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5G network slicing allows operators to deploy virtual connectivity services tailored for specific purposes on top of the same underlying physical infrastructure. For some 5G services, the telecommunication operator needs to provide the customer with real-time information of the end-to-end Quality of Service for a particular slice. This paper focuses on the challenges behind this target, how per-layer per-segment monitoring can be performed based on common open interfaces to standard OAM protocols, and provides practical rules to plan end-to-end latency for slices. Then it reviews a few latency engineering approaches for fronthaul traffic from work carried out in this research area. • End-to-end 5G network slicing has key implications on optical transport networks. • Providing slice users with real-time feedback of end-to-end QoS is a new 5G feature. • Integrated per-layer per-segment latency management is challenging though viable. • Open NETCONF/YANG interfaces to OAM enables multi-layer performance monitoring. • Practical rules to plan end-to-end latency for slices and fronthaul traffic are reviewed. [ABSTRACT FROM AUTHOR]

• Application of ML methods in lasers is limited by a number of significant factors. • ML methods is often claimed where simple automation of control is introduced. • It is not clear, what kind of advantages will result from ML technologies in lasers. • Penetration of ML methods is frequently limited by the relatively low level of AI. • Presently, ML is not a universal method of photonics. Machine learning methods are being successfully applied in various domains of human activity, including optics. Can they become a universal instrument capable of improving user aspect of photonic devices? Is their application a necessary element of such improvement? Answers to fundamental questions arising from application of machine learning methods in ultrashort-pulsed lasers are discussed. Future prospects and current fundamental limitations of such methods are analysed. [ABSTRACT FROM AUTHOR]

This paper introduces a practical comprehensive approach to optimize the cost of installed Optical Transport Network (OTN) interfaces, as well as the required number of wavelengths in the substrate Wavelength Division Multiplexing (WDM) optical network. The approach assumes grooming variable-bit-rate traffic demands on multi-rate OTN interfaces. We propose an Integer Linear Programming (ILP) formulation to address the combined problem of OTN interface deployment, virtual-network formation, traffic grooming on the established distinct-capacity virtual paths, and virtual network embedding on the WDM physical substrate. The presented model focuses on mitigating the capital expenditure required to deploy OTN interfaces, usually the most costly element in the network, as well as minimizing the required number of wavelengths in the Routing and Wavelength Assignment (RWA) problem, contributing to the overall reduction in network costs and ensuring open capacity for future expansions. As the RWA problem is NP-hard and involves significant computational costs, we also propose a multi-step heuristic approach to tackle larger network instances more efficiently. In this approach, the optimization steps for the OTN design and the RWA solutions are conducted independently. For the OTN-layer planning, the optimum ILP formulation (OTN-ILP) is maintained, so that the optimum solution for the cost of installed interfaces on the OTN layer is guaranteed. The RWA problem is proposed through either an ILP formulation (RWA-ILP) or a heuristic approach. The RWA-ILP model can find the same or slightly superior number of wavelengths compared to the optimum solution of the Integrated ILP formulation, but it can provide results in reasonable times only for small networks. On the other hand, the heuristic RWA is able to run any network size, but it requires more wavelengths compared to the RWA-ILP model. • An approach to optimize the cost of installed Optical Transport Network (OTN). • A formulation to address the OTN interface deployment and virtualization. • The model focuses on mitigating the capital expenditure required to deploy OTN. • The paper proposes a heuristic approach to tackle larger network instances. [ABSTRACT FROM AUTHOR]

• Novel Photonic Device Development : The paper introduces a groundbreaking approach to create a photonic device for chemical applications, utilizing an evanescent wave absorption technique-based optical fiber probe. • Free-base Porphyrin Monolayering: The sensing probe incorporates a Tetraamine porphyrin (TAPP) monolayer, exploiting the unique optical properties of TAPP to enhance chemical sensing capabilities through the optical fiber. • Distinct Optical Patterns: The study focuses on monitoring interactions between TAPP and nitrate and chloride ions in the solution phase, emphasizing on absorption spectra variations of porphyrin molecules significantly in Soret and Q-bands. Distinct optical patterns emerge from the interaction, and the paper thoroughly analyses ion-dependent shifts in both the bands across eight samples of nitrates and chlorides. • Spectral Pattern Recognition: It employs unsupervised learning algorithms for spectral pattern recognition, allowing the discernment of ion groups based on their unique optical signatures. The use of PCA and Dtrend techniques helps to extract significant data to cluster different compounds. The sensor probe however exhibits remarkable sensitivity to nitrate and chloride ions, showcasing an impressive rapid response time of 2-3 s. • Practical Implications: The findings highlight the potential practical applications of the developed photonic device, emphasizing its utility in environmental monitoring and chemical analysis. The study positions porphyrin-based optical fiber sensor as a valuable technology, demonstrating their efficacy in detecting and analysing chemical compounds, particularly nitrate and chloride ions. The paper introduces a novel approach to develop a photonic device for chemical applications using an evanescent wave absorption technique-based optical fiber probe layered with a Tetraamine porphyrin (TAPP) monolayer exploiting the optical properties of TAPP. The interactions between the TAPP and nitrate and chloride ions in the solution phase were monitored and the changes in the absorption spectra of TAPP molecules were recorded. Distinct optical patterns emerge, and ion-dependent shifts in the Soret and Q-bands are analyzed for eight samples of nitrates and chlorides. Principal Component Analysis (PCA) is employed to discern ion groups based on the spectral pattern recognition. These fiber probes exhibit sensitivity to nitrate and chloride ions, with enhanced selectivity, robustness, and a rapid response time of 2–3 seconds. The study demonstrates the emergence of porphyrin-based optical fiber sensors as a useful sensor technology in environmental monitoring. [ABSTRACT FROM AUTHOR]

