Microwave Clocks and Applications
Physics Metrology Division of INRIM
This tutorial will give an overview of the most common microwave atomic clocks developed by several research laboratories and industries. Three main topics will be covered: 1) Atomic fountains: they represent the state-of-the-art among microwave standards since realize the current definition of the second in the SI with the highest accuracy. Noise effects limiting the short-term stability and systematic contributions to the accuracy budget will be discussed. 2) Vapor cell rubidium clocks: they are particularly important in those applications where, rather than accuracy, small size and frequency stability performances are requested. Different kinds of vapor cell clocks will be presented, including high performing clocks, with frequency stability comparable to that of a hydrogen maser, and chip-scale clocks. 3) Applications: microwave atomic clocks are essential in many aspects nowadays life, it is sufficient to think, for instance, to telecommunications or navigation systems. In the tutorial, several examples of applications will be described, ranging from space missions, to sensors, to tests of fundamental physics.
Salvatore Micalizio is a researcher of the Physics Metrology Division of INRIM. After receiving the degree in physics from the University of Torino, he joined the Time and Frequency Division of IEN where he was involved in the realization of a Rb maser without inversion of population. In 2001, he received the PhD in Metrology from Politecnico of Torino, and since 2004 he has been on the permanent staff of INRIM. His research activity is mainly devoted to the development of vapor cell frequency standards. He made studies on coherent population trapping, pulsed optical pumping and their possible application to frequency metrology. He is also involved in studies on primary atomic frequency standards developed at INRIM. He coordinated several research projects funded by ASI, ESA and the European Metrological Research Program.
Optical Microresonators and Applications
National Institute of Standards and Technology (NIST)
Ultra-high-Q microresonators can confine extreme amounts of optical energy in tiny mode volumes. This tutorial will focus on applications of microresonators, in particular their use for optical frequency combs generation and for optical precision sensors. Microresonator-based frequency combs ("microcombs") have attracted a lot of attention for their potential applications in precision metrology, gas sensing, arbitrary optical waveform generation, telecommunication, and as components in integrated photonic circuits. We will cover recent results and research directions in the field of microresonator-based frequency combs, as well as promising out-of-the-lab applications for this technology.
The second part of the tutorial will cover results on nonlinear interaction of counter-propagating light in microresonators, leading to spontaneous symmetry breaking. This symmetry breaking can be used for precision sensors and the realization of nonreciprocal optical devices including chip-based isolators and circulators.
Pascal Del'Haye received his PhD 2011 from the University of Munich and the Max Planck Institute of Quantum Optics for pioneering work on optical frequency comb generation in microresonators. After his PhD, Pascal spent 4 years at the National Institute of Standards and Technology (NIST) in Boulder CO, USA. Since 2015 he is leading the microphotonics research team at the UK's National Physical Laboratory (NPL) south-west of London. For his work on nonlinear photonics and optical frequency metrology Pascal received several awards and prizes, including the Helmholtz prize for metrology, the EPS QEOD thesis prize, and the EFTF Young Scientist Award.
Optical Frequency Combs and their Applications
National Institute of Standards and Technology
Frequency combs, which combine pulsed laser technology with precision optical measurement capabilities represent an amazingly versatile tool in the domain of time and frequency measurement. Acting as precision optical and pulsed synthesizers, frequency combs can be used to transfer the timing, phase and frequency stability from a frequency reference to its optical pulse train and to hundreds of thousands of tones in the optical domain. This tutorial will explain how optical frequency combs work, and how their various technological strengths can be used in a vast array of applications, spanning precision optical measurement, timing distribution, trace gas detection and low-noise microwave generation.
Dr. Tara Fortier is a Project Leader at the National Institute of Standards and Technology and serves as Graduate Faculty at the University of Colorado, Boulder. Her research is focused on the development and application of optical frequency combs for high precision atomic clock comparisons and ultra-low- noise microwave generation.
