Lei Xu

Metasurfaces are considered the backbone of the ongoing photonics revolution to shape the electromagnetic waves on demand via a flat array of resonators. The beauty of metasurfaces lies in their ability to simultaneously control multiple waves. However, obtaining such multi-functionality often requires active components, such as active electronics and complex tuning mechanisms. A recent study demonstrates a fully passive architecture, composed of sliding metasurfaces that combines two distinct functionalities, i.e. frequency-selective filtering with wide-angle beam steering in a single platform. By replacing local phase reconfiguration with a simple geometric translation between complementary phase profiles, the work introduces a simple yet innovative route to a two-dimensional frequency-angle selection window. It opens new opportunities for passive wave-based information processing.

Phase‐change metasurfaces have attracted significant attention for reconfigurable photonic devices owing to their ability to tune optical responses between amorphous and crystalline phases. Despite their potential in optical switching, communications, and signal processing, achieving large optical modulation while maintaining low optical loss and strong field confinement remains a major challenge. Here, the unique properties of metasurfaces on monolithic and hybridized /Si platforms are experimentally demonstrated. In the telecommunications spectral range, both phases remain nearly lossless, with a large refractive‐index contrast. The monolithic metasurface enables transmission modulation depths of up to 92% and resonance shifts of 150 nm through laser‐induced phase transitions to 50% polycrystalline state. Integrating a silicon overlayer introduces hybrid resonance with enhanced near‐field confinement, achieving comparable modulation with nearly half the laser switching power required by the monolithic structure. Furthermore, the broad resonance tunability and strong third‐order nonlinearity of metasurface enable tunable third‐harmonic generation over a 40 nm spectral range. The hybrid /Si platform further demonstrates a threefold enhancement in tunable THG emission, benefiting from the combined nonlinear responses and strong resonance field confinement. These results highlight the potential of monolithic and hybrid metasurfaces for compact low‐power optical switching and tunable visible light sources.

Nonlinear optics underpins a broad range of photonic technologies, from classical and quantum light sources to emerging nonlinear photonic neural networks. Yet, conventional nonlinear-optical devices exhibit static functionality: Their transfer characteristics and emission profiles are dictated by the intrinsic nonlinear process and locked by fabrication, limiting adaptability. Here, we introduce an ultrathin metasurface platform that enables dynamic reconfiguration of nonlinear functionality in a contactless fashion. By leveraging all-optical control of the optical torque exerted on liquid crystal molecules infiltrating a resonant metasurface, we achieve tunable polynomial nonlinear transfer functions based on the third-harmonic generation process. This mechanism further allows reconfigurable modulation of nonlinear weighting across different diffraction orders, revealing a previously unexplored interplay between mode structure and nonlinear emission. Our approach opens up a pathway toward field-programmable nonlinear photonic systems, offering unprecedented flexibility for reconfigurable nonlinear signal processing and adaptive photonic computing.

Disorder in moir\'e superlattices simultaneously degrades flat-band localization and induces Anderson localization, yet how these two regimes interact has remained unclear. Here, we introduce a combined framework linking localization\penalty1000-\hskip0ptlength scaling with differential probability density analysis to map localization transitions in partially disordered one\penalty1000-\hskip0ptdimensional silicon moir\'e lattices. It is found that flat bands confined within the interband gap keep their strong localization even as disorder grows. In contrast, flat bands intersecting dispersive bands exhibit rich behaviors: the low\penalty1000-\hskip0ptfrequency branch undergoes an inverse Anderson transition, while the high\penalty1000-\hskip0ptfrequency branch supports coexisting flat-band and Anderson localization at strong disorder. Our results deliver direct evidence of competing localization mechanisms in disordered moir\'e systems and offer guiding principles for engineering robust, nonideal moir\'e photonic devices.

Polarization‐sensitive photodetectors can enhance the capability of target recognition in intelligent driving, security monitoring, and biomedical diagnostics. However, miniaturizing such devices to subwavelength scales introduces a fundamental trade‐off between light absorption efficiency and polarization extinction ratio. To address this, we integrate ultrathin metasurface polarization filter arrays (MPFAs) onto GaAsSb nanowire (NW) array photodetectors. The GaAsSb NW array geometry was designed and optimized for 93.5% average absorption across a broad wavelength range from 660 to 840 nm, to exhibit a high photodetector peak responsivity of 2.0 A W ⁻¹ and a specific detectivity of 4.3×10 ¹⁰ cm•√Hz W ⁻¹ under a low bias voltage of 1 V. The L‐shaped silver nanohole MPFA was designed and fabricated via focused ion beam, generating strong polarization‐selective plasmonic resonance in the near‐infrared region. This leads to the demonstration of an integrated device with a linear polarization extinction ratio of 3.5 and good device performance (peak responsivity of 1.5 A W ⁻¹ and detectivity of 2.3×10 ¹⁰ cm•√Hz W ⁻¹ ), enabling high‐resolution single‐pixel polarimetric imaging. The direct metasurface/III‐V semiconductor NW array integration strategy provides a new route toward next‐generation ultra‐compact, high‐performance polarimetric infrared imaging systems covering a broad spectrum from the near‐ to mid‐wave infrared for diverse applications.

