PATENT DOCUMENT

Publication Number: US-10634770-B2
Application Number: US-201715636566-A
Country: US
Kind Code: B2

Title: Optical systems for remote sensing receivers

Abstract:
Optical systems that may, for example, be used in remote sensing systems, for example in systems that implement combining laser pulse transmission in LiDAR and that include dual transmit and receive systems. A dual receiver system may include a receiver including an optical system with a relatively small aperture and wide field of view for capturing reflected light from short-range (e.g., &lt;20 meters) objects, and a receiver that includes an optical system with a relatively large aperture and small field of view for capturing reflected light from long-range (e.g., &gt;20 meters) objects. The optical systems may refract the reflected light to photodetectors (e.g., single photo-avalanche detectors (SPADs)) that capture the light. Light captured at the photodetectors may, for example, be used to determine range information for objects or surfaces in the environment.

Claims:
What is claimed is: 
     
       1. A remote sensing system, comprising:
 two transmitters that transmit light through a common optical path to an object field; and 
 two receivers that detect reflections of the transmitted light received at the system through the common optical path, wherein the two receivers include:
 a short-range optical system including a plurality of refractive lens elements that refract a portion of the light reflected from a range of 20 meters or less to a first sensor that captures the light, wherein field of view of the short-range optical system is between 45 and 65 degrees, and wherein F-number of the short-range optical system is 2.0 or less; and 
 a long-range optical system including a plurality of refractive lens elements that refract a portion of the light reflected from a range of 20 meters or more to a second sensor that captures the light, wherein field of view of the long-range optical system is 15 degrees or less, and wherein F-number of the long-range optical system is 1.2 or less. 
 
 
     
     
       2. The remote sensing system as recited in  claim 1 , wherein the long-range optical system includes five refractive lens elements, and wherein surfaces of the lens elements in the long-range optical system include one or more of spherical, even-aspheric, or flat/plano surfaces. 
     
     
       3. The remote sensing system as recited in  claim 1 , wherein the short-range optical system includes six refractive lens elements, wherein surfaces of the lens elements in the short-range optical system include one or more of spherical, even-aspheric, or flat/plano surfaces. 
     
     
       4. The remote sensing system as recited in  claim 1 , wherein the short-range optical system includes seven refractive lens elements, wherein surfaces of the lens elements in the short-range optical system include one or more of spherical, even-aspheric, or flat/plano surfaces. 
     
     
       5. The remote sensing system as recited in  claim 1 , wherein one or both of the short-range optical system and the long-range optical system are image-space telecentric lenses. 
     
     
       6. The remote sensing system as recited in  claim 1 , wherein one or both of the short-range optical system and the long-range optical system include an optical bandpass filter. 
     
     
       7. The remote sensing system as recited in  claim 1 , wherein the sensors each include one or more single photo-avalanche detectors. 
     
     
       8. A long-range optical system for receiving reflected light from an object field, comprising:
 five refractive lens elements that refract light reflected from a range of 20 meters or more to a photodetector, wherein surfaces of the refractive lens elements are spherical, even-aspheric, or flat/plano surfaces; 
 wherein field of view of the optical system is 15 degrees or less, and wherein F-number of the optical system is 1.2 or less. 
 
     
     
       9. The long-range optical system as recited in  claim 8 , wherein the five refractive lens elements include, in order from an object side of the optical system to an image side of the optical system:
 a first lens element, wherein the first lens element is a biconvex lens with positive refractive power; 
 a second lens element, wherein the second lens element is a plano-concave lens with negative refractive power; 
 a third lens element, wherein the third lens element is a meniscus lens with positive refractive power; 
 a fourth lens element, wherein the fourth lens element is a meniscus lens with positive refractive power; and 
 a fifth lens element, wherein the fifth lens element is a biconcave lens with negative refractive power. 
 
     
     
       10. The long-range optical system as recited in  claim 9 , wherein the optical system further comprises:
 a stop located between the second lens element and the third lens element; and 
 an optical bandpass filter located at the image side surface of the second lens element. 
 
     
     
       11. The long-range optical system as recited in  claim 8 , wherein the five refractive lens elements include, in order from an object side of the optical system to an image side of the optical system:
 a first lens element, wherein the first lens element is a plano-convex lens with positive refractive power; 
 a second lens element, wherein the second lens element is a meniscus lens with positive refractive power; 
 a third lens element, wherein the third lens element is a biconcave lens with negative refractive power; 
 a fourth lens element, wherein the fourth lens element is a biconvex lens with positive refractive power; and 
 a fifth lens element, wherein the fifth lens element is a meniscus lens with positive refractive power. 
 
     
     
       12. The long-range optical system as recited in  claim 11 , wherein the optical system further comprises:
 a stop located between the first lens element and the second lens element; and 
 an optical bandpass filter located at the image side surface of the first lens element. 
 
     
     
       13. The long-range optical system as recited in  claim 8 , wherein the long-range optical system is an image-space telecentric lens. 
     
     
       14. A short-range optical system for receiving reflected light from an object field, comprising:
 a plurality of refractive lens elements that refract light reflected from a range of 20 meters or less to a photodetector, wherein surfaces of the refractive lens elements are spherical, even-aspheric, or flat/plano surfaces; 
 wherein field of view of the short-range optical system is between 45 and 65 degrees, and wherein F-number of the short-range optical system is 2.0 or less. 
 
     
     
       15. The short-range optical system as recited in  claim 14 , wherein the plurality of refractive lens elements includes, in order from an object side of the optical system to an image side of the optical system:
 a first lens element, wherein the first lens element is a meniscus lens with negative refractive power; 
 a second lens element, wherein the second lens element is a biconvex lens with positive refractive power; 
 a third lens element, wherein the third lens element is a meniscus lens with positive refractive power; 
 a fourth lens element, wherein the fourth lens element is a plano-convex lens with positive refractive power; 
 a fifth lens element, wherein the fifth lens element is a meniscus lens with negative refractive power; and 
 a sixth lens element, wherein the sixth lens element is a biconvex lens with positive refractive power. 
 
     
     
       16. The short-range optical system as recited in  claim 15 , wherein the optical system further comprises:
 a stop located between the second lens element and the third lens element; and 
 an optical bandpass filter located at the object side surface of the fourth lens element. 
 
     
     
       17. The short-range optical system as recited in  claim 14 , wherein the plurality of refractive lens elements includes, in order from an object side of the optical system to an image side of the optical system:
 a first lens element, wherein the first lens element is a meniscus lens with negative refractive power; 
 a second lens element, wherein the second lens element is a meniscus lens with positive refractive power; 
 a third lens element, wherein the third lens element is a plano-convex lens with positive refractive power; 
 a fourth lens element, wherein the fourth lens element is a plano-convex lens with positive refractive power; 
 a fifth lens element, wherein the fifth lens element is a biconvex lens with positive refractive power; and 
 a sixth lens element, wherein the sixth lens element is a biconcave lens with negative refractive power; and 
 a seventh lens element, wherein the seventh lens element is a meniscus lens with positive refractive power. 
 
     
     
       18. The short-range optical system as recited in  claim 15 , wherein the optical system further comprises:
 a stop located on the object side of the first lens element; and 
 an optical bandpass filter located between the fourth lens element and the fifth lens element. 
 
