronics 508, (5) detector array 510, and (6) monitor 512. The controller and interface electronics 502 controls the overall functionality of the LiDAR system 500 and provides digital communication to the host system processor 514. The transmission electronics 504 controls the operation of the laser array 506 and, in some embodiments, sets the pattern and / or power of the laser emission of individual elements in the array 506. The receiving and time-of-flight calculation electronics 508 receives electrical detection signals from the detector array 510 and then processes these electrical detection signals to calculate the range distance through time-of-flight calculation.

[0057] The monitor 512 is connected to either or both the controller and interface electronics 502 and the transmission electronics 504, which includes a laser driver. The monitor 512 provides information about the detected signal power and, in combination with processing in either or both the controller and interface electronics 502 and the transmission electronics 504, provides information about parameters, among others, laser wavelength, optical power, pulse timing, pulse frequency, and / or pulse duration. In some embodiments, the controller and interface electronics 502 directly controls the monitor 512 and obtains information from it. An embodiment in Figure 5 shows a partial mirror 516 that directs light towards the monitor 512. However, as will be obvious to those skilled in the art, the LiDAR system 500 can operate using any of the monitor 512 configurations described herein and known modifications of these configurations.

[0058] In some embodiments, the lasers in the array 506 operate in a closed-loop configuration using either or both of the controller and interface electronics 502 and the transmission electronics 504, which include a laser driver, which respond to the photodiode current received from a monitor photodiode acting as an input to a bias control loop. This configuration allows the transmitter optical power, including the power from some or all of the optical beam generated by the laser array 506, to be maintained near a constant value. This allows the system to be more stable with respect to temperature and / or mechanical deviations. Furthermore, using a control loop via either or both of the controller and interface electronics 502 and the transmission electronics 504, which include monitoring of optical power and control of the laser bias, allows for adaptation to a certain amount of degradation of laser efficiency over the lifetime of the LiDAR system 500 without loss of optical power at the output.

[0059] In some embodiments, the controller and interface electronics 502 calculate the object reflectivity using the optical power reading generated by the monitor 512. The monitored optical power can be used as a reference, and then, based on the actual photon count / intensity and pre-calibration, improved reflectivity data can be achieved. This improved reflectivity data can be utilized within the system for use in various known LiDAR applications related to perception.

[0060] Another feature of the methods and apparatus of this teaching is that these monitor photodiode implementations can address the functional safety of the LiDAR system itself. For example, a control loop via the controller and interface electronics 502 and / or the transmission electronics 504 including the laser driver, including the power monitor 512, can be used to indicate that the LiDAR transmitter is malfunctioning if, for example, the measured optical power falls below or exceeds a certain threshold. For example, using either or both of the controller and interface electronics 502 and the transmission electronics 504 including the laser driver, and including the power monitor 512, a control loop can be used to indicate that the LiDAR transmitter is operating beyond an eye safety threshold if the optical power exceeds a certain threshold.

[0061] The monitoring transmitter for LiDAR systems described in this teaching are described in relation to various embodiments using a single VCSEL array. It should be understood that this teaching can be extended to LiDAR transmitters including more than one VCSEL array. In these embodiments including more than one VCSEL array, the VCSEL arrays are positioned such that the illumination area covering the monitor has distinctly different areas for each VCSEL array. In these embodiments, the monitor photodiode may be configured to include more than one photodiode, and separate monitor photodiodes may be used for each separate illumination area.

[0062] Equal portions The applicant's teachings are described in conjunction with various embodiments, but are not intended to be limited to such embodiments. Rather, the applicant's teachings include various substitutions, modifications, and equivalents that can be made within them without departing from the spirit and scope of the teachings, as will be understood by those skilled in the art.

Claims

1. A LiDAR (Light Detection and Ranging) transmitter with optical power monitoring, wherein the transmitter is a) A laser array positioned in a first plane, wherein the laser array generates a plurality of optical beams that propagate along an optical path in response to an electrical signal provided to the input, b) A first projection optical element, the first projection optical element being positioned within the optical path that projects the plurality of optical beams such that the plurality of optical beams overlap at least partially at their common points, c) A second projection optical element, the second projection optical element being positioned in the optical path of the plurality of optical beams after the first projection optical element and projecting light from the first projection optical element in the direction of transmission, d) A directional optical element positioned at a common point in the optical paths of the plurality of optical beams, wherein the directional optical element generates an illumination region in a second plane that includes at least a portion of the light from each of the plurality of optical beams, e) A monitor positioned within the illumination area in the second plane for collecting at least a portion of the light from each of the plurality of optical beams, the monitor comprising a photodiode that generates a detected signal at its output in response to the collected light, f) A controller having an input connected to the output of the monitor and an output connected to the input of the laser array, wherein the controller controls the laser in response to the detected signal and generates an electrical signal to achieve the desired operation of the LiDAR system transmitter. A LiDAR transmitter equipped with [the necessary features].

