Integrated nonlinear photonics struggles to deliver wafer-scale functional device yields: Nanometer-level fabrication variations compromise the strict frequency-phase matching mandated by energy- and momentum-conserving nonlinear processes. We introduce nested frequency-phase matching, a passive scheme that relaxes these constraints, and implement it in a two-timescale lattice of commercially available silicon nitride (SiN) coupled ring resonators for harmonic generation. The nested lattice simultaneously generates ultrabroad bandwidth light in the fundamental-, second-, third-, and fourth-harmonic bands and achieves 100% multifunctional wafer-scale device yield, all passively and without geometry fine-tuning. Distinct spatial and spectral signatures confirm the predicted relaxation of frequency-phase matching, establishing a scalable route for chip-scale nonlinear optics. Our approach provides possibilities for integrated frequency conversion and synchronization, self-referencing, precision metrology, squeezed-light sources, and nonlinear optical computing.

Barium titanate BaTiO3 (BTO) is an emerging material in silicon photonics with one of the largest known linear electro-optic coefficients. However, in current BTO-based devices, high optical losses are consistently observed, typically an order of magnitude larger than those observed in thin-film lithium niobate. We present a theoretical investigation into the origin of optical loss in BTO waveguides, suggesting that the higher loss is non-absorptive and is caused by planar defects such as ferroelectric domain walls. Our results suggest that the poling of the z-cut material could reduce the loss level to that reported for Si-integrated lithium niobate.

This paper presents a numerical demonstration of the use of the adjoint method for permittivity optimization to design a dielectric medium capable of object classification at the speed of light. In a two-dimensional setup, the system comprises an input waveguide, a design region, and three output ports made of a lossless dielectric material. The design medium is optimized to guide light into specific output ports based on the type and variation of scatterers placed between the input waveguide and the design region. For proof of concept, scatterers derived from the MNIST dataset’s digits 0, 1, and 2 are used to represent different object classes with varying shapes and sizes. The optimization process dynamically adjusts the material distribution within the design region to maximize classification performance. The final structure achieved a classification accuracy of 96.3%, with light successfully directed to the correct output port corresponding to each scatterer class. This work demonstrates the potential of permittivity optimization for developing advanced photonic devices capable of ultrafast object recognition, paving the way for future research in three-dimensional designs and more complex classification tasks.

Achieving low optical loss is critical for scaling complex photonic systems. Thin-film lithium niobate (TFLN) offers strong electro-optic and nonlinear properties in a compact platform, making it ideal for quantum and nonlinear optics. While Q factors above 107 are achieved, they remain below the intrinsic material limit. A systematic study of scattering losses due to roughness in TFLN racetrack cavities is presented, with isolating contributions from sidewall and interface roughness. Quality factors up to 2.7 × 107 are demonstrated in waveguides with widths of 2.2λ (≈3.5 µm), where interface roughness dominates, and up to 1.2 × 107 in narrower waveguides 0.8λ wide (≈1.2 µm), where sidewall roughness is the primary limitation. The modelling framework, based on 3D wave simulations informed by roughness measured by AFM, is applicable to any index contrast between waveguide core and cladding and widely applicable on integrated photonic platforms.

Cavity electro-optic (EO) modulation plays a pivotal role in optical pulse and frequency comb synthesis, supporting a wide range of applications including communication, computing, ranging, and quantum information. The ever-growing demand for these applications has driven efforts in enhancing modulation coupling strength and bandwidth towards advanced pulse-comb synthesis. However, the effects of strong-coupling and high-bandwidth cavity EO modulation remain underexplored, due to the lack of a general, unified model that captures this extreme condition. In this work, we present a universal framework for pulse-comb synthesis under cavity EO modulation, where coupling strength and modulation bandwidth far exceed the cavity’s free spectral range (FSR). We show that, under such intense and ultrafast driving conditions, EO-driven frequency combs and pulses exhibit rich higher-order nonlinear dynamics, including temporal pulse compression and comb generation with arbitrary pump detuning. Leveraging this framework, we reveal a direct link between the higher-order dynamics of EO pulse-comb generation and the band structure of synthetic dimension. Furthermore, we demonstrate arbitrary comb shaping via machine-learning-based inverse microwave drive design, achieving a tenfold enhancement in cavity EO comb flatness by exploring the synergistic effects of high-bandwidth driving and detuning-induced frequency boundaries. Our findings push cavity EO modulation into a new frontier, unlocking significant potential for universal and machine-learning-programmable EO frequency combs, topological photonics, as well as photonic quantum computing in the strong-coupling and high-bandwidth regimes.

The surge in deployment of Low Earth Orbit (LEO) satellites over the last two decades has resulted in a number of incompatible communication protocols, limiting efficient inter-satellite communication. In response, we present the first reconfigurable silicon photonic link supporting both coherent and intensity modulation with direct detection (IM-DD). Our link design supports transmission and reception of on-off keying (OOK), binary phase-shift keying (BPSK), and quadrature phase-shift keying (QPSK) modulated signals across two polarization states, enabling a single transceiver to accommodate multiple common modulation formats. We demonstrate successful operation of the custom transmitter, polarization multiplexer, and receiver portions of our link, including: 1) transmission of OOK, BPSK, and QPSK at symbol rates up to 10 GBaud with an error vector magnitude (EVM) <22% in all cases, 2) polarization cross-talk suppression of over 21 dB, and 3) reception of OOK, BPSK, and QPSK at rates up to 5 GBaud with resolved EVM <17%. This innovation can address the pressing need for standardized communication within LEO satellite constellations, improving interoperability and efficiency in satellite communications.

4H-silicon carbide is a promising platform for solid-state quantum technology due to its commercial availability as a wide bandgap semiconductor and ability to host numerous spin-active color centers. Integrating color centers into suspended nanodevices enhances defect control and readout, key advances needed to fully harness their potential. However, challenges in developing robust fabrication processes for 4H-SiC thin films, due to the material’s chemical and mechanical stability, limit their implementation in quantum applications. Here, we report on a new fabrication approach that first synthesizes suspended thin films from a monolithic platform and then patterns devices. With this technique, we fabricate and characterize structures tailored for defect integration, demonstrating 1D photonic crystal cavities, with and without waveguide interfaces, and lithium niobate on 4H-SiC acoustic cavities. This approach allows for greater fabrication flexibility, supporting high temperature annealing and heterogeneous material platform compatibility, providing a versatile platform for scalable fabrication of 4H-SiC devices for quantum technologies.

