System and method for real-time LIDAR distance calibration

Abstract

The present disclosure relates to light detection and ranging (LIDAR) devices and related methods of use thereof. An example LIDAR device includes a transmitter configured to transmit one or more light pulses into an environment of the LIDAR device via a transmit optical path. The LIDAR device also includes a detector configured to detect a first portion of the one or more transmitted light pulses and a second portion of the one or more transmitted light pulses, such that the detector receives the first portion of the one or more transmitted light pulses at a first time via an internal optical path within the LIDAR device and receives the second portion of the one or more transmitted light pulses at a second time via reflection from one or more objects in the environment of the LIDAR device. The second time occurs after the first time.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Patent Application No. 62 / 813,860, filed on March 5, 2019, entitled “SYSTEM AND METHOD FOR REAL-TIME LIDAR RANGE CALIBRATION,” the disclosure of which is incorporated herein by reference in its entirety. Background Art

[0003] Conventional light detection and ranging (LIDAR) systems can utilize a light emitting transmitter (e.g., a laser diode) to transmit light pulses into an environment. The emitted light pulses that interact with (e.g., reflect from) objects in the environment can be received by a receiver (e.g., a photodetector) of the LIDAR system. Distance information about objects in the environment can be determined based on the time difference between the initial time of transmitting the light pulse and the subsequent time of receiving the reflected light pulse. Summary of the invention

[0004] The present disclosure generally relates to certain aspects of optical systems (eg, LIDAR systems) and their transmitter and receiver subsystems.

[0005] In a first aspect, a light detection and ranging (LIDAR) device is provided. The LIDAR device includes a transmitter configured to transmit a light pulse into an environment of the LIDAR device via a transmit optical path. The LIDAR device also includes a detector configured to detect a first portion of the transmitted light pulse and a second portion of the transmitted light pulse, such that the detector receives the first portion of the transmitted light pulse at a first time via an internal optical path within the LIDAR device and receives the second portion of the transmitted light pulse at a second time via a reflection of an object in the environment of the LIDAR device. The second time occurs after the first time. The LIDAR device also includes a controller configured to determine a distance to an object based on a difference between the second time and the first time.

[0006] In a second aspect, a method is provided. The method includes causing a transmitter of a LIDAR device to transmit a first light pulse into an environment of the LIDAR device via a transmit optical path. The method also includes receiving, by a detector of the LIDAR device, a first portion of the first light pulse at a first time via an internal optical path within the LIDAR device, and receiving a second portion of the first light pulse at a second time via reflection from an object in the environment of the LIDAR device. Further, the method also includes determining a distance to the object based on a difference between the second time and the first time.

[0007] In a third aspect, a method is provided. The method includes positioning a mirror relative to a transmitter of a LIDAR device. The transmitter is configured to transmit at least one light pulse. The method also includes causing the transmitter to transmit a first light pulse to interact with the mirror. Positioning the mirror is performed so that the first light pulse is directed to an internal light path within the LIDAR device. The method also includes receiving, by a detector of the LIDAR device via the internal light path, the first light pulse at a first time. The method also includes determining a zero time based on the first time.

[0008] Other aspects, embodiments, and implementations will become apparent to those of ordinary skill in the art by reading the following detailed description and, where appropriate, referring to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 An optical system according to an example embodiment is shown.

[0010] Figure 2A A transceiver according to an example embodiment is shown.

[0011] Figure 2B A transceiver according to an example embodiment is shown.

[0012] Figure 2C A transceiver according to an example embodiment is shown.

[0013] Figure 3A A side view of an optical system according to an example embodiment is shown.

[0014] Figure 3B A side view of an optical system according to an example embodiment is shown.

[0015] Figure 4 An optical system according to an example embodiment is shown.

[0016] Figure 5A A vehicle according to an example embodiment is shown.

[0017] Figure 5B A vehicle according to an example embodiment is shown.

[0018] Figure 5C A vehicle according to an example embodiment is shown.

[0019] Figure 5D A vehicle according to an example embodiment is shown.

[0020] Figure 5E A vehicle according to an example embodiment is shown.

[0021] Figure 6 A method according to an example embodiment is shown.

[0022] Figure 7 A method according to an example embodiment is shown. DETAILED DESCRIPTION

[0023] Example methods, devices, and systems are described herein. It should be understood that the words "example" and "exemplary" as used herein mean "serving as an example, instance, or illustration." Any embodiment or feature described herein as "example" or "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments or features. Other embodiments may be utilized, and other changes may be made, without departing from the scope of the subject matter presented herein.

[0024] Therefore, the example embodiments described herein are not meant to be limiting.As generally described herein and illustrated in the accompanying drawings, various aspects of the present disclosure may be arranged, substituted, combined, separated and designed in a variety of different configurations, all of which are contemplated herein.

[0025] Furthermore, unless the context indicates otherwise, the features shown in each figure may be used in combination with each other. Figure 1 The illustrated features are generally viewed as forming aspects of one or more overall embodiments, with the understanding that not all illustrated features are necessary for each embodiment.

[0026] 1. Overview

[0027] LIDAR systems can obtain spatial distance information about an environment by measuring the round-trip time between a first time (e.g., the time when a light pulse is emitted) and a second time (e.g., the time when the light pulse is received after interacting with the environment). However, establishing an absolute time reference for a first time (e.g., the time when a light pulse is emitted from the LIDAR) can be challenging because there may be time-varying delays (e.g., finite RC response times) in electronic components and / or data processing components that are difficult to control or poorly controlled. For example, a delay may be introduced between the time when a controller instructs a laser diode to fire and the time when a light pulse is actually emitted from the laser diode. Therefore, in order to ensure accurate and repeatable distance determination in a LIDAR system, it is desirable to establish a "well-known" first time (e.g., time zero) when a light pulse is emitted.

[0028] In some embodiments, optical feedback such as internal system reflections can be beneficially used to determine the actual excitation time of the light pulse. That is, at the time of the excitation light pulse, some portion of the light may be reflected, routed, or otherwise received by the LIDAR receiver. This portion of the light is received almost instantly after being emitted from the laser diode. As such, "time zero" can be determined based on the initial signal from the receiver. Afterwards, after the remaining portion of the light of the light pulse interacts with the environment, a second time can be defined by a subsequent signal from the receiver, indicating the round-trip time required for the light to travel outward toward the environment and return to the LIDAR system. In such a case, the first time (e.g., time zero) can be subtracted from the second time to obtain a time delay from emission to signal reception that represents the true (or at least more accurate) round-trip time.