     
     
       19. The short-range optical system as recited in  claim 14 , wherein the plurality of refractive lens elements includes, in order from an object side of the optical system to an image side of the optical system:
 a first lens element, wherein the first lens element is a meniscus lens with positive refractive power; 
 a second lens element, wherein the second lens element is a meniscus lens with negative refractive power; 
 a third lens element, wherein the third lens element is a meniscus lens with positive refractive power; 
 a fourth lens element, wherein the fourth lens element is a biconvex lens with positive refractive power; 
 a fifth lens element, wherein the fifth lens element is a meniscus lens with negative refractive power; and 
 a sixth lens element, wherein the sixth lens element is a plano-convex lens with positive refractive power. 
 
     
     
       20. The short-range optical system as recited in  claim 15 , wherein the optical system further comprises:
 a stop located between the second lens element and the third lens element; and 
 an optical bandpass filter located at the object side surface of the sixth lens element. 
 
     
     
       21. The short-range optical system as recited in  claim 14 , wherein the short-range optical system is an image-space telecentric lens.

Description:
PRIORITY INFORMATION 
     This application claims benefit of priority of U.S. Provisional Application Ser. No. 62/356,454 entitled “OPTICAL SYSTEMS” filed Jun. 29, 2016, the content of which is incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     Remote sensing technologies provide different systems with information about the environment external to the system. Diverse technological applications may rely upon remote sensing systems and devices to operate. Moreover, as increasing numbers of systems seek to utilize greater amounts of data to perform different tasks in dynamic environments; remote sensing provides environmental data that may be useful decision-making. For example, control systems that direct the operation of machinery may utilize remote sensing devices to detect objects within a workspace. In some scenarios, laser based sensing technologies, such as light ranging and detection (LiDAR), can provide high resolution environmental data, such as depth maps, which may indicate the proximity of different objects to the LiDAR. 
     SUMMARY 
     Optical methods and systems are described that may, for example, be used in remote sensing systems such as light ranging and detection (LiDAR) applications, for example in systems that implement combining laser pulse transmission in LiDAR and that include dual transmit and receive systems. Receiver components of a dual receiver system in LiDAR applications may include an embodiment of a relatively small aperture wide field of view (FOV) optical system for short-ranges (referred to as short-range optical system), and an embodiment of a relatively large aperture optical system with a smaller FOV for long-ranges (referred to as long-range optical system). Both the long-range and short-range optical systems may utilize optical filters, scanning mirrors (e.g., micro electro-mechanical (MEMS) mirrors), and photodetectors (also referred to as photosensors or sensors), for example one or more one-dimensional single photo-avalanche detectors (SPADs) to increase the probability of positive photon events. 
     An example light ranging and detecting (LiDAR) device is described that combines laser pulse transmissions in a common optical path and in which embodiments of the short-range and long-range optical systems may be implemented. In the example LiDAR device, different laser transmitters may transmit respective trains of pulses which may be combined and separated in the optical path of the LiDAR according to the polarization state of the laser pulses. In this way different types of laser pulses may be combined, including laser pulses with different wavelengths, widths, or amplitudes. The transmission of laser pulses in the different trains of pulses may be dynamically modified to adjust the timing of when laser pulses are transmitted so that different scanning patterns may be implemented. Receiver components of the LiDAR device may incorporate embodiments of the long-range optical system and short-range optical system as described herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an example embodiment of an optical system that may, for example, be used as a long-range optical system in LiDAR applications. 
         FIG. 2  illustrates an example embodiment of an optical system that may, for example, be used as a short-range optical system in LiDAR applications. 
         FIG. 3  illustrates an example embodiment of an optical system that may, for example, be used as a short-range optical system in LiDAR applications. 
         FIG. 4  illustrates an example embodiment of an optical system that may, for example, be used as a long-range optical system in LiDAR applications. 
         FIG. 5  illustrates an example embodiment of an optical system that may, for example, be used as a short-range optical system in LiDAR applications. 
         FIGS. 6A and 6B  are logical block diagrams of an example LiDAR system that combines laser pulse transmissions in light ranging and detecting (LiDAR), according to some embodiments. 
         FIGS. 7A and 7B  illustrate an example common optical path for laser pulses emitted by transmitters and pulse reflections received by receivers that include optical systems as illustrated in  FIGS. 1 through 5 , according to some embodiments. 
         FIG. 8  is a high-level flowchart of a method of operation for a LiDAR system that includes light transmitters and long- and short-range receivers that include optical systems as illustrated in  FIGS. 1 through 5 . 
     
    
    
