ABSTRACT This paper presents a low‐complexity and low‐cost transmissive reconfigurable intelligent surface (TRIS) based on the phase‐change material vanadium dioxide (VO 2 ) for indoor millimeter‐wave (mm‐wave) communications. Although mm‐wave systems enable ultra‐high data rates and low latency, their performance is limited by severe path loss and non‐line‐of‐sight propagation. RISs offer a promising solution by dynamically controlling electromagnetic wave propagation. In particular, TRISs provide greater deployment flexibility than reflective RISs in indoor environments where transmitter–receiver links are blocked by walls, windows, or other barriers. However, wide phase tunability in TRISs typically requires complex circuit architectures. Moreover, conventional active components such as PIN and varactor diodes suffer from significant parasitic effects at mm‐wave frequencies, which degrade performance and increase design complexity. To address these limitations, the proposed TRIS exploits the metal–insulator phase transition of VO 2 and geometrically engineered VO 2 switch patterns to achieve flexible phase reconfiguration without complex biasing networks or lossy lumped components. The design is validated through theoretical analysis, full‐wave simulations, and measurements. The prototype steers transmitted waves from 0° to ± 20° at 65 GHz and achieves up to approximately 15 dB transmission enhancement between the programmed and reference states across 64–66 GHz, demonstrating its potential for indoor mm‐wave and WiGig applications.
ABSTRACT The continued advancement of silicon photonics increasingly relies on heterogeneous integration beyond monolithic fabrication, with transfer printing emerging as a powerful strategy for deterministic and high‐precision assembly. However, existing transfer‐printing strategies remain fundamentally limited to planar integration, restricting access to orientation‐dependent optical functionalities. Here, we introduce a rolling‐enabled transfer‐printing strategy that enables deterministic nonplanar heterogeneous integration through precise mechanical orientation control at the nanoscale. By exploiting rolling‐induced rotation during assembly, identical photonic‐crystal nanobeam lasers are integrated onto silicon waveguides in planar or orthogonal configurations, enabling selective coupling to TE‐like or TM‐like modes without modifying the cavity design or epitaxial structure. Both configurations exhibit stable lasing and polarization‐resolved coupling to silicon waveguides, in good agreement with numerical simulations, confirming that mechanical orientation alone can define optical functionality. By establishing orientation control as a new degree of freedom in heterogeneous integration, this work elevates transfer printing from a placement technique to a functionality‐defining platform, opening new opportunities for compact, multifunctional, and reconfigurable photonic systems on silicon.
ABSTRACT Conventional chiroptical spectroscopy relies on circularly polarized light (CPL), yet inherent retardance errors in CPL generation compromise signal fidelity and introduce artifacts from crosstalk with linear dichroism and birefringence. Here, we theoretically propose Chiroptical sensing via Linear dichroism of Anisotropic Plasmonic Slots (CLAPS), a CPL‐free chiroptical sensing scheme that employs two linearly polarized light (LPL) beams tilted with respect to the orientation axis of a plasmonic slot array filled with chiral analytes. Molecular optical activity perturbs the surface lattice resonance (SLR) of the array, producing a measurable reflectance difference between the two tilted LPL beams. Using an anisotropic chiral reflection model and numerical simulations, we reveal that the weak cross‐polarized reflection carrying chirality information is modulated by the strong co‐polarized response of the array. CLAPS circumvents the need for high‐purity CPL, offering a practically accessible route to trace‐level chiral molecule detection.
ABSTRACT Code‐division multiplexing (CDM) is essential for supporting massive connectivity in wireless networks, but its implementation typically requires complex and costly radio‐frequency (RF) chains. This work presents a simplified wireless CDM system based on a space‐time‐coding metasurface (STCM). By modulating distinct spatial partitions of the metasurface with data streams prespread via orthogonal pseudo‐random codes, the STCM functions as a distributed parallel modulator. This architecture enables the metasurface to perform simultaneous upconversion while directing modulated reflections from multiple spatial partitions toward either shared or distinct directions. Although these data‐carrying waves may physically overlap in the far‐field, the inherent orthogonality of the spread codes ensures that the receiver can successfully decorrelate and recover each multiplexed stream. Experimental validation demonstrates three core scenarios: multistream to a single direction, distinct single‐stream to distinct directions, and multistream to multiple directions (each direction gets multiple streams), all achieved without conventional RF chains. The proposed STCM‐based hybrid CDM and space‐division multiplexing (SDM) architecture enables simultaneous multiuser communication with a radically simplified RF front‐end, paving the way for simplified, high‐capacity wireless systems for future wireless networks.
