Patent Description:
A reference interferometer is used by conventional frequency FMCW LiDARs to help characterize and correct for non-linearity in laser chirp. Conventional lidar or optical coherence tomography (OCT) systems rely on a reference interferometer with balanced photodiode to estimate laser frequency indirectly and calibrate any measurement data. In order to ensure accuracy in the phase extraction from a reference interferometer and a balanced photodiode, the reference interferometer typically needs to have long delay lines, or short delay lines and careful bias control - i.e., it would be off chip. Moreover, long delay lines are typically a challenging problem for integrated photonics, due to the high losses incurred in small waveguides. In addition, performance of FMCW lasers may drift on various timescales, over the course of several measurements with temperature or other environmental conditions, or over the course of the lifetime of the FMCW sensor.

Moreover, conventional FMCW LiDAR systems use mechanical moving parts and bulk optical lens elements (i.e., a refractive lens system) to steer the laser beam in two directions. And for many applications (e.g., automotive) are too bulky, costly, and unreliable. <CIT> discloses an optical circuit comprising: a phased array of solid state waveguides to receive an optical signal and transmit the optical signal as a beamsteered optical signal; a modulator circuit coupled to modulate a bit sequence onto a carrier frequency of the optical signal; and a photodetector to detect a reflection signal of the beamsteered optical signal, and transmit the reflection signal for autocorrelation with the bit sequence to generate a processed signal.

According to an aspect of the present invention, there is provided a light detection and ranging (LiDAR) chip of a solid state frequency modulated continuous wave (FMCW) LiDAR system as set out in independent claim <NUM>. Other embodiments are described in the dependent claims.

Embodiments of the disclosure have other advantages and features which will be more readily apparent from the following detailed description and the appended claims, when taken in conjunction with the examples in the accompanying drawings, in which:.

A solid state FMCW LiDAR system determines depth information (e.g., distance, velocity, acceleration, for one or more objects) for a field of view of the system. The solid state FMCW LiDAR directly measures range and velocity of an object by directing a frequency modulated, collimated light beam into a local area. The light that is reflected from an object within the local area, Signal, is mixed with a tapped version of the beam, referred to as the local oscillator (LO). The frequency of the resulting radiofrequency (RF) beat signal is proportional to the distance of the object from the solid state FMCW LiDAR system once corrected for the doppler shift that requires an additional measurement. The two measurements, which may or may not be performed at the same time, provide range and velocity information of the target.

The solid state FMCW LiDAR system uses on-chip monitoring and calibration circuits for achieving high-performance solid-state beam steering and laser chirping. The solid state FMCW LiDAR system include a focal plane array (FPA) system. The FPA includes one or more switchable coherent pixel array (SCPAs). The one or more SCPAs may be positioned at a focal plane of a lens system, such that the FPA system can perform solid-state beam steering for a single dimension and/or two dimensions. The direction of the incoming beam is mapped into a discrete position of a focused spot, and vice versa. One challenge for an SCPA is to maintain optimal calibration settings for the switch network to achieve low insertion loss, high extinction ratio and low crosstalk at any time. The solid state FMCW LiDAR system uses an on-chip feedback mechanism to enable in situ calibration or real-time closed-loop control of high-performance solid-state beam steering.

The on-chip feedback mechanism facilitates maintaining a high-quality laser chirp by the solid state FMCW LiDAR, which senses range by measuring interference between optical signals from a local path and a target path. By sweeping a frequency of a laser, the interference signal becomes an oscillation with a frequency proportional to target distance. FMCW lasers are modulated to have a linear frequency sweep from lower frequency to higher frequency, and then from higher frequency to lower frequency, in a triangular fashion. Often, lasers tuned in this fashion must be tuned with a particular drive signal or the frequency sweeps can deviate significantly from linear. Linearity deviations cause significant inaccuracies in range and velocity measurements derived using the FMCW LiDAR.

In some embodiments, the solid state FMCW LiDAR system utilizes on-chip monitoring and calibration circuits for solid-state beam steering realized by one or more integrated SCPAs. The solid state FMCW LiDAR system uses on-chip optical power monitoring circuits to enable in situ calibration or real-time closed-loop control of the optical switch network. For example, the LiDAR chip includes (i.e., on-chip) an optical switch network, a switchable coherent pixel array (SCPA), and a monitoring assembly. The optical switch network is configured to selectively provide coherent light to one or more of a plurality of output waveguides. The SCPA includes coherent pixels (CPs), and each of the CPs is configured to emit coherent light provided by a corresponding output waveguide of the plurality of output waveguides. The monitoring assembly includes a plurality of photodetectors, and each of the plurality of photodetectors is configured to generate an output signal responsive to a level of light detected from a corresponding output waveguide of the plurality of output waveguides. The optical switch network is calibrated (e.g., by a controller) by adjusting a drive strength of switch drivers for the optical switch network based on output signals from the monitoring assembly.

