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 probe has a servo-control device connected to a measuring unit (106) and an optomechanical movement unit (112). The device determines, from knowledge of variation in intensity of a backscattered beam, offset between a measurement direction of a movable optical axis of one of telescopes (103, 104) and an optimal direction allowing maximization of the intensity. The device servo-controls the direction of the axis to the optimal direction, and has a synchronous demodulator (116) and a servo-control loop filter (117) respectively connected to an excitation generator (115) and a summer (118).

Power-assisted bistatic pressure sensor

Bi-axial laser anemometric probe

La presente invention a pour objet une sonde d'anemometrie laser de detection homodyne optique de decalage de frequence par effet Doppler, comprenant deux dispositif emetteur/recepteur (DERF1, DERF2) de faisceau selon deux directions differentes, evitant de dupliquer une pluralite d'elements d'une sonde d'anemometrie laser mono-axe.

Sonde d'anemometrie laser bi-axe

Le domaine general de l'invention est celui des sondes anemometriques optiques dite « bi-statique » comportant une premiere tete optique d'emission (103) eclairant une zone de mesure et une seconde tete optique de reception (104). La sonde selon l'invention comporte: 
- des moyens opto-mecaniques (112) de deplacement permettant de faire osciller l'un des axes optiques des tetes optiques autour d'une direction dite direction de mesure, l'axe oscillant deplace etant note axe optique mobile; 
- des moyens de mesure (106,107,108,109) agences de facon a fournir l'intensite du faisceau retrodiffuse en fonction de temps, ladite intensite variant dans le temps en fonction des oscillations de l'axe optique; 
- un dispositif d'asservissement (110,111) relie aux moyens de mesure et aux moyens opto-mecaniques de deplacement, ledit dispositif d'asservissement comprenant des fonctions permettant d'une part, de determiner, a partir de la connaissance de la variation de l'intensite du faisceau retrodiffuse, l'ecart entre la direction de mesure de l'axe optique mobile et une direction dite optimale permettant d'obtenir un maximum d'intensite du faisceau retrodiffuse et d'autre part, d'asservir la direction dudit axe optique mobile sur la direction dite optimale.

Philippe Rondeau

Papers

Power-assisted bistatic pressure sensor

Bi-axial laser anemometric probe

Sonde d'anemometrie laser bi-axe

Sonde anémométrique bi-statique asservie

Procede d'estimation de la composante transversale de la vitesse de l'air dans une mesure lidar doppler