Home“Optical Nanostructures for Advanced Communication Systems ”
Dr. Marko Loncar
Friday, September 18, 2009
11:00am to 12:00pm
307 Levine
Abstract:
Wavelength-scale optical resonators can enable on-chip manipulation of photons, and will be important building blocks for optical- and quantum-communication systems. We recently demonstrated photonic crystal nanobeam cavity1,2 , fabricated in silicon, that supports modes with quality factor Q~106. Furthermore, by taking advantage of mechanical degrees of freedom of two coupled-nanobeam cavities3, we demonstrated reconfigurable optical filters that could be dynamically and reversibly tuned. In our structure, that combines NEMS with nanophotonics, an external bias voltage controls the separation (<100nm) between the nanobeams via the electrostatic force, which in turn has a strong effect on the resonant wavelength of the structure. We demonstrate tunable filters with a tuning range of ~10nm, using less than 6V of external bias and negligible steady-state power consumption. Photonic crystal nanobeam approach allows realization of ultra-high Q cavities even in materials with low and moderate refractive indices2 (1.5<n<2.5). These materials typically have a wide electronic bandgap and therefore are suitable for realization of a low-loss nanophotonic platform operating in visible. I will present our work on silicon-nitride nanobeam cavities and discuss their potential for applications in QED experiments with nanocrystal quantum emitters (e.g. colloidal quantum dots, nano-diamonds). Bright single-photon source based on diamond nanowire4, that we recently discovered, is another example of novel functionalities enabled by nanostructuring. Nitrogen vacancy (NV) color center in diamond has emerged as promising quantum emitter that combines the key advantages of isolated atomic systems with solid-state integration. In order to further improve the efficiency of NV-based quantum-emitters, it is important to enhance the collection efficiency of emitted photons. We achieved this using nanowire-antenna approach, and demonstrated an order of magnitude larger collection efficiency over devices based on bulk diamond crystals.
Biography: MARKO LONCAR is Assistant Professor of Electrical Engineering at Harvard’s School of Engineering and Applied Sciences. He received his Diploma (1997) from University of Belgrade (Serbia), and his MS (1998) and PhD (2003) degrees from CalTech, all in electrical engineering. His expertise is in nanophotonics and nanofabrication technology, with significant contributions in the areas of photonic crystal waveguides and lasers. His recent research interests include nanoscale optomechanics with emphasis on reconfigurable nanophotonics, diamond nanophotonics and quantum optics, and cavity-enhanced nonlinear optics. Dr. Loncar has co-authored 50 journal articles and has given more than 40 invited talks and seminars. He is recipient of NSF CAREER Award in 2009.