An interventional fiber optic strategy, as a representative optical medical technology, is flexible, highly sensitive, minimally invasive, anti-electromagnetic, and has good biosafety. Fiber optics can approach deep cancer lesions and provide direct theranostics, which other optical technologies cannot achieve. However, the realization of cancer sensing and therapy relies on the functionalization of optical fibers, which requires the strict selection and optimization of functional materials used to modify the optical fibers, ensuring high photothermal conversion efficiency without affecting fluorescence detection efficiency. Herein, we propose the use of black phosphorus, which does not interfere with fluorescence and provides a safer and more efficient photothermal effect compared to other nanomaterials, such as graphene, graphene oxide, carbon nanotubes, and MXene. We propose a fiber-optic theranostic probe that combines nitroreductase (NTR) fluorescent molecules and a black phosphorus/gold nanostar (BP/AuNS) nanomaterial hydrogel to develop an integrated strategy for cancer sensing and photothermal therapy (PTT). The sensor has high sensitivity, and the limit of detection (LOD) is 1.61 ng mL-1. The BP/AuNS fibers have excellent photothermal effects, and the probe temperature reaches 212°C in air as 150 mW of pump power is delivered. In the phantom test, the simulation and test results showed that the fiber probe conferred hyperthermia (>45°C) to an area with a radius of 2.5 mm. These results indicate that the minimally invasive BP/AuNS fiber exhibits excellent sensing performance and high photothermal efficiency, making it promising for tumor diagnosis and treatment and potentially advancing the development of optical fiber medicine.

We propose a precise reconstruction, with crosstalk-free switching, of two holograms. Our approach utilizes orthogonal polarizations that illuminate the holograms to modulate both amplitude/phase and polarization, effectively mitigating crosstalk between the hologram data streams. Furthermore, the incorporation of a 90° interference angle facilitates the recording of multiple holograms. Experimental results have demonstrated the high-precision decoding of amplitude, phase, and polarization data for two reconstructed holograms. The integration of orthogonally polarized light with a 90° interference angle sets the stage for achieving multi-dimensional polarization modulation in systems with more than two channels.

High-speed single-carrier transmission can be achieved by increasing the modulation format cardinality for higher spectral efficiency. However, ultrahigh-order QAM signals are usually more susceptible to various impairments. Hence, we propose a temporal feature-based memory (TFM) neural network (NN) equalizer to effectively mitigate signals’ impairments in ultrahigh-order QAM. The temporal convolutional network is utilized as a feature extraction layer to significantly improve the performance of the bidirectional long short-term memory network. The TFM-NN equalizer was experimentally validated in a probabilistically shaped polarization-division multiplexed 1024/4096-QAM coherent optical transmission system, and raw spectral efficiencies of 16.190 and 21.188 bit/s/Hz have been achieved at normalized generalized mutual information thresholds.

In this paper, a quadrature phase shift keying (QPSK) phase-recovery algorithm is presented for coherent intersatellite optical wireless communication (IsOWC). From a theoretical perspective, we explain the process of the multiplier-free algorithm. Through simulations, we analyze key parameters and provide guidance on their optimal selection. Additionally, the proposed algorithm maintains stable phase tracking at bit energy to noise power spectral density (Eb/N0) as low as 4 dB. In an ob2b transmission test, our algorithm achieved a sensitivity of -49 dBm @5 Gbps QPSK [hard-decision forward-error-correction (HD-FEC) limit]. Compared to the Viterbi and Viterbi phase-recovery (V&V) algorithm, its receiving sensitivity is improved by 1 dB, resulting in a link distance extension of 1100 km. Our multiplier-free and robust algorithm meets the requirements of IsOWC systems and shows promise for future applications.

Polarization-dependent loss (PDL) of mode-division multiplexing (MDM) links has a direct influence on the effective transmission of dual-polarization (DP) signals for large-capacity communication. In this paper, we aim to identify the origin of PDL in MDM systems and optimize the transmission performance of DP signals. The PDL characteristic of the fundamental MDM system with a few-mode polarization controller (FMPC) is theoretically analyzed and verified by experiments. It is shown that the PDL of MDM links arrives at the minimum when the spatial pattern of mode channels is independent of the input polarization angle. The experimental data have good consistency with the theoretical curve. At the same time, the origin of PDL for MDM systems is identified, that is, the mode dependency can be converted into the polarization dependency in the MDM links. The theoretical and experimental results in the paper can guide PDL optimization of DP signals in MDM transmission.

Ghost imaging has shown promise for tracking the moving target, but the requirement for adequate measurements per motion frame and the image-dependent tracking process limit its applications. Here, we propose a background removal differential model based on asymptotic gradient patterns to capture the displacement of a translational target directly from single-pixel measurements. By staring at the located imaging region, we evenly distribute optimally ordered Hadamard basis patterns to each frame; thus, the image can be recovered from fewer intraframe measurements with gradually improved quality. This makes ghost tracking and imaging more suitable for practical applications.

