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Dual chirped microcomb based parallel ranging at megapixel-line rates

Maxim Karpov, Tobias Kippenberg, Junqiu Liu, Anton Lukashchuk

Photonic integrated systems can be harnessed for fast and efficient optical telecommunication and metrology technologies. Here the authors develop a dual-soliton microcomb technique for massively parallel coherent laser ranging that requires only a single laser and a single photoreceiver. Laser-based ranging (LiDAR) - already ubiquitously used in industrial monitoring, atmospheric dynamics, or geodesy - is a key sensor technology. Coherent laser ranging, in contrast to time-of-flight approaches, is immune to ambient light, operates continuous-wave allowing higher average powers, and yields simultaneous velocity and distance information. State-of-the-art coherent single laser-detector architectures reach hundreds of kilopixel per second sampling rates, while emerging applications - autonomous driving, robotics, and augmented reality - mandate megapixel per second point sampling to support real-time video-rate imaging. Yet, such rates of coherent LiDAR have not been demonstrated. Recent advances in photonic chip-based microcombs provide a route to higher acquisition speeds via parallelization but require separation of individual channels at the detector side, increasing photonic integration complexity. Here we overcome the challenge and report a hardware-efficient swept dual-soliton microcomb technique that achieves coherent ranging and velocimetry at megapixel per second line scan measurement rates with up to 64 optical channels. Multiheterodyning two synchronously frequency-modulated microcombs yields distance and velocity information of all individual ranging channels on a single receiver alleviating the need for individual separation, detection, and digitization. The reported LiDAR implementation is compatible with photonic integration and demonstrates the significant advantages of acquisition speed afforded by the convergence of optical telecommunication and metrology technologies.

NATURE PORTFOLIO2022

Experimental demonstration of dynamic spatiotemporal structured beams that simultaneously exhibit two orbital angular momenta by combining multiple frequency lines, each carrying multiple Laguerre-Gaussian modes

Maxim Karpov, Tobias Kippenberg, Hao Song, Xinzhou Su, Zhe Zhao

In general, there are different, relatively independent forms of orbital angular momenta at a given propagation distance, which might exhibit different dynamic spatial characteristics. One type involves a beam with a helical phase-front that rotates around its own beam center, such as a Laguerre-Gaussian (LG) beam with an azimuthal index not equal to zero. The other one is a Gaussian-like beam dot that revolves around a central axis. Here, we experimentally demonstrate the generation of a dynamic spatiotemporal (ST) structured beam that simultaneously exhibits both rotation and revolution at a given propagation distance. Nine Kerr frequency comb lines are coherently combined, each carrying a designed superposition of multiple LG modes containing one unique l value and multiple p values. Experimental results showthat the mode purity of the reconstructed revolving and rotating LG(30) beam is similar to 89% when both the beam waist and revolving radius (R) are 0.4 mm. Moreover, we explore the effects of the number of frequency comb lines and the R value on the mode purity of the generated ST beam. Consequently, we find that a higher mode purity can be achieved by involving more frequency comb lines or reducing the R. (C) 2022 Optica Publishing Group

Optica Publishing Group2022

Generation of OAM-carrying space-time wave packets with time-dependent beam radii using a coherent combination of multiple LG modes on multiple frequencies

Maxim Karpov, Tobias Kippenberg, Hao Song, Xinzhou Su, Zhe Zhao

Space-time (ST) wave packets, in which spatial and temporal characteristics are coupled, have gained attention due to their unique propagation characteristics, such as propagation invariance and tunable group velocity in addition to their potential ability to carry orbital angular momentum (OAM). Through experiment and simulation, we explore the generation of OAM-carrying ST wave packets, with the unique property of a time-dependent beam radius at various ranges of propagation distances. To achieve this, we synthesize multiple frequency comb lines, each assigned to a coherent combination of multiple Laguer re-Gaussian (LGl,p) modes with the same azimuthal index but different radial indices. The time-dependent interference among the spatial modes at the different frequencies leads to the generation of the desired OAM-carrying ST wave packet with dynamically varying radii. The simulation results indicate that the dynamic range of beam radius oscillations increases with the number of modes and frequency lines. The simulated ST wave packet for OAM of orders +1 or +3 has an OAM purity of >95%. In addition, we experimentally generate and measure the OAM-carrying ST wave packets with time-dependent beam radii. In the experiment, several lines of a Kerr frequency comb are spatially modulated with the superposition of multiple LG modes and combined to generate such an ST wave packet. In the experiment, ST wave packets for OAM of orders +1 or +3 have an OAM purity of >64%. In simulation and experiment, OAM purity decreases and beam radius becomes larger over the propagation.(c) 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

Optica Publishing Group2022