Fig. 5: Observation of coherent backscattering in a VH topological interface state.
From: Observation of strong backscattering in valley-Hall photonic topological interface modes
a, Microscopy image of a photonic circuit and overlaid vertically scattered far-fields at wavelength λ = 1,557 nm. Light polarized in the x direction is excited at the input grating coupler (indicated) and guided to a PTI waveguide. The cyan box highlights the scattering site at the strip-to-intermediate waveguide interface and the red box indicates the scattering sites in the sharp bend. The black box highlights the scattered fields along the waveguide axis after the second corner, a detail of which (labelled A) is given below. b, A representative set of far-fields (labelled B–E) at wavelengths corresponding to high-ng values of the underlying topological interface state. c, Spectral resonances associated with modes A–E obtained by averaging over a small set of pixels near the corresponding arrows in b. The horizontal axis shows detuning from the resonance wavelengths, δλ. d, Spatial and spectral mapping of the scattered far-fields after the second corner and along the waveguide axis. The wavelength range corresponds to the region around the degeneracy point. The modes shown in b are highlighted. e, Detailed view of the scattered fields at the vertices of the bend corresponding to modes A–E and to a wavelength well within the topologically trivial band. Light propagating in the trivial mode is lost from the waveguide due to strong scattering at the first bend, whereas the topological mode offers protection from scattering at the bends such that scattering from both bends can be observed, which allows a clear distinction between the trivial and topological modes.