ABSTRACT Exciton–polariton condensates are a promising platform for analog computation due to their macroscopic coherence and the ability to manipulate and address them optically. Patterned structures supporting these condensates further enable the realization of coherent polaritonic circuits. However, most demonstrations have relied on conventional III–V semiconductor platforms operating at cryogenic temperatures or requiring complex fabrication methods. Here, we realize molecular polariton condensate waveguides and related structures that support coherent condensate propagation at room temperature. The platform is based on a Tamm microcavity incorporating Rhodamine 3B Perchlorate embedded in a small‐molecule ionic isolation lattice (SMILES) complex as the excitonic medium, with photonic structures defined by focused ion beam milling. Spatial and momentum‐resolved photoluminescence measurements reveal room‐temperature propagation of polariton condensates in patterned waveguides. We further investigate the condensate blueshift and finite momentum, demonstrating that the condensate remains strongly confined during propagation. As a proof of concept, we also demonstrate condensation in custom geometries, including ring waveguides, Y‐splitters, and a Mach–Zehnder interferometer. These results establish a versatile platform for the rapid prototyping of polaritonic devices and represent an important step toward complex fully integrated polaritonic circuits operating at room temperature.
ABSTRACT Achieving continuous tunability and spin‐multiplexed functionality is essential for depth‐resolved imaging, yet existing approaches suffer from fixed focal lengths, transverse‐plane splitting, or inability to acquire two depth planes simultaneously. Here, we propose and experimentally demonstrate a cascaded liquid crystal Pancharatnam–Berry phase system. It comprises two phase elements and a classic convex lens, which enables continuously tunable axial spin‐dependent splitting via controlled lateral misalignment. A relative in‐plane displacement generates a spin‐dependent quadratic phase, yielding equivalent focal powers linear with displacement and opposite signs for orthogonal spins. This mechanism continuously tunes the focal lengths of left and right circularly polarized light, producing two separate foci at distinct axial positions for parallel depth acquisition. Reversing the displacement sign dynamically interchanges the two foci. Leveraging this capability, we demonstrate multiplane imaging in a single exposure, eliminating mechanical axial scanning required in traditional microscopes. An analytical model is established to quantitatively link the lateral misalignment to the two focal positions. This work establishes misalignment‐enabled axial spin splitting as a compact and efficient platform for depth‐resolved and spin‐dependent optical systems.
ABSTRACT Broadband high‐performance optical filters are fundamental building blocks for advancing mid‐infrared (MIR) integrated photonics, particularly for applications in molecular sensing and free‐space communication. Although dichroic filters offer robust high‐roll‐off performance in the near‐infrared, their realization in the critical MIR atmospheric transparency windows (3–5 μm) has remained largely unexplored. In this work, we demonstrate a high‐performance on‐chip dichroic filter on a silicon‐on‐insulator (SOI) platform, specifically engineered for the 3300–3700 nm spectral range. By integrating a longitudinally segmented subwavelength grating (SWG) waveguide, we effectively mitigate slot‐like propagation losses induced by sidewall roughness while simultaneously achieving precise control over mode dispersion. Through the synergistic adiabatic evolution and asymmetric directional coupler theory, the device achieves a maximum roll‐off rate of approximately 1 dB/nm and an extinction ratio exceeding 12 dB at a measured cut‐off wavelength of λ c ≈ 3460 nm. The filters exhibit flat‐top low‐pass and high‐pass characteristics over a 400‐nm bandwidth with negligible insertion loss. Our results demonstrate strong agreement between theoretical analysis and experimental validation, providing a scalable solution for interchannel crosstalk suppression and high‐SNR signal extraction in MIR photonic integrated circuits. This work fills a critical gap in the MIR toolkit, paving the way for sophisticated on‐chip spectroscopic systems and robust free‐space optical links.
ABSTRACT As a leading candidate for next‐generation electronics, high‐performance 2D Bi 2 O 2 Se has garnered significant interest in the scientific community. However, the understanding of its defect mechanisms remains elusive, hindering the development of further functionalities. In this study, we utilized Raman spectroscopy and ultrafast pump–probe experiments to investigate Bi 2 O 2 Se thin films prepared via a solution‐based technique. By comparing carrier decay times under low and high fluences in 25 nm‐ and 115 nm‐thick films, we proposed the defect mechanisms associated with two common defects in the thicker film: Se vacancies and Se–Bi antisites, which exhibit shallow donor and deep donor behaviors, respectively. Additionally, Se–Bi antisites became prominent under higher fluences. Our insights into these defect mechanisms offer valuable guidance for defect engineering in high‐power electronics.
