Focal Plane Array Systems for FMCW LIDAR

Abstract

A LiDAR system (e.g., a frequency modulated continuous wave (FMCW) LiDAR system) includes a focal plane array (FPA) system. The FPA system includes a coherent pixel array (CPA) and a diffraction grating stack (DGS). The CPA includes coherent pixels (CPs), and each CP is configured to emit coherent light. The DGS includes at least one diffraction grating positioned to diffract the coherent light emitted from the CPA into an environment as one or more light beams. Each of the one or more light beams is emitted at a specific angle, and the specific angle is based in part on the position of the CP that produces the coherent light that forms the one or more beams.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Provisional Patent Application Serial No. 62 / 879,382 filed on July 26, 2019 and U.S. Provisional Patent Application Serial No. 62 / 879,383 filed on July 26, 2019, all of which are incorporated herein by reference in their entireties. Technical Field

[0003] The present disclosure relates generally to frequency modulated continuous wave (FMCW) light detection and ranging (LiDAR), and more particularly to a focal plane array system for a FMCW LiDAR system. Background Art

[0004] Conventional LiDAR systems use mechanical moving parts and bulk optical lens elements (i.e., refractive lens systems) to steer the laser beam and are too bulky, expensive, and unreliable for many applications (e.g., automotive). Summary of the invention

[0005] A lensless (focal plane array) FPA system for a LiDAR system. The LiDAR system can be, for example, a frequency modulated continuous wave (FMCW) LiDAR system. The FPA system emits one or more beams of light into an environment. One or more beams are reflected and / or scattered from objects in the environment and detected by the FPA system. The LiDAR system uses the detected return light to generate depth information describing the environment. The FPA system includes a coherent pixel array (CPA) and a diffraction grating stack (DGS). The CPA includes a plurality of coherent pixels (CPs). The CP can be arranged in a 1D or 2D array. The CP emits coherent light and also receives return light. The DGS includes one or more diffraction gratings arranged in series. The DGS can be composed of a thin non-periodic diffraction grating that collimates the light emitted by each CPA in the CPA array. The DGS guides the coherent light emitted by the CPA into the environment as one or more beams of light. In some embodiments, the DGS also collimates the light emitted from the CP of the CPA. Each of the one or more light beams is emitted at a specific output angle, and the specific output angle is based in part on the position of the CP that produces the coherent light that forms the one or more beams. In some embodiments, the specific output angle is unique to each CP, and such light from each CP is output by the DGS as a beam at an angle unique to that CP.

[0006] The FPA system can scan one or more beams in 1D and / or 2D by selectively activating different CPs of the CPA. Depending on the position of the pixel in the CPA, the collimated beam leaving the DGS propagates at different output angles. Therefore, each CP has a unique position relative to the DGS, and in some embodiments, the DGS is positioned to diffract the coherent light emitted from each corresponding CP to form a corresponding beam output from the DGS at a unique angle. This effect enables the LiDAR beam to be manipulated in the detected environment. In this way, the FPA system can be configured to scan one or more beams over some (e.g., a portion) or all of the field of view of the FPA system. The FPA system can scan one or more beams in one or two dimensions. In turn, the beam propagating to the DGS at a specific return angle is focused by the DGS to a point on the CPA. For example, the CP of the emitted beam can be the CP that receives the reflected / scattered beam.

[0007] In some embodiments, the FPA system includes optical elements (e.g., a microprism array, a blazed grating, etc.) to convert off-axis light emitted from the CP of the CPA into on-axis light (e.g., the main emission axis is substantially perpendicular to the CPA array). In this way, the off-axis light emitted from the CP can be refracted to emit on-axis light, and the on-axis light is provided to the DGS. In turn, reflected light from the local environment can be detected at the CP after passing through the DGS and the optical elements).

[0008] In some embodiments, the FMCW LiDAR system includes an FPA system. The FPA system includes a CPA and a DGS. The CPA includes a CP, and each CP is configured to emit coherent light. The DGS includes at least one diffraction grating positioned to diffract the coherent light emitted from the CPA into the environment as one or more beams. And each of the one or more beams is emitted at a specific angle, and the specific angle is based in part on the position of the CP that produces the coherent light that forms the one or more beams.

