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Researchers report the observation of self-trapping of a white-light beam from an incandescent source.

A broadband, compact, all-electrically driven mid-infrared frequency comb based on a quantum cascade laser widens the scope of application of combs in this frequency range beyond that of sources which depend on a chain of optical components. A mid-infrared frequency comb Optical frequency combs are light sources that produce a comb-like spectrum, with sharp equidistant frequency modes, and have many uses in metrology and spectroscopy applications. The mid-infrared regime is particularly important for molecular fingerprinting, but so far the comb sources in this wavelength regime are bulky and rely on a chain of optical components. For wide practical applications, an electrically injected, compact scheme is desired. Andreas Hugi et al . now demonstrate a mid-infrared frequency comb generator based on a semiconductor device, a continuous-wave quantum cascade laser. Optical frequency combs 1 act as rulers in the frequency domain and have opened new avenues in many fields such as fundamental time metrology, spectroscopy and frequency synthesis. In particular, spectroscopy by means of optical frequency combs has surpassed the precision and speed of Fourier spectrometers. Such a spectroscopy technique is especially relevant for the mid-infrared range, where the fundamental rotational–vibrational bands of most light molecules are found 2 . Most mid-infrared comb sources are based on down-conversion of near-infrared, mode-locked, ultrafast lasers using nonlinear crystals 3 . Their use in frequency comb spectroscopy applications has resulted in an unequalled combination of spectral coverage, resolution and sensitivity 4 , 5 , 6 , 7 . Another means of comb generation is pumping an ultrahigh-quality factor microresonator with a continuous-wave laser 8 , 9 , 10 . However, these combs depend on a chain of optical components, which limits their use. Therefore, to widen the spectroscopic applications of such mid-infrared combs, a more direct and compact generation scheme, using electrical injection, is preferable. Here we present a compact, broadband, semiconductor frequency comb generator that operates in the mid-infrared. We demonstrate that the modes of a continuous-wave, free-running, broadband quantum cascade laser 11 are phase-locked. Combining mode proliferation based on four-wave mixing with gain provided by the quantum cascade laser leads to a phase relation similar to that of a frequency-modulated laser. The comb centre carrier wavelength is 7 micrometres. We identify a narrow drive current range with intermode beat linewidths narrower than 10 hertz. We find comb bandwidths of 4.4 per cent with an intermode stability of less than or equal to 200 hertz. The intermode beat can be varied over a frequency range of 65 kilohertz by radio-frequency injection. The large gain bandwidth and independent control over the carrier frequency offset and the mode spacing open the way to broadband, compact, all-solid-state mid-infrared spectrometers.

An artificial Kerr medium has been engineered using superconducting circuits, enabling the observation of the characteristic collapse and revival of a coherent state; this behaviour could, for example, be used in single-photon generation and quantum logic operations. Single-photon manipulation makes quantum logic Photons are ideal carriers of quantum information and a natural choice for quantum information processing, in part because they interact only weakly with the media through which they travel. But these same weak interactions make it difficult to manipulate the photons' quantum state. To create and manipulate the non-classical states of light needed for quantum information protocols, strong interactions between photons are required. Such photon–photon interactions occur in so-called Kerr media, but it has not been possible to reach a regime in which the interaction strength between individual photons exceeds the loss rate. Now Gerhard Kirchmair et al . have engineered an artificial Kerr medium using superconducting circuits that allow them to reach this regime and observe characteristic collapse and revivals of a coherent state. The authors suggest that this effect could be used in a range of quantum information protocols, such as single-photon generation, delicate measurement of photons and quantum logic operations. To create and manipulate non-classical states of light for quantum information protocols, a strong, nonlinear interaction at the single-photon level is required. One approach to the generation of suitable interactions is to couple photons to atoms, as in the strong coupling regime of cavity quantum electrodynamic systems 1 , 2 . In these systems, however, the quantum state of the light is only indirectly controlled by manipulating the atoms 3 . A direct photon–photon interaction occurs in so-called Kerr media, which typically induce only weak nonlinearity at the cost of significant loss. So far, it has not been possible to reach the single-photon Kerr regime, in which the interaction strength between individual photons exceeds the loss rate. Here, using a three-dimensional circuit quantum electrodynamic architecture 4 , we engineer an artificial Kerr medium that enters this regime and allows the observation of new quantum effects. We realize a gedanken experiment 5 in which the collapse and revival of a coherent state can be observed. This time evolution is a consequence of the quantization of the light field in the cavity and the nonlinear interaction between individual photons. During the evolution, non-classical superpositions of coherent states (that is, multi-component ‘Schrödinger cat’ states) are formed. We visualize this evolution by measuring the Husimi Q function and confirm the non-classical properties of these transient states by cavity state tomography. The ability to create and manipulate superpositions of coherent states in such a high-quality-factor photon mode opens perspectives for combining the physics of continuous variables 6 with superconducting circuits. The single-photon Kerr effect could be used in quantum non-demolition measurement of photons 7 , single-photon generation 8 , autonomous quantum feedback schemes 9 and quantum logic operations 10 .

