Fig. 1: Twisted optical fibre overview.
From: Twisted optical fibres as photonic topological insulators
a, Diagrammatic explanation of the drawing process. We rotate the preform while feeding it into the furnace to induce a twisted structure. The fibre cross-section features a notch to demonstrate that a topological mode can be guided around an arbitrarily shaped edge. The inset photograph shows a preform being twisted and the micrograph shows the fabricated fibre cross-section with light coupled into the Ge-doped cores. b, Fibre twist schematic showing the breaking of the effective time-reversal symmetry \(\widehat{{\mathcal{T}}}\) (equivalently, z-propagation symmetry) owing to the applied twist. The band structure shows Dirac points in an infinite untwisted system, which are gapped when an effective magnetic field is introduced. This infinite-lattice model captures the topology introduced through the vector potential, but misses the crucial effects of the periodicity-breaking scalar potential. c, Experimental set-up for observing the intensity profile of an excited edge. We use a supercontinuum-generating fibre as a source of white light, which we filter, and butt-couple light at a desired wavelength into our twisted fibre. d, Light has been injected into a single core on the edge of the fibre and propagated over a length of 24 mm. The injection core has been overexposed in this image to highlight the intensity distribution in the other excited cores and to show where light is initially injected (compare with Fig. 2). The edge cores are outlined for reference.
