Photonic integrated circuit and LIDAR based thereon

Abstract

A LiDAR system comprising a photonic integrated circuit using a switching tree 209 to provide directivity to both transmission of the ranging signal and reception of the reflection signal. The switching tree comprising plural switches 202 switching emission light 103 between a plurality of exit ports 204 for selectively illuminating a remote object to produce a reflection, and directing the reflection received at a same exit port to a common port 201. The system also splitting the light prior to being received by the switching tree and on reception of the reflection a coupler combines the reflection 105 at the common port with a split portion of the emission light for providing a signal at a beat frequency between the internal portion and the reflection. The PIC preferably includes a photodetector. The switching tree preferably comprises a transmitter switching tree and a matching receiver switching tree. The switching tress preferably being binary trees of Mach-Zehnder interferometer switches 202. The LIDAR system including first and second channels, each comprising a PIC as above and a controller to determine from the beat frequencies of the first and second channels a distance to or velocity of the object. The LIDAR light source preferably having an optical switch to switch emitted light between the two channels.

Description

[0001] The present disclosure relates to ranging devices, and in particular to light detection and ranging devices, systems, and methods. BACKGROUND

[0002] Light Detection And Ranging (LiDAR) is a remote sensing technology that uses pulsed or continuous light beams to provide three-dimensional maps of surroundings and outside objects. A light source emits light toward a target. The target scatters the light, reflecting a portion of it towards a receiver of a LiDAR system. The LiDAR system then determines the distance to the target in the direction of the light beam based on one or more characteristics associated with the reflected / scattered light, such as its arrival time, modulation phase, and / or optical frequency. LiDAR may be used in a wide variety of applications ranging from 3D imaging by a smartphone to automotive and even atmospheric sensing.

[0003] It is desirable for a LiDAR system to be able to operate over large distances, and to measure not only the distance to objects but also their relative velocities. It is further desirable to reduce the size, complexity, and power consumption of a LiDAR device while providing a high degree of reliability and fidelity of obtained 3D images and data. BRIEF DESCRIPTION OF THE DRAWINGS

[0004] Exemplary embodiments of this disclosure will now be described in conjunction with the drawings, in which:

[0005] FIG. 1A is a schematic diagram of a frequency-modulated continuous-wave (FMCW) LiDAR system of this disclosure;

[0006] FIG. IB is a block diagram of the FMCW LiDAR of FIG. 1A;

[0007] FIG. 2 is a schematic diagram of a switching tree with an optical circulator usable for beam redirection and signal path separation in the FMCW LiDAR of FIG. IB;

[0008] FIG. 3 A is a schematic diagram of an embodiment of the beam scanner of the FMCW LiDAR of FIG. IB including the switching tree of FIG. 2;

[0009] FIG. 3B is a schematic depiction of the field of view of the beam scanner of FIG. 3 A;

[0010] FIG. 3C is a schematic diagram of a beam scanner embodiment including the switching tree of FIG. 2 coupled to a 2D array of out-coupling gratings;

[0011] FIG. 4A is a schematic diagram of a transmitter switching tree of an FMCW LiDAR of this disclosure;

[0012] FIG. 4B is a schematic diagram of a receiver switching tree matching the transmitter switching tree of FIG. 4A;

[0013] FIG. 5 is a schematic diagram of a transmitter / receiver multiplexing configuration using polarization to separate the transmitter and receiver light paths, in accordance with an embodiment of this disclosure;

[0014] FIG. 6 is a block diagram of a multi-channel implementation of an FMCW LiDAR of this disclosure using separate digital signal processing (DSP) units for parallel data processing;

[0015] FIG. 7 is a timing diagram of the multi-channel FMCW LiDAR of FIG. 6 with simultaneous data processing;

[0016] FIG. 8 is a timing diagram of the multi-channel FMCW LiDAR of FIG. 6 with staggered or interleaved data processing, allowing one to potentially reduce the number of processing electronics channels;

[0017] FIG. 9A is a block diagram of a multi-channel FMCW LiDAR with parallel data processing;

[0018] FIG. 9B is a block diagram of a multi-channel FMCW LiDAR of this disclosure using a digital switch coupled to a common DSP unit for staggered data processing in accordance with the timing diagram of FIG. 8;

[0019] FIG. 9C is a block diagram of a multi-channel FMCW LiDAR of this disclosure using an analog switch coupled to a common analog-to-digital converter and DSP unit for staggered data processing in accordance with the timing diagram of FIG. 8;

[0020] FIG. 10 is a block diagram of a multi-channel FMCW LiDAR of this disclosure using a photodiode bias switch and / or optical attenuator / switch for turning the ranging light ON and OFF in different channels, to provide the staggered data processing of FIG. 8;

[0021] FIG. 11 is a flow chart of a ranging method of this disclosure;

[0022] FIG. 12A is a flow chart of an embodiment of the ranging method of FIG. 11 utilizing staggered ranging and data processing;

[0023] FIG. 12B is a flow chart of an embodiment of the ranging method of FIG. 11 utilizing electrical and / or optical switching of the measuring channels for staggered ranging and data processing; and

[0024] FIG. 12C is a flow chart of an embodiment of the ranging method of FIG. 11 utilizing photodetector bias switching of the measuring channels for staggered ranging and data processing. DETAILED DESCRIPTION

[0025] While the present teachings are described in conjunction with various embodiments and examples, it is not intended that the present teachings be limited to such embodiments. On the contrary, the present teachings encompass various alternatives and equivalents, as will be appreciated by those of skill in the art. All statements herein reciting principles, aspects, and embodiments of this disclosure, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future, i.e., any elements developed that perform the same function, regardless of structure.

[0026] As used herein, the terms "first", "second", and so forth are not intended to imply sequential ordering, but rather are intended to distinguish one element from another, unless explicitly stated. Similarly, sequential ordering of method steps does not imply a sequential order of their execution, unless explicitly stated.

[0027] A FMCW LiDAR system directs a frequency-modulated continuous-wave light beam to a remote object and detects reflected light using a heterodyne detector. The FMCW light beam may be created e.g. by modulating a monochromatic laser beam, or by cyclical wavelength tuning of a monochromatic laser source. A beamsplitter splits a portion of the generated FMCW light beam being sent to the remote object, to act as a local oscillator. This small split portion is then subsequently mixed with the reflected FMCW light. The resulting mixed signal is detected at the photodetector. Due to the time-of-flight delay of the frequency-modulated probing light beam, an instantaneous optical frequency of the reflected light is different from an instantaneous optical frequency of the portion of the probing light beam, which causes the mixed optical signal at the photodetector to oscillate at a differential frequency between the frequency of the light beam portion and the frequency of the reflection. The oscillations or beats are detected by the heterodyne detector, and a processor measures the frequency of the oscillations to determine a distance to the object. Both the distance to the object and a relative velocity of the object may be determined by scanning the optical frequency of the probing beam back and forth.

[0028] The probing light beam may scan an area by switching the frequency-modulated light between an array of output ports coupled to a collimator. Onedimensional or two-dimensional scanning may be configured this way. A switching tree may be used to switch the probing light beam between the output ports of the array. The switching tree, as defined in this disclosure, includes a sequence of branches coupled to one another such that, at each branch of the switching tree, the number of ports increases (for IxA tree) or decreases (for Axl tree). For example, in a binary switching tree, the number of ports doubles at each branch. A same or a matching switching tree portion of a switching tree structure may be used for reception to provide a directivity of detection. The directivity of detection may increase the signal-to-noise ratio as compared to cases where the detection is non-directional, i.e. where the reflected light is detected over an entire field of view of a LiDAR system, regardless of the instant direction of the ranging light beam.

