Abstract As an effective approach to image copyright protection, optical image watermarking has emerged as a prominent research focus in the field of image information security. However, current optical image watermarking schemes typically embed watermark information into the host image, which is not suitable for applications that require high integrity of the host image. Moreover, existing optical image watermarking schemes based on human biometrics require that the biometric features used in the encoding and decoding processes of the watermark image must be identical; otherwise, the original watermark’s valid information cannot be decoded. To address these issues, this paper proposes an optical robust zero-watermarking scheme based on chaotic facial phase masks and three-step phase-shifting digital holography. In the proposed scheme, we first construct a chaotic facial phase masks using the human face and chaotic systems. Next, we use the chaotic facial phase mask and three-step phase-shifting digital holography to encode the original watermark into three noise-like holograms. Finally, we combine the encoded watermark information with the Canny edge features of the host image to construct a zero-watermark. Since the proposed scheme does not require modification of the host image, it is suitable for application fields that demand high integrity of the host image. Furthermore, in the proposed scheme, even if there are slight deviations in the same user’s face during the encoding and decoding processes, the original watermark image’s valid information can still be decoded. Extensive experiments and analyses demonstrate that the proposed scheme not only has high security but also exhibits strong robustness against common image processing attacks and geometric attacks.

Abstract Janus metasurfaces, characterized by propagation-direction-dependent asymmetric transmission phenomena, provide an innovative design freedom for multiplexed optical systems. However, conventional approaches to asymmetric transmission typically employ three-dimensionally stacked architectures or heterogeneous material integration, exhibiting inherent limitations in fabrication complexity and intrinsic optical loss. This work presents a VO₂-based reconfigurable monolayer Janus metasurface enabling active asymmetric wavefront manipulation within the terahertz spectral range. Through synergistic utilization of VO₂'s reversible insulator-to-metal phase transition coupled with a dual-parameter modulation scheme governing incident direction, three functionally distinct optical operations are realized: an asymmetric focusing metalen, an asymmetric focusing vortex beam generator, and a Janus NOR logic gate. The proposed asymmetric wavefront modulation paradigm demonstrates advantages in fabrication cost-effectiveness and structural simplicity, thereby establishing a viable pathway toward high-efficiency, multifunctional, and chip-scale integrated photonic devices.

Abstract Underwater optical wireless communication systems offer a promising alternative to traditional acoustic methods for achieving high data rate transmission. However, the propagation of optical waves in underwater environments is severely impacted by oceanic turbulence, leading to intensity fluctuations and consequent performance degradation. In this work, we employ a laser beam array to model transmit spatial diversity for suppressing these fluctuations. The model uses annular-shaped lasers at the transmitter as a representation of beam shaping for turbulence mitigation, with a point detector assumed at the receiver. Through the use of the Huygens–Fresnel principle, we derive two key optical parameters: the average received intensity and the average of the intensity squared. We subsequently determine the scintillation index for this model. Our findings demonstrate reductions in scintillation under varying system parameters. For instance, increasing the number of beams in the array, the ring radius, and the secondary field amplitude of the annular beam leads to a lower scintillation index.

Abstract This paper investigates a study concerning the multi-mode multi-slot interference waveguide based on silicon nitride intended for optical biosensor applications for virus detection and compact optical sensing in both the visible and infrared regions. The proposed design consists of five parallel closed slot waveguides exited by launching the fundamental transverse electric mode through the central slot waveguide. The configuration enables strong coupling between the adjacent waveguides and enhances light-analyze interaction. An analytical expression for the self-imaging position is derived using both multimode interferometer (MMI) and coupled-mode theory, and the results are validated using commercial simulation software based on the finite-difference time-domain method. By tuning the geometry, we demonstrate enhanced optical confinement in the slot region, which improves the light-analyze interaction. The structure achieves a maximum sensitivity of 1722 nm/RIU in one of the ports in the visible region and 1898 nm/RIU in one of the ports in the infrared, with a compact device footprint of 170 µ m. Compared to previous slot or MMI-based sensors, our design has improved sensitivity, dual-band operation, and CMOS-compatible integration on the SiNOI platform, which makes it a promising candidate for label-free biochemical sensing applications.

Abstract Structured light refers to light fields that are specially customized by manipulating their properties across multiple physical dimensions, demonstrating immense potential in applications such as optical communications, precision measurement, advanced imaging, and quantum information. Structured light lasers, capable of directly generating light fields with complex spatial distributions, polarization states, and topological structures, provide efficient and versatile tools for light field manipulation and its applications. Unlike structured light generation techniques that rely on external modulation, structured light lasers achieve compact and high-quality structured light output through direct intracavity control, significantly enhancing system integration and efficiency. This review summarizes the latest research progress in structured light lasers, exploring their fundamental principles, design methodologies, and applications. It introduces the basic concepts of structured light, including typical structured beams such as vortex beams, vector beams, and propagation-invariant beams, as well as more complex topological and quantum structures like optical skyrmions, non-separable states, and ray-wave duality. The review elaborates on the categories of high-dimensional structured light lasers, covering design schemes such as on-cavity structures and intracavity geometries, and provides insight into different architectures ranging from free-space and fiber-based systems to integrated devices. We also discuss the broad applications and future prospects of structured light lasers, highlighting the challenges and opportunities in this rapidly evolving field. This review aims to serve as a resource for researchers who seek to design and develop structured light lasers, as well as for those looking to harness their potential to drive innovation in photonic techniques.

Abstract In this study, the digital optical phase conjugation method using cameras and spatial light modulators was employed to correct wavefront distortions over a 30 m distance. In the experiment, the system exhibited a delay of 12 ± 3 ms from camera exposure to phase-conjugated light (PCL) generation. The method was tested for its ability to track moving targets. By shifting the target at regular intervals, PCL tracked the target with a movement error of 1.9%, exhibiting a linear response. It compensated for artificial atmospheric disturbances, reducing beam fluctuation by 76% compared with non-PCL. This approach shows great potential for achieving stable optical transmission under real-world conditions.

Abstract Topological light fields represent a cutting-edge frontier at the intersection of modern optics and condensed matter physics, offering new dimensions for light field control and functional expansion through their distinctive topological structures. This review traces the progression from singular optics to optical skyrmions, providing an overview of representative real-space topological features, including phase singularities, polarization singularities, optical knots, and Möbius strips. It focuses on the generation mechanisms and characterization techniques of various types of optical skyrmions in parameter space, and reviews key studies that have shaped the development of the field. With ongoing advances in nano-optics and light-field manipulation, topological light fields exhibit strong potential in high-dimensional optical communication, massive data storage, all-optical computing, and precision metrology. This review aims to offer a coherent framework for researchers in topological optics and to support the further exploration of topological structures in optical devices and photonic information technologies.