Jiho Noh

Experimental observation of optical Weyl points and Fermi arc-like surface states

We present the experimental observation of type-II optical Weyl points and corresponding Fermi arcs in a three-dimensional photonic structure. We employ a system composed of an array of staggered helical waveguides fabricated using the direct laser writing technique. Weyl points are established by observing conical diffraction and Fermi arcs are demonstrated by showing surface confinement (and deconfinement) at wavelengths above (below) the Weyl point.

Topological protection of photonic mid-gap defect modes

Defect modes in two-dimensional periodic photonic structures have found use in diverse optical devices. For example, photonic crystal cavities confine optical modes to subwavelength volumes and can be used for enhancement of nonlinearity, lasing and cavity quantum electrodynamics. Defect-core photonic crystal fibres allow for supercontinuum generation and endlessly single-mode fibres with large cores. However, these modes are notoriously fragile: small structural change leads to significant detuning of resonance frequency and mode volume. Here, we show that photonic topological crystalline insulator structures can be used to topologically protect the mode frequency at mid-gap and minimize the volume of a photonic defect mode. We experimentally demonstrate this in a femtosecond-laser-written waveguide array by observing the presence of a topological zero mode confined to the corner of the array. The robustness of this mode is guaranteed by a topological invariant that protects zero-dimensional states embedded in a two-dimensional environment—a novel form of topological protection that has not been previously demonstrated.Eigenmodes of photonic crystal defects have now been topologically protected in an experimental demonstration that also shows how to minimize the mode volume.

Experimental observation of optical Weyl points

We present the experimental observation of type-II optical Weyl points and corresponding Fermi arcs in a three-dimensional photonic structure. We employ a system composed of an array of staggered helical waveguides fabricated using the direct laser writing technique. Weyl points are established by observing conical diffraction and Fermi arcs are demonstrated by showing surface confinement (and deconfinement) at wavelengths above (below) the Weyl point.

Photonic topological zero-modes in a 2D lattice

We propose the realization of topological zero-modes in a two-dimensional quantum spin Hall-like photonic topological insulator structure. Unlike topological edge or surface modes, these zero-modes are point-like and thus have two fewer dimensions than their host lattice.