[0029] In some embodiments, the LIDAR system may include a light pipe configured to "extract" a small amount of light from a light pulse (e.g., 0.001%-5% of the photons of the light pulse) and route (e.g., divert) them toward a receiver. The light pipe length may be relatively short (e.g., 0.1-10 cm) relative to the distance to a given object in the environment (e.g., 1-100 meters). Thus, the light from the light pipe may represent a nearly ideal time zero reference.

[0030] In other embodiments, the LIDAR system may include a dome or window structure. In such a case, at least a portion of the light pulse may be reflected from the inner surface of the dome or window (directly or indirectly). These reflections may be utilized to find a time zero reference.

[0031] It will be understood that LIDAR systems with other arrangements and / or components are possible and contemplated. For example, the LIDAR system may include one or more light emitter devices configured to emit light toward the environment of the LIDAR system via one or more optical elements. In some embodiments, the optical element may include a fast axis collimation (FAC) lens and / or a shared lens. In some embodiments, the shared lens may be configured to direct light to the environment and focus the incident light onto one or more photodetectors of the LIDAR system. In some embodiments, the optical element may additionally or alternatively include a planar waveguide structure and / or a light guide manifold.

[0032] In an alternative example, a LIDAR with a rotating mirror (e.g., a three-sided or four-sided reflective prism) can direct light pulses to the environment in a scanning manner. In such a case, at least a portion of the light from the light pulses can be reflected from the rotating mirror back to the receiver. For example, when the light pulse interacts with the surface of the rotating mirror, a portion of the photons can be reflected back to the receiver (directly or through stray light reflections). Additionally or alternatively, when the reflective surface of the rotating mirror is perpendicular to the emission axis of the laser diode, at least some of the photons can be directed back to the receiver. In such a case, a time zero reference can be obtained based on the portion of the photons received by the receiver.

[0033] In some embodiments, the LIDAR may include multiple light emitters configured to emit light pulses into multiple optical waveguide channels in a light guide manifold. The waveguide channels in the light guide manifold may be configured to route the light pulses to multiple output mirrors by total internal reflection. The output mirrors are configured to guide the corresponding light pulses out of the plane of the light guide manifold (and out of the light waveguide) and to the environment of the LIDAR. In such a case, some light from the light pulses may "overflow" into the light guide manifold. Such light can be received by one or more detectors in the receiving path. For example, one or more detectors can be optically coupled to the light guide manifold. In such an example, a portion of the light from the light pulses can be used to determine a time zero reference.

[0034] Furthermore, in some embodiments, such a LIDAR system may emit light pulses from multiple light emitters simultaneously or in very rapid succession (e.g., fired within a few nanoseconds of each other) based on various firing schedules. To help disambiguate the portion of light used for a given time zero reference, in some firing schedules, a single channel may be fired at a time independent of the other channels. That is, the laser diodes may be fired at temporally different times in order to distinguish light received from different transmission channels, thereby allowing a zero time reference to be established from a particular transmitter to a particular receiver. For example, discrete light emitters corresponding to a single transmitter channel may be fired at different times every few normal firing cycles, at predetermined times, or as needed.

[0035] 2. Example Optical System

[0036] Figure 1An optical system 100 is shown according to an example embodiment. The optical system 100 may include a light detection and ranging (LIDAR) device. The optical system 100 includes a transmitter 110 configured to transmit light pulses into an environment of the LIDAR device via a transmit optical path 114. The light pulses may be emitted by a light emitter device 120. The light emitter device 120 may be configured to emit emission light (e.g., infrared light pulses). In some embodiments, the light emitter device 120 may include a laser diode (which may be composed of a plurality of laser diode bars).

[0037] The optical system 100 also includes a receiver 160. In various embodiments, the optical system 100 may include a transmitting lens 112 and a receiving lens 164 disposed along a transmitting optical path 114 and a receiving optical path 166, respectively. The receiver 160 includes a detector 162, which is configured to detect a first portion of a transmitted light pulse and a second portion of a transmitted light pulse, such that the detector 162 receives the first portion of the transmitted light pulse at a first time via an internal optical path 130 within the optical system 100, and receives the second portion of the transmitted light pulse at a second time via a reflection of an object in the environment of the optical system 100. The second time occurs after the first time. For example, the second time may be 33 nanoseconds after the first time. In such a case, based on the speed of light, it can be determined that the second portion of the transmitted light pulse has traveled 10 meters more than the first portion of the transmitted light pulse. Therefore, it can be determined that the object is approximately 5 meters away from the optical system along the transmitting optical path 114 of the transmitted light pulse.

[0038] In some embodiments, detector 162 may include at least one of a silicon photomultiplier (SiPM) device, a single photon avalanche photodiode (SPAD), an avalanche photodiode (APD), or a multi-pixel photon counter (MPPC). It will be appreciated that other types of photodetector devices are possible and contemplated.

[0039] The optical system 100 also includes a controller 150. The controller 150 includes at least one of a field programmable gate array (FPGA) or an application specific integrated circuit (ASIC). Additionally or alternatively, the controller 150 may include one or more processors 152 and a memory 154. The one or more processors 152 may include a general purpose processor or a special purpose processor (e.g., a digital signal processor, etc.). The one or more processors 152 may be configured to execute computer readable program instructions stored in the memory 154. As such, the one or more processors 152 may execute program instructions to provide at least some of the functions and operations described herein.

[0040] The memory 154 may include or take the form of one or more computer-readable storage media that may be read or accessed by the one or more processors 152. The one or more computer-readable storage media may include volatile and / or non-volatile storage components (such as optical, magnetic, organic, or other types of memory or disk storage), which may be integrated in whole or in part with at least one of the one or more processors 152. In some embodiments, the memory 154 may be implemented using a single physical device (e.g., one optical, magnetic, organic, or other memory or disk storage unit), while in other embodiments, the memory 154 may be implemented using two or more physical devices.

[0041] As previously described, the memory 154 may include computer-readable program instructions related to the operation of the optical system 100. As such, the memory 154 may include program instructions to perform or facilitate some or all of the functions described herein. The controller 150 is configured to perform operations. In some embodiments, the controller 150 may perform operations by the processor 152 executing instructions stored in the memory 154.