ABSTRACT Wavelength‐tunable pulsed lasers have the ability to flexibly adjust laser energy and wavelength according to the properties of different materials platforms and experimental requirements, thereby markedly enhancing efficiency and precision. Thus, wavelength‐tunable pulsed lasers have attracted significant attention in fields such as wavelength division multiplexing, precision material processing, and spectroscopic analysis. Here, a polarization‐sensitive Au‐nanorod metasurface has been proposed that integrates saturable absorption with wavelength‐tuning capabilities. By fabricating this metasurface structure on the facet of the fiber, known as a metafiber, low‐loss coupling between the metasurface and the fiber laser system is achieved. In experiments, we have successfully demonstrated Q‐switched pulse, achieving precise control over pulse width (13.5–29.8 μs), repetition rate (15.3–43.7 kHz), and pulse energy (15.2–30.7 nJ) through meticulous adjustment of the pump power. Notably, by modulating the input polarization state, the response wavelength of the metafiber can be effectively controlled, enabling wavelength‐tunable pulsed laser output within a 5‐nm range. This achievement introduces a new concept and provides a viable solution for the design and development of next‐generation compact, high‐efficiency, and multifunctional laser systems.
ABSTRACT The synthesis of complex vectorial light fields with nontrivial topological polarization textures requires the coordinated control of spatial amplitude, phase, and polarization. A central challenge is to realize such multidimensional control in a compact physical architecture while retaining multiplexing capability. Here, we propose a vectorial diffractive neural network (VDNN) based on three cascaded metasurfaces for compact passive synthesis of topological vector light fields. By jointly encoding phase and polarization responses across the cascaded layers, the VDNN enables spatially multiplexed generation of multiple skyrmionic and bimeronic states. In a representative design, we demonstrate up to 16 topological textures with numerically evaluated average skyrmion numbers of , and an average orbital angular momentum (OAM) mode purity exceeding . Full‐wave simulations and tolerance analysis further show that this functionality can be preserved under realistic meta‐atom responses and inter‐layer perturbations. This work provides an inverse‐design approach for compact and multiplexed synthesis of complex topological vector light fields for potential applications in free‐space optical communications, particle manipulation, and polarization imaging.
ABSTRACT We present an easy access prototype solution using Fraunhofer‐HHI's open‐access indium phosphide photonic integrated circuits (PIC) platform. The process design kit enabled generic multiproject wafer process co‐integrates low‐loss passive components with gain, modulation, and detection. A high‐speed 80 GBaud traveling‐wave Mach–Zehnder modulator (MZM) is a key building block for emitter PICs. Accordingly, we demonstrate wafer‐scale, all‐electrical predicing tests using an MZM integrated with an on‐chip distributed‐feedback laser and photodiode. To showcase the platform's breadth, we highlight three emitter PICs. A widely tunable electro‐optic comb generator with a 20‐dB comb bandwidth of 480 GHz, a 670 MHz low‐repetition‐rate extended‐cavity mode‐locked laser, and a monolithic tunable ring laser with a 40 nm single‐mode tuning range and a 8.2 kHz intrinsic linewidth. All three PIC examples enable data‐rate scaling in optical communication by either increasing the number of channels or by increased symbol rate. Lastly, we present a convenient packaging solution that shortens lead time for prototype‐testing.
ABSTRACT Nonlinearity plays a central role in topological defect states, governing their stability, localization, and dynamics beyond the linear regime. However, investigating nonlinear dynamics of states in three‐ and higher‐dimensional systems remains highly challenging due to fabrication difficulties and the constraints imposed by spatial dimensionality. Here, we overcome this limitation by employing one‐dimensional synthesized lattices (1DSLs). Using anchor‐site and anchor‐mode mappings, we demonstrate that 1DSLs provide a versatile one‐dimensional platform for emulating the essential nonlinear dynamics and mode‐coupling pathways of disclination states in higher‐dimensional topological lattices. We show that different disclination states exhibit distinct nonlinear dynamics and mode‐coupling pathways, all of which are faithfully reproduced in the mapped 1DSLs. In particular, corner and disclination states exhibit fundamentally different nonlinear coupling mechanisms, whereas three‐dimensional disclination lattices support additional interactions between different classes of defect states. Our work extends dimensional synthesis beyond linear emulation and establishes a practical one‐dimensional platform for investigating nonlinear topological defect physics in higher dimensions. More broadly, it provides a route for exploring nonlinear topological phenomena that are otherwise difficult to access in higher‐dimensional photonic, acoustic, and mechanical wave systems.
