Shaolin Ke

Self‐imaging based on Bloch oscillations offers a promising approach for optical information transport and parallel signal processing. However, in conventional femtosecond laser‐written lattices, the achievable propagation‐constant gradient is limited by fabrication constraints, leading to long Bloch oscillation periods and reduced reconstruction fidelity. Here, we implement a gradient‐engineered platform based on femtosecond laser‐written composite waveguides, where each lattice site consists of coupled sub‐waveguides, enabling flexible control of the propagation constants. In addition, a sawtooth‐profile modulation is introduced to locally tailor the effective potential landscape. This combined design enables tunable Bloch oscillation dynamics with reduced oscillation periods and improved wavepacket confinement compared with conventional single‐waveguide lattices. Experimentally, point‐to‐point imaging with energy recovery exceeding 99% is demonstrated, with a compact oscillation period of 8 mm. This platform also enables parallel multi‐port transmission of binary‐encoded sequences and two‐dimensional images, with high reconstruction fidelity across a broad wavelength range from 633 to 852 nm. These results demonstrate a fabrication‐tolerant route toward compact self‐imaging for optical information processing.

Exceptional points (EPs), singularities in non‐Hermitian systems where eigenvalues and eigenstates coalesce, exhibit unique spectral responses and enhanced sensitivity. However, in quantum‐interference settings such as two‐photon measurements, the interference transition generally does not occur at the EPs, limiting their applications for quantum sensing. To address this issue, we develop an anti‐parity‐time‐symmetric model based on indirectly coupled waveguides and introduce a cascaded‐waveguide configuration that produces an effective rotation of the system's eigenbasis. This modification shifts the two‐photon bunching‐antibunching transition to coincide with the EP. Near the EP, a small refractive‐index perturbation leads to a sharp change in visibility, which becomes more pronounced by increasing waveguide length. This passive, gain‐free design may minimize noise and offer a feasible route toward EP‐enhanced quantum phase sensing on integrated platforms.

The interplay between flat bands and topology has the potential to enhance the localization and robustness of topological edge modes, yet their realization in planar waveguide platforms remains challenging. Here, we introduce a synthetic gauge flux by leveraging degenerate modes in planar subwavelength grating waveguides, enabling Aharonov–Bohm caging effect and the formation of a flat-band lattice. The resulting edge modes are ultracompact, which can be confined to the last two waveguides at the boundary. These robust modes remain highly localized against coupling coefficient and geometric variations. Our findings offer a route toward compact and robust light transport in integrated photonic circuits operating in the telecommunication band.

We propose a scheme based on synthetic-flux–induced topological edge modes for realizing Hong–Ou–Mandel (HOM) interference between spatial polarization modes in a long-period grating waveguide. By engineering the relative modulation phase of the gratings, a tunable synthetic magnetic flux is generated, enabling controlled conversion between the TE and TM modes and forming an effective mode lattice. At a flux of π, the coupled-waveguide system supports compact, highly localized topological edge modes. Harnessing these boundary states, we achieve HOM interference with near-unity visibility that is insensitive to propagation distance and robust against variations of the coupling coefficients. These results may provide a route for fault-tolerant on-chip photonic quantum circuits.

High-order harmonic generation with mid-infrared laser fields has been considered the most promising method to produce soft X-rays attosecond pulses, which provides an important tool for probing the ultrafast electronic dynamics in atoms, molecules, and solids in real time. However, quantum diffusion of the electron wavepacket can lead to a dramatic drop of the harmonic yield when a mid-infrared laser field is used. Here we theoretically demonstrate that a spatially structured (SS) laser field can suppress quantum diffusion of the electron wavepacket and lead to a significant enhancement of high-order harmonic generation, compared with those generated by the spatially homogeneous (SH) laser field. The SS laser field is inhomogeneous in transverse direction perpendicular to the laser polarization and homogeneous in the polarization direction of the laser field. The electric field presents a valley structure. It is found that this valley structure can confine the electron wavepacket around the parent ion, prevent the electron wavepacket spreading, and finally lead to the significant enhancement of the high-order harmonics. Our results provide a novel method for controlling the ultrafast electron wavepacket dynamics of HHG.

We propose and demonstrate a broadband 3-dB power splitter based on a non-Hermitian triplet waveguide fabricated on a silicon-on-insulator (SOI) platform. By exploiting mirror symmetry, we show that the triplet can be decoupled into two virtual subspaces: a Hermitian subspace featuring a lossless zero mode and a non-Hermitian subspace supporting lossy modes. The zero mode, with its intensity equally distributed between the outer two waveguides, plays a crucial role in achieving broadband performance, effectively suppressing mode competition and maintaining stable splitting against dimensional errors. Experimentally, the 1-dB operational bandwidth of the splitter is confirmed to exceed 70 nm, ranging from 1480 nm to 1550 nm. Furthermore, this approach can be directly extended to any 1×n power splitter, providing a scalable and robust solution for photonic integration.

We propose a method to convert fundamental modes into orbital angular momentum (OAM) modes through chiral dynamics induced by gauge fluxes in silicon waveguides. By integrating a trench into a few-mode waveguide, we induce the rotation of TE₁₀ and TE₀₁ modes, naturally generating the gauge flux for the synthesized OAM modes. By precisely controlling the gauge flux, we achieve chiral dynamics that optimize the conversion efficiency of OAM modes at specific propagation distances, addressing challenges posed by mode degeneracy. Additionally, we demonstrate an on-chip OAM mode (de)multiplexer based on flux-controlled mode conversion. Our findings offer new, to the best of our knowledge, strategies for creating artificial gauge fluxes in straight waveguides and open up possibilities for manipulating OAM modes on photonic chips.

A multiply-accumulator, often abbreviated as a MAC unit, is central to a multitude of computational tasks, particularly those tasks (such as neural networks) involving array-based mathematical computations. The quest for novel methods to efficiently store and process data in a MAC has become imperative. Recently, ternary logic has attracted significant attention due to its higher information density than conventional binary systems. However, though numerous studies have showcased ternary arithmetic circuits, advancements in ternary-based vector processing have been notably scarce. To bridge this gap, this work undertakes comprehensive study into the optimization of ternary MAC units. Firstly, we propose various ternary approximate algorithms which shows 30%-less power consumption and only 2% computation error when compared with the accurate design. Secondly, we design sophisticated ternary circuits and obtain 74% $\sim$ 80% lower power-delay-product (PDP) than previous works. Finally, we evaluate the proposed ternary MAC unit using both carbon-nanotube field-effect transistor (CNTFET) and silicon-based 180 nm CMOS processes. The simulation results show the ternary circuit is better than binary circuit in terms of both area ( $\sim$ 45% less) and power ( $\sim$ 30% less), highlighting its strong potential for practical applications.