[0009] In some embodiments, a DGS of a FMCW LiDAR system is described. The DGS includes at least one diffraction grating positioned to diffract coherent light emitted from a coherent pixel (CP) of a coherent pixel array (CPA) into an environment as one or more beams, and each of the one or more beams is emitted at a specific angle, and the specific angle is based in part on the corresponding position of the CP that produces the coherent light forming the one or more beams. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Embodiments of the present disclosure have other advantages and features that will become more readily apparent from the following detailed description and appended claims when taken in conjunction with the examples in the accompanying drawings, in which:

[0011] Figure 1A schematic diagram of an FPA system for LiDAR beam steering applications based on a combination of CPA and DGS is shown in accordance with some embodiments.

[0012] Figure 2 A LiDAR system including an FPA system is depicted in accordance with one or more embodiments.

[0013] Figure 3 is a FPA including a DGS including a blazed grating having a non-uniform grating period according to one or more embodiments.

[0014] Figure 4 is a FPA including a DGS including a digitally designed multi-step grating according to one or more embodiments.

[0015] Figure 5 is a schematic diagram of a microprism array located on top of a CPA according to one or more embodiments.

[0016] Figure 6 is a schematic diagram of a blazed grating on top of a CPA according to one or more embodiments.

[0017] Figure 7 An example microprism array (or equivalent blazed grating) arranged in two dimensions is shown in accordance with one or more embodiments.

[0018] Figure 8 An embedded version of an optical element according to one or more embodiments is shown.

[0019] Fig. 9 A schematic diagram of a switchable coherent pixel array FMCW LiDAR chip is shown according to one or more embodiments.

[0020] Figures 10a to 10d Four versions of coherent pixels are shown in accordance with one or more embodiments. DETAILED DESCRIPTION

[0021] The LiDAR system determines depth information (e.g., distance, velocity, acceleration of one or more objects) of the system's field of view. The LiDAR system may be a FMCW LiDAR system. The LiDAR system includes an FPA system.

[0022] The FPA system emits one or more beams of light into the environment. The FPA system can be configured to scan one or more beams over some (e.g., a portion) or all of the field of view of the FPA system. The FPA system can scan one or more beams in one or two dimensions. The FPA system does not use lenses to manipulate and / or shape one or more beams. One or more beams are reflected and / or scattered from objects in the environment and detected by the FPA system. The FPA system includes a switchable CPA and a DGS. The CPA includes a CP, and each CP is configured to emit coherent light. The DGS includes one or more diffraction gratings (e.g., non-periodic) arranged in series. In addition, in some embodiments, the DGS may also include additional diffraction gratings arranged in parallel. One or more diffraction gratings are positioned to guide the coherent light emitted from the CPA as one or more beams (e.g., via diffraction) into the environment. In some embodiments, the DGS also collimates the light emitted by the CP. And each of the one or more beams is emitted at a specific angle, and the specific angle is based in part on the position of the CP that produces the coherent light that forms the one or more beams. Thus, each CP has a unique position relative to the DGS, and in some embodiments, the DGS is positioned to diffract the coherent light emitted from each respective CP to form a respective beam output from the DGS at a unique angle. In this way, by selectively activating different CPs of the CPA, the FPA system can scan one or more beams in 1D and / or 2D across the field of view. The return light is incident on the DGS at a specific return angle, and the DGS directs the return light to a specific CP that is dependent on the return angle of the return light. Thus, if the output angle of the beam composed of light from a CP matches the return angle of the return light, the DGS directs the return light to that CP.

[0023] In some embodiments, the FPA system further includes an optical element (e.g., a microprism array, a blazed grating, etc.) to convert off-axis light emitted from the CP of the CPA into on-axis light (e.g., light whose primary emission axis is substantially perpendicular to the CPA). In some embodiments, light propagating perpendicular to the CPA is substantially parallel to the optical axis of the CPA. In this way, off-axis light emitted from the CP can be refracted to emit on-axis light, and the on-axis light is provided to the DGS. And in turn, reflected light from the local environment can be detected at the CP after passing through the DGS and the optical element). The optical element can be positioned between the CPA and the DGS, the optical element being positioned to redirect the off-axis light emitted by the CP so that it is coaxial, wherein the coaxial light is substantially parallel to the optical axis of the CPA.

