Inverse design of on-chip nanophotonic neural networks (ONNs) is often hindered by the prohibitive cost of repeated three-dimensional (3D) full-wave simulations, especially when the optimization is performed in a high-dimensional geometric design space. Here, we employ a computationally efficient multi-body shape optimization framework and integrate it with a wave-based linear-decoupling strategy to address this challenge. By reconstructing input-specific responses from pre-computed characteristic states, our approach bypasses the need for exhaustive, repetitive full-wave solutions of Maxwell’s equations inside the optimization loop. We utilize elliptical scatterers to enable anisotropic control over optical fields, reducing the nominal design-variable count by hundreds of times for the studied devices compared to an equivalent 40-nm pixel-based topology-optimization baseline. 3D finite-difference time-domain simulations on the Iris and MNIST classification benchmarks validate that the proposed framework yields compact ONN classifiers with high inference accuracy and significantly lower training cost. This work establishes a scalable, fabrication-aware methodology for high-performance on-chip photonic neural processors.
Quantum nanophotonics enables advanced functionalities in information processing and sensing by providing control over quantum-light emission. Introducing time modulation into nanophotonic environments adds an additional dimension, enabling dynamic reconfiguration of the local density of optical states (LDOS), access to Floquet harmonics, and simultaneous control of emission rate, spectrum, and direction, capabilities that are fundamentally inaccessible in static platforms. Designing such systems requires self-consistent treatment of temporal modulation, electrodynamics, and quantum dynamics. Here, we extend a quantum-electromagnetic framework by coupling time-modulated Maxwell electrodynamics, solved using an anisotropic discrete dipole approximation, with a harmonic-resolved Gorini–Kossakowski–Sudarshan–Lindblad master equation. This Floquet–Lindblad–DDA approach captures the quantum feedback induced by temporal modulation and enables evaluation of harmonic-resolved populations, radiated and dissipated power, Purcell enhancement, and quantum efficiency. We applied the method to control the emission of a diamond NV center using voltage-driven Pockels modulation of a barium titanate nanoantenna array. The optimized structure achieves Purcell enhancements exceeding 5000 and routes more than 75% of the power to the n = +1 Floquet harmonic, enabling electronic beam steering by more than 50°. These results demonstrate a platform for programmable quantum-light emission based on time-modulated nanophotonics.
Controlling single-photon emission at the nanoscale is vital for enabling scalable quantum information technologies. Nanophotonic structures have demonstrated remarkable capabilities in manipulating single-photon emission across multiple degrees of freedom. By exploiting nanoscale light-matter interactions, crucial functionalities, such as on-chip scalability, flexible wavefront shaping, and dynamic emission control, become feasible. This review summarizes recent advances in nanostructure-empowered single-photon emission and outlines key challenges and future opportunities.
We establish a kinetic framework for optical spin-caloritronic transport in exciton-polariton microcavities. We show that a neutral, incoherent polariton gas converts heat flow into particle and pseudospin currents whose directions are dictated by the topology of the spin-orbit interaction (SOI) induced effective field, while their magnitudes reflect the local imbalance between high- and low-momentum populations. Treating the momentum-dependent SOI as the key geometric constraint, we analyze the propagation of polaritons shaped by the intrinsic TE-TM polarization splitting and by the Zeeman splitting induced by an externally applied out-of-plane magnetic field, all within a smoothly varying temperature landscape. We identify four distinct optical analogues of thermoelectric effects. A thermal gradient alone drives the flow of radial density, resulting in the optical Seebeck effect. Adding a Zeeman field yields an optical spin Seebeck effect manifested by circular-polarization flows. The replacement of the Zeeman field with the TE-TM splitting deflects the pseudo-spin azimuthally, producing an optical spin Nernst effect. When both splittings act simultaneously, a longitudinal spin Nernst current emerges. This taxonomy of spin-caloritronic regimes links each effect to a symmetry of the effective field and provides design rules for heat-to-spin conversion in hybrid light-matter systems.
