A glucose biosensor with temperature and pH compensation based on mode resonance coupling in hole-assisted multi-core fiber

Multiscale modification of sulfoaluminate cement mortar using nano-calcium carbonate, polypropylene fiber and silane coupling agent: Mechanical performance, sulfate resistance and mechanism clarification

The ellipse fitting algorithm (EFA) is widely used to compensate for asymmetric parameters in phase demodulation based on a 3×3 fiber coupler. However, it is prone to demodulation distortion of the measured phase signals under small signal conditions. In this paper, an improved demodulation algorithm, referred to as EFA-C-ATAN, is proposed to enhance demodulation stability and accuracy. The proposed algorithm employs a geometric transformation method, including translation, rotation, and normalization, to remove asymmetric parameters in the interference signals, thereby achieving phase demodulation. Besides, a lower ellipse eccentricity leads to improved fitting precision during the demodulation procedure. Experimental results show that the signal-to-noise and distortion ratio (SINAD) is improved, and the total harmonic distortion (THD) is reduced, especially under the small signal case. In addition, the standard deviation (STD) of amplitude fluctuations is decreased in small signal conditions, and a linearity response of 0.9998 is achieved. Finally, the computation time and real-time implementation feasibility of the proposed algorithm are discussed.

We describe a novel method for adapting a two-photon scanning microscope to enable simultaneous detection of two-photon-generated visible fluorescence and single-photon-generated near-infrared (nIR) fluorescence. In this configuration, nIR fluorescence is routed through a single-mode optical fiber before detection by a photomultiplier tube. This fiber coupling offers two advantages: first, the optical fiber functions as a pinhole aperture, allowing for improved optical sectioning of the nIR signal; second, it minimizes nIR background fluorescence. To validate the effectiveness of this design, we conducted two sets of experiments in male and female C57B/6 mice. First, we compare two fluorescence indicators of the neurotransmitter dopamine: the genetically encoded indicator GRABDA and single walled carbon nanotube based optical nanosensors (nIRCats). Although nIRCats exhibit lower affinity for dopamine than GRABDA, this property allows for identification of high concentration release sites in the striatum. Second, we simultaneously imaged depolarization-induced calcium changes and dopamine release in the retina. Together, these results demonstrate the utility of integrating confocal nIR detection into a two-photon platform for simultaneous functional imaging across complementary spectral channels.Significance Statement Dual-color, real-time imaging is a powerful technique in biomedical imaging, including neuroscience. Here, we present a widely applicable modification to a standard two-photon scanning microscope that adds a near-infrared detection capability, a wavelength range that minimizes photon scattering and autofluorescence from biological samples. Using this microscope, we demonstrate the first direct comparison of two dopamine sensors: the genetically encoded sensor GRABDA3m detected in the visible channel and carbon-nanotube-based sensors detected in the near-infrared channel. We further demonstrate simultaneous imaging calcium activity and dopamine signaling in the developing retina. While we focused on dopamine sensors in this study, this platform is broadly applicable to a wide range of fluorophores and can be implemented on existing two-photon microscopes.

We evaluate the impact on transmission quality through side-polished fiber couplers during and after their installation on an existing single-mode fiber in optical access networks. An alignment method with which branching ratios can be estimated while keeping the impact on transmission quality low by using a transmission light and Fresnel reflection is proposed. We experimentally confirm that our fabrication process of side-polished fiber couplers minimizes the degradation in transmission quality both during and after the installation of side-polished fiber couplers. The findings of this study will contribute to implementing an optical-fiber-cable re-routing support system to maintain the transmission systems.

Adaptive optics plays a crucial role in improving the stability and correcting aberrations of optical systems, whose performance largely depends on the optimization capability and convergence characteristics of control algorithms. Traditional control algorithms, such as genetic algorithm (GA), simulated annealing (SA), and stochastic parallel gradient descent (SPGD), have been widely applied; however, they exhibit certain limitations in global optimization ability, convergence speed, and noise immunity. In recent years, quantum optimization algorithms have attracted extensive attention owing to their potential advantages in global search and acceleration. Focusing on the application scenario of using adaptive optics to enhance fiber coupling efficiency, this paper investigates the feasibility of quantum optimization control algorithms. Taking quantum particle swarm optimization (QPSO) as a representative, a systematic comparison is conducted with traditional methods including GA, SA, and SPGD. The results demonstrate that under typical disturbance conditions, quantum optimization methods show significant advantages in improving fiber coupling efficiency, reducing the search time for optimal solutions, and enhancing system stability. This study indicates that adaptive optics control methods based on quantum optimization can provide a novel technical approach for stable and efficient coupling of optical links, and possess important application potential in the construction of quantum networks with ion traps as nodes.

