Fig. 2: In-plane steering of polaritons with misaligned crystallographic orientations.

a Illustration of tailored α-MoO₃ microribbons with different cut angles β relative to the crystallographic orientation of a common source film. b–g Optical images (b, d, f) and atomic force microscopy (AFM) images (c, e, g) of different polaritonic devices composed of a bottom α-MoO₃ film and tailored α-MoO₃ microribbons. Two α-MoO₃ microribbons with β = 45° (labeled 1) and β = 135° (labeled 2) are used in (b–g). h, j, l Near-field amplitude images corresponding to the devices in (b, d, f), respectively. The polariton propagation path is controlled by the top tailored α-MoO₃ microribbons: one deflection at the microribbon labeled 1 in (j), leading to a lateral shift of polaritons; and two deflections with opposite angles in (l), leading to a final undeflected transmitted beam. Red-dashed arrows indicate the polariton propagation direction dictated by the Poynting vector S, as obtained from the IFCs analysis presented in (i, k, m). The thicknesses of the bottom film and top ribbons are t₀ = 184 nm and t₁ = 154 nm in (h, j, l). Scale bars in (b, d, f, h, j, l) indicate 3 μm. i, k, m Calculated isofrequency contours of polaritons (blue curves) corresponding to each region in the devices. Horizontal black lines (labeled ①-④) indicate interfaces between different regions. Red arrows represent Poynting vectors S, directed along the energy flow and normal to the IFCs. Scale bars indicate 20 k₀, where k₀ indicates the incident wavevector.