Controlling Random Lasing with Three-Dimensional Plasmonic Nanorod Metamaterials.

Plasmonics has brought revolutionary advances to laser science by enabling deeply subwavelength nanolasers through surface plasmon amplification. However, the impact of plasmonics on other promising laser systems has so far remained elusive. Here, we present a class of random lasers enabled by three-dimensional plasmonic nanorod metamaterials. While dense metallic nanostructures are usually detrimental to laser performance due to absorption losses, here the lasing threshold keeps decreasing as the volume fraction of metal is increased up to ∼0.07. This is ∼460 times higher than the optimal volume fraction reported thus far. The laser supports spatially confined lasing modes and allows for efficient modulation of spectral profiles by simply tuning the polarization of the pump light. Full-field speckle-free imaging at micron-scales has been achieved by using plasmonic random lasers as the illumination sources. Our findings show that plasmonic metamaterials hold potential to enable intriguing coherent optical sources.

Broadband high-efficiency half-wave plate: a supercell-based plasmonic metasurface approach.

We design, fabricate, and experimentally demonstrate an ultrathin, broadband half-wave plate in the near-infrared range using a plasmonic metasurface. The simulated results show that the linear polarization conversion efficiency is over 97% with over 90% reflectance across an 800 nm bandwidth. Moreover, simulated and experimental results indicate that such broadband and high-efficiency performance is also sustained over a wide range of incident angles. To further obtain a background-free half-wave plate, we arrange such a plate as a periodic array of integrated supercells made of several plasmonic antennas with high linear polarization conversion efficiency, consequently achieving a reflection-phase gradient for the cross-polarized beam. In this design, the anomalous (cross-polarized) and the normal (copolarized) reflected beams become spatially separated, hence enabling highly efficient and robust, background-free polarization conversion along with broadband operation. Our results provide strategies for creating compact, integrated, and high-performance plasmonic circuits and devices.

Electrical source of surface plasmon polaritons based on hybrid Au-GaAs QW structures.

In this paper, the electrical excitation of surface plasmon polaritons (SPPs) based on a hybrid metal-semiconductor quantum well (QW) structure is investigated by finite-difference time-domain (FDTD) simulations and experiments. The metal-QW hybrid structure is made of a metal grating structure deposited on a semiconductor QW with small separation between them. When electron-hole pairs are excited using current injection into the QW, SPPs are generated and coupled out by a metal grating. The spectral and imaging measurements were performed to confirm the electrical excitation of SPPs. The hybrid structure could serve as a plasmonic source for integrated plasmonic circuits.

Plasmonic amplification with ultra-high optical gain at room temperature.

Nanoplasmonic devices are promising for next generation information and communication technologies because of their capability to confine light at subwavelength scale and transport signals with ultrahigh speeds. However, ohmic losses are inherent to all plasmonic devices so that further development of integrated plasmonics requires efficient in situ loss compensation of signals with a wavelength and polarization of choice. Here we show that CdSe nanobelt/Al2O3/Ag hybrid plasmonic waveguides allow for efficient broadband loss compensation of propagating hybrid plasmonic signals of different polarizations using an optical pump and probe technique. With an internal gain coefficient of 6755 cm(-1) at ambient condition, almost 100% of the propagation loss of TM-dominant plasmonic signals is compensated. From comparison with a similar photonic structure we attribute the fast-increasing gain at low pump intensity in hybrid plasmonic waveguides to the transfer across the metal-oxide-semiconductor interface of 'hot' electrons photogenerated by the pump light.

Enormous surface-enhanced Raman scattering from dimers of flower-like silver mesoparticles.

The surface-enhanced Raman scattering (SERS) of flower-like silver mesoparticle dimers with large hot areas is ≈10 to 100 times higher than the individual mesoparticles. The dependence of incident polarization illustrates that, even in the rough-surface mesoparticle dimer system, the coupling effect still dominates the SERS. More importantly, the micro-manipulator can be used to form dimers controlled with high SERS quality.

Cascaded logic gates in nanophotonic plasmon networks.

Optical computing has been pursued for decades as a potential strategy for advancing beyond the fundamental performance limitations of semiconductor-based electronic devices, but feasible on-chip integrated logic units and cascade devices have not been reported. Here we demonstrate that a plasmonic binary NOR gate, a 'universal logic gate', can be realized through cascaded OR and NOT gates in four-terminal plasmonic nanowire networks. This finding provides a path for the development of novel nanophotonic on-chip processor architectures for future optical computing technologies.

Quantum dot-based local field imaging reveals plasmon-based interferometric logic in silver nanowire networks.

We show that the local electric field distribution of propagating plasmons along silver nanowires can be imaged by coating the nanowires with a layer of quantum dots, held off the surface of the nanowire by a nanoscale dielectric spacer layer. In simple networks of silver nanowires with two optical inputs, control of the optical polarization and phase of the input fields directs the guided waves to a specific nanowire output. The QD-luminescent images of these structures reveal that a complete family of phase-dependent, interferometric logic functions can be performed on these simple networks. These results show the potential for plasmonic waveguides to support compact interferometric logic operations.