• In this paper, the tunability and switchability of the proposed multi-wavelength erbium-doped fiber laser (EDFL) with a parallel Lyot filter are verified by experiments. • The parallel Lyot filter provides the polarization hole burning (PHB) effect to reduce the mode competition, resulting in a comb spectrum. • For the laser cavity, the polarization state can be changed by adjusting the polarization controllers (PCs) of the parallel Lyot filter. The proposed EDFL can laser up to six wavelengths. • The fiber laser not only has simple structure, good repeatability and high stability, but also can realize switchable wavelength number and tunable wavelength interval. In this paper, the tunability and switchability of the proposed multi-wavelength erbium-doped fiber laser (EDFL) with a parallel Lyot filter are verified by experiments. The parallel Lyot filter provides the polarization hole burning (PHB) effect to reduce the mode competition, resulting in a comb spectrum. For the laser cavity, the polarization state can be changed by adjusting the polarization controllers (PCs) of the parallel Lyot filter. By adjusting PC 2 , the wavelength intervals can be tuned to obtain dual wavelengths with 6 different wavelength intervals, three wavelengths with 15 different wavelength intervals, and four wavelengths with 3 different wavelength intervals. In addition, by adjusting PC 2 , dual and three wavelengths can be tuned in the range of 1525 nm–1560 nm. By adjusting PC 1 , stable single, dual, three, four, five, and six wavelengths can be excited. The proposed EDFL has good tunability, switchability and stability. [ABSTRACT FROM AUTHOR]

• A novel photonic skin flexible sensor based on partially neutralized sodium polyacrylate is reported for the first time in this paper. • This photon skin flexible sensor has achieved relative humidity sensing for the first time. • The photonic skin flexible sensor has a relative humidity sensitivity of up to 0.1411 dB/%, with a fast response time of 170 ms. • The temperature response exhibits outstanding sensitivity (0.4 dB/°C) in the human skin surface temperature range (30 ∼ 48 °C). Biomimetic skin sensing devices play an important role in next-generation healthcare, robotics, and bioelectronics. In recent years, biomimetic skin-sensing technologies have gained significant attention due to their broad-ranging utility in the fields of healthcare and automation, and future wearable devices designed for health monitoring, robotic applications, and ultra-precise industrial positioning will necessitate the incorporation of flexible optical systems. A novel photonic skin flexible sensor (PSFS) based on partially neutralized sodium polyacrylate (PAS-50) is reported for the first time in this paper. In this study, a novel wearable sensor was designed for real-time detection of temperature and humidity. A single-mode tapered fiber (SMTF) structure based on the principle of evanescent wave is proposed for fast response and real-time monitoring of humidity and temperature. The sensor incorporates an optical micro/nanofiber (MNF) as the core sensing node, while a hydrophilic and ductile Sodium Polyacrylate (PAS) is chosen as the humidity-sensitive material that overcomes the limitation of commonly reported electrical, optical, and material-based flexible devices. Due to the strain amplification effect of the MNF, the sensitivity of the material to relative humidity (RH) is significantly improved, reaching 0.1411 dB/%. In addition, the temperature response exhibits outstanding sensitivity (0.4 dB/°C) in the human skin surface temperature range (30 ∼ 48 °C). Notably, the sensor exhibits a rapid response with a remarkable response time of 170 ms. The proposed PSFS presents novel opportunities for the advancement of future biomimetic skin devices, thus playing a pivotal role in the advancement of next-generation robotics and medical monitoring technologies. [ABSTRACT FROM AUTHOR]

• This paper introduces a strain monitoring method where optical fibers are embedded along a spiral path in composite cylindrical structures. • A monitoring method is proposed to judge the health state of the structure by using the strain data monitored in this direction. • The comparison between the measurements of the embedded fiber optic and the surface-bonded strain gauges under various working conditions demonstrates excellent consistency, validating the fiber optic sensor's measurement accuracy. Composite cylinder structures are widely used in various engineering fields. Monitoring the health state is an essential method for ensuring the safe operation of the structures. Embedded distributed fiber optic sensors have gained significant interest as they effectively address issues related to aesthetics and protection. This paper presents a strain monitoring method that involves embedding optical fibers along a spiral path within composite cylindrical structures. Additionally, a monitoring method is proposed to evaluate the structure's health state using the strain data collected in this manner. To validate the measurement accuracy of the fiber optic sensors, a comparison is made between the measurements obtained from the embedded fiber optic sensors and surface-bonded strain gauges under different working conditions. The results demonstrate excellent consistency, establishing the reliability of the fiber optic sensors. In this study, a distributed fiber optic sensor network and embedding scheme are designed for large composite cylinder structures, and strain monitoring experiments at various conditions, including pressure, bending, and hoisting loads, are conducted. Finite element simulations are also performed at corresponding working conditions, and the effectiveness of fiber optic sensor measurement is confirmed by comparing normalized simulation results with measured results. The embedded distributed fiber optic sensors effectively capture the strain changes at the reinforcement frame located in the middle of the cylinder structure, which aligns with the theoretical analysis of the cylinder structure under varying loads. This study on the embedding of fiber optics in large composite cylinder structures provides valuable insights for structural health monitoring purposes. [ABSTRACT FROM AUTHOR]

