Wen-Di Li

We propose and experimentally demonstrate a compact optical switch based on a one-dimensional (1D) silicon nitride (Si ₃ N ₄ ) photonic crystal nanobeam cavity (PCNC) integrated with a graphene microheater. The PCNC exhibits a small optical mode volume of approximately 3.2 μm ³ , which enhances light-matter interaction and improves thermo-optic (TO) tuning efficiency. Graphene is positioned at the center of the cavity, and heat generation is induced by applying a bias voltage across it. The refractive index of the underlying PCNC is then changed due to the TO effect, thereby enabling resonance wavelength tuning. Additionally, fast thermal response is achieved owing to the high thermal conductivity of graphene. Measurements show a TO tuning efficiency of 0.21 nm/mW and an extinction ratio (ER) of 7 dB at an applied heating power of 5.2 mW. The thermal rise and fall time constants are 4.55 μs and 1.55 μs, respectively. This work achieves a microsecond-level Si ₃ N ₄ -based optical switch with a compact device footprint, offering a promising solution for high-density on-chip optical interconnects and routing systems.

Narrow-linewidth, frequency-modulated continuous-wave (FMCW) lasers are indispensable components in modern sensing and measurement systems. Toward their integrated photonic implementations, self-injection-locked lasers stand out for the ultralow noise and operational simplicity. However, their tuning range remains limited, primarily due to the restricted locking range imposed by the long-delay external cavities. In this work, we address this limitation by demonstrating a widely tunable FMCW integrated laser through self-injection locking to a strongly reflective multimode micro-ring resonator (MRR). This MRR adopts a tailored over-coupled design with negligible intermodal crosstalk, unifying large free spectral range and high-Q strong reflection, substantially extending the laser self-injection locking range. Experimental results reveal that the multimode MRR presents a high intrinsic Q value of 1.45×107 together with a reflectivity of −0.92 dB. The demonstrated hybrid integrated laser leverages a combination of exhibits, a static mode-hop-free tuning range up to 37.84 GHz, a side-mode suppression ratio exceeding 65 dB, and an intrinsic linewidth of 1.55 kHz. Furthermore, it achieves FMCW generation with a record-high chirp bandwidth of 25.42 GHz at a 100 Hz repetition rate. These results highlight the promising application prospects and practical value of the proposed laser in cutting-edge fields, including light detection and ranging, microwave photonics, and optical fiber sensing.

Perovskite quantum dots (PQDs) are promising chiroptical materials owing to their soft ionic lattice and strong surface-lattice coupling. However, achieving efficient chirality induction in solid-state chiral PQD (CPQD) thin films remains a fundamental challenge. Here, we establish sterically constrained surface coordination as a strategy to promote chirality induction and lattice asymmetry in PQD solids. Using a synthesis-on-substrate approach, CsPbBr₃ CPQD thin films with exclusive chiral ligand coverage are directly constructed, enabling well-defined ligand-surface interactions. Density functional theory calculations indicate that ligand coordination geometry, rather than ligand density, governs the strength of asymmetric interaction at the PQD surface. As a result, the CPQD films exhibit photoluminescence dissymmetry factors exceeding 10^-2 across the tunable range of 468-515 nm, reaching 3.47 × 10^-2 at 510 nm, and combine pronounced chirality-induced spin selectivity with high electrical conductivity. Spin light-emitting diodes based on the CPQD films achieve an electroluminescence dissymmetry factor of 0.15 and an external quantum efficiency of 17.9%. Our results highlight the role of coordination environment in chirality transfer and underscore the potential of CPQDs for spin-optoelectronic applications.

Thermal nanoimprint lithography (T-NIL) offers a compelling route for simultaneously patterning polymer surfaces and manipulating internal molecular order. However, the fundamental mechanisms governing flow-induced orientation in amorphous polymers and their functional exploitation remain underexplored. This study investigates molecular chain alignment in polycarbonate films during T-NIL, elucidating the link between processing rheology and optical functionality. We demonstrate that the geometry of imprinted structures, specifically gratings and square pillars, strictly dictates local flow fields, resulting in distinct, programmable orientation patterns confirmed by birefringence mapping. Critically, we reveal that the directionality of demolding dictates the interfacial shear stress, which induces a localized shear-aligned surface layer. This interfacial effect can reorient molecular chains at the polymer surface, potentially compromising both structural integrity and programmed optical properties. Furthermore, quantitative analysis reveals that the degree of orientation is tunable via nanoconfinement effects, scaling inversely with feature linewidth and proportionally with aspect ratio. Harnessing this tunable anisotropy, we demonstrate a novel polarization-responsive anticounterfeiting interface. Through the spatial engineering of local optical axes, the fabricated label conceals information under unpolarized ambient light while revealing dynamic, high-contrast patterns under polarized illumination. This study provides a mechanistic framework for nanoimprint-induced molecular alignment in amorphous polymers and demonstrates its potential application in optical anticounterfeiting.

A broadband silicon polarization beam splitter (PBS) is proposed and experimentally demonstrated based on Floquet-engineered directional couplers. The total length of the coupling structure is 20 μm. By periodically modulating the waveguide widths of the directional couplers, the power exchange between the two waveguides for the transverse-electric (TE) mode is suppressed, while the power coupling for the transverse-magnetic (TM) mode is enhanced. The fabricated PBS exhibits polarization extinction ratios (PERs) >20 dB for both polarizations over a broad wavelength range of 1483–1620 nm. Additionally, the measured insertion losses (ILs) are 0.15 dB and 1.2 dB at 1550 nm for TE and TM polarizations, respectively.

