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Additive manufacturing (AM) has gained popularity due to reduced production times of low-cost and geometrically complex structures. Due to technological constraints such as print volume, time, and thermal stability of large AM parts, adhesive joints are commonly used in assembling smaller components in large-scale polymeric structures. This work investigates the feasibility of using embedded optical fibers to monitor strain distributions within AM composite (carbon fiber/nylon) single-lap shear (SLS) joints. Internal strain distributions within the adhesive and surface strain fields of the SLS joints with AM adherends under tensile loads were obtained using optical fibers and digital image correlation, respectively. Results indicate negligible influence of optical fibers on the failure strength and axial stiffness of 3D-printed SLS joints under quasi-static loading. Higher strains were observed at the bond edges within the adhesive (using optical fiber) and the surface (using DIC) of the joints due to the rotation of the bond under loading. All specimens failed in the adherends beyond the bonded region due to their low interlaminar strength. [ABSTRACT FROM AUTHOR]

A Mach-Zehnder interferometer (MZI) sensor based on thin-core fiber (TCF) is proposed. Sensitive materials such as polydimethylsiloxane (PDMS) or gelatin are coated on the surfaces of MZIs to achieve temperature, pressure, and humidity measurements. MZI is composed of single mode fiber (SMF), TCF, and multimode fiber (MMF) spliced together to form a "SMF-MMF-TCF-MMF-SMF" structure. The core/cladding diameters of TCF are 3.8 µm and 80 µm respectively. When three types of optical fibers with different core diameters are cascaded together, many cladding modes are excited to form MZI. Firstly, two similar MZI structures were fabricated designated by MZI1 and MZI2. In order to improve the sensitivity and mechanical strength, a layer of PDMS film was coated on the TCF surface of MZI1. Then, a layer of gelatin film is covered on the TCF surface of MZI2. PDMS has the high thermal expansion coefficient, thermal optical coefficient, and elasticity, and gelatin has good humidity sensitivity properties. The experimental results showed that the temperature and pressure sensitivity of MZI1 coated with PDMS reached −340 pm/°C and −14.3 nm/MPa, respectively, while the humidity sensitivity of MZI2 coated with gelatin reached −112.57 pm/% RH. When a fiber Bragg grating is cascaded with the MZI1, the sensor can achieve simultaneous measurement of temperature and pressure, eliminating crosstalk. The proposed sensor has an extremely simple structure and manufacturing method, which only involves the splicing of optical fiber and the coating by the film. In addition, the proposed sensor has a robust structure, good repeatability and stability, and high sensitivity, which has broad application prospects. [ABSTRACT FROM AUTHOR]

The service life assessment of previous fatigue stress has a fundamental role in estimating the reliability of products like fiber optical connectors, and should replicate use in severe environments in telecommunications systems. However, the vibration prediction models used in the literature present limitations in vibration life prediction. In this paper, we propose using the insertion loss fatigue life and including it in the Weibull distribution to determine the Weibull parameters ƞ and β to evaluate fiber optic connector reliability R(t) under environmental and mechanical testing stress. We analyzed the failure data of a standard telecommunication fiber optical connector under a program of service life stress testing against that of a fiber optical connector under only mechanical vibration stress testing. The fiber connectors were monitored during the vibration testing to review the transient change of the optical signal. Their results showed that the reliability of the fiber connectors submitted to the service life program was R t = 0.694 , while that of the fiber connectors submitted to mechanical vibration only was R t = 0.970 . In addition, the analysis showed that the service life testing consumed 70.2% of the product's lifetime. We present in Numerical Validation the steps to determine the acceleration factors of the vibration test developed. [ABSTRACT FROM AUTHOR]

Aerospace optical cables and fiber-optic connectors have numerous advantages (e.g., low loss, wide transmission frequency band, large capacity, light weight, and excellent resistance to electromagnetic interference). They can achieve optical communication interconnections and high-speed bidirectional data transmission between optical terminals and photodetectors in space, ensuring the stability and reliability of data transmission during spacecraft operations in orbit. They have become essential components in high-speed networking and optically interconnected communications for spacecrafts. Thermal stress simulation analysis is important for evaluating the temperature stress concentration phenomenon resulting from temperature fluctuations, temperature gradients, and other factors in aerospace optical cables and connectors under the combined effects of extreme temperatures and vacuum environments. Considering this, advanced optical communication technology has been widely used in high-speed railway communication networks to transmit safe, stable and reliable signals, as high-speed railway optical communication in special areas with extreme climates, such as cold and high-temperature regions, requires high-reliability optical cables and connectors. Therefore, based on the finite element method, comprehensive comparisons were made between the thermal distributions of aerospace optical cables and J599III fiber optic connectors under different conditions, providing a theoretical basis for evaluating the performance of aerospace optical cables and connectors in space environments and meanwhile building a technical foundation for potential optical communication applications in the field of high-speed railways. [ABSTRACT FROM AUTHOR]