ABSTRACT This paper gives an overview of the 3 μm SOI PIC platform and explains its unique characteristics, such as ultra‐high mode confinement, low losses, dense integration, polarization‐independent operation, small phase errors, ultra‐broadband operation, and ability to handle relatively large optical powers. Examples of monolithically integrated passive and active waveguide components are given, including couplers, wavelength (de)multiplexers, phase modulators, and Ge photodiodes. Hybrid integration and packaging possibilities are briefly addressed. As examples of potential applications, some results are provided for tunable lasers, optical beam steering, medical imaging, and RF beam steering. Ongoing and targeted developments for this PIC platform are also briefly discussed, and a comparison to some alternative PIC platforms is made. Access to this technology in VTT’s Micronova cleanroom with 200 mm wafer size is supported by process design kits and the PIXEurope pilot line.
ABSTRACT Planar surface plasmon polaritons (SPPs) at metal–oxide–semiconductor (MOS) interfaces are central to plasmon‐assisted optoelectronic and tunneling devices, where ultrathin dielectrics govern field confinement and energy transfer. However, a direct link between electron energy‐loss spectroscopy (EELS) measurements and electromagnetic power dissipation at buried interfaces remains unclear. Here, we combine STEM–EELS with full‐wave electromagnetic simulations to investigate SPP excitation in planar and stacks with 10 nm dielectric spacers. Using a finite‐difference time‐domain approach, the fast electron is modeled as a broadband electromagnetic source, enabling decomposition of extinction into absorbed and scattered power and direct comparison with EEL spectra. We show that extinction is dominated by non‐radiative absorption, confirming that the observed resonances originate from SPPs confined to the buried Au–oxide interface. Increasing dielectric permittivity induces a redshift and modifies modal confinement, while losses remain Au‐dominated. Kramers–Kronig analysis and simulations further confirm dielectric dispersion effects and exponential evanescent decay across the oxide layer.
ABSTRACT As a type of inverse‐designed micro/nanophotonic device, planar super‐oscillation diffractive lenses (PSODLs) require complex trade‐offs among multiple key performance metrics to optimize their performance, including spot size, focusing efficiency, field of view (FOV), depth of focus (DOF), and working bandwidth. This review focuses on two representative types of PSODLs, super‐oscillatory lenses (SOLs) and supercritical lenses (SCLs). Both can generate far‐field focal spots with sizes below the diffraction limit, but they exhibit distinct optical‐field focusing characteristics, and there are trade‐offs among performance parameters. Therefore, this review provides specific guidance for the selection and optimization of PSODLs in accordance with application scenarios. To better promote the practical application of these kinds of lenses, a systematic analysis of typical applications in areas such as super‐resolution imaging, micro/nanofabrication, and high‐precision measurement is provided. Potential extensions of PSODLs to integrated optical imaging systems, optical sensing, particle manipulation, and optical storage are also discussed. Future practical deployment of PSODLs will rely on application‐oriented multiobjective optimization, robust and scalable fabrication, active system integration, and standardized performance evaluation.
Dual-comb spectroscopy, constructed from two frequency combs with slightly different repetition frequencies, enables real-time and high-precision measurements without mechanical scanning. In the terahertz spectral range, dual-comb techniques provide a powerful tool for high-resolution and rapid spectroscopy. Quantum cascade lasers (QCLs), owing to their compact footprint and favorable size, weight, and power, have emerged as promising sources for THz dual-comb systems. In QCL frequency combs, the repetition frequency generated through intrinsic four-wave mixing is typically equal to the cavity round-trip frequency, corresponding to the fundamental comb. Although this repetition frequency can be tuned via current and temperature control, the accessible tuning range remains limited. Recently, harmonic frequency combs, whose repetition frequencies are integer multiples of the cavity round-trip frequency, have attracted increasing attention, offering enhanced single-line signal-to-noise ratios and providing direct insight into the strong nonlinearity of QCLs. Here, we demonstrate a reconfigurable multi-harmonic dual-comb system realized on a single self-detected THz QCL platform. By precisely controlling the driving current and thermal conditions, we achieve and switch between multiple dual-comb configurations, including fundamental-fundamental, fundamental-second-harmonic, second-harmonic-second-harmonic, and second-harmonic-third-harmonic dual-combs. These results establish harmonic order as an additional degree of freedom for dual-comb operation within a single laser system. The demonstrated platform enables high-resolution and high-sensitivity measurements while significantly simplifying the system architecture. This reconfigurable multi-band dual-comb approach based on a single QCL opens new opportunities for compact THz spectroscopy and frequency metrology.