Integrated optical circuits based on silicon-on-insulator technology are likely to become the mainstay of the photonics industry. Over recent years an impressive range of silicon-on-insulator devices has been realized, including waveguides 1 , 2 , filters 3 , 4 and photonic-crystal devices 5 . However, silicon-based all-optical switching is still challenging owing to the slow dynamics of two-photon generated free carriers. Here we show that silicon–organic hybrid integration overcomes such intrinsic limitations by combining the best of two worlds, using mature CMOS processing to fabricate the waveguide, and molecular beam deposition to cover it with organic molecules that efficiently mediate all-optical interaction without introducing significant absorption. We fabricate a 4-mm-long silicon–organic hybrid waveguide with a record nonlinearity coefficient of γ  ≈ 1 × 10 5  W −1  km −1 and perform all-optical demultiplexing of 170.8 Gb s −1 to 42.7 Gb s −1 . This is—to the best of our knowledge—the fastest silicon photonic optical signal processing demonstrated. A silicon–organic hybrid slot waveguide with a strong optical nonlinearity is demonstrated to perform ultrafast all-optical demultiplexing of high-bit-rate data streams. The approach could form the basis of compact high-speed optical processing units for future communication networks.

Temporal cavity solitons are packets of light persisting in a continuously driven nonlinear resonator. They are robust attracting states, readily excited through a phase-insensitive and wavelength-insensitive process. As such, they constitute an ideal support for bits in an optical buffer that would seamlessly combine three critical telecommunication functions, namely all-optical storage, all-optical reshaping and wavelength conversion. Here, with standard silica optical fibres, we report the first experimental observation of temporal cavity solitons. The cavity solitons are 4 ps long and are used to demonstrate storage of a data stream for more than a second. We also observe interactions of close cavity solitons, revealing for our set-up a potential capacity of up to 45,000 bits at 25 Gbit s −1 . More fundamentally, cavity solitons are localized dissipative structures. Therefore, given that silica exhibits a pure instantaneous Kerr nonlinearity, our experiment constitutes one of the simplest examples of self-organization phenomena in nonlinear optics. Using standard silica optical fibres, scientists observe temporal cavity solitons — packets of light persisting in a continuously driven nonlinear resonator. Cavity solitons 4 ps long are reported and used to demonstrate storage of a data stream for more than a second. The findings represent one of the simplest examples of self-organization phenomena in nonlinear optics.

Photonic integrated circuits are a key component 1 of future telecommunication networks, where demands for greater bandwidth, network flexibility, and low energy consumption and cost must all be met. The quest for all-optical components has naturally targeted materials with extremely large nonlinearity, including chalcogenide glasses 2 and semiconductors, such as silicon 3 and AlGaAs (ref.  4 ). However, issues such as immature fabrication technology for chalcogenide glass and high linear and nonlinear losses for semiconductors motivate the search for other materials. Here we present the first demonstration of nonlinear optics in integrated silica-based glass waveguides using continuous-wave light. We demonstrate four-wave mixing, with low (5 mW) continuous-wave pump power at λ = 1,550 nm, in high-index, doped silica glass ring resonators 5 . The low loss, design flexibility and manufacturability of our device are important attributes for low-cost, high-performance, nonlinear all-optical photonic integrated circuits. The ability to perform low-power, continuous-wave nonlinear optics, in particular four-wave mixing, is demonstrated in doped-silica-glass waveguide ring resonators. The device's low loss and ease of manufacture may make the approach suitable for nonlinear all-optical photonic integrated circuits.

