Metasurfaces serve as a pivotal platform integrating orbital angular momentum (OAM) encoded holography and nanoprinting technology, boasting broad application prospects. Nevertheless, nanoprinting techniques struggle to achieve in-depth integration with multi-channel OAM modulation, failing to meet the demands of integrated and broadband applications. This paper proposes a broadband, multi-channel, single-layer all-dielectric metasurface architecture. By utilizing customized polarization-sensitive nanopillar structures, two transmission channels and independent decoding of distinct OAM holographic patterns are realized under the illumination of circularly polarized vortex beams. The proposed scheme enables multi-channel multiplexing of OAM holographic images and nanoprinted images across a broad visible spectrum, and is further applied to multi-level information encryption. Herein, polarization states and OAM modes function as secret keys, and information decryption is completed through joint decoding. This study breaks through the application restrictions of single-function metasurfaces and provides an innovative solution for the design of broadband, multi-channel integrated photonic devices.

Skin diseases are one of the most common diseases, affecting approximately 1.9 billion people worldwide, and early detection of skin diseases can help avoid deterioration and improve treatment outcomes. Existing clinical detection methods have drawbacks such as high subjectivity and complexity, as existing diagnostic algorithms pay less attention to interpretability, and research mainly focuses on Caucasian skin. Therefore, we designed a multi-spectral skin disease detection system based on multi-model multi-layer networks to accurately differentiate similar skin diseases. The results show that the system has great potential in assisting the detection of skin diseases and can effectively improve the diagnostic accuracy and medical efficiency of skin diseases.

Integrating orbital angular momentum (OAM) holography and nanoprinting holds great potential for high-capacity optical multiplexing. However, realizing this integration on a single metasurface faces bottlenecks, including severe mode coupling and OAM crosstalk. Moreover, physical-layer encoding may provide limited information protection when used alone. To address these challenges, we propose an optical information system that integrates metasurface-based physical encoding with neural network steganography. On the hardware front, we engineer a multifunctional metasurface that synergizes Malus’s law, optimized phase modulation, and mode separation algorithms to achieve low-crosstalk, multi-channel nearfield nanoprinting and farfield OAM holography. On the software front, we introduce a U-Net steganography network as a post-processing layer. By combining metasurface-based physical modulation with neural network processing, we establish a dual-layer information-protection architecture. This approach provides a potential framework for secure optical storage and communication, with potential applications in anti-counterfeiting and privacy protection.

Abstract Conventional optical lenses achieve focusing and zooming through curved surfaces and stacked structures, which inherently suffer from large volume, complex configuration, and low integration. These drawbacks make them difficult to adapt to miniaturized and high-precision optical systems. Metalenses have emerged as ideal alternatives due to their planar configuration and exceptional wavefront manipulation capabilities. However, achieving high-quality simultaneous multi-physics manipulation and multispectral independent response within a single all-dielectric device remains a widely researched focus and technical difficulty in the field. Accordingly, this paper proposes a multispectral varifocal metalens based on spin–orbit angular momentum multidimensional multiplexing. Using the geometric phase modulation mechanism, we successfully construct a variety of metalens platforms that enable the cooperative control of multiple parameters including spin angular momentum, orbital angular momentum, and wavelength, and realize their selective addressing and focusing at arbitrary positions in three-dimensional space. By precisely regulating the polarization state, topological charge, and operating wavelength of the incident vortex beam, we achieve six-step focal length switching within the range of 20–80 μ m along the optical axis, high-quality bifocal output, and distributed focusing of multiple foci in 3D space. This work exploits multidimensional physical properties to realize selective addressing and focusing of incident vortex beams, with high polarization conversion efficiency maintained over a broad visible band. It opens new avenues for transformative applications in high-resolution bioimaging, multidimensional precision detection, wavelength-division-multiplexed micro-optical communication systems, and other fields.

