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

Abstract

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.

Wide-range line shape control of Fano-like resonances in all-dielectric multilayer structures based on enhanced light absorption in photochromic waveguide layers

“…However, in spite of the great efforts devoted so far, the active control of the resonances in photonic structures is still at the initial stage, and further experimental and theoretical studies are highly required. Although we have demonstrated the tuning and line shape control of the Fano-like line shape by light irradiation in the multilayer structures containing the photochromic layer, 41,42,44 the dynamical range of light control achieved was very small.…”

“…The structure of the sample is very similar to that used in our previous work of light-controllable Fano-like resonance. 44 Since both the prism and the substrate are made of SF11 glass and the multilayer structure is attached to the prism with the aid of index matching fluid, the substrate can be regarded as a part of the prism. We denote the complex refractive indices of the prism, ith layer (i = 1, 2, 3), and air, as N p , N i , and N a , respectively.…”

“…Note that the same relationships were satisfied in the samples used in our previous work. 44 Under the condition of n 3 > n 2 , n a , it is well known that the third layer with n 3 can support PWG modes; 30 a PWG mode is an EM wave that propagates inside the waveguide layer in a planar direction [x direction in Fig. 1(a)] and accompanies evanescent fields inside the adjacent layers.…”

“…Motivated by previous reports on the successful active control of strong light-matter coupling 57 and plasmonic resonances 58,59 based on photochromic responses of spiropyran (SP) molecules, we extended our previous work 41,42,44 to realize a wide-range control of the Fano-like resonance in all-dielectric structures. In this paper, we show that incorporation of a waveguide layer doped with SP molecules into the multilayer structures makes it possible to change continuously the ATR line shape by UV irradiation from the EIT-like to EIA-like line shape passing through the Fano-like line shape, which was not possible in the previous work.…”

“…[41][42][43] Furthermore, in an all-dielectric multilayer structure that also contains a DR1-doped dielectric waveguide layer, we demonstrated systematic changes in the line shape caused by blue light irradiation. 44 In exactly the same context as the active control of plasmonic resonances (active plasmonics 45 ) and electric and magnetic resonances in dielectric nanostructures, 46 the active control of the Fano-like, EIT-like, and EIA-like resonances is extremely important to push forward the resonances to real applications, such as optical modulators, switches, and circuits. During the past few years, attempts to control the Fano-like and EIT-like resonances by mechanical stresses, 47 electric fields, [48][49][50] temperature, [51][52][53] and light 41,42,44,[54][55][56] have been reported.…”