We benchmark Lumerical FDTD and Tidy3D for 3D simulations of passive silicon photonic components on the silicon-on-insulator (SOI) platform. Six devices—including an MMI, directional coupler, waveguide crossing, mode converter, polarization splitter rotator, and ring resonator—are simulated under matched conditions using geometries from the generic process design kit (PDK) from GDSFactory. Our study emphasizes comparing simulation accuracy across both solvers, alongside an analysis of runtime and broadband behavior over varying resolutions and bandwidths. Results show that both solvers are reliable with minimal discrepancies.

We present a mid-wave infrared photonic integrated circuit platform based on germanium-on-silicon waveguides – the first to include dielectric top cladding, which improves robustness and allows for the complicated metal routing needed for practical, large-scale photonic integrated circuits. We conduct the first comprehensive review of top cladding materials for germanium-on-silicon waveguides and find that Nb2O5 (loss: 3.5–4.6 dB/cm at 4.6 µm; ring resonator loaded Q >37,000 and unloaded Q >58,000) and epitaxial Si (loss: 4.1-6.3 dB/cm at 4.6 µm; ring resonator loaded Q >23,000 and unloaded Q >40,000) achieve the best results. For sensing applications, which can require waveguides exposed to the environment, we demonstrate state-of-the-art air-clad waveguides and ring resonators that achieve losses of 0.6–2.5 dB/cm for both TE and TM light and high-Q factors (loaded Q of >106,000 and unloaded Q >190,000 for TE light).

Programmable photonic circuits are versatile platforms that route light through multiple interference paths using reconfigurable optoelectronic elements to perform complex discrete linear operations. These circuits offer the potential for high-speed and low-power photonic information processing in various applications. The mainstream research on programmable photonics has focused on implementing linear operations on discrete signals encoded in the modal amplitudes of an array of spatially separated single-mode waveguides. However, many photonic device applications require simultaneous transformations in the space-frequency domain, where information is encoded in both the spatial modes of waveguides and their spectral content. Here, we experimentally demonstrate linear space-frequency transformations using a four-port programmable silicon photonic circuit with an alternating architecture. This design leverages the limited dispersion of coupled waveguide arrays to enable linear operations with reconfigurable frequency-dependent matrix elements. We utilize this device to perform wavelength demultiplexing and filtering. This architecture platform can pave the way for versatile devices with applications ranging from wavelength routing to programmable dispersion control.

We present a novel finite-difference frequency-domain formulation for accurate and efficient modal analysis of dielectric ring resonators, a critical component in microresonator-based optical frequency comb (OFC) generation. Unlike previous methods, our approach solves for both electric and magnetic fields simultaneously in cylindrical coordinates, eliminating spurious modes and ensuring high fidelity at material boundaries. The solver enables rapid computation of resonant modes without requiring manual input for azimuthal mode numbers, significantly streamlining dispersion engineering for OFC design. We validate our method against experimental data and the results generated with commercial solvers, demonstrating excellent agreement in effective indices, integrated dispersion, and resonance linewidths for silicon nitride resonators excited with lasers operating at 1060 nm and 1550 nm. Our results highlight the solver’s utility in predicting anomalous dispersion and coupling dynamics, offering a robust tool for designing high-performance OFC devices.

The development of color centers in silicon enables scalable quantum technologies by combining telecom-wavelength emission and compatibility with mature silicon fabrication. However, large-scale integration requires precise control of each emitter’s optical transition to generate indistinguishable photons for quantum networking. Here, we demonstrate a foundry-fabricated photonic integrated circuit (PIC) combining suspended silicon waveguides with a microelectromechanical (MEMS) cantilever to apply local strain and spectrally tune individual G-centers. Applying up to 35 V between the cantilever and the substrate induces a reversible wavelength shift of the zero-phonon line exceeding 100 pm, with no loss in brightness. Moreover, by modeling the strain-induced shifts with a digital twin physical model, we achieve vertical localization of color centers with sub-3 nm vertical resolution, directly correlating their spatial position, dipole orientation, and spectral behavior. This method enables on-demand, low-power control of emission spectrum and nanoscale localization of color centers, advancing quantum networks on a foundry-compatible platform.

Mid-infrared (Mid-IR) spectroscopy offers powerful label-free molecular analysis capabilities but faces significant challenges when analyzing complex biological samples. Here, a transformative surface-enhanced infrared absorption spectroscopy (SEIRAS) platform is presented that overcomes fundamental limitations through key innovations. First, high-throughput wafer-scale fabrication of mid-IR plasmonic micro-hole-array (MHA) metasurfaces is demonstrated on free-standing silicon nitride (Si3N4) membranes, yielding ≈400 sensor chips per 6-inch wafer. Second, the gradient MHA metasurface design supports spectrally cascaded plasmonic modes, generating over 400 sharp resonance peaks across the 1200–2000 cm−1 fingerprint region. This approach enables comprehensive molecular fingerprinting using simple imaging optics in transmission mode. Third, the SEIRAS platform is validated using a model polymer system and clinical peritoneal fluid samples from ovarian cancer patients, demonstrating its capability to resolve complex molecular signatures in real biological specimens. The platform's dense spectral coverage ensures optimal on-resonance enhancement across the broad fingerprint region, revealing previously obscured vibrational bands that conventional IR spectroscopy cannot distinguish. By combining high-throughput fabrication with simplified optical readout and the capability to analyze complex biological samples, this work establishes a foundation for translating SEIRAS technology into practical biomedical applications, promising a real-world impact.