Arrays of resonant nanoparticles, so-called metasurfaces, have been developed and demonstrated as the first generation of meta-operators. Unlike today’s electronic systems, the demonstrated compact, scalable platform enables ultrafast, energy-efficient all-optical image processing, extending to holographic wavefront shaping with a single-layer metasurface. These results open new opportunities for advanced optical computational microscopy and intelligent sensing.

The realization of high-speed, low-power computing beyond conventional electronics demands new paradigms for optical logic processing. Here, we present a passive terahertz (THz) metasurface platform that enables intrinsic frequency-multiplexed logic operations within a single, compact device. By encoding logical inputs through orthogonal polarization states and exploiting the multi-resonant response of fractal H-shaped metastructures, the proposed system performs multiple logic operations simultaneously across the 0.2–2.0 THz band. Unlike existing approaches that rely on active tuning or sequential execution, our design achieves parallel logic functionality in a fully passive and multiplexed architecture. Experimental validation using THz time-domain spectroscopy confirms broadband operation with extinction ratios up to 9.09 dB and robust safety margins exceeding 10%. This work establishes a scalable route toward compact, energy-efficient, and all-optical parallel computing systems in the THz regime.

Precise manipulation of terahertz (THz) wave polarization is essential for enabling high‐performance THz imaging, wireless communication, and spectroscopy. However, existing birefringent and metasurface‐based polarization controllers typically offer either cross‐polarization conversion (CPC) or waveplate functionality and often operate over limited bandwidths with restricted angular tolerance. In this work, we experimentally demonstrate a compact, dual‐functional reflective metasurface that unifies high‐efficiency narrowband CPC with wideband quarter‐wave plate (QWP) operation. Both simulations and measurements confirm near‐unity cross polarization conversion at 0.65, 0.80, 2.02, and 2.48 THz, as well as QWP bands at 0.86–1.95 THz (fractional bandwidth, 77%) and 2.08–2.45 THz (FBW 16%). The measured results further reveal high polarization efficiency and angular stability up to 50°, validating the metasurface's practical potential. This experimentally verified design offers a significant step toward multifunctional, compact, and broadband THz polarization‐control components for next‐generation THz systems.

Conventional infrared (IR) imaging techniques depend on IR cameras based on narrow-bandgap semiconductors, which offer limited spectral bandwidth, coupled with a separate lens. Recently, advances in nonlinear flat optics have opened a novel pathway for converting IR signals into the visible through nonlinear generations, enabling the direct visualisation of IR images using standard visible cameras. However, the narrow spectral bandwidth and the requirement for an additional lens remain the key challenges. Here, we address both issues via a novel adaptive and multifunctional IR-to-visible imaging platform offering tunable bandwidth and focusing simultaneously. We utilise sum-frequency generation (SFG) to convert IR light into the visible, by introducing a pump beam modulated by a spatial light modulator (SLM) to construct a virtual metalens enabling precisely controlled focusing of the generated nonlinear optical field. As a result, we demonstrate both theoretically and experimentally an optical focusing mechanism with a tunable focal length, achieved by varying the pump and signal wavelengths and modulating the phase distribution. Furthermore, since the focal length depends on the input signal wavelength, the imaging plane position varies accordingly, indicating a promising potential for the multispectral IR imaging applications. Our upconversion platform delivers SLM-controlled, programmable multispectral focusing for next-generation IR imaging, opening new avenues in the fields of computational and multispectral imaging techniques.

This study examines burst laser-induced pitting (BLIP), an understudied surface modification phenomenon driven by ultrafast laser bursts with sub-picosecond to picosecond inter-pulse delays. Through SEM and AFM analysis, we characterize BLIP as sub-micron pits with polarization-dependent oval shapes, alongside high-fluence melting zones and localized ripple-like structures. Unlike conventional laser-induced periodic surface structures (LIPSS), BLIP demonstrates exceptional energy coupling efficiency, evidenced by 10× greater damage areas and a steeper fluence-scaling expansion rate than LIPSS, attributed to transient carrier-mediated processes. Pit density decays exponentially with delay ( τ ≈ 6.6–8.9 ps), matching the timescale of self-trapped exciton relaxation, while spatial statistics reveal a delay-driven transition from field-guided ordering (1–5 ps) to randomized distributions (>10 ps). The resonant-like angular distributions and delay-dependent ellipticity reduction indicate competing mechanisms: optical field enhancement dominates at short delays, while energy dissipation and structure disordering prevail at longer delays. Simulation of nanoplasma excitation reveals near-field optical field enhancements responsible for the ellipticity and ripple-like structures. Beyond their fundamental significance, these BLIP nanostructures offer practical functionalities, including use as anti-reflection coatings and hydrophobic surfaces. These findings establish BLIP as a new paradigm in ultrafast laser-material interactions, where burst parameters selectively activate defect-mediated or field-driven modification pathways in dielectrics.