  Angle-resolved second harmonic generation (SHG) spectra of ZnO microwires
show characteristic Fano resonances in the spectral vicinity of
exciton-polariton modes. The output SHG spectra after SHG interacting with
exciton polariton shows a resonant enhancement peak accompanied by a
suppression dip originating from the constructive and destructive interference
respectively. It is demonstrated that the Fano line shape, and thus the Fano
asymmetry parameter q, can be tuned by the phase-shift of the two channels. The
phase-dependent q was calculated and the model describes our experimental
results well. In particular, the phase-to-q relation unveil the crucial
information about the dynamics of the system, e.g., defining the line shape of
output SHG spectra in a superposition of quantum states.