[0029] One issue with utilizing switching trees in scanning LiDAR systems is that the process of switching is not instantaneous. If there are too many branches in the switch tree, the time of reconfiguration of the switching tree for a new point of scanning becomes too large, thus the LiDAR system becomes unusable. To overcome this problem and to increase the total number of ranging directions, a plurality of LiDAR channels may be provided. Data gathering and processing in these channels may be staggered or interleaved to reduce the number of DSP units required. Multiplexing multiple LiDAR channels to a single signal processing train allows one to significantly reduce the system complexity and power consumption. The multiplexing may also facilitate the reduction of the overall size of the LiDAR system, which is highly desirable from the system integration standpoint.

[0030] In accordance with the present disclosure, there is provided a photonic integrated circuit (PIC) comprising a switching tree for switching light between a plurality of exit ports for selectively illuminating a remote object to produce a reflection, and for directing the reflection received at a same exit port of the plurality of exit ports to a common port; and a coupler for combining the reflection at the common port with a portion of the light, for providing a signal at a beat frequency between the portion and the reflection. The PIC may further include a photodetector for detecting the signal.

[0031] The switching tree may include a transmitter switching tree for switching the light between a plurality of transmitter ports for selective illumination of the remote object to produce the reflection, and a matching receiver switching tree for directing the reflection received at a corresponding receiver port of a plurality of receiver ports to the common port. In such embodiments, the PIC may further include a plurality of polarization converters each coupled to one of the plurality of receiver ports, and a plurality of polarization combiners each coupled, on one end, to one of the plurality of transmitter ports and one of the plurality of polarization converters and, on the other end, to an exit port of the plurality of exit ports.

[0032] The polarization converters may be placed into the transmission signal path instead, i.e. the plurality of polarization converters may each be coupled to one of the plurality of transmitter ports, and the plurality of polarization combiners may each be coupled, on one end, to one of the plurality of receiver ports and one of the plurality of polarization converters and, on the other end, to an exit port of the plurality of exit ports. The transmitter and receiver switching trees may include binary trees of Mach-Zehnder interferometer switches.

[0033] In accordance with the present disclosure, there is provided a LiDAR system comprising first and second channels each comprising a PIC as defined above, and a controller for determining, from the beat frequencies of the first and second channels, at least one of a distance to or a velocity of the object. In embodiments where the switching trees of the first and second channels have a transition time interval and a steady-state time interval, the controller may be configured to overlap the transition time interval of the second channel with the steady-state time interval of the first channel, and vice versa.

[0034] The LiDAR system may further include first and second amplifiers for amplifying signals of the first and second channels, respectively, where the signals are detected by the respective photodetectors. For such embodiments, the controller may include: first and second analog to digital converters (ADCs) coupled to the first and second amplifiers, respectively, for digitizing the signals; a digital switch coupled to the first and second ADCs; and a signal processor coupled to the digital switch for determining, from the beat frequencies, the at least one of a distance to the object or velocity of the object.

[0035] In some embodiments, the controller includes an analog switch coupled to the first and second amplifiers, and a signal processor coupled to the analog switch for determining, from the beat frequencies, the at least one of the distance to the object or the velocity of the object. Furthermore, in embodiments where the photodetectors of the first and second channels have a bias switchable by the controller, the latter may be configured to switch ON the bias of the photodetector of the first channel and switch OFF the bias of the photodetector of the second channel, and determine, from the beat frequency of the first channel signal, the at least one of the distance to the object or the velocity of the object.

[0036] The LiDAR system may further comprise a light source for providing the light to the first and second channels. The controller may be configured to sweep an optical frequency of the light source up and down. The light source may include an optical switch for switching the light between the first and second channels. In such embodiments, the controller may be configured to use the optical switch to switch ON the light coupled to the first channel, and to switch OFF the light coupled to the second channel; and determine, from the beat frequency of the first channel signal, the at least one of the distance to the object or the velocity of the object. The first and second channels may, but do not have to, be implemented in a same PIC chip.

[0037] In accordance with the present disclosure, there is further provided a ranging method comprising the following for each of first and second channels: switching frequency-modulated light between ports of an optical switching tree for directing the light to a remote object at a port-specific angle; receiving a reflection from the object and propagating the reflection back through the optical switching tree; and combining a portion of the light and the reflection for providing a signal at a beat frequency between the portion and the reflection. At least one of a distance to or a velocity of the object may be determined from the beat frequencies.

[0038] In embodiments where the optical switching trees of the first and second channels have a transition time interval and a steady-state time interval, the method may further include overlapping the transition time interval of the second channel with the steady-state time interval of the first channel, and determining, from the beat frequency of the first channel, at least one of a distance to a first portion of the object or a velocity of the first portion. The method may further include overlapping the transition time interval of the first channel with the steady-state time interval of the second channel, and determining, from the beat frequency of the second channel, at least one of a distance to a second portion of the object or a velocity of the second portion. Processing in more than two channels may be staggered in this way.

[0039] In some embodiments, the ranging method may further include amplifying the signals of the first and second channels; using a digital signal processor (DSP) to determine the at least one of the distance to or velocity of the first portion of the object; and using the DSP to determine the at least one of the distance to or velocity of the second portion of the object. The signal at the beat frequency in each channel may be detected using a photodetector; the method may further include switching a bias of the first channel photodetector ON, switching a bias of the second channel photodetector OFF, and determining the at least one of the distance to or velocity of the first portion of the object, and switching the bias of the second channel photodetector ON, switching the bias of the first channel photodetector OFF, and determining the at least one of the distance to or velocity of the second portion of the object.

[0040] The frequency-modulated light may be applied to the first channel while attenuating / blocking the frequency-modulated light applied to the second channel, and the at least one of the distance to or velocity of the first portion of the object may be determined. The frequency-modulated light may be applied to the second channel while attenuating / blocking the frequency-modulated light applied to the first channel, and the at least one of the distance to or velocity of the second portion of the object may be determined.

[0041] In some embodiments, in a third channel, the light may be directed to the remote object by switching frequency-modulated light between ports of an optical switching tree, where each port is configured to direct the light to the remote object at a port-specific angle. A reflection may be received from the object and propagated back through the optical switching tree of the third channel. A portion of the light and the reflection may be combined at a photodetector for providing a signal at a beat frequency between the portion and the reflection. More than three channels may be provided.

[0042] Referring now to FIG. 1 A, a LiDAR system 100 of this disclosure may include a light source 102 emitting a frequency-modulated light beam 103, or simply light 103. The light source 102 may include e.g. a continuous-wave monochromatic laser coupled to a modulator for modulating optical frequency of the output laser beam, and / or a wavelength-tunable monochromatic laser source. By way of a nonlimiting illustrative example of the latter option, the tunable laser may have the center wavelength of 1550nm, corresponding to the optical frequency of 193.5THz. The laser may be tunable by the wavelength equivalent of several GHz (e.g. l-3GHz) with the frequency of the wavelength tuning cycle of 100 KHz. Herein, the term “frequency-modulated” or “frequency modulation” is intended to cover all cases of periodic optical frequency shifting or “chirping” of ranging light, including without limitation using an external modulator, wavelength tuning or wavelength / frequency chirping the light source, or any other mechanism or method of optical frequency modulation.