Dr. Fortier received her Ph.D at JILA/ University of Colorado in 2003 developing phase-stabilized ultra- fast lasers for quantum coherent control experiments. She was a Postdoctoral Director’s fellow at Los Alamos National Laboratory from 2004-2006 developing optical frequency combs to searches for time variation of fundamental constants and violations of physical laws via the comparison of atomic clocks. She was awarded the 2009 European Time and Frequency Forum Young Scientist Award for her contributions to optical frequency comb development, was a successful champion in the DARPA PULSE Program, and has served as the government evaluator for the DARPA EPHI and STOIC programs. Her work has resulted in greater than 60 peer reviewed journal articles in optical frequency comb development and applications.
Finally, Dr. Fortier serves on the NIST board of directors for Women in STEM and is committed to serving and advancing the representation of women and minorities in physics and photonics.
Optical Atomic Clocks and Applications
Quantum Science Department, National Physical Laboratory
Optical frequency standards based on atomic references are now demonstrating accuracies at the 10-18 level. With this level of accuracy and sensitivity, these clock systems can also be used as exquisite quantum sensors, with the ability keep track of more than just time and frequency. In this tutorial we will focus on laser-cooled ion- and neutral-atom-based frequency standards, and what it takes to evaluate and reduce systematic uncertainties in optical clocks to the 10-18 level and below. We will also discuss the methods by which direct frequency comparisons are being made between optical frequency standards around the globe, and how the data from these measurement campaigns are being used not only in the evaluation of clock systems, but also in tests of fundamental physics. We will finish by discussing applications of optical clock technology for geodesy and environmental monitoring, tests of the Standard Model and General Relativity, and how future space-based optical clocks will extend the frontier for frequency metrology, satellite navigation, and improved tests of fundamental physics.
Anne Curtis received her PhD from the Department of Physics at the University of Colorado, Boulder, USA. Her thesis research was conducted at the National Institute for Standards and Technology (NIST), Boulder, and focused on the neutral calcium optical frequency standard located there. She was then awarded a three-year Royal Society USA Research Fellowship enabling her to do postdoctoral research in the UK, where she worked with permanent-magnet-based atom chips for creating low-dimensional Bose-Einstein condensates at Imperial College London. At the end of the fellowship she joined the UK National Physical Laboratory (NPL) to initiate a project on a next-generation neutral atom frequency standard, this one made from strontium atoms held in a lattice trap. Her current research focuses on ion-based optical frequency standards, as well as molecular spectroscopy methods for detection of trace gases with relevance to industrial, environmental, and medical sectors.
Low-noise Digital Electronics for Time and Frequency Metrology
This tutorial focuses on the role of electronics in time and frequency metrology. It shows why a proper design of the electronic apparatus is a key aspect of an application: a new experiment, instrument or facility. After a brief comparison of off-the-shelf commercial versus custom solutions, the tutorial will show how to develop a custom high-performance and flexible apparatus. High performance is provided by low noise components, while flexibility is guaranteed by digital devices, in particular by Field Programmable Gate Arrays (FPGAs). Two practical examples are then provided for clarifying the advantages of this approach: 1) clock electronics for vapor cell clocks and 2) frequency dissemination through fiber links.
Claudio Eligio Calosso was born in Asti (Italy) in 1973. In 2002, he received his Ph.D. degree in communication and electronic engineering at the Polytechnic of Turin (Italy) and, in the same year, he joined to IEN. Now he is permanent researcher at INRIM (Italy), where he develops low noise digital electronics for time and frequency applications. His activities include primary frequency standards, vapor cells clocks, frequency dissemination over fiber links, phasemeters, frequency division and synthesis and, recently, real-time time scale generation. He is also interested in signal analysis, with particular attention to the role of aliasing in time interval counters and two-sample variances.
Phase Noise Measurement Techniques
Time and Frequency Division of the National Institute of Standards and Technology
Noise, present everywhere, causes a signal source to deviate from its ideal performance. This noise introduces time dependent phase and amplitude fluctuations on the signal. The spectral purity of a frequency source can be characterized in terms of phase modulation (PM) and amplitude modulation (AM) noise. This tutorial will cover the basic theory of modulation noise, the origin of different noise types, and the effects of signal manipulation such as amplification, frequency translation, and multiplication on the spectral purity of a signal. Various phase noise measurement techniques will be discussed, in particular, advantages and drawbacks of the cross-spectrum technique.