A wearable sensor with environmental robustness based on tapered optical fiber coupling for respiration monitoring

Two-stage concentration for broadband solar energy transmission: Theory and experiment of high-energy-density fiber optical coupling

With quantum optical technologies advancing toward real-world deployment, their success depends on reducing the size, weight, and power (SWaP) of the laser sources that drive them. While photonic integrated circuit (PIC)-based lasers have emerged as promising replacements to traditional bulky lasers, achieving a PIC-based laser system that satisfies both optical and functional requirements demands a system-level co-design of optics, electronics, and software that has not yet been realized. Here, we demonstrate a low-SWaP, tunable, and narrow-linewidth laser system based on PICs and programmable control electronics for the 780nm region of the near-infrared spectrum. By leveraging the Vernier effect between a Fabry-Pérot laser diode (FPLD) and a microring resonator (MRR), we design the PIC to serve as an external cavity to self-injection lock the FPLD, resulting in a tunable laser with narrow linewidth. We package this PIC-laser into a standard butterfly package and drive it using a custom digital laser controller with a user-friendly interface. We design the programmable control electronics to meet the specific requirements of a PIC-laser as well as enable advanced functionalities that support cutting-edge quantum and classical optical applications. The complete laser system, which also includes optical isolators and fiber coupling, achieves up to 9.5 nm coarse tuning, 50 GHz mode-hop-free fine tuning, 30 mW free-space output power (before isolators), kHz-level intrinsic linewidth, and over 50 dB side-mode suppression ratio (SMSR). To exemplify the applicability of our laser system for quantum technologies, we perform spectroscopy on rubidium D2 transition lines and frequency-lock it to the cycling transition for days in a non-controlled environment with significant temperature fluctuations. We envision that our compact, fully integrated laser system will be a key enabler for scalable and deployable quantum and classical optical technologies.

The Adaptive Fiber Coupler (AFC) array is an innovative device designed to achieve the stable and efficient coupling of free-space light into optical fibers. To mitigate the effects of atmospheric turbulence, the Stochastic Parallel Gradient Descent (SPGD) algorithm has been predominantly adopted as the control method for AFC systems. However, due to the dynamic nature of atmospheric turbulence, the relatively slow convergence speed of the SPGD algorithm poses significant challenges for practical applications. This paper presents a model-based AFC control system that effectively mitigates wavefront aberrations caused by atmospheric turbulence. The performance of this system was evaluated in comparison with the SPGD algorithm under different turbulence levels and different sub-aperture numbers. Results show that the model-based AFC system converges faster than the SPGD-based AFC system under identical conditions. Additionally, the number of iterations required by the model-based AFC system remains relatively stable, whereas the SPGD-based AFC system demonstrates substantial variability depending on the number of sub-apertures and turbulence levels. As the turbulence level increases, the SPGD-based AFC system requires a greater number of iterations to achieve convergence. The proposed model-based method offers a robust and efficient solution for adaptive multi-aperture fiber coupling systems, which provides theoretical and technical support for the practical application of AFC array.

This article investigates fiber coupling techniques for low numerical aperture 808 nm semiconductor lasers. A coupling optical system combining fast-axis/slow-axis collimators (FAC/SAC) with a focusing lens was designed, achieving efficient coupling through high-precision optical integration packaging. First, a high-power GaAs-based 808 nm semiconductor laser chip was designed and fabricated. Its thermal performance and operational stability were enhanced by optimizing packaging materials and structures. The coupling system employs a fast-axis collimating lens, slow-axis collimating lens, and aspheric focusing lens to shape the beam and focus it into a 200 μm/0.12 NA fiber. Experimental results show that the developed coupling module achieves the threshold current of 1.2 A at 298 K, the continuous output power of 9.59 W, with the slope efficiency of 1.1 W/A, a coupling efficiency of 95%, the maximum output numerical aperture of 0.116, the wavelength temperature drift coefficient of approximately 0.2 nm/°C, and the peak brightness of 0.72 MW/cm2·sr. This study validates the feasibility and superiority of the FAC/SAC combined with focusing lens approach for low-NA fiber coupling. It provides theoretical and practical foundations for fiber coupling in high-brightness, high-power laser systems, offering promising applications in solid-state laser pumping, enhancing system integration, and enabling long-distance, high-brightness transmission.

