Fig. 3. Principle and modulation of the asymmetric photon transport.

(A) Schematic of the exciton diffusion in the absence and presence of an external electric field. With respect to the exciton diffusion without the electric field effect, the applied electric field would alter the exciton diffusion ability through the extra interaction potential V_ext = −μ_e·E, resulting in the increase or decrease in the local potential. (B) Schematic depiction of the spatial relationship between BPEA molecular transition dipole moment (blue arrows) and the growth direction (red arrow) of the nanowire. The projection of the transition dipole (light blue arrow) leans at an angle of 45° to the long wire axis. (C) Plots of forward and backward photoluminescence intensity modulations at 610 nm versus α. (D) I_forward/I_backward versus α at an electric field strength of 1.0 × 10⁶ V/m. The line is fitted with the cos(α − 45°) function. Error bars represent the SD of three representative measurements.