[0024] The CP uses the returned light to generate one or more output signals. The one or more output signals are used to determine depth information of the LiDAR system's field of view. The depth information describes the distance to various surfaces within the LiDAR system's field of view and may also include information describing the velocity of objects within the LiDAR system's field of view.

[0025] Note that the FPA system can manipulate light in at least one dimension. And in some embodiments, the CP is arranged in two dimensions so that the FPA system can manipulate the light beam in two dimensions. Being able to manipulate the light beam without moving parts can alleviate the size, cost, and reliability issues present in many traditional mechanically driven LiDAR systems. In addition, in FPA-based LiDAR systems, the DGS of the FPA system is a low-cost, lightweight, and compact lens alternative. In addition, the DGS adds additional degrees of freedom beyond what is provided by traditional lenses, potentially achieving higher performance than would otherwise be possible.

[0026] Figure 1 A schematic diagram of an FPA system 111 according to some embodiments is shown. For LiDAR, the FPA system 111 includes a CPA 100 and a DGS 110. The CPA 100 includes a plurality of CPs 102. The CPA 100 may be, for example, a 1D or 2D array of a single CP. Each CP emits a beam of light perpendicularly to the DGS 110, and the properties of the beam may be different depending on the position of the CP (e.g., as shown by beams 103 and 104). The beams 103, 104 propagate through the DGS 110, exiting at respective angles depending on the position of the source CP in the CPA 100. For example, when CP 101 is turned on, the DGS 110 converts the incident beam 103 into a collimated exit beam 107 (depicted with a solid line). Conversely, light from CP 102 is shown as beam 104, which the DGS 110 outputs as a collimated exit beam 108 (depicted with a dashed line). At any given time, one or more CPs may be enabled in the array.

[0027] The DGS 110 is composed of one or more non-periodic diffraction gratings 105. In general, the DGS 110 includes multiple non-periodic diffraction gratings 105. In some embodiments where there is a small amount of CP near the central axis of the DGS 110, a single non-periodic diffraction grating can be used. The non-periodic diffraction gratings 105 in the DGS 110 can be arranged in series and / or in parallel. For example, Figure 1A plurality of non-periodic diffraction gratings 105 are shown connected in series. In other embodiments, the DGS 110 may include a plurality of non-periodic diffraction gratings connected in parallel, and at least some of the plurality of non-periodic diffraction gratings are also connected in series. For example, the DGS 110 may include a central region centered on the optical axis of the DGS 110, and the central region is surrounded by a peripheral region. In some embodiments, the central region may include a first group of one or more non-periodic diffraction gratings, and the peripheral region may include a different group of non-periodic diffraction gratings connected in series with each other. This arrangement may allow light passing through the peripheral region to be manipulated in a different manner than light passing through the central region. For example, the central region may produce a beam angle range (e.g., output beam angle) that is smaller than the beam angle range produced by the peripheral region. In another embodiment, the number of non-periodic diffraction gratings in the central region is greater than the number in the peripheral region. This may be useful, for example, to improve the aperture of a beam emitted from a CP near the central region in a low-cost manner.

[0028] These diffraction gratings can have a continuously modulated phase or a set of discrete phase levels. The grating 105 can be made of a lower refractive index material (such as glass) or a higher refractive index material (such as silicon or other semiconductors). The gratings can take a variety of forms, such as surface relief gratings, sinusoidal gratings, blazed gratings, step gratings, or some combination thereof. They can be manufactured using nanoimprint lithography, deep ultraviolet lithography, or other manufacturing techniques available to those skilled in the art. In embodiments where there are multiple diffraction gratings in the DGS 110, the gratings can be separated by a medium 106. Depending on the requirements of the system parameters, the medium can be air or another higher refractive index material, such as a polymer or glass. One or more non-periodic diffraction gratings 105 are arranged in series with each other and the CPA 100.