Intracranial pressure monitoring is critically important for the diagnosis and management of patients in neurocritical care. To address the limitations of existing invasive sensors, including infection risks, high cost, and susceptibility to electromagnetic interference, as well as the insufficient accuracy of non-invasive sensors, this work presents the design and fabrication of a miniaturized optical fiber sensor based on a polydimethylsiloxane membrane Fabry-Perot interferometer and a fiber Bragg grating for simultaneous temperature and pressure monitoring. Experimental results demonstrate that within the clinically critical pressure range of 7-70 cmH2O, the sensor exhibits high linearity (R2 > 0.99), high pressure sensitivity (0.20 μm/cmH2O), and high accuracy (single-measurement error ≤ 2.1 cmH2O). In the physiological temperature range of 35-41°C, its temperature measurement sensitivity reaches 8 pm/°C. The Fabry-Perot interferometer and fiber Bragg grating signals operate without mutual interference, enabling decoupled measurement of temperature and pressure. Repeatability tests conducted over 21 days and extended stability tests confirm the sensor's exceptional long-term stability and reproducibility. Compared with conventional sensors based on silicon or metal diaphragms, the PDMS membrane employed in our design can be fabricated using a straightforward spin-coating process, eliminating the need for complex micromachining. This approach not only significantly reduces the sensor probe's fabrication complexity and cost but also, owing to the high elasticity of polydimethylsiloxane, yields enhanced pressure sensitivity. This research provides a highly promising technological solution for high-performance, cost-effective, and accurate intracranial pressure monitoring.

Conventional metasurfaces suffer from fixed functions and single-mode responses, which can hardly meet the practical demands of dynamic reconfiguration and multi-channel multiplexing. To address this issue, in this work, a polarization-multiplexed binary-switching metasurface is developed based on the phase-change material Ge2Sb2Te5 (GST). The particle swarm optimization algorithm is employed to globally optimize the structural parameters of the metasurface nanopillars. By leveraging the crystalline/amorphous phase transition characteristics of GST, the dynamic switching modulation of metasurface functions is realized. Combined with polarization manipulation parameters, it is clarified that Gaussian focusing can be achieved under the condition of x-polarization and crystalline state, and vortex beam generation can be realized under y-polarization and amorphous state, thereby constructing a binary switching system with synergistic polarization-phase interaction. The proposed strategy exhibits promising application prospects in optical communications, quantum information, imaging systems and other related fields.

In this work, a three-stage Time-to-digital converter (TDC) based on the average measurement in the system is proposed for ranging. The ranging chip needs to provide 20 MHz reference clock signal externally, which is doubled to 1 GHz through the Phase-Locked Loop (PLL) circuit and sent to TDC to provide stable high frequency reference clock signal for the circuit. The circuit uses PLL cascaded oscillator units to generate multiple clock signals and vernier delay structures to construct two-stage interpolation. During the measurement process, the input signal is allocated to different channels of the TDC for multiple measurements and averaging. This not only reduces the random error caused by clock jitter due to noise, but also improves the utilization of TDC channels. The chip is based on X-Fab 0.18 μm CMOS process, the core TDC layout area is 500 μm × 350 μm, the power consumption is about 16.55 mW, and the resolution is 14 ps. Analysis of the results of the post-simulation shows that the differential nonlinear peak is less than 0.4 LSB, and the integral nonlinear peak is less than 0.6 LSB. The dynamic range can increase the number of high-segment counter bits according to the needs of actual application scenarios. High measurement accuracy, linearity and wide dynamic range are achieved.

The propagation of vortex beams in anisotropic nonlocal nonlinear media(ANNM) gives rise to distinctive structural transformations. This paper investigates the dynamical behavior of an off-axis chirped Laguerre-elliptic Gaussian vortex beam (OACLEGVB) in such media, employing a combined approach of analytical derivation and high-resolution numerical simulation. Anisotropic nonlocality makes it difficult for OACLEGVB to maintain structural stability, and instead enables the periodic conversion between Laguerre-Gaussian (LG) modes and Hermite-Gaussian (HG) modes. The normalized rotation angular momentum J_o is effectively governed solely by the second-order chirp parameter(SOCP), the mode parameter, and the anisotropic nonlocality parameter(ANP). The normalized revolution angular momentum J_e is precisely manipulated by the off-axis parameter(OAP), the SOCP, the ANP and the incident direction. Interestingly, when the power is constant( P = P_cx = P_cy ), the parameters of the higher-order mode beams have a linear relationship with those of the fundamental mode beams. The anisotropic nonlocal modulation breaks the rotational symmetry of the beam, resulting in the normalized orbital angular momentum not being a constant value and triggering periodic oscillation phenomena. This study provides a theoretical foundation for the precise control of propagation trajectory, mode interconversion, and optical field structuring of the OACLEGVB in anisotropic nonlocal nonlinear media.