The one or more SCPAs are placed at a focal plane of a lens system for fast solid-state beam steering and co-axial FMCW LiDAR operation. On-chip optical monitoring circuits with optical couplers and monitoring photodetectors (PD) monitor the optical power at the output ports of an optical switch network. With this design, in situ calibration and real-time closed-loop control can be performed without affecting the coherent pixels or interrupting the normal operation of the LiDAR. For large-scale or multi-channel switchable coherent pixel arrays, a crossbar-type or a hierarchical (e.g., a binary tree) connection scheme can be used to read the signal from any arbitrary monitoring PD with significantly reduced number of I/Os and receivers for the monitoring circuits.

In some embodiments, the solid state FMCW LiDAR system utilizes on-chip monitoring and calibration circuits for generating a high-quality laser chirp signal. For example, the LiDAR chip may include (i.e., on-chip) a splitter, an interferometer, an optical switch network, and a SCPA. The splitter is configured to split coherent light into a first portion and a second portion. The coherent light is chirped according to a waveform. The interferometer is configured to generate an in-phase (I) signal and a quadrature(Q) signal using the first portion of the coherent light. The optical switch network is configured to selectively provide the second portion of the coherent light to one or more of a plurality of output waveguides. The SCPA includes coherent pixels (CPs), and each of the CPs is configured to emit coherent light provided by a corresponding output waveguide of the plurality of output waveguides. A controller is configured to identify deviations in frequency of the coherent light based in part on the I and Q signals, and control a shape of the waveform to compensate for the identified deviations. Note that in some embodiments, the LiDAR chip may also include the monitoring assembly as described in the previous paragraph.

The solid state FMCW LiDAR system uses a swept-source laser and a frequency-discrimination interferometer with optical hybrid for laser driver calibration. In some embodiments, a programmable laser driver (current or voltage source) directly drives a tuning laser source to create alternating positive and negative frequency sweeps. In other embodiments, a programmable modulator driver directly drives a modulator to induce positive and negative frequency sweeps on the seed laser beam. This is followed by the interferometer that includes a splitter, which sends light down two paths, one "local" path and one "reference" path, an optical combiner known as an "<NUM>-degree optical hybrid," a photoreceiver with multiple photodetectors, and a controller for signal processing. The controller calculates an instantaneous signal phase and laser frequency using the outputs from the optical hybrid. The resulting instantaneous laser frequency is fed back to the drive signal generator to compensate for deviations in laser frequency from linear. In addition, the interferometer and optical hybrid can be used to calibrate for any non-linearity that results from residual error in the predistortion process or from laser/environmental drift. Accordingly, the solid state FMCW LiDAR system performs in situ generation of laser driver signals, and in situ calibration of residual non-linearity and laser performance drifts.

Note that in some embodiments, both the monitoring assembly for calibration of the optical switch network, and the interferometer with optical hybrid for laser driver calibration can be implemented on the same LiDAR chip. As such the LiDAR chip would be able to not only calibrate the optical switch network but also calibrate the laser driver.

As noted above, conventional LiDAR systems that use an interferometer to help characterize and correct for non-linearity in laser chirps have long delay lines or short delay lines and careful bias control. Long delay lines are problematic for integrated photonics, due to the high losses incurred in small waveguides, and may be off-chip. Likewise careful bias control generally correlates with an increase in complexity of control circuitry. In contrast, the solid state FMCW LiDAR system performs laser frequency measurement using on-chip short delay lines without complex bias controls. Moreover, the solid state FMCW LiDAR system is configured to measure laser frequency and dynamically adjust the drive waveform of the laser to account for changes of the laser characteristics over time or over environmental conditions.

Note that the LiDAR chip can steer the light emitted from the solid state LiDAR system in at least a first angular dimension (e.g., elevation). And the solid state FMCW LiDAR system may include, e.g., a scanning mirror (e.g., moving mirror, polygon mirror, etc.) to steer the light in a different angular dimension (e.g., azimuth). And in some embodiments, optical antennas within the one or more SCPAs are arranged in two-dimensions such that the LiDAR chip can steer the optical beam two-dimensions (e.g., azimuth and elevation). Being able to steer the beam without moving parts may mitigate form factor, cost, and reliability issues found in many conventional mechanically driven LiDAR systems.

