Dual chirped micro-comb based parallel ranging at megapixel-line rates

Laser based ranging (LiDAR) - already ubiquitously used in industrial monitoring, atmospheric dynamics, or geodesy - is 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 rates. While emerging applications such as 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. Here we report a swept dual-soliton microcomb technique enabling coherent ranging and velocimetry at megapixel per second line scan measurement rates with up to 64 spectrally dispersed optical channels. It is based on recent advances in photonic chip-based microcombs that offer a solution to reduce complexity both on the transmitter and receiver sides. Multi-heterodyning 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 hardware-efficient, compatible with photonic integration, and demonstrates the significant advantages of acquisition speed afforded by the convergence of optical telecommunication and metrology technologies. We anticipate our research will motivate further investigation of frequency swept microresonator dual-comb approach in the neighboring fields of linear and nonlinear spectroscopy, optical coherence tomography

Massively parallel coherent laser ranging using soliton microcombs

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.Comment: 18 pages, 12 Figure

Cryogenic electro-optic interconnect for superconducting devices

Encoding information onto optical fields is the backbone of modern telecommunication networks. Optical fibers offer low loss transport and vast bandwidth compared to electrical cables, and are currently also replacing coaxial cables for short-range communications. Optical fibers also exhibit significantly lower thermal conductivity, making optical interconnects attractive for interfacing with superconducting circuits and devices. Yet little is known about modulation at cryogenic temperatures. Here we demonstrate a proof-of-principle experiment, showing that currently employed Ti-doped LiNbO modulators maintain the Pockels coefficient at 3K---a base temperature for classical microwave amplifier circuitry. We realize electro-optical read-out of a superconducting electromechanical circuit to perform both coherent spectroscopy, measuring optomechanically-induced transparency, and incoherent thermometry, encoding the thermomechanical sidebands in an optical signal. Although the achieved noise figures are high, approaches that match the lower-bandwidth microwave signals, use integrated devices or materials with higher EO coefficient, should achieve added noise similar to current HEMT amplifiers, providing a route to parallel readout for emerging quantum or classical computing platforms.Comment: Experimental details added. The heating experiment update

Ultrafast optical circuit switching for data centers using integrated soliton microcombs

Networks inside current data centers comprise a hierarchy of power-hungry electronic packet switches interconnected via optical fibers and transceivers. As the scaling of such electrically-switched networks approaches a plateau, a power-efficient solution is to implement a flat network with optical circuit switching (OCS), without electronic switches and a reduced number of transceivers due to direct links among servers. One of the promising ways of implementing OCS is by using tunable lasers and arrayed waveguide grating routers. Such an OCS-network can offer high bandwidth and low network latency, and the possibility of photonic integration results in an energy-efficient, compact, and scalable photonic data center network. To support dynamic data center workloads efficiently, it is critical to switch between wavelengths in sub nanoseconds (ns). Here we demonstrate ultrafast photonic circuit switching based on a microcomb. Using a photonic integrated Si3N4 microcomb in conjunction with semiconductor optical amplifiers (SOAs), sub ns (< 500 ps) switching of more than 20 carriers is achieved. Moreover, the 25-Gbps non-return to zero (NRZ) and 50-Gbps four-level pulse amplitude modulation (PAM-4) burst mode transmission systems are shown. Further, on-chip Indium phosphide (InP) based SOAs and arrayed waveguide grating (AWG) are used to show sub-ns switching along with 25-Gbps NRZ burst mode transmission providing a path toward a more scalable and energy-efficient wavelength-switched network for future data centers.Comment: 11 pages, 6 figure