With the rapid advancement of three-dimensional (3D) scanners and 3D point cloud acquisition technology, the application of 3D point clouds has been increasingly expanding in various fields. However, due to the limitations of 3D sensors, the collected point clouds are often sparse and non-uniform. In this work, we introduce local tactile information into the point cloud super-resolution task to aid in enhancing the resolution of the point cloud using fine-grained local details. Specifically, the local tactile point cloud is denser and more accurate compared to the low-resolution point cloud. By leveraging tactile information, we can obtain better local features. Therefore, we propose a feature extraction module that can efficiently fuse visual information with dense local tactile information. This module leverages the features from both modalities to achieve improved super-resolution results. In addition, we introduce a point cloud super-resolution dataset that includes tactile information. Qualitative and quantitative experiments show that our work performs much better than existing similar works that do not include tactile information, both in terms of handling low-resolution inputs and revealing high-fidelity details.

Hyperspectral-depth imaging is of great importance in many fields. However, it is difficult for most systems to achieve good spectral resolution and accurate location at the same time. Here, we present a hyperspectral-depth single-pixel imaging system that exploits the two reflection beam paths of a spatial light modulator to provide one-dimensional depth and spectral information of the object; then, they are combined with the modulation patterns and compressed-sensing algorithm to construct the hyperspectral-depth image, even at a sampling ratio of 25%. In our experiments, a spectral resolution of 1.2 nm in the range of 420 to 780 nm is achieved, with a depth measurement error of less than 1 cm. Our work thus provides a new way for hyperspectral-depth imaging.

Fiber specklegram sensors are widely studied for their high sensitivity and compact design. However, as the number of modes in the fiber increased, the speckle sensitivity heightened along with the correlation diminished, lowering the sensing performance. In this paper, an innovative method is introduced based on digital aperture filtering (DAF) that adopts physical principle analysis, which reduces the collection aperture by computationally screening out the energy of higher-order modes within the speckle, therefore enhancing the correlation among speckles. Subsequently, a multi-layer convolutional neural network is designed to accurately and efficiently identify the measurands represented from the filtered speckles. By comparing the experimental results of the speckle demodulation method on different multimode fibers in light field direction sensing, the DAF method has shown outstanding performance in sensing accuracy, sensing range, stability, resolution, and generalizability, fully demonstrating its tremendous potential in the advancement of fiber sensing technology.

Thin-film lithium niobate (TFLN) modulators have gained significant attention for their high electro-optic modulation efficiency and large bandwidth. However, achieving efficient coupling to single-mode fibers remains a challenge. In this work, we present a large-bandwidth TFLN modulator with a low fiber-to-fiber loss, employing grating couplers with metal mirrors for perfectly vertical coupling, which facilitates wafer-scale testing and packaging. The modulator with electrodes and metal mirrors is initially fabricated on a lithium niobate (LN)-on-insulator with a silicon substrate, followed by bonding to a quartz wafer using UV adhesive, with subsequent removal of the silicon substrate. By incorporating periodic capacitively loaded traveling-wave electrodes, the modulator achieves high modulation efficiency while maintaining a large bandwidth. The final device demonstrates a low fiber-to-fiber loss of 6.5 dB, a 3-dB bandwidth exceeding 67 GHz, and a half-wave voltage of 3.8 V in a 7 mm long modulation section. Additionally, successful data transmission using on–off keying modulation at rates up to 100 Gbit/s is achieved. The proposed modulator is compatible with wafer-scale production and holds promising potential for high-capacity, low-loss optical communication systems.

In this study, we present a comprehensive thermo-optic characterization of an on-chip thin-film lithium niobate asymmetric Mach–Zehnder interferometer (aMZI) across a temperature range of 290 to 10 K. We observe that the spectral shift of the aMZI is closely associated with changes in the environmental temperature. We experimentally observed a 4.88 nm wavelength shift of the aMZI from 290 to 10 K. Moreover, the shift diminished gradually below 50 K. Our observations highlight a distinctive non-linear temperature sensitivity, particularly pronounced at cryogenic temperatures. The high-resolution setup revealed a thermo-optic coefficient as low as 5.29 × 10-8 K-1 at 10 K. The presented results provide new practical guidelines for designing photonic circuits for applications in cryogenic optoelectronics.

Silicon-organic hybrid (SOH) modulators have garnered sustained interest due to their superior performance, with low driving voltage and compact footprint. However, concerns regarding their reliability have greatly hindered their widespread deployment. Recent progress in molecular synthesis significantly improves the thermal stability of SOH modulators. However, the reliability of the damp heat aging test has not been reported. In this paper, we report on a thin-film SOH modulator with a half-wave voltage–length product (VπL) of 1.18 V·cm. The device’s frequency response extends beyond 33 GHz without degradation. After exposure to 85°C and 85% relative humidity for 1000 h without packaging, the electro-optic response of the modulator degrades by only 7.3%. This demonstration may help resolve doubts regarding the durability of SOH modulators.