Nanophotonic freeform design has the potential to push the performance of optical components to new limits, but there remains a challenge to effectively perform optimization while reliably enforcing design and manufacturing constraints. We present Neuroshaper, a framework for freeform geometric parameterization in which nanophotonic device layouts are defined using an analytic neural network representation. Neuroshaper serves as a qualitatively new way to perform shape optimization by capturing multi-scalar, freeform geometries in an overparameterized representation scheme, enabling effective optimization in a smoothened, high dimensional geometric design space. We show that Neuroshaper can enforce constraints and topology manipulation in a manner where local constraints lead to global changes in device morphology. We further show numerically and experimentally that Neuroshaper can apply to a diversity of nanophotonic devices. The versatility and capabilities of Neuroshaper reflect the ability of neural representation to augment concepts in topological design.

Nanophotonic cavities are the foundation for a broad spectrum of applications, including quantum sensing, on-chip communication, and cavity quantum electrodynamics. In van der Waals (vdW) materials, these cavities can harness polaritons, which are quasiparticles emerging from photon interactions with excitons, plasmons, or phonons that are confined in microscopic sample flakes. Hybrid phonon–plasmon cavities leverage the long lifetimes of phonons and good tunability of plasmons, but their reconfigurability remains fundamentally limited. Here, we introduce a magnetic-field-tuning mechanism for polaritonic cavities in a vdW heterostructure. Specifically, we demonstrate that the primary Landau transition in magnetized charge-neutral graphene can be harvested for controlling polaritonic cavity modes in a graphene-based phononic heterostructure. Additionally, we predict a magnetic-field-induced topological transition in the polariton isofrequency contour, causing a nontrivial cavity mode profile redistribution. Our study underscores the versatility of Landau-based nanophotonic cavities, offering new paradigms for the design and manipulation of light–matter interactions at the nanoscale.

We report a novel ultra-thin metalens design based on photonic crystal slab (PCS) resonance modes. We experimentally verified with a metalens structure based on amorphous silicon on a quartz material platform by implementing the optical guided resonance on the PCS. The PCS metalens designs feature an ultra-thin device layer of about 160 nm at an operation wavelength of 940 nm. A full 2π transmission phase transition is realized by varying the air hole sizes at the design wavelength. Metalens devices with different phase change gradients were designed and fabricated to achieve different NAs. A maximum of 86.4% focusing efficiency is achieved. Imaging capabilities are characterized, and clear images are observed within the field of view. The PC resonance-based phase modulation design can be applied to optical beam manipulation, phase plate design, imaging, and laser beam formation applications.

Arrayed waveguide gratings (AWGs) are widely used photonic components for splitting and combining different wavelengths of light. They play a key role in wavelength-division multiplexing (WDM) systems by enabling efficient routing of multiple data channels over a single optical fiber and as a building block for various optical signal processing, computing, imaging, and spectroscopic applications. Recently, there has been growing interest in integrating AWGs in ferroelectric material platforms, as the platform simultaneously provides efficient electro-optic modulation capability and thus holds the promise for fully integrated WDM transmitters. To date, several demonstrations have been made in the X-cut thin-film lithium niobate (LiNbO3) platform, yet the large anisotropy of LiNbO3 complicates the design and degrades the performance of the AWGs. To address this limitation, we use the recently developed photonic integrated circuits (PICs) based on thin-film lithium tantalate (LiTaO3), a material with a similar Pockels coefficient as LiNbO3 but significantly reduced optical anisotropy, as an alternative viable platform. In this work, we manufacture LiTaO3 AWGs using deep ultraviolet lithography on a wafer scale. The fabricated AWGs feature a channel spacing of 100 GHz, an insertion loss of < 4 dB, and cross talk of < −14 dB. The wafer-scale fabrication of these AWGs not only ensures uniformity and reproducibility, but also paves the way for realizing volume-manufactured integrated WDM transmitters in ferroelectric photonic integrated platforms.

The Lorentz–Drude model for electric dipoles is a classical framework widely used in the study of dipole dynamics and light-matter interactions. This article focuses on the behavior of Lorentz–Drude dipoles when their radiative rate dominates their energy loss. It is asserted that dipole radiation losses do not count toward phenomenological dipole losses if the driving field is interpreted as the total field at the dipole. In particular, if the dipole does not contain non-radiative losses, then the Lorentz–Drude damping term should be removed. This is verified by self-consistent implementations of point dipoles in finite-difference time-domain simulations, which also provide a method to directly compute the transport properties of light when dipoles are present.

Exciton–polaritons emerging from the interaction of photons and excitons in the strong coupling regime are intriguing quasiparticles for the potential exchange of energy during light–matter interaction processes, such as light harvesting. The coupling causes an energy anticrossing in the photon dispersion centered around the exciton resonance, i.e., a Rabi splitting between a lower and upper energetic branch. The size of this splitting correlates with the coupling strength between the exciton and photonic modes. In this work, we investigate this coupling between excitons and photonic waveguide modes excited simultaneously in thin-film flakes of the transition-metal dichalcogenide WSe2. Using a photoemission electron microscope, we are able to extract the dispersion of the transverse electric and magnetic modes propagating through these flakes as well as extract the energy splitting. Ultimately, our findings provide a basis for the investigation of the propagation of exciton–polaritons in the time-domain via time-resolved photoemission.

Charge transfer at material interfaces governs a wide range of physical properties, from electronic band structures to emergent collective excitations. In two-dimensional (2D) material heterostructures, charge transfer phenomena play important roles in enabling novel quantum phases, proximity effects, and tunable plasmonic responses. One representative charge transfer interface is formed between α-RuCl3, a van der Waals material with high electron affinity, and graphene. Significant charge transfer across this interface induces the formation of charge-transfer plasmon polaritons (CPPs), hybrid excitations between light and charge oscillations. However, previous studies found that as the charge transfer process takes place, α-RuCl3 becomes lossy, which limits the quality factor of CPPs. Here, we investigate CPPs down to 10 K using a home-built scattering-type scanning near-field optical microscope (*s*\-SNOM) optimized for low-temperature measurements. Our study reveals a dramatic suppression of plasmon loss channels below 40 K, contributing to a significant enhancement in the plasmonic quality factor. This reduction in loss is likely attributed to the blue shift of the correlation-induced Mott gap in α-RuCl3 with decreasing temperature, along with the reduction of phonon scattering at low temperature. Our results highlight the potential of using *s*\-SNOM and CPPs to study complex 2D interfaces and reveal correlated electron dynamics in the underlying material.

