Nonlinear Effects in Photonic Materials - Abstract
Husakou, Anton
The interaction of light with metal-dielectric nanostructured materials has attracted significant interest in the last decades due to possible applications in nanoscience, plasmonics and information processing. Among the different geometrical structures studied up to now a metal-dielectric multilayer structure is a particularly simple , easy to create and compact device, which exhibit bandgaps [1] and shows a strongly enhanced nonlinear transmission compared with a bulk metal with the same total thickness of the metallic layers [2]. In the present talk, we report the results of a theoretical study of light propagation through a specially designed nonlinear metal-dielectric multilayer structure with a small negative linear effective dielectric constant. We predict a highly-nonlinear, bistable transmission due to the change of the effective nonlinear dielectric constant from negative (low-transmission state) to positive (high-transmission state) values. Consider a multilayer structure consisting of many thin metallic layers embedded in a dielectric with a pitch much smaller than the wavelength. An understanding of the transmission properties of such structure can be obtained using the effective-medium approach. For appropriate volume fractions of the metal and the dielectric, one can achieve a real part of the effective linear dielectric constant slightly below zero. In this case, the linear transmission is very small. However, a field inside of the slab can increase the effective dielectric constant to positive values due to the optical nonlinearity. In turn, the positive effective dielectric constant results in a high transmission and sustains the field inside of the slab. For the calculation of light transmission through this multilayer structure we use the FDTD approach for the full numerical solution of the Maxwell equations. We consider the propagation of a cw beam with a wavelength of 633 nm through a fused-silica slab with a thickness of 950 nm which incorporates 9 silver layers with thinkness of 14 nm. The effective dielectric constant of the composite with the given parameters has a small negative real part. The calculated transmitted intensity as a function of the input intensity shows a bistable behavior with a contrast of around 4 between the high-transmission and the low-transmission states. For the lower-transmission state, the intensity of the wave near the output surface is low, and this part remains effectively 'metallic'. For an input intensity in the range of GW/cm2 the system goes over into the higher-transmission state, in this case the field penetrates deeper into the structure and the real part of the average effective dielectric constant becomes about 0.05. The transient response of the considered system is not determined by the response time of the bulk silver nonlinearity, but by the feedback of the multilayer structure. We have calculated that switching to the high-transmission state occurs with a transition time below 1 ps. In conclusion, we have numerically predicted all-optical bistable switching due to sign change of the effective dielectric constant in an ultra-compact metal-dielectric multilayer structure with an overall length of only 1 micron and an ultrafast response in the order of 1 ps. [1] M. J. Bloemer and M. Scalora, Appl. Phys. Lett. 72, 1676 (1998). [2] N.N. Lepeshkin et al. Phys. Rev. Lett. 93, 123902 (2004).