     This specification includes references to “one embodiment” or “an embodiment.” The appearances of the phrases “in one embodiment” or “in an embodiment” do not necessarily refer to the same embodiment. Particular features, structures, or characteristics may be combined in any suitable manner consistent with this disclosure. 
     “Comprising.” This term is open-ended. As used in the appended claims, this term does not foreclose additional structure or steps. Consider a claim that recites: “An apparatus comprising one or more processor units . . . .” Such a claim does not foreclose the apparatus from including additional components (e.g., a network interface unit, graphics circuitry, etc.). 
     “Configured To.” Various units, circuits, or other components may be described or claimed as “configured to” perform a task or tasks. In such contexts, “configured to” is used to connote structure by indicating that the units/circuits/components include structure (e.g., circuitry) that performs those task or tasks during operation. As such, the unit/circuit/component can be said to be configured to perform the task even when the specified unit/circuit/component is not currently operational (e.g., is not on). The units/circuits/components used with the “configured to” language include hardware—for example, circuits, memory storing program instructions executable to implement the operation, etc. Reciting that a unit/circuit/component is “configured to” perform one or more tasks is expressly intended not to invoke 35 U.S.C. § 112(f), for that unit/circuit/component. Additionally, “configured to” can include generic structure (e.g., generic circuitry) that is manipulated by software and/or firmware (e.g., an FPGA or a general-purpose processor executing software) to operate in manner that is capable of performing the task(s) at issue. “Configure to” may also include adapting a manufacturing process (e.g., a semiconductor fabrication facility) to fabricate devices (e.g., integrated circuits) that are adapted to implement or perform one or more tasks. 
     “First,” “Second,” etc. As used herein, these terms are used as labels for nouns that they precede, and do not imply any type of ordering (e.g., spatial, temporal, logical, etc.). For example, a buffer circuit may be described herein as performing write operations for “first” and “second” values. The terms “first” and “second” do not necessarily imply that the first value must be written before the second value. 
     “Based On.” As used herein, this term is used to describe one or more factors that affect a determination. This term does not foreclose additional factors that may affect a determination. That is, a determination may be solely based on those factors or based, at least in part, on those factors. Consider the phrase “determine A based on B.” While in this case, B is a factor that affects the determination of A, such a phrase does not foreclose the determination of A from also being based on C. In other instances, A may be determined based solely on B. 
     DETAILED DESCRIPTION 
     Optical methods and systems are described herein that may, for example, be used in remote sensing systems such as light ranging and detection (LiDAR) applications, for example in systems that implement combining laser pulse transmission in LiDAR as illustrated in  FIGS. 6A and 6B . LiDAR is a remote sensing technology that directs a laser or lasers at a target and measures a distance to the target according to reflections of the laser(s) detected at the LiDAR. The distance may be calculated based on the difference between a time at which a laser pulse transmission is sent and a time at which a reflection of the laser pulse transmission is received. Distance measures calculated by LiDAR are used in many different applications. For instance, multiple distance measures taken over an area can be processed to generate a high resolution map, which can be used in a variety of different applications, including, but not limited to, geological surveys, atmospheric measurements, object detection, autonomous navigation, or other remote environmental sensing applications. Note that the term “LiDAR” as used herein is sometimes designated or referred to in other texts differently, including such terms as “Lidar”, “lidar”, “LIDAR”, or “light radar.” 
     Long-range and Short-range Receiver Optics 
       FIGS. 1 through 5  and Tables 1 through 5 illustrate various embodiments of optical systems that may, for example, be used as long-range and short-range optical systems in long-range and short-range receivers of remote sensing systems such as LiDAR systems, for example as illustrated in  FIGS. 6A through 7B . An advantage of the dual transmit and receive system for LiDAR is a realizable architecture that includes scanning mirrors, micro electro-mechanical (MEMS) mirrors, single photo-avalanche detectors (SPADs) for counting single photoelectron events from close (short) range (e.g., 20 meters or less) and long-range (e.g., 20 meters to 200 meters) with acceptable manufacturing risk, eye safety margin, and probability of photon detection. 
     Components of a dual receiver system in LiDAR applications may include a relatively small aperture wide field optical system for short-ranges (referred to as a short-range optical system), and a relatively large aperture optical system with a smaller field for long-ranges (referred to as a long-range optical system). Both the long-range and short-range optical systems may utilize optical filters, scanning mirrors, and a sensor, for example one or more single photo-avalanche detectors (SPADs), to increase the probability of positive photon events. 
     In some embodiments, the dual receiver system may include two light transmitters (e.g., lasers) that transmit light through a common optical path to an object field, and two light receivers that detect reflections of the transmitted light received at the system through the common optical path. The light receivers may include a short-range optical system including lens elements that refract a portion of the light reflected from within a range of, for example, 20 meters or less to a first sensor configured to capture the light, and a long-range optical system including one or more lens elements that refract a portion of the light reflected from within a range of, for example, 20 meters or more to a second sensor configured to capture the light. In some embodiments, the short-range optical system has a small aperture and provides a wide field of view, and the long-range optical system has a large aperture and provides a small field of view. 
     In some embodiments, the long-range optical system may include five refractive lens elements. In some embodiments, field of view of the long-range optical system may be 15 degrees or less. In some embodiments, F-number of the long-range optical system may be 1.2 or less. In some embodiments, the surfaces of the lens elements in the long-range optical system are one of spherical, even-aspheric, or flat/plano surfaces. In some embodiments, the long-range optical system may include an optical bandpass filter, or alternatively an optical bandpass filter coating on a plano surface of one of the lens elements. 
     In some embodiments, the short-range optical system may include seven refractive lens elements. In some embodiments, the short-range optical system may include six refractive lens elements. In some embodiments, the short-range optical system has a field of view of between 45 and 65 degrees. In some embodiments, F-number of the short-range optical system may be 2.0 or less. In some embodiments, the surfaces of the lens elements in the short-range optical system are one of spherical, even-aspheric, or flat/plano surfaces. In some embodiments, the short-range optical system may include an optical bandpass filter, or alternatively an optical bandpass filter coating on a flat/plano surface of one of the lens elements. 
     Note that the various parameters of the optical systems are given by way of example and are not intended to be limiting. For example, the optical systems may include more or fewer lens elements than described in the example embodiments, shapes of the lens elements may vary from those described, and the optical properties (e.g., field of view, aperture, F-number, etc.) of the optical systems may be different than those described while still providing similar performance for the optical systems. Further note that the optical systems may be scaled up or down to provide larger or smaller implementations of the optical systems as described herein. 
     While embodiments of optical systems are described in reference to use in systems such as LiDAR systems, the optical systems described herein may be used in a variety of other applications. Also note that while embodiments are described in reference to dual receiver systems, embodiments of the optical systems may be used in systems that include one or more than two receivers. 
     Tables 1 through 5 provide example values for various optical and physical parameters of the example embodiments of the optical systems described in reference to  FIGS. 1 through 5 . In the Tables, all dimensions are in millimeters (mm) unless otherwise specified. “S#” stands for surface number. A positive radius indicates that the center of curvature is to the right (object side) of the surface. A negative radius indicates that the center of curvature is to the left (image side) of the surface. “Infinity” stands for infinity as used in optics. The thickness (or gap/separation) is the axial distance to the next surface. 
     In the example embodiments of the optical systems described in reference to  FIGS. 1 through 5 , the lens elements may be formed of various plastic or glass materials. Two or more of the lens elements in a given optical system may be formed of different materials. For the materials of the lens elements, a refractive index (e.g., N d  at the helium d-line wavelength) may be provided, as well as an Abbe number V d  (e.g., relative to the d-line and the C- and F-lines of hydrogen). The Abbe number, V d , may be defined by the equation:
 
 V   d =( N   d −1)/( N   F   −N   C ),
 
where N F  and N C  are the refractive index values of the material at the F and C lines of hydrogen, respectively.
 
     Note that the values given in the following Tables for the various parameters in the various embodiments of the optical systems are given by way of example and are not intended to be limiting. For example, one or more of the parameters for one or more of the surfaces of one or more of the lens elements in the example embodiments, as well as parameters for the materials of which the elements are composed, may be given different values while still providing similar performance for the optical systems. In particular, note that some values in the Tables may be scaled up or down for larger or smaller implementations of the optical systems as described herein. 
     Further note that surface numbers (S#) of the elements in the various embodiments of the optical systems as shown in the Tables are listed from a first surface ( FIG. 1 ), stop ( FIG. 3 ), or object-side surface of a first lens element ( FIGS. 2, 4, and 5 ), to a last surface at the image plane/photosensor surface. 
       FIG. 1  and Table 1—Long-range Optical System  100   
       FIG. 1  and Table 1 illustrate an example embodiment  100  of an optical system that may, for example, be used as a long-range optical system in LiDAR applications. In some embodiments, optical system  100  may have five refractive lens elements  101 - 105  arranged in order from a first lens element  101  on the object side of optical system  100  to a last lens element  105  on the image side of optical system  100 . Optical system  100  may include a stop, for example located between lens  102  and lens  103  as shown in  FIG. 1 . Optical system  100  may also include an optical bandpass filter, for example located at or on surface S 4  of lens  102  as shown in  FIG. 1 . Optical system  100  may be configured to refract light from an object field to an image plane formed at or near the surface of a sensor  190 . Sensor  190  may, for example, include one or more single photo-avalanche detectors (SPADs). However, other types of photodetectors may be used in some embodiments. 
     Lens element  101  may be a biconvex lens with positive refractive power. In some embodiments, both surfaces of lens element  101  may be spherical. Lens element  102  may be a plano-concave lens with negative refractive power. Lens element  102  may have a concave object side surface and a plano (flat) image side surface. In some embodiments, the object side surface of lens element  102  may be spherical. In some embodiments, the object side surface of lens element  102  may contact the image side surface of lens  101 . Lens element  103  may be a meniscus lens with positive refractive power. Lens element  103  may have a convex object side surface and a concave image side surface. In some embodiments, both surfaces of lens element  103  may be spherical. Lens element  104  may be a meniscus lens with positive refractive power. Lens element  104  may have a convex object side surface and a concave image side surface. In some embodiments, both surfaces of lens element  104  may be spherical. Lens element  105  may be a biconcave lens with negative refractive power. In some embodiments, both surfaces of lens element  105  may be spherical. 
     Properties and advantages of optical system  100  may include one or more of, but are not limited to:
         The optical system  100  may have five or fewer lenses.   One or more of the lenses may have spherical surfaces; in some embodiments, all of the lenses have spherical surfaces.   The optical system  100  may have a large entrance pupil (e.g., 40 mm) and a small F-number (e.g., 1.125 or less), and may provide a small field of view (e.g., 15 degrees or less).   The optical system  100  may be a telecentric lens (e.g., an image-space telecentric lens) to provide minimum image scale change when a focal plane is introduced and during variations in temperature.   The optical system  100  may include an optical bandpass filter for optimum probability of detection for photoelectric events. For example, the optical system  100  may include a filter at or on surface S 4  of lens  102  as shown in  FIG. 1  to mitigate the likelihood of unwanted pupil ghosts at the focus (image plane).   The optical system  100  may achieve system specifications over a large temperature range (e.g., −40 degrees C. to 80 degrees C.) and source bandwidth (e.g., 900 nanometers (nm)-1000 nm).   The optical system  100  may be optimized for compact SPAD configurations.   The optical system  100  may have less than 0.2% negative distortion and almost 100% relative illumination over the field of view for optimum photon probability of detection.   The optical system  100  may include a stop (aperture), for example located between lens  102  and lens  103  as illustrated in  FIG. 1 .       