Femtosecond (fs) laser irradiation of La3+\-doped tellurium–zinc (TZL) glass induces structural transformations within the glass surface or volume, resulting in modified chemical compositions and network structures distinct from those of the bulk material. Fs-laser processing promotes the formation of TeO4 by transforming TeO3 with nonbridging oxygens (NBOs), stabilizing the network and reducing susceptibility to further structural rearrangements. Techniques such as Raman spectroscopy, SEM, and optical microscopy were used to investigate these structural changes and analyze the effects of La3+ doping, with a particular focus on identifying TeO3 and TeO4 bonds and their impact on waveguide optical properties. Conventional methods for characterizing glass surface modifications often lack the sensitivity to capture the extensive, three-dimensional changes induced by femtosecond laser processing, underscoring the need for comprehensive spectroscopic and optical analyses. Using confocal 2D Raman spectroscopy and propagation loss measurements, we examined the laser-modified regions in the TZL glass waveguides. We found that structural changes driven by La3+ concentration and the *I*(TeO3)/*I*(TeO4) ratio significantly influence light confinement and scattering. Complementary simulations validated these trends analytically; modeled electric field and refractive index profiles quantitatively confirmed that energy-induced densification in TeO4\-rich regions enhances mode confinement and reduces propagation loss. Reduced propagation losses were observed in TeO4\-rich regions (TZL9), whereas higher losses occurred in TeO3\-rich regions (TZL5), highlighting the effectiveness of compositional tuning in enhancing waveguide performance through La3+\-induced structural modifications. This represents a significant advance over previous studies by quantitatively correlating spectroscopic structural changes via the *I*(TeO3)/*I*(TeO4) ratio with waveguide optical performance. This ability to achieve low-loss waveguides through targeted structural adjustments in tellurite-based glasses offers promising applications in advanced photonic devices, such as all-optical switches and modulators, that require precise control over the optical loss and mode confinement.

3D nanoprinting enables the fabrication of photonic freeform structures with critical features on the sub-micrometer scale and a significant spatial extent. This ability can be exploited to print photonic wire bonds (PWB) that optically interconnect different components in photonic integrated circuits (PICs). However, efficient and compact couplers between PWBs and other PIC components remain a prime challenge. Despite the immense design flexibility afforded by 3D nanoprinting, the absence of suitable design methodologies has hindered the full exploitation of its potential. Here, this challenge is addressed by, exemplarily, focusing on 3D nanoprinted couplers between a single-mode fiber and a PWB. Using topology optimization enhanced by a novel parameterization scheme, ultra-short, fabrication-robust, and highly efficient broadband couplers are designed. Our results are benchmarked against a state-of-the-art global Bayesian optimization approach, providing comparative insights into the advantages and limitations of these methods. These findings pave the way for broader application of 3D nanoprinting in designing next-generation photonic components.

Efficiently coupling light from optical fibers into photonic integrated circuits is a key step toward practical photonic devices. While a notable coupling can be achieved by out-of-plane couplers such as grating couplers, their basic planar geometry typically tends to be sensitive to the polarization of light. This is partly due to the fact that the design spaces of such grating structures—typically fabricated with techniques such as electron-beam lithography—are only two-dimensional with a simple extrusion into the vertical dimension. This makes it challenging to optimize for both polarizations simultaneously, as performance typically degrades when trying to achieve high efficiency in both. As a result, conventional approaches either suffer from increased losses or require additional filtering components to account for different polarizations. In this work, we present a fully three-dimensional, polarization-insensitive grating coupler which has a highly efficient simulated coupling efficiency of over 80% in both polarizations. This performance matches that of state-of-the-art couplers that are performant for one polarization only. This comes at the cost of a moderately larger size due to the lower refractive index materials typically available in 3D nanoprinting. Our design method uses densitybased topology optimization with a multi-objective approach that combines electromagnetic simulations with a fictitious heatconduction model acting as a soft constraint to promote structural integrity. This ensures that the designed structures are feasible for fabrication. Our work opens new possibilities for robust 3D photonic devices, enabling advanced integration, fabrication, and applications across next-generation photonics and electronics.

3D additive manufacturing enables the fabrication of nanophotonic structures with subwavelength features that control light across macroscopic scales. Gradient-based optimization offers an efficient approach to design these complex and non-intuitive structures. However, expanding this methodology from 2D to 3D introduces complexities, such as the need for structural integrity and connectivity. This work introduces a multi-objective optimization method to address these challenges in 3D nanophotonic designs. Our method combines electromagnetic simulations with an auxiliary heat-diffusion solver to ensure continuous material and void connectivity. By modeling material regions as heat sources and boundaries as heat sinks, we optimize the structure to minimize the total temperature, thereby penalizing disconnected regions that cannot dissipate thermal loads. Alongside the optical response, this heat metric becomes part of our objective function. We demonstrate the utility of our algorithm by designing two 3D nanophotonic devices. The first is a focusing element. The second is a waveguide junction, which connects two incoming waveguides for two different wavelengths into two outgoing waveguides, which are rotated by 90° to the incoming waveguides. Our approach offers a design pipeline that generates digital blueprints for fabricable nanophotonic materials, paving the way for practical 3D nanoprinting applications.

Multi-layered meta-optics have enabled complex wavefront shaping beyond their single layer counterpart owing to the additional design variables afforded by each plane. For instance, lossless complex amplitude modulation, generalized polarization transformations, and wide field of view are key attributes that fundamentally require multi-plane wavefront matching. Nevertheless, existing embodiments of bilayer metasurfaces have relied on configurations which suffer from Fresnel reflections, low mode confinement, or undesired resonances which compromise the intended response. Here, we introduce bilayer metasurfaces made of free-standing meta-atoms working in the visible spectrum. We demonstrate their use in wavefront shaping of linearly polarized light using pure geometric phase with diffraction efficiency of 80% — expanding previous literature on Pancharatnam-Berry phase metasurfaces which rely on circularly or elliptically polarized illumination. The fabrication relies on a two-step lithography and selective development processes which yield free standing, bilayer stacked metasurfaces, of 1200 nm total thickness. The metasurfaces comprise TiO2 nanofins with vertical sidewalls. Our work advances the nanofabrication of compound meta-optics and inspires new directions in wavefront shaping, metasurface integration, and polarization control.