[0042] The operations may include operating various elements of the optical system 100 to obtain distance information about the environment of the optical system 100. For example, the controller 150 may be configured to determine a distance to an object in the environment of the optical system 100 based on a difference between the second time and the first time. The controller 150 may also be configured to perform other operations, such as Figure 6 and Figure 7 The operations shown and described are those related to method 600 and method 700. For example, the controller 150 can be configured to add or subtract a constant offset time. The constant offset time can correspond to an offset distance calculated by subtracting the difference between the second time and the first time from the total transit time to and from the object. In some embodiments, the offset distance can correspond to the time for light to travel the distance along the internal light path 130. Other constant offset times are possible and are contemplated.

[0043] In some embodiments, the optical system 100 may include a light pipe 140 within the optical system 100. In such a case, the internal light path 130 may include a light path extending through the light pipe 140. The light pipe 140 may include, for example, an opening between the transmitter 110 portion and the receiver 160 portion of the optical system 100. Such an opening may allow a portion of a transmitted light pulse to "shortcut" through the opening in order to be received by the detector 162 prior to receiving light from a reflected light pulse.

[0044] In some embodiments, the light pipe 140 is configured to receive a predetermined percentage of photons in the transmitted light pulses. For example, the light pipe 140 may be positioned, sized, or otherwise selected to receive 0.00001%, 0.1%, 1%, 10%, or another predetermined percentage of photons in the transmitted light pulses. Additionally or alternatively, the predetermined percentage may be less than one percent or ten percent of the photons in the transmitted light pulses. Other predetermined percentages of transmitted light pulses are possible and are contemplated within the context of the present disclosure.

[0045] In various example embodiments, the internal optical path 130 may include reflections of a portion of a transmitted light pulse by one or more components of the optical system 100 .

[0046] Additionally or alternatively, the optical system 100 can include a transparent structure 180. For example, the transparent structure 180 can include an optical window 182 and / or a dome 184 configured to be mounted on a carrier (e.g., as described with respect to FIG. Figure 5A-5E In such a case, the transmission light path 114 passes through the transparent structure 180, and the internal light path 130 includes reflections of at least a portion of the transmission light pulse by the transparent structure 180.

[0047] In some embodiments, the optical system 100 may include a mirror 170. In such a case, the transmit light path 114 includes reflections by the mirror 170. Furthermore, in such a case, the internal light path 130 includes reflections by the mirror 170 of at least a portion of the transmit light pulses.

[0048] In some examples, the optical system 100 may include a light guide 142 configured to guide light from an input end to an output end by total internal reflection. In such a case, the transmission optical path 114 includes a first optical path extending from the input end of the light guide 142 to the output end of the light guide 142. The internal optical path 130 includes the first optical path and also includes a second optical path extending from the input end of the light guide 142 to the output end of the light guide 142 and further extending to the detector 162.

[0049] In embodiments including a light guide 142 , the output end of the light guide 142 may include a mirror 170 .

[0050] Figure 2A , Figure 2B and Figure 2C 2 shows a transceiver 200, a transceiver 220, and a transceiver 230 according to an example embodiment. The transceiver 200, the transceiver 220, and / or the transceiver 230 may include a device such as the one described above. Figure 1Similar elements are shown and described for optical system 100. Transceiver 200, transceiver 220, and / or transceiver 230 may comprise a transmitter portion and / or a receiver portion of a LIDAR system.

[0051] Reference Figure 2A , the transceiver 200 may include a housing 210. The transceiver 200 may also include a transmitter 110 and a corresponding optical transmitter device 120 coupled to the housing 210. In some embodiments, the transmitter 110 may include a fast axis collimation (FAC) lens 122 that may be optically coupled to the optical transmitter device 120. The transmitter may be configured to transmit optical pulses along a transmit optical path 114. Such optical pulses may be transmitted through the transmit lens 112 into the environment of the transceiver 200.

[0052] In some embodiments, FAC lens 122 may include a cylindrical lens. However, other optical elements (eg, molded lenses) are possible and contemplated within the context of the present disclosure.

[0053] The transceiver 200 also includes a receiver 160. The receiver 160 includes a detector 162 optically coupled to a receiving lens 164. As described elsewhere herein, the detector 162 can be a SiPM or another type of photodetector or photodetector array. The receiver 160 can be configured to receive light from the environment of the system along a receiving optical path 166.

[0054] In some embodiments, the housing 210 can include an opening 202 disposed between the receiver 160 and the transmitter 110. The opening 202 can be located, shaped, sized, and / or otherwise configured to transmit a portion of the light emitted by the optical transmitter device 120 along the internal optical path 130 toward the receiver 160 and the detector 162.

[0055] Figure 2B FIG. 2 shows a transceiver 220 according to an example embodiment. The transceiver 220 may be similar in some aspects to the Figure 2A The transceiver 220 is similar to that shown and described. However, the transceiver 220 may additionally or alternatively include a light pipe 140 along at least a portion of the internal optical path 130. The light pipe 140 may include an optical fiber, a light guide, an optical waveguide, or another structure configured to route light from a first location (e.g., the transmit optical path 114) to a second location (e.g., the receive optical path 166).

[0056] Although Figure 2B The light pipe 140 is shown as providing a substantially vertical path from the transmitter 110 to the receive optical path 166, but it will be understood that the light pipe 140 may be curved and / or include one or more branches.

[0057] In some embodiments, the light pipe 140 can extend beyond the leakage path to explicitly capture some light. In other embodiments, the light pipe 140 can include one or more facets configured to collect light from the transmission light path 114 and / or provide light to the receiver 160. It should be understood that other optical configurations are possible and considered. In some embodiments, the light pipe 140 may not fill the entire opening 202 between the transmitter portion and the receiver portion of the system. In such a case, the light pipe 140 can be configured to utilize total internal reflection.

[0058] Figure 2C FIG. 2 shows a transceiver 230 according to an example embodiment. The transceiver 230 may be used with Figure 2A and Figure 2B The transceiver 200 and transceiver 220 shown and described are similar. In some embodiments, the transceiver 230 may include a light pipe 140 that can direct at least a portion of the light emitted along the transmit optical path 114 toward the receive optical path 166. For example, an optical fiber can be optically coupled between the transmit lens 112 and the receive lens 164. In other embodiments, the transmit lens 112 and the receive lens 164 can be physically connected and may be molded from the same material. Other ways of optically coupling the transmit lens 112 and the receive lens 164 are possible and are contemplated.

