MULTI-WAVELENGTH PULSE STEERING IN LIDAR SYSTEMS
A LiDAR system includes a steering system and a light source. In some cases, the steering system includes a rotatable polygon with reflective sides and/or a dispersion optic. The light source produces light signals, such as light pulses. In some cases, the light sources products light pulses at different incident angles and/or different wavelengths. The steering system scans the light signals. In some cases, the light pulses are scanned based on the wavelength of the light pulses.
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This application claims priority to U.S. Provisional Patent Application Ser. No. 62/634,665, filed Feb. 23, 2018, entitled “Multi-wavelength Pulse Steering in LiDAR Systems,” the content of which is hereby incorporated by reference for all purposes.
FIELDThis disclosure relates generally to laser scanning and, more particularly, to using steering pulses in laser scanning systems based on pulse wavelength.
BACKGROUNDLight detection and ranging (LiDAR) systems use light pulses to create an image or point cloud of the external environment. Some typical LiDAR systems include a light source, a pulse steering system, and light detector. The light source generates light pulses that are directed by the pulse steering system in particular directions when being transmitted from the LiDAR system. When a transmitted light pulse is scattered by an object, some of the scattered light is returned to the LiDAR system as a returned pulse. The light detector detects the returned pulse. Using the time it took for the returned pulse to be detected after the light pulse was transmitted and the speed of light, the LiDAR system can determine the distance to the object along the path of the transmitted light pulse. The pulse steering system can direct light pulses along different paths to allow the LiDAR system to scan the surrounding environment and produce an image or point cloud. LiDAR systems can also use techniques other than time-of-flight and scanning to measure the surrounding environment
SUMMARYAn embodiment of a LiDAR system includes a rotatable polygon having a plurality of reflective sides including a first reflective side. A first light source guides a first pulse signal of a first plurality of pulse signals to the first reflective side of the rotatable polygon. The first pulse signal has a first incident angle on the first reflective side and having a first wavelength. A second light source guides a second pulse signal of a second plurality of pulse signals to the first reflective side of the rotatable polygon. The second pulse signal has a second incident angle on the first reflective side and having a second wavelength.
Another embodiment of a LiDAR system includes a light source configure to produce first plurality of pulses including a first pulse and a second plurality of pulses including a second pulse. The first plurality of pulses has a first wavelength and the second plurality of pulse has a second wavelength different than the first wavelength. A pulse steering system includes a dispersion optic configured to receive along a receive path the first pulse and the second pulse from the light source and to direct the first pulse along a first scan path and the second pulse along a second scan path different than the first scan path.
The present application can be best understood by reference to the figures described below taken in conjunction with the accompanying drawing figures, in which like parts may be referred to by like numerals.
In the following description of examples, reference is made to the accompanying drawings which form a part hereof, and in which it is shown by way of illustration specific examples that can be practiced. It is to be understood that other examples can be used and structural changes can be made without departing from the scope of the disclosed examples.
Some light detection and ranging (LiDAR) systems using a single light source to produce pulse of a single wavelength that scan the surrounding environment. The pulses are scanned using steering systems direct the pulses in one or two dimensions to cover an area of the surround environment (the scan area). When these systems use mechanical means to direct the pulses, the system complexity increases because more moving parts are required. Additionally, only a single pulse can be emitted at any one time because two or more identical pulses would introduce ambiguity in returned pulses. In some embodiments of the present technology, these disadvantages and/or others are overcome.
For example, some embodiments of the present technology use two light sources that produce pulses of different wavelengths. These light sources provide the pulses to a pulse steering system at different angles so that the scan area for each light source is different. This allows for tuning the light source to appropriate powers and the possibility of having overlapping scan areas that cover scans of different distances. Longer ranges can be scanned with pulses having higher power and/or slower repetition rate. Shorter ranges can be scanned with pulses having lower power and/or high repetition rate to increase point density.
As another example, some embodiments of the present technology use pulse steering systems with one or more dispersion elements (e.g., gratings, optical combs, prisms, etc.) to direct pulses based on the wavelength of the pulse. A dispersion element can make fine adjustments to a pulse's optical path, which may be difficult or impossible with mechanical systems. Additionally, using one or more dispersion elements allows the pulse steering system to use few mechanical components to achieve the desired scanning capabilities. This results in a simpler, more efficient (e.g., lower power) design that is potentially more reliable (due to few moving components).
