DE102018116956B4 - DUAL LASER CHIP-SCALE LIDAR FOR SIMULTANEOUS DOPPLER AREA DETECTION - Google Patents

Abstract

A chip-scale lidar system (110), comprising: a first light source (210) configured to output a first signal; a second light source (205) configured to output a second signal; a transmit beam coupler (230 ) configured to provide an output signal (225) for transmission, the output signal (225) including a portion of the first signal and a portion of the second signal;a receive beam coupler (240) configured to provide a receive signal (247 ) resulting from reflection of the output signal (225) by a target (140);a first set of photodetectors (260a, 260b) configured to respectively output a first set of electrical currents (270a, 270b). a first set of combined signals (255a, 255b), each of the first sets of combined signals (255a, 255b) including a first portion of the received signal (247); a second set of photodetectors (260c, 260d) configured rt to obtain a second set of electrical currents (270c, 270d) from a second set of combined signals (255c, 255d), each of the second sets of combined signals (255c, 255d) including a second portion of the received signal (247). ; and a processor (280) configured to obtain Doppler information about the target (140) from the second set of electrical currents (270c, 270d) and to obtain range information about the target (140) from the first set of electrical currents (270a , 270b) and the second set of electrical currents (270c, 270d), wherein the first light source (210) is configured to output a frequency modulated continuous wave, FMCW signal as the first signal, and the second light source (205) is configured , to output a continuous wave signal, CW signal, as the second signal.

Description

technical field

The present disclosure relates to a dual laser chip scale lidar for simultaneous range-doppler detection.

introduction

Vehicles (e.g., automobiles, trucks, construction machinery, farm machinery, automated factory equipment) are increasingly being equipped with sensors that provide information to enhance or automate vehicle operation. Example sensors include radio detection and ranging systems (radar systems), cameras, microphones, and light detection systems (lidar systems). An example lidar system is a coherent lidar system that transmits a frequency-modulated continuous wave (FMCW) signal, also known as chirp, and relies on optical coherence between the transmitted signal and a return signal resulting from reflected scattering of the transmitted signal by a target to perform target acquisition. When a radar or lidar signal is transmitted, the frequency shift in the return signal reflected from a target compared to the transmitted signal is called the Doppler effect. This Doppler shift makes it easier to determine the relative speed and direction of movement of the target. In a typical coherent lidar system, a single light source is used to perform both range and Doppler detection.

the EP 1 853 952 B1 describes a precision non-contact optical device, including methods for measuring ranges to any target and various configuration geometries, for using polarization-maintaining (PM) optical fiber components in a polarization-diplexing scheme to construct a version of a double-chirped coherent laser radar that is insensitive to environmental influences.

the US 2014 / 0 376 001 A1 describes optical integration technologies, designs, systems, and methods for optical coherence tomography (OCT) and other interferometric optical sensing, ranging, and imaging systems. Such systems, methods, and structures use tunable optical sources, coherent detection, and other structures on a single or multiple monolithically integrated chips. The systems and methods described use one or more photonic integrated circuits (PICs), utilize swept source techniques, and use a widely tunable optical source(s). A variant is also described in which the system uses an optical photonic phased array. The phased array can be a static phased array to eliminate or enhance the lens that couples the light to and from the sample of interest, or it can be static and use a spectrally dispersive antenna and a tunable source to provide angular scanning to perform. The phased array can be active in 1 or 2 dimensions to scan the light beam at an angle. The phased array can also adjust the focus. The phased array can implement an optical waveform that extends the depth of field for imaging. The phased array can also be a separate, self-contained element that is fed via one or more optical fibers. The phased array can be used to scan a biomedical sample in conjunction with a swept-source OCT system, it can be used in a free-space coherent optical communication system for beam alignment or tracking, it can be used in LIDAR applications or in many other applications for beam control or beam guidance.

the U.S. 2015/0 378 012 A1 describes a chip-scale scanning lidar that includes a two-dimensional (2D) scanning micromirror for a transmit beam and a 2D scanning micromirror for a receive beam, a laser diode and a photodetector, a first waveguide, and a first grating outcoupler connected to a front face of the laser diode second waveguide and a second grating outcoupler connected to a rear surface of the laser diode on a substrate. A first stationary micro-mirror, a second micro-mirror, a third micro-mirror, and a focusing component reside in a dielectric layer bonded to the substrate over the laser diode and photodetector. The photodetector is optically coupled to the second fixed micromirror and the third fixed micromirror for coherent detection.