[0059] In such a case, a light pulse emitted from the light emitter device 120 along the transmit optical path 114 may interact with the transmit lens 112 and may be partially directed to the receive lens 164 via the light pipe 140. A portion of the light coupled into the receive lens 164 may be transferred to the detector 162. Such a portion of the light may be, for example, in the range of between one part per million (0.000001) and one part per trillion (0.000000000001). For example, between 0.00001% and 5% of the photons of a given light pulse may be transferred to the detector 162 via the light pipe 140. Other portions of the light are possible and are contemplated within the context of the present disclosure.

[0060] Figure 3A and Figure 3B 2 shows a side view of an optical system 300 according to an example embodiment. The optical system 300 may be used in conjunction with the reference Figure 1 The optical system 100 shown and described is similar. For example, the optical system 300 can include the transmitter 110 and the receiver 160, which can be mounted to a rotatable stage 310. The rotatable stage 310 can be configured to rotate about an axis of rotation 302. In some embodiments, the rotatable stage 310 can be actuated by a stepper motor or another device configured to mechanically rotate the rotatable stage 310.

[0061] In some embodiments, the optical system 300 may include a rotatable mirror 170. The rotatable mirror 170 may be shaped as a triangular prism or a rectangular prism and may be configured to rotate about a rotation axis 304. The rotatable mirror 170 may include a plurality of reflective surfaces 172a, 172b, and 172c.

[0062] Additionally or alternatively, the optical system 300 may include an optical window 180a and an optical window 180b. The reflective surfaces 172a-172c may be configured to reflect light pulses emitted by the optical system 100 along the transmit optical path 114. For example, the light pulses may be reflected through the optical windows 180a and 180b into the environment of the optical system 300. Furthermore, reflected light pulses from the environment may be reflected from the reflective surfaces 172a-172c along the receive optical path 164.

[0063] In this manner, the optical system 300 can be configured to emit light pulses into a 360 degree area of ​​the environment (e.g., around the z-axis) and receive reflected light pulses from a 360 degree area of ​​the environment. Thus, the optical system 300 can be configured to determine distance information based on the time-of-flight of the corresponding reflected light pulses.

[0064] Reference Figure 3A , the rotatable mirror 170 may be rotated at an angle so as to reflect light along a primary reflection path 306 corresponding to a primary elevation angle 307. In some embodiments, at least a portion of the light emitted along the primary reflection path 306 may be reflected by the optical window 180a so as to reflect portions of the light along a secondary reflection path 308. At least some of the portions of the light along the secondary reflection path 308 may be received by the receiver 160 (e.g., by the detector 162). Figure 3A Only one possible configuration of the rotatable mirror 170 is shown, however other multipath reflections of light back to the detector 162 are possible and are contemplated.

[0065] Reference Figure 3BIn some embodiments, the rotatable mirror 170 can be rotated to reflect light directly back to the receiver 160. That is, the rotatable mirror 170 can be positioned so that the reflective surface (e.g., reflective surface 172b) reflects at least a portion of the light toward the receiver 160 and the detector 162. That is, the reflective surface 172b can be positioned so that it is substantially perpendicular (e.g., orthogonal) relative to the transmit optical path 114. In some embodiments, the rotatable mirror 170 can be rotated to reflect light toward the light pipe 140. The portion of the light reflected back to the receiver 160 (by direct reflection from the reflective surface 172b and / or via the light pipe 140) can be detected by the detector 162. The corresponding signal can be used as the first time t1. Similar to the transceiver 200, the first time can be used to determine the transmission path length based on the subsequent pulse time.

[0066] Figure 4 A cross-sectional view of an optical system 400 is shown according to an example embodiment. Figure 4 Can include references Figure 1 Elements similar or identical to those of optical system 100 are shown and described.

[0067] For example, in some embodiments, optical system 400 may include light emitter device 120, detectors 162a-162d, and optical window 182. Optical system 400 may include spacing structure 420 having first surface 422 and second surface 424. Spacing structure 420 may also include cavities 426a-426d extending through spacing structure 420.

[0068] One or more light emitter devices 120 may be coupled to the second surface 424 of the spacing structure 420. The light emitter devices 120 may each include one or more light emitting regions. Figure 4 As shown, the second surface 424 may include an upper portion 424a and a lower portion 424b. For example, the upper portion 424a may define a first plane and the lower portion 424b may define a second plane. Therefore, in some embodiments, the second surface 424 may include an upper portion 424a that "steps down" to the lower portion 424b.

[0069] In some embodiments, detectors 162a-162d may be disposed within cavities 426a-426d. For example, as shown, each cavity may include a detector device. Alternatively, multiple detector devices and / or detector arrays may be disposed in a single cavity. Detectors 162a-162d may be configured to detect light emitted by one or more light emitter devices 120 after interacting with an external environment.

[0070] like Figure 4As additionally shown in FIG. 4 , the intermediate cover 450 can be coupled to the second surface 424 (e.g., the lower surface 424b) of the spacing structure 420. In an embodiment, the intermediate cover 450 can include a plurality of holes 452a-452d that can be aligned with the cavities 426a-426d, respectively. In some embodiments, the holes 452a-452d can have a diameter of 150 microns. However, other pore sizes are also possible and are contemplated.

[0071] In some embodiments, the plurality of apertures 452a-452d may include holes drilled or photolithographically etched through a material that is substantially opaque to light emitted by the light emitter device 120. In other embodiments, the plurality of apertures 452a-452d may include optical windows that are substantially transparent to light emitted by the light emitter device 120.

[0072] Although Figure 4 The middle cover 450 is shown as including a plurality of holes 452a-452d, but it will be understood that in some embodiments, the plurality of holes 452a-452d can be formed in the spacing structure 420. For example, the spacing structure 420 can include one or more holes that form the plurality of holes 452a-452d. In an example embodiment, the plurality of holes 452a-452d can be formed between the upper portion 424a and the lower portion 424b of the spacing structure 420.

[0073] Figure 4 Also shown is an optical window 182 including a mounting surface 462. In some embodiments, the optical window 182 can be substantially transparent to light emitted by the light emitter device 120. At least one FAC lens 122 can be coupled to the mounting surface 462 of the optical window 182. In addition, at least one light guide 142 is coupled to the mounting surface 462 of the optical window 182. In an embodiment, at least one light guide 142 can include reflective surfaces 467a-467d (e.g., mirror-like facets).

