## Exciting bulk topological modes in photonic graphene

**Speaker:**Adrian Menssen, University of Oxford

**When:**February 8, 2019 (Fri), 12:00PM to 01:00PM (add to my calendar)

**Location:**SCI 352

**Hosted by:**Claudio Chamon

*This event is part of the Biophysics/Condensed Matter Seminar Series. *

Topological photonics sheds light on some of the surprising phenomena seen in condensed matter physics that arise with the appearance of topological invariants. Optical waveguides provide a well-controlled platform to investigate effects that relate to different topological phases of matter, providing insight into phenomena such as topological insulators by direct simulation of the states that are protected by the topology of the system. Previous work has largely focussed on the investigation of states that appear at the edge of domains which have different topological invariants. Here, we observe a mode associated with a topological defect in the bulk of a 2+1D photonic material by introducing a vortex distortion to an hexagonal lattice and analogous to graphene. Our photonic crystal is fabricated by writing waveguides in a glass substrate with a femtosecond laser using adaptive optics aberration correction. In order to excite the topological mode, we developed a method based on a SLM (Spatial Light Modulator) to simultaneously illuminate multiple waveguides. This allows us to excite an optical mode consisting of more than a dozen waveguides with beams of independently controlled phase, amplitude and mode-shape.