A fiber image bundle is a key component connecting a high-density micro-display panel and an imaging lens group in a near-eye display (NED) system. Its inherent flexibility, high resolution, and aperture confinement capabilities bring unique features to micro-LED NED applications. However, the coupling and image transmission processes of these systems are influenced by multiple factors, and existing theoretical models often fail to accurately capture the complex interactions between microscale light sources and the fiber interface. This study presents a three-dimensional (3D) model that integrates micro-LED emission profiles with fiber acceptance cones, employing multiple integrals and radiative transfer theory to analyze the coupling efficiency. A piecewise function characterizes efficiency variations over distance, while different array models are used to describe crosstalk, clarifying critical conditions for vertical and diagonal configurations. Simulations and experiments validate the theoretical models, revealing how the pixel misalignment and tilt significantly affect both efficiency and crosstalk. Results show that coupling performance can be substantially enhanced by higher fiber numerical aperture, smaller micro-LED size and pitch, and improved alignment precision. This work provides a crucial theoretical basis for flexible NED systems and outlines optimization pathways for future fiber-optic imaging applications.

High-efficiency quantum frequency conversion (QFC) for group-IV color centers, such as silicon vacancies (SiV), is required for long-distance quantum networking protocols. Performance of QFC depends on the choices of network and pump wavelengths and the choice between bulk crystal and waveguide, since these directly determine the dominant noise processes. These furthermore lead to fiber-based or free-space, single- or multi-pass setups with different complexities, power requirements, losses, and hence, external efficiencies. Here, we present a QFC device design for SiV QFC with simultaneous state-of-the-art performance and simple setup. Namely, by choosing the C-band pump wavelength of λp = 1561 nm, which leads to an E-band network wavelength of λn = 1398 nm, we remain in the anti-Stokes noise regime in a one-stage, single-pass conversion scheme. The high-quality erbium-doped fiber amplifiers in this band aid in maximizing the internal nonlinear process. We measure an external (internal) photon conversion efficiency of 44.5 ± 1.8 % (8.5 ± 1.8 %) at an external (internal) pump power of 1.51 W (0.97 W), limited by fiber coupling efficiencies. This is an increase in efficiency by 9% (25 %) compared to prior demonstrations for SiV QFC, which were limited by factors such as internal device efficiencies, limited available pump power, and losses. We measure a pump-generated noise spectral density of 4913 counts/s/nm, which can be attributed to the anti-Stokes Raman scattering, in line with other one-stage demonstrations, though higher by an order of magnitude than that obtained in two-stage conversion. Without extra filtering, we expect this to lead to a networking photon signal-to-noise ratio of above 7000 for cavity-integrated SiVs in emission-based schemes.

We present the design, fabrication, and characterization of broadband graphene-silicon nitride integrated mode filters working in the optical C-band, centered at a wavelength of 1.55 μm. The devices presented here prevent modal crosstalk, thus avoiding signal degradation in multimode communication systems. In particular, the fabricated filters are based on a dual-mode silicon nitride waveguide, partially covered by a centered graphene nanoribbon that induces a stronger absorption for the TE0 mode than for the TE1 mode. The geometry of the design has been optimized to minimize the length and insertion losses of the device. A complete fabrication process, including the transfer and lithography of commercial graphene, has been developed. A novel approach was introduced during the etching step, which entailed the simultaneous curing of the resist to encapsulate the graphene nanoribbons prior to the deposition of the upper cladding. Finally, transmission through an array of fully fabricated filters of varying lengths was characterized with a measurement setup employing optical fiber coupling. The maximum experimentally measured contrast between the TE0 and TE1 modes is 123 dB/cm, achieved at a wavelength of 1569 nm, simultaneously with a minimum loss of -38 dB/cm for the TE1 mode. Overall, we fully demonstrate an integrated mode filter based on commercial graphene that paves the way for the implementation of integrated multimode optical communication systems.

Thermal treatment effect on the performance of fused polymer optical fiber coupler device

Vacuum-assisted headspace solid-phase microextraction in food analysis: basics and applications.

Photothermal-responsive liquid crystal elastomers (LCEs) face critical barriers in biomedical applications: phase transition temperatures exceeding80°C risk thermal injury, and free-space optical actuation fails in confined spaces. Here, a thiol-ene crosslinked LCE is developed with a biocompatible phase transition temperature (37.6°C), enabling safe actuation within biological tissues. Through coaxial extrusion, the fabrication of waveguide-structured LCE optical fibers is pioneered, achieving ultralow optical loss (0.76 dBcm-1) and enabling long-range light transmission and remote actuation via silica optical fiber coupling. Under 808 nm laser stimulation (375 mW), these LCE optical fibers generate 30% contraction strain in 23 s, maintaining maximum surface temperature < 48°C. Integrated into an endoscopic system, LCE optical fibers replaced rigid mechanical components. Ex vivo characterization reveals their omnidirectional bending capability (94° angular range), while in vivo trials on live rats and rabbits validate their operational functionality in anatomical environments, enabling hemorrhage detection and laser-steered tumor ablation via controlled navigation. Histopathological analysis confirms no thermal damage at fiber-tissue interfaces. This work establishes biocompatible LCE optical fibers as a photonic platform integrating photonic-driven soft actuation and tissue-compliant adaptability, enabling mechanically safe interventions in confined anatomical environments.