Infrared (IR) spectroscopic fingerprinting is a powerful analytical tool for characterizing molecular compositions across biological, environmental, and industrial samples through their specific vibrational modes. Specifically, when the sample is characterized in resonant plasmonic cavities, as in the surface-enhanced mid-IR absorption spectroscopy (SEIRAS), highly sensitive and specific molecular detection can be achieved. However, current SEIRAS techniques rely on nanofabricated subwavelength antennas, limited by low-throughput lithographic processes, lacking scalability to address broad biochemical sensing applications. To address this, we present an on-resonance SEIRAS method utilizing silver (Ag) cubic microparticles (Ag-CMPs) with robust mid-IR plasmonic resonances. These monocrystalline Ag-CMPs, featuring sharp edges and vertices, are synthesized via a high-throughput, wet-chemical process. When dispersed on gold mirror substrates with an aluminum oxide spacer, Ag-CMPs support enhanced near-field light–matter interactions in nanocavities while enabling far-field imaging-based optical interrogation due to their strong extinction cross sections. We demonstrate the detection of polydimethylsiloxane (PDMS) and bovine serum albumin (BSA) monolayers by simply probing individual Ag-CMPs, enabled by the resonant amplification of the characteristic vibrational absorptions. Furthermore, our single-particle SEIRAS (SP-SEIRAS) approach effectively analyzes complex human peritoneal fluid (PF) samples, eliminating the challenges of standard bulk sample measurements. This scalable and efficient SP-SEIRAS method addresses key limitations of IR spectroscopic fingerprinting techniques, unlocking possibilities for their widespread adoption in real-world biochemical sensing applications.

Nitrogen-vacancy centers have demonstrated significant potential as quantum magnetometers for nanoscale phenomena and sensitive field detection, attributed to their exceptional spin coherence at room temperature. However, it is challenging to achieve solid-state magnetometers that can simultaneously possess high spatial resolution and high field sensitivity. Here we demonstrate nanoscale quantum sensing with high field sensitivity by using on-chip diamond micro-ring resonators. The ring resonator enables the efficient use of photons by confining them in a nanoscale region, enabling the magnetic sensitivity of 1.0 μT/Hz1/2 on a photonic chip with a measurement contrast of theoretical limit. We also show that the proposed on-chip approach can improve the sensitivity via efficient light extraction with photonic waveguide coupling. Our work provides a pathway toward the development of chip-scale packaged sensing devices that can detect various nanoscale physical quantities for fundamental science, chemistry, and medical applications.

Imaging of subcellular structures, which underpins many of the advances in biological and medical sciences, requires microscopes with high numerical aperture (N.A.) objectives which are costly, complex, requires oil immersion and have very limited field-of-view, typically covering a handful of cells. Here, we leverage a low N.A. objective to simultaneously capture scattering, phase, and fluorescence images of subcellular structures in breast cancer cells (BT-20) and observe nanoparticle uptake, with sub-diffraction-limited resolution (<400nm with a 0.25 N.A. objective) utilizing a 2-dimensional (2-D) microlens substrate. High resolution labeled and label-free images of subcellular components is made possible by implementing a specific configuration, wherein the sample is placed in close proximity to the microlens substrate, which results in efficient collection of the rapidly decaying evanescent waves that contains the high frequency information, thereby improving resolution and the light capture efficiency. The microlens-assisted imaging provides an easy-to-implement and cost-effective means of drastically improving the resolution of any microscope with low N.A. objective lenses, paving the way for the development of affordable, portable multi-modal imaging systems with high-resolution imaging capabilities. This technology has broad implications for various fields and could democratize access to high-quality microscopy, particularly for application in resource-limited settings.

Whispering gallery mode (WGM) resonators provide an essential platform for various optical applications but are typically limited to mode volumes V≈2𝝅R(𝝀0 /2n)2 where R is the bend radius and n is the refractive index. Here, the theory, simulation, and experimental realization of WGM resonator scapable of achieving deeply sub-diffractive mode volumes are presented,V << 2𝝅R(𝝀0 /2n)2 , while preserving high Q factors. Rather than relying on plasmonics to reduce the mode volume, the work relies on all-dielectric metamaterial waveguides that support localized field enhancements within the high index medium. Combined with the excitation of standing wave rather than traveling wave WGM resonances, it is shown how the mode volume of a silicon microring resonator can be reduced by factors >10 – 100 depending upon nanostructure dimensions and choice of cladding. The analysis further suggests a lower bound for the sub-diffractive all-dielectric mode volume, Vmin’, which scales in proportion to the mode order m times the refractive index raised to the seventh power, i.e.: Vmin’ ≈ mn−7 . Experimentally, these sub-diffractive WGM devices are shown to support standing wave resonances while maintaining high intrinsic quality factors ≈ 104 – 105 . These metawaveguide ring resonators present a promising WGM platform for interfacing wavelength-scale optics with sub-wavelength matter.

Optical metasurfaces provide solutions to label-free biochemical sensing by localizing light resonantly beyond the diffraction limit, thereby selectively enhancing light–matter interactions for improved analytical performance. However, high-*Q* resonances in metasurfaces are usually achieved in the reflection mode, which impedes metasurface integration into compact imaging systems. Here, we demonstrate a metasurface platform for advanced biochemical sensing based on the physics of the bound states in the continuum (BIC) and electromagnetically induced transparency (EIT) modes, which arise when two interfering resonances from a periodic pattern of tilted elliptic holes overlap both spectrally and spatially, creating a narrow transparency window in the mid-infrared spectrum. We experimentally measure these resonant peaks observed in transmission mode (Q∼734 at µλ∼8.8µm) in free-standing silicon membranes and confirm their tunability through geometric scaling. We also demonstrate the strong coupling of the BIC-EIT modes with a thinly coated PMMA film on the metasurface, characterized by a large Rabi splitting (32cm−1) and biosensing of protein monolayers in transmission mode. Our new photonic platform can facilitate the integration of metasurface biochemical sensors into compact and monolithic optical systems while being compatible with scalable manufacturing, thereby clearing the way for on-site biochemical sensing in everyday applications.