Some LiDAR systems use the time-of-flight of light signals (e.g., light pulses) to determine the distance to objects in the path of the light. For example, with respect to
Referring back to
By directing many light pulses, as depicted in
If a corresponding light pulse is not received for a particular transmitted light pulse, then it can be determined that there are no objects within a certain range of LiDAR system 100 (e.g., the max scanning distance of LiDAR system 100). For example, in
In
The density of points in point cloud or image from a LiDAR system 100 is equal to the number of pulses divided by the field of view. Given that the field of view is fixed, to increase the density of points generated by one set of transmission-receiving optics, the LiDAR system should fire a pulse more frequently, in other words, a light source with a higher repetition rate is needed. However, by sending pulses more frequently the farthest distance that the LiDAR system can detect may be more limited. For example, if a returned signal from a distant object is received after the system transmits the next pulse, the return signals may be detected in a different order than the order in which the corresponding signals are transmitted, thereby causing ambiguity if the system cannot correctly correlate the returned signals with the transmitted signals. To illustrate, consider an exemplary LiDAR system that can transmit laser pulses with a repetition rate between 500 kHz and 1 MHz. Based on the time it takes for a pulse to return to the LiDAR system and to avoid mix-up of returned pulses from consecutive pulses in conventional LiDAR design, the farthest distance the LiDAR system can detect may be 300 meters and 150 meters for 500 kHz and 1 MHz, respectively. The density of points of a LiDAR system with 500 kHz repetition rate is half of that with 1 MHz. Thus, this example demonstrates that, if the system cannot correctly correlate returned signals that arrive out of order, increasing the repetition rate from 500 kHz to 1 MHz (and thus improving the density of points of the system) would significantly reduce the detection range of the system.
LiDAR system 100 can also include other components not depicted in
Some other light sources include one or more laser diodes, short-cavity fiber lasers, solid-state lasers, and/or tunable external cavity diode lasers, configured to generate one or more light signals at various wavelengths. In some examples, light sources use amplifiers (e.g., pre-amps or booster amps) include a doped optical fiber amplifier, a solid-state bulk amplifier, and/or a semiconductor optical amplifier, configured to receive and amplify light signals.
Returning to
Some implementations of signal steering systems include one or more optical redirection elements (e.g., mirrors or lens) that steers returned light signals (e.g., by rotating, vibrating, or directing) along a receive path to direct the returned light signals to the light detector. The optical redirection elements that direct light signals along the transmit and receive paths may be the same components (e.g., shared), separate components (e.g., dedicated), and/or a combination of shared and separate components. This means that in some cases the transmit and receive paths are different although they may partially overlap (or in some cases, substantially overlap).
Returning to
Controller 408 optionally is also configured to process data received from these components. In some examples, controller determines the time it takes from transmitting a light pulse until a corresponding returned light pulse is received; determines when a returned light pulse is not received for a transmitted light pulse; determines the transmitted direction (e.g., horizontal and/or vertical information) for a transmitted/returned light pulse; determines the estimated range in a particular direction; and/or determines any other type of data relevant to LiDAR system 100.
Mirror 704 is positioned next to polygon 702 so that pulses emitted from fiber 706 and 708 that are reflected off rotating polygon 702 are reflected again along a desired optical path. Mirror 704 tilts so as to scan pulses from fiber 706 and 708 in a direction different than the direction that polygon 702 scans pulses (e.g., edge 704A tilts towards and away from polygon 702 so as to scan pulses along a path that is parallel to the axis of rotation of polygon 702). In some examples, polygon 702 is responsible for scanning pulses in the vertical direction of the LiDAR system and mirror 704 is responsible for scanning pulses in the horizontal direction. In some other examples, polygon 702 and mirror 704 are configured in the reverse manner.