     In some embodiments, the optical system  100  may be integrated with a multiple scanning mirror system (e.g., a MEMS mirror) to collect laser radiation from long-range objects and image the objects with sufficient precision to one or more SPAD chips at the focus (image plane). 
                     TABLE 1                  Receiver optical system 100                                                 Radius of                           curvature   Thickness or           Surface   Type   (mm)   Gap   Material                                                     Object   STANDARD   Infinity   Infinity               S1   STANDARD   Infinity   25.40005       Lens 101   S2   STANDARD   50.52775   12.62115   BK7       Lens 102   S3   STANDARD   −47.35588   5.635905   SF6           S4   STANDARD   Infinity   0.6117068       Stop   Stop   STANDARD   Infinity   2.391139       Lens 103   S6   STANDARD   30.71983   10.29709   S-LAL9           S7   STANDARD   52.66062   20.62353       Lens 104   S8   STANDARD   23.27457   6.938469   SF6           S9   STANDARD   166.2798   5.000918       Lens 105   S10   STANDARD   −27.73724   4.946685   SF6           S11   STANDARD   139.1987   5.0       Sensor   Image   STANDARD   Infinity       190                      FIG. 2  and Table 2—Short-range Optical System  200 
 
       FIG. 2  and Table 2 illustrate an example embodiment  200  of an optical system that may, for example, be used as a short-range optical system in LiDAR applications. In some embodiments, optical system  200  may have six refractive lens elements  201 - 206  arranged in order from a first lens element  201  on the object side of optical system  200  to a last lens element  206  on the image side of optical system  200 . Optical system  200  may include a stop, for example located between lens  202  and lens  203  as shown in  FIG. 2 . Optical system  200  may also include an optical bandpass filter, for example located at or on surface S 12  of lens  204  as shown in  FIG. 2 . Optical system  200  may be configured to refract light from an object field to an image plane formed at or near the surface of a sensor  290 . Sensor  290  may, for example, include one or more single photo-avalanche detectors (SPADs). However, other types of photodetectors may be used in some embodiments. 
     Lens element  201  may be a meniscus lens with negative refractive power. Lens element  201  may have a convex object side surface and a concave image side surface. In some embodiments, surface S 4  of lens element  201  may be even aspheric or spherical, and surface S 5  of lens element  201  may be spherical. Lens element  202  may be a biconvex lens with positive refractive power. In some embodiments, surface S 6  of lens element  202  may be spherical, and surface S 7  of lens element  202  may be even aspheric or spherical. Lens element  203  may be a meniscus lens with positive refractive power. Lens element  203  may have a concave object side surface and a convex image side surface. In some embodiments, surfaces S 10  and S 11  of lens element  203  may be spherical. Lens element  204  may be a plano-convex lens with positive refractive power. Lens element  204  may have a plano (flat) object side surface and a convex image side surface. In some embodiments, surface S 13  of lens  204  may be spherical. Lens element  205  may be a meniscus lens with negative refractive power. In some embodiments, surface S 14  of lens element  205  may be convex, and surface S 15  of lens element  205  may be concave. In some embodiments, surface S 14  of lens element  205  may be spherical, and surface S 15  of lens element  205  may be even aspheric or spherical. Lens element  206  may be a biconvex lens with positive refractive power. In some embodiments, surface S 16  of lens element  206  may be spherical, and surface S 17  of lens element  206  may be even aspheric or spherical. 
     Properties and advantages of optical system  200  may include one or more of, but are not limited to:
         The optical system  200  may have six or fewer lenses.   One or more of the lenses may have spherical surfaces; in some embodiments, all of the lenses have spherical surfaces.   The optical system  200  may have a small F-number (e.g., 2.0 or less), and may provide a large field-of-view (e.g., 60 degrees or greater).   The optical system  200  may be a telecentric lens (e.g., an image-space telecentric lens) to minimize the effects of photon centroid motion and triangulation for short optical ranges.   The optical system  200  may include an optical bandpass filter for optimum probability of detection for photoelectric events. For example, the optical system  200  may include a filter at or on a flat surface S 12  of lens  204  as shown in  FIG. 2 .   The optical system  100  may system specifications over a large temperature range (e.g., −40 degrees C. to 80 degrees C.) and source bandwidth (e.g., 900 nm-1000 nm).   The optical system  200  may be optimized for compact SPAD configurations.   The optical system  200  may have less than 5% negative distortion and greater than 60% relative illumination over the field for optimum photon probability of detection.   The optical system  200  may include a stop (aperture), for example located between lens  202  and lens  203  as illustrated in  FIG. 2 .       

     In some embodiments, the optical system  200  may be integrated with a multiple scanning mirror system (e.g., a MEMS mirror) to collect laser radiation from short-range objects and image the objects with sufficient precision to one or more SPAD chips at the focus (image plane). 
                     TABLE 2                  Receiver optical system 200                                                 Radius of   Thickness or   Ma-           Surface   Type   curvature   Gap   terial                                                 Lens 201   S4   Even Aspheric   160.0949   2.0   BK7           S5   STANDARD   9.310111   1.705925       Lens 202   S6   STANDARD   44.142   3.000001   SF6           S7   Even Aspheric   −20.31882   0.1999999           Stop   STANDARD   Infinity   0       Lens 203   S9   STANDARD   Infinity   4.144555           S10   STANDARD   −8.87866   5.0   SF6           S11   STANDARD   −10.73887   0.4619624       Lens 204   S12   STANDARD   Infinity   5.017804   SF6           S13   STANDARD   −23.29207   0.6136292       Lens 205   S14   STANDARD   21.1782   6.056791   SF6           S15   Even Aspheric   11.76076   5.193445       Lens 206   S16   STANDARD   19.42751   4.478419   SF6           S17   Even Aspheric   −120.8147   7.127467       Sensor   Image   STANDARD   Infinity       290                      FIG. 3  and Table 3—Receiver Optical System  300 
 