Photonic synapses that transcend the von Neumann architecture by integrating sensing, memory, and processing capability are fundamentally limited by the trade-off between rapid response (~μs or less) and persistent photoconductivity (>s). This multi-order-of-magnitude gap in response time has made it challenging for any single conventional device to simultaneously fulfill both real-time photodetection and neuromorphic vision perception. Here, we report a monolithic GeSe/CsPbBr₃ heterojunction device featuring a seven-order tunable photoresponse timescale (from 20 μs to over 500 s). The wide temporal tunability originates from the bias-controlled transition between two distinct carrier dynamic regimes within a single heterostructure. At zero bias, the device operates as a self-powered ultrafast photodetector due to drift-dominated transport with a response time of 23 μs rise/20 μs fall, responsivity of 362.4 mA/W @400 nm, 1.5 mA/W @ 808 nm, detectivity of 2.52 × 1013 @400 nm, 1.04 × 1011 Jones @808 nm. It supports real-time broadband sensing (365-1,050 nm) with polarization resolution (dichroic ratio: 2.58 @ 808 nm). Under a 0.05 V bias, the device emulates biological synapses with persistent photoconductivity due to the coupling between photocarriers and ionized selenium vacancies, enabling neuromorphic visual perception for applications such as motion trajectory prediction and in-sensor image denoising. The dual-mode reconfiguration enables sensing, memory, and processing capability on a single device, representing a significant advance in multifunctional photonic synapses with exceptional simplicity, performance, and energy efficiency. It opens various possibilities for future adaptive vision systems.
Semiconductor lasers have evolved into the cornerstone of modern photonics infrastructure. The transition from fundamental homojunction and heterojunction devices to advanced quantum well architectures has enabled superior characteristics—including high monochromaticity, high collimation, and high power density—thereby driving their deployment in core modern laser technologies. Although silicon-based hybrid tunable lasers have been extensively reviewed recently, monolithic integrated tunable lasers based on pure III–V compounds remain dominant in high-performance applications due to their compact footprint, superior mechanical stability, and the elimination of complex inter-chip coupling processes. This review systematically examines the principles and recent advancements in monolithic integrated tunable lasers. Devices are categorized by their mode selection mechanisms: laser arrays based on DFB architectures, structures based on distributed Bragg reflectors (DBR), and grating-free designs relying on interferometric principles, such as V-coupled cavity and multi-channel interference (MCI) lasers. The physical mechanisms of mode selection and phase control strategies underlying these architectures are thoroughly analyzed. In addition, key challenges that are often overlooked in this field were also discussed, including long-term frequency stability (aging effect), the risk of mode transitions during dynamic tuning, etc. Additionally, the trade-offs between grating-based and grating-free interferometric devices regarding tuning range, linewidth, and fabrication complexity are evaluated, providing a technical roadmap for the development of light sources for next-generation optical communications, light detection and ranging sensing, and high-resolution spectral analysis.
We demonstrate a novel approach for site-controlled growth of InAs quantum dots on InP substrates emitting at telecom wavelengths, including the C-band, for quantum photonics applications. Regular nanohole arrays were defined by electron-beam lithography and dry etching, followed by InP regrowth. Quantum dots were then formed via droplet epitaxy in MOVPE, in which indium droplets were localised within the nanoholes and subsequently crystallised into site-controlled InAs quantum dots. Micro-photoluminescence measurements on a quantum dot array (2.5 µm pitch over 14 × 14 sites) reveal single-line emission in the telecom bands, with narrow linewidths reaching the instrument resolution, approximately 50 µeV for 60% of the dots and a single dot occupancy for over 80% of the nanoholes in the array.
Recent experiments have demonstrated the successful generation and detection of moderately squeezed vacuum states with integrated photonics. However, in order to benefit from the reduced noise of highly squeezed light, many different noise sources must be mitigated. Here, we quantify the fundamental limits these noise sources impose on squeezing measurements and find surprising generality across different platforms and designs. We combine these different limitations into a simple model that provides practical guidance for the design and benchmarking of next-generation integrated squeezed-light systems.
Flexible infrared photodetectors are key building blocks for next-generation sensing systems demanding mechanical compliance, lightweight form factors, and seamless integration with conventional platforms. We review recent progress in infrared-sensitive materials, strain engineering strategies, fabrication processes, and device architecture that enable high performance under mechanical deformation. Key application domains and emerging research directions toward scalable, robust, and application-ready flexible infrared photodetectors are outlined, offering a forward-looking roadmap for the field.
Nitrogen-vacancy (NV) centers in diamond are versatile platforms for quantum technologies, for which engineering microwave magnetic-field confinement and polarization are key elements. However, current microwave devices lack the capability to flexibly manipulate both. In this study, we address this issue by investigating a spoof surface plasmon polariton (SSPP)-based metasurface for engineering strongly confined microwave magnetic fields. Within the propagating SSPP mode, we reveal a rich texture of three-dimensionally oriented polarization, including circular polarization. In addition, we demonstrate the generation of a circularly polarized microwave magnetic field for an NV-containing diamond nanostructure, evidenced by spin-resonance spectra probed via the SSPP. We further confirm the non-reciprocal behavior of spin excitation due to the magnetic spin-momentum locking of propagating SSPPs. Furthermore, the circularly polarized field can be engineered to align with NV axes, enabling spin- and axis-selective control. This architecture could potentially enable on-chip zero-field vector magnetometry, overcoming a significant hurdle in compact quantum device integration.
