Showing papers in "Nature Photonics in 2016"
TL;DR: In this paper, the electronic and optical properties and the recent progress in applications of 2D semiconductor transition metal dichalcogenides with emphasis on strong excitonic effects, and spin- and valley-dependent properties are reviewed.
Abstract: The electronic and optical properties and the recent progress in applications of 2D semiconductor transition metal dichalcogenides with emphasis on strong excitonic effects, and spin- and valley-dependent properties are reviewed. Recent advances in the development of atomically thin layers of van der Waals bonded solids have opened up new possibilities for the exploration of 2D physics as well as for materials for applications. Among them, semiconductor transition metal dichalcogenides, MX2 (M = Mo, W; X = S, Se), have bandgaps in the near-infrared to the visible region, in contrast to the zero bandgap of graphene. In the monolayer limit, these materials have been shown to possess direct bandgaps, a property well suited for photonics and optoelectronics applications. Here, we review the electronic and optical properties and the recent progress in applications of 2D semiconductor transition metal dichalcogenides with emphasis on strong excitonic effects, and spin- and valley-dependent properties.
2,612 citations
TL;DR: In this article, a plasmon-enhanced solar desalination device, fabricated by the self-assembly of aluminium nanoparticles into a three-dimensional porous membrane, is demonstrated.
Abstract: Self-assembling aluminium nanoparticles are used to make a plasmon-enhanced device for desalination. Plasmonics has generated tremendous excitement because of its unique capability to focus light into subwavelength volumes1, beneficial for various applications such as light harvesting2,3, photodetection4, sensing5, catalysis6 and so on. Here we demonstrate a plasmon-enhanced solar desalination device, fabricated by the self–assembly of aluminium nanoparticles into a three-dimensional porous membrane. The formed porous plasmonic absorber can float naturally on water surface, efficiently absorb a broad solar spectrum (>96%) and focus the absorbed energy at the surface of the water to enable efficient (∼90%) and effective desalination (a decrease of four orders of magnitude). The durability of the devices has also been examined, indicating a stable performance over 25 cycles under various illumination conditions. The combination of the significant desalination effect, the abundance and low cost of the materials, and the scalable production processes suggest that this type of plasmon-enhanced solar desalination device could provide a portable desalination solution.
1,567 citations
TL;DR: Perovskite quantum wells yield highly efficient LEDs spanning the visible and near-infrared as discussed by the authors. But their performance is not as good as those of traditional LEDs, and their lifetime is shorter.
Abstract: Perovskite quantum wells yield highly efficient LEDs spanning the visible and near-infrared.
1,419 citations
TL;DR: In this article, a review summarizes recent progress of single-photon emitters based on defects in solids and highlights new research directions, including photophysical properties of singlephoton emissions and efforts towards scalable system integration.
Abstract: This Review summarizes recent progress of single-photon emitters based on defects in solids and highlights new research directions. The photophysical properties of single-photon emitters and efforts towards scalable system integration are also discussed.
1,387 citations
TL;DR: In this article, the authors discuss the properties of perovskites that benefit light emission, review recent progress in perov-skite electroluminescent diodes and optically pumped lasers, and examine the remaining challenges in achieving continuous-wave and electrically driven lasing.
Abstract: The prospects for light-emitting diodes and lasers based on perovskite materials are reviewed. The field of solution-processed semiconductors has made great strides; however, it has yet to enable electrically driven lasers. To achieve this goal, improved materials are required that combine efficient (>50% quantum yield) radiative recombination under high injection, large and balanced charge-carrier mobilities in excess of 10 cm2 V−1 s−1, free-carrier densities greater than 1017 cm−3 and gain coefficients exceeding 104 cm−1. Solid-state perovskites are — in addition to galvanizing the field of solar electricity — showing great promise in photonic sources, and may be the answer to realizing solution-cast laser diodes. Here, we discuss the properties of perovskites that benefit light emission, review recent progress in perovskite electroluminescent diodes and optically pumped lasers, and examine the remaining challenges in achieving continuous-wave and electrically driven lasing.