Parallel convolution processing using an integrated photonic tensor core

With the proliferation of ultra-high-speed mobile networks and internet-connected devices, along with the rise of artificial intelligence, the world is generating exponentially increasing amounts of data - data that needs to be processed in a fast, efficient and smart way. These developments are pushing the limits of existing computing paradigms, and highly parallelized, fast and scalable hardware concepts are becoming progressively more important. Here, we demonstrate a computational specific integrated photonic tensor core - the optical analog of an ASIC-capable of operating at Tera-Multiply-Accumulate per second (TMAC/s) speeds. The photonic core achieves parallelized photonic in-memory computing using phase-change memory arrays and photonic chip-based optical frequency combs (soliton microcombs). The computation is reduced to measuring the optical transmission of reconfigurable and non-resonant passive components and can operate at a bandwidth exceeding 14 GHz, limited only by the speed of the modulators and photodetectors. Given recent advances in hybrid integration of soliton microcombs at microwave line rates, ultra-low loss silicon nitride waveguides, and high speed on-chip detectors and modulators, our approach provides a path towards full CMOS wafer-scale integration of the photonic tensor core. While we focus on convolution processing, more generally our results indicate the major potential of integrated photonics for parallel, fast, and efficient computational hardware in demanding AI applications such as autonomous driving, live video processing, and next generation cloud computing services

Dissipative dispersion-managed solitons in fiber-optic systems with lumped amplification

We numerically and experimentally studied the shape of the dissipative dispersion-managed solitons (DM-solitons) stably propagating over the lossy DM fiber-optic systems with lumped amplification. We found that, contrary to the lossless case, the chirp-free points of the dissipative DM-solitons are not located in the middle of the fiber spans in the dispersion map. This constitutes a qualitative difference between the dissipative DM-solitons of the lossy systems and the conservative ones of the lossless systems. The applied numerical method was verified both experimentally and by numerically solving nonlinear Schrodinger equation. (C) 2019 Optical Society of Americ

Photonic chip-based soliton frequency combs covering the biological imaging window

Dissipative Kerr solitons (DKS) in optical microresonators provide a highly miniaturised, chip-integrated frequency comb source with unprecedentedly high repetition rates and spectral bandwidth. To date, such frequency comb sources have been successfully applied in the optical telecommunication band for dual-comb spectroscopy, coherent telecommunications, counting of optical frequencies and distance measurements. Yet, the range of applications could be significantly extended by operating in the near-infrared spectral domain, which is a prerequisite for biomedical and Raman imaging applications, and hosts commonly used optical atomic transitions. Here we show the operation of photonic-chip-based soliton Kerr combs driven with 1 micron laser light. By engineering the dispersion properties of a Si3N4 microring resonator, octave-spanning soliton Kerr combs extending to 776 nm are attained, thereby covering the optical biological imaging window. Moreover, we show that soliton states can be generated in normal group–velocity dispersion regions when exploiting mode hybridisation with other mode families

Microresonator Dual-Comb Coherent FMCW LiDAR

We introduce a novel architecture for parallel frequency-modulated continuous wave (FMCW) laser ranging (LiDAR). Using dual soliton microcombs, we demonstrate a parallel distance measurement with 24 channels requiring only a single FMCW pump laser and coherent receiver for read-out. (C) 2020 The Author(s

Massively parallel coherent LiDAR using dissipative Kerr solitons

We demonstrate an architecture for massively parallel frequency-modulated continuous wave (FMCW) laser ranging (LiDAR) by transferring linear chirps of a single narrow linewidth laser onto all soliton comb teeth though generation of a dissipative Kerr soliton in an integrated Si3N4 microresonator. (C) 2020 The Author(s

Reconfigurable radiofrequency filters based on versatile soliton microcombs

The rapidly maturing integrated Kerr microcombs show significant potential for microwave photonics. Yet, state-of-the-art microcomb-based radiofrequency filters have required programmable pulse shapers, which inevitably increase the system cost, footprint, and complexity. Here, by leveraging the smooth spectral envelope of single solitons, we demonstrate microcomb-based radiofrequency filters free from any additional pulse shaping. More importantly, we achieve all-optical reconfiguration of the radiofrequency filters by exploiting the intrinsically rich soliton configurations. Specifically, we harness the perfect soliton crystals to multiply the comb spacing thereby dividing the filter passband frequencies. Also, the versatile spectral interference patterns of two solitons enable wide reconfigurability of filter passband frequencies, according to their relative azimuthal angles within the round-trip. The proposed schemes demand neither an interferometric setup nor another pulse shaper for filter reconfiguration, providing a simplified synthesis of widely reconfigurable microcomb-based radiofrequency filters. For microcomb-based radiofrequency filters pulse shapers are required, which increase the system cost, footprint, and complexity. Here, the authors bypass this need by exploiting versatile soliton states inherent in microresonator and achieve reconfigurable radiofrequency filters