Letters in 2009

Based on a passively phase-locked superposition of a dispersive wave and a soliton from two branches of a femtosecond Er-doped fibre laser, researchers demonstrate that single cycles of light can be achieved using existing fibre technology and standard free-space components. The pulses have a pulse duration of 4.3 fs, close to the shortest possible value for a data bit of information transmitted in the near-infrared.

Nanocavity plasmons are exploited as a coherent optical source with tunable energy and to actively control the radiative channels of molecules. Intense resonance enhancement of both excitation and emission, in an effect called resonant hot-electroluminescence, is demonstrated for porphyrin molecules confined inside a nanocavity.

A monolithically integrated CMOS-compatible source is demonstrated using an optical parametric oscillator based on a silicon nitride ring resonator on silicon. Generating more than 100 wavelengths simultaneously and operating at powers below 50 mW, scientists say that it may form the basis of an on-chip high-bandwidth optical network.

Through optical ‘hyper-parametric’ oscillation in a high-index silica glass microring resonator, scientists demonstrate a fully integrated CMOS-compatible low-loss multiple-wavelength source that has high differential slope efficiency at only a few tens of milliwatts of continuous-wave power. The achievement has significant implications for telecommunications and on-chip optical interconnects in computers.

Utilizing a self-referenced detection scheme based on the mode-splitting in an ultrahigh-Q microresonator, scientists realize the real-time in situ detection and sizing of single nanoparticles with radii as small as 30 nm. Labelling of the particles and a priori information on the presence of nanoparticles in the medium are not required, thus providing an effective platform for studying nanoparticles at the single-particle resolution level.

By combining Fourier transform spectroscopy with two frequency-shifted combs and cavity ring-down spectroscopy, scientists demonstrate a powerful new tool for ultrahigh sensitivity spectroscopy. The scheme can measure broadband, high-resolution spectra in tens of microseconds, does not require detector arrays and may allow tuning from terahertz to ultraviolet frequencies.

A compact source of 60-fs pulses is demonstrated, based on a semiconductor laser that is mode-locked using a saturable absorber mirror in an external cavity.

Mechanisms of distinct resonance in microcavities driven by strongly detuned single quantum dots are not well understood. Investigation of non-resonant dot–cavity coupling of individual quantum dots in micropillars now suggests a dominant role of phonon-mediated dephasing. This new perspective may have implications for single-photon sources, quantum information applications and spectroscopy.

The first observation of the Hong–Ou–Mandel coalescence of photons with orbital angular momentum (OAM) is demonstrated, and this is exploited for optimal quantum cloning of OAM-encoded qubits. OAM states may function as units of quantum information in higher-dimensional space and allow increased information content per photon.

An amplifier for terahertz pulses is demonstrated using an Auston switch to perform ultrafast gain switching in a quantum cascade laser. The approach may benefit terahertz imaging and sensing schemes as it overcomes the phenomenon of gain clamping, which usually limits the amplification available in a laser.

Adding electron-withdrawing groups to the backbone of the polymer PBDTTT is shown to increase the open-circuit voltage of photovoltaic cells, resulting in a polymer solar-cell that has a certified power-conversion efficiency of 6.77%.

It is now possible to acoustically control the transfer of electrons and holes between a quantum well and a quantum dot by exploiting the moving piezoelectric potential modulation induced by an acoustic phonon. The effect has been used to demonstrate a high-frequency single-photon source with tunable emission energy, by acoustically transferring carriers to selected quantum dots.

A natural quarter-wave retarder in the eye of a stomatopod is demonstrated to have an achromaticity in the visible wavelength regime that outperforms existing designs of synthetic optical retarders. The performance is shown to be due to compensatory birefringent effects that eliminate wavelength dependence, resulting in an almost constant retardation at 450–700 nm.

So-called photonic-crystal-excitonic-lattice polaritons can be observed by coupling excitons and Bloch waves in a periodic arrangement of GaAs/AlGaAs quantum wells. The effect can be tuned by using an electric field. These hybrid states may allow slow-light-enhanced nonlinear effects and enable observation of macroscopic coherence phenomena in solid-state systems.

A 1,340-fold increase in single-molecule fluorescence has been observed from a lithographically fabricated gold bowtie nanoantenna — approximately an order of magnitude greater than that achieved in previous reports on such structures. The improvement results from an estimated ninefold increase in quantum efficiency, caused by enhanced absorption and an increased radiative emission rate.

Single SiC whiskers can be made into infrared emitters by thermal excitation. The broadband thermal emission is coupled to the electromagnetic resonances of the whisker, allowing relatively narrowband emission at infrared frequencies. The emission frequency can be tuned by adjusting the size of the whiskers.

Exciton optoelectronic devices have been demonstrated previously at an operating temperature of 1.5 K. Here, experimental proof-of-principle for excitonic switching devices at approximately 100 K is demonstrated. Excitonic devices promise high operation speed and optoelectronic integration in compact dimensions.

A terahertz quantum cascade laser that uses a grating etched into a double-metal waveguide to greatly improve the laser's performance is reported. The grating enhances the laser's optical power extraction and provides control over its emission wavelength and beam quality, yielding a single-mode beam that has a divergence of less than 10 degrees in both axes and a power of up to 15 mW.

By exploiting the nonlinearity of on-chip silicon nanowaveguides, a parametric temporal imaging system that can compress optical waveforms in time is demonstrated, enabling generation of complex and rapidly updatable ultrafast optical waveforms.

A handheld and battery-operated far-ultraviolet plane-emission device is demonstrated. The device has low current consumption and stable operation at an output power of 0.2 mW at 225 nm, and may be useful in photochemical and biotechnological applications such as photo catalysis, sterilization and the modification of chemical substances.