A method has been developed for securing an optical fiber in a quartz connector by using sodium polysilicate hydrogel formed in a cylindrical gap between a connector and an optical fiber by means of alkaline decomposition of the quartz surfaces of manufactured components. The conditions for the thermal decomposition of hydrogel are determined, and it is shown that hydrogel decomposition with cellular structure formation is possible at temperatures below the thermal decomposition temperature of the polymer coating of the optical fiber. The hydrogel formation conditions and the thermal properties of the hydrogel are determined. Conclusions regarding the suitability of the proposed method for securing an optical fiber in a quartz connector are drawn. [ABSTRACT FROM AUTHOR]

Hollow-core optical fibers (HCFs) have unique properties like low latency, negligible optical nonlinearity, wide low-loss spectrum, up to 2100 nm, the ability to carry high power, and potentially lower loss then solid-core single-mode fibers (SMFs). These features make them very promising for communication networks and similar applications. However, this class of fibers is still in development. Current applications are almost exclusively limited to low-latency data links for High-Speed Trading (HST); other uses are in the trial stage now. In this paper, we comprehensively review the progress in the development of HCFs including fiber design, fabrication and parameters (with comparisons to conventional single-mode fibers) and support technologies like splicing and testing. A variety of HCF applications in future telecom networks and systems is analyzed, pointing out their strengths and limitations. Additionally, we review the influence of filler gas and entry of contaminants on HCF attenuation, and propose a new fusion splicing technique, avoiding the destruction of the fiber's photonic cladding at high temperature. [ABSTRACT FROM AUTHOR]

Waveguided beam splitters were microfabricated by using a commercial two-photon lithography system (Nanoscribe), Ip-Dip as the waveguides and fused silica as the substrate, and they were covered with Loctite. The gap between the waveguides in the coupler was used to determine the transmission and reflection coefficients, and our results were compared with simulation results (using OptiFDTD software). The input and output ports of the beam splitters were spliced with multimode optical fibers in a robust system that can easily be handled. Then, they were tested by leading single photons (from an SPDC) to the beam splitters to produce different quantum statistics that were rated using the Fano factor. [ABSTRACT FROM AUTHOR]

Cerium-doped-silica glasses are widely used as ionizing radiation sensing materials. However, their response needs to be characterized as a function of measurement temperature for application in various environments, such as in vivo dosimetry, space and particle accelerators. In this paper, the temperature effect on the radioluminescence (RL) response of Cerium-doped glassy rods was investigated in the 193–353 K range under different X-ray dose rates. The doped silica rods were prepared using the sol-gel technique and spliced into an optical fiber to guide the RL signal to a detector. Then, the experimental RL levels and kinetics measurements during and after irradiation were compared with their simulation counterparts. This simulation is based on a standard system of coupled non-linear differential equations to describe the processes of electron-hole pairs generation, trapping-detrapping and recombination in order to shed light on the temperature effect on the RL signal dynamics and intensity. [ABSTRACT FROM AUTHOR]

In this paper, a temperature sensing probe is designed using two cascaded Fabry‐Perot interferometers (FPIs). FPI1 is made by splicing single‐mode optical fiber (SMF)‐no‐core optical fiber‐capillary‐SMF in turn, and then drilling a micro‐hole on the capillary wall of FPI1 with femtosecond laser, and injecting dimethyl silicone oil (DSO) into the capillary through the micro‐hole with immersion method. FPI2 is made by splicing SMF‐capillary‐SMF sequentially. Due to the thermal sensitivity of DSO, the temperature sensitivity of a single FPI1 reaches −0.3674 nm/°C. When the free spectral ranges of FPI1 and FPI2 are close, their cascaded sensor will produce a Vernier effect for improving the sensitivity. The experimental results show that the sensitivity of the sensing probe is as high as 1.8456 nm/°C. In addition, the sensor has a compact structure and can be used flexibly in confined space temperature measurement. [ABSTRACT FROM AUTHOR]

