Ultrafast optical ranging using microresonator soliton frequency combs

Light detection and ranging (LIDAR) is critical to many fields in science and industry. Over the last decade, optical frequency combs were shown to offer unique advantages in optical ranging, in particular when it comes to fast distance acquisition with high accuracy. However, current comb-based concepts are not suited for emerging high-volume applications such as drone navigation or autonomous driving. These applications critically rely on LIDAR systems that are not only accurate and fast, but also compact, robust, and amenable to cost-efficient mass-production. Here we show that integrated dissipative Kerr-soliton (DKS) comb sources provide a route to chip-scale LIDAR systems that combine sub-wavelength accuracy and unprecedented acquisition speed with the opportunity to exploit advanced photonic integration concepts for wafer-scale mass production. In our experiments, we use a pair of free-running DKS combs, each providing more than 100 carriers for massively parallel synthetic-wavelength interferometry. We demonstrate dual-comb distance measurements with record-low Allan deviations down to 12 nm at averaging times of 14 $\mu$s as well as ultrafast ranging at unprecedented measurement rates of up to 100 MHz. We prove the viability of our technique by sampling the naturally scattering surface of air-gun projectiles flying at 150 m/s (Mach 0.47). Combining integrated dual-comb LIDAR engines with chip-scale nanophotonic phased arrays, the approach could allow widespread use of compact ultrafast ranging systems in emerging mass applications.Comment: 9 pages, 3 figures, Supplementary information is attached in 'Ancillary files

Frequency stability in resonator-stabilized oscillators

A simplified stability analysis of resonator-stabilized oscillators is carried out by using the describing function approach. On this basis a criterion for the evaluation and optimization of the frequency stabilization introduction in an oscillator by a resonating element with a large quality factor is proposed. In particular, a frequency-stabilization index which can be conveniently used in the design of highly stable oscillators is defined. The validity of this performance index has been verified in the design of microwave oscillators using dielectric resonators as frequency-stabilizing element

Design of FIR digital filters for pulse shaping and channel equalization using time-domain optimization

Three algorithms are developed for designing finite impulse response digital filters to be used for pulse shaping and channel equalization. The first is the Minimax algorithm which uses linear programming to design a frequency-sampling filter with a pulse shape that approximates the specification in a minimax sense. Design examples are included which accurately approximate a specified impulse response with a maximum error of 0.03 using only six resonators. The second algorithm is an extension of the Minimax algorithm to design preset equalizers for channels with known impulse responses. Both transversal and frequency-sampling equalizer structures are designed to produce a minimax approximation of a specified channel output waveform. Examples of these designs are compared as to the accuracy of the approximation, the resultant intersymbol interference (ISI), and the required transmitted energy. While the transversal designs are slightly more accurate, the frequency-sampling designs using six resonators have smaller ISI and energy values

Nanoelectromechanical systems

Nanoelectromechanical systems (NEMS) are drawing interest from both technical and scientific communities. These are electromechanical systems, much like microelectromechanical systems, mostly operated in their resonant modes with dimensions in the deep submicron. In this size regime, they come with extremely high fundamental resonance frequencies, diminished active masses,and tolerable force constants; the quality (Q) factors of resonance are in the range Q~10^3–10^5—significantly higher than those of electrical resonant circuits. These attributes collectively make NEMS suitable for a multitude of technological applications such as ultrafast sensors, actuators, and signal processing components. Experimentally, NEMS are expected to open up investigations of phonon mediated mechanical processes and of the quantum behavior of mesoscopic mechanical systems. However, there still exist fundamental and technological challenges to NEMS optimization. In this review we shall provide a balanced introduction to NEMS by discussing the prospects and challenges in this rapidly developing field and outline an exciting emerging application, nanoelectromechanical mass detection

Photonic chip based optical frequency comb using soliton induced Cherenkov radiation

By continuous wave pumping of a dispersion engineered, planar silicon nitride microresonator, continuously circulating, sub-30fs short temporal dissipative solitons are generated, that correspond to pulses of 6 optical cycles and constitute a coherent optical frequency comb in the spectral domain. Emission of soliton induced Cherenkov radiation caused by higher order dispersion broadens the spectral bandwidth to 2/3 of an octave, sufficient for self referencing, in excellent agreement with recent theoretical predictions and the broadest coherent microresonator frequency comb generated to date. In a further step, this frequency comb is fully phase stabilized. The ability to preserve coherence over a broad spectral bandwidth using soliton induced Cherenkov radiation marks a critical milestone in the development of planar optical frequency combs, enabling on one hand application in e.g. coherent communications, broadband dual comb spectroscopy and Raman spectral imaging, while on the other hand significantly relaxing dispersion requirements for broadband microresonator frequency combs and providing a path for their generation in the visible and UV. Our results underscore the utility and effectiveness of planar microresonator frequency comb technology, that offers the potential to make frequency metrology accessible beyond specialized laboratories.Comment: Changes: - Added data (new Fig.4) on the first full phase stabilization of a dissipative Kerr soliton (or dissipative cavity soliton) in a microresonator - Extended Fig. 8 in the SI - Introduced nomenclature of dissipative Kerr solitons - Minor other change

