Optical frequency combs are lightwaves composed of a large number of equidistant spectral lines. They are important for metrology, spectroscopy, communications and fundamental science. Frequency combs are most often generated by exciting dissipative solitons in lasers or in passive resonators, both of which suffer from important limitations. Here we show that the advantages of each platform can be

Sources of quantum light, in particular correlated photon pairs that are indistinguishable for all degrees of freedom, are the fundamental resource for photonic quantum computation and simulation. Although such sources have been recently realized using integrated photonics, they offer limited ability to tune the spectral and temporal correlations between generated photons because they rely on a single

One of the most fascinating aspects of quantum networks is their capability to distribute entanglement as a nonlocal communication resource1. In a first step, this requires network-ready devices that can generate and store entangled states2. Another crucial step, however, is to develop measurement techniques that allow for entanglement detection. Demonstrations for different platforms3,4,5,6,7,8,9

Photonics offers high hopes for next-generation neural network processors. Now it has been shown that even entirely using off-the-shelf photonics allows surpassing speed and energy efficiency of cutting-edge GPUs.

Colloidal quantum dots are promising photoactive materials that enable plentiful photonic and optoelectronic applications ranging from lasers, displays and photodetectors to solar cells1,2,3,4,5,6,7,8,9. However, these applications mainly utilize the linear optical properties of quantum dots, and their great potential in the broad nonlinear optical regime is still waiting for full exploration10,11

Nonlinearity in complex systems leads to pattern formation through fundamental interactions between components. With integrated photonics, precision control of nonlinearity explores novel patterns and propels applications. In particular, Kerr-nonlinear resonators support stationary states—including Turing patterns—composed of a few interfering waves, and localized solitons composed of waves across

On-chip spectrometers with compact footprints are being extensively investigated owing to their promising future in critical applications such as sensing, surveillance and spectral imaging. Most existing miniaturized spectrometers use large arrays of photodetection elements to capture different spectral components of incident light, from which its spectrum is reconstructed. Here, we demonstrate a mid-infrared

A Correction to this paper has been published: https://doi.org/10.1038/s41566-021-00817-8

Rapid progress in the development of metamaterials and metaphotonics allowed bulky optical assemblies to be replaced with thin nanostructured films, often called metasurfaces, opening a broad range of novel and superior applications of flat optics to the generation, manipulation and detection of classical light. Recently, these developments started making headway in quantum photonics, where novel opportunities

Optical-domain transient grating (TG) spectroscopy is a versatile background-free four-wave-mixing technique that is used to probe vibrational, magnetic and electronic degrees of freedom in the time domain1. The newly developed coherent X-ray free-electron laser sources allow its extension to the X-ray regime. X-rays offer multiple advantages for TG: their large penetration depth allows probing the

Optical frequency division via optical frequency combs has enabled a leap in microwave metrology, leading to noise performance never explored before. Extending this method to the millimetre-wave and terahertz-wave domains is of great interest. Dissipative Kerr solitons in integrated photonic chips offer the unique feature of delivering optical frequency combs with ultrahigh repetition rates from 10 GHz

Viscosity is an important property of out-of-equilibrium systems such as active biological materials and driven non-Newtonian fluids, and for fields ranging from biomaterials to geology, energy technologies and medicine. Non-invasive viscosity measurements typically require integration times of seconds. Here, we demonstrate measurement speeds reaching 20 μs, with uncertainty dominated by thermal molecular

The Indian scientist and passionate entrepreneur responsible for pioneering work on optical fibres and biomedical optics has passed away aged 94.

A Correction to this paper has been published: https://doi.org/10.1038/s41566-021-00816-9.

Optical acoustic sensors have gained interest for use in photoacoustic imaging systems, but can they dethrone conventional piezoelectric sensors altogether?

We demonstrate an on-chip, optoelectronic device capable of sampling arbitrary, low-energy, near-infrared waveforms under ambient conditions with sub-optical-cycle resolution. Our detector uses field-driven photoemission from resonant nanoantennas to create attosecond electron bursts that probe the electric field of weak optical waveforms. Using these devices, we sampled the electric fields of ~5 fJ

There is an ever-growing demand for artificial intelligence. Optical processors, which compute with photons instead of electrons, can fundamentally accelerate the development of artificial intelligence by offering substantially improved computing performance. There has been long-term interest in optically constructing the most widely used artificial-intelligence architecture, that is, artificial neural

Random scattering of light in disordered media is an intriguing phenomenon of fundamental relevance to various applications1. Although techniques such as wavefront shaping and transmission matrix measurements2,3 have enabled remarkable progress in advanced imaging concepts4,5,6,7,8,9,10,11, the most successful strategy to obtain clear images through a disordered medium remains the filtering of ballistic

An exclusive advantage of semiconductor spintronics is its potential for opto-spintronics, which will allow integration of spin-based information processing/storage with photon-based information transfer/communications. Unfortunately, progress has so far been severely hampered by the failure to generate nearly fully spin-polarized charge carriers in semiconductors at room temperature. Here we demonstrate

When the nanophotonics research community finally gets back to in-person conferences, the rooms will have empty chairs on the first row. The chairs will be reserved for Professor Mark I. Stockman.