Archita Hati is an electronics engineer at the Time and Frequency Division of the National Institute of Standards and Technology. She received her M.Sc and Ph.D degrees in Physics from University of Burdwan, W.B., India, in 1992 and 2001 respectively. Her current field of research includes phase noise metrology, ultra-low noise frequency synthesis, development of low-noise microwave and opto-electronic oscillators, and vibration analysis. She is the calibration service leader for the Time and Frequency Metrology Group at NIST. In 2015 she was awarded the Allen V. Astin Measurement Science Award for developing a world-leading program of research and measurement services in phase noise.
The Physics of Atomic Clocks
Jet Propulsion Laboratory, California Institute of Technology
The basic fundamentals of atomic clocks are derived from work performed by Rabi and Ramsey in the 1930’s on magnetic resonance. In this tutorial we will introduce magnetic resonance as it applies to clocks. In particular we will describe the types of internal atomic states used in atomic clocks and will describe the Bloch sphere and how it can be used to visualize various clock interrogation methods. We will then discuss the underlying principles of several key clock technologies including optical pumping, Lamb-Dicke confinement, laser-cooling, and both neutral atom and ion trapping. Finally, we will cover some of the primary systematic frequency shifts that atomic clocks experience. These include the magnetic Zeeman shift, electric effects such as the AC Stark shift, or light shift and its various orders, collision shifts, and the Doppler shift.
Eric Burt received a B.S. degree with honors in mathematics from the University of Michigan, Ann Arbor, Michigan in 1979, a M.S. degree in physics from the University of Washington, Seattle, Washington in 1990 and a Ph.D. in physics from the University of Washington in 1995. His Ph.D. thesis, supervised by Prof. Warren Nagourney, was in the field of experimental atomic physics on the trapping and laser-cooling of single indium ions. From 1995 to 1997 he was a postdoctoral fellow at the University of Colorado, in Boulder, Colorado working with Carl Wieman and Eric Cornell on experiments with Bose-Einstein condensates including the first experiment to demonstrate a dual-species condensate and the first experiment to demonstrate higher-order (laser-like) coherence in condensate atoms. From 1997 to 2001 he worked at the U.S. Naval Observatory in Washington, D.C. developing a laser-cooled cesium fountain atomic clock. From 2001 to the present he has worked at the Jet Propulsion Laboratory, California Institute of Technology most recently as a Principal Member of Technical Staff. His work at JPL has included development of both ion and laser-cooled neutral atomic clocks and using atomic clocks to place limits on fundamental constant variation. Dr. Burt is a member of the American Physical Society, and a senior member of the IEEE. He is on the technical program committee for the IEEE Frequency Control Symposium and has served as the chair of that committee as well as vice-chair for group 3 (microwave atomic clocks). He has also served on the steering committee for the APS Topical Group on Precision Measurement and Fundamental Constants.
Atomic Time Scales
Time Department, BIPM
Realizing a time scale means having at one’s disposal atomic clocks, a measurement system, and the capacity to process data to establish an ensemble time possibly steered on the international reference time UTC. The necessary tools to realize a time scale, mostly related to the algorithms, are reviewed. The tutorial presents in some detail the time scales under the responsibility of the BIPM (TAI, UTC, UTCr and TT(BIPM)) which all provide realizations of Terrestrial Time TT, a coordinate time of the geocentric system. The ensemble of atomic clocks, the time transfer techniques and the algorithms for TAI are presented along with the achieved performance in stability and in accuracy. TAI accuracy is provided by primary frequency standards (mostly Cs fountains) regularly operated in a number of contributing time laboratories and a few secondary frequency standards. Frequency standards also form the basis for TT(BIPM), the ultimate reference time coordinate produced by the BIPM. Finally, some information is given on upcoming and future developments of atomic clocks and time transfer techniques and on their potential impact on atomic timescales.