1,306 citations
TL;DR: In this paper, the state-of-the-art technologies on photonics-based terahertz communications are compared with competing technologies based on electronics and free-space optical communications.
Abstract: This Review covers the state-of-the-art technologies on photonics-based terahertz communications, which are compared with competing technologies based on electronics and free-space optical communications. Future prospects and challenges are also discussed. Almost 15 years have passed since the initial demonstrations of terahertz (THz) wireless communications were made using both pulsed and continuous waves. THz technologies are attracting great interest and are expected to meet the ever-increasing demand for high-capacity wireless communications. Here, we review the latest trends in THz communications research, focusing on how photonics technologies have played a key role in the development of first-age THz communication systems. We also provide a comparison with other competitive technologies, such as THz transceivers enabled by electronic devices as well as free-space lightwave communications.
1,238 citations
TL;DR: In this paper, the state of the art of optical modulators based on 2D materials, including graphene, transition metal dichalcogenides and black phosphorus, is reviewed.
Abstract: Light modulation is an essential operation in photonics and optoelectronics. With existing and emerging technologies increasingly demanding compact, efficient, fast and broadband optical modulators, high-performance light modulation solutions are becoming indispensable. The recent realization that 2D layered materials could modulate light with superior performance has prompted intense research and significant advances, paving the way for realistic applications. In this Review, we cover the state of the art of optical modulators based on 2D materials, including graphene, transition metal dichalcogenides and black phosphorus. We discuss recent advances employing hybrid structures, such as 2D heterostructures, plasmonic structures, and silicon and fibre integrated structures. We also take a look at the future perspectives and discuss the potential of yet relatively unexplored mechanisms, such as magneto-optic and acousto-optic modulation.
1,158 citations
TL;DR: In this paper, single-crystal perovskite devices 2-3 mm thick exhibit 16.4% X-ray detection efficiency with sensitivity four times higher than α-Se detectors.
Abstract: Single-crystal perovskite devices 2–3 mm thick exhibit 16.4% X-ray detection efficiency with sensitivity four times higher than α-Se X-ray detectors.
1,136 citations
TL;DR: In this article, a single photon with near-unity indistinguishability was generated from quantum dots in electrically controlled cavity structures, which allowed for efficient photon collection while application of an electrical bias cancels charge noise effects.
Abstract: A single photon with near-unity indistinguishability is generated from quantum dots in electrically controlled cavity structures. The cavity allows for efficient photon collection while application of an electrical bias cancels charge noise effects.
1,049 citations
TL;DR: In this article, a novel approach for making reconfigurable optical components that are created with light in a non-volatile and reversible fashion is reported, where components are written, erased and rewritten as two-dimensional binary or greyscale patterns into a nanoscale film of phase-change material by inducing a refractive index-changing phase transition with tailored trains of femtosecond pulses.
Abstract: Photonic components with adjustable parameters, such as variable-focal-length lenses or spectral filters, which can change functionality upon optical stimulation, could offer numerous useful applications. Tuning of such components is conventionally achieved by either micro- or nanomechanical actuation of their constituent parts, by stretching or by heating. Here, we report a novel approach for making reconfigurable optical components that are created with light in a non-volatile and reversible fashion. Such components are written, erased and rewritten as two-dimensional binary or greyscale patterns into a nanoscale film of phase-change material by inducing a refractive-index-changing phase transition with tailored trains of femtosecond pulses. We combine germanium–antimony–tellurium-based films with a diffraction-limited resolution optical writing process to demonstrate a variety of devices: visible-range reconfigurable bichromatic and multi-focus Fresnel zone plates, a super-oscillatory lens with subwavelength focus, a greyscale hologram, and a dielectric metamaterial with on-demand reflection and transmission resonances.