• An efficient hybrid network for supercontinuum generation prediction proposed. • Wasserstein generative adversarial network augments the original dataset. • Deep neural network with a TCN layer predicts supercontinum spectrum accurately. In this paper, a Hybrid Network is reported for predicting the output pulse shape parameters of the supercontinuum in optical fibers. The network incorporates the Wasserstein generative adversarial network (WGAN) and the deep neural network (DNN) with a TCN layer. The WGAN augments a limited set of original data, while the designed DNN accurately predicts supercontinuum. The simulation results show the spectra agreement (A gm) of the predictions by individual DNN is 89% and the root mean square error (RMSE) is 0.1092. After retraining with WGAN's extended dataset, the A gm of DNN predictions is improved to 98% and the RMSE is reduced to 0.0513. The input pump power corresponding to the appearance of the fourth soliton peak can be predicted by the retrained DNN. Numerical analysis demonstrates the effectiveness and generalization ability of a Hybrid Network in predicting pulse parameters. The network fits the propagation dynamics in the spectral domain of SC, which provides a promising tool for further research in this field. [ABSTRACT FROM AUTHOR]

The main advantage of multi-band (MB) networks is to provide more capacity than C-band networks by using other unused bands like the L- and S-bands and, in this way, postpone the announced optical network capacity crunch. However, MB nodes have a more complex structure than C-band nodes, impacting their cost and enhancing their induced physical layer impairments (PLIs). The main goal of this paper is to analyze the impact of several MB node architectures (namely baseline, common-band and compact MB node architectures) on the total network capacity and total network cost-per-bit, using a routing, modulation format, and spectrum assignment (RMSA) network planning tool based on a Monte–Carlo simulation that also incorporates the impact of network PLIs. When the PLIs are neglected, the common-band architecture presents the lowest cost-per-bit compared to the remaining MB architectures, since only lower cost C-band components are used. However, with the PLIs impact, the common-band architecture leads to the lowest total network capacity and highest cost-per-bit due to additional noise coming from all-optical wavelength converters. In particular, the common-band total network capacity is less than half the baseline and compact total network capacities for a blocking probability of 1%, considering the best channel launch power. Also, the common-band cost-per-bit is almost twice the baseline and compact cost-per-bit due to the PLIs-induced degradation. • Four multiband nodes are compared in terms of cost and capacity in a network scenario. • Common-band node loses the cost advantage in presence of physical layer impairments. • Common-band node capacity is less than half the baseline and compact nodes capacity. • Baseline and compact nodes have similar costs and capacities. [ABSTRACT FROM AUTHOR]

• We clarify the concept of the FADD, which uses optical filters to achieve optical field recovery of CV-DSB signals via direct detection. • The CV-DSB signals for the proposed scheme can be retrieved at low CSPR without the SSBI elimination algorithm. • The simulation results indicate that three FADD receivers can achieve signal field recovery at −5 dB CSPR after 80 km fiber transmission. • By using cost-effective FADD receiver, the proposed FADD scheme provides an effective approach for low CSPR field recovery. Double-sideband self-coherent detection (DSB-SCD) can achieve optical field recovery of complex-valued double-sideband (CV-DSB) signals without a local oscillator laser. To date, various proposed DSB-SCD schemes require a high carrier-to-signal power ratio (CSPR) to mitigate the inherent signal-signal beat interference (SSBI) induced by direct detection. Aiming at relaxing the high CSPR requirement for the DSB-SCD, filter-assisted direct detection (FADD) is proposed to retrieve the CV-DSB signals. In this paper, we clarify the concept of the FADD, which uses optical filters in the receiver to achieve optical field recovery of CV-DSB signals via direct detection. The CV-DSB signals can be retrieved at low CSPR with the aid of optical filters. We also propose a novel FADD receiver that uses an optical bandstop filter (OBSF) to obtain CV-DSB signals from self-coherent signals, called OBSF-DD with 90° hybrid. Considering the high complexity of the OBSF-DD with 90° hybrid, a simplified OBSF-DD receiver with 2 × 2 coupler is put forward as well, which uses a 2 × 2 coupler instead of optical hybrid, and three single-ended photodiodes are required to achieve signal reception. By using cost-effective FADD receiver, the proposed FADD scheme provides an effective approach for low CSPR field recovery. [ABSTRACT FROM AUTHOR]