       FIG. 3  and Table 3 illustrate an example embodiment  300  of an optical system that may, for example, be used as a short-range optical system in LiDAR applications. In some embodiments, optical system  300  may have seven refractive lens elements  301 - 307  arranged in order from a first lens element  301  on the object side of optical system  300  to a last lens element  307  on the image side of optical system  300 . Optical system  300  may include a stop, for example located between lens  301  and the object field as shown in  FIG. 3 . Optical system  300  may also include an optical bandpass filter  310 , for example located between lens  304  and  305  as shown in  FIG. 3 , or alternatively may have an optical bandpass filter coating on surface S 9  of lens  304  as shown in  FIG. 3 . Optical system  300  may be configured to refract light from an object field to an image plane formed at or near the surface of a sensor  390 . Sensor  390  may, for example, include one or more single photo-avalanche detectors (SPADs). However, other types of photodetectors may be used in some embodiments. 
     Lens element  301  may be a meniscus lens with negative refractive power. Lens element  301  may have a concave object side surface and a convex image side surface. In some embodiments, both surfaces of lens element  301  may be spherical. Lens element  302  may be a meniscus lens with positive refractive power. In some embodiments, both surfaces of lens element  302  may be spherical. Lens element  302  may have a concave object side surface and a convex image side surface. Lens element  303  may be a plano-convex lens with positive refractive power. Lens element  303  may have a plano (flat) object side surface and a convex image side surface. In some embodiments, the image side surface of lens element  303  may be spherical. Lens element  304  may be a plano-convex lens with positive refractive power. Lens element  304  may have a convex object side surface and a plano (flat) image side surface. In some embodiments, the object side surface of lens  304  may be spherical. Lens element  305  may be a biconvex lens with positive refractive power. In some embodiments, both surfaces of lens element  305  may be spherical. Lens element  306  may be a biconcave lens with negative refractive power. In some embodiments, both surfaces of lens element  206  may be spherical. In some embodiments, the object side surface of lens element  306  may contact the image side surface of lens  305 . Lens element  307  may be a meniscus lens with positive refractive power. In some embodiments, both surfaces of lens element  307  may be spherical. Lens element  702  may have a convex object side surface and a concave image side surface. 
     Properties and advantages of optical system  300  may include one or more of, but are not limited to:
         The optical system  300  may be a fast lens with a low F-number, for example within a range of 1.5 to 1.6, for example 1.53.   The optical system  300  may provide 45 degree field of view coverage in both azimuth and elevation.   The optical system  300  may be corrected over a wide spectral range to account for source wavelength variability (unit to unit). For example, in some embodiments, up to +/−50 nm can be tolerated with a simple refocus of the optical system  300  during assembly.   The optical system  300  may be corrected for up to 12 nm spectral width to accommodate the source spectral width and the drift of the source spectrum with temperature.   The optical system  300  may include seven lens elements. In some embodiments all of the lens elements have spherical surfaces, which may lower costs.   The optical system  300  design allows for easy manufacturing tolerances for the lens elements as well as for lens assembly.   The optical system  300  may be athermalized over a temperature range of −40 degrees C. to 80 degrees C. when assembled with a stainless steel barrel. This may, for example, help to ensure the resolution of the system  300  over a wide operating range while preserving both the focus and the focal length of the system  300 .   The optical system  300  may have a low distortion design that allows pre-mapping of object angle to sensor position without losing angular resolution.   The optical system  300  may be a telecentric lens (e.g., an image-space telecentric lens) to ensure that the signal at the sensor is correctly mapped from angle in the object space to placement in the image space irrespective of object distance.   In some embodiments, a plano (flat) surface (e.g., surface S 9  of lens  304  as shown in  FIG. 3 ) is available internal to the optical system  300  in a space that is collimated or nearly collimated to allow the deposition of a narrow pass band coating directly on the plano surface of the lens (e.g., surface S 9  of lens  304  as shown in  FIG. 3 ), thus obviating the need for a filter element. Alternatively, in some embodiments, a separate filter  310  may be placed in the same collimated space (between lens  304  and lens  305 ), and performance can be recovered by a simple refocus during assembly.   The optical system  300  may include a stop (aperture), for example at or in front of lens  301  as illustrated in  FIG. 3 .       

     In some embodiments, the optical system  300  may be integrated with a multiple scanning mirror system (e.g., a MEMS mirror) to collect laser radiation from short-range objects and image the objects with sufficient precision to one or more SPAR chips at the focus (image plane). 
                     TABLE 3                  Receiver optical system 300                                                     Radius of   Thickness                       Surface   curvature   or Gap   Refractive   Abbe       Element   Surface   type   (mm)   (mm)   Index   Number                   Object       Infinity   Infinity               Stop   S1   Stop   Infinity   19.90       Lens 301   S2   Spherical   −27.52   10.75   1.784701   26.08           S3   Spherical   −289.00   1.7       Lens 302   S4   Spherical   −165.66   8.00   1.804200   46.50           S5   Spherical   −45.74   1.00       Lens 303   S6   Spherical   Infinity   7.50   1.804200   46.50           S7   Spherical   −79.90   1.00       Lens 304   S8   Spherical   76.20   8.84   1.753930   52.27           S9   Plano   Infinity   1.00       Filter   S10   Plano   Infinity   2.00   1.516800   64.17       (optional)           S11   Plano   Infinity   1.00       Lens 305   S12   Spherical   43.70   15.00   1.743972   44.85       Lens 306   S13   Spherical   −162.65   8.50   1.805182   25.43           S14   Spherical   26.16   8.013       Lens 307   S15   Spherical   53.00   15.00   1.696800   55.41           S16   Spherical   261.00   10.687262       Sensor 390   Sensor   Plano   Infinity   0.00                      FIG. 4  and Table 4—Receiver Optical System  400 
 