[0074] In some examples, a spacer 470 can be disposed between the upper portion 424a of the spacing structure 420 and the mounting surface 462 of the optical window 182. The spacer 470 can be selected so that the light emitter device 120 is disposed in a predetermined or desired position relative to the at least one FAC lens 122 and / or the at least one light guide 142. For example, the spacer 470 can be selected so that light emitted from the light emitter device 120 is efficiently collected by the at least one FAC lens 122 and is efficiently coupled into the at least one light guide 142.

[0075] Although Figure 4The spacer 470 is shown as being located near the side of the optical system 400, but it will be understood that the spacer 470 can be located elsewhere. For example, the spacer 470 can be disposed between the intermediate cover 450 and the mounting surface 462 of the optical window 182. Additionally or alternatively, the spacer 470 can be present in other areas of the optical system 400, for example, to provide a baffle (e.g., to prevent stray light from propagating).

[0076] The optical system 400 may additionally include a circuit board 490 that may be physically coupled to the first substrate 410 via controlled-collapse solder balls 480. Other ways of physically and / or electrically connecting the first substrate 410 to the circuit board 490 are possible and contemplated, such as, but not limited to, conventional solder balls, ball grid arrays (BGA), land grid arrays (LGA), conductive pastes, and other types of physical and electrical sockets.

[0077] In some embodiments, the reflective surfaces 467a-467d can be configured to direct light primarily in the +z direction toward the environment of the optical system 400. Additionally or alternatively, at least a portion of the reflective surfaces 467a-467d can be configured to direct at least a portion of the emitted light in the -z direction (e.g., toward the corresponding detectors 162a-162d). In other words, a first portion of each light pulse can be provided directly to the detectors 162a-162d, while a second portion of each light pulse can be directed to the environment of the optical system 400. In such a case, the first time t1 can be determined based on the arrival time of the first portion of the light at the detectors 162a-162d. In addition, the second time t2 can be determined based on the arrival time of the reflected portion of the second portion of the light at the detectors 162a-162d. It will be appreciated that in some embodiments, stray light (e.g., due to direct reflection or diffuse reflection within the optical system 400) can be used to determine the first time t1.

[0078] Other ways of determining the zero time and / or receiving a time reference signal within the context of the present disclosure are contemplated. For example, the zero time t0 or another time reference signal may be determined based on direct reflection and / or multipath reflection of a light pulse from reflective surfaces 467a-467d, light guide 142, optical window 182, and / or other portions of optical system 400.

[0079] 3. Example Vehicle

[0080] Figure 5A , Figure 5B , Figure 5C , Figure 5D and Figure 5EA vehicle 500 is shown according to an example embodiment. The vehicle 500 may be a semi-autonomous vehicle or a fully autonomous vehicle. Figure 5A-5E Vehicle 500 is shown as an automobile (e.g., a passenger van), but it will be understood that vehicle 500 may include another type of autonomous vehicle, robot, or drone that can navigate its environment using sensors and other information about its environment.

[0081] Vehicle 500 may include one or more sensor systems 502, 504, 506, 508, and 510. In an example embodiment, one or more of sensor systems 502, 504, 506, 508, and 510 may include Figure 1 The optical system 100 is shown and described. For example, in such a case, the sensor systems 502, 504, 506, 508, and 510 may include a LIDAR sensor having a plurality of light emitter devices arranged within an angular range relative to a given plane (eg, an xy plane).

[0082] One or more of sensor systems 502, 504, 506, 508, and 510 may be configured to rotate about an axis perpendicular to a given plane (e.g., the z-axis) to illuminate the environment around vehicle 500 with pulses of light. Based on detecting various aspects of the reflected light pulses (e.g., elapsed time of flight, polarization, intensity, etc.), information about the environment may be determined.

[0083] In an example embodiment, sensor systems 502, 504, 506, 508, and 510 may be configured to provide corresponding point cloud information that may be associated with physical objects within the environment of vehicle 500. Although vehicle 500 and sensor systems 502, 504, 506, 508, and 510 are illustrated as including certain features, it will be appreciated that other types of sensor systems are contemplated within the scope of the present disclosure.

[0084] Example embodiments may include a system having multiple light emitter devices. The system may include a transmit block of a LIDAR device. For example, the system may be a LIDAR device of a vehicle (e.g., a car, truck, motorcycle, golf cart, aircraft, boat, etc.) or may be part of it. Each of the multiple light emitter devices is configured to emit light pulses along a corresponding beam elevation angle. The corresponding beam elevation angle may be based on a reference angle or a reference plane, as described elsewhere herein. In some embodiments, the reference plane may be based on an axis of motion of the vehicle 500.

[0085] Although a LIDAR system with multiple light emitter devices is described and illustrated herein, LIDAR systems with fewer light emitter devices (e.g., a single light emitter device) are also contemplated. For example, light pulses emitted by a laser diode can be controllably directed to the environment surrounding the system. The emission angle of the light pulses can be adjusted by a scanning device (such as, for example, a mechanical scanning mirror and / or a rotary motor). For example, the scanning device can rotate in a reciprocating motion around a given axis and / or rotate around a vertical axis. In another embodiment, the light emitter device can emit light pulses toward a spinning prism mirror, which can cause the light pulses to be emitted into the environment based on the angle of the prism mirror when interacting with each light pulse. Additionally or alternatively, scanning optics and / or other types of electro-optical mechanical devices may scan light pulses around the environment.

[0086] In some embodiments, a single light emitter device may emit light pulses according to a variable firing schedule and / or emit light pulses with variable power per shot, as described herein. That is, the emission power and / or timing of each laser pulse or shot may be based on the corresponding elevation angle of the shot. In addition, the variable firing schedule may be based on providing a desired vertical spacing at a given distance from the LIDAR system or at a given distance from the surface of a given vehicle supporting the LIDAR system (e.g., the front bumper). As an example, when light pulses from a light emitter device are directed downward, the power per shot may be reduced due to a shorter expected maximum distance to the target. In contrast, light pulses emitted by a light emitter device at an elevation angle above a reference plane may have a relatively high power per shot in order to provide a sufficient signal-to-noise ratio to adequately detect pulses that travel longer distances.

[0087] In some embodiments, the power / energy per shot can be controlled in a dynamic manner for each shot. In other embodiments, the power / energy per shot can be controlled for a continuous set of several pulses (e.g., 10 light pulses). That is, the characteristics of the light pulse train can be changed on a per pulse basis and / or on a per several pulse basis.

