Active Plasmonics: Physics and Applications.
Optical chips with sophisticated functionalities could solve the problem of cross-talk, power dissipation and interconnects that microelectronic circuits are soon expected to experience. Plasmonics, with its ability to confine and guide optical signals in structures with a footprint much smaller than the wavelength of light, promises to deliver enabling technologies to bridge the size-mismatch gap between conventional dielectric waveguides and microelectronic devices [1]. Several devices which make use of surface plasmon polaritons (SPPs) as the carrier information medium have been proposed in the past, which employ thermo-optic effects [2,3], phase transformations [4,5] and electro-optic effects [6] to modulate the amplitude of the SPP. All of the previous works recur to grating or prism coupling techniques to excite the propagating SPPs. These conventional incoupling techniques are typically bulky and therefore not amenable for on-chip large scale integration of optical functionalities. In the present work we study the physics of individual subwavelength scatterers, such as holes, grooves and slits milled in a metal film, and we demonstrate that these can act as efficient, localized, and coherent sources of SPPs. By opportunely arranging several individual scatterers according to periodic and quasi-periodic geometries, we fabricate compact planar plasmonic interferometers, which allow us to precisely measure and then modulate the propagation constants of the generated SPPs. Active manipulation of the SPP is achieved by coating the arms of the fabricated plasmonic interferometers with an active medium, consisting, for instance, of CdSe semiconductor quantum dots (QDs) or of thin perovskites oxide dielectric layers. Thanks to the highly confined nature of the SPP field and to the interference effects in the plasmonic cavity, all-optical and electro-optical modulation can be achieved at very-low power densities, in micrometer-scale planar devices [7,8].Finally, we present a design study for three-dimensional plasmonic vias, interconnects, and modulators, and investigate several schemes for coupling light into such devices, evaluating their respective power efficiency.[1] Atwater, H. A., Sci. Am. 296, 56–63 (2007).[2] Passian, A., Lereu, A.L., Arakawa, E.T., Wig, A., Thundat, T., Ferrell, T.L., Opt. Express 30, 41-43 (2005).[3] Nikolajsen, T., Leosson, K., Bozhevolnyi, S.I., Optics Communications 244, 455–459 (2005).[4] Krasavin, A.V., and Zheludev, N. I., Appl. Phys. Lett. 84, 1416-1418 (2004).[5] Krasavin, A.V., MacDonald, K.F., Zheludev, N.I., and Zayats, A.V., Appl. Phys. Lett. 85, 3369 (2004). [6] Schildkraut, J.S., Appl. Optics 27, 4587-4590 (1988)[7] Pacifici, D., Lezec, H.J. and Atwater, H.A., Nature Photon. 1, 402–406 (2007).[8] Dicken, M.J., Sweatlock, L.A., Pacifici, D., Lezec, H.J., Bhattacharya, K., and Atwater, H.A., Nano Letters (2008).