934 citations
TL;DR: In this article, the authors resolve the long-debated issue of the nature and value of the bandgap in hexagonal boron nitride by providing evidence for an indirect bandgap at 5.955 eV and an exciton binding energy of about 130 meV.
Abstract: Scientists resolve the long-debated issue of the nature and value of the bandgap in hexagonal boron nitride by providing evidence for an indirect bandgap at 5.955 eV and an exciton binding energy of about 130 meV by means of optical spectroscopy.
TL;DR: In this article, the authors study the carrier dynamics in planar methyl ammonium lead iodide perovskite films using broadband transient absorption spectroscopy and show that the sharp optical absorption onset is due to an exciton transition that is inhomogeneously broadened with a binding energy of 9'meV.
Abstract: We study the carrier dynamics in planar methyl ammonium lead iodide perovskite films using broadband transient absorption spectroscopy. We show that the sharp optical absorption onset is due to an exciton transition that is inhomogeneously broadened with a binding energy of 9 meV. We fully characterize the transient absorption spectrum by free-carrier-induced bleaching of the exciton transition, quasi-Fermi energy, carrier temperature and bandgap renormalization constant. The photo-induced carrier temperature is extracted from the transient absorption spectra and monitored as a function of delay time for different excitation wavelengths and photon fluences. We find an efficient hot-phonon bottleneck that slows down cooling of hot carriers by three to four orders of magnitude in time above a critical injection carrier density of ∼5 × 1017 cm−3. Compared with molecular beam epitaxially grown GaAs, the critical density is an order of magnitude lower and the relaxation time is approximately three orders of magnitude longer. Hot carriers in perovskites experience slow cooling.
TL;DR: In this paper, the authors demonstrate continuous-wave InAs/GaAs quantum dot lasers directly grown on silicon substrates with a low threshold current density of 62.5 cm−2, a room-temperature output power exceeding 105mW and operation up to 120°C.
Abstract: Reliable, efficient electrically pumped silicon-based lasers would enable full integration of photonic and electronic circuits, but have previously only been realized by wafer bonding. Here, we demonstrate continuous-wave InAs/GaAs quantum dot lasers directly grown on silicon substrates with a low threshold current density of 62.5 A cm–2, a room-temperature output power exceeding 105 mW and operation up to 120 °C. Over 3,100 h of continuous-wave operating data have been collected, giving an extrapolated mean time to failure of over 100,158 h. The realization of high-performance quantum dot lasers on silicon is due to the achievement of a low density of threading dislocations on the order of 105 cm−2 in the III–V epilayers by combining a nucleation layer and dislocation filter layers with in situ thermal annealing. These results are a major advance towards reliable and cost-effective silicon-based photonic–electronic integration.
TL;DR: Femtosecond two-photon direct laser writing was used to create 100µm-scale high-performance multi-lens objectives in this paper, where the authors used a two-phase direct laser writer.
Abstract: Femtosecond two-photon direct laser writing is used to create 100-µm-scale high-performance multi-lens objectives.
TL;DR: In this article, a W/CoFeB/Pt trilayer was used to generate a 1.30 THz range of trilayers from photo-induced spin currents, the inverse spin Hall effect and a broadband Fabry-Perot resonance.
Abstract: Ultrashort pulses covering the 1–30 THz range are generated from a W/CoFeB/Pt trilayer and originate from photoinduced spin currents, the inverse spin Hall effect and a broadband Fabry–Perot resonance. The resultant peak fields are several 100 kV cm–1.
TL;DR: An inverted bulk heterojunction perovskite-PCBM solar cell with a high fill factor of 0.82 and a power conversion efficiency of up to 16.0% was fabricated by a low-temperature two-step solution process as discussed by the authors.