We study Anderson transition for light in three dimensions by performing large-scale simulations of electromagnetic wave transport in disordered ensembles of perfect-electric-conducting spatially overlapping spheres. A mobility edge that separates diffusive transport and Anderson localization is identified, revealing a sharp transition from diffusion to localization for light. Critical behavior in the vicinity of the mobility edge is well described by a single-parameter scaling law. The critical exponent is found to be consistent with the value known for the Anderson transition of the orthogonal universality class. Statistical distribution of total transmission at the mobility edge is described without any fit parameter by the diagrammatic perturbation theory originally developed for scalar wave diffusion, but notable deviation from the theory is found when Anderson localization sets in.

Miniaturized pixel sizes in near-eye digital displays lead to pixel emission patterns with large divergence angles, necessitating efficient beam collimation solutions to improve the light coupling efficiency. Traditional beam collimation optics, such as lenses and cavities, are wavelength-sensitive and cannot simultaneously collimate red (R), green (G), and blue (B) light. In this work, we employed inverse design optimization and finite-difference time-domain (FDTD) simulation techniques to design a collimator comprised of nano-sized photonic structures. To alleviate the challenges of the spatial incoherence nature of micro-LED emission light, we developed a strategy called dual-task optimization. Specifically, the method models light collimation as a dual task of color routing. By optimizing a color router, which routes incident light within a small angular range to different locations based on its spectrum, we simultaneously obtained a beam collimator, which can restrict the output of the light emitted from the routing destination with a small divergence angle. We further evaluated the collimation performance for spatially incoherent RGB micro-LED light in an FDTD using a multiple-dipole simulation method, and the simulation results demonstrate that our designed collimator can increase the light coupling efficiency from approximately 30% to 60% within a divergence angle of ±20° for all R/G/B light under the spatially incoherent emission.

Optical metasurfaces can manipulate electromagnetic waves in unprecedented ways at ultra-thin engineered interfaces. Specifically, in the mid-infrared (mid-IR) region, metasurfaces have enabled numerous biochemical sensing, spectroscopy, and vibrational strong coupling (VSC) applications via enhanced light-matter interactions in resonant cavities. However, mid-IR metasurfaces are usually fabricated on solid supporting substrates, which degrade resonance quality factors (Q) and hinder efficient sample access to the near-field electromagnetic hotspots. Besides, typical IR-transparent substrate materials with low refractive indices, such as CaF2, NaCl, KBr, and ZnSe, are usually either water-soluble, expensive, or not compatible with low-cost mass manufacturing processes. Here, we present novel free-standing Si-membrane mid-IR metasurfaces with strong light-trapping capabilities in accessible air voids. We employ the Brillouin zone folding technique to excite tunable, high-Q quasi-bound states in the continuum (qBIC) resonances with our highest measured Q-factor of 722. Leveraging the strong field localizations in accessible air cavities, we demonstrate VSC with multiple quantities of PMMA molecules and the qBIC modes at various detuning frequencies. Our new approach of fabricating mid-IR metasurfaces into semiconductor membranes enables scalable manufacturing of mid-IR photonic devices and provides exciting opportunities for quantum-coherent light-matter interactions, biochemical sensing, and polaritonic chemistry.

Controlling the propagation of light in the form of surface modes on miniaturized platforms is crucial for multiple applications. For dielectric multilayers that sustain Bloch surface waves at their interface to an isotropic dielectric medium, a conventional approach to manipulate them exploits shallow surface topographies fabricated on top of the truncated stack. However, such structures typically exhibit low index contrasts, making it challenging to confine, steer, and guide the Bloch surface waves. Here, we theoretically and experimentally demonstrate a device for a Bloch surface wave platform that resonantly couples light from a cavity to a straight waveguide. The structure is designed using topology optimization in a 2D geometry under the effective index approximation. In particular, the cavity–waveguide coupling efficiency of the radiation emitted by an individual source in the cavity center is optimized. The cavity is experimentally found to exhibit a narrow resonant peak that can be tuned by scaling the structure. The waveguide is shown to guide only light that resonates in the cavity. Fully three-dimensional simulations of the entire device validate the experimental observations.

Large-area imprinting stamps with nanometer-scale features are a rapidly developing area of research in plasmonics. In integrated photonic structures, surface plasmon (SPs) and surface plasmon polaritons (SPPs) are tuned by selecting both the appropriate wavelength and the angle of incidence of the excitation light. The resulting exponential fields can be studied by an optical technique such as scanning near-field optical microscopy (SNOM). Here, we report on the application of the aperture-type SNOM technique to characterize, at nanoscopic and microscopic scales, the formation of the SPPs and the beat pattern formed with the superposition of SPs and the effective component of the probing light formed in discrete metallic nanostructures of Au fabricated on imprinting stamps. We discuss a model to describe the beat pattern in terms of this superposition and demonstrate that the dominant SPs have a transverse nature. Our experiments are supported by modeling the optical response and near-field in gold nanostructures using the simulation tool Tidy3D. Our results provide a straightforward way to investigate and characterize SPPs at the nanostructure level.

Hardware advances are enabling simulations of Maxwell’s equations at unprecedented speed and scale. Graphics processing units (GPUs) designed for high-performance computing (HPC) have recently seen dramatic performance improvements driven by the needs of artificial intelligence. The same hardware advances, it turns out, can also serve to significantly speed up numerical simulations of physical phenomena.

The presence of long-range interactions is crucial in distinguishing between abstract complex networks and wave systems. In photonics, because electromagnetic interactions between optical elements generally decay rapidly with spatial distance, most wave phenomena are modeled with neighboring interactions, which account for only a small part of conceptually possible networks. Here, we explore the impact of substantial long-range interactions in topological photonics. We demonstrate that a crystalline structure, characterized by long-range interactions in the absence of neighboring ones, can be interpreted as an overlapped lattice. This overlap model facilitates the realization of higher values of topological invariants while maintaining bandgap width in photonic topological insulators. This breaking of topology-bandgap tradeoff enables topologically protected multichannel signal processing with broad bandwidths. Under practically accessible system parameters, the result paves the way to the extension of topological physics to network science.