[0088] While FIG5 illustrates various LIDAR sensors attached to vehicle 500, it will be appreciated that vehicle 500 may incorporate other types of sensors, such as multiple optical systems, as described herein. Additionally or alternatively, it will be appreciated that in some embodiments, one possible source of calibration light pulses may include light reflected from a surface at a known distance from the LIDAR system. As an example, a light pulse reflected from a side mirror or another surface of vehicle 500 may be utilized to determine t1 or another time reference in order to more accurately calculate the distance of a light pulse reflected from elsewhere within the environment of vehicle 500 back to the LIDAR system.

[0089] 4. Example Method

[0090] Figure 6 600 according to an example embodiment is shown. It will be understood that method 600 may include fewer or more steps or blocks than are explicitly shown or otherwise disclosed herein. Furthermore, the respective steps or blocks of method 600 may be performed in any order and each step or block may be performed one or more times. In some embodiments, some or all blocks or steps of method 600 may be performed by Figure 1 The controller 150 and / or other components of the optical system 100 shown and described may be implemented. Additionally or alternatively, the Figure 2A , Figure 2B and Figure 2C Method 600 is performed by transceiver 200 , transceiver 220 , and / or transceiver 230 as shown and described.

[0091] Block 602 includes causing a transmitter of the LIDAR device (e.g., transmitter 110) to transmit a first light pulse into an environment of the LIDAR device via a transmit optical path. The first light pulse may be, for example, an infrared light pulse emitted from a laser diode at an initial trigger time t0. Light pulses having other wavelengths are also possible and contemplated.

[0092] Block 604 includes detecting, by a detector of the LIDAR device (e.g., detector 162) via an internal optical path within the LIDAR device (e.g., internal optical path 130) at a first time t l In some embodiments, the LIDAR device may receive a first portion of the first light pulse at a first time t2, and receive a second portion of the first light pulse at a second time t3 via reflection from an object in the environment of the LIDAR device. In other words, a portion of the first light pulse may be reflected, routed, or otherwise redirected along the internal light path so as to arrive at the detector at an earlier time than the remainder of the first light pulse. In some embodiments, due to the short transmission path length of the internal light path (e.g., 10 centimeters, 1 centimeter, or less), the first portion of the first light pulse may take less than half a nanosecond (e.g., 0.33 nanoseconds) or less than 50 picoseconds (e.g., 33 picoseconds) from its initial emission from the transmitter to arriving at the detector.

[0093] Block 606 includes determining the distance to the object based on the difference between the second time and the first time. By subtracting the first time from the second time, the travel time to and from the object in the environment can be roughly estimated and / or determined. For example, for a first time of t1 = 50 picoseconds and a second time of t2 = 33.38 nanoseconds, then t 差 = t2-t1 = 33.33 nanoseconds. Based on the speed of light (e.g., 3×10 8m / s), the total transmission distance can be about 10 meters. Therefore, considering the incoming and outgoing parts of the transmission distance, the object distance can be determined to be about half of the total transmission distance, that is, 5 meters.

[0094] In some embodiments, the method 600 may further include determining a zero time (e.g., t0) based on the first time. As an example, the zero time may represent a time reference point to which one or more light pulse arrival times are compared to determine distance information. It will be appreciated that the zero time may represent a time reference point that may be modified (e.g., added to or subtracted from), for example, by an additional constant offset time. The constant offset time may correspond to an offset distance calculated by subtracting the zero distance from the target distance. For example, the offset distance time may correspond to the time that light travels along an internal path length distance or other type of adjusted distance.

[0095] In some embodiments, method 600 may additionally include causing the transmitter to transmit a subsequent plurality of light pulses via the transmit optical path. Each subsequent light pulse is fired according to a predetermined light pulse schedule.

[0096] In such a case, method 600 may also include receiving, by the detector, subsequent reflected light pulses at subsequent times via reflections from objects in the environment of the LIDAR device. In addition, method 600 may include determining a distance to the object based on the respective subsequent times, the predetermined light pulse schedule, and the first time. For example, t1 may be used as a time offset that is subtracted from the subsequent received pulses. In this manner, t1 need only be measured once, periodically, or occasionally. In addition, the predetermined light pulse schedule may include a schedule for transmitting a plurality of light pulses, each of which is based on a respective t after t0. 延迟 That is, for a time t after t0 延迟 In the case where a subsequent light pulse is emitted at time t and a reflected light pulse is received at time t3, the total transmission time can be given by t 传输 =t3–t 延迟 -t1 to calculate.

[0097] Figure 7 700 according to an example embodiment is shown. It will be understood that the method 700 may include fewer or more steps or blocks than are explicitly shown or otherwise disclosed herein. Furthermore, the respective steps or blocks of the method 700 may be performed in any order and each step or block may be performed one or more times. In some embodiments, some or all of the blocks or steps of the method 700 may be performed by the method 700 as described above. Figure 1 The controller 150 and / or other components of the optical system 100 shown and described may be implemented. Additionally or alternatively, the Figure 3A , Figure 3B and Figure 4 Method 700 is performed using optical system 300 and / or optical system 400 as shown and described.

[0098] Block 702 includes positioning a mirror (e.g., mirror 170) relative to a transmitter (e.g., transmitter 110) of a LIDAR device. In such a case, the transmitter may be configured to transmit at least one light pulse. Figure 3A and Figure 3B , positioning the mirror may include rotating the mirror 170 about the rotation axis 304 to a desired position.

[0099] Block 704 includes causing the transmitter to transmit a first light pulse to interact with the mirror. Positioning of the mirror is performed so that the first light pulse is directed to an internal light path (e.g., internal light path 130) within the LIDAR device. As described elsewhere herein, the internal light path may include, for example, light pipe 140, light guide 142, mirror 170, optical window 182, and / or dome 184.

[0100] Block 706 includes detecting, by a detector of the LIDAR device (e.g., detector 162) via an internal optical path at a first time t l A first light pulse is received at a location. As described with respect to optical systems 300 and 400, a first light pulse can be emitted toward a mirror and along an internal light path in order to provide a time "reference pulse" against which subsequent pulse times can be calibrated, adjusted, and / or offset. In some embodiments, performing block 706 (e.g., obtaining a light pulse via an internal light path) can provide benefits in several respects. First, some angles of the rotatable mirror will not produce a reference pulse because substantially all of the light from a given light pulse can be diverted to the environment. Second, utilizing a portion of the light pulse reflected back from outside the LIDAR device can cause objects in the scene very close to the device to cause a return that is "mixed" with the feedback pulse, making zero distance difficult or impossible to determine.

