Topological Insulator Laser

Wednesday, November 2, 2016 - 2:00pm - 2:50pm
Keller 3-180
Miguel Bandres (Technion-Israel Institute of Technology)
Topological insulators are a phase of matter with an insulating bulk and conducting edges. A topological insulator is characterized by a bulk bandgap where topological gapless unidirectional edge states reside. These edge states are robust to any perturbation that does not close the bandgap. In this way, deformations of the system like disorder, strain, or imperfections have little effect on the transport of such topological edge modes. The discovery of topological insulators has subsequently motivated the search of topological systems in optics and photonics with the aim to engineer robust optical devices. In photonics, the first topological insulators were demonstrated using strong magnetic fields in microwave frequencies, and more recently at optical frequencies in a modulated photonic lattice and silicon ring resonators arrays. On this background, it is reasonable to ask: how can topological protection improve optical devices?
Here, we proposed the topological insulator laser: a photonic topological insulator that lases. The design of such a laser system is highly non-standard - a laser is an open, non-Hermitian (due to gain/loss) and nonlinear (due to saturation) system. Our model consists of an array of microring resonators arranged in a honeycomb pattern with hopping terms emulating the so called topological Haldane mode. By selecting where to add the gain (via an optical pump), the configuration of the edges and the shape of the lattice, we designed a topological system in which the topological edge-states are the first modes to lase. In this way, the lasing modes are confined to the edge of the cavity, and are topologically protected: the lasing mode is unidirectional and robust to backscattering and imperfections. This creates a laser cavity that is topological protected: robust to disorder and defects, with high slope efficiency that remains unchanged even under large disorder.
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