[0043] The light source 102 is coupled to a beamsplitter 104, which splits off a portion 105 of the light beam 103, and directs the split off portion 105 to a heterodyne detector 106. The light beam 103 propagates through a director 108, which has a dual function. One function of the director 108 is to separate the light beam 103 sent to a remote object or target 110 from a reflection 105’ from the target 110. The other function of the director 108 is to angularly scan the light beam 103, and to angularly scan the direction in which the reflection 105’ may be received. The angular scanning of the reception directivity, i.e. scanned directional reception sensitivity, suppresses noise from other directions and thus considerably increases the signal to noise ratio as compared to the non-direction-selective reception.

[0044] The scanning function may be implemented in a variety of ways including, without limitation, mechanical scanning using a tiltable reflector, scanning by switching the light beam 103 between different output ports placed at a focal plane of a collimator, and / or optical phase array (OPA) scanning. The OPA scanning may operate by having all ports emit light at a same power or having an apodized power distribution, with a controllable and variable phase difference between neighbouring ports. The phase difference of the neighbouring ports determines the direction of the output light. By controlling the magnitude of the phase difference, the output beam can be scanned across a wide angle e.g. 120 degrees. The switching-based LiDAR scanning options will be considered in detail further below with reference to FIGs. 3A-3C.

[0045] Still referring to FIG. 1 A, the ranging beam portion 105 and the reflection 105’ are directed to the heterodyne detector 106, which includes a mixer 112 coupled to a balanced photodetector 114. The balanced photodetector 114 may include a matched pair of photodiodes 116. The photodiodes 116 of the balanced photodetector 114 are coupled to a transimpedance amplifier (TIA) 118. The function of the TIA 118 is to convert a current signal generated by the photodetectors 116 into a voltage signal at an optical beating frequency between the portion 105 and the reflection 105’, and to amplify the signal at the optical beating frequency. The amplified signal is directed to a processing unit 120, which digitizes and processes the amplified signal.

[0046] The LiDAR system 100 of FIG. 1A operates in the following manner. An optical frequency of the light beam 103 is modulated by linearly ramping the optical frequency up and down, as illustrated by a symmetrical sawtooth dependence^) of the light source 102 in FIG. 1 A. The frequency-modulated, continuous-wave light beam 103 propagates to the target 110 located a distance L from the LiDAR system 100. By the time the reflection 105’ of the emitted light beam 103 from the object 110 returns to the LiDAR system 100, the instantaneous optical frequency of the light beam portion 105 shifts due to the frequency scanning. The frequency shift causes a beating between the portion 105 and the reflection 105’ at a heterodyne frequency proportional to the distance L between the LiDAR system 100 and the object 110. The mixer 112, implemented in this embodiment as a 2x2 coupler, directs the optical beating signals to the photodiodes 116 in counter-phase. This causes the photodiodes 116 of the balanced photodetector 114 to produce photocurrents oscillating in counter-phase for providing a differential current signal. The TIA 118 converts the differential current signal to a voltage signal, and amplifies the voltage signal to levels sufficient for subsequent digitization and processing.

[0047] When the object 110 moves at a velocity V along the line of sight, the reflection 105’ undergoes an additional optical frequency shift due to Doppler effect. The resulting ambiguity between the distance L and velocity Vdetermination may be resolved by comparing the measured heterodyne frequencies when ramping the optical frequency of the light beam 103 up and down. When the velocity Fis zero, the heterodyne frequency shifts when scanning optical frequency up and down are equal. When the velocity Vis not zero, the heterodyne frequency shifts are no longer equal, the difference between the heterodyne frequency shifts being proportional to the velocity V. Thus, both the distance L and velocity V may be determined during a same bidirectional optical frequency scan.

[0048] The wavelength (inverse of the optical frequency) of the light source 102 may be in the infrared region to make the optical ranging by the LiDAR 100 inconspicuous. The infrared region may be centered around the wavelength of 1 micrometer, 1.55 micrometers, etc., depending on the available light source, detectors, range, the nature of the target, and the intended purpose of the LiDAR 100. The heterodyne detector 106 may have a single photodiode 116, and may omit the mixer 112 by combining the portion 105 and the reflection 105’ directly on the single photodetector. Many other variants and modifications of the LiDAR system 100 are possible.

[0049] Turning to FIG. IB, the light source 102 may include a frequency-swept laser 121 coupled to an optical amplifier 122 for amplifying the light beam 103 to an optical power level sufficient for ranging over a required distance. The optical amplifier 122 is coupled to the beamsplitter 104. The director 108 includes a beam scanner 109 coupled to a path separator 111. The beam scanner 109 angularly scans the light beam 103. In any scanning state / scanning direction, the beam scanner 109 also receives the reflection 105’ from a remote object or a feature of an outside scenery at a same angle as the ranging light beam, and directs the reflection to the path separator 111. The path separator 111 separates the paths of the ranging and reflected light, directing the reflection 105’ to the heterodyne detector 106.

[0050] The heterodyne detector 106 produces an electrical current signal at a beat frequency between the portion 105 and the reflection 105’. The electrical current signal is converted to a voltage signal and amplified by the TIA 118. The TIA 118 is coupled to the processing unit 120, which includes an analog-to-digital converter (ADC) 131 coupled to a digital signal processing (DSP) unit 132. The processing unit 120 may further include a chain of gain / amplifier (AMP) stages 130, which may be cascaded to sufficiently amplify the signal to fit the full conversion range of the ADC 131.

[0051] The ADC 131 digitizes the amplified electrical signal. The DSP unit 132 determines the beat frequencies of the digitized amplified signal. The processing unit 120 is configured to then determine at least one of a distance to the remote object or a radial velocity of the remote object. The scanning allows one to obtain a 3D map (point cloud) of the outside scenery, together with the 3D map of the velocities of different scenery portions. The 3D velocity map may be used, for example, to determine relative speed of traffic participants in an automotive LiDAR application.

[0052] In accordance with this disclosure, the scanner 109 of the director 108 may be implemented using a switching tree for switching light between a plurality of exit ports, each port corresponding to a different ranging direction. The switching tree may then be used to route the reflection received at a same exit port as the transmitted light, to a reception port. Referring to FIG. 2 for a non-limiting illustrative example, a switching tree 209 is implemented in a photonic integrated circuit (PIC). A common port 201 of the switching tree 209 is coupled to an optical circulator 211, which performs the function of the path separator 111 of FIG. IB. The switching tree 209 (FIG. 2) includes a plurality of 1x2 optical switches 202 in a binary tree configuration, where two outputs of a particular switch are coupled to inputs of two switches. The 1x2 optical switches 202 may be implemented, for example, as Mach-Zehnder interferometer (MZI) switches, which may be thermally actuated to provide the required switching function. Other types of switches may be used.