<FIG> shows solid-state scanning with a switchable coherent pixel array chip on a LiDAR chip <NUM>, according to one or more embodiments. The LiDAR chip <NUM> is part of a FPA system that is configured to scan a local area. The LiDAR chip <NUM> is based on photonic integrated circuits (e.g., silicon photonics). The LiDAR chip <NUM> includes one or more FMCW LiDAR transceiver channels <NUM>. A FMCW LiDAR transceiver channel <NUM> includes a FMCW light source <NUM>, an optical switch network <NUM>, monitoring assembly <NUM> and a SCPA <NUM>. As shown, the FMCW light source <NUM> is integrated directly on the LiDAR chip <NUM>. In other embodiments, the FMCW light source <NUM> is not part of the LiDAR chip <NUM> and instead light from the FMCW light source <NUM> is coupled into the LiDAR chip <NUM> from an external source. The FMCW light source <NUM> may be split light between different FMCW LiDAR transceiver channels that are on the LiDAR chip <NUM>, or even on different LiDAR chips. The light can be also amplified by a fiber amplifier or semiconductor amplifier chips. The optical switch network <NUM> switches the guided light between the output ports and activates the coherent pixel associated with the selected port. The optical switch network <NUM> is configured to selectively provide coherent light to one or more of a plurality of output waveguides that couple to various coherent pixels of the SCPA <NUM>. The monitoring assembly <NUM> can be placed anywhere on the chip after the optical switch network <NUM> or as an integral part of the optical switch network <NUM>. As an example, as shown the monitoring assembly <NUM> is placed between the optical switch network <NUM> and the SCPA <NUM>. The monitoring assembly <NUM> including a plurality of photodetectors. Each of the plurality of photodetectors is configured to generate an output signal responsive to a level of light detected from a corresponding output waveguide of the plurality of output waveguides. The optical switch network <NUM> is calibrated by adjusting a drive strength of switch drivers for the optical switch network <NUM> based on output signals from the monitoring assembly <NUM>. Embodiments of the monitoring assembly <NUM> are described below with regard to <FIG>, <FIG>, <FIG>, and <FIG>.

The SCPA <NUM> includes coherent pixels, and each of the coherent pixels is configured to emit coherent light provided by a corresponding output waveguide of the plurality of output waveguides. Each coherent pixel includes an optical antenna <NUM> for emitting and receiving optical signals and other passive and active optical components such as waveguides, couplers, hybrids, gratings and photodetectors for generating the RF signals. The SCPA <NUM> is placed at a focal plane of a lens system <NUM>. The lens system <NUM> includes one or more optical elements (e.g., positive lens, freeform lens, Fresnel lens, etc.) which map a physical location of each coherent pixel, to a unique direction. In some embodiments, the lens system <NUM> is positioned to collimate the transmitted signals emitted via the plurality of optical antennas <NUM>. The lens system <NUM> is configured to project a transmitted signal emitted from an optical antenna of the plurality of antennas into a corresponding portion of a field of view of the FPA system, and to provide a reflection of the transmitted signal to the optical antenna. Each optical antenna sends and receives light from a different angle. Therefore by switching to different antennas, a discrete optical beam scanning is achieved. The FPA system scans a laser beam <NUM> across targets in the field-of-view of the FPA system, and the coherent pixels in the FPA system generate electrical signals which are then digitally processed to create LIDAR point clouds. The lens system <NUM> produces collimated transmitted signals that scan the transceiver field of view along one or more angular dimensions (e.g., perform a <NUM>-D scan of the local area). Note that by switching the light to different coherent pixels, the LiDAR chip <NUM> emits or receives collimated laser beam <NUM> at different angles, enabling discrete solid-state scanning and co-axial optical sensing for a single channel or multiple channels in parallel.