[0029] One skilled in the art can design the diffraction grating of DGS 110 to maximize the power coupled into the collimated beam from the different CPs in CPA 100. Note that Figure 1The FPA system 111 in FIG. 1 shows light emitted from the FPA system 111 into the environment, and the light may be reflected / scattered from the environment back to the FPA system 111 as return light (not shown). In some embodiments, the DGS 110 causes the return light to return to the emitting CP (e.g., the return light from beam 107 is detected by CP 101, and the return light corresponding to beam 108 is detected by CP 102). For example, in the emission direction, the light emitted by the CP will pass through the DGS 110. As the beam propagates through the stack and diffracts, it is molded into a collimated beam at a specific angle (e.g., the output beam angle). When the beam is reflected from a (diffusing) surface, the light returns to the DGS at the same angle as the return light (e.g., the return beam angle), and thus along the return path, there is an approximately "collimated" wave that hits the DGS 110. In the return direction, the DGS 110 focuses the return light back onto the CP in the opposite manner. In the case where the reflective surface is a perfect reflector, the return light is almost perfectly refocused onto the emitting CP. Thus, each transmitting CP also detects the return light it transmits - referred to herein as a "reciprocal system". In this manner, one or more CPs transmit light, the DGS 110 diffracts that light into one or more beams, and the DGS 110 diffracts the corresponding return light to one or more CPs. One skilled in the art can design the gratings in the DGS to work optimally for all CPs in the CPA.

[0030] Figure 2 A LiDAR system including an FPA system according to one or more embodiments is depicted. The FPA system may be the one described above with reference to Figure 1 The FPA system 111 described above. For example, the FPA system may be a reciprocal system. The FPA system includes a DGS 200, an optional optical element 202, and a CPA 201. The DGS 200 may be substantially the same as the DGS 110, and the CPA 201 may be substantially the same as the CPA 100. Figure 2 In FIG. 1 , DGS 200 takes input from CPA 201, which may optionally use optical element 202 (e.g., prism, microprism array, diffraction grating, etc.) to correct the output beam angle. Note that in some cases, optical element 202 may have CPA 201 embedded therein (e.g., as described below with reference to FIG. 1 ). Figure 8201). The DGS 200 outputs a beam 207 of a certain angular range. The CPs in the CPA 201 are controlled by the FPA driver 205. One or more individual CPs in the CPA 201 can be activated to emit and receive light. The light emitted by the CPA 201 is generated by the Q-channel laser array 204. The Q-channel laser array 204 is a laser array with Q parallel channels, where Q is an integer. The Q-channel laser array 204 can be directly integrated with the CPA 201, or it can be a separate module packaged with the CPA 201. The Q-channel laser array 204 is controlled by a laser controller 206. The laser controller 206 receives control signals from the LiDAR processing engine 203 via a digital-to-analog converter 208. The process also controls the FPA driver 205 and sends and receives data from the CPA 201.

[0031] The LiDAR processing engine 203 includes a microcomputer 209. The microcomputer 209 processes data from the FPA system and sends control signals to the FPA system via the FPA driver 205 and the laser controller 206. The LiDAR processing engine 203 also includes an N-channel receiver 210. The signal is received by the N-channel receiver 210 and digitized using a set of M-channel analog-to-digital converters (ADCs) 211.

[0032] Figure 33 is an FPA system 311 including a DGS 310 including a blazed grating having a non-uniform grating periodicity according to one or more embodiments. The FPA system 311 is an embodiment of the FPA system 111. The FPA 311 includes a CPA 300 and a DGS 310. Note that, although not shown, the FPA 311 may also include an optical element (e.g., a prism, a prism array, or a separate diffraction grating) located between the CPA 300 and the DGS 310, which converts off-axis light emitted from the CP of the CPA into on-axis light (e.g., light with a primary emission axis perpendicular to the CPA). In some embodiments, the light propagating perpendicular to the CPA is substantially parallel to the optical axis of the CPA. The optical element may also refract the on-axis return light (part of the beam reflected from the environment) so that it is off-axis light. As shown, the CP 301 emits an expanded light beam 303, which propagates through the DGS 310. The DGS 310 includes a plurality of blazed gratings 305 arranged in series. A plurality of blazed gratings 305 produce collimated beams 306 that propagate perpendicularly out of the DGS 310. In this embodiment, each blazed grating has a periodicity that evolves monotonically (i.e., generally increases - but may remain constant in certain portions, but not decrease) with distance from the center of the grating so as to mimic the behavior of a conventional bulk optical lens element. Note that conventional bulk optical lens elements have many disadvantages (e.g., are relatively heavy, bulky, expensive) compared to the DGS embodiments described herein. Similarly, a second CP 302 located off-center from the CPA 300 emits a beam 304 that propagates through the DGS 310, which converts the light into an angled collimated beam 307. Note that light from different CPs has different beam angles (e.g., output beam angle) at the output of the DGS 310. Thus, the FPA system can manipulate beams through the environment by selectively activating different CPs.