We demonstrate a 202 W all polarization-maintaining (PM) single-frequency fiber amplifier operating at the C band. Simulations show that the length of the output fiber pigtail following the gain fiber critically has a great impact on stimulated Brillouin scattering (SBS), posing a major obstacle for high-power single-frequency amplification. Optimizing the length to suppress the backward SBS by ∼10 dB, we experimentally achieved a maximum output power of 202 W, yielding an optical-to-optical efficiency of 42%. The signal-to-noise ratio (SNR) of signal light, relative to amplified spontaneous emission (ASE) in Er3+ and Yb3+ bands, was measured to be 23 and 32 dB, respectively, and it can be further improved by ASE suppression and filtering techniques during amplification. To the best of our knowledge, this is the all-PM single-frequency fiber amplifier with the highest power reported in the C band.

We demonstrated a fiber–terahertz (THz)–fiber communication system at the D-band based on full photonic conversions, exploiting a modified unitraveling-carrier photodiode (MUTC-PD) module to achieve optical-to-THz conversion at the transmitter end and an ultrabroadband packaged thin-film lithium niobate Mach–Zehnder modulator (MZM) to convert the THz signal to the optical signal at the receiver end. This system successfully realized the transmission of 33-Gbaud 16-quadrature amplitude modulation (QAM) and 31-Gbaud probabilistic shaping-64-QAM signals through 10-km standard single-mode fiber (SSMF), 0.6-m wireless distance, and the subsequent 5-km SSMF, achieving net data rates of 116.03 and 123.72 Gbps, respectively.

In this paper, we propose a new strategy based on the interconversion between two symmetry-protected bound states in the continuum (SP-BICs) to break the high symmetry dependency of the SP-BIC. The excitation of four high-Q quasi-BIC resonances is supported by disrupting both the translational and structural symmetry of the metasurface using spacing and length perturbations, respectively. Furthermore, interconversion between the two SP-BICs can be achieved via length perturbation, significantly diminishing the radiative attenuation rate of the quasi-BIC. Despite a relative asymmetric parameter reaching 97.2%, the Q-factor order of magnitude of the quasi-BIC can remain constant. Compared with previous studies, our approach significantly enhances the robustness of the Q-factor for the quasi-BIC by a minimum of two orders of magnitude, although our relative asymmetric parameter is approximately 10 times the corresponding work.

We propose a modular designed over-coupled (OC) metasurface for the broadband surface-enhanced infrared absorption spectroscopy (SEIRAS) by analyzing the combined properties in the far field and near field. The customized sensors can independently modify the coupling mode, the resonance frequency, and the coupling efficiency by adjusting the vertical and horizontal structures and hybrid dielectric layers of the metasurface, respectively. Based on the independent regulation of the sensor properties, the influence of the detuning properties, the level of OC coupling, and the coupling efficiency of the signal amplification can be clearly presented through the single variable-controlling approach. These design principles are universal for customized sensors and herald possibilities for machine-learning-aided surface-enhanced infrared absorption (SEIRA) biosensing.

Randomness describes one inherent property of self-assembled metamaterials and greatly limits the practical applications of metamaterials based on bottom-up techniques, such as the microsphere lithography technique. Herein, by subtly utilizing the randomness in long-range disorder metasurfaces, we demonstrate a high-performance one-shot full-Stokes polarimeter in the visible waveband. The long-range disorder metasurfaces, i.e., chiral shells, were realized by depositing Ag on the self-assembled microsphere monolayer comprised of many micro-domains of random lattice directions and areas. The distinct optical anisotropy and chirality in different micro-domains can result in distinct photo-currents to the photodetector array placed underneath upon the injection of polarized lights. Through establishing the mapping relationship S^=f(I^) between the detected photo-currents I^ and the states of polarization (SoP) S^ with the convolutional neural network (CNN) algorithm, we realize a high-precision full-Stokes polarimeter in the waveband ranging from 500 to 650 nm, and the minimum mean square errors (MSEs) can reach about 0.37% (S1), 0.33% (S2), and 0.19% (S3) at 566 nm. The average MSEs in the investigated waveband are 0.49% (S1), 0.45% (S2), and 0.31% (S3), respectively. We have systematically investigated the macro- and micro-optical properties of chiral shells, the optical randomness of chiral shells in different domains, the reference SoP number, the exposure time and pixel number of the CCD, as well as the reliability and stability of the system.