Recently, the first experimental observation of a new class of non-diffracting optical beams that freely accelerate in space was reported 1 . These so-called Airy beams were shown to be useful for optical micro-manipulation of small particles 2 and for the generation of curved plasma channels in air 3 . To date, these beams have been generated only by using linear diffractive elements. Here, we show a new way of generating Airy beams by using three-wave mixing processes, which occur in asymmetric nonlinear photonic crystals. We experimentally generated a second-harmonic Airy beam and examined the tuning properties of the nonlinear interaction and propagation dynamics of the pump and second-harmonic output beams. This nonlinear generation process enables Airy beams to be obtained at new wavelengths, and opens up new possibilities for all-optical switching and manipulation of Airy beams. Airy beams have so far been generated by linear diffractive elements. Now, scientists show that they can also be created by a nonlinear process, opening the door to all-optical beam control and production at wavelengths unavailable by conventional methods.

An optimized design for a broadband Raman optical amplifier in standard single-mode fiber covering the C and L bands is presented, to be used in combination with wideband optical phase conjugation (OPC) nonlinearity compensation. The use of two Raman pumps and fiber Bragg grating reflectors at different wavelengths for the transmitted (C band) and conjugated (L band) WDM channels is proposed to extend bandwidth beyond the limits imposed by single-wavelength pumping, for a total 10 THz. Optimization of pump and reflector wavelength, as well as pump powers, allows us to achieve low asymmetry across the whole transmission band for optimal nonlinearity compensation. System performance is simulated to estimate OSNR, gain flatness and nonlinear Kerr distortion.

From the concepts of the dispersion-folded digital backward propagation (DBP) and optical phase conjugation (OPC), a hybrid optical-electronic nonlinearity-compensation scheme is proposed to enhance the system performance of the dispersion-managed transmission. The computational complexity of the proposed scheme, compared with that of the conventional DBP method, is reduced significantly while the performance penalty is negligible. The compensation efficiency of the proposed scheme has been validated in a 5 (and 9)-channel PM-16QAM system at 256 Gbit/s.

Light–matter interactions are ubiquitous, and underpin a wide range of basic research fields and applied technologies. Although optical interactions have been intensively studied, their microscopic details are often poorly understood and have so far not been directly measurable. X-ray and optical wave mixing was proposed nearly half a century ago as an atomic-scale probe of optical interactions but has not yet been observed owing to a lack of sufficiently intense X-ray sources. Here we use an X-ray laser to demonstrate X-ray and optical sum-frequency generation. The underlying nonlinearity is a reciprocal-space probe of the optically induced charges and associated microscopic fields that arise in an illuminated material. To within the experimental errors, the measured efficiency is consistent with first-principles calculations of microscopic optical polarization in diamond. The ability to probe optical interactions on the atomic scale offers new opportunities in both basic and applied areas of science. A free-electron laser provides a sufficiently intense source of X-rays to allow X-ray and optical wave mixing, here demonstrated by measuring the induced charge density and associated microscopic fields in single-crystal diamond. Now X-rays and light do mix Interactions between light and matter are central to many areas of science, but the microscopic details of how light can change matter remain unclear because of observational difficulties. These details can be probed by mixing X-rays and optical waves, an X-ray-scattering process that was proposed nearly half a century ago, but was beyond the technology of the time. Now, with the advent of free-electron lasers, X-rays of sufficient intensity have become available. In this week's Nature , Ernie Glover et al ., working with the Linac Coherent Light Source, report X-ray and optical mixing (or sum-frequency generation) in diamond. The new capability may enable direct visualization of the making and breaking of chemical bonds.