Advanced Photonics associate editor Dr. Jennifer Dionne interviewed Dr. Harry Atwater, Otis Booth Leadership Chair of the Division of Engineering and Applied Science at Caltech, Howard Hughes Professor of Applied Physics and Material Science, and director of the Liquid Sunlight Alliance.

Low-Earth orbit, the primary operational domain for the international space station and commercial satellites, presents a severe thermodynamic environment for spacecraft. Current testing methodologies, such as thermal cycling and damp-heat assessments, are inadequately aligned with the characteristics of perovskites. The commentary suggests a tiered thermal stress testing framework to enhance existing standards and support a robust and standardized framework for certification.

Laser excitation of nanoparticles can excite vibrational modes of the particles that correspond to changes in size and shape. The frequencies and lifetimes of these modes provide information about the mechanical properties of the particles, and how they interact with their environment. Studies of these modes in virus particles can thus provide unique information about viruses, and how their properties change during their lifecycle.

Lightweight augmented reality (AR) eyeglasses have been increasingly integrated into human daily life for navigation, education, training, healthcare, digital twins, maintenance, and entertainment, just to name a few. To facilitate an all-day comfortable wearing, AR glasses must have a small form factor and be lightweight while keeping a sufficiently high ambient contrast ratio, especially under outdoor diffusive sunlight conditions and low power consumption to sustain a long battery operation life. These demanding requirements pose significant challenges for present AR light engines due to the relatively low efficiency of the optical combiners. We focus on analyzing the power consumption of five commonly employed microdisplay light engines for AR glasses, including micro-LEDs, OLEDs, liquid-crystal-on-silicon, laser beam scanning, and digital light processing. Their perspectives and challenges are also discussed. Finally, adding a segmented smart dimmer in front of the AR glasses helps improve the ambient contrast ratio and reduce the power consumption significantly.

The femtosecond laser direct writing technique is a highly precise processing method that enables the rapid fabrication of three-dimensional (3D) micro- and nanoscale photonic structures in transparent materials. By focusing ultrashort laser pulses into transparent optical materials, such as crystals and glasses, it is possible to efficiently modify specific optical properties, including refractive indices and ferroelectric domains, at the laser focus. By carefully designing and optimizing the movement trajectory of the femtosecond laser, one can achieve periodic modulation of the optical features of these materials in 3D space. The resulting changes in material properties are closely linked to both the processing parameters of the femtosecond laser and the types of materials used. Through ongoing optimization of these parameters, desired periodic photonic structures can be created in specific transparent optical materials, leading to the development of 3D nonlinear photonic crystals (NPCs) and 3D waveguide arrays. Femtosecond laser direct writing breaks through the limitations of traditional techniques to fabricate 3D NPCs [e.g., 3D lithium niobate (LiNbO3) NPCs] and complex waveguide arrays (e.g., 3D helical waveguide arrays), realizing a paradigm shift in the fabrication of complex periodic photonic structures. To date, femtosecond-laser-written 3D NPCs and waveguide arrays have found extensive applications in integrated photonics, nonlinear optics, quantum optics, and topological photonics. We highlight recent advancements in femtosecond-laser-written 3D NPCs and waveguide arrays, such as pivotal breakthroughs in the fabrication of nanoscale-resolution 3D NPCs in LiNbO3. Finally, several potential research directions, such as the formation mechanism of domain wall and inducing millimeter-scale domain inversion with femtosecond Bessel beam, have been proposed at the end of this article.

Lead halide perovskites have started a new era for solar cells. However, the toxicity of lead poses a challenge for their practical applications. Replacing lead with tin provides a feasible way to reduce the toxicity of lead perovskites and can further promote the applications of perovskites. Due to their reduced toxicity with advantageous optical and electronic properties compared to their lead counterparts, tin (II) perovskites (TiPes) have attracted significant interest in recent years, not only for pursuing high-performance solar cells but also in other application fields. We aim to provide a comprehensive overview of recent advances in TiPes, covering fundamental crystal structure, optoelectronic properties, fabrication methods, and applications. A detailed comparison with lead perovskites is included, emphasizing TiPes’ unique strengths while presenting their application challenges. Finally, potential solutions to the challenges are proposed, along with a vision for their future development and potential.