Polarization singularities beyond the bound states in the continuums (BICs) have garnered significant interest due to their potential for light manipulation. The conservation of topological charge has proven crucial in various photonic systems, and it guides the behavior of these singularities, including the generation and annihilation of BICs. This work theoretically reveals the simultaneous generation of two distinct polarization singularity types, which include off-Γ accidental BICs and Dirac-type band degeneracy points. The generation is driven by a quadratic degeneracy of symmetry-protected BICs in a photonic crystal slab. It should be noted that this is achieved through continuously tuning a geometric parameter without breaking symmetry. Importantly, the generation of both singularity types can be explained by the topological charge conservation law. This adherence ensures the stability of these singularities and allows for continuous tuning of their positions in momentum space by continuously tuning a geometric parameter while preserving symmetry. This study presents a novel framework for synthesizing and manipulating complex polarization states by combining polarization singularities from both BICs and band degeneracies and holds promise for application in other wave systems beyond photonics.

Precise control of the polarization state of light on ultrafast time scales plays a key role in revealing the inherent chiral or anisotropic optical responses in various material systems, and it is crucial for applications that require complex polarization encoding. Here, we explore ultrafast polarization control enabled by silicon-based chiral bound state in the continuum (BIC) metasurfaces. By utilizing the intrinsic chiral mode, we achieve high-purity chiral reflection light (S3 ∼ -0.92) and rapid modulation (∼0.4 ps) of polarization states through all-optical methods. Unlike traditional polarization modulation techniques, our approach leverages the unique advantages of slanted etching dielectric chiral BIC metasurfaces, which facilitate high-Q resonance and exhibit narrow linewidths. These advantages allow swift alterations in polarization states with minimal modulation energy consumption, which should help for greater control of light in integrated photonic applications.

We experimentally demonstrate an optical isolator utilizing high-quality-factor whispering gallery modes in a yttrium iron garnet (YIG) microsphere, coupled with an integrated Si3N4 waveguide. By applying a magnetic field in the vertical direction of the resonator equator, we achieve the breaking of degeneracy between the clockwise (CW) and counterclockwise (CCW) modes, driven by photonic spin–orbit coupling (SOC) and the Faraday effect. The maximum wavelength separation observed is about 7.9 pm, comparable with the linewidth of the mode. The better effect of the refractive index matching between the YIG microsphere and the Si3N4 waveguide enables an isolation ratio of 16.9 dB under the critical coupling condition. This work presents a novel integrated approach for realizing non-reciprocity in photonic circuits, advancing the development of compact high-performance photonic devices.

In quantum information processing, unitary transformations are oftentimes used to implement computing tasks. However, unitary transformations are not enough for all situations. Therefore, it is important to explore non-unitary transformations in quantum computing and simulation. Here, we introduce non-unitary transformations by performing singular value decomposition (SVD) on two-photon interference. Through simulation, we show that losses modeled by non-unitary transformation can be perceived as variables to control two-photon interference continuously, and the coincidence statistics can be changed by an appropriate choice of observation basis. The results are promising in the design of integrated optical circuits, providing a way toward fabricating large-scale programmable circuits.

The heterogeneity of applications and their divergent resource requirements lead to uneven traffic distribution and imbalanced resource utilization across data center networks (DCNs). We propose a fine-grained baseband function reallocation scheme in heterogeneous optical switching-based DCNs. A deep reinforcement learning-based functional split and resource mapping approach (DRL-BFM) is proposed to maximize throughput in high-load server racks by implementing load balancing in DCNs. The results demonstrate that DRL-BFM improves the throughput by 20.8%, 22.8%, and 29.8% on average compared to existing algorithms under different computational capacities, bandwidth constraints, and latency conditions, respectively.

The rapid growth of new services has led to a significant increase in data traffic, which brings challenges for data centers in supporting high-speed processing of large volumes of data. Traditional electrical interconnects are becoming increasingly inadequate, leading to increasing attention to optical interconnects to achieve high-speed data center interconnects (DCIs). Visible light laser communication (VLLC) inherits the advantages of free-space optics (FSO), allowing it to circumvent the limitations of conventional fiber-based optical interconnects. In addition, VLLC offers other advantages such as high thermal stability, low power consumption, and low packaging cost. In this Letter, a novel differential pilot coding (DPC) scheme is proposed to achieve precise channel estimation and compensation for linear impairments without halving the effective data rate. A data rate of 601.46 Gbps with a constellation size up to 1024QAM over a 1 m multimode fiber (MMF)-1 m FSO-1 m MMF link is successfully achieved based on a 50-channel wavelength division multiplexer (WDM) VLLC system utilizing DPC and bit-power-loading discrete multitone (DMT) modulation. To the best of our knowledge, this is the highest data rate and constellation size ever the reported for a WDM VLLC system, which proves that VLLC is a promising candidate solution for achieving high-capacity and cost-effective optical interconnects in data centers.