Time-reversal symmetry is a property shared by wave phenomena in linear stationary media. However, broken time-reversal symmetry is required for producing essential nonreciprocal devices like isolators, circulators, and gyrators. Magnetic fields can enable nonreciprocal behavior for electromagnetic waves, but this method does not translate to the microscale or to the mechanical domain, compelling us to search for nonmagnetic solutions. This talk will describe our work to exploit light-sound interactions for producing strongly nonreciprocal behavior in chip-scale resonator systems. The optomechanical physics within these devices enable fundamental experiments having analogies to quantum condensed matter phenomena, including phonon laser action, cooling, and electromagnetically induced transparency [1,2]. We demonstrate how mechanics is uniquely positioned to solve long standing challenges for photonic integrated circuits that are required for cold-atom microsystems and new quantum technologies . Moreover, the underlying nonreciprocal behavior enables robust photonic devices that are immune to backscattering induced by material defects and disorder [4,5]. Finally, we show how a synthetic Hall effect can be leveraged in optics, microwave, and acoustic domains to produce strongly nonreciprocal metamaterials .
- G. Bahl et al, Nature Physics 8(3), pp. 203-207, 2012.
- J. Kim et al, Nature Physics 11, pp. 275-280, 2015.
- D. Sohn et al, Nature Photonics 12, 91-95, 2018.
- S. Kim et al, Nature Communications 8, 205, 2017.
- S. Kim et al, Optica 6(8), pp.1016-1022, 2019.
- C.W. Peterson et al, Science Advances 4(6), eaat0232, 2018.
Dr. Gaurav Bahl is an Associate Professor of Mechanical Science and Engineering at the University of Illinois at Urbana-Champaign, and is an Affiliate in the ECE and Physics Departments. He received his PhD and MS degrees in Electrical Engineering from Stanford University in 2010 and 2008, and the BEng degree from McMaster University in 2005. Dr. Bahl has pioneered the development of Brillouin optomechanics in ultra-high-Q resonators, nonreciprocal systems, and optomechanofluidic devices for extremely high-throughput particle sensing in fluids. His work on these topics has been featured three times as a top-30 development in optics by the Optical Society of America. Presently, his group’s research focus is expanding towards high-order topological insulators, and how topological metamaterials can be exploited for engineering applications. He is a recipient of the Presidential Early Career Award for Scientists and Engineers (PECASE) in 2019, the ONR Director of Research Early Career Grant in 2016, the AFOSR Young Investigator Award in 2015, and was elevated to Senior Member of the IEEE in 2016.