[0033] Notice Figure 3 Light is shown emitted from FPA system 311 into the environment, and may be reflected / scattered from the environment back to FPA system 311 as return light (not shown). In some embodiments, the stack of blazed gratings 305 is designed as a reciprocal system so that the return light is returned to the emitting CP (e.g., return light from beam 306 is detected by CP 301, and return light corresponding to beam 307 is detected by CP 302).

[0034] Figure 44 is an FPA system 411 including a DGS 410 including a digitally designed multi-step grating according to one or more embodiments. The FPA system 411 is an embodiment of the FPA system 111. The FPA 411 includes a CPA 400 and a DGS 410. Note that, although not shown, the FPA system 411 may also include an optical element (e.g., a prism, a prism array, or a separate diffraction grating) located between the CPA 400 and the DGS 410, which converts off-axis light emitted from the CP of the CPA into on-axis light (e.g., whose main emission axis is substantially perpendicular to the CPA). In some embodiments, the light propagating perpendicular to the CPA is substantially parallel to the optical axis of the CPA. The optical element may also refract the on-axis return light (part of the beam reflected from the environment) so that it is off-axis light. As shown, the CP 401 emits an expanded light beam 403, which propagates through the DGS 410. The DGS 410 includes a plurality of multi-step gratings 405 arranged in series. The multi-step grating has a non-trivial thickness distribution, which can be designed using numerical optimization methods. Similarly, a second pixel located off-center in CPA 402 emits a beam 404 that propagates through DGS 410. DGS 410 converts the light into an angled collimated beam 407.

[0035] Notice Figure 4 Light is shown emitted from FPA system 411 into the environment, and may be reflected / scattered from the environment as return light (not shown) back to FPA system 411. In some embodiments, DGS 410 is a reciprocal system such that the return light returns to the transmitting CP (e.g., return light from beam 406 is detected by CP 401, and return light corresponding to beam 407 is detected by CP 402).

[0036] Figure 5 is a schematic diagram of a microprism array 502 located on top of a CPA 100 according to one or more embodiments. The microprism array 502 is one embodiment of an optical element 202. The microprism array 502 includes an arrangement of transparent (at least in the light band emitted by the CPA 100) triangular elements made of a material having a higher refractive index than the surrounding medium (e.g., air). The CPA 100 includes an array of individual CPs. As described above, the CPs of the CPA 100 can be turned on and off one at a time and / or in groups.

[0037] Each CP includes an emission region that emits light according to an emission distribution. For example, CP 101 has an emission distribution with a primary emission axis 520 and off-axis boundaries 525 and 530. The primary emission axis 520 is the direction in which the emission region emits the most light. The emission distribution can be rotationally symmetric or rotationally asymmetric about the primary emission axis 520.

[0038] As shown, each CP emits a beam of light at an angle 505, so the light emitted by each CP is off-axis light. Off-axis light is light whose main emission axis is not parallel to an axis perpendicular to the CPA 100. In some embodiments, the axis can be the optical axis of the FPA system. In contrast, on-axis light is light whose main emission axis is substantially parallel to the axis. Note that as shown, the angle 505 is the same for each CP, but in other embodiments, some or all of the angles may be different from each other. Each microprism of the microprism array 502 includes one or more facets 504. Each CP is covered with at least one facet of the microprism. Note that in some embodiments, a single microprism may cover multiple CPs. The microprism is configured to refract incident light (e.g., via the material of the microprism and the shape of the one or more facets 504) so ​​that off-axis light is redirected to on-axis light, and similarly, on-axis light (i.e., return light) is redirected to off-axis light (so that it is incident on the CP).

[0039] Figure 6 is a schematic diagram of a blazed grating 602 located on top of CPA 100 according to one or more embodiments. Blazed grating 602 is an embodiment of optical element 202. Blazed grating 602 achieves the same function as microprism array 502, except that it operates under the principle of diffraction rather than refraction.