<FIG> shows a basic structure and signal flow of an on-chip monitoring assembly <NUM>, according to one or more embodiments. The on-chip monitoring assembly <NUM> monitors coherent light emitted from outputs of the optical switch network <NUM> The on-chip monitoring assembly <NUM> includes one or more monitoring circuits <NUM>. A monitoring circuit <NUM> may include, e.g., an optical coupler <NUM>, a monitoring photodetector (PD) <NUM>, output waveguides 204A and 204B. The optical switch network <NUM> has as a plurality of output ports. The optical switch network <NUM> is configured to switch the light from an FMCW source between the output ports. And each output port is coupled to a respective output waveguide (e.g., the output waveguide <NUM>). Additionally, some of the output waveguides <NUM> can be internal routing waveguides within the optical switch. The monitoring assembly <NUM> includes a plurality of optical couplers that are configured to tap a portion of the coherent light provided to the plurality of output waveguides, and provide the portion of light to a plurality of photodetectors. In some embodiments, each of the optical couplers has a different corresponding photodetector of the plurality of photodetectors to which the optical coupler provides a tapped portion of the coherent light. For example, the optical coupler <NUM> taps optical power (i.e., coherent light) from an output waveguide <NUM> at the output ports of the optical switch network <NUM>, and provides the tapped optical power (i.e., a portion of the coherent light output from the output port) to the monitoring PD <NUM> via the output waveguide 204A. The optical power is converted to electrical signals via the monitoring PD <NUM>. The optical coupler <NUM> outputs the rest of the optical power via the output waveguide 204B. The output waveguide 204B provides the light to a next stage (e.g., a coherent pixel) in the FMCW LiDAR Transceiver channel <NUM>.

Electrical signals from the one or more monitoring circuits <NUM> are then processed via a receiver <NUM>. The receiver may include, e.g., an amplifier, integrator, switches, etc. Data output from the receiver <NUM> is quantized by an analog-to-digital converter (ADC) <NUM>. The output of the ADC <NUM> is then processed in a controller <NUM>. The controller <NUM> may include, e.g., control circuits, computer processor, field-programmable gate array (FPGA), digital signal processor, microcontroller, application specific integrated circuit (ASIC), or some combination thereof. As illustrated the receiver <NUM>, the ADC <NUM>, the controller <NUM>, and the switch driver <NUM> are separate from the LiDAR chip <NUM>. In other embodiments, some or all of the receiver <NUM>, the ADC <NUM>, the controller <NUM>, and the switch driver <NUM> may be also be integrated into the LiDAR chip <NUM>. Additionally, while a single receiver <NUM>, and a single ADC <NUM> are shown, in some embodiments, there may be a plurality of receivers <NUM> and a corresponding plurality of ADCs. For example there may be a separate receiver <NUM> and a separate corresponding ADC <NUM> for each monitoring circuit.

Closed-loop calibration and/or control are done by adjusting a drive strength of switch drivers <NUM> for the optical switch network <NUM> based on the outputs of monitoring circuits. The calibration of the optical switch network <NUM> helps ensure light is passed to one or more target CPs using minimal power, and mitigates light being passed to non-target CPs. Note that the calibration of the optical switch network <NUM> occurs within the solid state FMCW LiDAR system and no external equipment is needed. For a large-scale or multi-channel switchable coherent pixel array, there could be hundreds of coherent pixels, hundreds of switch ports and therefore hundreds of monitoring PDs. As such, in some instances it may become impractical to assign individual electrical I/O pads/traces to each monitoring PD due to electrical I/O constraints.

<FIG> is a diagram of a crossbar readout scheme for linear arrays of monitoring photodetectors in a multi-channel switchable coherent pixel array with a reduced number of Inputs/Outputs(I/Os), according to one or more embodiments. The crossbar-type connection scheme can read signals from any arbitrary monitoring PD <NUM> while significantly reducing number of electrical I/Os needed for the monitoring circuits. In <FIG>, a FPA system includes the LiDAR chip <NUM>, and the LiDAR chip <NUM> includes multiple LiDAR transceiver channels <NUM>. The LiDAR transceiver channels <NUM> can also be subblocks in a larger switch network. The LiDAR chip includes "n" channels and "N" rows of monitoring circuits (and corresponding coherent pixels), where n and N are integers. As such each monitoring PD may be identified using the channel and row. As such, each photodetector of each of the monitoring assemblies has a corresponding row value that ranges from <NUM> to N and has a corresponding channel value that ranges from <NUM> to n. For example, a monitoring PD for channel "k" and row "j" is labeled as "PD_k_j.