[0053] In a binary transmitter switching tree, having n switching stages provides a switch with one input and 2" outputs. In the example shown in FIG. 2, there are four stages and accordingly sixteen outputs. The last (rightmost) stage of the 1x2 optical switches 202 has its outputs coupled to output ports 204. Herein and throughout the specification, the term “port” is used to denote a terminal or a waveguide of a waveguide device, and may, but does not have to, mean an actual opening or a dedicated structure. The switching tree 209 can switch the frequency-swept light provided by the light source between sixteen individual output ports 204. When combined with a collimator, the switching tree 209 may be used to switch the light beam between sixteen different directions. The reflection from remote scenery or objects coming in from the location being probed (i.e. in the opposite direction to that of the ranging beam) may be brought back by the switching tree in a reverse direction. The reflection 105’ may be separated from the ranging light beam 103 by the optical circulator 211. In embodiments where the ranging light and reflected light have orthogonal polarizations, the optical circulator 211 may be replaced with a polarization coupler, e.g. a polarization beam splitter (PBS). The polarization orthogonality of the probing and reflected light may be achieved e.g. by placing a quarter-wave plate (QWP) in a common path of the probing and reflected light, provided that the probing light upstream of the QWP is linearly polarized.

[0054] Referring to FIG. 3A, an embodiment 309A of the scanner 109 of the LiDAR system 100 of FIGs. 1A and IB includes the switching tree 209 of FIG. 2 implemented in a PIC chip 300A. The plurality of output ports 204 of the switching tree 209 are disposed along a right-hand side of the PIC chip 3 00A. The light beam 203 is coupled to the common port 201 of the switching tree 209.

[0055] As explained above, the function of the switching tree 209 is to switch the light beam between the output ports 204. The output ports 204 of the switching tree 209 are disposed in a focal plane of a collimating lens 306, which converts the beam coordinate, i.e. a serial number of the output port 204 presently connected to the input port 201 of the switching tree 209, into an angle of a collimated beam 123 downstream of the collimating lens 306. Thus, switching the light beam 103 between the output ports 204 of the switching tree 209 is equivalent to steering the collimated light beam 123 in XY plane in FIG. 3 A.

[0056] In some embodiments, the switching tree 209 may include several common ports 201 for simultaneous switching of several input light beams between pluralities of output ports 204. The pluralities of output ports 204 corresponding to different common ports 201 may form separate blocks of output ports 204 disposed along a common plane or in different planes for 2D scanning, or may be interleaved with one another on the common plane. Having several switching trees, each coupled to its own frequency-swept laser source, facilitates faster scanning by a LiDAR, better spatial resolution, or both. A collimator other than the collimating lens 306 may be used to provide the desired beam coordinate to beam angle (and back from the beam angle to the beam coordinate) transformation. The collimator may include a diffractive lens, a concave reflector, etc.

[0057] In some embodiments, the scanner 309A may further include a tiltable reflector 344, e.g. a microelectromechanical system (MEMS) reflector, coupled to the collimating lens 306 for scanning the collimated light beam 123 in YZ plane. The combination of switching and scanning illustrated in FIG. 3A provides a scanning capability in two dimensions, allowing the generation of 3D point clouds of the outside objects’ coordinates and / or velocities.

[0058] The angular scanning space is illustrated in FIG. 3B where a horizontal direction 311 corresponds to the scanning via output port switching of the switching tree 209, and a vertical direction 312 corresponds to the scanning using the tiltable reflector 344. At each angle of tilt of the tiltable reflector 344, the light beam 103 may be quickly switched between different output ports 204 (FIG. 3 A), forming a two-dimensional field of view 310 including a two-dimensional array of ranging angles 320. Other types of beam scanners may be used in place of the tiltable reflector, including liquid crystal redirectors, MEMS structured surfaces, etc.

[0059] In some embodiments of a beam scanner, the PIC chip may include a 2D array of out-coupling gratings to provide the two-dimensional field of view 310 of FIG. 3B without having to rely on an additional scanner, such as the tiltable reflector 344 of FIG. 3 A, or any other type of mechanical or non-mechanical beam scanning. Turning to FIG. 3C, an embodiment 309C of the scanner 109 of FIGs. 1A and IB includes the switching tree 209 of FIG. 2 implemented in a PIC chip 300C. The PIC chip 300C of FIG. 3C includes a 2D array of out-coupling gratings 340 disposed in XY plane, i.e. in-plane of the PIC chip 300C, for out-coupling the ranging light beam away from the PIC chip 300C in Z-direction, or upwards in FIG. 3C. The collimating lens 306 may be disposed over the PIC chip 300 to receive and collimate the ranging beams out-coupled by the 2D array 340 of out-coupling gratings. In the embodiment 309C, the direction of the ranging light beam is determined by the coordinate of the out-coupling grating of the array 340. For example, when a first out-coupling grating 341 of the array 340 outputs light, the collimating lens 306 forms a first collimated ranging beam 351 propagating straight up along Z-axis, and when a second out-coupling grating 342 of the array 340 outputs light, the collimating lens 306 forms a second collimated ranging beam 352 propagating at an acute angle to Z-axis.

[0060] Utilizing a switching tree for both the transmission and the reception improves the directivity of reception and thus improves the signal to noise ratio. However, utilizing a same switching tree for the forward and backward light path in a LiDAR system may present challenges such as a high optical loss due to having to use an optical circulator for separation of the forward and backward paths, and a higher noise level due to unwanted backreflections in the forward beam path. To reduce the optical loss and improve signal to noise ratio, the forward path and return path may be routed using separate switching trees, a transmitter switching tree and a matching receiver switching tree. The switching trees may be driven in coordination with one another to provide the required synchronicity of ranging and detection.

[0061] Referring first to FIG. 4A, a PIC-implemented transmitter switching tree 400A includes a plurality of 1x2 optical switches 402A connected into a binary tree where two outputs of a particular switch are coupled to inputs of two downstream switches. The 1x2 optical switches 402A may be implemented, for example, as thermally actuated MZI switches. Other types of switches may be employed.

[0062] In the example shown in FIG. 4A, there are four stages and accordingly sixteen outputs. The last (rightmost) stage of the 1x2 optical switches 402A has its outputs coupled to output ports 404A. The transmitter switching tree 400A can switch the frequency-modulated light 103 provided by the light source 102 between sixteen individual output ports 404A. When combined with a collimator as depicted in FIG. 3 A, the transmitter switching tree 400A may be used to switch the collimated ranging light beam 123 between sixteen different directions. The PIC-implemented transmitter switching tree 400A may be used for selective illumination of a remote object to produce a reflection.

[0063] Turning to FIG. 4B, a PIC-implemented receiver switching tree 400B matches, in its structure, the transmitter switching tree 400A of FIG. 4A. The receiver switching tree 400B of FIG. 4B includes a plurality of the 2x1 optical switches 402B in a binary tree configuration where two inputs of a particular switch are coupled to outputs of two upstream switches. The 2x1 optical switches 402B may be implemented, for example, as thermally actuated MZI switches. Other types of switches may be used, as well.

[0064] In the example shown in FIG. 4B, there are four stages and accordingly sixteen input ports 404B. The receiver switching tree 400B can direct the light reflected from remote scenery at different directions or incoming angles to a single output port. When combined with a collimator, the receiver switching tree 400B may be used to couple the reflections 105’ arriving from sixteen different directions to a single output port for high sensitivity detection. The last (leftmost) stage of the 2x1 optical switches 402B has its output coupled one of the input ports of the heterodyne detector 106. The portion 105 of the ranging light is coupled to the other input of the heterodyne detector 206.