A Correction to this paper has been published: https://doi.org/10.1038/s41566-021-00805-y.

Optical materials with colour changing abilities have been explored for use in display devices1, smart windows2,3 or in the modulation of visual appearance4,5,6. The efficiency of these materials, however, has strong wavelength dependence, which limits their functionality to a specific spectral range. Here, we report graphene-based electro-optical devices with unprecedented optical tunability covering

Imaging evanescent waves is of crucial importance for sub-wavelength-scale investigation of various phenomena. However, frequently used techniques for near-field imaging require either a strong perturbation of the field, long acquisition times or complex electron-based tools. Here, we introduce nonlinear near-field optical microscopy (NNOM), which is capable of real-time evanescent wave imaging by

Four-wave mixing near atomic resonances offers new opportunities for spectral control of extreme ultraviolet pulses.

All light has structure, but only recently has it been possible to control it in all its degrees of freedom and dimensions, fuelling fundamental advances and applications alike. Here we review the recent advances in ‘pushing the limits’ with structured light, from traditional two-dimensional transverse fields towards four-dimensional spatiotemporal structured light and multidimensional quantum states

InGaN-based blue light-emitting diodes (LEDs), with their high efficiency and brightness, are entering the display industry. However, a significant gap remains between the expectation of highly efficient light sources and their experimental realization into tiny pixels for ultrahigh-density displays for augmented reality. Herein, we report using tailored ion implantation (TIIP) to fabricate highly

A Correction to this paper has been published: https://doi.org/10.1038/s41566-021-00795-x.

Laser-like radiation with a very large spectral coverage is obtained with a comb-like spectrum by concatenating nonlinear processes. Such a light source is extremely useful for detecting molecular trace gases.

We introduce MINSTED, a fluorophore localization and super-resolution microscopy concept based on stimulated emission depletion (STED) that provides spatial precision and resolution down to the molecular scale. In MINSTED, the intensity minimum of the STED doughnut, and hence the point of minimal STED, serves as a movable reference coordinate for fluorophore localization. As the STED rate, the background

A self-seeded X-ray free-electron laser (XFEL) is a promising approach to realize bright, fully coherent free-electron laser (FEL) sources in the hard X-ray domain that have been a long-standing issue with longitudinal coherence remaining challenging. At the Pohang Accelerator Laboratory XFEL, we have demonstrated a hard X-ray self-seeded XFEL with a peak brightness of 3.2 × 1035 photons s–1 mm–2 mrad–2

A Correction to this paper has been published: https://doi.org/10.1038/s41566-021-00794-y.

More atoms can not only absorb more light but, if prepared in a particular quantum state, can also do so faster than single atoms. Now, researchers have experimentally demonstrated this time-reversed process of superradiance.

Terahertz-driven acceleration has recently emerged as a route for delivering ultrashort bright electron beams efficiently, reliably and in a compact set-up. Many working schemes and key technologies related to terahertz-driven acceleration have been successfully demonstrated and are being developeds1,2,3,4,5,6,7,8,9,10. However, the achieved acceleration gradient and energy gain remain low, and the

A coherent, compact and robust light source with coverage from the ultraviolet to the infrared is desirable for heterodyne super-resolution imaging1, broadband infrared microscopy2, protein structure determination3 and standoff trace-gas detection4. To address these demanding problems, frequency combs5 combine absolute frequency accuracy with sub-femtosecond timing and waveform control to enable high-resolution

Ultrasonography1 and photoacoustic2,3 (optoacoustic) tomography have recently seen great advances in hardware and algorithms. However, current high-end systems still use a matrix of piezoelectric sensor elements, and new applications require sensors with high sensitivity, broadband detection, small size and scalability to a fine-pitch matrix. This work demonstrates an ultrasound sensor in silicon photonic

Scintillators, materials that produce light pulses upon interaction with ionizing radiation, are widely employed in radiation detectors. In advanced medical-imaging technologies, fast scintillators enabling a time resolution of tens of picoseconds are required to achieve high-resolution imaging at the millimetre length scale. Here we demonstrate that composite materials based on fluorescent metal–organic

Realizing high-peak-power (tens to hundreds of watts or higher) short-pulse (tens of picoseconds or less) operation in semiconductor lasers is crucial for state-of-the-art applications including eye-safe high-resolution remote sensing and non-thermal ultrafine material processing. However, it has been challenging to introduce mechanisms that enable stable high-peak-power short-pulse operation in conventional

Emission and absorption of light lie at the heart of light–matter interaction1. Although emission and absorption rates are regarded as intrinsic properties of atoms and molecules, various ways to modify these rates have been sought in applications such as quantum information processing2, metrology3 and light-energy harvesting4. One promising approach is to utilize collective behaviour of emitters in

The thermal quenching of light emission is a critical bottleneck that hampers the real-world application of lead halide perovskite nanocrystals in both electroluminescent and down-conversion light-emitting diodes. Here, we report CsPbBr3 perovskite nanocrystals with a temperature-independent emission efficiency of near unity and constant decay kinetics up to a temperature of 373 K. This unprecedented

The quantum repeater protocol is a promising approach for implementing long-distance quantum communication and large-scale quantum networks. A key idea of the quantum repeater protocol is to use long-lived quantum memories to achieve an efficient entanglement connection between different repeater segments, with polynomial scaling. Here, we report an experiment that realizes the efficient connection

A Correction to this paper has been published: https://doi.org/10.1038/s41566-021-00781-3.