Reducing the width and space of copper lines on advanced organic packaging substrates is a direct way to increase the circuit density for multifunctional applications. Herein, a new process called copper tooth transfer printing (CTTP) is reported that can manufacture substrates with fine line width and space using traditional low‐cost printed circuit board manufacture equipment. A scalable SiO ₂ /epoxy composite film is fabricated by die coating and performed high performance for realizing the CTTP process. Two types of copper foils of high temperature elongation electrodeposited (HTE) and reverse treat foil (RTF) with different surface roughness are used to evaluate the CTTP process. The pit structure observed on the composite film surface after CTTP process offers rivet point for the forming of copper seed layer. High values of peel strength about 0.48 and 0.33 N mm ⁻¹ are achieved by using HTE and RTF copper foils, respectively. Importantly, a high automated optical inspection yield rate of the lines above 96% on both side of the substrate with line width and space of 40/20 μm is achieved by using the RTF copper foil owing to the less copper tumor formed. The CTTP process will be a promising route for fabricating advanced high‐density packaging substrates.

The escalating demand for wearable electrodes in the era of digital healthcare underscores the urgent need for more efficient and accurate biopotential monitoring techniques. Here, we report a scalable and facile approach to the fabrication of microneedle electrodes (MNEs) for accurate and imperceptible biopotential monitoring, leveraging a unique micro/nanoelectroforming technique. We exploited magnetron sputtering of indium tin oxide on an inverse-microneedle mold and subsequent electrodeposition of metal layers to produce ultrathin, flexible, and highly conductive MNEs. These MNEs outperformed the planar metal electrodes and commercial silver/silver chloride gel electrodes. The microstructured surface of MNEs increases the contact area and bypasses sweat and grease on uneven skin surfaces, leading to lower electrode-skin interface impedance. This innovative design enhances the signal-to-noise ratio, enabling more accurate and noninvasive detection of electrophysiological signals, such as electromyograms and electrocardiograms. In addition, the MNEs exhibited superior mechano-electrical stability, biocompatibility, and comfort, making them suitable for long-term healthcare monitoring and human-robot interactions. This work illuminates a pathway toward more reliable and adaptable biopotential monitoring technologies.

Compact chiral meta‐devices capable of directly emitting circularly polarized light are increasingly in demand in applications such as sensing, imaging, and information processing. However, practical application of emissive chiral metasurfaces with complex meta‐atoms is currently hindered by their reliance on costly and time‐consuming fabrication techniques, such as electron‐beam lithography. Recently, twisted moiré chiral metasurfaces have attracted significant attention for their unique electromagnetic responses, achieving intrinsic chirality through lattice twists rather than intricate designs. Nonetheless, the emission properties of these lattice‐twisted moiré chiral metasurfaces remain to be investigated. In this paper, an efficient and cost‐effective fabrication method is presented for the first time, enabling the creation of large‐area twisted moiré chiral metasurfaces that incorporate reusable structural layers and an emissive gap made from materials including dyes, quantum dots, and halide perovskite. A remarkably high luminescence dissymmetry factor of −1.21 is achieved. Furthermore, their exceptional capabilities in tuning emission chirality are experimentally demonstrated. Reciprocity‐based simulations reveal a strong correlation between the emission chirality and the asymmetry of field enhancements. This work paves the way for the development of large‐area, cost‐effective chiral light sources with exceptional tunability.

Oxygen-assisted PLD enables phase-selective growth of wafer-scale α-/β-Sb ₂ O ₃ films with high dielectric constants (>100). Pure α-Sb ₂ O ₃ shows excellent dielectric properties, and its relaxation mechanisms are elucidated.

Ultrasmall CsPbI₃ perovskite quantum dots (QDs) are the most promising candidates for realizing efficient and stable pure-red perovskite light-emitting diodes (PeLEDs)^1,2,3,4,5. However, it is challenging for ultrasmall CsPbI₃ QDs to retain their solution-phase properties when they assemble into conductive films, greatly hindering their device application^3,6. Here we report an approach for in situ deposit stabilized ultrasmall CsPbI₃ QD conductive solids, by constructing CsPbI₃ QD/quasi-two-dimensional (quasi-2D) perovskite heteroepitaxy. The well-aligned periodic array of edge-oriented ligands at heterointerface triggers a substantial octahedral tilting in a critical layer thickness of CsPbI₃ QDs, which heightens the Gibbs free energy difference between the tilted-CsPbI₃ and δ-CsPbI₃ leading to thermodynamic stabilization of CsPbI₃ QDs. The approach allows us to fabricate stabilized CsPbI₃ QD conductive films with tunable emission covering the entire red spectral region from 600 nm to 710 nm. Here we report the pure-red PeLEDs with narrow electroluminescence peak centred at 630 nm, matching the Rec. 2100 standard for ultrahigh-definition display. The champion device exhibits a certified external quantum efficiency of 24.6% and a half-lifetime of 6,330 min, ranking as one of the most efficient and stable pure-red PeLED reported to date. The approach is also compatible with large-area manufacturing, enabling 1 cm² PeLED to exhibit the best external quantum efficiency of 20.5% at 630 nm.