the EP 3 081 956 A1 describes a laser radar device with multiple CW laser light sources that oscillate laser light at different frequencies. The device further includes a plurality of optical branching couplers each branching an oscillating laser light. Furthermore, the device has a plurality of optical modulators, each of which modulates laser light after the branching. In addition, the device has an optical combination coupler that combines laser light modulated by the optical modulators, and an optical combination coupler that which combines other laser lights after branching, and a transmitting and receiving optical system which emits a composite light output from the one optical combining coupler and receives the light scattered from a target. The laser radar device also includes a combination optical coupler that combines the received scattered lights and a composite light output from the combination optical coupler, and an optical detector that detects beat signals from a composite light output from the combination optical coupler. A signal processing unit is provided which extracts information about the target from the detected beat signals. Further, the laser radar device has a diffraction grating which is arranged forward or backward with respect to the transmission and reception optical system and emits light incident thereon in a specific direction according to the angle and frequency of the incident light.

the DE 10 2012 001 754 A1 describes a method and a corresponding device for distance and optionally speed measurement, in particular for multi-scale distance measurement. The method includes generating a first and a second frequency comb signal, the first and the second frequency comb signal having different line spacings, a reference measurement comprising superimposing the at least part of the first frequency comb signal and at least part of the second frequency comb signal in a reference beam path, and detecting the through beat signal propagated through the reference beam path. The method also includes a first measurement comprising superimposing the at least part of the first frequency comb signal with at least part of the second frequency comb signal, coupling the superimposed signal into a measurement beam path and detecting the superimposed signal propagated through the measurement beam path. The method also includes determining the path difference between the reference beam path and the measuring beam path from the detected superimposed signals.

Accordingly, it is an object of the invention to provide a dual laser chip scale lidar for simultaneous range-doppler detection.

Description of the invention

According to a first aspect of the invention, a chip-scale lidar system includes a first light source for outputting a first signal and a second light source for outputting a second signal. A transmit beamcoupler provides an output signal for transmission, the output signal including a portion of the first signal and a portion of the second signal, and a receive beamcoupler receives a received signal resulting from reflection of the output signal by a target. The system also includes a first set of photodetectors for respectively obtaining a first set of electrical currents from a first set of combined signals, each of the first sets of combined signals including a first portion of the received signal, and a second set of photodetectors for generating a obtain a second set of electrical currents from a second set of combined signals, each of the second sets of combined signals including a second portion of the received signal. A processor obtains Doppler information about the target from the second set of electrical currents and obtains range information about the target from the first set of electrical currents and the second set of electrical currents. The first light source is configured to output a frequency modulated continuous wave (FMCW) signal as the first signal, and the second light source is configured to output a continuous wave (CW) signal as the second signal.

According to one embodiment, the second signal has a frequency f _D and the lidar system further comprises a modulator and an optical filter to generate a shifted signal with a frequency of f _m +f _D .

According to another embodiment, the modulator is a Mach-Zehnder modulator.

According to another embodiment, the shifted signal is combined with the second portion of the received signal to generate the second set of combined signals.

According to another embodiment, the second signal is at two different optical frequencies f _D1 and f _D2 and the second set of electrical currents indicates a frequency shift f _D2 -f _D1 to determine a direction of the target relative to the lidar system.

According to another embodiment, the system also includes a transmit beam steering device to direct the output signal transmitted through the transmit beam coupler and a receive beam steering device to direct the received signal to the receive beam coupler.

According to a further embodiment, the lidar system is located in a vehicle.

In a second aspect of the invention, a method of fabricating a chip-scale lidar system includes forming a first light source to output a first signal and forming a second light source to output a second signal. The method also includes arranging a transmit beamcoupler to provide an output signal for transmission, the output signal including a portion of the first signal and a portion of the second signal, and arranging a receive beamcoupler to obtain a receive signal resulting from reflection of the output signal from a target results. A first set of photodetectors are formed to each receive a first set of electrical currents from a first set of combined signals, each of the first sets of combined signals including a first portion of the received signal. A second set of photodetectors are formed to each receive a second set of electrical currents from a second set of combined signals, each of the second sets of combined signals including a second portion of the received signal. A processor obtains Doppler information about the target from the second set of electrical currents and to obtain range information about the target from the first set of electrical currents and the second set of electrical currents. Forming the second light source includes forming the second light source to output a continuous wave, CW signal as the second signal and outputting the second signal at a frequency f _D . The method further includes arranging a modulator and an optical filter to generate a shifted signal having a frequency of f _m +f _D . The method further includes combining the shifted signal with the second portion of the received signal to generate the second set of combined signals. Outputting the second signal occurs at two different optical frequencies f _D1 and f _D2 and obtaining the second set of electrical currents indicates a frequency shift f _D2 -f _D1 to determine a direction of the target relative to the lidar system.

