Figure 2

Experimental and theoretically simulated performance of asymmetric light propagation.

(a) SEM image of an examined composition-graded nanowire. Scale bar, 7 μm. (b) Real-color PL photograph of the nanowire under the illumination of a diffused 405-nm semiconductor laser, taken with a 405-nm notch filter. (c, d) Real-color PL photographs with local excitation at one of its ends. (e) Corresponding PL spectra at the output ends. The solid lines (red and orange) represent the experimental results and dashed lines (blue and green) representing the theoretical results, respectively. Inset is the enlarged backward output PL spectra. See Supplementary Fig. S4 for more simulation details. (f) Real-color PL photographs of the nanowire, with local excitation at different spots (E1–E5) along its length. W1–W5 and N1–N5 showing the emission of the guided light at the WBG and NBG ends, respectively. Scale bar, 7 μm. (g) Propagation distance-dependent PL integrated intensity (integral area) at the WBG end (forward) and the NBG end (backward), respectively.