Coherent ranging, also known as frequency-modulated continuous-wave (FMCW) laser-based light detection and ranging (lidar)1 is used for long-range three-dimensional distance and velocimetry in autonomous driving2,3. FMCW lidar maps distance to frequency4,5 using frequency-chirped waveforms and simultaneously measures the Doppler shift of the reflected laser light, similar to sonar or radar6,7 and coherent detection prevents interference from sunlight and other lidar systems. However, coherent ranging has a lower acquisition speed and requires precisely chirped8 and highly coherent5 laser sources, hindering widespread use of the lidar system and impeding parallelization, compared to modern time-of-flight ranging systems that use arrays of individual lasers. Here we demonstrate a massively parallel coherent lidar scheme using an ultra-low-loss photonic chip-based soliton microcomb9. By fast chirping of the pump laser in the soliton existence range10 of a microcomb with amplitudes of up to several gigahertz and a sweep rate of up to ten megahertz, a rapid frequency change occurs in the underlying carrier waveform of the soliton pulse stream, but the pulse-to-pulse repetition rate of the soliton pulse stream is retained. As a result, the chirp from a single narrow-linewidth pump laser is transferred to all spectral comb teeth of the soliton at once, thus enabling parallelism in the FMCW lidar. Using this approach we generate 30 distinct channels, demonstrating both parallel distance and velocity measurements at an equivalent rate of three megapixels per second, with the potential to improve sampling rates beyond 150 megapixels per second and to increase the image refresh rate of the FMCW lidar by up to two orders of magnitude without deterioration of eye safety. This approach, when combined with photonic phase arrays11 based on nanophotonic gratings12, provides a technological basis for compact, massively parallel and ultrahigh-frame-rate coherent lidar systems. A massively parallel coherent light detection and ranging (lidar) scheme using a soliton microcomb—a light source that emits a wide spectrum of sharp lines with equally spaced frequencies—is described.

Massively parallel coherent laser ranging using a soliton microcomb

Disclosed is a laser radar device having a wide two-dimensional field of view, a large receiving aperture, and responsivity to short pulse light. Specifically disclosed is a laser radar device provided with a laser light source which generates pulse laser light, a scanner which transmits a transmission pulse to a target while two-dimensionally scanning a pencil-shaped transmission beam and outputs scan angle information, a reception lens which receives reception light that has arrived, a long light-receiving element array which converts the reception light to reception signals and outputs the reception signals, a transimpedance amplifier array which amplifies the reception signals, an adder circuit which adds the reception signals from respective elements of the transimpedance amplifier array, a distance detection circuit which measures the light round-trip time to the target of an output signal from the adder circuit, and a signal processing unit which obtains the distances to multiple points on the target on the basis of the light round-trip time and the light speed by causing the scanner to perform a two-dimensional scan operation while associating the two-dimensional scan operation with the scan angle information to thereby measure the three-dimensional shape of the target.

Laser radar device

Lidar imaging systems are one of the hottest topics in the optronics industry. The need to sense the surroundings of every autonomous vehicle has pushed forward a race dedicated to deciding the final solution to be implemented. However, the diversity of state-of-the-art approaches to the solution brings a large uncertainty on the decision of the dominant final solution. Furthermore, the performance data of each approach often arise from different manufacturers and developers, which usually have some interest in the dispute. Within this paper, we intend to overcome the situation by providing an introductory, neutral overview of the technology linked to lidar imaging systems for autonomous vehicles, and its current state of development. We start with the main single-point measurement principles utilized, which then are combined with different imaging strategies, also described in the paper. An overview of the features of the light sources and photodetectors specific to lidar imaging systems most frequently used in practice is also presented. Finally, a brief section on pending issues for lidar development in autonomous vehicles has been included, in order to present some of the problems which still need to be solved before implementation may be considered as final. The reader is provided with a detailed bibliography containing both relevant books and state-of-the-art papers for further progress in the subject.

An Overview of Lidar Imaging Systems for Autonomous Vehicles

We present the demonstration of an integrated frequency modulated continuous wave LiDAR on a silicon platform. The waveform calibration, the scanning system, and the balanced detectors are implemented on a chip. Detection and ranging of a moving hard target at upto 60 m with less than 5 mW of output power is demonstrated in this paper.