We propose a design method for few-mode erbium-doped fiber (FM-EDF) incorporating stratified doping. In the simulation design, the FM-EDF effectively reduces the differential mode gain (DMG) through the utilization of stratified doping. Simulations indicate that at an input signal power of -30 dBm, the designed fiber achieves a DMG of less than 0.5 dB across five spatial modes spanning the entire C-band (1530-1570 nm) and exceeds 20 dB gain within the range of 1530-1560 nm. Additionally, experiments using unidirectional pumping demonstrate that the FM-EDF achieves full-band gain greater than 20 dB, with a maximum gain approaching 30 dB and DMG <1 dB, across the C-band in three spatial modes. In summary, the proposed FM-EDF enhances the efficiency and reliability of long-distance signal transmission in optical communication networks, making it suitable for high-capacity optical fiber communication systems as well as long-distance sensing systems.

The work describes a surface plasmon resonance (SPR) sensor that measures the liquid level and refractive index (RI) simultaneously. The sensor is fabricated by a polymer optical fiber (POF) with a side-polished spiral structure. The POF is wound around a plastic rod with the same pitch and polished into a series of separated side-polished areas to form the sensor probe. Afterwards, the polished surfaces are coated with a gold layer to construct the SPR sensor. The proposed sensor can provide multi-point liquid-level measurement besides RI sensing. The influences of structural parameters such as the bending radius, polishing depth, and pitch on the sensing performance are experimentally studied. The experimental results indicate that the RI could be determined by employing the SPR wavelength shift, and the RI sensitivity of 1862 nm/RIU within the 1.34–1.40 range is obtained. Moreover, the SPR peak’s depth variation can be utilized to monitor the liquid level, and the sensor can provide adjustable resolution and a measurement range for liquid level sensing. With its simple fabrication, low cost, and flexible sensing ability, this sensor probe is suitable for the usage in biochemical applications.

This paper describes a laser ranging system based on modulation signal resampling to address the nonlinearity of Frequency-modulated in frequency-modulated continuous wave (FMCW) lidar. Using a 1550 nm DFB laser as a frequency-modulated light source, the modulation scheme adopts direct modulation of the injected current into the semiconductor laser. Based on the equal-frequency resampling method, the clock signal used for resampling undergoes data acquisition, data analysis, and data processing steps to identify and eliminate erroneous sampling points caused by laser frequency noise, mode hopping in frequency-modulated lasers, and sweep reversal points in the injection current. It solves the nonlinear error caused by the relaxation-oscillation effect of the prior art. Additionally, compared with the manual division of sampling points, the algorithm dividing the sampling area can retain as many correct sampling points as possible to improve the distance resolution and repeatability accuracy of the FMCW ranging system. Under the condition of approximately 20 GHz laser modulation bandwidth, the resolution of 10 m in free-space optical ranging is about 6.8 mm and the standard deviation (STD) of 1 m in free-space optical ranging is 0.19 mm.

Metasurfaces have demonstrated significant potential for applications in high-resolution imaging and information security. However, conventional metasurfaces holographic techniques are constrained by low transmittance and limited tunability. In this study, we propose a color image encryption scheme based on a metasurface composed of "dynamic" pixels (Sb2S3) and "static" pixels (Silicon), wherein the color information of the image serves as an integral component of the encrypted data. By manipulating parameters such as polarization state, wavelength of incident light, and crystallization level of Sb2S3, we can flexibly control the display of multichannel color images in both near-field and far-field scenarios. Specifically, images containing specific color information can be displayed only when the incident light is at two specific wavelengths and the crystallization level of Sb2S3 is known. Conversely, at a single wavelength, only a predetermined portion of the image can be displayed. The proposed metasurface represents a potential approach for ultra-high capacity dynamic holographic displays, color image encryption, and efficient information storage.

A polymer optical fiber SPR sensor for detecting Cu2+ ion concentration in water is proposed. The sensor employs a simple side-polish structure and realizes the detection of Cu2+ ion concentration by employing the chitosan (CS)/polyacrylic acid (PAA) bilayer film on the gold film of the optical fiber surface. The structure of the fiber probe is optimized, and the sensing performances for the Cu2+ ion detection are analyzed experimentally. The experimental results demonstrate that the sensor exhibits a high sensitivity of 465.539 nm/ppm for the Cu2+ ion detection in the concentration range of 0–0.04 ppm. And it has a fast response speed and good selectivity for Cu2+ ions. The sensor has the advantages of simple structure and low cost, and has potential applications in the field of heavy metal detection.