Polar skyrmion bubbles are nanoscale ferroelectric domain configurations with swirling polarization textures, and often emerge in ferroelectric oxide systems. Owing to their inhomogeneous polarization patterns, which endow them with distinct topologies and electrical responses from homogeneous monodomains, polar skyrmion bubbles are envisaged to be promising candidates for non-volatile memory devices. In such device, the recorded information density is directly proportional to the density of bubbles, underscoring the need for precise control over bubble nucleation. Here, using first-principles-based calculations, we demonstrate that when assisted with a DC electric field, twisted light, which has a spatially inhomogeneous field pattern, can robustly tune the density of polar skyrmion bubbles in ferroelectric ultrathin films between 102 ~ 104bit/μm2. Moreover, by modulating DC and optical field strengths together with the beam radius, the nucleation rate, which characterizes the creation and annihilation speed of polar skyrmion bubbles, can also be well controlled. These findings highlight the unique response of ferroelectric nanofilms to optical and electric fields, which is crucial for employing polar skyrmion bubbles in the next-generation of ultrahigh-density memory technologies.
We present a self-traceable grating interferometer (STGI) based on chromium (Cr) atomic transition frequency (7S₃ → 7P₄), achieving direct length traceability to a natural constant. Cr gratings fabricated by atom lithography provide a pitch of 212.7779 nm (4700 lines mm⁻¹) with a measurement uncertainty of 0.0021 nm (k = 1), demonstrating excellent pitch precision. Combining the direct traceability of laser interferometry with the environmental robustness of grating interferometry, the STGI achieves sub-nanometer repeat positioning accuracy. Comparison with a laser interferometer calibrated by the national metrology institute shows excellent consistency, while 1 nm and 0.3 nm displacement tests reveal lower noise and higher sensitivity. This work establishes a novel length traceability chain linking atomic frequency standards to solid gratings, offering a compact, calibration-free, and highly stable approach for precise displacement metrology in advanced manufacturing and nanoscopic instrumentation.
Abstract Achromatic metalenses, planar diffractive devices structured with subwavelength nanostructures, are central to the development of compact, integrable alternatives to bulky multi-element optics. Yet their progress is fundamentally constrained by chromatic dispersion, which imposes trade-offs among operational bandwidth, numerical aperture (NA), aperture size, and efficiency. In this review, we introduce a unified framework that classifies achromatization strategies into four distinct paradigms: dispersion engineering, algorithm-aided method, architecture modification, and wavefront engineering. For each category, we analyze the underlying mechanisms, performance trade-offs, and fabrication limits, while identifying opportunities for cross-strategy synergies. Building on this framework, we highlight a forward-looking challenge: the realization of high-efficiency, centimeter-scale broadband achromatic metalenses from visible to infrared, an essential milestone toward application-ready flat optical systems in imaging, sensing, and augmented/virtual reality. This classification and roadmap aim to guide future efforts in overcoming long-standing bottlenecks of dispersion, scalability, and manufacturability.
To propel the advancement of quantum emitter-based capabilities, the coupling of semiconductor nanocrystals (NCs) with high-quality resonators is gaining traction as a promising platform for amplifying and controlling light-matter interactions. Herein, we demonstrate the modulation of the emission properties of perovskite NCs within the visible spectral region by integrating them with a silicon (Si) grating that sustains symmetry-protected bound states in the continuum. The dielectric metasurface nanostructures, composed of periodic Si bars fabricated via thermal scanning probe lithography, can be precisely manipulated to advance the development of photonic devices operating within the visible range. By adjusting the geometry of the Si bars, we achieve selective enhancement and shaping of specific wavelength ranges within the emission spectrum. Experimental investigation reveals a sixfold enhancement of photoluminescence (PL) attributable to the integration of the Si gratings. Furthermore, the directional emission of NCs is achieved with the help of the angle-dependent properties of the proposed metasurface. The excitation position also provides an additional degree of freedom to manipulate the emission direction of the PL. The enhanced and shaped emission is attributed to light-matter interactions, as further confirmed in transient absorption microscopy spectra. Our switchable emission strategy holds considerable promise for advanced light-emitting devices, with substantial implications for radiation control and optical imaging.
Abstract Underwater optical ranging has attracted growing attention due to its potential for higher accuracy than acoustic-based approaches. Alternative to typical ranging systems using the temporal/frequency information of lightwaves, a ranging scheme that utilizes spatially structured beams for distance retrieval has been demonstrated recently. In this approach, the beams are composed of Bessel-Gaussian modes carrying different orbital angular momentum orders and longitudinal wavenumbers, exhibiting a two-petal-like transverse intensity profile that rotates along the longitudinal propagation direction. This technique has shown relatively accurate ranging performance in scattering media by retrieving the rotation angle of the structured beam, and it operates using only a continuous-wave laser, without the need for high-bandwidth modulation or detection. This paper reviews the background and recent progress in underwater ranging using longitudinally structured beams and provides a perspective on several research topics for the future implementation of this approach.