Dissipative Kerr solitons from optical microresonators, commonly referred to as soliton microcombs, have been developed for a broad range of applications, including precision measurement, optical frequency synthesis, and ultra- stable microwave and millimeter wave generation, all on a chip. An important goal for microcombs is self-referencing, which requires octave-spanning bandwidths to detect and stabilize the comb carrier envelope offset frequency. Further, detection and locking of the comb spacings are often achieved using frequency division by electro-optic modulation. The thin-film lithium niobate photonic platform, with its low loss, strong second- and third-order nonlinearities, as well as large Pockels effect, is ideally suited for these tasks. However, octave-spanning soliton microcombs are challenging to demonstrate on this platform, largely complicated by strong Raman effects hindering reliable fabrication of soliton devices. Here, we demonstrate entirely connected and octave-spanning soliton microcombs on thin-film lithium niobate. With appropriate control over microresonator free spectral range and dissipation spectrum, we show that soliton-inhibiting Raman effects are suppressed, and soliton devices are fabricated with near-unity yield. Our work offers an unambiguous method for soliton generation on strongly Raman-active materials. Further, it anticipates monolithically integrated, self-referenced frequency standards in conjunction with established technologies, such as periodically poled waveguides and electro-optic modulators, on thin-film lithium niobate.

Silicon carbide (SiC)’s nonlinear optical properties and applications toquantum information have recently brought attention to its potential as anintegrated photonics platform. However, despite its many excellent materialproperties, such as large thermal conductivity, wide transparency window, andstrong optical nonlinearities, it is generally a difficult material formicrofabrication. Here, it is shown that directly bonded silicon-on-siliconcarbide can be a high-performing hybrid photonics platform that does notrequire the need to form SiC membranes or directly pattern in SiC. Theoptimized bonding method yields defect-free, uniform films with minimaloxide at the silicon–silicon–carbide interface. Ring resonators are patternedinto the silicon layer with standard, complimentary metal–oxide–semicond-uctor (CMOS) compatible (Si) fabrication and measure room-temperature,near-infrared quality factors exceeding 10 5 . The corresponding propagationloss is 5.7 dB cm−1 . The process offers a wafer-scalable pathway to theintegration of SiC photonics into CMOS devices.

Modeling metasurfaces with high accuracy and efficiency is challenging because they have features smaller than the wavelength but sizes much larger than the wavelength. Full wave simulation is accurate but very slow. Popular design paradigms like locally periodic approximation (LPA) reduce the computational cost by neglecting, partially or fully, near-field interactions between meta-units and treating them in an isolated manner. The coupling between meta-units has been fully considered by applying the temporal coupled mode theory to model the metasurface. However, this method only works for resonance-based metasurfaces. To model the broadly studied dielectric metasurfaces based on the propagation of guided modes, we propose to model the whole system using a spatial coupled mode theory where the dielectric metasurface can be viewed as an array of truncated waveguides. An inverse design routine based on this model is then devised and applied to gain improvements over LPA in several scenarios, such as high numerical aperture lens, multiwavelength focusing, and suppression of coma aberrations. With its accuracy and efficiency, the proposed framework can be a powerful tool to improve the performance of dielectric metasurfaces on various tasks.

Extracting photons efficiently from quantum sources, such as atoms, molecules, and quantum dots, is crucial for various nanophotonic systems used in quantum communication, sensing, and computation. To improve the performance of these systems, it is not only necessary to provide an environment that maximizes the number of optical modes, but it is also desirable to guide the extracted light toward specific directions. One way to achieve this goal is to use a large area metasurface that can steer the beam. Previous work has used small aperture devices that are fundamentally limited in their ability to achieve high directivity. This work proposes an adjoint-based topology optimization approach to design a large light extractor that can enhance the spontaneous decay rate of the embedded quantum transition and collimate the extracted photons. With the help of this approach, we present all-dielectric metasurfaces for a quantum transition emitting at λ = 600 nm. These metasurfaces achieve a broadband improvement of spontaneous emission compared to that in the vacuum, reaching a 10× enhancement at the design frequency. Furthermore, they can beam the extracted light into a narrow cone (±10°) along a desired direction that is predefined through their respective design process.

Phonon polaritons, the hybrid quasiparticles resulting from the coupling of photons and lattice vibrations, have gained significant attention in the field of layered van der Waals heterostructures. Particular interest has been paid to hetero-bicrystals composed of molybdenum oxide (MoO3) and hexagonal boron nitride (hBN), which feature polariton dispersion tailorable via avoided polariton mode crossings. In this work, we systematically study the polariton eigenmodes in MoO3-hBN hetero-bicrystals self-assembled on ultrasmooth gold using synchrotron infrared nanospectroscopy. We experimentally demonstrate that the spectral gap in bicrystal dispersion and corresponding regimes of negative refraction can be tuned by material layer thickness, and we quantitatively match these results with a simple analytic model. We also investigate polaritonic cavity modes and polariton propagation along “forbidden” directions in our microscale bicrystals, which arise from the finite in-plane dimension of the synthesized MoO3 micro-ribbons. Our findings shed light on the unique dispersion properties of polaritons in van der Waals heterostructures and pave the way for applications leveraging deeply sub-wavelength mid-infrared light matter interactions.

Optical microcavities confine light to wavelength-scale volumes and are a key component for manipulating and enhancing the interaction of light, vacuum states, and matter. Current microcavities are constrained to a small number of spatial mode profiles. Imaging cavities can accommodate complicated modes but require an externally preshaped input. Here, we experimentally demonstrate a visible-wavelength, metasurface-based holographic microcavity that overcomes these limitations. The micrometer-scale metasurface cavity fulfills the round-trip condition for a designed mode with a complex-shaped intensity profile and thus selectively enhances light that couples to this mode, achieving a spectral bandwidth of 0.8 nm. By imaging the intracavity mode, we show that the holographic mode changes quickly with the cavity length and that the cavity displays the desired spatial mode profile only close to the design cavity length. When a metasurface is placed on a distributed Bragg reflector and steep phase gradients are realized, the correct choice of the reflector’s top layer material can boost metasurface performance considerably. The applied forward-design method can be readily transferred to other spectral regimes and mode profiles.

