Ruihuan Duan

Niobium oxide dihalide films show a second-harmonic generation (SHG) efficiency scaling with their thickness, owing to their weak interlayer electronic coupling, but their use in integrated nonlinear photonics has been limited by the lack of robust electrical tuneability. Here we integrate ferroelectric NbOBr₂, of thicknesses ranging from 20 nm to 40 nm, with a silicon nitride microring resonator to realize electrically reconfigurable SHG on a photonic chip. NbOBr₂ combines strong second-order susceptibility from intrinsic inversion-symmetry breaking with electrically switchable in-plane ferroelectric polarisation. By modulating the Schottky barrier at the NbOBr₂-metal interface, ferroelectric switching controls carrier injection, free carrier absorption and dispersion, thereby tuning the cavity-enhanced nonlinear response. The device achieves an SHG conversion efficiency of 158% W^-1 under continuous-wave excitation and a 53% electrical modulation depth. The polarisation states can also be programmed over multiple levels and retained after switching, enabling non-volatile control of the optical response. Using the fundamental and frequency-converted outputs as complementary channels, we further demonstrate dual-channel edge detection.

Twisted bilayer transition metal dichalcogenides, governed by a single twisted interface, offer a versatile platform for manipulating interlayer coupling and emergent optical behavior. However, despite extensive studies on single twisted interface systems, how multi‐interface twisted stacking influences nonlinear optical behavior remains unclear. Here, we address this gap by systematically investigating the nonlinear optical performance of chemical vapor deposition (CVD) grown twisted trilayer MoS ₂ (TT‐MoS ₂ ) with multi‐interface twisted stacking. We fabricate all nine distinct trilayer MoS ₂ configurations by CVD. Raman and photoluminescence show that twisted interfaces modulate interlayer coupling, giving rise to stacking‐dependent phonon and excitonic responses. Atomic‐resolution scanning, transmission electron microscopy, and selected area electron diffraction confirm dual twisted interfaces and a supermoiré lattice. Guided by these structural insights, we examine the second harmonic generation (SHG) response across all nine trilayer configurations. Extending the coherent SH field superposition model to a trilayer system with two independent twisted interfaces, we develop a framework that describes how the dual interfaces govern the SHG intensity and polarization orientation across stacking configurations. Our findings establish TT‐MoS ₂ as a versatile nonlinear platform and open new avenues for understanding and exploiting multi‐interface twisted coupling to engineer nonlinear optical responses in van der Waals materials.

Ferroelectric tunnel junctions (FTJs) hold great promise for neuromorphic computing due to their advantages of low energy consumption, high speed, and nonvolatile multi‐level resistance states. However, achieving a programming voltage below 1 V in FTJs, a critical requirement for neuromorphic computing, is hindered by the high energy barrier of traditional ferroelectric materials. Here, we report an all‐two‐dimensional (2D) FTJ based on the van der Waals (vdW) ferroelectric semiconductor AgBiP ₂ Se ₆ . Benefiting from the low polarization‐switching barrier of AgBiP ₂ Se ₆ and the high‐quality interface of the all‐2D structure, the vdW ferroelectric semiconductor tunnel junction (FSTJ) demonstrates robust memory characteristics. Reproducible DC resistive switching over 600 cycles at an operating voltage below 0.2 V can be achieved in the FSTJ, coupled with outstanding memory performance including long data retention (>10 ⁴ s) and a fast write speed of 100 ns. Beyond basic memory functions, the device also serves as a promising platform for neuromorphic computing. Potentiation and depression (LTP/LTD) synaptic behaviors with high linearity (0.68 for LTP, 0.23 for LTD) and symmetricity (94.7) can be emulated at a minimum programming voltage of 0.05 V, enabling successful system‐level image recognition simulations. These results highlight the potential of vdW FSTJs for low‐power memory and neuromorphic computing applications. image

