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Conventional nanophotonic schemes minimise multiple scattering to realise a miniaturised version of beam-splitters, interferometers and optical cavities for light propagation and lasing. Here instead, we introduce a nanophotonic network built from multiple paths and interference, to control and enhance light-matter interaction via light localisation. The network is built from a mesh of subwavelength waveguides, and can sustain localised modes and mirror-less light trapping stemming from interference over hundreds of nodes. With optical gain, these modes can easily lase, reaching ~100 pm linewidths. We introduce a graph solution to the Maxwell’s equation which describes light on the network, and predicts lasing action. In this framework, the network optical modes can be designed via the network connectivity and topology, and lasing can be tailored and enhanced by the network shape. Nanophotonic networks pave the way for new laser device architectures, which can be used for sensitive biosensing and on-chip optical information processing. The modes of random lasers, by their very nature, are difficult to design and control. Here, Gaio, Saxena et al. demonstrate a laser based on a nanophotonic network, instead of random scatterers, which allows tailoring of the optical properties and the lasing output via the network topology.

Imaging can take many forms—from optical microscopes and telescopes through ultrasonography to X-ray tomography. However, regardless of the imaging modality, the presence of a complex heterogeneous structure between the imaging system and the scene of interest limits the quality of the images that can be conventionally obtained. In this Review we outline recently introduced strategies to overcome the detrimental effects of scattering in optical imaging. In particular, we focus on approaches that either physically correct scattering using computer-controlled devices or employ computational inversion based on intrinsic correlations of light scattering. Despite focusing on optical techniques, this Review emphasizes the fundamental equivalence of the effects of scattering in different fields of imaging, using the scattering matrix formalism as a bridge that allows techniques developed in one field to be translated to another. Seeing—and consequently imaging—through turbid media such as fog is a difficult task, as multiple scattering scrambles the visual information. This Review summarizes techniques that physically or computationally reconstruct the images.

The next generation of smart imaging and vision systems will require compact and tunable optical computing hardware to perform high-speed and low-power image processing. These requirements are driving the development of computing metasurfaces to realize efficient front-end analog optical pre-processors, especially for edge detection capability. Yet, there is still a lack of reconfigurable or programmable schemes, which may drastically enhance the impact of these devices at the system level. Here, we propose and experimentally demonstrate a reconfigurable flat optical image processor using low-loss phase-change nonlocal metasurfaces. The metasurface is configured to realize different transfer functions in spatial frequency space, when transitioning the phase-change material between its amorphous and crystalline phases. This enables edge detection and bright field imaging modes on the same device. The metasurface is compatible with a large numerical aperture of ~0.5, making it suitable for high resolution coherent optical imaging microscopy. The concept of phase-change reconfigurable nonlocal metasurfaces may enable emerging applications of artificial intelligence-assisted imaging and vision devices with switchable multitasking.

Metasurfaces can in principle provide a versatile platform for optical functionalities, but in practice designing and fabricating them to specifications can be difficult. Now, the realization of metasurfaces with engineered disorder allows for versatile optical components that combine the best features of periodic and random systems.

The control of a lens’s numerical aperture has potential applications in areas such as photography and imaging, displays, sensing, laser processing and even laser-implosion fusion. In such fields, the ability to control lens properties dynamically is of much interest, and active meta-lenses of various kinds are under investigation due to their modulation speed and compactness. However, as of yet, meta-lenses that explicitly offer dynamic control of a lens’s numerical aperture have received little attention. Here, we design and simulate active meta-lenses (specifically, focusing meta-mirrors) using chalcogenide phase-change materials to provide such control. We show that, operating at a wavelength of 3000 nm, our devices can change the numerical aperture by up to a factor of 1.85 and operate at optical intensities of the order of 1.2 × 109 Wm−2. Furthermore, we show the scalability of our design towards shorter wavelengths (visible spectrum), where we demonstrate a change in NA by a factor of 1.92.

Terahertz Nonlinear Ghost Imaging introduces a groundbreaking method for object sampling at spatial-temporal levels, achieving super-resolution (i.e., beyond the diffraction limit). Our theoretical and experimental endeavour seeks to leverage this technique, enabling arbitrary field-level waveform manipulation through intricate propagation in scattering environments. This approach facilitates essential agile waveform adjustment, made possible through near-field interactions between terahertz sources and scattering media.

Materials of which the refractive indices can be thermally tuned or switched, such as in chalcogenide phase-change alloys, offer a promising path towards the development of active optical metasurfaces for the control of the amplitude, phase, and polarization of light. However, for phase-change metasurfaces to be able to provide viable technology for active light control, in situ electrical switching via resistive heaters integral to or embedded in the metasurface itself is highly desirable. In this context, good electrical conductors (metals) with high melting points (i.e., significantly above the melting point of commonly used phase-change alloys) are required. In addition, such metals should ideally have low plasmonic losses, so as to not degrade metasurface optical performance. This essentially limits the choice to a few noble metals, namely, gold and silver, but these tend to diffuse quite readily into phase-change materials (particularly the archetypal Ge2Sb2Te5 alloy used here), and into dielectric resonators such as Si or Ge. In this work, we introduce a novel hybrid dielectric/plasmonic metasurface architecture, where we incorporated a thin Ge2Sb2Te5 layer into the body of a cubic silicon nanoresonator lying on metallic planes that simultaneously acted as high-efficiency reflectors and resistive heaters. Through systematic studies based on changing the configuration of the bottom metal plane between high-melting-point diffusive and low-melting-point nondiffusive metals (Au and Al, respectively), we explicitly show how thermally activated diffusion can catastrophically and irreversibly degrade the optical performance of chalcogenide phase-change metasurface devices, and how such degradation can be successfully overcome at the design stage via the incorporation of ultrathin Si3N4 barrier layers between the gold plane and the hybrid Si/Ge2Sb2Te5 resonators. Our work clarifies the importance of diffusion of noble metals in thermally tunable metasurfaces and how to overcome it, thus helping phase-change-based metasurface technology move a step closer towards the realization of real-world applications.

Chiral HHG detection is a novel approach to chiroptical spectroscopy, capable of characterizing molecular chirality on femtosecond timescales4. Chiroptical spectroscopy relies on a dierence between the response of le-handed and right-handed molecules to light, which in this case is observed in the HHG-maximizing ellipticity, which has opposite sign for the dierent chiralities. Furthermore, the absolute value of the HHG-maximizing ellipticity at a certain harmonic order (proportional to the emitted photon energy) reects electronic chiral dynamics. Such sub-femtosecond dynamics carry information on the density and population evolution of electronically excited states of the molecular cation transiently generated during the HHG process. Indeed, the HHG yield spectrum resulting from chiral response gives surprising insight into the chemical structure and proximal functional groups around each chiralcentre.