One-Dimensional Planar Topological Laser

We report a one-dimensional (1D) planar topological laser, based on a topological interface state formed when two 1D photonic crystals with overlapping band gaps are brought into contact. We use a planar binary structure and achieve an interface state in the visible spectral region. The unit cell of each crystal is composed of two dielectric materials A and B with different refractive indices. A topological Zak phase can be ascribed to the photonic bands for such 1D crystals. The Zak phase depends on thicknesses ratio of these two materials d_A⁄d_B while the optical length of the unit cell remains constant. We incorporate a thin layer of an active organic material into the resonant structure, providing gain under an optical excitation and lasing under sufficiently strong pump energy density was observed. We show that the topological nature of the interface state leads to a topological protection i.e. stability against layer thickness ratio variations.