• We developed a high-speed Raman temperature sensor with enhanced compatibility with existing strain sensors. • We revealed that the optimal Raman power measurement frequency is ∼195 THz, near the Rayleigh peak, not the traditional 206 THz. • We demonstrated effective real-time temperature sensing by monitoring Raman power variations at this specific frequency. This paper presents a high-speed Raman temperature sensor that is highly compatible with current strain sensors. Challenging conventional assumptions, we found that at a communication wavelength of 193 THz, the optimal frequency for measuring Raman scattering power is not the typically dominant 206 THz, linked to stimulated Raman scattering, but rather around 195 THz, in proximity to the Rayleigh scattering peak. Our study demonstrates the effectiveness of real-time temperature sensing through the monitoring of power fluctuations in Raman scattering at this particular frequency. © 2024 Elsevier Science. All rights reserved. [ABSTRACT FROM AUTHOR]

• Integration of Explainable Artificial Intelligence (XAI) models on fiber optic SPR sensors. • Insights into the intricate patterns and features learned by the model are attained. • A comparative analysis of XAI models, namely SHAP and LIME is carried out. • LIME and SHAP methods jointly find that metal layer thickness has considerably greater influence than wavelength on sensing performance. • This finding is consistent with the concept of radiation damping related to fiber optic SPR sensor. In recent years, there has been a significant surge in interest surrounding the utilization of machine learning techniques to optimize the performance of fiber optic sensors. This paper delves into the integration of machine learning methodologies, with a specific focus on Explainable Artificial Intelligence (XAI) models, within the domain of fiber optic surface plasmon resonance (SPR) sensors. We implement XAI techniques into a previously-trained Gaussian Process Regression (GPR) model to gain insights into the intricate patterns and features learned by the model, thereby providing valuable insights into its decision-making process. Furthermore, we present a comparative analysis of XAI models, namely SHAP and LIME , to elucidate the individual impact of light wavelength (λ) and metal layer thickness (d m) on the enhancement of sensor's figure of merit (FOM). The results obtained from both LIME and SHAP methods lead to a common finding that compared to λ, it is the value of d m that possesses a significantly greater influence on achieving maximum FOM. Furthermore, this finding is in complete agreement with the concept of radiation damping related to fiber optic SPR sensor structures. This study has the potential to contribute to the refinement of design and fabrication processes related to fiber optic SPR sensor for a wide variety of applications. [ABSTRACT FROM AUTHOR]

Fiber optic curvature sensors face several challenges that limit their application in structural health monitoring. These include high fabrication and demodulation costs, poor stability and robustness. In this paper, we propose a novel Mach–Zehnder interferometer (MZI) sensor that overcomes these limitations.The sensor was fabricated through the splicing of a seven-core fiber(SCF) and two single-mode fibers (SMF) with a common fusion splicer. The proposed sensor exhibited a good linear response, with a sensitivity of 22 nm/m − 1 in the range of 0–0.313 m − 1. The MZI sensor was demodulated by a neural network-based system and a data augmentation algorithm, reducing the need for large data samples and improving demodulation accuracy on sparse datasets. Overall, the sensor is characterized by fabrication simplicity, high mechanical strength, and compatibility with existing optical devices, making it applicable to various fields, such as aerospace, civil engineering, and mechanical manufacturing. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate a simple structure, ultra-narrow linewidth, extremely high stability and high optical signal to noise ratio single-longitudinal-mode (SLM) erbium-doped fiber laser (EDFL). Nested Fiber Ring (NFR), nested in the ring cavity of EDFL, is employed to serve as a high quality mode filter to eliminate the dense longitudinal mode of the EDFL. The mode-selection capability of the RIR is investigated and discussed theoretically and experimentally. Saturable absorber, which composes of a section of unpumped polarization maintaining erbium-doped fiber and a Fabry–Perot fiber Bragg grating (FP-FBG), is employed to produce a dynamic narrowband grating to ensure the SLM laser output. Saturable absorber, consisted of a section of unpumped polarization maintaining erbium-doped fiber, produces a dynamic narrowband grating to ensure the SLM laser output. We achieve a ultra-narrow linewidth SLM laser output of 550 Hz. The laser has an optical signal-to-noise ratio (OSNR) of more than 59 dB. In addition, the stability of the wavelength and power fluctuations below 0.03 nm and 0.02 dB, respectively. The single-longitudinal-mode fiber laser has a compact structure, ultra-narrow linewidth, and excellent performance, and is expected to be used in the fields of coherent communications, precision metrology, and so on. • We propose a new structure of ultra-narrow linewidth single-longitudinal-mode erbium-doped fiber laser based on Nested Fiber Ring structure and Saturable Absorber. • The new structure has the advantages of simple structure, easy preparation and high stability. • The output performance of the proposed fiber laser is excellent, the 3-dB linewidth is 550 Hz and the optical signal-to-noise ratio is 59 dB. • The filtering function of the Nested Fiber Ring was theoretically derived and its filtering effect was analyzed. [ABSTRACT FROM AUTHOR]