[0065] The output ports 404A and the input ports 404B may be multiplexed to a set of common exit ports disposed in a focal plane of a collimator, to provide the beam scanning capability. Referring to FIG. 5 for a non-limiting illustrative example, a Tx / Rx (transmission / reception) multiplexing circuit 500 includes a plurality of polarization converters 502 each coupled to one of the plurality of receiver (input) ports 404B of the receiver switching tree 400B. The function of the polarization converters 502 is to convert the propagating light between Te and Tm polarizations. A plurality of polarization splitters / combiners 508 is provided. Each polarization splitter / combiner 508 is coupled, on one end, to one of the plurality of transmitter ports 404A of the transmitter switching tree 400A and one of the plurality of polarization converters 502 and, on the other end, to an exit port 504 of a plurality of exit ports. The function of the splitters / combiners 508 is to combine or split the Te and Tm polarizations, depending on the direction of light propagation. Both the polarization converters 502 and the splitters / combiners 508 may be implemented in a PIC, e.g. in the same PIC as the transmitter 400A and / or receiver 400B switching trees.

[0066] The exit ports 504 may be disposed at an edge of the PIC in a focal plane of a collimator 506, e.g. a collimating lens. The function of the collimator 506 is to collimate the light beams emitted from the exit ports 504 at an angle of propagation depending on the port location, similarly to the configuration depicted in FIG. 3A. In FIG. 5, the transmitted light has Te polarization and the received reflection has Tm polarization. A QWP 510 may be provided in the light path of the light beams, for rotating the linear polarization by 90 degrees upon double-pass propagation through the QWP 510. As an illustration, the Te polarized ranging light beam becomes lefthand circular polarized (LCP) upon propagation through the QWP 510. Assuming that the target is not polarization-selective or polarization-rotating, after reflecting from a target the light beam becomes right-hand circular polarized (RCP). The RCP reflection propagates through the QWP 510 and becomes Tm polarized. The Tm polarized reflection is directed by one of the polarization splitters / combiners 508, which directs the reflection to one of the polarization converters 502.

[0067] Many other configurations of Tx / Rx multiplexing are possible. The polarization converters 502 may be provided in the transmitter path, not the receiver path as illustrated in FIG. 5. In some embodiments, the polarization splitting may be performed upstream of the collimator 506, downstream of a switching tree, etc. By way of a non-limiting example, the QWP 510 may be placed in between the splitters / combiners 508 and the collimator 506. The QWP 510 may be provided on the PIC chip 300, mounted to the PIC chip 300, or be placed in the optical path as a discrete component. Furthermore, some multiplexing configurations may not be based on polarization.

[0068] In the examples of switching trees provided above in FIGs. 4A and 4B, only sixteen input / output ports are provided, which corresponds to only sixteen pixels in a 3D point cloud obtained by a LiDAR. The number of ports may be increased by increasing the number of stages in switching tree(s), but there is a limit because every stage adds optical loss. An alternative approach to increasing the tree length is to provide several parallel ranging channels, each having its own switching tree(s).

[0069] Referring for a non-limiting illustrative example to FIG. 6, a multi-channel LiDAR system 600 includes a plurality of identical channels CHI, CH2, ..., CH [N], which may share a common scanner, e.g. a collimator and / or tiltable reflector. Each channel CHI, CH2, ..., CH [N] of the multi-channel LiDAR system 600 may be implemented in a PIC chip including the switching trees of FIGs. 2 and / or FIGs. 4A-4B with the Tx / Rx multiplexing circuit 500, as explained above. Each channel CHI, CH2, ..., CH [N] may include a frequency-modulated local oscillator 602 (LOI, LO2, ..., LO [N]), such as a frequency-modulated or wavelength-tunable laser, for example. Each local oscillator 602 may be coupled to a corresponding switching tree 604 (STI, ST2, ..., ST [N]), which may be coupled to the common scanner, not shown for brevity.

[0070] Reflections 605’ (R) from different portions of the remote scenery are received and propagated through respective receiver switching trees (not shown for brevity), and are detected by respective heterodyne detectors 606 (HD1, HD2,..., HD [N]), as explained above with reference the heterodyne detector 106 of FIG. 1 A. The detected signals are conditioned and amplified by respective transimpedance amplifiers 608 (TIA1, TIA2, ..., TIA [N]), digitized by respective analog-to-digital converters 610 (ADC1, ADC2,..., ADC [N]), and processed by respective digital signal processors 612 (DSP1, DSP2, ..., DSP [N]). The processing determines, from the respective beat frequencies, a distance to remote objects being sensed, a velocity of the remote objects being sensed, or both the distance and the velocity of the remote objects or their portions. At least two channels may be provided.

[0071] In some embodiments, the switching trees 604 (STI, ST2, ..., ST [N]) may be implemented in thermally driven MZI switches. The ADCs 610 and DSP units 612 may be considered to be portions of a LiDAR system controller 620. The function of the LiDAR system controller 620 is to coordinate the switching timing, detection timing, the frequency sweeping by the LOs 602, etc. The total number of channels in the LiDAR system 600 depends on the required total port count.

[0072] FIG. 7 illustrates the timing of the operation of the multi-channel LiDAR system 600. The timing of three channels CHI, CH2, and CH3 are shown for brevity. Each channel includes an IC (integrated circuit) that controls the thermally driven MZI switches of a corresponding switching tree. During a first time interval termed “IC Switch” (see the bottom of FIG. 7), the IC switches a set of thermal heaters of MZI switches for routing the ranging light to a corresponding exit port, e.g. Port 1 in this example, and for routing the reflection back from the exit port to a photodetector. Due to finite thermal inertia of the thermally driven MZI switches, it takes time for the MZI switches to reach their intended switching states, as indicated by a time lag between Optical Switch Power and Optical Switch Output in FIG. 7. This transition time interval is denoted as “Thermal Switch”. Once all MZI switches reached steady switching states, the ranging light is routed to Port 1, and the reflections traveling to Port 1 of each channel are detected and processed during a first steady-state time interval 701. This interval is indicated by non-shaded portions of the “LiDAR detection” bars. The ranging process repeats by switching to a next state that delivers the ranging light to Port 2 of each channel, and delivers the reflections from Port 2 of each channel to corresponding photodetectors during a second steady-state time interval 702. After the second Thermal Switch or transition time interval, the Port 2 detection is performed on all channels, and so on.

[0073] One drawback of the LiDAR of FIG. 6 operating according to the timing diagrams of FIG. 7 is the complexity of having an electric signal processing train including a TIA, an ADC, and a DSP circuit for each LiDAR channel, which increases overall system size and cost. Another drawback is related to a significant power consumption of multiple TIAs and DSP units of the LiDAR of FIG. 6, which simultaneously process the channel data to determine at least one of a distance to or a velocity of the remote object portions from the beat frequencies. Some of these drawbacks may be overcome by staggering the signal detection timing between different channels of a multichannel LiDAR system, as illustrated below with reference to FIG. 8.