Abstract: An inverted bulk heterojunction perovskite–PCBM solar cell with a high fill factor of 0.82 and a power conversion efficiency of up to 16.0% was fabricated by a low-temperature two-step solution process. The cells exhibit no significant photocurrent hysteresis and their high short-circuit current density, fill factor and efficiency are attributed to the advantageous properties of the active layer, such as its high conductivity and the improved mobility and diffusion length of charge carriers. In particular, PCBM plays a critical role in improving the quality of the light-absorbing layer by filling pinholes and vacancies between perovskite grains, resulting in a film with large grains and fewer grain boundaries. Bulk heterojunction perovskite solar cells with a high fill factor are reported.
TL;DR: In this paper, the underlying concepts, breakthroughs and remaining challenges in photodetector technologies based on lead sulphide (PbS) nanocrystals have been reviewed and compared.
Abstract: Light detection is the underlying principle of many optoelectronic systems. For decades, semiconductors including silicon carbide, silicon, indium gallium arsenide and germanium have dominated the photodetector industry. They can show excellent photosensitivity but are limited by one or more aspects, such as high production cost, high-temperature processing, flexible substrate incompatibility, limited spectral range or a requirement for cryogenic cooling for efficient operation. Recently lead sulphide (PbS) nanocrystals have emerged as one of the most promising new materials for photodetector fabrication. They offer several advantages including low-cost manufacturing, solution processability, size-tunable spectral sensitivity and flexible substrate compatibility, and they have achieved figures of merit outperforming conventional photodetectors. We review the underlying concepts, breakthroughs and remaining challenges in photodetector technologies based on PbS nanocrystals.
TL;DR: In this paper, the angular momentum of light can be described by positions on a higher-order Poincare sphere, where superpositions of spin and orbital angular momentum states give rise to laser beams that have many applications.
Abstract: The angular momentum of light can be described by positions on a higher-order Poincare sphere, where superpositions of spin and orbital angular momentum states give rise to laser beams that have many applications, from microscopy to materials processing. Many techniques exist to create such beams but none so far allow their creation at the source. Here we report on a new class of laser that is able to generate all states on the higher-order Poincare sphere. We exploit geometric phase control inside a laser cavity to map polarization to orbital angular momentum, demonstrating that the orbital angular momentum degeneracy of a standard laser cavity may be broken, producing pure orbital angular momentum beams, and that generalized vector vortex beams may be created with high purity at the source. This work paves the way to new lasers for structured light based on intracavity geometric phase control. By exploiting geometric phase control inside a laser cavity to map polarization to orbital angular momentum, a new class of laser that is able to generate all states on the higher-order Poincare sphere is reported.
TL;DR: In this paper, non-magnetic non-reciprocal transparency and amplification is achieved by optomechanics using a whispering gallery microresonator, and the idea may lead to integrated all-optical isolators or non-receptive phase shifters.
Abstract: Non-magnetic non-reciprocal transparency and amplification is experimentally achieved by optomechanics using a whispering-gallery microresonator. The idea may lead to integrated all-optical isolators or non-reciprocal phase shifters.
TL;DR: In this article, a solid-state thin film for infrared-to-visible upconversion that employs lead sulphide colloidal nanocrystals as a sensitizer was proposed.
Abstract: Lead sulphide colloidal nanocrystals offer a solid-state answer for infrared-to-visible upconversion. Optical upconversion via sensitized triplet–triplet exciton annihilation converts incoherent low-energy photons to shorter wavelengths under modest excitation intensities1,2,3. Here, we report a solid-state thin film for infrared-to-visible upconversion that employs lead sulphide colloidal nanocrystals as a sensitizer. Upconversion is achieved from pump wavelengths beyond λ = 1 μm to emission at λ = 612 nm. When excited at λ = 808 nm, two excitons in the sensitizer are converted to one higher-energy state in the emitter at a yield of 1.2 ± 0.2%. Peak efficiency is attained at an absorbed intensity equivalent to less than one sun. We demonstrate that colloidal nanocrystals are an attractive alternative to existing molecular sensitizers, given their small exchange splitting, wide wavelength tunability, broadband infrared absorption, and our transient observations of efficient energy transfer. This solid-state architecture for upconversion may prove useful for enhancing the capabilities of solar cells and photodetectors.