• Multiparameter sensing system using a single FBG with a polarization-assisted analysis. • Strain, torsion and temperature for the analysis of polarization and spectral components. • The relative errors are below 0.5% for each mechanical load condition. • A root mean squared error of 2.91 °C is obtained for the temperature analysis. This paper presents the development of a multiparameter sensing system using a single fiber Bragg grating (FBG) with a polarization-assisted analysis. In this case, the FBG sensor is subjected to axial strain, torsion angle and temperature for the analysis of polarization components and spectral features variations. In addition, the responses at two orthogonal polarization states are compared to evaluate the feasibility of developing a polarization-based analysis for multifeature regression. Results show the differences in the sensors responses considering the full spectrum and the polarization components, where non uniform strain components lead to differences in the polarization states, which are used on the simultaneous analysis of different mechanical loadings combinations. Furthermore, the simultaneous estimation of axial strain, torsion angle and temperature resulted in small relative errors when the whole range of the tests are considered. The relative errors are below 0.5 % for each mechanical load condition, whereas a root mean squared error of 2.91 °C is obtained for the temperature analysis. Thus, the proposed approach resulted in a suitable alternative for three parameters sensing using only one FBG in standard single mode silica optical fiber without any structural modification, which can lead to a new approach on spectrally efficient sensor systems for practical applications. [ABSTRACT FROM AUTHOR]

• Mode-locked figure-9 fiber laser has been proved to exhibit excellent performance. • Increase SNR and output stability by introducing a saturable absorber mirror(SESAM) to the single arm end of the figure-9 laser as a mode-locked auxiliary device. • Be a stable and reliable ultrafast optical seed for improving the performance of high-power laser facilities or all-optical modulation. The mode-locked figure-9 fiber laser has been proved to exhibit excellent performance, but improvement of its output signal-to-noise ratio(SNR) and stability are restricted by the laser structure design. In this paper, we propose and verify a modified laser cavity to increase SNR and output stability by introducing a saturable absorber mirror(SESAM) to the single arm end of the figure-9 laser as a mode-locked auxiliary device instead of the typical mirror. Numerical simulations based on the model of the figure-9 fiber and SESAM lasers clearly indicate that modified structure has better output performance than typical one. Additionally, the related experimental results also demonstrate that at the same pump power of 150mW and compare the typical structure, the modified one outputs a higher SNR of 70 dB, together with 12 h output lower RMS of 0.23 %. We believe that the presented laser design could be a stable and reliable ultrafast optical seed for improving the performance of high-power laser facilities, which also has potential applications in optical frequency comb and all-optical modulation. [ABSTRACT FROM AUTHOR]

In this paper, the Demand Clustering and Spectrum Allocation (DCSA) problem in a point-to-multipoint (P2MP) network with time-varying traffic is studied. This article introduces several heuristic techniques that can be applied to traffic aggregation for P2MP optical network architectures employing digital subcarrier multiplexing. Based on the transmitter constraint, the algorithms assign individual subcarriers (SCs) to receiving nodes with uncorrelated traffic profiles. The simulation results show that the proposed algorithms outperform the clustering methods. [ABSTRACT FROM AUTHOR]

• A optical fiber sensor for detecting vitamin B1 has been proposed for the first time. • Accurately and efficiently detect vitamin B1 within a large concentration range. • Red and green dual channel detection of vitamin B1 reduces detection errors. • Optical fiber sensing based on smartphones has broad prospects in low-cost detection. This paper introduces an innovative optical fiber surface plasmon resonance (SPR) biosensor designed for smartphone assistance, aiming at detecting vitamin B1 in synthetic urine. The key novelty lies in the amalgamation of silver nanocoated cysteine with a gold-plated optical fiber probe, fostering efficient detection through the robust electrostatic interaction between negatively charged Cys-capped AgNPs and positively charged vitamin B1 molecules. Notably, this biosensor leverages the smartphone's digital camera capabilities to discern varying color intensities. A self-developed application ensures real-time monitoring of green and red channel intensities in the SPR signal, thereby mitigating the risk of false detections. Moreover, the integration of the fabricated optical fiber probe with the smartphone is achieved through a 3D-printed casing, endowing the biosensor with the advantages of portability, handheld operation, and cost-effectiveness. The proposed U-shaped optical fiber SPR biosensor, coupled with smartphone technology, demonstrates the ability to detect vitamin B1 within the concentration range of 2–10 μM, yielding a commendable R2 value of 0.9973. Experimental findings affirm that this novel biosensor, built on the U-shaped SPR optical fiber architecture and empowered by smartphones, is an economical, uncomplicated, and portable device adept at accurately and efficiently detecting vitamin B1 across a broad concentration spectrum. Its potential applications extend to the area of low-cost biochemical component identification. [ABSTRACT FROM AUTHOR]

• This paper proposes a wavelength tunable ring cavity erbium-doped fiber laser based on Fabry Perot filter fabricated by hydrofluoric acid corrosion for stretch sensing. • In the design of the laser, hydrofluoric acid is employed for chemical etching to prepare the F-P cavity, and tapering is applied to the F-P cavity to enhance sensitivity. In this study, the erbium-doped fiber laser with a ring cavity and a Fabry-Perot (F-P) filter was proposed and experimentally verified. In the design of the laser, hydrofluoric acid was employed for chemical etching to prepare the F-P cavity, and tapering was applied to the F-P cavity to enhance sensitivity. The experimentally prepared F-P filter was placed in the resonant cavity and served as a frequency-selective device for the fiber laser. At a laser threshold of 48 mW, we obtained a single-wavelength laser output at 1565.28 nm, with a 3 dB linewidth of 0.29 nm. To evaluate the stretching sensing performance of the EDFL system, we performed stretching of the F-P filter. The experimental results demonstrated that within a stretching length range of 0 to 3 mm, we could obtain a single-wavelength laser that could be tuned from 1559.57 to 1567.04 nm, corresponding to a tuning range of 7.47 nm. The laser showed a sensitivity of 2.73 nm/mm and a goodness of fit 0.999. Monitoring the stability of a single-wavelength laser within 30 min, the signal-to-noise ratio was greater than 27.212 dB, and the power fluctuation was less than 0.712 dB. Additionally, the polarization controller was adjusted to obtain two different dual-wavelength lasers with a power fluctuation of less than 0.71 dB. [ABSTRACT FROM AUTHOR]