[0101] Block 708 includes determining a zero time (eg, t0) based on the first time. As an example, the zero time may represent a time reference point to which one or more light pulse arrival times are compared to determine distance information.

[0102] In some embodiments, method 700 may additionally include repositioning the mirror to direct subsequent light pulses into the environment of the LIDAR device via the transmit optical path. In such a case, method 700 may include causing the transmitter to transmit subsequent multiple light pulses via the transmit optical path.

[0103] The method 700 may also include receiving, by the detector, subsequent reflected light pulses at subsequent times via reflections from objects in the environment of the LIDAR device.

[0104] Still further, method 700 may include determining the distance to the object based on the difference between the corresponding subsequent time and the zero time. In some embodiments, the subsequent light pulses may be excited according to a predetermined light pulse schedule. In such a case, the distance to the object may be further determined based on the predetermined light pulse schedule.

[0105] In example embodiments, the mirror may be a rotatable mirror. For example, the rotatable mirror may have a triangular prism shape. In such a case, the rotatable mirror may have three reflective surfaces corresponding to each of the three facets of the triangular prism. In some embodiments, the rotatable mirror may have a rectangular prism shape. In such a case, the rotatable mirror may include four reflective surfaces corresponding to each of the four main facets of the rectangular prism.

[0106] Additionally, positioning and repositioning the mirror may include causing a motor to rotate the rotatable mirror about an axis of rotation so as to adjust respective angles of the three or four reflective surfaces.

[0107] The specific arrangements shown in the accompanying drawings should not be considered limiting. It should be understood that other embodiments may include more or less of each element shown in a given drawing. In addition, some of the elements shown may be combined or omitted. Still further, the illustrative embodiments may include elements not shown in the accompanying drawings.

[0108] The steps or boxes representing the processing of information may correspond to circuits that may be configured to perform specific logical functions of the methods or techniques described herein. Alternatively or additionally, the steps or boxes representing the processing of information may correspond to a portion, segment, or module of a program code (including associated data). The program code may include one or more instructions executable by a processor for implementing specific logical functions or actions in a method or technique. The program code and / or associated data may be stored on any type of computer-readable medium, such as a storage device including a disk, a hard drive, or other storage medium.

[0109] Computer readable media may also include non-transitory computer readable media, such as computer readable media (such as register memory, processor cache and random access memory (RAM)) for storing data for a short period of time. Computer readable media may also include non-transitory computer readable media for storing program code and / or data for a longer period of time. Therefore, computer readable media may include secondary or persistent long-term storage devices, such as read-only memory (ROM), optical disk or magnetic disk, compact disk read-only memory (CD-ROM). Computer readable media may also be any other volatile or non-volatile storage system. Computer readable media may be considered as computer readable storage media, for example, or tangible storage devices.

[0110] While various examples and embodiments have been disclosed, other examples and embodiments will be apparent to those skilled in the art. The various disclosed examples and embodiments are for purposes of illustration and are not intended to be limiting, with the true scope being indicated by the following claims.

[0111] This specification includes the following subject matter in the form of clauses 1-20: 1. A light detection and ranging (LIDAR) device, comprising: a transmitter configured to transmit one or more light pulses into an environment of the LIDAR device via a transmit optical path; a detector configured to detect a first portion of the one or more transmitted light pulses and a second portion of the one or more transmitted light pulses, such that the detector receives the first portion of the one or more transmitted light pulses at a first time via an internal optical path within the LIDAR device and receives the second portion of the one or more transmitted light pulses at a second time via reflection from one or more objects in the environment of the LIDAR device, wherein the second time occurs after the first time; and a controller, wherein the controller is configured to determine a distance to at least one of the objects based in part on a difference between the second time and the first time. 2. The LIDAR device of clause 1, further comprising a light pipe within the LIDAR device, wherein the internal optical path comprises a light path extending through the light pipe. 3. The LIDAR device of clause 2, wherein the light pipe is configured to receive a predetermined percentage of photons in the one or more transmitted light pulses. 4. The LIDAR device of clause 3, wherein the predetermined percentage is less than ten percent. 5. The LIDAR device of any of clauses 1-4, wherein the internal optical path includes reflections from one or more components of the LIDAR device. 6. The LIDAR device of any of clauses 1-5, further comprising: a transparent structure, wherein the transmission optical path passes through the transparent structure, wherein the internal optical path includes reflections from the transparent structure. 7. The LIDAR device of clause 6, wherein the transparent structure is a dome configured to be mounted on a vehicle. 8. The LIDAR device of clauses 6 or 7, wherein the transparent structure includes an optical window. 9. The LIDAR device of any of clauses 1-8, further comprising: a mirror within the LIDAR device, wherein the transmission optical path includes reflections from the mirror, wherein the internal optical path includes reflections from the mirror. 10. The LIDAR device of any of clauses 1-9, further comprising: a light guide configured to guide light from an input end to an output end by total internal reflection or a reflective coating, wherein the transmit light path comprises a first light path extending from an input end of the light guide to an output end of the light guide, wherein the internal light path comprises the first light path and further comprises a second light path extending from the output end of the light guide to a detector. 11. The LIDAR device of clause 10, wherein the output end of the light guide comprises a mirror. 12. A method comprising: causing a transmitter of the LIDAR device to transmit a first light pulse into an environment of the LIDAR device via the transmit light path; receiving, by a detector of the LIDAR device, a first portion of the first light pulse at a first time via the internal light path within the LIDAR device, and receiving a second portion of the first light pulse at a second time via reflection from one or more objects in the environment of the LIDAR device; and determining a distance to at least one of the objects based in part on a difference between the second time and the first time.13. The method of clause 12, further comprising: determining a zero time based on the first time. 14. The method of clause 12 or 13, further comprising: causing a transmitter to transmit a subsequent plurality of light pulses via a transmit optical path, wherein each subsequent light pulse is excited according to a predetermined light pulse schedule; receiving, by a detector, subsequent reflected light pulses at subsequent times via reflections from one or more objects in an environment of the LIDAR device; and determining a distance to a respective object based on the respective subsequent times, the predetermined light pulse schedule, and the first time. 15. A method comprising: positioning a mirror relative to a transmitter of a LIDAR device, wherein the transmitter is configured to transmit at least one light pulse; causing the transmitter to transmit a first light pulse to interact with the mirror, wherein the positioning of the mirror is performed such that the first light pulse is directed to an internal optical path within the LIDAR device; receiving, by a detector of the LIDAR device at a first time via the internal optical path; and determining a zero time based in part on the first time. 16. The method of clause 15, further comprising: repositioning the mirror to direct subsequent light pulses into the environment of the LIDAR device via the transmit light path; causing the transmitter to transmit a subsequent plurality of light pulses via the transmit light path; receiving the subsequent reflected light pulses at a subsequent time by the detector via reflection from one or more objects in the environment of the LIDAR device; and determining the distance to at least one of the objects based on a difference between the respective subsequent times and the zero time. 17. The method of clause 16, wherein the subsequent light pulses are fired according to a predetermined light pulse schedule, and wherein the distance to the objects is also determined based on the predetermined light pulse schedule. 18. The method of any of clauses 15-17, wherein the mirror comprises a rotatable mirror. 19. The method of clause 18, wherein the rotatable mirror comprises a triangular or rectangular prism shape, wherein the rotatable mirror comprises three or four reflective surfaces. 20. The method of clause 19, wherein positioning and repositioning the mirror comprises causing a motor to rotate the rotatable mirror about an axis of rotation so as to adjust respective angles of the three or four reflective surfaces.