Gérard Petit graduated as an engineer from Ecole Polytechnique, France, in 1979 and from Ecole Nationale des Sciences Géographiques, France, in 1981. He obtained a PhD in astronomy from Paris Observatory in 1994. After working in the field of geodesy at the French National Geographic Institute, he joined the International Bureau of Weights and Measures (BIPM), where he now is a Principal Research Physicist with the Time Department. His research interests concern all aspects of the elaboration and usage of timescales, especially time and frequency transfer techniques using GNSS, relativistic treatment for time and frequency applications and the use of frequency standards in generating International Atomic Time TAI. He received the 2010 European Frequency and Time Award.
Time Transfer and Dissemination Using GNSS
Department of Electrical and Computer Engineering of University of Colorado at Boulder
The first use of Global Navigation Satellite Systems (GNSS) to compare two clocks at remote location happened more than 30 years ago, using the Global Positioning System (GPS). It allowed an order of magnitude improvement in clock comparisons with respect to Loran-C, with global coverage. Today, GNSS-based time transfer is still the technique used by most timing laboratories contributing to UTC (Universal Coordinate Time) with techniques like carrier-phase and all-in-view that have been developed in addition to the initial common-view method. GNSS also remains the most common means to disseminate UTC, generally using GNSS-disciplined oscillators.
This tutorial will explain the basic mechanism of time transfer using GNSS, with a look at the most recent opportunity of using timing information from satellites belonging to different constellations, and will describe the advantages and limitations of time dissemination using global satellite systems.
Stefania Römisch is originally from Torino, Italy and received her Ph.D. in Electronic Instrumentation from Politecnico di Torino, Italy. She was with the Department of Electrical and Computer Engineering of University of Colorado at Boulder and after a few years of work as an independent contractor at Spectral Research, LLC, she joined the Time and Frequency Division of NIST in Boulder, CO. She now leads the Atomic Standards Group, whose activities include the generation of UTC(NIST), and the use of GPS and TWSTFT to contribute to Universal Coordinated Time. Her research interests span from time scale generation to the calibration of time transfer links and the development of secure time dissemination.
Optical Time-Frequency Transfer Over Fiber and Free-Space
Applied Physics Division at NIST
Optically based methods of time-frequency transfer have been developed to support long distance connections between clocks over both fiber-optic networks and free-space (i.e. the air). As with optical clocks, these methods often exploit the high coherence possible with cavity-stabilized lasers and frequency combs. I will discuss and compare the approaches of optical time-frequency transfer over fiber optics and free space. The tutorial will discuss the basics of fiber-optic based methods, which are now well-developed and varied, and will then focus in more detail on recent work in free-space time-frequency transfer.
Nathan Newbury leads the Fiber Sources and Applications group in the Applied Physics Division at NIST. He also currently serves as the acting Division Chief. He received a Ph.D. from Princeton University in 1992 and has been at NIST since 2000. His research at NIST has focused on the development and application of fiber-laser-based frequency combs, with a recent emphasis on time-frequency transfer and dual-comb spectroscopy. He is a fellow of NIST and of the Optical Society (OSA).
Roy Olsson III
Department of Electrical and Systems Engineering at the University of Pennsylvania
This tutorial will cover the fundamentals, design, applications, and different types of microacoustic resonators, including bulk acoustic wave (BAW), piezoelectric Lamb wave, and silicon MEMS resonators. The key microacoustic resonator performance metrics will be identified and related to equivalent circuit models describing the resonator electromechanical response. We will explore the different types of microresonator vibration modes, transduction mechanisms, the different materials used to realize microresonators, and the impact of these choices on microacoustic resonator performance metrics such as electromechanical coupling, quality factor, linearity, thermal stability, and aging. We will discuss how to design microacoustic resonators to achieve a targeted response. Finally, we will learn to synthesize filter and oscillator circuits utilizing microacoustic resonators and to evaluate how microacoustic resonator properties translate to filter and oscillator performance.