• The effect of gamma rays on two experimental fiber-optic cables was studied. • The cables were irradiated using the dose of 80.5 kGy and rate of 5.5 Gy/h. • The cables were irradiated using the dose of 65.5 kGy and rate of 0.94 Gy/h. • MM fibers after irradiation have lower optical losses at 1300 nm than 850 nm. • SM fiber with the lowest influence of gamma rays had losses of 3.5 dB at 1310 nm. This paper reports on our study of the effect of gamma-ray irradiation on two types of experimental fiber-optic cables. The first type of cable, CTFS, had a jelly-filling compound, whereas the second type, CTDS, was without the jelly. The cables contained three multi-mode (A, B, C) and five single-mode (D, E, F, G, H) optical fibers. The study was performed using two gamma-irradiation facilities with 60Co sources for slow long-term irradiation with the dose of 80.5 kGy at the low dose rate of 5.5 Gy/h and with the dose of 65.5 kGy at the higher dose irradiation rate of 0.94 kGy/h. After the irradiation with the dose of 80.5 kGy, the C fiber in the CTDS cable had the optical loss of 5.91 dB; 140 days after the gamma treatment at the wavelength of 1300 nm, it was 4.96 dB. The lowest optical losses for a single-mode fiber after irradiation with the dose of 65.5 kGy were found for the D fiber in the cable CTFS, namely 3.26 dB at 1490 nm and 3.49 dB at 1310 nm. In the fiber E in the CTDS cable, the optical loss was 3.62 dB at 1550 nm. In the fiber F in the CTDS cable, it was 3.86 dB at 1310 nm. [ABSTRACT FROM AUTHOR]

• Machine learning approach for automatic estimation of responses using different TFBGs. • Estimation based on the optical spectral characteristics of TFBGs as a function of RI. • Root mean squared errors as small as 0.008 RIU for the trained samples. • The approach can be used to enhance the reproducibility of large set of TFBG sensors. This paper presents the development of an approach for automatic estimation of the regression coefficients as a function of the refractive index (RI) in Tilted Fiber Bragg Gratings (TFBGs) based on their optical spectral characteristics. The methodology is based on machine learning approach, where different samples are analyzed in various test conditions to obtain a dataset for the training of a kNN regression algorithm. In this case, the spectral characteristics related to the wavelength spacing between adjacent cladding mode resonances, number of valleys and amplitude of the normalized spectra are correlated with the linear regression algorithm for RI estimation using the machine learning approach. The analysis are performed as a function of the wavelength shift and optical power, considering two regions on the transmitted spectrum and the envelope of the curve. Furthermore, the number of valleys and the area of the envelope curve are also analyzed as a function of the refractive index, which result in six analyzed features. The Principal Components Analysis (PCA) is used to reduce the number of features to two principal components. The results of the proposed algorithm are obtained with different trained and untrained samples, which indicates a root mean squared error (RMSE) of around 0.003 RIU for the trained samples and 0.008 RIU for the untrained ones. Therefore, the results indicate the usefulness of the proposed approach, which can be used to enhance the reproducibility of large set of TFBG sensors in practical applications. [ABSTRACT FROM AUTHOR]

• An optical fiber weak magnetic sensing system based on Michelson interferometer is proposed. • A new improved phase-generated carrier demodulation algorithm. • Suitable for optical fiber interference weak signal demodulation. • The sensing unit support frame was fabricated using 3D printing. The detection of weak magnetic fields is integral to applications in geophysical monitoring, biomagnetism, and remote sensing. This paper presents a new sensing unit structure and signal demodulation algorithm for optical fiber weak magnetic sensing system. The system uses a strip-ring sensing unit structure that combines magnetostrictive effects with optical fibers through 3D printing technology. This integration facilitates the conversion of magnetostrictive displacement into optical phase. An improved Phase Generated Carrier (PGC) algorithm is employed to demodulate the phase information, enhancing the signal to noise ratio (SNR) by 4.33 dB compared to the traditional PGC algorithm, and achieving a phase resolution of 29.51 µrad/Hz1/2 at 500 Hz. Experimental results demonstrate that the suggested sensing system can detect a minimum magnetic field of 140 nT, with an AC magnetic field phase resolution of 15.78 nT/Hz1/2 at 500 Hz. The demodulation sensitivity reaches 1.87 × 10−6 rad/nT under a magnetic field of 140–1400 nT. The capability of the proposed system demonstrated great potential as an efficient approach for detecting weak magnetic signals in many practical applications. [ABSTRACT FROM AUTHOR]