The majority of current beam conversion techniques rely on bulky lens systems for operation. In this paper, we propose a terahertz metasurface that can effectively convert a Gaussian beam into a flat-top beam and convert linearly polarized terahertz waves into their orthogonal counterparts. An improved Gerchberg-Saxton (GS) algorithm was employed in this study to precisely calculate the required phase distribution for the beam shaping device. By adjusting the opening angle of the metal split ring in the middle layer of the metasurface, a full 2π phase coverage was achieved, ensuring precise control over the phase distribution. Simulation results indicate that within the range of 0.4-1.1 THz, the cross-polarization conversion efficiency is greater than 70%, with a relative bandwidth of 93.3%. The root-mean-square error (RMS) can reach 0.143 at 0.75 THz, the non-uniformity of the rectangular spot in the target region is 0.126, and the energy ratio of the rectangular spot to the whole focal plane is 78.03%, demonstrating the achievement of a high-quality flat-top beam. The metasurface beam shaping device we proposed, with its wide operating bandwidth, low transmission loss, high shaping efficiency, and compact structural design, offers an innovative solution for beam shaping techniques in the terahertz frequency band.

Objective With the rapid advancement of information technology and the increasing depth of research on metasurfaces, the static and uncontrollable nature of traditional metasurfaces has limited their further development. As a result, dynamically tunable chiral metasurfaces are in high demand across many application fields. Vanadium dioxide (VO2), a novel two-dimensional material with dynamic tunability, offers significant potential in this regard. In recent years, the integration of metasurfaces with VO2 has led to the design of various dynamically tunable metasurfaces. However, most of the proposed tunable chiral metasurfaces feature complex unit structures, suffer from low efficiency in practical applications, and are limited to single-band functionality. Therefore, when designing new chiral metasurface devices, factors such as material loss, structural simplicity, and the tunability of achievable functionalities must be considered. These challenges have become a critical topic in current research on chiral metasurfaces. Methods The metasurface we designed consists of a three-layer unit cell (Fig. 1). The bottom layer is a metallic reflective layer, the middle layer is a dielectric layer made of Topas (cyclic olefin copolymer), and the top layer is composed of a composite material of VO2 and gold. The top-layer resonant pattern comprises two sets of semicircular arcs and rectangular patches. Each semicircular arc, with a width of w, is connected to a rectangular patch with a length of l(1) at its outer edge. Both sets of elements are made of gold and are arranged in a centrosymmetric configuration to form the overall resonant structure. The left gold rectangular patch is extended by a rectangular VO2 patch with a length of l(2). Other parameters include period of P, representing the period of the unit cell. The bottom gold layer serves to suppress electromagnetic wave transmission, with its thickness set to 0.1 mu m to ensure that all incident electromagnetic waves are reflected. The dielectric layer is made of Topas, which has a relative permittivity of 2.57. Characterized by transparency, thermally stable, and exhibits excellent optical properties, this material demonstrates negligible absorption coefficient in the terahertz range. The thickness of the dielectric layer is h(1). The top layer has a thickness of h(2), with the ring's width w, outer radius R, gold rectangular patch length l(1), and VO2 rectangular patch length l(2). Through simulation, the optimized geometric dimensions of the structure are as follows: l(1)=10 mu m, l(2)=6 mu m, R=14 mu m, w=5 mu m, h(1)=15 mu m, h(2)=1.5 mu m, P=50 mu m. In the simulations, we use CST Microwave Studio software to calculate the optical properties of the structure through full-wave simulations in the frequency domain. Periodic boundary conditions are applied along the x-axis and y-axes for the basic unit cell, with the light source incident along the -z direction. Open boundary conditions are set along the z-axis. Results and Discussions We have proposed a dual-band terahertz chiral metasurface based on VO2 material. The designed structure achieves remarkable circular dichroism (CD) responses of up to 0.91 and 0.82 at 1.93 THz and 3.83 THz, respectively, demonstrating excellent dual-band performance (Fig. 2). The dynamic tunability of the chiral response is enabled by the phase transition properties of VO2 between its insulating and metallic states (Fig. 3). Additionally, leveraging the Fabry?P & eacute;rot resonance effect between the top layer and the metallic bottom layer, the circular dichroism response can be switched from dual-band to single-band by adjusting the thickness of the dielectric layer (Fig. 3). Based on this characteristic, we designed a multi-frequency circularly polarized wave detection and image encryption scheme. By combining single-band and dual-band metasurfaces, the system generates distinct imaging signals for different polarized waves at two frequencies (Fig. 7), enabling multiplexed digital imaging functionality. Conclusions In summary, we have proposed a design for a dynamically tunable dual-band chiral metasurface absorber based on VO2 material. Theoretical results show that when VO2 is in its metallic state, the metasurface achieves left-circularly polarized (LCP) absorption rates of up to 98.56% and 93.90% at 1.93 THz and 3.83 THz, respectively, while the absorption rate for right-circularly polarized (RCP) is less than 12% across the 1?4 THz. The CD values at the two resonant frequencies, 1.93 THz and 3.83 THz, are 0.91 and 0.82, respectively. When VO2 is in its insulating state, the CD effect is significantly reduced. By adjusting the conductivity of VO2, the optical response of the metasurface can be effectively controlled, enabling selective absorption of circularly polarized light in different states. Additionally, due to the Fabry?P & eacute;rot resonance, the CD response can be switched from dual-band to single-band by varying the thickness of the dielectric layer. Furthermore, based on terahertz near-field imaging, this structure shows potential applications in dual-frequency circularly polarized wave detection and image encryption.