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Photonic Integrated Circuit-Based FMCW Coherent LiDAR

Coherent ranging, also known as frequency-modulated continuous-wave (FMCW) laser based ranging (LIDAR) is currently developed for long range 3D distance and velocimetry in autonomous driving. Its principle is based on mapping distance to frequency, and to simultaneously measure the Doppler shift of reflected light using frequency chirped signals, similar to Sonar or Radar. Yet, despite these advantages, coherent ranging exhibits lower acquisition speed and requires precisely chirped and highly-coherent laser sources, hindering their widespread use and impeding Parallelization, compared to modern time-of-flight (TOF) ranging that use arrays of individual lasers. Here we demonstrate a novel massively parallel coherent LIDAR scheme using a photonic chip-based microcomb. By fast chirping the pump laser in the soliton existence range of a microcomb with amplitudes up to several GHz and sweep rate up to 10 MHz, the soliton pulse stream acquires a rapid change in the underlying carrier waveform, while retaining its pulse-to-pulse repetition rate. As a result, the chirp from a single narrow-linewidth pump laser is simultaneously transferred to all spectral comb teeth of the soliton at once, and allows for true parallelism in FMCW LIDAR. We demonstrate this approach by generating 30 distinct channels, demonstrating both parallel distance and velocity measurements at an equivalent rate of 3 Mpixel/s, with potential to improve sampling rates beyond 150 Mpixel/s and increase the image refresh rate of FMCW LIDAR up to two orders of magnitude without deterioration of eye safety. The present approach, when combined with photonic phase arrays based on nanophotonic gratings, provides a technological basis for compact, massively parallel and ultra-high frame rate coherent LIDAR systems.

Massively parallel coherent laser ranging using soliton microcombs

The subject of the present invention is a laser anemometry probe for optical homodyne detection of frequency offset by Doppler effect, comprising two devices (DERF1, DERF2) for transmitting/receiving beams in two different directions, avoiding duplicating a plurality of elements of a mono-axial laser anemometry probe.

Biaxial laser anemometry probe

A method for determining the speed vector ({right arrow over (Vd)}), with respect to the surrounding air, of a rotary wing aircraft (HL) equipped with a beam scanning Doppler laser anemometry device for measuring (Step 1 ) a set of projections (Vm) of said speed vector ({right arrow over (Vd)}) in at least four non-coplanar directions, comprising the following steps:
 detecting (Step 2 ) any anomaly of at least one element from the set of measured projections (Vm), from a comparison with respect to a first threshold (S 1 ), of a deviation between the measurements (Vm) and the measurements (Vp) predicted from a predetermined model depending on values of beam scanning parameters of the anemometry device; and reducing (Step 3 ) the effect of a detected anomaly by invalidating measurements corresponding to said anomaly and computing the components of the speed vector from valid measurements.

Method for determining the speed of a rotocraft relative to the surrounding air

The general field of the invention is that of Doppler lidars intended to measure the speed of a target. The lidar according to the invention comprises: First means for modulating the optical frequency of the transmission signal, said frequency being the sum of a constant frequency and of a variable frequency of determined amplitude modulated by a periodic temporal function; Second means for computing the spectrum of the measured heterodyne signal and for creating two measurement spectra obtained by shifting the spectrum of the heterodyne signal by a positive and negative frequency value, said realignment frequency equal to the difference between the instantaneous frequency of the transmission signal and the frequency of a signal transmitted at a time shifted by the round-trip travel time between the lidar and the target; Third means for comparing the two measurement spectra, the difference in amplitude between the two spectra at the Doppler frequency determining the direction of the speed of the target.

Relative speed measuring doppler lidar

The general field of the invention is that of "bistatic" anemometric optical probes comprising an emitting first optical head (103) that illuminates a measurement region and a receiving second optical head (104). The probe according to the invention comprises: - optomechanical movement means (112) for moving one of the optical axes of the optical heads in at least one direction called the measurement direction, the optical axis moved being denoted movable optical axis; - measuring means (106, 107, 108, 109) arranged so as to distribute the intensity of the beam backscattered from the measurement region in at least two directions located on either side of the measurement direction and denoted servo-control directions; and - a servo-control device (110, 111) connected to the measuring means and to the optomechanical means of moving, said servo-control device comprising functions making it possible, on the one hand, to determine, from knowledge of the intensity of the backscattered beam in the two servo-control directions, the offset between the measurement direction of the movable optical axis and a direction, called the optimal direction, making it possible to maximize the intensity of the backscattered beam and, on the other hand, to servo-control the direction of said movable optical axis to the optimal direction.

Servo-Controlled Bistatic Anemometric Probe

Optical system has a passive optical chip on the top surface with a first wave guide and a laser diode arranged on the edge of the chip. The chip has a reflecting structure on the top surface at the wavelength of the laser diode and a thin layer portion powered by the laser diode and covering a part of the first wave guide. The first wave guide input is linked to the laser diode, passing through the reflecting structure. The chip has a second wave guide on the top surface, a first coupler formed by two first portions of the first wave guide not covered by the thin layer portion and situated on either side of the thin layer portion along the optical path, and a second coupler formed by two second portions, respectively of the first and second wave guides, not covered by the thin layer portion.

Philippe Rondeau

Papers

Biaxial laser anemometry probe

Method for determining the speed of a rotocraft relative to the surrounding air

Relative speed measuring doppler lidar

Servo-Controlled Bistatic Anemometric Probe

Optical signal emission system