Articles in 2012

A hybrid laser that combines silicon photonic-crystal reflectors with transfer-printed InGaAsP quantum wells offers a convenient means of realizing surface-emitting lasers on silicon.

Scientists report the observation of ultralow-power resonant optical bistability, self-induced regenerative oscillations and coherent four-wave mixing in graphene–silicon hybrid optoelectronic devices at cavity recirculating energies of a few femtojoules. The findings indicate the feasibility and versatility of such devices for use in next-generation chip-scale high-speed optical communications, radiofrequency optoelectronics and all-optical signal processing.

Researchers demonstrate an approach for upconverting near-infrared light in solar cells using an organic dye as an antenna for nanoparticles. Increased absorptivity and overall broadening of the upconverter's absorption spectrum enhance the upconversion process by a factor of around 3,300.

Researchers demonstrate the ability to multiplex and transfer data between twisted beams of light with different amounts of orbital angular momentum — a development that provides new opportunities for increasing the data capacity of free-space optical communications links.

Researchers use spatial light modulators to create beams with locally varying spatial coherence, and show that the space and spatial frequency information of the beams can be measured simultaneously.

Based on observations in crystalline MgF₂ and planar Si₃N₄ microresonators, scientists reveal that the existence of multiple and broad-beat notes in a Kerr-frequency comb is due to the formation dynamics of the comb itself. This work identifies the conditions requires for low-phase-noise performance and also helps to elucidate a number of yet-unexplained phenomena.

Researchers demonstrate a silicon nanowire photodetector whose gold electrical contacts render the device ‘invisible’. The wire and gold coating have opposing dipole moments that almost cancel each other out in the far-field. Although the net dipole moment is zero, a significant photocarrier population is generated in the wire.

Researchers experimentally demonstrate the first joint-detection receiver capable of performing a joint measurement over pulse-position-modulation codewords. This result — the largest improvement over the standard quantum limit reported to date — is accomplished by using a conditional nulling receiver, which uses optimized-amplitude coherent pulse nulling, single-photon detection and quantum feedforward.

Scientists employ a micromachining-based technology to achieve significant enhancements in light emission from highly strained germanium-on-insulator samples.

Researchers demonstrate, in both normal and degenerate rat retinas, a photovoltaic subretinal prosthesis in which the silicon photodiodes in each pixel receive power and data through pulsed near-infrared illumination.

Researchers accelerate neutral-charge atoms from rest to a speed of 191 m s⁻¹ over a distance of 10 µm in 70 ns. This method is applicable to many atomic and molecular species, including those without permanent electric or magnetic dipole moments, which is a requirement of some alternative techniques.

Researchers demonstrate that wrinkles and folds on polymer surfaces can improve the light-harvesting capabilities of solar cells, increasing external quantum efficiencies by up to 600% in the near-infrared. This fabrication method, which employs elastic instabilities of thin, layered materials, may be economical for patterning photonic structures over large areas.

By placing a thin silver grating inside a microcavity comprised of an organic semiconductor and two dielectric mirrors, researchers show that coherent emission can be selectively stimulated between in- and out-of-phase-locked arrays at room temperature. This work demonstrates that incorporating a lossy metal into a cavity does not suppress lasing.

Using a photoluminescence-based carrier multiplication mechanism recently proposed for closely spaced silicon nanocrystals in SiO₂, scientists demonstrate that adjacent nanocrystals are excited directly upon absorption of a single high-energy photon. They also demonstrate efficient carrier multiplication with an onset close to the energy conservation threshold of twice the bandgap energy.

High-efficiency fluorescent organic light-emitting diodes have been realized by employing custom-designed molecules that make it possible to convert non-radiative triplet states into radiative singlet states.

Researchers consider electromagnetic dissipation in metamaterials and plasmonic systems comprised of various materials. They predict that graphene and high-temperature superconductors may not be suitable for practical resonant metamaterial applications and are unlikely to outperform conventional metals in plasmonics. Transition metals, alkali metals and transparent conducting oxides are also discussed.

Using photonic crystal cavities with a buried heterostructure design, scientists demonstrate all-optical RAM at power levels 300 times lower than previous attempts. The 30 nW devices could enable low-power large-scale optical RAM systems for handling high-bit-rate optical signals.

Inspired by thermal expansion and refractive index changes in the nanostructures of iridescent Morpho butterfly scales, scientists demonstrate upconverted mid-wave infrared detection with a temperature sensitivity of 18–62 mK and a heat-sink-free response speed of 35–40 Hz.

Researchers demonstrate that PBDTT-DPP, a semiconducting polymer with a low bandgap of 1.44 eV, allows tandem polymer solar cells to reach power conversion efficiencies of around 8.6%.

Using electro-optically generated frequency combs, scientists demonstrate radiofrequency photonic filters that can potentially provide simultaneous high stopband attenuation, fast tunability and bandwidth reconfiguration.