[0040] Figure 7 An example microprism array (or equivalent blazed grating) in a two-dimensional arrangement according to one or more embodiments is shown. The microprism array can be an embodiment of the optical element 202 and / or the microprism array 502. In 700, the microprism array is laid out as a 1D linear array that is compatible with a regular grid of equiangular CPs. In 701, the microprism array is radially symmetric, which is compatible with a radially symmetric grid of CPs. In 702, the position and orientation of the microprisms are arbitrary, which is compatible with any arrangement of CPs. For example, each microprism shown in 702 can cover one or more corresponding CPs, and in some cases, each microprism in 702 covers a single corresponding CP. In all three examples, the outgoing beam propagates at the same coaxial angle.

[0041] Figure 8An embedded version of an optical element according to one or more embodiments is shown. In this case, a coherent pixel array 800 (e.g., an embodiment of CPA 100) includes a CP 801 embedded in a high refractive index medium 802. The optical element is a single piece of material that overmoldes the coherent pixel array 800, and a surface 804 of the single piece of material is angled relative to the CP 801 so that light emitted by the CP 801 is refracted to be coaxial. The CP emits a light beam 803 that propagates at a small angle. The beam impinges on the polished surface 504 at a small angle so that the transmitted beam 805 propagates vertically (i.e., substantially coaxial). In other embodiments, the angle of the surface can be such that the transmitted beam 8-5 is emitted at some other target angle.

[0042] Fig. 9 A schematic diagram of a switchable coherent pixel array (SCPA) FMCW LiDAR chip 911 according to one or more embodiments is shown. The LiDAR chip is a photonic integrated circuit. The chip may include multiple basic functional subarrays 900. Each subarray 900 includes: an optical input / output (I / O) port 902 and an optional 1-to-K optical separator 903, where K is an integer; and one or more SCPAs 901. The 1-to-K optical separator 903 can be passive or active. Each optical I / O is fed by a frequency modulated light source provided by an off-chip or on-chip laser. Optical power can be distributed on the chip through an optional 1-to-K optical separator to reduce the number of optical I / Os. In the embodiment shown, the corresponding outputs of the 1-to-K optical separators 903 are fed to corresponding SPCAs 901. In the embodiment shown, each SCPA 901 includes M coherent pixels 905 and an optical switching network 904, where M is an integer. Note that in some cases, one or more of the optical switching network 904, the optional 1-to-K optical splitter 903, or some combination thereof may be simply referred to as an optical switch. The optical switch is configured to switchably couple the input port 902 to an optical antenna within a coherent pixel, thereby forming an optical path between the input port and the optical antenna. The optical switch may include a plurality of active optical splitters. In some embodiments, the optical switch optically couples the frequency modulated laser signal to each optical antenna one at a time during a scan cycle of the FMCW transceiver.

[0043] The optical switching network 904 selects one or more of the M coherent pixels to send and receive frequency modulated (FM) light for ranging and detection. The coherent pixels can be physically arranged on the chip in a one-dimensional (e.g., linear array) or a two-dimensional array (e.g., rectangular, regular (e.g., non-random arrangement like a grid)). In some embodiments, the selected coherent pixels are capable of transmitting light into free space, receiving a returning optical signal, performing coherent detection, and converting the optical signal directly into an electrical signal for digital signal processing. Note that the received optical signal does not propagate through the switching network again in order to be detected, but is routed out separately (not shown in the illustrated embodiment), which reduces losses and thus improves signal quality.