AbstractThis work proposes a design of a dynamic range adjustable laser ranging chip based on element sharing, which combines single photon avalanche diodes and direct time‐of‐flight (dToF) to address the uncertainty of detection distance in different usage scenarios of laser ranging technology. To achieve adjustable dynamic range of the chip, an element shared control logic circuit based on external control signals is designed and integrated, which can adjust the measurement dynamic range of the chip through external control signals, making it suitable for different usage scenarios. Moreover, when the dynamic range of the chip changes, the measurement resolution of the time‐to‐digital converter (TDC) in the chip can remain unchanged. Through the analysis of simulation results, it is found that the laser ranging chip designed in this work can adjust the dynamic range from 3 ns to 4.29 s based on external control signals at a resolution of 125 ps, with a reference clock signal input frequency of 20 MHz. The differential non‐linearity (DNL) error of TDC is −0.22 LSB to 0.19 LSB, and the integral non‐linearity (INL) error is −0.82 LSB to 0.52 LSB. The dynamic range adjustable laser ranging chip based on element sharing designed in this work provides a feasible solution to address the uncertainty of detection distance in laser ranging technology.

We propose a glue-filled hollow core fiber (HCF) based Fabry-Perot (FP) interferometric sensor for temperature and pressure measurement. Two types of sensor probes using polydimethylsiloxane (PDMS) or ultraviolet (UV) glue as filling materials are fabricated, respectively. The temperature and pressure sensing characteristics of each sensor were analyzed. Results demonstrate that the PDMS filled sensor exhibits the higher sensitivity to temperature and pressure, which are 0.1594 nml degrees C and -2.0548 nm/MPa, respectively. In contrast, the sensor filled with UV glue demonstrates the low sensitivities to temperature and pressure, which are -0.1072 nm/degrees C and -0.8309 nm/MPa, respectively. The study provides valuable guidance for material selection in practical temperature and pressure sensing applications.

An optical fiber sensor based on Michelson interferometer (MI) cascaded with Fabry-Perot interferometer (FPI) is proposed for simultaneous monitoring of high-temperature and high-pressure. The MI comprises a tapered single-mode fiber (SMF) spliced with a section of no-core fiber (NCF), while the FPI cavity is formed by sealing the fiber MI into a silica capillary tube. The temperature and pressure can be detected by monitoring the spectral features of the MI and FPI, respectively. The experimental results demonstrate that the sensor achieves a temperature sensitivity of 42.95 pm/degrees C and a pressure sensitivity of -195.38 nm/MPa in a temperature range of 25-150 degrees C and a pressure range of 0-35 MPa. The sensor has the advantages of high sensitivity, cost-effectiveness, and ease of preparation.