Claims

1. A light detection and ranging LIDAR device, comprising: A transmitter configured to transmit one or more optical pulses into an environment of the LIDAR device via a transmit optical path; a detector configured to detect a first portion of the one or more transmitted light pulses and a second portion of the one or more transmitted light pulses, such that the detector receives the first portion of the one or more transmitted light pulses at a first time via an internal optical path within the LIDAR device and receives the second portion of the one or more transmitted light pulses at a second time via reflection from one or more objects in an environment of the LIDAR device, wherein the second time occurs after the first time; and a controller, wherein the controller is configured to determine a distance to at least one of the objects based in part on a difference between the second time and the first time; wherein the transmitter is further configured to transmit a subsequent plurality of optical pulses via the transmit optical path, wherein each subsequent optical pulse is excited according to a predetermined optical pulse schedule; wherein the detector is further configured to receive subsequent reflected light pulses at subsequent times via reflection from one or more objects in the environment of the LIDAR device; and Wherein, the controller is further configured to determine a distance to a corresponding object based on the corresponding subsequent time, the predetermined light pulse schedule and the first time.

2. The LIDAR device of claim 1, further comprising a light pipe within the LIDAR device, wherein: The internal light path includes a light path extending through the light pipe.

3. The LIDAR device according to claim 2, wherein: The light pipe is configured to receive a predetermined percentage of photons in one or more transmitted light pulses.

4. The LIDAR device according to claim 3, wherein: The predetermined percentage is less than ten percent.

5. The LIDAR device according to claim 1, wherein: The internal optical path includes reflections from one or more components of the LIDAR device.

6. The LIDAR device according to claim 1, further comprising: A transparent structure, wherein the transmitted light path passes through the transparent structure, and wherein the internal light path includes reflections from the transparent structure.

7. The LIDAR device according to claim 6, wherein: The transparent structure is configured as a dome mounted on a vehicle.

8. The LIDAR device according to claim 6, wherein: The transparent structure includes an optical window.

9. The LIDAR device according to claim 1, further comprising: A mirror within a LIDAR device, wherein the transmit optical path includes reflections from the mirror, and wherein the internal optical path includes reflections from the mirror.

10. The LIDAR device according to claim 1, further comprising: A light guide configured to guide light from an input end to an output end by total internal reflection or a reflective coating, wherein the transmitting light path comprises a first light path extending from the input end of the light guide to the output end of the light guide, wherein the internal light path comprises the first light path and also comprises a second light path extending from the output end of the light guide to a detector.

11. The LIDAR device according to claim 10, wherein: The output end of the light guide includes a mirror.

12. A light detection and ranging (LIDAR) method, comprising: Cause a transmitter of the LIDAR device to transmit a first light pulse into an environment of the LIDAR device via a transmission optical path; receiving, by a detector of the LIDAR device via an internal optical path within the LIDAR device at a first time, a first portion of a first light pulse, and receiving a second portion of the first light pulse at a second time via reflection from one or more objects in an environment of the LIDAR device; as well as determining a distance to at least one of the objects based in part on a difference between the second time and the first time; causing the transmitter to transmit a subsequent plurality of light pulses via a transmit optical path, wherein each subsequent light pulse is excited according to a predetermined light pulse schedule; receiving, by the detector, subsequent reflected light pulses at subsequent times via reflections from one or more objects in the environment of the LIDAR device; and A distance to a corresponding object is determined based on the corresponding subsequent time, the predetermined light pulse schedule, and the first time.

13. The method according to claim 12, further comprising: The zero time is determined based on the first time.

14. A light detection and ranging (LIDAR) method, comprising: positioning the mirror relative to a transmitter of the LIDAR device, wherein the transmitter is configured to transmit at least one light pulse; causing the transmitter to transmit a first light pulse to interact with a mirror, wherein positioning of the mirror is performed such that the first light pulse is directed to an internal optical path within the LIDAR device; receiving, by a detector of the LIDAR device via an internal optical path, a first light pulse at a first time; repositioning the mirror to direct subsequent light pulses into the environment of the LIDAR device via a transmit light path; causing the transmitter to transmit a subsequent plurality of light pulses via a transmit optical path, wherein each subsequent light pulse is excited according to a predetermined light pulse schedule; receiving, by the detector, subsequent reflected light pulses at subsequent times via reflections from one or more objects in the environment of the LIDAR device; and A distance to a corresponding object is determined based on the corresponding subsequent time, the predetermined light pulse schedule, and the first time.

15. The method according to claim 14, further comprising: determining a zero time based in part on the first time; as well as A distance to at least one of the objects is determined based on a difference between a corresponding subsequent time and the zero time.

16. The method according to claim 14, wherein: The mirror comprises a rotatable mirror.

17. The method according to claim 16, wherein: The rotatable mirror comprises a triangular or rectangular prism shape, wherein the rotatable mirror comprises three or four reflective surfaces.

18. The method according to claim 17, wherein: Positioning and repositioning the mirror includes causing a motor to rotate the rotatable mirror about an axis of rotation so as to adjust the respective angles of the three or four reflective surfaces.

Images