Wireless-optical broadband access network (WOBAN) or fiber-wireless (FiWi) is a robust and cost-effective solution to provide high bandwidth network connectivity to mobile subscribers. Optical network unit (ONU) placement is a topological optimization problem that plays a vital role in effective deployment of FiWi network. Recently, some artificial intelligence-based approaches for positioning ONUs were proposed and generated promising results. However, the reported performance in the literature is far from the ideal state. This issue emphasizes the necessity of introducing new placement methods or improving the performance of existing methods. This paper presents a hybrid clustering algorithm for finding the optimal position of multiple ONUs. The proposed backtracking K -harmonic means (BKHM) is an integration of K -harmonic means (KHM) and a backtracking search algorithm (BSA). BKHM not only efficiently specifies the optimal positions of ONUs but also significantly decreases the implementation cost. To demonstrate the performance of the BKHM, we evaluate it on well-known placement benchmarks compared with BSA, KHM, whale optimization algorithm (WOA), enhanced backtracking search (EBS), harris hawks optimization (HHO), and chaotic local search-based levy flight distribution (CLF) algorithms. The experimental results and statistical analysis proved that the proposed BKHM algorithm outperformed its counterparts on most benchmarks in terms of cost optimization, convergence accuracy, and solution quality. • Proposing a hybrid clustering algorithm: The proposed not only solves the slow convergence of the BSA algorithm but also helps the KHM to escape from local optimal. • Using the BKHM for solving ONU placement problem: The BSA algorithm is suitable for solving permutation problems, therefore combining it with KHM can work better than other algorithms for the problem of ONU placement. • Improving the performance of the existing ONU placement methods. Simulation results confirm the superiority of the BKHM compared with other methods. [ABSTRACT FROM AUTHOR]

• Reveal the design principles of trench-assisted bridge fibers (TABFs), offering an effective methodology for fabricating TABFs for FIFO devices. • Demonstrate the feasibility of utilizing TABFs for fabricating low-loss FIFO devices. • The results indicated that the fabricated FI/FO device exhibited a remarkably low loss (<0.50 dB), and relatively low crosstalk (<-55.2 dB) in the C-band. Multi-core fibers (MCF) technology is the feasible path to extend the capacity of optical fiber communication systems. However, there is a lack of low-loss and low-crosstalk multi-core fan-in and fan-out (FIFO) devices for MCF communication in the C-band. In this paper, we proposed all-fiber FIFO devices with seven trench-assisted bridge fibers (TABFs). The special structure of the TABFs could facilitate the matching of single-core fiber with MCF during the tapering progress. By using the TABFs, the average taper loss was less than 0.06 dB. The novel method can reduce the insertion loss of FIFO devices. The experiments indicated that the fabricated FIFO devices exhibited lower than 0.50 dB insertion loss and less than −55.2 dB crosstalk in the C-band. This work provides novel TABFs and an efficient way to fabricate low-loss low-crosstalk FIFO devices for MCF communication systems. [ABSTRACT FROM AUTHOR]

• Over the years 2 µm mode-locked fiber laser has been widely developed as an important light source for various significant applications, such as ultrafast mid-infrared spectroscopy. Besides, as the solutions of CGLE governed by the composite balance among dispersion, nonlinearity, gain and loss in dissipative systems, the field of solitons has become subject to extensive study. • Worth to note that, the rise of time-stretched dispersive Fourier transform (TS-DFT) technique has significantly enhanced the understanding of soliton dynamics, including bound solitons, optical rogue waves and others. However, due to the lack of appropriate dispersive components at 2 µm band with low optical transmission loss for TS-DFT measurement, direct real-time observations of ultrafast soliton dynamical phenomena in the 2 µm mode-locked fiber lasers is still limited. • In the present paper, we utilize DFT method to investigate the ultrafast nonlinear soliton dynamics in a 2 µm Tm-doped mode-locked fiber laser. The real-time observation of the nonlinear dynamics of the soliton explosions and pulsations are successively investigated. Moreover, the real-time observation of the soliton explosions associated with soliton pulsations is demonstrated in 2 µm wavelengths for the first time. In addition, soliton rains with dual-wavelength operation are also observed. Our work will benefit the development of 2 µm ultrafast light source, as well as enhance a comprehensive understanding of the soliton nonlinear dynamics in mode-locked fiber lasers. Over the years, 2 μm mode-locked fiber laser has been widely developed as an important light source for various significant applications. Worth to note that, with the help of real-time spectroscopy technique, i.e., time-stretched dispersive Fourier transformation (TS-DFT), various complex nonlinear soliton dynamics have been revealed, such as soliton molecules, soliton explosions and soliton pulsations, enhancing our understanding of the ultrafast physics. However, due to the lack of appropriate dispersive components at 2 μm band with low optical transmission loss for TS-DFT measurement, the investigation of ultrafast soliton dynamical phenomena in the 2 μm mode-locked fiber lasers is still limited. In this work, we demonstrate the direct real-time observation of soliton explosion and pulsation phenomena at 2 μm band mode-locked fiber laser, for the first time as far as we know, by using specially designed linearly chirped fiber Bragg gratings as dispersive component for TS-DFT measurement. For explosions, we observe slight explosion and drastic explosion, respectively. Particularly, the soliton pulsating explosions are also characterized in real time where the explosions occur in the process of soliton pulsation. In addition, dual-wavelength soliton rains are also observed by carefully adjusting the cavity parameters. Our work provides supplements to the current investigation of 2 μm band ultrafast science, and might enrich our understanding of soliton dynamics. [ABSTRACT FROM AUTHOR]