With the large-scale deployment of unmanned aerial vehicles (UAVs), long-range, high-precision detection and tracking face severe challenges. Although Gm-APD-based single-photon LiDAR systems exhibit outstanding sensitivity under ultra-low SNR and weak echo conditions, the employment of multimode fiber (MMF) coupling to achieve high energy output tends to introduce strong speckle noise, which significantly degrades echo photons’ stability and imaging quality, thereby reducing the accuracy of target tracking. This study proposes a speckle suppression method that integrates MMF vibration with the time-domain RANSAC with spatial consistency enhancement (TRSCE) reconstruction algorithm, which combines temporal RANSAC and spatial neighborhood structural consistency. Additionally, an improved MeanShift-Kalman algorithm is proposed to achieve robust tracking of UAVs under low SNR. Monte Carlo simulations demonstrate that under an average single-pixel echo photon count of 0.4481 and an SNR of −6.85 dB , the speckle contrast within the target region decreases significantly from 0.7592 to 0.0748, corresponding to a reduction of 73.2%. In field experiments conducted under weak solar illumination and light fog, the proposed Gm-APD single-photon LiDAR system demonstrated robust tracking capability of UAV targets at a distance of 200 m. At an SNR of approximately −4.53 dB , with an average signal return of 1.0859 photons per target pixel and a background noise level of 3.0829 photons, the system achieved a mean tracking error of 0.6572 pixels (approximately 6.44 cm) and an inter-frame model similarity of 0.9764. Compared to publicly reported speckle suppression methods, the proposed approach reduced the tracking error by approximately 45.3%. Furthermore, at a range of 300 m under strong solar illumination, with an average signal-photon count of 0.8769 and background noise of 4.0611 photons per pixel, the system achieved a mean tracking error of 0.6975 pixels (approximately 9.66 cm), improving accuracy by 43.2% compared to spatial-correlation-based algorithms. Finally, by integrating phased-array radar, the system extends effective detection and tracking distances of UAVs to 10 km, surpassing existing LiDAR capabilities. The proposed speckle suppression and robust tracking framework significantly enhances tracking stability of LiDAR operating in complex airspace environments and provides a viable theoretical foundation and engineering solution for future low-altitude defense and airspace security applications.

We describe a novel method for adapting a two-photon scanning microscope to enable simultaneous detection of two-photon generated visible fluorescence and single-photon generated near-infrared (nIR) fluorescence. In this configuration, nIR fluorescence is routed through a single-mode optical fiber before detection by a photomultiplier tube. This fiber coupling offers two advantages: first, the optical fiber functions as a pinhole aperture, allowing for improved optical sectioning of the nIR signal; second, it minimizes nIR background fluorescence. To validate the effectiveness of this design, we conducted two sets of experiments. First, we compare two fluorescence indicators of the neurotransmitter dopamine: the genetically encoded indicator GRABDA and single walled carbon nanotube based optical nanosensors (nIRCats). Although nIRCats exhibit lower affinity for dopamine than GRABDA, this property allows for identification of high concentration release sites in the striatum. Second, we simultaneously imaged depolarization-induced calcium changes and dopamine release in the retina. Together, these results demonstrate the utility of integrating confocal nIR detection into a two-photon platform for simultaneous functional imaging across complementary spectral channels.

50 GHz colliding-pulse mode-locked lasers with an integrated front-side spot-size converter have been investigated. These devices achieve sub-400 fs pulse durations after external compression, timing jitters as low as 135 fs, and optical peak power up to 5 W. The integrated spot-size converter provides a circular, narrow far field for efficient fiber coupling. The colliding-pulse mode-locked lasers exhibit superior characteristics, achieving an RF linewidth of 3.5 kHz and a Lorentzian optical linewidth of 740 kHz. To evaluate the impact of the cavity design, a direct comparison is performed with a conventional mode-locked laser featuring two separate gain sections. Both devices have identical InGaAsP multi-quantum well active layer structures, and both have electrically isolated gain sections for fair comparison. A threshold current of 8 mA and a time-averaged output power of 110 mW are obtained in both cases, even though the colliding-pulse configuration has double the cavity length.