The rapid advancement of renewable energy technologies is essential for combating global climate change and achieving energy sustainability. Among the various renewable sources, solar energy stands out, with silicon playing a pivotal role in solar energy conversion. However, traditional silicon-based devices often face challenges due to high surface reflectance, which limits their efficiency. The emergence of black silicon (b-Si) offers a transformative solution, thanks to its micro- and nanoscale structures that provide ultra-low reflectivity and enhanced light absorption. This makes b-Si an ideal candidate for improving solar energy devices. Beyond solar energy applications, b-Si has drawn notable interest in photonics, including applications in photodetectors, surface-enhanced Raman scattering, and imaging. This review explores b-Si comprehensively, discussing its fabrication processes, distinctive properties, and contributions to both solar energy conversion and photonic technologies. Key topics include its roles in solar cells, photoelectrochemical systems, solar thermal energy conversion, and advanced photonic devices. Furthermore, the review addresses the challenges and future directions for optimizing b-Si to facilitate its practical deployment across a range of energy and photonic applications.

Metasurface modeling, designs, and applications using computational approaches are by now well established as an essential pillar in photonics, physics, and materials science. The past years have witnessed tremendous advances in methodologies and technologies to unearth the intricate light–matter interaction and promote adaptive metadevices. They have pushed the studies of metasurfaces from early passive, reconfigurable modalities to the next generation of intelligent metasurfaces. In this review, we elaborate general architecture for intelligent metasurfaces, constructed by the algorithm layer, tunable metasurface layer, and application layer. We first discuss a variety of deep learning models, ranging from the fundamental neural networks inspired by computer science to sophisticated algorithms embedded with physical specialty, highlighting their potential in the forward prediction, inverse design, and spectral correlation of metasurfaces. We then discuss adaptive metadevices in the main applications of invisibility cloaks, smart vision, intelligent sensing, and wireless communication. Finally, we pinpoint current challenges and future perspectives to embrace the coming era of intelligent metasurfaces.

Photonic devices that exhibit both sensitivity and robustness have long been sought; yet, these characteristics are thought to be mutually exclusive; through sensitivity, a sensor responds to external stimuli, whereas robustness embodies the inherent ability of a device to withstand weathering by these same stimuli. This challenge stems from the inherent contradiction between robustness and sensitivity in wave dynamics, which require the coexistence of noise-immune sensitive states and modulation-sensitive transitions between these states. We report and experimentally demonstrate a subwavelength phase singularity in a chiral medium that is resilient to fabrication imperfections and disorder while remaining highly responsive to external stimuli. The combination of subwavelength light confinement and its robustness lays the foundation for the development of hitherto unexplored chip-scale photonics devices, enabling a simultaneous development of high-sensitivity and robust devices in both quantum and classical realms.

Hyperbolic materials are highly anisotropic optical media that provide valuable assistance in emission engineering, nanoscale light focusing, and scattering enhancement. Recently discovered organic hyperbolic materials (OHMs) with exceptional biocompatibility and tunability offer promising prospects as next-generation optical media for nanoscopy, enabling superresolution bioimaging capabilities. Nonetheless, an OHM is still less accessible to many researchers because of its rarity and narrow operating wavelength range. Here, we employ first-principles calculations to expand the number of known OHMs, including conjugated polymers with multiple assembly units. Through the systematic investigation of structural and optical properties of the target copolymers, we discover extraordinary multiband hyperbolic dispersions from candidate OHMs. This approach provides a new perspective on the molecular-scale design of broadband, low-loss OHMs. It aids in identifying potential hyperbolic material candidates applicable to optical engineering and super-resolution bioimaging, offering new insights into nanoscale light–matter interactions.