[0044] Figures 10a to 10d Four versions of coherent pixels according to one or more embodiments are shown. The four versions of coherent pixels can be, for example, Fig. 9 An embodiment of a coherent pixel as described in . Fig.10a and Fig.10b , light from an optical switching network (e.g., optical switching network 904) is provided to the optical input port 1003 of the coherent pixel. A bidirectional optical 2×2 splitter 1002 splits the light into two output ports, which are called TX signal 1005 and local oscillator LO 1006. The TX signal 1005 is sent out of the chip using an optical antenna 1000. An optical antenna is a device that launches light from an on-chip waveguide into free space or couples light from free space to an on-chip waveguide, such as a grating coupler, edge coupler, integrated reflector, or any spot size converter. Optical antennas are typically polarization sensitive and have much higher launch / coupling efficiency for light with one specific polarization (e.g., TE). The antenna is reciprocal, so it collects the reflected beam from the object being measured and sends it back to the bidirectional 2×2 splitter 1002, which in turn splits the beam between ports 1004 and 1006. The bidirectional optical 2×2 splitter 1002 acts as a "pseudo-circulator" in this monostatic configuration where the transmitter and receiver are co-located. The received signals output from port 1004 and LO 1006 are combined for coherent detection by an optical hybrid, which may be a Fig.10a The balanced 2×2 optical combiner 1001 shown or Fig.10b The optical mixer 1009 is shown. Finally, Fig.10a A pair of photodiodes (PD) 1007 and Fig.10b The four PDs in the system convert the optical signal into an electrical signal for beat note detection. Fig.10a The version in is called the balanced photodiode (BPD) version. Fig.10bThe version in is called a hybrid version. The hybrid version provides in-phase and quadrature outputs (I / Q) and can be used to resolve velocity-range ambiguity or enable advanced DSP algorithms in FMCW LiDAR systems. Using a bidirectional optical 2×2 splitter as a “pseudo-circulator” eliminates the need for a discrete circulator for each pixel, which is impractical for large-scale arrays with hundreds of pixels. As a result, coherent pixels can significantly reduce cost and volume with a loss in signal-to-noise ratio (SNR) of up to 6 dB (because some of the guided optical power cannot be used for coherent detection). For example, the received optical signal can be divided between port 1003 and port 1004, the latter of which is used for coherent detection. Fig.10c and Fig.10d The coherent pixel design shown addresses this limitation by introducing a polarization-splitting antenna 1010 in a new structure. Light from the optical switching network is provided to the optical input port 1003 of the coherent pixel. An optical splitter 1012 splits the light into two output ports, which are called the TX signal 1015 and the local oscillator LO 1014. The TX signal 1015 is sent directly out of the chip using a polarization-splitting optical antenna 1010 with one polarization (e.g., TM). The antenna collects the reflected beam from the object under test, couples the orthogonal polarization (e.g., TE) into the waveguide 1013, and sends it directly to the optical mixer. In this case, the optical signal received by the antenna is not further split by any additional splitters or "pseudo-circulators". The received signals output from port 1013 and LO 1014 are mixed by the optical mixer for coherent detection, which can be as shown in Figure 1. Fig.10c The balanced 2×2 optical combiner 1001 shown or Fig.10d The optical mixer 1009 is shown. Finally, Fig.10c A pair of photodiodes (PD) 1007 and Fig.10d The 4 PDs in the chip convert the optical signal into an electrical signal for beat sound detection. This design realizes a highly efficient integrated circulator for each single coherent pixel and enables the on-chip monostatic FMCW LiDAR with ultra-high sensitivity. Details will be given in Figure 8 to Figure 1 0. In some embodiments, Figure 2 In the context of Figures 10a to 10d The coherent pixel enables each of the multiple optical antennas to have a separate splitter, and each splitter is coupled along a corresponding optical path between the optical switch and the corresponding antenna.

[0045] Additional configuration information

[0046] The drawings and the foregoing description relate to the preferred embodiments by way of illustration only. It should be noted that from the foregoing discussion, it will be readily appreciated that alternative embodiments of the structures and methods disclosed herein are viable alternatives that may be used without departing from the principles of the claimed invention.

[0047] Although the detailed description contains many details, these details should not be interpreted as limiting the scope of the present invention, but are merely illustrative of different examples. It should be understood that the scope of the present disclosure includes other embodiments that are not discussed in detail above. Various other modifications, changes and variations that are obvious to those skilled in the art may be made to the arrangement, operation and details of the methods and devices disclosed herein without departing from the spirit and scope defined by the appended claims. Therefore, the scope of the present invention should be determined by the appended claims and their legal equivalents.

[0048] Alternative embodiments are implemented in computer hardware, firmware, software, and / or a combination thereof. Implementations may be implemented in a computer program product tangibly embodied in a machine-readable storage device executed by a programmable processor; and method steps may be performed by a programmable processor executing a program of instructions to perform functions by operating on input data and generating output. Embodiments may advantageously be implemented in one or more computer programs executable on a programmable system including at least one programmable processor coupled to receive data and instructions from a data storage system, at least one input device, and at least one output device, and to send data and instructions to a data storage system, at least one input device, and at least one output device. Each computer program may be implemented in a high-level procedural or object-oriented programming language, or, if desired, in assembly or machine language; and in any case, the language may be a compiled or interpreted language. Suitable processors include, by way of example, general-purpose and special-purpose microprocessors. Typically, the processor will receive instructions and data from a read-only memory and / or a random access memory. Typically, a computer will include one or more mass storage devices for storing data files; such devices include disks, such as internal hard disks and removable disks; magneto-optical disks; and optical disks. Storage devices suitable for tangibly embodying computer program instructions and data include all forms of non-volatile memory, including, for example, semiconductor memory devices such as EPROM, EEPROM, and flash memory devices; magnetic disks, such as internal hard disks and removable disks; magneto-optical disks; and CD-ROM disks. Any of the above may be supplemented or incorporated by ASICs (application specific integrated circuits) and other forms of hardware.