[0074] Referring to FIG. 8 specifically, the start times for reconfiguring the switching trees of different channels CHI, CH2, and CH3 may be staggered such that the detection and data processing in different channels occurs at different time intervals. For example, the IC switch times of CHI, CH2, and CH3 may be selected such that during a first time interval 801, the ranging and processing is performed for Port 1 of CHI. During a second, subsequent time interval 802, the ranging and processing is performed for Port I of CH2. During a third, subsequent time interval 803, the ranging and processing is performed for Port 1 of CH3. During a fourth, subsequent time interval 804, the ranging and processing is performed for Port 2 of CHI. During a fifth, subsequent time interval 805, the ranging and processing is performed for Port 2 of CH2. During a sixth, subsequent time interval 806, the ranging and processing is performed for Port 2 of CH3, and so on. In other words, the LiDAR controller is configured to overlap the transition time interval of the one channel with the steady-state time interval of another channel, and vice versa. More than two or three channels may be accommodated, depending on the ratio between the durations of the transition and steady-state time intervals for particular implementations of the switching trees.

[0075] Referring to FIG. 9A, a multichannel LiDAR system 900A includes a plurality of identical channels CHI, CH2, ..., CH [N], Each channel CHI, CH2, ..., CH N may be implemented in a PIC chip including the switching trees of FIGs. 2 and / or FIGs. 4A-4B with the Tx / Rx multiplexing circuit 500. Each channel CHI, CH2, ..., CH [N] may include a frequency-modulated local oscillator, not shown for brevity, coupled to a corresponding switching tree 904 (STI, ST2, ..., ST [X])

[0076] In operation, reflections 905’ (R) from different portions of the remote scenery or different remote objects, propagated back through respective switching trees, detected by respective heterodyne detectors 906 (HD1, HD2, ..., HD [N]) and conditioned / amplified by respective transimpedance amplifiers 908 (TIA1, TIA2, ..., TIA [N]). A system controller 920A receives the signals from the TIA 908, and digitizes the signals. The system controller 920A includes a plurality of analog-to-digital converters 910 (ADC1, ADC2, ..., ADC [N]), one ADC per channel, and a plurality of DSP units 912, DSP1, DSP2, ..., DSP [N], one per channel. In FIG. 9A, each DSP unit 912 is dedicated to one channel only. As explained above with reference to FIGs. 7 and 8, having a dedicated DSP unit 912 per channel may be excessive, with or without data processing interleaving or staggering in different channels, due to considerable idling time in each channel, the idling time being associated with the transition time of the respective switching trees during which no remote sensing data may be taken or processed.

[0077] Operating the multichannel LiDAR system 900A of FIG. 9A in accordance with the timing diagram of FIG. 8 opens a possibility of sharing computational resources between different channels. The computational resources may be shared because the computation of distance to and / or velocity of a remote object in directions corresponding to the current states of the switching trees is not simultaneous in different channels. The computational resources may be used in a sequential manner to a degree that a single DSP unit may be shared between several or even all available channels.

[0078] Turning to FIG. 9B for a non-limiting illustrative example of this, a multichannel LiDAR system 900B includes a plurality of identical channels CHI, CH2, ..., CH [N], which may share a common scanner, e.g. a collimator and / or tiltable reflector as illustrated in FIG. 3A. Each channel CHI, CH2,..., CH [N] of the multichannel LiDAR system 900B of FIG. 9B may be implemented in a PIC chip including the switching trees of FIGs. 2 and / or 4A-4B with the Tx / Rx multiplexing circuit 500. Each channel may include a frequency-modulated local oscillator (not shown for brevity) coupled to a corresponding switching tree 904 (STI, ST2, ..., ST [N]) optionally coupled to the common scanner.

[0079] Reflections 905’ (R) from different portions of the remote scenery, or different remote objects, are received and propagated back through respective receiver switching trees (not illustrated for brevity), are detected by respective heterodyne detectors 906 (HD1, HD2, ..., HD [N]), and conditioned and amplified by respective transimpedance amplifiers 908 (TIAI, TIA2, ..., TIA [N]). A system controller 920B receives the signals from the transimpedance amplifiers 908, and digitizes the signals. To that end, the system controller 920B may include a plurality of analog-to-digital converters 910 (ADC1, ADC2, ..., ADC [N]), one ADC per channel. A digital switch 911 (DS) may be coupled to the ADCs 910, and a DSP unit 912 may be coupled to the digital switch 911. The function of the digital switch 911 is to sequentially couple the digital output from each one of ADCs 910 to the DSP unit for data processing, i.e. for determining, from the beat frequencies in the respective channels, the at least one of a distance to the remote object or velocity of the object. The total number of channels in the LiDAR system 900B depends on the required total port count, and generally may include two or more channels. Using the DS 911 allows one to use only one DSP unit instead of N DSP units as in the multichannel LiDAR system 900A of FIG. 9 A.

[0080] Referring now to FIG. 9C, a multichannel LiDAR system 900C includes a plurality of identical channels CHI, CH2, ..., CH [N], which may share a common scanner, e.g. a collimator and / or tiltable reflector illustrated in FIG. 3A. Each channel CHI, CH2, ..., CH [N] of the multi-channel LiDAR system 900C of FIG. 9C may be implemented in a PIC chip including the switching trees of FIGs. 2 and / or 4A-4B plus the Tx / Rx multiplexing circuit 500 of FIG. 5. Each channel may include a frequency-modulated local oscillator. Each local oscillator may be coupled to the corresponding switching tree 904 (STI, ST2, ..., ST [N]), which may be coupled to a common beam scanner.

[0081] Reflections 905’ (R) from different portions of the scenery or different objects of the scenery are received and propagated back through respective receiver switching trees, detected by the respective heterodyne detectors 906 (HD1, HD2,..., HD [N]) and conditioned and amplified by the respective transimpedance amplifiers 908 (TIA1, TIA2, ..., TIA [N]). A system controller 920C includes an analog switch 909 (AS), the ADC 910 coupled to the analog switch 909, and the DSP unit 912 coupled to the ADC 910. The function of the analog switch 909 is to sequentially couple the analog output from each one of the TIAs 908 (TIA1, TIA2,..., TIA [N]) to the ADC 910 for digitizing and conveying the digitized signal to the DSP unit 912. In other words, the analog switch 909 is configured to switch analog electrical signals, as opposed to digital electrical signals switched by the digital switch 911 of FIG. 9B. In the configuration shown in FIG. 9C, the analog switch 909 switches several analog input ports to a single analog output port, which is coupled to the ADS 910. The DSP unit 912 determines, from the beat frequencies in the respective channels, the at least one of a distance to the remote object or velocity of the object. The total number of channels in the LiDAR system 900C depends on the required total port count, and may include two or more channels.

[0082] Other multiplexing configurations of a multichannel LiDAR of this disclosure are possible. In some embodiments, the optical signal in different channels and / or the photodetector signals may be switched ON and OFF or attenuated, to provide a multiplexing capability. Referring to FIG. 10 for a non-limiting illustrative example, a multichannel LiDAR system 1000 includes a plurality of channels CHI, CH2, ..., CH [N], which may share a common scanner, e.g. a collimator and / or tiltable reflector as illustrated in FIG. 3 A. Each channel CHI, CH2, ..., CH [N] of the multichannel LiDAR system 1000 of FIG. 10 may be implemented in a PIC chip including the switching trees of FIGs. 2 and / or 4A-4B equipped with the Tx / Rx multiplexing circuit 500 of FIG. 5. Each channel may include a frequency-modulated local oscillator 1002 (LOI, LO2, ..., LO [N]) coupled to a variable optical attenuator (VOA). The VOA may be integrated into the LO, or may be a separate part optically coupled to the corresponding LO. Herein and throughout the specification, the terms “VOA” or “optical switch” are used interchangeably, denoting an attenuator providing a smoothly varying attenuation, as well as an optical switch providing attenuation or blocking in an ON / OFF manner. Each oscillator / VOA 1002 is coupled to a corresponding switching tree 1004 (STI, ST2, ..., ST [N]) coupled to a common scanner, not shown for brevity.