The crossbar-type connection scheme is independent of the polarity of the monitoring PDs. In this example, cathodes of the monitoring PDs with the same row numbers are connected to form corresponding signal groups (also referred to as nodes) and anodes of monitoring PDs with a same channel value are connected to form corresponding bias groups. For example, as illustrated there are n channels, and cathodes associated with row N are connected to form a corresponding signal group <NUM>. As such there are N signal groups. Similarly, anodes of monitoring PDs with a same channel value are connected to form corresponding signal groups (also referred to as nodes), as such there are n signal groups. For example, as illustrated the anodes of the monitoring PDs of channel <NUM> are connected to form a corresponding signal group <NUM>.

Any monitoring PD can be selected for readout by selecting the corresponding pixel and row numbers on one or two analog multiplexers (MUX) - e.g., multiplexer(MUX) <NUM> and MUX <NUM>. The MUX <NUM> and/or the MUX <NUM> may be controlled by the controller <NUM>. For example, the controller <NUM> may configured the MUX <NUM> and/or the MUX <NUM> to read out one or more of the monitoring PDs. The MUX <NUM> and <NUM> (e.g., switches) can be implemented on the same LiDAR chip <NUM> or outside the LiDAR chip <NUM>. For example, the output of MUX <NUM> can be connected to a constant bias voltage <NUM> to provide a reverse bias for the monitoring PDs and the signal groups (e.g., the signal group <NUM>) can be used for outputting current signals. To read current from PD_k_j, the FPA system opens all switches except switch "j" and process the signal from the kth monitoring PD output. In this example, when switch <NUM> of the MUX <NUM> is on and the rest of the switches are off, only the third monitoring PD in each channel is activated. The monitoring PDs outputs can further be multiplexed to reduce the number of receiver channels with the MUX <NUM>. This scheme enables independent optical power monitoring at all the ports of the entire switch network without assigning individual electrical I/O traces/pads to each monitoring PD. To avoid any leakage current from unselected monitoring PDs from other active channels, it is preferred to keep one channel active during monitoring and calibration process, which can be achieved by turning off laser sources or laser amplifiers for the other channels where no monitoring PD is selected. The monitoring and calibration processes for this scheme can happen during power-on or frame transitions.

<FIG> and <FIG> show a hierarchical readout scheme for monitoring photodetectors that overcomes the limitation of crossbar readout scheme. <FIG> is a diagram of a hierarchical readout scheme for monitoring photodetectors in a single channel switchable coherent pixel array with a reduced number of I/Os, according to one or more embodiments. In <FIG>, the optical switch network is in a form of a binary tree. In <FIG>, a plurality of optical switch cells, a plurality of optical couplers, and a plurality of photodetectors are positioned to form the binary tree that has a plurality of levels. In this example, a <NUM>-to-<NUM> switch tree takes a single input and routes it to one of the eight coherent pixels (P0 to P7) via three stages of 1x2 optical switch cells <NUM>. Each optical switch cell can steer the optical power from the input waveguide into one of the two output waveguides. In this scheme, there are optical couplers <NUM> and monitoring PDs <NUM> at both output ports of each switch cell to monitor the power flow and calibrate the switch tree in a hierarchical manner. For a <NUM>-to-<NUM> switch, there is a total of <NUM> monitoring PDs.

To reduce the number of electrical I/Os, the PD bias <NUM> and PD output signals may be connected together. For each level in the binary tree, outputs of monitoring PDs with odd indices are connected together to form a first signal and outputs of monitoring PDs with even indices are connected together to form a second signal. For a <NUM>-to-<NUM> switch with <NUM> hierarchical monitoring PDs, a total number of electrical I/Os and corresponding receivers <NUM> for optical power monitoring are reduced from <NUM> to <NUM>. More generally, for a <NUM>-to-<NUM>N switch, the number of monitoring I/Os and receivers are reduced from <NUM>N+<NUM> to 2N, which is more significant as N grows.

For an example, to calibrate switch settings to direct all the light into coherent pixel P2. The controller <NUM> starts with reading monitoring signals from receiver L0 and H0 and optimizing control signals for SW0 that maximize L0 reading and minimize H0 reading. The controller (e.g., the controller <NUM>) then moves to the next stage and optimizes control signals for SW1_0 that maximize H1 and minimize L1. For the last stage SW2_1, the controller attempts to maximize L2 and minimize H2. This hierarchical calibration process minimizes leakage and crosstalk from unselected photodetectors. It is also electrically decoupled from the electrically sensitive coherent pixel cells which requires low-noise and high-speed operation for FMCW LiDAR. This enables in situ calibration and real-time closed-loop control without affecting the coherent pixels or interrupting the normal operation of the LiDAR.