Eingangsadmittanz-Modellierung und passivitätsbasierte Stabilisierung von digital-stromgeregelten, netzgebundenen Umrichtern

Due to the ever increasing number of renewable energy systems in the electrical power grid, the application of power electronic-based circuits is gaining more and more importance. It has however been known for a while that interactions of one or multiple converters with resonances in the grid can lead to poorly damped oscillations, and thus, may threaten the stability of parts of the power system. The passivity theory has proven to be particularly powerful in preventing such situations. Accordingly, the stability of the power grid can be guaranteed by design if all components act passive. This means that all active loads and energy feeding converters have an input admittance with a non-negative real part. This can theoretically be achieved using passive or active damping strategies, but most research neglects real-world effects, which arise from the sampling of high-frequency switching harmonics. The aim of this dissertation is therefore to review the complete modeling and analysis of digitally current-controlled grid-connected converters and to extend the controller as well as filter design. On the basis of typical single-input single-output models of the converter’s input admittance, methods for the design of a passive damping or an active feed-forward are proposed and it is discussed which aspects have to be considered when implementing the filters. However, since the used models cannot reproduce all alias effects, in the further part of the thesis a multiple-input multiple-output converter model is developed. It is shown that the mirroring of high-frequency signal components onto low-frequency components can in principle be described by a dynamic uncertainty that affects the behavior of the converters' baseband dynamics. Due to this new insight it becomes clear which criteria passive or active filters should fulfill in order to specifically counteract the often negative mirroring effects of digital control. Finally, it is demonstrated that a robust passivation of the converter input admittance can prevent a destabilization of the power system by harmonics for a large number of grid impedances. The presented theory and the developed controller design are illustrated and verified by various simulations of an exemplary converter system.Aufgrund der immer größer werdenden Anzahl von erneuerbaren Energieanlagen im elektrischen Energieversorgungsnetz gewinnt der Einsatz von leistungselektronischen Schaltungen immer mehr an Bedeutung. Es ist jedoch seit längerem bekannt, dass Wechselwirkungen von einem oder mehreren Umrichtern mit Resonanzen im Netz zu schlecht gedämpften Schwingungen führen und damit die Stabilität von Teilen des Energienetzes gefährden können. Die Passivitätstheorie hat sich als besonders wirkungsvoll erwiesen, um solche Situationen zu verhindern. Demnach kann die Stabilität des Stromnetzes bereits in der Designphase gewährleistet werden, indem alle Komponenten passiv wirken. Das bedeutet, dass alle aktiven Verbraucher und einspeisenden Umrichter eine Eingangsadmittanz mit nicht negativem Realteil besitzen. Dies ist theoretisch mit Hilfe von passiven oder aktiven Dämpfungsstrategien zu erreichen. Die meisten Forschungsarbeiten vernachlässigen jedoch reale Effekte, die bei der Abtastung von hochfrequenten Harmonischen entstehen. Ziel dieser Dissertation ist es daher, den kompletten Modellierungs-, Analyse- und Regler- sowie Filterentwurfsprozess von digital-stromgeregelten, netzgebundenen Umrichtern zu überprüfen und zu erweitern. Auf der Basis typischer Eingrößenmodelle der Umrichter-Eingangsadmittanz werden Verfahren für die Auslegung einer passiven Dämpfung bzw. einer aktiven Vorsteuerung vorgeschlagen und es wird diskutiert, welche Aspekte bei der Implementierung der Filter zu berücksichtigen sind. Da sich mit den Modellen jedoch nicht alle Alias-Effekte abbilden lassen, wird im weiteren Teil der Arbeit ein Mehrgrößen-Umrichtermodell entwickelt. Es zeigt sich, dass die Spiegelung hochfrequenter Signalanteile auf niederfrequente Anteile prinzipiell durch eine dynamische Unsicherheit beschrieben werden kann, die das Grundfrequenzverhalten der Umrichter beeinflusst. Dank dieser neuen Erkenntnisse wird deutlich, welche Kriterien passive oder aktive Filter erfüllen sollten, um den oft negativen Spiegeleffekten der digitalen Regelung gezielt entgegenzuwirken. Es wird demonstriert, dass eine robuste Passivierung der Umrichter-Eingangsadmittanz eine Destabilisierung des Energienetzes durch Harmonische für eine Vielzahl von Netzimpedanzen verhindern kann. Die vorgestellte Theorie und der erarbeitete Reglerentwurf werden anhand diverser Simulationen eines beispielhaften Umrichtersystems verdeutlicht und validiert