Light-controllable Fano resonance in azo-dye-doped all-dielectric multilayer structure

Active modulation of Fano resonance by light is demonstrated for an all-dielectric multilayer system containing an azo-dye-doped layer. The sample studied consists of a polystyrene layer doped with disperse red 1 (azo dye) molecules, a polyvinyl alcohol layer, and a pure polystyrene layer. In a Kretschmann attenuated-total-reflection configuration, angle-scan reflection spectra of the sample were measured with blue probe light under blue light pumping. The Fano line shape was found to change systematically depending on the intensity of the pump light. Analyses based on electromagnetic calculations of the spectra and field distributions in the layers indicate that the Fano resonance observed is generated by coupling between a broad half-leaky guided mode supported by the azo-dye-doped layer and a sharp planar waveguide mode supported by the pure polystyrene layer. The systematic changes in the Fano line shape under pump light irradiation can be well understood by a systematic decrease in light absorption in the azo-dye-doped polystyrene layer; the decrease in light absorption is due to a decrease in the extinction coefficient of the layer arising from the photoisomerization of azo dye molecules.