ABSTRACT We theoretically investigate the vortical differential scattering (VDS) of spatiotemporal optical vortex (STOV) carrying arbitrary orbital angular momentum (OAM) orientation by chiral particles within the framework of polychromatic generalized Lorenz–Mie theory (GLMT). Numerical results show that STOVs with a nonzero longitudinal OAM component exhibit significant vortical dichroism (VD), whereas those with purely transverse OAM do not. Mechanistically, transverse OAM's zero net optical chirality density and collapsed spatial energy flow vortex lack the requisite torque and asymmetric multipolar excitations to drive chiral responses. Furthermore, it is found that the larger topological charges and tighter spatiotemporal scales significantly enhance the VD. Our work establishes a solid theoretical foundation for future explorations of the chiral dynamics of STOV, paving the way for applications in enantiomer sensing, advanced chiral spectroscopy, and precise optical manipulation.
ABSTRACT Terahertz (THz) optical components for power attenuation and dispersion management require materials that provide isotropic and band‐selective control of electromagnetic waves. However, two‐dimensional (2D) metasurfaces based on coherent lattice coupling exhibit polarization anisotropy and angular dispersion, which lead to phase distortion. Here, three‐dimensional (3D) bulk metamaterials (MMs) functioning as THz attenuators are proposed and experimentally demonstrated based on a de‐latticing strategy inspired by amorphous natural materials. Periodic arrays of cross‐bar meta‐atoms are encapsulated by cyclo‐olefin polymer (COP) as randomly oriented cubic meta‐grains and dispersed within a COP matrix, forming an amorphous composite that eliminates in‐plane coherence. The fabricated samples exhibit band‐selective and thickness‐tunable attenuation with a smooth refractive‐index variation across 0.3–0.4 THz. Compared with the 2D metasurface, the dispersion slope decreases from 8.37 to 0.36 at the resonant frequency, indicating an order‐of‐magnitude suppression of phase dispersion. The attenuation scales continuously with thickness owing to incoherent resonant scattering from randomly oriented dipoles, providing a practical pathway to thickness‐dependent and band‐selective response. This work demonstrates an isotropic, low‐dispersion, and thickness‐tunable 3D bulk MMs THz attenuator that overcomes the polarization anisotropy and strong dispersion of conventional 2D attenuators, offering a practical pathway toward integrated THz photonic systems.
We present a first-principles study of the nonlinear optical response of transparent conducting oxides at the nanoscale due to excitation by intense, extremely short pulses based on a density matrix framework. We identify a strong (O(1)) thermal nonlinearity, which is complemented with stimulated emission and excited-state absorption; it yields a cumulative permittivity change decorated by quantum coherent oscillations. Further, rigorous calculations under far-from-equilibrium conditions show that electron-electron thermalization occurs within a few femtoseconds, supporting interpretations of high-harmonic generation measurements and in agreement with a generalization of Fermi liquid theory.
ABSTRACT The topological nature of bound states in the continuum (BICs) has attracted significant interest in manipulating resonant states and light radiation through topological singularities in momentum space. In this work, we present a scheme to realize tunable unidirectional guided resonances (UGRs) based on interactions between multiple circularly polarized states (C points) in momentum space. We first demonstrate that C points can intrinsically exist around symmetry‐protected BICs in photonic crystal slabs even without any symmetry reduction. Through controlled symmetry breaking, the BIC splits into a pair of C points, which can interact with the intrinsic ones. Their interactions lead to rich evolution processes of C points, including formation of two UGRs at different k points with opposite topological charges, and generation of two UGRs with identical charges accompanied by the annihilation and regeneration of C points. Furthermore, it is demonstrated that directional radiation with high asymmetry ratio can be achieved across a broad parameter range via the interactions between multiple C points. These findings suggest that the involvement of multiple singularities provides additional degrees of freedom for resonant mode manipulation, opening new avenues for investigating singularity dynamics in momentum space and applying unidirectional guided resonances in optical field control.