According to one embodiment, forming the first light source includes forming the first light source to output a frequency modulated continuous wave (FMCW) signal as the first signal.

The above features and advantages as well as other features and functions of the present disclosure are readily apparent from the following detailed description when read in conjunction with the accompanying drawings.

character list

• 1 ist ein Blockdiagramm eines Szenarios, das ein kohärentes Dual-Laser-Chip-Scale-Lidar-System gemäß Ausführungsformen beinhaltet;
• 2 ist ein Blockdiagramm des Lidar-Systems gemäß einer oder mehreren Ausführungsformen; und
• 3 ist ein Blockdiagramm des Lidar-Systems gemäß einer oder mehreren Ausführungsformen.

Other features, advantages and details appear only by way of example in the following detailed description of the embodiments, which detailed description refers to the drawings, where:

• 1 12 is a block diagram of a scenario involving a coherent dual laser chip scale lidar system according to embodiments;
• 2 12 is a block diagram of the lidar system, in accordance with one or more embodiments; and
• 3 10 is a block diagram of the lidar system in accordance with one or more embodiments.

Detailed description

The following description is merely exemplary in nature and is not intended to limit the present invention to its application or uses. It should be understood that throughout the drawings, corresponding reference numbers indicate like or corresponding parts and features.

As previously mentioned, traditional lidar systems use a single light source to perform both the range and Doppler measurements. Embodiments of the systems and methods detailed herein relate to dual laser chip scale lidar for simultaneous range-doppler detection. Dual laser refers to the fact that two different light sources are used. Compared to the traditional lidar system using a single light source, the signal-to-noise ratio (SNR) can be improved on the order of 3 decibels (dB). In the dual laser embodiments, one light source provides an FMCW signal and another light source provides a continuous wave (CW) signal without frequency modulation. The FMCW signal may be in the form of a triangular wave with a portion called up-chirp showing a linear increase in frequency versus time and a portion called down-chirp showing a linear decrease in frequency versus time. The unmodulated CW signal is used in Doppler velocity detection and the FMCW signal is used to obtain target range, with Doppler velocity information obtained from the unmodulated CW signal. Two exemplary embodiments of dual laser chip scale lidar systems are described in detail.

According to an exemplary embodiment 1 12 is a block diagram of a scenario involving a coherent dual laser chip scale lidar system 110. FIG. This in 1 The vehicle 100 illustrated is an automobile 101. A lidar system 110 described with reference to FIG 2 and 3 described in more detail is shown on the roof of motor vehicle 101 . According to alternative or additional embodiments, one or more lidar systems 110 may be located elsewhere in or on the vehicle 100 (eg, front and rear bumpers, sides). Another sensor 115 (e.g. camera, sonar, radar system) is also shown. Information obtained from the lidar system 110 and one or more other sensors 115 may be provided to a controller 120 (e.g., an electronic control unit (ECU)) for image or data processing, target detection, and subsequent vehicle control.

The controller 120 can use the information to control one or more vehicle systems 130 . In an exemplary embodiment, vehicle 100 may be an autonomous vehicle, and controller 120 may perform known vehicle operation controls using information from lidar system 110 and other sources. In alternative embodiments, the controller 120 may augment vehicle operation using information from the lidar system 110 and other sources as part of a known system (e.g., collision avoidance system, adaptive cruise control system). The lidar system 110 and one or more other sensors 115 can be used to detect objects 140, such as. B. the pedestrian 145, who in 1 is shown. The controller 120 may include processing circuitry, which may include an application specific integrated circuit (ASIC), electronic circuitry, a hardware computer processor (shared or dedicated or group), and memory, one or more software or firmware programs, a combinatorial Executes logic circuit and / or other suitable components that provide the functionality described.