TL;DR: In this article, a solid-state gamma-radiation detector made from solution-grown perovskites has been demonstrated for multiple practical applications, including defence, medical and research applications.
Abstract: Cheap and sensitive gamma-ray detectors are desired for defence, medical and research applications. Solid-state gamma-radiation detectors made from solution-grown perovskites have now been demonstrated for multiple practical applications.
TL;DR: The proposed photonic signal processor is capable of performing reconfigurable signal processing functions including temporal integration, temporal differentiation and Hilbert transformation and suggests great potential for chip-scale fully programmable all-optical signal processing.
Abstract: Photonic signal processing has been considered a solution to overcome the inherent electronic speed limitations. Over the past few years, an impressive range of photonic integrated signal processors have been proposed, but they usually offer limited reconfigurability, a feature highly needed for the implementation of large-scale general-purpose photonic signal processors. Here, we report and experimentally demonstrate a fully reconfigurable photonic integrated signal processor based on an InP–InGaAsP material system. The proposed photonic signal processor is capable of performing reconfigurable signal processing functions including temporal integration, temporal differentiation and Hilbert transformation. The reconfigurability is achieved by controlling the injection currents to the active components of the signal processor. Our demonstration suggests great potential for chip-scale fully programmable all-optical signal processing. Scientists experimentally demonstrate a fully configurable photonic integrated signal processor based on an InP–InGaAs material system by controlling the injection currents to the active components.
TL;DR: An acoustic wave interference effect, similar to atomic coherent population trapping, is demonstrated, in which RF-driven coherent mechanical motion is cancelled by optically-driven motion.
Abstract: Optomechanical cavities have been studied for applications ranging from sensing to quantum information science. Here, we develop a platform for nanoscale cavity optomechanical circuits in which optomechanical cavities supporting co-localized 1550 nm photons and 2.4 GHz phonons are combined with photonic and phononic waveguides. Working in GaAs facilitates manipulation of the localized mechanical mode either with a radio frequency (RF) field through the piezo-electric effect, which produces acoustic waves that are routed and coupled to the optomechanical cavity by phononic crystal waveguides, or optically through the strong photoelastic effect. Along with mechanical state preparation and sensitive readout, we use this to demonstrate an acoustic wave interference effect, similar to atomic coherent population trapping, in which RF-driven coherent mechanical motion is cancelled by optically-driven motion. Manipulating cavity optomechanical systems with equal facility through both photonic and phononic channels enables new architectures for signal transduction between the optical, electrical, and mechanical domains.
TL;DR: In this article, a hybrid QD-in-perovskite matrix was proposed to enhance radiative recombination in the dots by preventing transport-assisted trapping losses, achieving a record electroluminescence power conversion efficiency of 4.9%.
Abstract: Embedding quantum dots in a perovskite matrix yields efficient light emitters. Colloidal quantum dots (CQDs) are emerging as promising materials for constructing infrared sources in view of their tunable luminescence, high quantum efficiency and compatibility with solution processing1. However, CQD films available today suffer from a compromise between luminescence efficiency and charge transport, and this leads to unacceptably high power consumption. Here, we overcome this issue by embedding CQDs in a high-mobility hybrid perovskite matrix. The new composite enhances radiative recombination in the dots by preventing transport-assisted trapping losses; yet does so without increasing the turn-on voltage. Through compositional engineering of the mixed halide matrix, we achieve a record electroluminescence power conversion efficiency of 4.9%. This surpasses the performance of previously reported CQD near-infrared devices two-fold, indicating great potential for this hybrid QD-in-perovskite approach.