[0083] Reflections 1005’ (R) from different portions of the remote scenery and / or different remote objects are received and propagated back through respective receiver switching trees, and are detected by respective heterodyne detectors 1006 (HD1, HD2, ..., HD N). It is to be noted that the heterodyne detectors 1006 receive input from the LO 1002 signal and the return signal 1005’. Thus, the LO 1002 contributes most of energy to heterodyne detectors 1006; accordingly, switching the LO 1002 ON and OFF may be used to provide efficient multiplexing.

[0084] Furthermore, in some embodiments, photodiodes of the heterodyne detectors 1006 (HD1, HD2, ..., HD [N]) may be reverse biased by a bias voltage that can be switched ON and OFF by a controller 1020. When the bias voltage is ON, the photodiodes are sensitive to light. When the bias voltage is OFF, the photodiodes lose most of their sensitivity to light. Due to this, photodiodes of several heterodyne detectors 1006 may be connected to a same TIA 1008, and the multiplexing may be achieved by switching the corresponding bias voltages ON and OFF. For instance, photodiodes of M heterodyne detectors 1006 may be coupled to a same TIA 1008 in the multi-channel LiDAR 100 including N channels. In some embodiments, M = N, i.e. all heterodyne detectors 1006 are connected to the same TIA 1008. In some embodiments, M <N, and the required number of TIAs 1008 is N / M. The switching of the LO / VOA may be complemented by the switching of the photodiodes’ bias.

[0085] The TIA(s) 1008 (TIA1 to TIA [A7A / ]) may be coupled to an optional analog switch 1009 (AS), which may sequentially couple the TIAs 1008 to an ADC 1010 digitizing the amplified electrical signals, similarly to the analog switch 909 in FIG. 9C. A DSP unit 1012 (FIG. 10) may perform all data processing, e.g. determining, from the beat frequencies in the respective channels, the at least one of a distance to the remote object or velocity of the object. The total number of channels in the LiDAR system 1000 depends on the required total port count, and may include at least two channels.

[0086] Referring now to FIG. 11, a ranging method 1100 of this disclosure includes the following actions performed in each of first and second channels of a LiDAR system. Frequency-modulated light is switched (1102) between ports of an optical switching tree of the LiDAR system to direct the light to a remote object at a port-specific angle. A reflection from the remote object is received (1104) from the object, and propagated back through a same or a matching optical switching tree. In other words, the reflected light can be propagated through the same portion of the optical switching tree as in FIG. 2, or through a dedicated receiver portion of the switching tree, as illustrated in FIGs. 4B and 5.

[0087] A portion of the light is combined (1106) with the reflection to produce a signal at a beat frequency between the split off portion and the reflection, as explained above with reference to FIGs. 1 and 2. For each channel, at least one of a distance to or a velocity of the object may be determined (1108) from the beat frequencies of the detected signals. Different channels may determine different distances or velocities, in accordance with the shape and a state of movement or rotation of the remote object.

[0088] As explained above, the data collection in the first and second channels (or in a higher number of channels) may be staggered to use the available computational resources more efficiently. An optical switching tree is not reconfigured instantaneously, and the optical switching trees of each channel may have a transition time interval. During the transition time interval, individual switches of the switching tree reach their nominal switching states. During a subsequent steady-state time interval, all switches of the switching tree hold their intended switching configuration. The ranging measurements are normally possible during these steady-state time intervals. For example, a ranging method 1200A of FIG. 12A may include all steps of the method 1100 of FIG. 11 plus overlapping (1202) the transition time interval of the second channel with the steady-state time interval of the first channel, followed by determining (1204), from the beat frequency of the first channel, at least one of a distance to a first portion of the object or a velocity of the first portion. Then, the transition time interval of the first channel may be overlapped (1206) with the steadystate time interval of the second channel, and at least one of a distance to a second portion of the object or a velocity of the second object portion may be determined (1208) from the beat frequency of the second channel.

[0089] Once the steady states of the switching tree(s) have been achieved, the ranging measurements may be performed in the respective channels. Referring to FIG. 12B, a ranging method 1200B may include, in combination with actions of the method 1100 of FIG. 11 and the method 1200A of FIG. 12 A, amplifying (1210) the signals of the first and second channels. A digital signal processor (DSP) may be used to determine (1212) the at least one of the distance to and / or velocity of the first portion of the object, by processing the signal of the first channel, and to determine (1214) the at least one of the distance to or velocity of the second portion of the object, by processing the signal of the second channel. A digital switch (e.g. the digital switch 911 shown in FIG. 9B) or an analog switch (e.g. the analog switch 909 of FIG. 9C or the analog switch 1009 of FIG. 10) may be employed to have the same DSP process both channels in a time-sequential manner.

[0090] To further reduce complexity and provide power savings, not only a DSP unit but also a transimpedance amplifier may be shared between different channels of a LiDAR system. Sharing transimpedance amplifier(s) also lowers the LiDAR system size and cost, which is highly desirable for efficient system integration. For LiDAR embodiments with switchable detector bias, e.g. the ones of FIG. 10, a method 1200C (FIG. 12C) may include, in addition to the steps of the method 1100 of FIG. 11 and the methods 1200A and 1200B of FIGs. 11A and 1 IB respectively, switching (1216) a bias of the first channel photodetector ON and switching a bias of the second channel photodetector OFF, and determining (1220) the at least one of the distance to or velocity of the first portion of the object. In embodiments where an optical switch / VOA is provided for each light source, the frequency-modulated light may be applied (1218) to the first channel while attenuating or blocking the frequency-modulated light applied to the second channel. The at least one of the distance to or velocity of the first portion of the object may then be determined (1220), as noted above.

[0091] The bias of the second channel photodetector may be switched ON (1222), and the bias of the first channel photodetector may be switched OFF. In embodiments where an optical switch / VOA is provided for each light source, the frequency-modulated light may be applied (1224) to the second channel while attenuating / blocking the frequency-modulated light applied to the first channel. The at least one of the distance to or velocity of the second portion of the object may then be determined (1226).

[0092] The above-described methods 1100 of FIG. 11, and 1200A-1200C ofFIGs. 12A-12C may be extended to an arbitrary number of channels of a LiDAR system. By way of a non-limiting example, the above methods may include the following: in a third channel, directing the light to the remote object by switching frequency-modulated light between ports of an optical switching tree, where each port is configured to direct the light to a remote object at a port-specific angle; receiving a reflection from the object and propagating the reflection back through the optical switching tree of the third channel; and combining, at a photodetector of the third channel, a portion of the light and the reflection for providing a signal at a beat frequency between the portion and the reflection. Fourth, fifth, etc. channels may be added as required. The processing in the LiDAR channels may be staggered to allow a common controller to process the ranging signals one by one. The switching trees of different channels may be controlled such that, by the time the controller is prepared to process data from a particular channel, all the switches in the switching tree of that channel have reached their steady states. The switches of switching trees of remaining channels may at this point still be in a transitional state.

