Multiplexing holography with orbital angular momentum
University of Shanghai for Science and Technology, China
ABSTRACT: Holography offers an approach to reconstructing both the intensity and phase information of an object under investigation and has been implemented with X-ray, electron beams, neutron beams and photons. In the area of optical holography, this technology has been applied in three-dimensional holographic display, data storage, optical encryption, holographic interferometry, and microscopy. Although, orbit angular momentum (OAM) has been exploited as an information carrier in free space, optical fibre communications, and on-chip information processing and display, the helical wavefront of an OAM bean has imposed a fundamental physical limit for its use as an information carrier in optical holography. Here, we propose the concept of OAM holography through Fourier domain division, encoding and selection, information of the reconstructed images can be carried by different orders of OAM of helical phase. Two-dimensional and three-dimensional OAM multiplexed holography in display and ultra-security all-optical encryption has been experimentally demonstrated with high orders of helicity.
BIOGRAPHY: Professor Gu is Executive Chancellor of the University Council and Distinguished Professor of University of Shanghai for Science and Technology. He was Distinguished Professor and Associate Deputy Vice-Chancellor at RMIT University and a Laureate Fellow of the Australian Research Council. He is an author of four standard reference books and has over 500 publications in nano/biophotonics. He is an elected Fellow of the Australian Academy of Science and the Australian Academy of Technological Sciences and Engineering as well as Foreign Fellow of the Chinese Academy of Engineering. He is also an elected fellow of the AIP, the OSA, the SPIE, the InstP, and the IEEE. He was President of the International Society of Optics within Life Sciences, Vice President of the Board of the International Commission for Optics (ICO) (Chair of the ICO Prize Committee) and a Director of the Board of the Optical Society of America (Chair of the International Council). He was awarded the Einstein Professorship, the W. H. (Beattie) Steel Medal, the Ian Wark Medal, the Boas Medal and the Victoria Prize for Science and Innovation. Professor Gu is a winner of the 2019 Dennis Gabor Award of SPIE.
A Revolution in Miniature Optical Clocks and Frequency Synthesizers
Kerry J. Vahala
California Institute of Technology, USA
ABSTRACT: Over the last few decades, the distinctly different strengths of photonics and electronics have been harnessed in entirely new ways by the optical frequency comb. As a bi-directional and coherent link, it has enabled sharing of performance attributes previously unique to these two worlds. The end result has been transformative for time keeping, frequency metrology, precision spectroscopy, microwave-generation, ranging and other technologies. Over the same span of time, resonantly enhanced parametric gain and four-wave mixing in high-Q microcavities were observed. And by cascading the four-wave mixing process to many orders a miniature frequency comb or `microcomb’ was demonstrated. Even more recently, the demonstration of coherently-pumped soliton mode locking in fiber resonators and in micro-resonators has been a major advance for these miniature frequency comb devices. As mode-locked optical oscillators, soliton operation provides stable repetition rates and reproducible waveforms, which are essential ingredients in all comb applications. Referred to as both `cavity solitons’ and `dissipative Kerr’ solitons, they have opened new perspectives on optical soliton physics and integrated comb systems on-a-chip. The latter includes system-level demonstration of massively-parallel WDM channel generation for coherent communication, C-band optical frequency synthesis with Hertz-level absolute accuracy, and optical clocks. In this talk the physics of soliton generation in high-Q micro-cavities that underlies these systems is reviewed. Finally, details on the integrated photonic synthesizer and its closely-related converse, the optical clock, are described.
BIOGRAPHY: Kerry Vahala is the Jenkins Professor and Professor of Applied Physics at Caltech. He has pioneered nonlinear optics in high-Q optical micro resonators. His research group has launched many of the areas of study in this field and invented optical resonators that hold the record for highest optical Q on a semiconductor chip. Vahala has applied these devices to a wide range of nonlinear phenomena and applications. This includes the first demonstration of parametric oscillation and cascaded four-wave mixing in a micro cavity - the central regeneration mechanisms for frequency micro combs; electro-optical frequency division - used in the most stable commercial K-band oscillators; and the first observation of dynamic back action in cavity optomechanical systems. His micro-resonator devices are used at the National Institute of Standards and Technology (NIST) in chip-based optical clocks and frequency synthesizers. They have also been used at the Keck II observatory in Hawaii as miniature astrocombs in the search for exoplanets. Vahala's current research is focused on the application of high-Q optical micro resonators to miniature precision metrology systems as well as monolithic optical gyroscopes. Professor Vahala was involved in the early effort to develop quantum-well lasers for optical communications and received the IEEE Sarnoff Award for his research on quantum-well laser dynamics. He has also received an Alexander von Humboldt Award for his work on ultra-high-Q optical microcavities, a NASA achievement award for application of frequency combs to exoplanet detection and is a fellow of the IEEE, the IEEE Photonics Society and the Optical Society of America.
Terahertz Frequency Topological Switches
Stanford University, USA
ABSTRACT: In this talk I will describe femtosecond-resolution crystallographic measurements probing dynamic switching responses driven by terahertz light pulses in topological Weyl semimetals, focusing on the 2D transition metal dichalcogenide WTe2. I will show that one can induce large amplitude interlayer shear oscillations with ~1% strain amplitudes, leading to a topologically distinct metastable phase not found under equilibrium conditions. Separate nonlinear optical measurements confirm that this transition is associated with a symmetry change and therefore corresponds to a transition to a topologically trivial phase. We further show that such shear strain serves as an ultrafast, energy-efficient means to induce more robust, well-separated Weyl points or to annihilate all Weyl points of opposite chirality. I will also discuss initial efforts investigating other means for manipulating the topological and ferroelectric phase diagram of this material through the application of pure electric fields and through doping/intercalation, showing a new low energy ferroelectric switching mechanism through interlayer gliding and the observation of controllable topological transport via a structural phase transition. This work defines new possibilities for ultrafast manipulation of the topological and ferroelectric properties of solids and for a topological switch operating at THz frequencies.
BIOGRAPHY: Aaron M. Lindenberg is an Associate Professor at Stanford University with joint appointments in the Department of Materials Science and Engineering and the Department of Photon Science. He received his B.A. from Columbia University in 1996 and his Ph.D. in Physics from the University of California, Berkeley in 2001. He was named a Faculty Fellow at Berkeley from 2001-2003 and then became a staff scientist at the SLAC National Accelerator Laboratory from 2003-2007. He is a winner of the DARPA Young Faculty Award, the Department of Energy Outstanding Mentor Award, the Alfred Moritz Michaelis Prize, and was named a Terman Fellow and a Chambers Faculty Scholar at Stanford and an I.I. Rabi Scholar at Columbia.