       FIG. 4  and Table 4 illustrate an example embodiment  400  of an optical system that may, for example, be used as a long-range optical system in LiDAR applications. In some embodiments, optical system  400  may have five refractive lens elements  401 - 405  arranged in order from a first lens element  401  on the object side of optical system  400  to a last lens element  405  on the image side of optical system  400 . Optical system  400  may include a stop, for example located between lens  401  and lens  402  as shown in  FIG. 4 . Optical system  400  may also include an optical bandpass filter, for example located at or on the image side surface (surface S 2 ) of lens  401  as shown in  FIG. 4 . Optical system  400  may be configured to refract light from an object field to an image plane formed at or near the surface of a sensor  490 . Sensor  490  may, for example, include one or more single photo-avalanche detectors (SPADs). However, other types of photodetectors may be used in some embodiments. 
     Lens element  401  may be a plano-convex lens with positive refractive power. Lens element  401  may have a convex object side surface and a plano (flat) image side surface. In some embodiments, the object side surface of lens element  401  may be spherical. Lens element  402  may be a meniscus lens with positive refractive power. Lens element  402  may have a convex object side surface and a concave image side surface. In some embodiments, both surfaces of lens element  402  may be spherical. Lens element  403  may be a biconcave lens with negative refractive power. In some embodiments, both surfaces of lens element  403  may be spherical. Lens element  404  may be a biconvex lens with positive refractive power. In some embodiments, both surfaces of lens element  404  may be spherical. Lens element  405  may be a meniscus lens with positive refractive power. In some embodiments, both surfaces of lens element  405  may be spherical. Lens element  405  may have a convex object side surface and a concave image side surface. 
     Properties and advantages of optical system  400  may include one or more of, but are not limited to:
         The optical system  400  may be a fast lens with a low F-number, for example within a range of 1.1 to 1.2, for example 1.125.   The optical system  400  may provide a 10 degree field of view.   The optical system  400  may be corrected over a wide spectral range to account for source wavelength variability (unit to unit). For example, in some embodiments, up to +/−50 nm can be tolerated with a simple refocus of the optical system  400  during assembly.   The optical system  400  may be corrected for up to 12 nm spectral width to accommodate the source spectral width and the drift of the source spectrum with temperature.   The optical system  400  may include five lens elements. In some embodiments all of the lens elements have spherical surfaces, which may lower costs.   The optical system  400  design allows for easy manufacturing tolerances for the lens elements as well as for lens assembly.   The optical system  400  may be athermalized over a temperature range of −40 degrees C. to 80 degrees C. when assembled with a stainless steel barrel. This may, for example, help to ensure the resolution of the system  400  over a wide operating range while preserving both the focus and the focal length of the system  400 .   The optical system  400  may have a low distortion design (e.g., distortion &lt;−0.2%).   The optical system  400  may be a telecentric lens (e.g., an image-space telecentric lens) to ensure that the signal at the sensor is correctly mapped from angle in the object space to placement in image space irrespective of object distance.   In some embodiments, a plano surface (e.g., surface S 2  of lens element  401  in  FIG. 4 ) is available internal to the optical system  400  in a space that is collimated or nearly collimated to allow the deposition of a narrow pass band coating directly on the plano surface of the lens (e.g., surface S 2  of lens element  401  in  FIG. 4 ), thus obviating the need for a filter element.   The optical system  400  may include a stop (aperture), for example located between lens  401  and lens  402  as illustrated in  FIG. 4 .       

     In some embodiments, the optical system  400  may be integrated with a multiple scanning mirror system (e.g., a MEMS mirror) to collect laser radiation from long-range objects and image the objects with sufficient precision to one or more SPAR chips at the focus (image plane). 
                     TABLE 4                  Receiver optical system 400                                                     Radius of   Thickness                       Surface   curvature   or Gap   Refractive   Abbe       Element   Surface   type   (mm)   (mm)   Index   Number                   Object       Infinity   Infinity               Lens 401   S1   Spherical   65.700   6.400   1.743972   44.85           S2   Plano   Infinity   0.000       Stop   S3   Stop   Infinity   9.144       Lens 402   S4   Spherical   36.000   8.000   1.717360   29.62           S5   Spherical   89.650   6.120       Lens 403   S6   Spherical   −209.900   8.000   1.487490   70.41           S7   Spherical   23.000   19.167       Lens 404   S8   Spherical   48.300   5.000   1.805180   25.36           S9   Spherical   −81.240   1.002       Lens 405   S10   Spherical   16.500   8.000   1.805180   25.36           S11   Spherical   13.500   4.168       Sensor 490   Sensor   Plano   Infinity   0.000                      FIG. 5  and Table 5—Receiver Optical System  500 
 
       FIG. 5  and Table 5 illustrate an example embodiment  500  of an optical system that may, for example, be used as a short-range optical system in LiDAR applications. In some embodiments, optical system  500  may have six refractive lens elements  501 - 506  arranged in order from a first lens element  501  on the object side of optical system  500  to a last lens element  506  on the image side of optical system  500 . Optical system  500  may include a stop, for example located between lens  502  and lens  503  as shown in  FIG. 5 . Optical system  500  may also include an optical bandpass filter, for example located at or on surface S 13  of lens  506  as shown in  FIG. 5 . Optical system  500  may be configured to refract light from an object field to an image plane formed at or near the surface of a sensor  590 . Sensor  590  may, for example, include one or more single photo-avalanche detectors (SPADs). However, other types of photodetectors may be used in some embodiments. 
     Lens element  501  may be a meniscus lens with positive refractive power. Lens element  501  may have a concave object side surface and a convex image side surface. In some embodiments, both surfaces of lens element  501  may be spherical. Lens element  502  may be a meniscus lens with negative refractive power. Lens element  502  may have a convex object side surface and a concave image side surface. In some embodiments, both surfaces of lens element  502  may be spherical. Lens element  503  may be a meniscus lens with positive refractive power. Lens element  503  may have a concave object side surface and a convex image side surface. In some embodiments, both surfaces of lens element  503  may be spherical. Lens element  504  may be a biconvex lens with positive refractive power. In some embodiments, both surfaces of lens  504  may be spherical. Lens element  505  may be a meniscus lens with negative refractive power. In some embodiments, the object side surface of lens element  505  may be convex, and the image side surface of lens element  505  may be concave. In some embodiments, both surfaces of lens element  505  may be spherical. Lens element  506  may be a plano-convex lens with positive refractive power. Lens element  506  may have a convex object side surface and a plano (flat) image side surface. In some embodiments, the object side surface of lens element  506  may be spherical. 
     Properties and advantages of optical system  500  may include one or more of, but are not limited to:
         The optical system  500  may provide moderately fast optics (e.g. F-number of 2.0) in a compact form.   The optical system  500  may provide a 60 degree field of view   The optical system  500  may be corrected over a wide spectral range to account for source wavelength variability (unit to unit). For example, in some embodiments, up to +/−50 nm can be tolerated with a simple refocus of the optical system  500  during assembly.   The optical system  500  may be corrected for up to 12 nm spectral width to accommodate the source spectral width and the drift of the source spectrum with temperature.   The optical system  500  may include six lens elements. In some embodiments all of the lens elements have spherical surfaces, which may lower costs.   The optical system  500  design allows for easy manufacturing tolerances for the lens elements as well as for lens assembly.   The optical system  500  may be athermalized over a temperature range of −40 degrees C. to 80 degrees C. when assembled with a stainless steel barrel. This may, for example, help to ensure the resolution of the system  500  over a wide operating range while preserving both the focus and the focal length of the system  500 .   The optical system  500  may have a low distortion design that allows pre-mapping of object angle to sensor position without losing angular resolution.   The optical system  500  may be a telecentric lens (e.g., an image-space telecentric lens) to ensure that the signal at the sensor is correctly mapped from angle in the object space to placement in image space irrespective of object distance.   In some embodiments, a plano surface (e.g., surface S 13  of lens element  506  in  FIG. 5 ) is available internal to the optical system  500  in a space with a low diversity of angles to allow the deposition of a narrow pass band coating directly on the plano surface of the lens (e.g., surface S 13  of lens element  506  in  FIG. 5 ), thus obviating the need for a filter element.   The optical system  500  may include a stop (aperture), for example located between lens  502  and lens  503  as illustrated in  FIG. 5 .       