Reducing geometrical complexity while preserving desired wave properties is critical for proof-of-concept studies in wave physics, as evidenced by recent efforts to realize photonic synthetic dimensions, isospectrality, and hyperbolic lattices. Laughlin's topological pump, which elucidates quantum Hall states in cylindrical geometry with a radial magnetic field and a time-varying axial magnetic flux, is a prime example of these efforts. Here we propose a two-dimensional dynamical photonic system for the topological pumping of pseudospin modes by exploiting synthetic frequency dimensions. The system provides the independent control of pseudomagnetic fields and electromotive forces achieved by the interplay between mode-dependent and mode-independent gauge fields. To address the axial open boundaries and azimuthal periodicity of the system, we define the adjusted local Chern marker with rotating azimuthal coordinates, proving the nontrivial topology of the system. We demonstrate the adiabatic pumping for crosstalk-free frequency conversion with wave front molding. Our approach allows for reproducing Laughlin's thought experiment at room temperature with a scalable setup.

Space-division multiplexing (SDM) with multicore fibers (MCFs) is envisioned to overcome the capacity crunch in optical fiber communications. Within these systems, the coupling optics that connect single-mode fibers (SMFs) to MCFs are key components in achieving high data transfer rates. Designing a compact and scalable coupler with low loss and crosstalk is a continuing challenge. Here, we introduce a metasurface-based free-space coupler that can be designed for any input array of SMFs to a MCF with arbitrary core layout. An inverse design technique – adjoint method – optimizes the metasurface phase profiles to maximize the overlap of the output fields to the MCF modes at each core position. As proof-of-concepts, we fabricated two types of 4-core couplers for MCFs with linear and square core arrays. The measured insertion losses were as low as 1.2 dB and the worst-case crosstalk was less than -40.1 dB in the O-band (1260-1360 nm). Owing to its foundry-compatible fabrication, this coupler design could facilitate the widespread deployment of SDM based on MCFs.

Passive daytime radiative cooling materials, capable of reducing building cooling energy by up to 60%, reflect sunlight and emit infrared radiation. The challenge lies in producing practical, durable structures. A recent publication in the Science magazine proposed the solution of using microporous glass composite with selective infrared emission and high solar reflectance, enhanced with aluminum oxide for sunlight scattering. This coating can lower temperatures by 3.5° to 4°C, even under high humidity. Remarkably, it maintains effectiveness under harsh conditions such as water, UV radiation, and extreme temperatures.

This paper discusses Anderson localization, which is the phenomenon where the propagation of diffusive waves is halted in disordered systems. Despite extensive research spanning 40 years, the localization of light in three dimensions has remained elusive, raising questions about whether it actually occurs. The text presents numerical evidence of three-dimensional localization of vector electromagnetic waves occurring within random collections of metallic spheres that overlap, which is in stark contrast to the lack of localization observed in dielectric spheres with refractive indices as high as 10 in air.

This paper presents photonic-crystal surface-emitting lasers (PCSELs) and their potential for creating large-area single-mode lasers. Scaling up PCSELs while maintaining single-mode operation is challenging, and it has impeded progress in achieving very large PCSELs. This scaling challenge arises from the diminishing quality-factor (Q) contrast between the fundamental laser mode and higher-order modes as the lateral size of the crystal increases. The text introduces the concept of bound states in the continuum (BIC), which can address this challenge.

This paper introduces a novel approach using Graph Neural Networks (GNN). This GNN architecture is designed to learn and model electromagnetic scattering and can be applied to metasurfaces of arbitrary sizes. Importantly, it considers the coupling between scatterers. As a result, this approach allows for the rapid calculation of near-fields for metasurfaces. Additionally, the approach can also be used for the inverse design of large metasurfaces, offering a versatile tool for electromagnetic field modeling and design.

In this paper, the authors propose a programmable photonic crystal cavity array and demonstrate near-complete control over the spatiotemporal properties of a 64 resonator, two-dimensional spatial light modulator with nanosecond- and femtojoule-order switching. Simultaneously operating wavelength-scale modes near the space–bandwidth and time–bandwidth limits, this work opens a new regime of programmability at the fundamental limits of multimode optical control.

In this work, the authors present a design for planar photonic topological waveguides characterized by low index contrast. Notably, they create these waveguides using polymeric materials through three-dimensional printing, allowing for rapid device fabrication. To assess the topological protection of these waveguides, they employ high-speed finite-difference time-domain simulations, particularly focusing on "omega" shaped bent topological waveguides.

Metalenses for optical beam manipulation have a significant impact in many exciting applications due their compact, planar geometry and ease of fabrication. However, the enormous physical size of metalenses relative to the optical wavelength provides a barrier to performing accurate simulations in a reasonable time frame. In principle, full-wave simulation techniques, such as the finite-difference time-domain (FDTD) method, are ideal for metalens modeling as they give an accurate picture of the device performance. However, when applied using traditional computing platforms, this approach is infeasible for large-diameter metalenses and requires hours and days to simulate even devices of modest size. To alleviate these issues, the standard approach has been to apply approximations, which typically employ simplified models of the metalens unit cells or ignore coupling between cells, leading to inaccurate predictions. In this Perspective, first, we summarize the current state of the art approaches in simulating large scale, three-dimensional metalenses. Then, we highlight that advances in computing hardware have now created a scenario where the full-wave simulation of large area metalenses is feasible within a reasonable time frame, providing significant opportunities to the field. As a demonstration, we show that a hardware-accelerated FDTD solver is capable of simulating a fully 3D, large area metalens of size 100λ × 100λ, including the focal length, in under 5 min. The application of hardware-accelerated, full-wave simulation tools to metalens simulation should have a significant impact in the metalens field and the greater photonics community. The authors wish to acknowledge the help of Lei Zheng for technical assistance. All authors have a financial interest in Flexcompute, Inc., which developed the Tidy3D solver used in this work.