2. The LiDAR transmission device according to claim 1, wherein the laser array comprises a VCSEL array.

3. The LiDAR transmitter according to claim 1, wherein the laser array comprises a two-dimensional array, and at least two lasers in the array can be operated independently.

4. The LiDAR transmitter according to claim 1, wherein the first and second planes are in the same plane.

5. The LiDAR transmitter according to claim 1, wherein the first and second planes are positioned in different planes.

6. The LiDAR transmission device according to claim 1, wherein the directional optical element and the second projection optical element are the same optical element.

7. The LiDAR transmitter according to claim 1, wherein the directional optical element comprises a partially reflective element.

8. The LiDAR transmitter according to claim 1, wherein the directional optical element comprises a diffraction element.

9. The LiDAR transmitter according to claim 1, wherein the directional optical element comprises a prism.

10. The LiDAR transmission device according to claim 1, wherein the directional optical element comprises a holographic element.

11. The LiDAR transmitter according to claim 1, wherein the directional optical element is both a partially reflective mirror and an optical filter.

12. The LiDAR transmitter according to claim 1, wherein the directional optical element comprises a flat optical element.

13. The LiDAR transmission device according to claim 1, wherein the directional optical element is a transparent element.

14. The LiDAR transmission device according to claim 1, wherein the directional optical element has an optical coating on the second projection optical element.

15. A LiDAR system transmitter according to claim 1, wherein achieving the desired operation of the LiDAR system transmitter includes achieving a predetermined performance metric.

16. The LiDAR system transmitter according to claim 1, wherein achieving the desired operation of the LiDAR system transmitter includes achieving eye safety.

17. Achieving the desired operation of the LiDAR system transmitter is a LiDAR transmitter according to claim 1, wherein achieving functional safety is a requirement.

18. The LiDAR transmission device according to claim 1, wherein the monitor comprises a photodiode.

19. The LiDAR transmitter according to claim 1, wherein the monitor comprises a sampling prism.

20. The LiDAR transmission device according to claim 1, wherein the monitor comprises a light pipe optically coupled to a photodiode.

21. The LiDAR transmission device according to claim 20, wherein the light pipe is positioned on the same substrate as the laser array.

22. The LiDAR transmitter according to claim 1, wherein the monitor comprises a multi-wavelength monitor that provides wavelength information about the collected light.

23. A method of optical detection and ranging (LiDAR) with optical power monitoring, wherein the method is: a) Generating multiple optical beams that propagate along an optical path in a first plane, b) Projecting the plurality of optical beams such that they overlap at least partially at common points, c) Directing light from the common point, thereby generating an illumination region in a second plane that includes at least a portion of the light from each of the plurality of optical beams, d) Collecting at least a portion of the light from each of the plurality of optical beams in the second plane, and generating a detected signal in response to the collected light, e) In response to the detected signal, control the generation of the plurality of optical beams and generate an electrical signal to achieve the desired operation of the LiDAR system transmitter. Methods that include...

24. The method according to claim 23, wherein the first and second planes are in the same plane.

25. The method according to claim 23, wherein the first and second planes are positioned in different planes.

26. The method according to claim 23, wherein directing light from the common point includes diffracting the light.

27. The method according to claim 23, wherein directing light from the aforementioned common point includes reflecting and filtering the light.

28. The method according to claim 23, wherein directing light from the common point includes transmitting the light.

29. The method according to claim 23, wherein achieving the desired operation of the LiDAR system transmitter includes achieving a predetermined performance metric.

30. The method according to claim 23, wherein achieving the desired operation of the LiDAR system transmitter includes achieving eye-safe operating conditions.

31. The method according to claim 23, wherein achieving the desired operation of the LiDAR system transmitter includes achieving functional safety.

32. The method according to claim 23, wherein generating the electrical signal in response to the detected signal includes generating multi-wavelength information about the collected light.

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