Research articles

A seeded free-electron laser with a two-stage harmonic upshift configuration provided tunable and coherent soft-X-ray pulses. The configuration produced single-transverse-mode, narrow-spectral-bandwidth femtosecond pulses with energies of several tens of microjoules and a low pulse-to-pulse wavelength jitter at wavelengths of 10.8 nm and below.

A simple, rapid and inexpensive nanolithography technique is demonstrated that exploits nonlinear feedback mechanisms to tightly regulate the formation of nanostructures induced by femtosecond laser pulses. The nonlocal nature of the feedback allows the nanostructures to be seamlessly stitched, resulting in large-area nanostructuring whose periodicity is uniform on a subnanometre scale.

Topological edge states of light are observed in a two-dimensional array of coupled optical ring resonators, which induce a virtual magnetic field for photons using silicon-on-insulator technology. The edge states are experimentally demonstrated to be robust against intrinsic and introduced disorder, which is a hallmark of topological order.

Transparent polymer solar cells are demonstrated that can transmit 30% of visible light and operate with a power conversion efficiency of 5.6%. The cells employ photonic crystals to trap ultraviolet and infrared light.

Polymer hydrogel patches that are capable of supporting living cells and guiding light are used to perform in-vivo optical sensing and therapy in living mice. Tasks performed include toxicity testing and glucose regulation.

A wireless communication system with a maximum data rate of 100 Gbit s⁻¹ over 20 m is demonstrated using a carrier frequency of 237.5 GHz. The photonic schemes used to generate the signal carrier and local oscillator are described, as is the fast photodetector used as a mixer for data extraction.

Silver and silicon nitride metamaterial structures with dielectric permittivities close to zero are demonstrated at visible wavelengths. In such materials, the optical phase advance during propagation can be very small.

Excitation with thermal light from a superluminescent diode is shown to yield enhanced fluorescence from both quantum dots and dyes, potentially enabling higher-sensitivity biological imaging.

The self-organization of many laser modes in phase and frequency realized by minimizing radiation losses in a cavity enables the complex wavefront required to focus light scattered by turbid samples to be generated on sub-microsecond timescales without employing electronic feedback, spatial light modulators or phase-conjugation crystals.

Tamm states on subwavelength, reconfigurable plasmonic crystals are studied in the terahertz regime. By introducing an independently controlled plasmonic defect, an electromagnetically induced transparency phenomenon is revealed.

By utilizing a microstructured optical waveguide around a microsphere, an optical anlogue of the effects of gravity on the motion of light rays is demonstrated. Both far-field gravitational-lensing effects and the critical phenomenon that occurs close to the photon sphere of astrophysical objects under hydrostatic equilibrium are experimentally demonstrated.

The transition between operation in a stable coherent state and that in a disordered turbulent state is studied in a fibre laser. The loss of coherence following the transition is associated with the appearance of solitons, which proliferate and cluster.

A confocal fluorescence microscopy scheme that maps the image to the radiofrequency spectrum by beating together two optical fields offers enhanced read-out speeds at kilohertz frame rates. It provides a new way for observing dynamic phenomena in cells.

A stretchable polymer LED is fabricated that is capable of emitting light when subjected to strains as large as 120%. A prototype 5 × 5 pixel monochrome display based on an array of these LEDs is demonstrated.

A chip-integrated graphene photodetector with a high responsivity of over 0.1 A W⁻¹, high speed and broad spectral bandwidth is realized through enhanced absorption due to near-field coupling. Under zero-bias operation, response rates above 20 GHz and an instrumentation-limited 12 Gbit s⁻¹ optical data link are demonstrated.

A CMOS-compatible photodetector based on graphene with multi-gigahertz operation ranging from the O- to U-band of telecommunication bands is demonstrated, highlighting the promise of graphene as a new material for integrated photonics.

A CMOS-compatible graphene/silicon-heterostructure photodetector formed by integrating graphene onto a silicon optical waveguide on silicon-on-insulator and operating in the near- and mid-infrared regions is demonstrated. A responsivity as high as 0.13 A W⁻¹ is obtained at a bias of 1.5 V for 2.75-μm light at room temperature.

Femtosecond laser pulses were used to heat dense matter, converting it into an extremely hot plasma. 52-times ionized gold was achieved as well as gigabar pressures, which can be exceeded only in the central hot spots of thermonuclear fusion plasmas.

A chip-compatible beamsplitter that can separate left- and right-handed circularly polarized light is promising for constructing more sophisticated integrated optical circuits. The prism-shaped device, which operates around the telecommunication wavelength of 1.5 μm, consists of a photonic crystal composed of an array of helical structures.

Previously demonstrated zero- or negative-refractive-index metamaterials at optical frequencies suffer from large ohmic losses because of the need to use metals. Metamaterials formed by stacked silicon rod unit cells allow the realization of all-dielectric impedance-matched zero-index metamaterials operating at optical frequencies, potentially benefiting the development of angular-selective optical devices.