<FIG> is a diagram of a hierarchical readout scheme for monitoring photodetectors in a multi-channel switchable coherent pixel array with a reduced number of I/Os, according to one or more embodiments. <FIG> shows how to scale the scheme of <FIG> from a single channel to multiple channels. In <FIG>, the LiDAR chip includes n channels (n = <NUM> in this case - but may have some other value in other embodiments), and each channel includes a respective optical switch network, a respective SCPA, and a respective monitoring assembly. Each channel includes a plurality of optical switch cells, a plurality of optical couplers, and a plurality of photodetectors that are positioned to form a binary tree having a plurality of levels. In <FIG>, the output signals from even and odd monitoring PDs at each level are tied together on the LiDAR chip <NUM> across different channels. The same calibration and closed-loop control can be performed by a controller (e.g., the controller <NUM>) simultaneously for all the channels as long as the same pixel is active at any moment.

<FIG> is a diagram of a hybrid-coupled interferometer with post-process feedback to a direct laser driver, according to one or more embodiments. A waveform of a periodic wave (voltage or current) on a laser driver <NUM> is used to drive a laser <NUM>. In general, the output of the laser <NUM> is a sequence of up- and down-sweeps of the laser frequency, referred to as up- and down-chirps respectively. This sequence of laser chirps is used for both FMCW probing and in the frequency discrimination process described hereafter. A splitter <NUM> diverts some laser power to a LiDAR transceiver <NUM>, so that the chirped laser is used as the probing field in an FMCW sensor. The LiDAR transceiver <NUM> may include one or more FMCW LiDAR transceiver channels <NUM> that include respective monitoring assemblies <NUM>. As such the hybrid-coupled interferometer with post-process feedback to the direct laser driver shown here may also be combined with features shown in <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, or some combination thereof. In some embodiments, the LiDAR transceiver <NUM> may not include the monitoring assembly <NUM>. The splitter <NUM> of the present invention is configured to split coherent light into a first portion and a second portion, wherein the coherent light is chirped according to the waveform. An interferometer <NUM> of the present invention is configured to generate an in-phase (I) signal and a quadrature(Q) signal using the first portion of the coherent light. The splitter <NUM> also diverts some power to another splitter <NUM> of the interferometer <NUM>. The splitter <NUM> divides power between two arms, one of which has a delay arm <NUM>. The delayed arm <NUM> is delayed with respect to the other arm such that a beat signal is generated when the two arms are combined at an optical hybrid combiner <NUM>. The optical hybrid combiner <NUM> has four outputs which are configured to be optically phase shifted relative to each other to create <NUM>-degree shifted, <NUM>-degree shifted, <NUM>-degree shifted, and <NUM>-degree shifted optical signals. The <NUM>- and <NUM>-degree shifted signals are measured at one balanced photodetector <NUM>, creating an "I-channel" signal, and the <NUM>- and <NUM>-degree shifted signals are measured at another balanced photodetector, creating a "Q-channel" signal. The I- and Q-channel signals are <NUM>-degree phase-shifted from one another. Each channel is buffered and amplified by a receiver circuit <NUM>, and sampled by an ADC <NUM>. The sampled I and Q signals are used by a controller <NUM>. The controller <NUM> may be an embodiment of the controller <NUM>. The resulting measured laser frequency is used by the controller <NUM> to generate a new waveform to compensate for linear deviations in laser frequency. The waveform is generated by the controller <NUM> and used to drive the laser driver <NUM>. Deviations in interferometer temperature can cause deviations in effective index of the delay arm <NUM>, so a temperature sensor <NUM> may be used to compensate for this deviation in a calculation performed by the controller <NUM>.

<FIG> is a diagram of a hybrid-coupled interferometer with post-process feedback to a modulator driver, according to one or more embodiments. <FIG> is a substantially similar to <FIG> except: the laser chirp is generated using a seed laser <NUM> and a laser modulator <NUM>. The laser modulator <NUM> may be a phase modulator, such as a dual Mach-Zehnder modulator for I/Q modulation, or an intensity modulator. The laser modulator <NUM> is driven by a voltage or current signal from the modulator driver <NUM>. The chirps generated at the output of the laser modulator <NUM> are sent through the splitter <NUM>. The components inside the dotted line <NUM> may be the same blocks as those inside <NUM> in <FIG>. In the same fashion as in <FIG>, the controller <NUM> generates a control signal that is used as input to the modulator driver <NUM>, which compensates for deviations from linear laser frequency chirps at the output of laser modulator <NUM>.