[0093] The multichannel data processing may be implemented on a same chip. By way of a non-limiting example, eight LiDAR channels, each having 16 ports, may be implemented on a single chip to control a 128-port LiDAR system. Alternatively, a single chip may control two LiDAR channels, and four such chips would be enough to control the 128-port LiDAR system. A further increase on the number of ports and PIC chips with staggered processing and control may be used to relax requirements on the mechanical scanning system. By way of a non-limiting example, having four side-emitting PIC chips disposed one over another allows one to reduce a 120 degrees angular scanning range by a factor of four, to 30-40 degrees total angular scanning range (to provide some sub-range overlap), with the same overall system field of view of 120 degrees.

[0094] The present disclosure is not to be limited in scope by the specific embodiments described herein. Indeed, other various embodiments and modifications, in addition to those described herein, will be apparent to those of ordinary skill in the art from the foregoing description and accompanying drawings. Thus, such other embodiments and modifications are intended to fall within the scope of the present disclosure. Further, although the present disclosure has been described herein in the context of a particular implementation in a particular environment for a particular purpose, those of ordinary skill in the art will recognize that its usefulness is not limited thereto and that the present disclosure may be beneficially implemented in any number of environments for any number of purposes. Accordingly, the claims set forth below should be construed in view of the full breadth and spirit of the present disclosure as described herein.

Claims

1. A photonic integrated circuit (PIC) comprising:a switching tree for switching light between a plurality of exit ports for selectively illuminating a remote object to produce a reflection, and for directing the reflection received at a same exit port of the plurality of exit ports to a common port; anda coupler for combining the reflection at the common port with a portion of the light, for providing a signal at a beat frequency between the portion and the reflection.

2. The PIC of claim 1, further comprising a photodetector for detecting the signal.

3. The PIC of any preceding claim, wherein the switching tree comprises:a transmitter switching tree for switching the light between a plurality of transmitter ports for selective illumination of the remote object to produce the reflection; anda matching receiver switching tree for directing the reflection received at a corresponding receiver port of a plurality of receiver ports to the common port.

4. The PIC of claim 3, further comprising:a plurality of polarization converters each coupled to one of the plurality of receiver ports; anda plurality of polarization combiners each coupled, on one end, to one of the plurality of transmitter ports and one of the plurality of polarization converters and, on the other end, to an exit port of the plurality of exit ports;ora plurality of polarization converters each coupled to one of the plurality of transmitter ports; anda plurality of polarization combiners each coupled, on one end, to one of the plurality of receiver ports and one of the plurality of polarization converters and, on the other end, to an exit port of the plurality of exit ports.

5. The PIC of any preceding claim, wherein the transmitter and receiver switching trees are binary trees of Mach-Zehnder interferometer switches.

6. A Li DAR system comprising:first and second channels each comprising a PIC of any one of claims 2 to 5; anda controller for determining, from the beat frequencies of the first and second channels, at least one of a distance to or a velocity of the object.

7. The LiDAR system of claim 6, wherein the switching trees of the first and second channels have a transition time interval and a steady-state time interval, wherein the controller is configured to overlap the transition time interval of the second channel with the steady-state time interval of the first channel, and vice versa.

8. The LiDAR system of claim 6 or claim 7, further comprising first and second amplifiers for amplifying signals of the first and second channels, respectively, detected by the respective photodetectors;wherein the controller comprises:first and second analog to digital converters (ADCs) coupled to the first and second amplifiers, respectively, for digitizing the signals;a digital switch coupled to the first and second ADCs; anda signal processor coupled to the digital switch for determining, from the beat frequencies, the at least one of a distance to the object or velocity of the object.

9. The LiDAR system claim 6 or claim 7, further comprising first and second amplifiers for amplifying the signals of the first and second channels, respectively, detected by the respective photodetectors;wherein the controller comprises:an analog switch coupled to the first and second amplifiers; anda signal processor coupled to the analog switch for determining, from the beat frequencies, the at least one of a distance to the object or velocity of the object.

10. The LiDAR system of claim 6 or claim 7, wherein the photodetectors of the first and second channels have a bias switchable by the controller, wherein the controller is configured to:switch ON the bias of the photodetector of the first channel and switch OFF the bias of the photodetector of the second channel; anddetermine, from the beat frequency of the first channel signal, at least one of a distance to the object or a velocity of the object.

11. The LiDAR system of any one of claims 6 to 10, further comprising a light source for providing the light to the first and second channels, wherein the controller is configured to sweep an optical frequency of the light source up and down.

12. The LiDAR system of claim 11, wherein the light source comprises an optical switch for switching the light between the first and second channels, and wherein the controller is configured to:use the optical switch to switch ON the light coupled to the first channel, and to switch OFF the light coupled to the second channel; anddetermine, from the beat frequency of the first channel signal, the at least one of a distance to the object or a velocity of the object.

13. The LiDAR system of any one of claims 6 to 12, wherein the first and second channels are implemented in a same PIC chip.

14. A ranging method comprising:in each of first and second channels:switching frequency-modulated light between ports of an optical switching tree for directing the light to a remote object at a port-specific angle;receiving a reflection from the object and propagating the reflection back through the optical switching tree; andcombining a portion of the light and the reflection for providing a signal at a beat frequency between the portion and the reflection; anddetermining, from the beat frequencies, at least one of a distance to or a velocity of the object.

15. The method of claim 14, wherein the optical switching trees of the first and second channels have a transition time interval and a steady-state time interval, the method further comprising:overlapping the transition time interval of the second channel with the steady-state time interval of the first channel; anddetermining, from the beat frequency of the first channel, at least one of a distance to a first portion of the object or a velocity of the first portion.

16. The method of claim 14 or claim 15, further comprising:overlapping the transition time interval of the first channel with the steady-state time interval of the second channel; anddetermining, from the beat frequency of the second channel, at least one of a distance to a second portion of the object or a velocity of the second portion.

17. The method of claim 16, further comprising:amplifying the signals of the first and second channels;using a digital signal processor (DSP) to determine the at least one of the distance to or velocity of the first portion of the object; andusing the DSP to determine the at least one of the distance to or velocity of the second portion of the object.

18. The method of claim 16, wherein the signal at the beat frequency in each channel is detected using a photodetector, the method further comprising:switching a bias of the first channel photodetector ON, switching a bias of the second channel photodetector OFF, and determining the at least one of the distance to or velocity of the first portion of the object; andswitching the bias of the second channel photodetector ON, switching the bias of the first channel photodetector OFF, and determining the at least one of the distance to or velocity of the second portion of the object.

19. The method of claim 16 or claim 18, further comprising:applying the frequency-modulated light to the first channel while attenuating the frequency-modulated light applied to the second channel, and determining the at least one of the distance to or velocity of the first portion of the object; andapplying the frequency-modulated light to the second channel while attenuating the frequency-modulated light applied to the first channel, and determining the at least one of the distance to or velocity of the second portion of the object.

20. The method of any one of claim 14 to claim 19, further comprising:in a third channel, directing the light to the remote object by switching frequency-modulated light between ports of an optical switching tree, wherein each port is configured to direct the light to the remote object at a port-specific angle;receiving a reflection from the object and propagating the reflection back through the optical switching tree of the third channel; andcombining, at a photodetector of the third channel, a portion of the light and the reflection for providing a signal at a beat frequency between the portion and the reflection.

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