In some cases, fiber 706 and fiber 708 provide pulses of different wavelengths (e.g., fiber 706 only provides pulses of a wavelength that is different than the wavelength of pulses provided from fiber 708). For example, the fibers may be connected to different light sources that are designed/tuned to provide pulses of different wavelengths or the fibers may be connected to the same light source that is capable of producing pulses of different wavelengths). In some systems, the power for pulses of each wavelength are tuned based on the distances anticipated in the scan area covered by those pulses. In other cases, fiber 706 and fiber 708 provide light signals of the same wavelength (e.g., fiber 706 and fiber 708 are connected to the same light source that only provides one wavelength). Fiber 706 and fiber 708 are positioned to provide their respective pulses to polygon 702 at different incident angles, which results in the pulses having different reflection angles from polygon 702. This causes the scan area provided by the pulses from the two fibers to have different scan areas, as illustrated in the example of
Because pulses from fiber 706 and fiber 708 have different wavelengths, they can be triggered without regard to each other (e.g., triggered at the same time, in close proximity to each other, at different rates, at the same rate, synchronously, asynchronously, etc.). The wavelength of a returned pulse will indicate to the LiDAR system along which optical path the pulse traveled. The pulses of each fiber can have other different properties as well. For example, pulses from fiber 706 might have a slow repetition rate but have a higher power. These pulses, in some cases, are more suited for detecting ranges of far away objects but at a lower resolution (e.g., lower density of points). In this example, pulses form fiber 708 might have a high repetition rate but have lower power, and are more suited for detecting ranges to nearby objects with higher resolution (e.g., more points).
While the example in
In the example in
By using dispersion element 804 with pulses of different wavelengths, as depicted in
Various exemplary embodiments are described herein. Reference is made to these examples in a non-limiting sense. They are provided to illustrate more broadly applicable aspects of the disclosed technology. Various changes may be made and equivalents may be substituted without departing from the true spirit and scope of the various embodiments. In addition, many modifications may be made to adapt a particular situation, material, composition of matter, process, process act(s) or step(s) to the objective(s), spirit or scope of the various embodiments. Further, as will be appreciated by those with skill in the art, each of the individual variations described and illustrated herein has discrete components and features which may be readily separated from or combined with the features of any of the other several embodiments without departing from the scope or spirit of the various embodiments.
Claims
1-17. (canceled)
18. A light detection and ranging (LiDAR) system comprising:
- a light source configured to produce a first plurality of pulses including a first pulse and a second plurality of pulses including a second pulse, wherein the first plurality of pulses have a first wavelength and the second plurality of pulses have a second wavelength different than the first wavelength; and
- a pulse steering system having a dispersion optic configured to receive along a receive path the first pulse and the second pulse from the light source and to direct the first pulse along a first scan path and the second pulse along a second scan path different than the first scan path.
19. The system of claim 18, wherein the pulse steering system further includes a rotatable polygon having a plurality of reflective sides.
20. The system of claim 19, wherein the rotatable polygon has an axis of rotation parallel to a direction of dispersion of the dispersion optic.
21. The system of claim 18, wherein the pulse steering system further includes a scanning mirror.
22. The system of claim 21, wherein the scanning mirror is a mirror galvanometer.
23. The system of claim 18, wherein the dispersion optic is a prism or an optical grating.
24. The system of claim 18, wherein the light source includes a tunable seed laser.
25. The system of claim 18, wherein the light source includes a fiber configured to deliver the first plurality of light pulses and the second plurality of light pulses to the dispersion optic.
26. The system of claim 18, wherein the light source is further configured to produce a third plurality of pulses, wherein the third plurality of pulses have a third wavelength different than the first wavelength and the second wavelength.
27. The system of claim 18, wherein the light source is configured to provide light pulses of at least 50 different wavelengths.
28. The system of claim 18, wherein the light source is configured to provide light pulses of at least 300 different wavelengths.
29. The system of claim 18, wherein the light source is configured to provide light pulses having wavelengths that differ by less than 1 nm.
Type: Application
Filed: Oct 2, 2023
Publication Date: Jan 25, 2024
Applicant: Innovusion, Inc. (Sunnyvale, CA)
Inventors: Rui Zhang (Palo Alto, CA), Yimin Li (Cupertino, CA), Junwei Bao (Los Altos, CA)
Application Number: 18/375,961