<FIG> shows a process for laser waveform generation and FMCW calibration, according to one or more embodiments. The calibration process may reduce and remove non-linearity from laser up- and down-chirps. The process shown in <FIG> may be performed by a controller of a solid state FMCW LiDAR system. Other entities may perform some or all of the steps in <FIG> in other embodiments. Embodiments may include different and/or additional steps, or perform the steps in different orders.

The solid state FMCW LiDAR system loads <NUM> a driving waveform. For example, a microcomputer of a LiDAR processing engine of the solid state FMCW LiDAR system may load the driving waveform. The driving waveform may be a generic or previously stored driving waveform.

The solid state FMCW LiDAR system frequency modulates <NUM> a laser source with the loaded driving waveform. The modulated light forms one or more laser chirps. The frequency modulation may be performed by a laser controller that modulates a K-channel laser array in accordance with instructions from a LiDAR processing engine.

The solid state FMCW LiDAR system measures <NUM> the one or more laser chirps to form I and Q signals. For example, the solid state FMCW LiDAR system may measure the one or more laser chirps using optical hybrid photodetectors to generate the I/Q signals as shown and described above with regard to, e.g., <FIG> and <FIG>.

The solid state FMCW LiDAR system processes <NUM> the I and Q signals. For example, the solid state FMCW LiDAR system may filter and/or sample the I and Q signals. The solid state FMCW LiDAR system may process the I and Q signals using a LiDAR processing engine.

The solid state FMCW LiDAR system determines <NUM> phases of the processed I and Q signals. The solid state FMCW LiDAR system may determine the phases of the processed I and Q signals using the LiDAR processing engine. Phase may be determined by, e.g., calculating an arc-tangent of a quotient of the processed I and Q signals. This is equivalent to measuring the phase angle of a signal created by adding the I-channel to the Q-channel modified by multiplying the Q-channel by the imaginary number i.

The solid state FMCW LiDAR system determines <NUM> an instantaneous frequency of the laser using the phases. The instantaneous frequency of the laser may be determined by, e.g., dividing the phase calculated in the previous step by an optical path time delay of a delay arm (e.g., the delay arm <NUM>).

The solid state FMCW LiDAR system controls <NUM> the drive waveform of the laser source based in part on the instantaneous frequency to generate a modified output beam. The solid state FMCW LiDAR system monitors a strength of deviations in the instantaneous frequency of the laser at different time instances. Based on the strength of the deviations, the solid state FMCW LiDAR system adjusts the driving waveform (e.g., adjusts a shape of the driving waveform) to compensate for slower or faster chirp rates. Such adjustment can be done at once by updating pre-loaded laser model and adapting drive waveform through analytical solutions, or iteratively by tuning the parameterized drive waveform through gradient descent optimization algorithms. The controlled drive waveform is then re-applied to the laser source to generate a modified output beam. Note that steps <NUM>-<NUM> may be iterative and loop one or more times in performing the calibration.

The solid state FMCW LiDAR system collects <NUM> FMCW measurements using the modified output beam. The solid state FMCW LiDAR system scans (e.g., via the FPA system) the modified output beam across a local area, and measures reflections of the modified output beam from one or more objects in the local area to generate the FMCW measurements.

The solid state FMCW LiDAR system determines <NUM> range and/or velocity data using the FMCW measurements. The solid state FMCW LiDAR system estimates range and velocity data using the FMCW measurements based on an expected chirp rate of the laser. If residual deviations from linear still exist, they are measured by the same process <NUM>-<NUM> and used to adjust the calculation of range and/ velocity data. This process results in more accurate point clouds.

<FIG> depicts a solid state LiDAR system containing an FPA system <NUM>, according to one or more embodiments. The FPA system <NUM> may be a reciprocal system. The FPA system <NUM> includes a lens system <NUM>, and LIDAR chip <NUM>. The LiDAR chip <NUM> and the FPA system <NUM> includes some or all of the components and/or some or all of the functionality as described above with regard to <FIG>. The CPs in the LiDAR chip <NUM> are part of one or more SPCAs (e.g., of FMCW LiDAR Transceiver channels <NUM>) that are controlled by a FPA driver <NUM>. One or more individual CPs in the LiDAR chip <NUM> may be activated to emit and receive light. Light emitted by the LiDAR chip <NUM> is produced by a K-channel laser array <NUM>. The K-channel laser array <NUM> is a laser array that has K parallel channels, where K is an integer. The K-channel laser array <NUM> may be integrated directly with the LiDAR chip <NUM> or may be a separate module packaged alongside the LiDAR chip <NUM>. The K-channel laser array <NUM> is controlled by a laser controller <NUM>. In some embodiments, the K-channel laser array <NUM> is tunable over a range of wavelengths.