2 11 is a block diagram of lidar system 110 in accordance with one or more embodiments. Some or all of the in 2 Components shown can be part of a photonic chip. Therefore, the lidar system 110 can be referred to as a chip-scale lidar. Two light sources 205, 210 are used in the dual laser lidar system 110. The light sources 205, 210 can be laser diodes formed on the photonic chip. The light source 205 outputs CW signals with frequencies f _D1 and f _D2 . The light source 210 outputs FMCW signals with a center frequency f _R . As previously mentioned, the FMCW signal may contain an up chirp and a down chirp, and the difference Δf is the frequency difference between the highest and lowest frequencies in each chirp. The light source 210 may include a controllable current source that is modulated to modulate the output of a laser diode to thereby generate the FMCW light. In the 2 Resonators 215a, 215b, 215c, 215d (generally denoted as 215) shown function as add, drop or through ports. The resonator 215a acts as a drop port, dropping (ie, up-coupling) the frequency f _R onto the bus waveguide 217 . Resonator 215b acts as a drop port for frequency f _D1 and a through port for frequency f _D2 . Thus, the CW signal at frequency f _D1 is coupled to combine with the FMCW signal at frequency f _R as shown in waveguide 217, while the CW signal at frequency f _D2 is separated and combiner 250b is provided, which will be discussed further.

At the splitter 220, a combination of the FMCW signal with the frequency f _R and the CW signal with the frequency f _D1 is divided. According to an exemplary embodiment, most of the signal (e.g., 90 percent) is routed to the transmit beam coupler 230 (e.g., grating coupler, edge coupler) as the output signal 225, while another portion as signal 227 is split. A transmit beam scanner 235 (e.g., a two-dimensional (2D) microelectromechanical system (MEMS) scanner) directs the output signal 225 from the lidar system 110. When the output signal 225 hits a target 140, a portion of the resulting scattered light will pass through a receive beam scanner 245 into a receive beam coupler 240 (e.g. grating coupler, edge coupler) as a receive signal 247 . Based on the Doppler frequency shift in the receive signal 247 due to the relative velocity between the lidar and the target, the FMCW component is shifted from f _R by Δf _D and the CW component is shifted from f _D1 by Δf _D .

Resonator 215d is used to drop (ie, up-couple) only the shifted FMCW component of receive signal 247 at frequency f _R ±Δf _D onto waveguide 218 . The CW component of receive signal 247 at frequency f _D1 ±Δf _D is provided to combiner 250b along with the CW signal at frequency f _D2 , which is the CW LO signal from light source 205 . The combiner 250b combines the CW component of the received signal 247 at frequency f _D1 ± Δf _D and the CW LO signal from the light source 205 at frequency f _D2 and splits the combination into combined signals 255c, 255d (combined signals 255a, 255b , 255c, 255d, the all commonly referred to as 255). The combined signals 255c, 255d are provided to two photodetectors 260c, 260d, respectively (photodetectors 260a, 260b, 260c, 260d are referred to generally as 260). Photodetectors 260 may be germanium-on-silicon photodetectors, for example. The components of each combined signal 255c, 255d interfere with each other in each photodetector 260c, 260d.

Photodetectors 260c, 260d convert the result of the interference into electrical currents 270c, 270d, also referred to as clock signals. The electrical currents 270c, 270d from each of the photodetectors 260c, 260d are combined and processed to obtain Doppler velocity information about the target 140. FIG. The received Doppler frequency Δf _D in the photodetectors 260c and 260d are shifted by the difference in the two optical frequencies of the laser 205, f _D2 -f _D1 , to enable determination of the direction of the target's Doppler velocity relative to the lidar. The processing may be performed within the lidar system 110 by a processor 280 or external to the lidar system 110 by the controller 120, for example. Processor 280 may include processing circuitry similar to that discussed for controller 120 .

The portion of receive signal 247 that is dropped (ie, coupled up) onto waveguide 218 by resonator 215d, the shifted FMCW component of receive signal 245 at frequency f _R ±Δf _D , is input to combiner 250a. The signal 227 from the splitter 220 is provided to the resonator 215c. Only the FMCW component at frequency f _R is dropped (ie, coupled up) by resonator 215c as local oscillator (LO) signal 229 onto waveguide 219 and is also provided to combiner 250a. The combiner 250a combines the LO signal 229 and the FMCW signal from the resonator 215d, which has a frequency f _R ±Δf _D . The combiner 250a divides the combined signal into combined signals 255a, 255b, which are provided to photodetectors 260a, 260b, respectively.