     In some embodiments, the optical system  400  may be integrated with a multiple scanning mirror system (e.g., a MEMS mirror) to collect laser radiation from short-range objects and image the objects with sufficient precision to one or more SPAR chips at the focus (image plane). 
                     TABLE 5                  Optical system 500                                                     Radius of   Thickness                       Surface   curvature   or Gap   Refractive   Abbe       Element   Surface   type   (mm)   (mm)   Index   Number                   Object       Infinity   Infinity               Lens 501   S1   Spherical   −380.00   2.65   1.805180   25.36           S2   Spherical   −112.90   5.40       Lens 502   S3   Spherical   19.20   5.40   1.487490   70.41           S4   Spherical   6.95   5.96       Stop   S5   Plano   Infinity   9.40       Lens 503   S6   Spherical   −23.33   3.60   1.805180   25.36           S7   Spherical   −14.40   1.00       Lens 504   S8   Spherical   127.00   3.70   1.805180   25.36           S9   Spherical   −40.16   1.00       Lens 505   S10   Spherical   17.93   6.00   1.805180   25.36           S11   Spherical   13.243   2.681       Lens 506   S12   Spherical   24.41   6.00   1.805180   25.36           S13   Plano   Infinity   9.853431       Sensor 590   Sensor   Plano   Infinity   0.000                    
Example LiDAR System
 
       FIGS. 6A-6B and 7A-7B  illustrate an example LiDAR system in which embodiments of the optical systems as described herein may be implemented. 
       FIGS. 6A and 6B  are logical block diagrams of an example LiDAR system that combines laser pulse transmissions in light ranging and detecting (LiDAR), and in which embodiments of the optical systems as illustrated in  FIGS. 1 through 5  may be implemented, according to some embodiments. In  FIG. 6A , LiDAR  1000  illustrates the combined transmission of two different pulses, outbound pulse  1042  and  1044  via a common optical path  1030 . LiDAR  1000  may implement two laser transmitters  1012  and  1014 . Each laser transmitter  1012  and  1014  may be configured to transmit a separate train of one or more laser pulses (the reflections of which may be captured to determine distance measurements). The type of laser pulses transmitted by the transmitters  1012  and  1014  may be the same or different. For example transmitter  1012  may transmit a laser pulse with a same or different wavelength, pulse width, or amplitude than a laser pulse transmitted by transmitter  1014 . In addition the different types of laser pulses transmitted by transmitters  1012  and  1014 , the timing of transmitting the laser pulses may be different. For example, in some embodiments, laser pulses from transmitter  1012  may be transmitted according to one PRR (e.g., 1 megahertz), whereas laser pulses from transmitter  1014  may be transmitted according to an increased or decreased PRR (e.g., 0.5 megahertz). Transmissions between the two transmitters may also be interleaved according to a transmission timing difference (i.e., delta) between the two laser transmitters. 
     LiDAR  1000  may also implement a common optical path  1030  which combines pulses  1032  sent from the two different transmitters, transmitters  1012  and  1014 . For example, as illustrated in  FIG. 6A , outbound pulse  1042  may be a pulse transmitted from transmitter  1012  and outbound pulse  1044  may be a pulse transmitted from transmitter  1014  which are sent via the same optical path, common optical path  1030 . Different combinations of optical devices (e.g., lenses, beam splitters, folding mirrors, or other any other device that processes or analyzes light waves) may be implemented as part of common optical path  1030  to combine pulses from transmitter  1012  and  1014  which may be transmitted with orthogonal polarizations (e.g., two different linear polarization states). For instance, laser pulses sent from transmitter  1012  may have vertical polarization state and laser pulses sent from transmitter  1014  may have a horizontal polarization state. To combine the pulses of orthogonal polarization states, the various combinations of optical devices in common optical path  1030  may be implemented to ensure that polarization states of the two different laser pulses are distinguishable, both on transmission and reflection, in various embodiments. In this way, reflections of the different pulses received via common optical path  1030  may be separated  1034  (as illustrated in  FIG. 6B ) and directed to the appropriate receiver for calculating a distance measure particular to the pulse transmitted from a particular transmitter (e.g., pulse  1042  transmitted from transmitter  1012  may be matched with the detection of inbound pulse reflection  1052  at receiver  1022 , and outbound pulse  1044  may be matched with the detection of inbound pulse reflection  1054  at receiver  1024 ).  FIGS. 7A-7B , discussed below, provide different examples of common optical paths which may be implemented. 
     As trains of laser pulses transmitted from transmitter  1012  and  1014  may be combined and transmitted via common optical path  1030  the distance measures which can be captured by LiDAR  1000  may vary. For instance, as the transmission delta between pulses may be configurable, the density or location distance measurements provided by LiDAR  1000  may be changed accordingly. Similarly, the PPR for transmitter  1012  may be slower to cover longer ranges. In some scenarios, transmitter  1012  may be configured to provide long-range distance measures and transmitter  1014  may be configured to provide close range distance measures, effectively providing a larger range of distance measures (e.g., dynamic range) that may be determined by LiDAR  1000 . For example, transmitter  1012  may send laser pulses with a 1550 nm wavelength for a larger range of distance measures and transmitter  1014  may send laser pulses with a 930 nm wavelength to capture a close in range of distance measures. In some embodiments, receiver  1022  may include a long-range optical system as described herein in reference to  FIG. 1 or 4  to receive return light from transmitter  1012 , and receiver  1024  may include a short-range optical system as described herein in reference to  FIG. 2, 3 , or  5  to receive return light from transmitter  1014 . 
     As noted above, different optical devices may be implemented to combine and separate laser pulses sent from different laser transmitters so that corresponding reflections are directed to the appropriate receivers.  FIGS. 7A and 7B  illustrate an example optical path for laser pulses and pulse reflections, according to some embodiments. In  FIG. 7A , the outbound pulse path ( 1470  and  1472 ) for two different laser transmitters ( 1410  and  1412 ) is illustrated. Optics  1400  may implement transmitter  1410  which may send a laser pulse in a linear polarization state to beam splitter  1434  which in turn may direct the pulse to polarizing beam splitter  1430 . Polarizing beam splitter  1430  may direct the pulse through quarter wave plate  1440 , which may transform the polarization state from a linear polarization state to a circular polarization state. The transformed pulse may then be reflected off scanning mirror  1460  out into the environment. Optics  1400  may implement transmitter  1412  which may send a laser pulse to beam splitter  1432 . The laser pulse sent from transmitter  1412  may be in a linear polarization state orthogonal the polarization state of pulses sent from transmitter  1410 . Beam splitter  1432  may direct the pulse to polarizing beam splitter  1430 . Polarizing beam splitter  1430  may direct the pulse through quarter wave plate  1440 , which may transform the polarization state from a linear polarization state to a circular polarization state. The transformed pulse may then be reflected off scanning mirror  1460  which may direct the pulse out into the environment. 
     In  FIG. 7B , pulse reflection path  1480  (which corresponds to reflections of pulses transmitted according to outbound pulse path  1470 ) and pulse reflection path  1482  (which corresponds to reflections of pulses transmitted according to outbound pulse path  1472 ) are illustrated. A pulse reflection of a pulse transmitted by transmitter  1410  may be received and reflected off scanning mirror  1460 , directing the pulse through quarter-wave plate  1440 . As the pulse was transmitted into the environment in a circular polarization state, the reflection may also be in a circular polarization state that is the reverse of the circular polarization state transmitted. For example, if outbound path  1470  transmits laser pulses in right-handed circular polarization state, the corresponding reflections will be received in left-handed circular polarization state. Thus, when quarter-wave plate  1440  transforms the polarization of the reflection the resulting linear polarization is orthogonal to the linear polarization state in which the laser pulse was originally transmitted from transmitter  1410 . Thus, polarizing beam splitter  1430  directs the pulse through beam splitter  1432  and optical system  1452  in order to reach and be detected by sensor  1492  of receiver  1422 . A pulse reflection of a pulse transmitted by transmitter  1412  may be received and reflected off scanning mirror  1460 , directing the pulse through quarter-wave plate  1440 . Again, the reflection may also be in a circular polarization state that is the reverse of the circular polarization state transmitted. For example, if outbound path  1472  transmits laser pulses in left-handed circular polarization state, the corresponding reflections will be received in right-handed circular polarization state. Thus, when quarter-wave plate  1440  transforms the polarization of the reflection the resulting linear polarization is orthogonal to the linear polarization state in which the laser pulse was originally transmitted from transmitter  1412 . Thus, the pulse passes through polarizing beam splitter  1430 , beam splitter  1434 , and optical system  1450  in order to reach and be detected by sensor  1490  of receiver  1420 . 