Conventional image sensors are intrinsically limited to detecting optical intensity, thereby missing the rich phase and polarization dimensions of the light field. While characterizing these parameters is essential for understanding the intrinsic properties of objects, current multidimensional imaging techniques are often plagued by bulky optical setups, time-sequential scanning, or coherent noise artifacts. Here, we present a compact, single-shot imaging strategy capable of simultaneously retrieving full-Stokes polarization and quantitative phase information using a single-layer metalens. Our design utilizes the metalens to project the incident light onto distinct regions of a polarization camera. By introducing a predefined focal shift between isotropic sub-regions, we enable motion-free phase retrieval via the transport-of-intensity equation, while simultaneously separating chiral polarization states to reconstruct the complete Stokes vector. Using speckle-suppressed LED illumination, we experimentally demonstrate simultaneous full-Stokes polarization and quantitative phase imaging. This miniaturized architecture may pave the way for portable, real-time multidimensional optical sensing platforms.
Photonic integrated circuits (PICs) are central to scalable nanophotonics and are widely regarded as the most viable platform for large-scale quantum photonic systems. However, as quantum PICs increase in complexity, fabrication variability, optical loss accumulation, planar integration constraints and heterogeneous material stacking have emerged as primary bottlenecks, shifting the challenge from device physics to manufacturability. The pursuit of room-temperature quantum photonic chips further intensifies requirements for low-loss routing, thermal stability, packaging tolerance and multi-material co-integration. Here we argue that laser nanoprinting, particularly femtosecond laser direct writing, enabling three-dimensional photonic interconnects, permanent phase correction and localized refractive index control, directly addressing yield and scalability challenges. Integrating laser-based correction and 3D structuring within heterogeneous PIC platforms may therefore provide a practical pathway toward reproducible, manufacturable and room-temperature deployable quantum photonic systems.
Abstract Mid-infrared molecular sensing offers molecule-specific vibrational fingerprints, yet practical implementation with nanophotonic platforms is challenged by system complexity and strong signal damping in aqueous environments. Dielectric metasurfaces overcome ohmic losses and local heating constraints of metallic resonators and can support high-quality-factor resonances with spectral selectivity, suitable for image-based spectrometer-less sensing. However, their spatially extended near-fields typically render them susceptible to environmental absorption, preventing operation in water. We demonstrate a compact dielectric perfect-absorber metasurface combining C4-symmetric quasi-bound states in the continuum (qBICs) with a dual-gradient architecture. The C4-symmetric unit cells ensure polarization-independent resonances, enabling efficient utilization of incident light under arbitrary polarization states. The gradient architecture independently controls radiative loss and resonance wavelength, allowing distinct coupling regimes within one metasurface while achieving high absorbance (>0.8). We demonstrate poly(methyl methacrylate) sensing in air with ~20% absorbance envelope modulation under arbitrary polarization. Furthermore, we introduce a sensing configuration utilizing a 700 nm residual thin-water film that preserves qBIC (absorbance ~0.5) near the prominent water absorption peak. This enables the first demonstration of dielectric metasurface-based mid-infrared molecular sensing under a water background, achieving >30% absorbance envelope modulation. This platform extends the utility of dielectric metasurfaces to aqueous environments and supports versatile, spectrometer-less sensing schemes.
Achieving broadband second-order nonlinear processes in a fully integrated fiber platform has long been a challenge, as silica fibers intrinsically lack second-order nonlinear susceptibility due to their centrosymmetric and amorphous structure. Here, we introduce an all-fiber strategy that overcomes this limitation by integrating microfibers with few-layer gallium selenide crystals, enabling controlled and broadband optical frequency mixing. We reveal the critical role of time-domain synchronization in sum-frequency generation (SFG) and demonstrate multi-frequency mixing from four continuous-wave sources, producing ten converted wavelengths through simultaneous second-harmonic generation (SHG) and SFG. Remarkably, the system operates at low excitation thresholds, supporting broadband SFG with two superluminescent diode sources and yielding an unprecedented SHG continuum extending to ~180 nm with a supercontinuum source. Furthermore, the broadband SFG spectrum can be tuned over 70 nm by coupling with a quasi-monochromatic laser. This approach establishes a scalable and versatile platform for regulating the wavelength and bandwidth of nonlinear processes in optical fibers, opening pathways toward tunable broadband light sources and advanced all-fiber photonic technologies.