Roy (Troy) H. Olsson III is an Assistant Professor in the Department of Electrical and Systems Engineering at the University of Pennsylvania His research interests include materials, devices, and architectures for low-power processing of wireless, sensor, and biological signals. Prior to joining UPenn, Troy was a Program Manager in the DARPA Microsystems Technology Office (MTO), where he led multiple programs in the areas of low energy sensing and communications. From 2004 to 2014, Troy was a Principal Electronics Engineer in the MEMS Technologies Department at Sandia National Laboratories where he established research efforts in aluminum nitride and lithium niobate piezoelectric microdevices for processing of RF, inertial and optical signals. He received his Ph.D. degree in electrical engineering from the University of Michigan, Ann Arbor in 2004. His graduate research was in the areas of low-power electronics and sensor arrays for interfacing with the central nervous systems. Troy has authored more than 100 technical journal and conference papers and holds 30 patents in the areas of microelectronics and microsystems. He was awarded an R&D100 award in 2011 for his work on Microresonator Filters and Frequency References and was named the 2017 DARPA program manager of the year.
Resonant Micro/Nanoelectromechanical Systems (M/NEMS) for Quantum Engineering
Electrical Engineering, Case School of Engineering, Case Western Reserve University
An essential theme of the ongoing ‘second quantum revolution’ is to realize human-made structures and devices where ‘quantum phenomena’ can be sustained and harnessed to enable radically new approaches to information processing. These require exquisite creation and scalable fabrication of atom-like devices, design and engineering of new information carriers and transduction schemes. Only recently have quantum phenomena been incorporated into technologies for next-generation computers, sensors, and detectors that demonstrate performance characteristics rivaling those of their conventional counterparts, thus promising enormous potential for future quantum technologies. This tutorial aims to capture state-of-the-art knowledge of quantum materials, devices, and technology platforms. It will particularly focus on resonant micro/nanoelectromechanical systems (M/NEMS) in quantum regime, and their roles in quantum signal transduction, metrology, and development of hybrid quantum systems and networks.
Philip Feng is currently the Theodore L. & Dana J. Schroeder Associate Professor in EECS at the Case School of Engineering, Case Western Reserve University (CWRU). His research is primarily focused on emerging solid-state devices and integrated micro/nanosystems, especially those based on advanced semiconductors, 2D materials and heterostructures with novel properties. He received his Ph.D. in Electrical Engineering from Caltech. He was among the young engineers selected to participate in the National Academy of Engineering (NAE) 2013 U.S. Frontier of Engineering (USFOE) Symposium, and subsequently, a recipient of the NAE Grainger Foundation Frontiers of Engineering (FOE) Award in 2014. His recent awards include the NSF CAREER Award, several Best Paper Awards (with his advisees, at IEEE and American Vacuum Society (AVS) conferences), the T. Keith Glennan Fellowship, the Case School of Engineering Graduate Teaching Award (2014) and the Case School of Engineering Research Award (2015). A Senior Member of IEEE, he is serving as an associate editor of IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control (UFFC), and he has served on the Technical Program Committees (TPC) and as Track/Session Chairs for IEEE IEDM, IEEE MEMS, Transducers, IEEE IFCS, IEEE SENSORS, IEEE NANO, etc., and as the MEMS/NEMS Chair for AVS’ 61st to 63rd Int. Symposia.
Ferroelectric Thin Films for Acoustic Applications
FEMTO-ST Institute, University of Franche-Comté
The next generation of high –frequency wide-band RF filters or frequency-agile filters are urgently needed for the development of 5G infrastructures/networks/communications. This motivates further development of acoustic wave devices based on piezoelectric/ferroelectric thin films of alkali metal niobates (LiNbO3, LiTaO3, etc.), adapted to the high-frequency applications. In this tutorial, the requirements, challenges and achievements in the ferroelectric thin films and their integration with silicon technology and with acoustic devices will be presented in detail. The basic principles of crystallization and epitaxial/textured film growth used to control the film quality, morphology, roughness and orientation will be introduced. The deposition techniques enabling the control of film composition/nonstoichiometry of volatile alkali metal oxides & the methods of compositional analysis will be compared. Future prospects of potential applications and the expected performances of thin film devices are overviewed, as well.