The results of the interference between the combined signals 255a, 255b at each of the photodetectors 260a, 260b are converted into electrical signals 270a, 270b, referred to as clock signals. The frequency f _b ⁺ is the frequency of the clock signals during the up chirp and the frequency f _b ^- is the frequency of the clock signals during the down chirp. The photodetectors 260a, 260b are used in accordance with a known balanced detector technique to cancel the intensity noise in the LO signal 229 that is common to both photodetectors 260a, 260b.

Electrical signals 270a, 270b and electrical signals 270c, 270d are used to determine the range to target 140. FIG. The distance determination is performed for each up chirp and each down chirp in the FMCW signal output from the light source 210 . The range determination for the up-chirp region is given by: $$R=\frac{c\left({ƒ}_b^{+}+\Delta {ƒ}_D\right)T}{2\Delta ƒ}$$

In GL. 1, T is the time of the chirp and c is the speed of light. The range determination for the down chirp region is given by: $$R=\frac{c\left({ƒ}_b^{-}-\Delta {ƒ}_D\right)T}{2\Delta ƒ}$$

3 11 is a block diagram of lidar system 110 in accordance with one or more embodiments. like the inside 2 embodiment shown includes the in 3 embodiment shown has two light sources 305, 310. The light sources 305, 310 can, like the light sources 205, 210, be laser diodes which are formed on the photonic chip. The light source 310 provides an FMCW signal with the frequency f _R like the light source 210 in 2 , but the light source 305, unlike the light source 205 in 2 a CW signal at only one frequency _fD ready. Based on the resonators 315a, 315b, the splitter 320 is provided with a signal having an FMCW component at f _R and a CW component at f _D . The splitter 320 provides an output signal 325 to the transmit beam coupler 230 for transmission by the transmit beam scanner 235. As with reference to FIG 2 as noted, the majority (e.g., 90 percent) of the signal containing the FMCW component at frequency f _R and the CW component at frequency f _D may be split as the output signal 325 . The remaining part of the split is provided as signal 327 .

Signal 327 is provided to resonator 315c, which lowers (i.e., couples up) only the FMCW portion of the signal at frequency f _R as LO signal 329 and provides it to combiner 350a. The CW portion of signal 327 at frequency f _D is provided to a modulator 352 (e.g., a Mach-Zehnder modulator (MZM)) to induce a frequency shift about frequency f _m . The frequency f _m can be in the range from 100 MHz to 1 GHz, for example. This is followed by a narrow-band optical filter 357, so that the shifted signal 358 has a frequency f _D + f _m .

When the output signal 325 strikes a target 140, a portion of the resulting scattered light is directed by a receive beam scanner 245 into a receive beam coupler 340 as a receive signal 347. FIG. Based on the Doppler frequency shift in the received signal 347, the FMCW component is shifted from f _R by Δf _D and the CW component is shifted from f _D by Δf _D . Resonator 315d is used to couple only the shifted FMCW component of receive signal 347 at frequency f _R ±Δf _D . The CW component of receive signal 347 at frequency f _D ±Δf _D is provided to combiner 350b along with shifted signal 358 at frequency f _D +f _m . Combiner 350b splits its output as combined signals 355c, 355d which are provided to photodetectors 360c, 360d, respectively (generally photodetectors 360a, 360b, 360c, 360d are referred to as 360). Photodetectors 360 may be germanium-on-silicon photodetectors, for example. As related to 2 As noted, the photodetectors 360c, 360d convert the result of the interference from each of the combined signals 355c, 355d into respective electrical currents 370c, 370d, also referred to as clock signals.

At the combiner 350a, together with the LO signal 329, that part of the received signal 347 that is coupled up by the resonator 315d is also input. The combination of the two signals is split into combined signals 355a, 355b which are provided to photodetectors 360a, 360b, respectively. The electrical currents 370a, 370b obtained from the photodetectors 360a, 360b, respectively, are provided for processing along with the electrical currents 370c, 370d. The processing can be performed by the processor 280 of the lidar system 110 or by the controller 120 .

As referring to 2 , a set of electrical currents 370c, 370d are used to perform Doppler velocity detection. All four electric currents 370a, 370b, 370c, 370d are involved in determining the range to the target 140, and the determination of the range is performed for each up-chirp and each down-chirp of the FMCW signal output from the light source 310. From the electrical currents 370a, 370b provided by the photodetectors 360a, 360b, the frequency f _b ⁺ is the frequency of the clock signals during the up chirp and the frequency f _b ^- is the frequency of the clock signals during the down chirp. The distance determination is in GL. 1 and 2 described. The frequency shift f _m makes it easier to determine the direction of the target's Doppler velocity relative to the lidar.