Claims

1. A focal plane array (FPA) system for a frequency modulated continuous wave (FMCW) light detection and ranging LiDAR system, the FPA system comprising: A switchable coherent pixel array, the switchable coherent pixel array comprising a plurality of coherent pixels, wherein each of the plurality of coherent pixels comprises an optical antenna configured to emit coherent light into free space and collect reflected light from the object under test; an optical switch configured to couple a laser optical signal to each of the corresponding optical antennas within a coherent pixel of the plurality of coherent pixels one at a time during a scan cycle of the LiDAR system; and a diffraction grating stack DGS, the diffraction grating stack DGS comprising at least one diffraction grating positioned to diffract the coherent light emitted from the array of switchable coherent pixels into the environment as one or more light beams, wherein each of the one or more light beams is emitted at a specific angle, and the specific angle is based on a position of the coherent pixels among the plurality of coherent pixels that generate the coherent light that forms the one or more beams, thereby steering the one or more beams through the environment.

2. The FPA system according to claim 1, wherein: The at least one diffraction grating is a non-periodic diffraction grating.

3. The FPA system according to claim 2, wherein: The at least one diffraction grating is a blazed grating.

4. The FPA system according to claim 2, wherein: The at least one diffraction grating is a multi-step grating.

5. The FPA system according to claim 1, wherein: The at least one diffraction grating is selected from the group consisting of a surface relief grating, a sinusoidal grating, a blazed grating, and a step grating.

6. The FPA system according to claim 1, wherein: The one or more light beams are reflected from the objects in the environment to form return light, and the DGS is positioned to: The return light is diffracted to one or more coherent pixels that produce the one or more light beams.

7. The FPA system according to claim 1, wherein: The light emitted by the coherent pixels of the switchable coherent pixel array is off-axis, and the FPA system further comprises: an optical element positioned between the array of switchable coherent pixels and the DGS, the optical element being positioned to redirect off-axis light emitted by the coherent pixels so that it is on-axis, The coaxial light is substantially parallel to the optical axis of the coherent pixel array.

8. The FPA system according to claim 7, wherein: A first light beam of the one or more light beams is formed from light from the coherent pixel, and the first light beam is reflected from the object in the environment to form return light, and the optical element is positioned to receive the return light from the DGS, redirect the received return light off-axis, and detect the off-axis return light at the coherent pixel.

9. The FPA system according to claim 7, wherein: The optical element is a blazed grating, and light emitted from the coherent pixels is diffracted to be coaxial.

10. The FPA system according to claim 7, wherein: The optical element is a single piece of material overmolded to the array of coherent pixels, and a surface of the single piece of material is angled relative to the coherent pixels such that light emitted by the coherent pixels is refracted to be coaxial.

11. The FPA system according to claim 7, wherein: The optical element is a microprism array.

12. The FPA system according to claim 11, wherein: The microprism array is a linear array of microprisms.

13. The FPA system of claim 11, wherein: The microprism array is a circular array of microprisms, wherein the microprisms form a series of rings, and the plurality of coherent pixels in the switchable coherent pixel array have a radial distribution pattern, and each microprism covers at least one coherent pixel in the coherent pixel array.

14. The FPA system of claim 11, wherein: Each microprism in the microprism array covers a single coherent pixel in the coherent pixel array.

15. The FPA system of claim 1, wherein: The light emitted by the switchable coherent pixel array is off-axis, and the FPA system further comprises: an optical element positioned between the switchable coherent pixel array and the DGS, the optical element positioned to redirect off-axis light emitted by the switchable coherent pixel array so that it is on-axis, wherein the on-axis light is substantially parallel to the optical axis of the coherent pixel array.

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