Broadband imaging across visible, near‐infrared, and mid‐infrared (VIS‐NIR‐MIR) is a long‐standing goal for applications spanning machine vision, autonomous navigation, remote sensing, and biomedical monitoring. However, current approaches typically require multiple single‐band detectors or heterogeneous material stacks to cover different spectral windows, which add substantial optical and fabrication complexity. Here, we report a large‐pixel‐count, room‐temperature VIS‐NIR‐MIR broadband image sensor enabled by a detector‐array vertical photodiode architecture that uses large‐scale two‐dimensional (2D) black phosphorus (BP) films as a single active material. Operating at room temperature under zero bias, the BP film photodiodes exhibit an intrinsically broadband response spanning 532 nm to 6.2 µm, with specific detectivity ranging from 1.36 × 10 ⁷ cm Hz ^1/2 W ⁻¹ at 6.2 µm to 1.0 × 10 ⁸ cm Hz ^1/2 W ⁻¹ at 3.7 µm. We further achieve monolithic integration of the 2D BP film photodiodes with a 640 × 512 silicon readout integrated circuit (ROIC), enabling large‐pixel‐count VIS‐NIR‐MIR broadband imaging using a single active material for the first time, to the best of our knowledge. This work establishes a scalable, ROIC‐compatible, chip‐scale imaging platform and provides a pathway toward compact, low‐cost, large‐pixel‐count broadband cameras operating across the VIS‐NIR‐MIR spectral regions.

The optical properties of quantum systems are fundamentally governed by their electromagnetic environment through the local density of optical states (LDOS), enabling powerful control over atomic, excitonic, and electronic transitions. However, the radiative properties of phonons have remained largely unexplored within this framework of environmental engineering. Here we demonstrate LDOS control of terahertz (THz) phonon emission in the van der Waals ferroelectric NbOI ₂ using a simple mirror geometry. By modifying the photonic environment, we achieve pronounced and reversible tuning of the phonon Q ‐factor, peak frequency, linewidth, and emission intensity, with modulation approaching an order of magnitude. The observed behavior arises from Purcell‐like enhancement and suppression of the phonon radiative rate, revealing a near‐unity radiative quantum efficiency in NbOI ₂ . Our results establish radiative phonons as tunable quasiparticles governed by photonic boundary conditions, extending LDOS engineering from electronic to lattice excitations. This framework enables deterministic control of phonon lifetimes and emission spectra, opening new opportunities for compact tunable THz sources and phonon‐based quantum and photonic technologies.

NbOX ₂ van der Waals ferroelectric materials exhibit large second‐order nonlinear responses and strong light‐matter interactions, making them promising candidates for ultrafast optoelectronic and quantum photonic applications. However, their terahertz (THz) electro‐optic (EO) properties remain experimentally unexplored. Here, we report the first experimental study of NbOX ₂ thin films subjected to intense THz electric fields, combining both the frequency‐dependent electro‐optic (EO) effect and the THz‐field‐induced modulation of second‐harmonic generation (SHG). We observed a pronounced phonon resonance enhanced EO response with effective EO coefficients reaching 332 pm/V at 3.1 THz in NbOI ₂ and 192 pm/V at 3.7 THz in NbOBr ₂ . Under a 150 kV/cm THz pump field, we further observe a non‐resonant SHG modulation of 4% and a resonant phonon‐enhanced modulation. These results establish NbOX ₂ as a class of high‐performance, phase‐matching‐free THz electro‐optic platform for ultrabroadband time‐domain spectroscopy, high‐speed optical switching, and phonon‐enhanced nonlinear optical response in 2D ferroelectrics.

Photodetectors that can achieve both high sensitivity and fast speed remain a challenge due to inherent trade-offs, particularly limiting in photonic integrated circuits. While substantial progress has been made in broadening spectral response, few strategies have directly addressed the simultaneous enhancement of sensitivity and speed. Here, we introduce a two-dimensional photodetector incorporating a functional interlayer, monolayer tungsten oxyselenide (TOS), formed between n-type PdPSe and p-type WSe₂. TOS serves multifunctional roles to overcome the trade-offs: suppressing dark current as a hole barrier, enhancing responsivity via photogating, and preserving speed through trap-assisted tunneling and direct tunneling. Under spatially resolved illumination, the device shows a detectivity (D*) of 3.78 × 10¹⁵ Jones at 520 nm, with a bandwidth of 0.055 GHz at 785 nm. When integrated onto a silicon photonic platform, it achieves D* of 3.69 × 10¹¹ Jones and a bandwidth of 0.11 GHz at 785 nm, outperforming most reported on-chip photodetectors. These results establish a route to sensitive, high-speed photodetectors for optical interconnect, communications, and sensing applications.