TL;DR: In this article, non-equilibrium photo-induced plasmons in a high-mobility graphene monolayer were investigated at infrared wavelengths, and the properties of carrier relaxation in heterostructures based on high-purity graphene were revealed.
Abstract: Non-equilibrium photoinduced plasmons in a high-mobility graphene monolayer are investigated at infrared wavelengths. The success of metal-based plasmonics for manipulating light at the nanoscale has been empowered by imaginative designs and advanced nano-fabrication. However, the fundamental optical and electronic properties of elemental metals, the prevailing plasmonic media, are difficult to alter using external stimuli. This limitation is particularly restrictive in applications that require modification of the plasmonic response at sub-picosecond timescales. This handicap has prompted the search for alternative plasmonic media1,2,3, with graphene emerging as one of the most capable candidates for infrared wavelengths. Here we visualize and elucidate the properties of non-equilibrium photo-induced plasmons in a high-mobility graphene monolayer4. We activate plasmons with femtosecond optical pulses in a specimen of graphene that otherwise lacks infrared plasmonic response at equilibrium. In combination with static nano-imaging results on plasmon propagation, our infrared pump–probe nano-spectroscopy investigation reveals new aspects of carrier relaxation in heterostructures based on high-purity graphene.
TL;DR: In this article, a new architecture for dual-comb spectroscopy based on all-fibre tunable frequency comb sources using standard telecommunication fibre optics components is proposed.
Abstract: Scientists propose and experimentally demonstrate a new architecture for dual-comb spectroscopy based on all-fibre tunable frequency comb sources using standard telecommunication fibre optics components, opening the way for practical dual-comb spectroscopy.
TL;DR: In this paper, the Shockley-Queisser limit for solar cells was overcome in the ferroelectric insulator BaTiO3, which is the same insulator used in this paper.
Abstract: The Shockley–Queisser limit for solar cells is overcome in the ferroelectric insulator BaTiO3.
TL;DR: Using time-stretch dispersive Fourier transform (TDFT) as mentioned in this paper, the authors directly observed the spectro-temporal dynamics of the mode-locking transition on a single-shot basis over long record lengths of ∼900,000 consecutive pulses.
Abstract: Using time-stretch dispersive Fourier transform, scientists directly observe the spectro-temporal dynamics of the mode-locking transition on a single-shot basis over long record lengths of ∼900,000 consecutive pulses.
TL;DR: In this paper, a three-photon entangled state with 3 × 3 × 2 dimensions of its orbital angular momentum is created by using two independent entangled photon pairs from two nonlinear crystals, enabling the development of a new layered quantum communication protocol.
Abstract: A three-photon entangled state with 3 × 3 × 2 dimensions of its orbital angular momentum is created by using two independent entangled photon pairs from two nonlinear crystals, enabling the development of a new layered quantum communication protocol. Forming the backbone of quantum technologies today, entanglement1,2 has been demonstrated in physical systems as diverse as photons3, ions4 and superconducting circuits5. Although steadily pushing the boundary of the number of particles entangled, these experiments have remained in a two-dimensional space for each particle. Here we show the experimental generation of the first multi-photon entangled state where both the number of particles and dimensions are greater than two. Two photons in our state reside in a three-dimensional space, whereas the third lives in two dimensions. This asymmetric entanglement structure6 only appears in multiparticle entangled states with d > 26. Our method relies on combining two pairs of photons, high-dimensionally entangled in their orbital angular momentum7. In addition, we show how this state enables a new type of ‘layered’ quantum communication protocol. Entangled states such as these serve as a manifestation of the complex dance of correlations that can exist within quantum mechanics.
TL;DR: In this article, a technique to enhance optical absorption by platinum nanoparticles is exploited for driving photocatalytic redox reactions, which can be used to enhance the performance of redox reaction.
Abstract: A technique to enhance optical absorption by platinum nanoparticles is exploited for driving photocatalytic redox reactions.