     In some embodiments, receiver  1420  may include a long-range optical system  1450  and a sensor  1490  as described herein in reference to  FIG. 1 or 4  to receive return light from transmitter  1412 , and receiver  1422  may include a short-range optical system  1452  and a sensor  1492  as described herein in reference to  FIG. 2, 3 , or  5  to receive return light from transmitter  1410 . 
       FIG. 8  is a high-level flowchart of a method of operation for a LiDAR system that includes transmitters and long- and short-range receivers that include optical systems as illustrated in  FIGS. 1 through 5 . The method of  FIG. 8  may, for example, be implemented in a LiDAR system as illustrated in  FIGS. 6A through 7B . 
     As indicated at  2000 , transmitters (e.g., two laser transmitters) emit light to a common optical path, for example as illustrated in  FIGS. 6A and 7A . As indicated at  2010 , the light is directed by the common optical path to an object field. In some embodiments, as illustrated in  FIG. 7A , each transmitter may send a laser pulse in a linear polarization state to respective beam splitters, which in turn may direct the pulses to a polarizing beam splitter. In some embodiments, the linear polarization state of one transmitter may be orthogonal to the linear polarization state of the other transmitter. The polarizing beam splitter may direct the pulses through a quarter wave plate, which may transform the polarization state from a linear polarization state to a circular polarization state. The transformed pulses may then be reflected by a scanning mirror (e.g., a MEMS mirror) into the environment (i.e., the object field). The light (pulses) may be reflected by surfaces or objects in the object field. At least some of the reflected light may return to the LiDAR system. 
     As indicated at  2020 , reflected light from the object field may be directed by the common optical path to long-range and short-range receivers. The common optical path may be configured to direct light that was emitted by one of the transmitters to the long-range receiver, and to direct light that was emitted by the other transmitter to the short-range receiver, for example as illustrated in  FIG. 7B . In some embodiments, the reflected light from each transmitter may be in a circular polarization state that is the reverse of the circular polarization state that was transmitted. For example, if the light from one transmitter was transmitted in a left-handed circular polarization state, the corresponding reflections will be received in a right-handed circular polarization state. When the quarter-wave plate transforms the polarization of the reflected light, the resulting linear polarization is orthogonal to the linear polarization state in which the laser pulse was originally transmitted from a respective transmitter. The reflected light from each transmitter then passes through or is directed by the beam splitters in the optical path to reach the receiver corresponding to the transmitter. 
     As indicated at  2030 , optical systems of the long-range and short-range receivers refract the light to respective photodetectors or sensors), for example one or more one-dimensional single photo-avalanche detectors (SPADs). Example optical systems that may be used in a long-range receiver are illustrated in  FIGS. 1 and 4 . Example optical systems that may be used in a short-range receiver are illustrated in  FIGS. 2, 3, and 5 . 
     As indicated at  2040 , light captured at the photodetectors may be analyzed, for example to determine range information for objects or surfaces in the environment. In some embodiments, light captured by the long-range receiver may be analyzed to determine ranges for long-range objects or surfaces (e.g., 20 meters to 200 meters), and light captured by the short-range receiver may be analyzed to determine ranges for short-range objects (e.g., 20 meters or less). For example, distances may be calculated based on the difference between a time at which a laser pulse transmission is sent and a time at which a reflection of the laser pulse transmission is received. The analysis of the reflected light received at and captured by the long-range and short-range receivers may be used in many different applications. For instance, multiple distance measures taken over an area can be processed to generate a high resolution map, which can be used in a variety of different applications, including, but not limited to, geological surveys, atmospheric measurements, object detection, autonomous navigation, or other remote environmental sensing applications. 
     The arrow returning from element  2040  to element  2000  indicates that the method may continuously emit light (e.g., laser pulses) and receive and process reflections of the light as long as the system (e.g., LiDAR system) is in use. 
     Although specific embodiments have been described above, these embodiments are not intended to limit the scope of the present disclosure, even where only a single embodiment is described with respect to a particular feature. Examples of features provided in the disclosure are intended to be illustrative rather than restrictive unless stated otherwise. The scope of the present disclosure includes any feature or combination of features disclosed herein (either explicitly or implicitly), or any generalization thereof, whether or not it mitigates any or all of the problems addressed herein. Accordingly, new claims may be formulated during prosecution of this application (or an application claiming priority thereto) to any such combination of features. In particular, with reference to the appended claims, features from dependent claims may be combined with those of the independent claims and features from respective independent claims may be combined in any appropriate manner and not merely in the specific combinations enumerated in the appended claims. 
     Various ones of the methods described herein may be implemented in software, hardware, or a combination thereof, in different embodiments. In addition, the order of the blocks of the methods may be changed, and various elements may be added, reordered, combined, omitted, modified, etc. Various modifications and changes may be made as would be obvious to a person skilled in the art having the benefit of this disclosure. The various embodiments described herein are meant to be illustrative and not limiting. Many variations, modifications, additions, and improvements are possible. Boundaries between various components and operations are somewhat arbitrary, and particular operations are illustrated in the context of specific illustrative configurations. Other allocations of functionality are envisioned and may fall within the scope of claims that follow. Finally, structures and functionality presented as discrete components in the exemplary configurations may be implemented as a combined structure or component. These and other variations, modifications, additions, and improvements may fall within the scope of embodiments as defined in the claims that follow.

Metadata:
Filing Date: 20170628
Publication Date: 20200428
Grant Date: 20200428
Priority Date: 20160629
Inventors: KAKANI, Chandra S.
SHPUNT, ALEXANDER
REZK, MINA A.
UPTON, Robert S.
GERSON, YUVAL
Assignee: APPLE INC
CPC Classifications: [{"code": "G02B13/0045", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B9/60", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B9/62", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B13/22", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B9/60", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01S17/87", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01S7/4816", "inventive": true, "first": true, "tree": "[]"}, {"code": "G01S7/4816", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B9/64", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01S7/4815", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B13/004", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B9/62", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B13/22", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01S17/89", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B9/62", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01S17/87", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B9/64", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B13/0045", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B13/22", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B9/60", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B13/004", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01S7/4816", "inventive": true, "first": true, "tree": "[]"}, {"code": "G01S7/4815", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01S17/89", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B9/64", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B13/004", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01S17/89", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01S17/87", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01S7/4815", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B13/0045", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 59297449