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FOJI technology framework diagram. [Display omitted] Prefabricated assembly structures have been extensively applied for the construction of low carbon and cost effective underground subway stations in China. Engineers faced significant challenges in dealing with the assessment of mechanical performance of structures joints within prefabricated underground station (PUS) structures during construction process. Manual assembly of large-scale prefabricated structures may lead to significant disturbance of structures joints, resulting in structures joints failure in construction process or even water leakage in maintenance of underground stations. To address these issues, this study proposed an integrated theory-monitoring method for joint performance assessment. The initial step involved the establishment of a fiber optical sensors (FOS) monitoring system for PUS joints. A joint performance assessment module was then developed utilizing the Joint Interfaces Contact Model (JICM) and was subsequently integrated into monitoring system, forming a joint performance assessment method, namely FOS-JICM (FOJI). A case study was finally conducted on a Shenzhen pipe jacking PUS to evaluate the effectiveness of FOJI. Main research findings of this study include (a) FOS monitoring system demonstrated excellent adaptability, accuracy, and real-time performance in practical applications; (b) FOS monitoring system effectively captured joint deformation and stress evolution throughout the entire construction process, providing insights into the impact of complex geological conditions and box culverts on joint behavior; (c) FOJI, with its integration of the JICM module, enabled safety assessment of joint performance during pipe jacking process; (d) FOJI successfully identified joint damage, offering valuable guidance for engineering restoration and protective measures. It facilitated prompt updates and adjustments based on the actual construction conditions, establishing a cycle mechanism for safety protection. These achievements not only establish a theoretical foundation for ensuring the construction safety of PUS joints but also present substantial practical application value. [ABSTRACT FROM AUTHOR]

In this study, we proposed and validated a temperature fiber sensor based on optical signal capture Mach-Zehnder Interferometer (OSC-MZI) with high-precision temperature measurement capabilities. By creating three air cavities on a continuously offset-spliced no-core fiber (NCF), the optical signal experiences reflection and divergence within these cavities, which enhances the optical path of propagating light. Gradually, filling these NCF cavities with polymethyl methacrylate (PMMA) microspheres to increase the light coupling efficiency and as a sensing unit. Due to the directly contact between the optical fiber waveguide and PMMA, the state of incident lights is easily influenced by the refractive index (RI) variations of PMMA. When the environmental temperature changes, RI of the PMMA with high thermal-optic coefficient shows marked change, which finally leads to the obvious wavelength shift of interference dips in the transmission spectrum. Experimental results show that MZI coated with the polymer materials achieves a temperature sensitivity of up to 2.04 nm/°C within the temperature range of 25–50 °C. Furthermore, as an interference-based MZI sensor, its total length is only 4.75 mm. The proposed OSC-MZI provides a new approach for combining optical fiber sensors with polymer materials. [Display omitted] • A high sensitive temperature sensor is achieved by offset-spliced and point coating method. • The highest temperature sensitivity achieves 2.08 nm/°C within the temperature range of 25–50 °C. • The total length of the fiber sensing structure is only 4.75 mm. • Simple structure, easy fabrication, high mechanical strength, good repeatability. [ABSTRACT FROM AUTHOR]

The monitoring of mine pressure, division of vertical zoning of the overburden, discrimination of key stratum structure of the overburden and monitoring of advanced abutment pressure are still the main research problems in the field of coal mining. Therefore, the promotion of development of a monitoring technology of mining-induced rock mass deformation has important research value in the mining field. There are many problems to be solved in the application of optical fiber sensing (OFS) to deformation monitoring, such as the corresponding relationship between actual deformation and optical parameters, the coupling relationship between the optical fiber and rock mass and the reasonable division of vertical zoning of the overburden. In this study, a quantitative index of coupling action between the mining rock mass and optical fiber is put forward, and the coupling coefficient of different vertical zonings is quantitatively analyzed and discussed. Based on this, five different media in contact with optical fiber are proposed. The relationship between the strain curve form, the development height of the fracture zone and the activity of key stratum is established. It is of great academic value and research significance to establish a characterization system of displacement, deformation and structural evolution of overlying strata based on optical fiber sensing technology. [ABSTRACT FROM AUTHOR]

Nonlinear optical effects in optical waveguides play an important role in the development of fiber and integrated optics systems for optical communication and information processing. On the one hand, nonlinear effects impose restrictions on the radiation power that can be transmitted through an optical fiber or light guide. In this paper, the problem of the occurrence of the phenomenon from the stimulated Brillouin scattering (SBS) effect is investigated using two optical sources of rays in a single-mode optical fiber at joint waves of 1310 nm and 1550 nm. Due to the fact that in all trunk fiber-optic lines, the intensity and energy of input signals is limited due to the influence of SBS, methods are currently being sought to reduce the influence of this phenomenon. It was found that the energy of the input beam in the combined propagation of the compound did not reach the value of the threshold of SBS in the values of 25 dBm and 27 dBm due to the discrepancy between the experimental results and the results of the model. The SBS effect was not observed when the threshold threshold of 15 dBm and 27 dBm – SBS was reached when combining a dual beam along a single optical fiber in one direction. As a result, by double integration, the value of the SBS threshold was raised, and the direction for future scientific research was determined. If the possibility of increasing the threshold of SBS is proved, then increasing the distance of amplifiers in the main networks, respectively, its economic effect increases. In addition, it can be noted that there are no scientific papers devoted to the study of the effects of optical nonlinear effects by combining and distributing these two compounds along a single optical fiber. This article discusses the issues of improving the capacity and determination of the threshold for stimulated Brillouin scattering. To increase the power threshold is invited to consider the dependence of the phase modulation frequency of the spectral width of the laser radiation. In addition, the fact that the SBS threshold did not reach the value at an energy of 27 DB in the case of the double-beam distribution can be proved by discrepancies in comparison with the results of experimental studies and the results of the model that determines the SBS effect [ABSTRACT FROM AUTHOR]

