Title: Symmetry Breaking in Photonic Crystals: On-Demand Dispersion from Flatband to Dirac Cones and Multivalley dispersion

Venue: 806, T5 building, VNU University of Science, 334 Nguyen Trai, Thanh Xuan, Hanoi

Time: 10h, Tuesday, 27th February 2018

Speaker: Nguyen Hai Son

Affiliation: Ecole Centrale de Lyon – Institut des Nanotechnologies de Lyon, INL/CNRS


Abstract: Engineering the energy-momentum dispersion of photonic structures is at the heart of photonic research. In contemporary optics, two types of dispersions have been extensively studied: flatband dispersion and Dirac dispersion. The first one gives rise to localized stationary eigenstates which are extremely sensitive to disorder effects due to an infinite effective mass, thus suggests a new regime of light localization.  Being an opposite extreme to flat dispersion, Dirac dispersion corresponds to massless photonic states and enables many exotic physical features such as Klein tunneling, zero-refractive index materials and photonic topological insulator. Other than flatband and Dirac dispersions, most recently, it is also suggested that photonic multi-valley dispersion can provide squeezed light, as well as Josephson oscillation in momentum space.


In this presentation, I will show that symmetry breaking can opens a new degree of freedom to tailor energy-momentum dispersion in photonic crystal. This enables an on-demand tuning of the local density of states of the same photonic band from zero (Dirac cone dispersion) to infinity (flatband dispersion), as well as any constant density over an adjustable spectral range. As a proof-of-concept, we demonstrate experimentally the transformation of the very same photonic band from conventional quadratic shape to a Dirac dispersion, a flatband dispersion and a multivalley one. This transition is achieved by finely tuning the vertical symmetry breaking of the photonic structures. Our results provide an unprecedented degree of freedom for optical dispersion engineering in planar integrated photonic devices. As application, making use of W-shaped dispersion, we demonstrate for the first time a mono-mode micro laser emitting at high oblique angle (20 degrees), operating at room temperature, on Silicon substrate and in the telecom range.


Biography: Hai Son NGUYEN obtained his PhD at the Laboratoire Pierre Aigrain, Ecole Normale Supérieure de Paris in 2011 on single photon emission of semiconductor quantum dots. From 2011-2014, he was CNRS researcher at Laboratoire de Photonique et de Nanostructures, working on polaritonic physics for all-optical integrated circuit and gravitational analogous. He joined Ecole Centrale de Lyon, Institut des Nanotechnologies de Lyon (INL-CNRS, France) as Associate Professor since September 2014. His research topic are Perovskite-based optoelectronic devices, Intergrated silicon photonic and Novel photonic crystal concepts.