The laser controller <NUM> receives control signals from a LiDAR processing engine <NUM>, via a digital to analog converter <NUM>. The processing also controls the FPA driver <NUM> and sends and receives data from the LiDAR chip <NUM>.

The LiDAR processing engine <NUM> includes a microcomputer <NUM>. The microcomputer <NUM> processes data coming from the FPA system and sends control signals to the FPA system via the FPA driver <NUM> and laser controller <NUM>. Note that the microcomputer <NUM> may include the controller <NUM> and/or the controller <NUM>. The LiDAR processing engine <NUM> also includes a N-channel receiver <NUM>. Signals are received by the N-channel receiver <NUM>, and the signals are digitized using a set of M-channel analog to digital converters (ADC) <NUM>.

Note that the LiDAR chip <NUM> can steer the light emitted from the solid state LiDAR system over one or more angular dimensions. In some embodiments, the LiDAR chip <NUM> is configured to steer the beam only over a first angular dimension (e.g., elevation). The FPA system <NUM> may include one or more scanning mirrors (not shown) that can steer the optical beam in a second dimension (e.g., orthogonal to the first angular dimension - e.g., azimuth). The scanning mirror receives light from the lens system <NUM> and directs it into the target area along a particular angular field of view determined by the first angular dimension (controlled by the LiDAR chip <NUM>) and the second angular dimension (controlled by the one or more scanning mirrors). Note that the above example of use of one or more scanning mirrors is in the context of the LiDAR chip <NUM> being configured to scan only over a first angular dimension. However, in some embodiments, the one or more scanning mirrors may be used with a LiDAR chip <NUM> that is configured to scan in a plurality of angular dimensions (e.g., azimuth and elevation). For example, with a two dimensional arrangement of the optical antennas (e.g., rectangular grid) signals from the plurality of optical antennas may be scanned in two dimensions within the field of view of the one or more scanning mirrors.

The figures and the preceding description relate to preferred embodiments by way of illustration only. It should be noted that from the preceding discussion, alternative embodiments of the structures and methods disclosed herein will be readily recognized as viable alternatives that may be employed without departing from the principles of what is claimed.

Although the detailed description contains many specifics, these should not be construed as limiting the scope of the invention but merely as illustrating different examples. It should be appreciated that the scope of the disclosure includes other embodiments not discussed in detail above. Therefore, the scope of the invention should be determined by the appended claims and their legal equivalents.

Claim 1:
A light detection and ranging, LiDAR, chip (<NUM>) of a solid state frequency modulated continuous wave, FMCW, LiDAR system, the LiDAR chip comprising:
an optical switch network (<NUM>) on the LiDAR chip, the optical switch network configured to selectively provide coherent light to one or more of a plurality of output waveguides (<NUM>);
a switchable coherent pixel array (<NUM>), SCPA, on the LiDAR chip, the SCPA including coherent pixels (<NUM>), CPs, and each of the CPs configured to emit coherent light provided by a corresponding output waveguide of the plurality of output waveguides;
a monitoring assembly (<NUM>) that is on the LiDAR chip, the monitoring assembly including a plurality of photodetectors (<NUM>), and each of the plurality of photodetectors configured to generate an output signal (<NUM>) responsive to a level of light detected from a corresponding output waveguide of the plurality of output waveguides;
a first splitter (<NUM>) on the LiDAR chip, the first splitter configured to split coherent light into a first portion and a second portion, wherein the coherent light is chirped according to a waveform and the second portion of coherent light is the coherent light that the optical switch network selectively provides to the one or more of the plurality of output waveguides; and
an interferometer (<NUM>) on the LiDAR chip, the interferometer configured to generate an in- phase, I, signal and a quadrature, Q, signal using the first portion of the coherent light, wherein a shape of the waveform is controlled based in part on the I and Q signals in order to compensate for deviations in a laser frequency,
wherein the optical switch network (<NUM>) is calibrated by adjusting a drive strength of switch drivers for the optical switch network based on output signals from the monitoring assembly.