Claims (8)

A chip-scale lidar system (110) comprising: a first light source (210) configured to output a first signal; a second light source (205) configured to output a second signal; a transmit beam coupler (230) configured to provide an output signal (225) for transmission, the output signal (225) including a portion of the first signal and a portion of the second signal; a receive beam coupler (240) configured to receive a receive signal (247) resulting from reflection of the output signal (225) by a target (140); a first set of photodetectors (260a, 260b) configured to respectively obtain a first set of electrical currents (270a, 270b) from a first set of combined signals (255a, 255b), each of the first sets of combined signals ( 255a, 255b) contains a first part of the received signal (247); a second set of photodetectors (260c, 260d) configured to receive a second set of electrical currents (270c, 270d) from a second set of combined signals (255c, 255d), respectively, each of the second sets of combined signals (255c , 255d) contains a second part of the received signal (247); and a processor (280) configured to obtain Doppler information about the target (140) from the second set of electrical currents (270c, 270d) and range information about the target (140) from the first set of electrical currents (270a , 270b) and the second set of electrical currents (270c, 270d). wherein the first light source (210) is configured to output a frequency modulated continuous wave, FMCW signal as the first signal and the second light source (205) is configured to output a continuous wave, CW signal as the second signal. chip-scale lidar system (110). claim 1 , wherein the second signal has a frequency f _D and the chip-scale lidar system (110) further comprises a modulator (352) and an optical filter (357) to receive a shifted signal (358) with a frequency of f _m +f _D to generate. chip-scale lidar system (110). claim 2 , wherein the modulator (352) is a Mach-Zehnder modulator. chip-scale lidar system (110). claim 2 , wherein the shifted signal (358) is combined with the second portion of the received signal (247) to produce the second set of combined signals (255c, 255d). chip-scale lidar system (110). claim 1 , wherein the second signal is at two different optical frequencies f _D1 and f _D2 and the second set of electrical currents (270c, 270d) indicates a frequency shift f _D2 -f _D1 to indicate a direction of the target (140) relative to the chip Determine scale lidar system (110). chip-scale lidar system (110). claim 1 , wherein the chip-scale lidar system (110) is located in a vehicle (100). A method of fabricating a chip-scale lidar system (110), the method comprising: forming a first light source (210) for outputting a first signal; forming a second light source (205) for outputting a second signal; arranging a transmit beamcoupler (230) to provide an output signal (225) for transmission, the output signal (225) including a portion of the first signal and a portion of the second signal; arranging a receive beam coupler (240) configured to receive a receive signal (247) resulting from reflection of the output signal (225) by a target (140); forming a first set of photodetectors (260a, 260b) configured to respectively obtain a first set of electrical currents (270a, 270b) from a first set of combined signals (255a, 255b), each of the first sets of combined signals (255a, 255b) contains a first part of the received signal (247); Forming a second set of photodetectors (260c, 260d) configured to receive a second set of electrical currents (270c, 270d) from a second set of combined signals (255c, 255d), each of the second sets of combined signals ( 255c, 255d) contains a second part of the received signal (247); and configuring a processor (280) to obtain Doppler information about the target (140) from the second set of electrical currents (270c, 270d) and to obtain range information about the target (140) from the first set of electrical currents (270a, 270b ) and the second set of electrical currents (270c, 270d); wherein forming the second light source (205) includes forming the second light source (205) to output a continuous wave, CW signal as the second signal, wherein the outputting of the second signal occurs at a frequency f _D , and the method further comprises arranging a modulator (352) and an optical filter (357) to produce a shifted signal (358) having a frequency of f _m + f _D , the method further comprising combining the shifted signal (358) with the second portion of the received signal (247) to generate the second set of combined signals (255c, 255d), wherein the outputting of the second signal occurs at two different optical frequencies f _D1 and f _D2 and wherein the obtaining of the second set of electrical currents (270c , 270d) indicating a frequency shift f _D2 -f _D1 to determine a direction of the target (140) relative to the chip-scale lidar system (100). procedure after claim 7 wherein forming the first light source (210) includes forming the first light source (210) to output a frequency modulated continuous wave, FMCW signal as the first signal.

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