Surface defects on optical fiber end-face, such as scratches, cause heavy loss and low data-transfer rate. Therefore, the inspection of optical fiber end-face defect cannot be neglected. Most optical fiber defect detection methods ignore the striped pattern of scratches and easily cause incomplete segmentation. In this article, a novel method based on deep convolutional neural networks (DCNNs) for weak microscratches inspection in the optical fiber end-face is proposed. First, a new feature pyramid structure with criss-cross max-pooling (CCMP) block is developed to extract precise boundary features in all directions and generate feature maps. Second, these feature maps are fed into the spatial attention upsample (SAU) module to recover a full-resolution feature map and localize the defects. Finally, multiple scratches with various types can be detected in the images. This article uses many real optical fiber images as experimental images. The experimental results demonstrate that the proposed method yields good comprehensive performance with a mean pixel accuracy (mPA) of 92.70% and a mean intersection over union (mIoU) of 85.35%. [ABSTRACT FROM AUTHOR]

In this work, we present a fiber optic refractive index (RI) sensor based on a dual inline semi-distributed interferometer (SDI) device. The SDI is formed within a telecom-grade optical fiber by simply splicing a short length of a high-scattering fiber; the presence of a high density of scattering centers induces a distributed cavity effect, forming a low-finesse interferometer. Here, we propose an approach based on two serial SDIs, with few millimeters spacing between the two cavities; the outer SDI encodes the changes of surrounding RI, while the inner probe is RI-insensitive and can be used as a reference. Experimental analysis shows that the dual-SDI device has RI sensitivity of 111.2–466.2 dB/RIU with RI-sensitive mode, and 0.4–3.7 dB/RIU with RI-insensitive mode, with a ratio up to 1165.5 between sensitive and insensitive modes. In addition, the Vernier effect can be interrogated by detecting the wavelength shift of the narrow spectral lines, with sensitivity of 0.303 nm/RIU. The dual-SDI structure maintains the same fabrication ease of a single SDI, since all process is made through splicing and cleaving fibers with a telecom-grade fiber. The key advantage is the availability of modes having both high and near-zero RI sensitivity, which therefore can be used for a referenced RI detection as an in-situ probe. • A new dual semi-distributed interferometer (SDI) sensor for refractive index (RI) detection is proposed. • The spectrum of the dual-SDI structure shows features that are both sensitive and insensitive to the RI change. • The Vernier spectrum can be observed when interrogating the whole spectrum of the dual-SDI. • Three dual-SDI probes with varying scattering defects within the core have been manufactured and analyzed. [ABSTRACT FROM AUTHOR]

This study aims to improve bacterial laccase enzyme activity (LEA) and dehydrogenase activity (DHA) affecting acetylsalicylic acid (ASA) biodegradation using an alternating current (AC). A microbial consortium was inoculated in an electroactive bioreactor supplied with an AC by a function generator under operating conditions of amplitude (AMPL) = 2–10 peak-to-peak voltage (Vpp), optical fiber splice tray (OFST) = 0.1 V, and sine wave frequency = 10 Hz. The obtained results revealed that at an applied voltage of 8 Vpp and an OFST of 0.1 for 12 h, the maximum bacterial LEA and DHA were 30.6 U/mL and 75.5 micro grTF/cm2.gr biomass; respectively. Cell viability and permeability were equal to 95.7% and 0.3%; respectively, at the voltage of 8 Vpp. Moreover, liquid chromatography–mass spectrometry (LC-MS) and gas chromatography–mass spectrometry (GC-MS) analyses showed that by-products had lower intensity at 8 Vpp compared with that of 2 Vpp voltage. Finally, the results demonstrated an optimum applied voltage of the AC, which could stimulate and promote bacterial LEA and DHA. Therefore, an electroactive bioreactor supplied with an AC can be a novel system for stimulation of enzyme activities in the process of ASA biodegradation. [ABSTRACT FROM AUTHOR]