A new paradigm is emerging in which molecular properties are controlled by modifying the local electromagnetic environment, rather than the traditional approach of changing their composition or structure. Now, a tool to investigate such effects has been demonstrated that should accelerate progress in this exciting field.

Radiation pressure exerted by light was a lifelong passion for Arthur Ashkin. He foresaw that light pressure could do useful work and invented the optical tweezers that can trap microscopic objects, from small ‘living things’ down to individual atoms.

Two independent studies employing the same narrowband deep-blue emitter, ν-DABNA, but different energy transfer schemes, achieve efficient and stable deep-blue electroluminescence.

Simultaneously achieving both a high efficiency and long lifetime in deep-blue organic light-emitting diodes is challenging. Here we report thermally activated delayed fluorescence (TADF) organic light-emitting diodes that aim to meet this goal by combining a new design of blue TADF materials with a triplet-exciton recycling protocol. Two TADF materials, one distributing and one emitting, were doped

Photonic quantum information processing, one of the leading platforms for quantum technologies1,2,3,4,5, critically relies on optical quantum interference to produce an indispensable effective photon–photon interaction. However, such an effective interaction is fundamentally limited to bunching6 due to the bosonic nature of photons7 and the restricted phase response from conventional unitary optical

Driven by narrow-linewidth bench-top lasers, coherent optical systems spanning optical communications, metrology and sensing provide unrivalled performance. To transfer these capabilities from the laboratory to the real world, a key missing ingredient is a mass-produced integrated laser with superior coherence. Here, we bridge conventional semiconductor lasers and coherent optical systems using CM

Holography is a powerful tool to record waves without loss of information that has benefited optical, X-ray and electronic imaging applications by quantifying phase delays induced by light–matter interactions. However, holographic imaging is technically demanding in that it generally requires an interferometric setup, a coherent source and long-term stability. Here, we present holographic imaging in

A Correction to this paper has been published: https://doi.org/10.1038/s41566-021-00767-1.

Artificial intelligence deployment in photonics has spawned much research activity during 2020, but optimism must be balanced by realism. This month we celebrate the advances in the field with a focus issue.

A network of quantum sensors for estimating phase shifts is shown to operate with superior sensitivity when delocalized highly entangled states are employed.

A method to quantitatively map transient electromagnetic waveforms with atomic-spatial resolution is now possible using lightwave-driven scanning tunnelling microscopy featuring a single-molecule switch.

Nature Photonics spoke to Aydogan Ozcan about the rise of artificial intelligence-enabled optics and the hurdles ahead.

Research in photonic computing has flourished due to the proliferation of optoelectronic components on photonic integration platforms. Photonic integrated circuits have enabled ultrafast artificial neural networks, providing a framework for a new class of information processing machines. Algorithms running on such hardware have the potential to address the growing demand for machine learning and artificial

Femtosecond mode-locked lasers producing visible/infrared frequency combs have steadily advanced our understanding of fundamental processes in nature. For example, optical clocks employ frequency-comb techniques for the most precise measurements of time, permitting the search for minuscule drifts of natural constants. Furthermore, the generation of extreme-ultraviolet attosecond bursts synchronized

Polarization plays a key role in science; hence its versatile manipulation is crucial. Existing polarization optics, however, can only manipulate polarization in a single transverse plane. Here we demonstrate a new class of polarizers and wave plates—based on metasurfaces—that can impart an arbitrarily chosen polarization response along the propagation direction, regardless of the incident polarization

Extreme-ultraviolet (XUV) sources including high-harmonic generation (HHG), free-electron lasers (FELs), soft-X-ray lasers and laser-driven plasmas are widely used for applications ranging from femtochemistry and attosecond science to coherent diffractive imaging and EUV (or XUV) lithography. The bandwidth of the XUV light emitted by these sources reflects the XUV generation process used. Whereas light

The invention of phase contrast microscopy revolutionized optics, enabling the visualization of highly optically transparent samples without the need for staining. The technique utilizes phase shifts within the sample and is routinely employed in the characterization of biological material and other weakly interacting objects. However, the demand for increased contrast and quantification has continued

Many physical systems display quantized energy states. In optics, interacting resonant cavities show a transmission spectrum with split eigenfrequencies, similar to the split energy levels that result from interacting states in bonded multi-atomic—that is, molecular—systems. Here, we study the nonlinear dynamics of photonic diatomic molecules in linearly coupled microresonators and demonstrate that

Distance measurements are commonly performed by phase detection based on a lock-in strategy. Super-resolution fluorescence microscopy is still striving to perform axial localization but through entirely different strategies. Here we show that an illumination modulation approach can achieve nanometric axial localization precision without compromising the acquisition time, emitter density or lateral