Research articles

Large-scale densely integrated optical memory on a single photonic crystal chip is demonstrated. The wavelength-division-multiplexing (WDM) capabilities of nanophotonic memories are exploited for optical addressing. This work may enable optical random-access memories and a large-scale WDM photonic network-on-chip.

A new ‘photon–photon collider’, which may enable elusive Breit–Wheeler pair production in an optics laboratory setting, is predicted. Using this concept, it is potentially possible to produce 10⁵ Breit–Wheeler electron–positron pairs by firing a gamma-ray beam into a high-temperature radiation field of a laser-heated hohlraum cavity.

Recent demonstrations of modulators, polarization rotators and isolators have indicated the potential of graphene for photonic applications. The present study investigates the fundamental limits and near-optimal design of graphene modulators and non-reciprocal devices.

Theoretical analysis reveals that spasers do not differ fundamentally from conventional semiconductor lasers; differences are mainly technical and result from loss in the metal. Spasers are shown to have significantly inferior threshold currents and linewidths to those of vertical-cavity surface-emitting lasers, but their speed can be slightly greater.

High-resolution diffuse optical tomography employing a large array of light sources and detectors arranged around the head can perform functional brain imaging. It provides an alternative to magnetic resonance imaging for monitoring activity in different areas of the brain.

By integrating a photoacoustic transmitter based on a carbon nanotube nanocomposite and an optical microring resonator as an ultrasonic sensor, a low-noise terahertz pulse detection system is demonstrated at room temperature. The response time and the noise-equivalent detectability energy are on the order of 0.1 µs and 220 pJ, respectively.

Frequency combs based on terahertz quantum cascade lasers, which combine the high power of lasers with the broadband capabilities of pulsed sources, are demonstrated. The frequency combs generate 5 mW of terahertz power covering a frequency range of almost 500 GHz and produce more than 70 lines at 3.5 THz.

An investigation of the use of nonlinear upconversion effects like second-harmonic generation and four-wave mixing within biological tissue indicates that it should be possible to perform photodynamic therapy with near-infrared laser light at greater depths than previously.

The integration of germanium quantum-well devices and low-loss waveguides with silicon substrates shows promise for realizing low-loss, on-chip photonic interconnects.

Little attention has been devoted to development and characterization of below-threshold harmonic sources, which are critical for extending time-resolved photoemission spectroscopy to megahertz repetition rates and for developing high-average-power vacuum-ultraviolet sources. Now, a new regime of below-threshold harmonic generation accompanied by the bright, coherent emission of vacuum-ultraviolet lines is reported.

Perovskite solar cells containing tin rather than lead, which is usually employed, are reported. These cells have a power conversion efficiency of 5.7% and retain 80% of their performance over a period of 12 hours.

Cavity-stimulated Raman spin-flip emission is demonstrated by coupling a negatively charged InAs/GaAs quantum dot to a photonic crystal defect cavity. The emission is spectrally narrow and tunable over a range of about 125 GHz. The process can be made spin selective by tuning the scattered photons to be in resonance with the cavity.

An optical parametric oscillator in the telecom wavelength range is realized in a diamond system consisting of a ring resonator coupled to a diamond waveguide. Threshold powers as low as 20 mW are measured and up to 20 new wavelengths are generated from a single-frequency pump laser.

With the help of two photonic controlled-NOT gates, a three-logical-qubit concatenated Greenberger–Horne–Zeilinger (C-GHZ) state encoded by a six-photon graph state is experimentally created. Observation of the dynamics of distillability evolving under a collective noisy environment revealed that the C-GHZ state is more robust than the conventional GHZ state.

The first X-ray-pump–X-ray-probe measurement of the nonlinear response of a plasma amplifier perturbed by a ultrashort soft-X-ray pulse is demonstrated. Two time-delayed 18.9-nm-wavelength pulses were incident on a plasma, and the gain depletion induced by saturated amplification of the pump was measured with a femtosecond resolution.

Through shaping of colloidal particles, optical traps with prescribed force–displacement profiles are generated and are used to design a microscopic constant-force spring capable of delivering a constant piconewton-scale restoring force for displacements of several micrometres. Potential future applications include the imaging of sensitive biological membranes.

By exploiting hot-carrier injection, the photodetection capabilities of a semiconductor structure have been extended to wavelengths as long as 55 µm, which is well beyond the usual spectral limits determined by energy levels.

Kerr frequency combs are well suited for high-capacity data transmission with phase-sensitive modulation formats. This work demonstrates error-free transmission with data rates of up to 1.44 Tbit s⁻¹, spectral efficiencies of up to 6 bit s⁻¹ Hz⁻¹ and transmission distances of up to 300 km.

Researchers demonstrate a watt-class high-power, single-mode photonic-crystal laser operating continuously at room temperature. A beam quality of M² ≤ 1.1 is achieved.

Stokes-shift-engineered CdSe/CdS quantum dots are used to fabricate luminescent solar concentrators that are tens of centimetres long and do not exhibit reabsorption losses. With efficiencies of over 10% and an effective concentration factor of 4.4, they demonstrate the potential of using Stokes-shift-engineered quantum dots in large-area luminescent solar concentrators.