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Nano- and micro-scale devices for photonic signal processing

Plasmon-assisted metal nanostructures enable concentration of optical fields in sub-wavelength volumes. If active material (e.g., a quantum dot) is placed in such a nanostructure, its interaction with localized field is dramatically enhanced, leading to enhanced optical nonlinearity and manifestations of cavity quantum electrodynamics effects (e.g., increase in spontaneous emission rate), which can be used for making nanoscale nonlinear- (wavelength converters, parametric amplifiers, etc.) and quantum-optical (single-photon sources) devices.

One of the common needs of such sub-wavelength structures is the efficient coupling between them and the free space. We have designed [1] and demonstrated [2] a nanoantenna that shapes the spontaneous emission pattern from a single quantum dot into a narrow beam (see Figs. 1 and 2a).

In a quest to avoid the non-radiative relaxation inherent to active materials in plasmonic structures, we have recently studied [3] embedding of quantum dots in high-index dielectrics and observed that the high-index surrounding can significantly enhance the spontaneous emission rates (see Fig. 2 b,c) and potentially lead to the colloidal-quantum-dot-based single-photon emitters with near-nanosecond or even sub-nanosecond decay times and high fluorescence efficiency.

Fig. 1. SEM images of the top view (left) and cross-section (middle) of the plasmonic nanoantenna (slit nanoaperture surrounded by periodic corrugations), also showing the location of the quantum dot. (Right) Emission pattern of a single quantum dot with plasmonic nanoantenna, showing dramatic beam narrowing compared to the emission patterns of quantum dot on silver and glass [2]; inset shows angular emission spectra of multiple quantum dots embedded into the nanoantenna.
Fig. 2. Experimental setups of (a) home-made confocal microscope with spatially-resolving spectrometer and (b) single-quantum-dot imaging and photon-counting system. (c) Spontaneous-decay measurements for toluene, silicon, and CaF2; the straight lines are the exponential fits yielding t = 13.6, 4.6, and 25.6 ns, respectively [3]; inset shows SEM image of quantum dots deposited on a silicon substrate.

Selected publications

  1. M. Annamalai and M. Vasilyev, “Optimization of coupling from a sub-wavelength nanoaperture to the fundamental Gaussian mode,” J. Mod. Opt. 57, 1954–1960 (2010).
  2. L. Zhu, M. Annamalai, N. Stelmakh, and M. Vasilyev, “Shaping spontaneous emission from a single quantum dot into a narrow beam pattern,” Conference on Lasers and Electro-Optics / International Quantum Electronics Conference, Baltimore, MD, May 31–June 5, 2009, post-deadline paper IPDB4.
  3. L. Zhu, S. Samudrala, N. Stelmakh, and M. Vasilyev, “Spontaneous decay of CdSe / ZnS core-shell quantum dots at the air-dielectric interface,” Opt. Express 20, 3144–3151 (2012), http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-20-3-3144 ; also selected for publication in Virtual J. Biomed. Opt. 7 (3), http://www.opticsinfobase.org/vjbo/abstract.cfm?URI=oe-20-3-3144 .