Ausrine Bartasyte is an associate professor—chair of excellence of Labex ACTION at the Institute FEMTO-ST, University of Bourgogne Franche-Comté (Besançon, France). A. Bartasyte has an experience of 17 years in deposition of epitaxial multifunctional oxides and their heterostructures (superconductors, mixed conductors, high-k dielectrics and ferroelectrics. She received her Ph.D. in 2007 from Grenoble Institute of Technology. She was a postdoctoral research assistant in Prof. A. M. Glazer’s group at the University of Oxford, UK, working on the crystal growth of LiNbO3–LiTaO3 solid solutions. She took her sabbatical leave to Harvard University. At present, her research is focused on strain and chemical engineering of structural and physical properties of alkaline niobate/tantalate single crystals, films, heterostructures & nanostructures for miniaturized and/or integrated devices with better performance in acoustics, optics and energy harvesting.
Is it now the right time for FM MEMS inertial sensors?
Politecnico di Milano
Through a few decades, AM MEMS inertial sensors have seen enormous evolution and progress from the device topology, electronic circuits and packaging points of view, and have historically led the development of micromachining fabrication processes. The continuous demand for new functionalities and fields of application is now challenging some fundamental limits that the traditional capacitive transduction intrinsically shows.
The tutorial will briefly review the physics and working principle behind capacitive AM MEMS accelerometers and gyroscopes, with a focus on typical sources of offset drift and scale-factor drift. A system-level vision will be adopted to clarify trade-offs between sensors parameters (area), electronics parameters (consumption), packaging parameters (pressure and co-integration needs) and final performance (noise, linearity, full-scale).
The discussion will then move to alternative working principles based on frequency modulated sensing, which claim help from the frequency-control community for the development of next-generation inertial units.
Giacomo Langfelder received his MS in Electrical Engineering in 2005, and his PhD in Information Technology in 2009 from Politecnico di Milano, Italy, where he is currently an Associate Professor and Reader of MEMS and Microsensors at the Department of Electronics, Information Technology and Bioengineering.
His scientific interests include sensors, their front-end electronics, and related applications. He is now researching in the field of MEMS sensors and electronics for low-noise, low-power applications, including MEMS magnetometers operated off-resonance, MEMS gyroscopes based on nano-gauge NEMS detection, FM accelerometers and gyroscopes, micromachined ultrasonic transducers and MEMS micromirrors.
In recent years, he served as TPC member for the IEEE MEMS and the IEEE Inertial Sensors conferences, and as an Associate Editor for IEEE Sensors Letters.
Within his research, he has been tightly collaborating with industries for more than a decade. In 2014, he was the co-founder of ITmems s.r.l., a spin-off company dedicated to the development of Instrumentation for the characterization of MEMS inertial sensors.
Growth, Properties, and Applications of Al1-xScxN Thin Films
Electroceramic Thin Films Group, EPFL, Lausanne, Switzerland
The discovery of enhanced piezoelectricity in solid solutions of AlN and ScN  is certainly one of the most important events in piezoelectric MEMS. As compared to pure AlN, it brought a crucial factor 2 to 3 improvement in a number of figures of merit governing the performance of MEMS devices. The aim of this tutorial is to give an overview of the present knowledge about this material, its synthesis as thin film, its properties, and demonstrated device performance. Growth issues, phase stability of metastable AlScN, and the disturbing formation of abnormally oriented grains in otherwise perfect (0001)-textured columnar microstructures are addressed. Piezoelectric and dielectric properties obtained from experiments are compared with results from density functional theory. Figure of merits for a number of applications are presented and compared with the ones of AlN and PZT thin films. In ultrasonic devices for communication and sensors, AlScN will replace in many cases AlN. The higher coupling factors allow for the exploitation of new resonator types that previously did not reach a high enough coupling. This is the case for instance with Lamb wave resonators. The strong coupling will also help to push thin film SAW devices for wireless sensors with identification tags. A darker side of AlScN lies in its strong chemical stability. It is in fact difficult to etch the material in a selective way. This hampers for the time being the achievement of precisely patterned structures in microsonic devices with micron feature sizes. In this regard, we have to wait until industrial efforts will overcome this problem.