Landau–Zener (LZ) tunneling, i.e., the nonadiabatic level transition under strong parameter driving, is a fundamental concept in modern quantum mechanics. With the advent of non-Hermitian physics, research interest has been paid to the LZ tunneling involving level dissipations. However, experimental demonstrations of such an interesting non-Hermitian LZ problem remain yet elusive. By harnessing a synthetic temporal lattice using a fiber-loop circuit, we report on the first real-time measurement of non-Hermitian LZ tunneling in a dissipative two-band lattice model. An innovative approach based on mode interference is developed to measure the transient band occupancies, providing a powerful tool to explore the non-Hermitian LZ tunneling dynamics in non-orthogonal eigenmodes. We find that the loss does not change the final LZ tunneling probability but can highly affect the tunneling process by modifying the typical band occupancies oscillation behaviors. We initiate exploring intriguing LZ physics and measurements beyond the standard Hermitian paradigm, with potential applications in coherent quantum control and quantum technologies.

Super-resolution microscopy techniques have revolutionized biological imaging by breaking the optical diffraction limit, yet most methods rely on fluorescent labels that provide limited chemical information. Although vibrational imaging based on Raman and infrared (IR) spectroscopy offers intrinsic molecular contrast, achieving both high spatial resolution and high chemical specificity remains challenging due to weak signal levels. We demonstrate structured illumination mid-infrared photothermal microscopy (SIMIP) as an emerging imaging platform that provides chemical bond selectivity and high-speed, widefield detection beyond the diffraction limit. By modulating fluorescence quantum yield through vibrational infrared absorption, SIMIP enables both nanoscale spatial resolution and high-fidelity IR spectral acquisition. The synergy of enhanced resolution and chemical specificity positions SIMIP as a versatile tool for studying complex biological systems and advanced materials, offering new opportunities across biomedicine and materials science.

Although predicting light scattering by homogeneous spherical particles is a relatively straightforward problem that can be solved analytically, manipulating and studying the scattering behavior of non-spherical particles is a more challenging and time-consuming task, with a plethora of applications ranging from optical manipulation to wavefront engineering, and nonlinear harmonic generation. Recently, physics-driven machine learning (ML) has proven to be instrumental in addressing this challenge. However, most studies on Mie-tronics that leverage ML for optimization and design have been performed and validated through numerical approaches. Here, we report an experimental validation of an ML-based design method that significantly accelerates the development of all-dielectric complex-shaped meta-atoms supporting specified Mie-type resonances at the desired wavelength, circumventing the conventional time-consuming approaches. We used ML to design isolated meta-atoms with specific electric and magnetic responses, verified them within the quasi-normal mode expansion framework, and explored the effects of the substrate and periodic arrangements of such meta-atoms. Finally, we proposed implementing the designed meta-atoms to generate a third harmonic within the vacuum ultraviolet spectrum. Because the implemented method allowed for the swift transition from design to fabrication, the optimized meta-atoms were fabricated, and their corresponding scattering spectra were measured.

Organic light-emitting diodes (OLEDs) offer advantages for device-integrated transmitters for optical wireless communication because of their simple fabrication, mechanical flexibility, and integration of multiple color devices on a single substrate. However, they are generally considered to be slow due to low charge mobilities. Here, we show they can be made faster by suitable material selection and device design to achieve record-fast transmission by an OLED. We achieve a data rate of 2.9 Gbps in a 10-m data link at a bit error ratio (BER) of 5.54 × 10 - 3, corresponding to a coded data transmission rate of 2.7 Gbps after accounting for 7.15% overhead. This performance is comparable to the previous record for single-OLED transmitters but over a link 40 times longer. In addition, for a 2-m link, we obtain a record data rate of 4.0 Gbps at a BER of 5.54 × 10 - 3 (coded data rate of 3.7 Gbps). Our results show that the operational stability of OLEDs is important for high-speed operation. Thus, with synergetic developments in the stability of OLEDs for displays and lighting industries, OLEDs will become increasingly faster, expanding their applications for spectroscopy, communications, and sensing.

We investigate near-field radiative heat transfer between a current-driven graphene metasurface and an anisotropic magneto-dielectric hyperbolic metamaterial covered with a graphene metasurface according to fluctuational electrodynamics theory. Remarkably, we discover an unconventional radiative cooling flux accompanied by a heating–cooling transition. This phenomenon results from the competition between the high-frequency heating modes and low-frequency cooling modes. Our findings demonstrate a characteristic modulation of radiative heat transfer with implications for efficient thermal management applications.