• Phase noise induces ICI in optical coherent OFDM transmission. • For DFT-S OFDM, phase noise in symbol domain is similar to that in time domain. • The proposed phase noise compensation is operated in time domain and symbol domain. • The compensation scheme can efficiently suppress ICI induced by phase noise. Previous studies have revealed the similarity between phase noise in the symbol domain of discrete Fourier transform spread (DFT-Spread) coherent orthogonal frequency division multiplexing (CO-OFDM) systems and that in the time domain. This paper further details this characteristic through both formulas and simulation results, while also analyzing and summarizing its formation conditions and influencing factors. Based on this, a phase noise compensation (PNC) scheme based on DFT-Spread OFDM is proposed for high-order quadrature amplitude modulation (QAM) transmission with large fast Fourier transform (FFT) sizes. The proposed scheme effectively suppresses inter-carrier interference (ICI) introduced by phase noise in OFDM systems, as verified through simulations of dual-polarization (DP) 64-QAM CO-OFDM transmission over 80 km single-mode fiber (SMF). This work suggests that proposed PNC scheme enhance the tolerance for laser linewidth in OFDM systems, and may offer a possible solution for short distance high-baud-rate high-order QAM coherent transmission. [ABSTRACT FROM AUTHOR]

• Aiming at the demand of pressure monitoring of flammable and explosive gases in industrial production, a diaphragm-type FBG high-pressure gas sensor is designed to realize long-term high accuracy pressure measurement in the range of 0–50 MPa, with good static characteristics under experimental conditions, which verifies the feasibility of the pressure sensing model. • The use of glass welding encapsulation instead of the traditional adhesive encapsulation to produce FBG pressure sensors improves the durability and long-term stability of FBG pressure sensors, and provides the necessary data support and reference for the subsequent use of glass welding encapsulation of FBG sensors. • The use of glass welding encapsulation helps to maintain the long-term high accuracy measurement of the FBG pressure sensor. Large quantities of flammable and explosive gases are often used in various production processes in the chemical and energy industries. these gases, if leaked or improperly operated, can cause serious production accidents. Therefore, in order to meet the requirement for miniaturized, highly accurate, long-term stable and large-range high pressure sensors for flammable and explosive gases in industrial production, a highly accurate diaphragm fiber Bragg grating (FBG) high pressure gas sensor is designed in this paper. In this work, the working principle of the sensor is first analyzed theoretically, the circular elastic metal diaphragm of the sensor will strain under the action of pressure load, and then the strain will be transmitted to FBG. The wavelength drift of FBG is measured to achieve the measurement of the pressure load. Then finite element simulation was carried out for the diaphragm strain of the sensor to verify the feasibility of the sensor design scheme. The traditional adhesive encapsulation is then replaced with a glass welded encapsulation to improve the durability and long-term stability of the sensor. Finally, calibration experiments was conducted on the sensor, and the experimental results were compatible with the theoretical simulation analysis. The results show that the sensor realizes long-term highly accurate measurement of pressure in a large range of 0–50 MPa, and has good static characteristics under experimental conditions. [ABSTRACT FROM AUTHOR]

• GaS nanosheets used for the first time as a sensitizer material in optical fiber SPR sensors is proposed. • GaS modification of optical fiber is achieved through layer-by-layer self-assembly. • The experimental results show that the SPR sensor based on GaS nanosheets offers high sensitivity and FOM value. Optical fiber Surface plasmon resonance (SPR) sensors are applied in the field of biological monitoring widely. This paper presents a novel method to improve the sensitivity of optical fiber SPR sensor by using gallium sulfide (GaS) nanosheets. Compared with traditional two-dimensional materials, gallium sulfide has a higher refractive index and higher carrier mobility, which can effectively enhance the surface plasma wave (SPW), thereby improving the sensitivity. By testing sensors coated with gallium sulfide of different thicknesses, the team finally found that when the sensor structure is set to MSM, the thickness of gold film and gallium sulfide nanosheets dispersion is 50 nm and 40 nm, the sensitivity and the FOM value of SPR fiber sensor are 5858.78 nm/RIU and 36.62 RIU−1. The sensitivity to refractive index is 2.9 times that of the traditional gold film sensor, and the sensor has good stability and reliability, and can be reused. This sensor can be applied to monitor low concentrations of biomolecules and weak signals. The use of this material has great implications for the production of new SPR-based chemical and biosensing devices. [ABSTRACT FROM AUTHOR]

• We designed and manufactured a 40-channel array waveguide grating (AWG) based on a silicon dioxide planar light wave circuit (PLC). • Using hybrid integration technology to couple AWG and photodetector arrays together. • The hybrid integrated demodulation chip achieves precise wavelength demodulation of C-band FBG sensors. • The designed AWG has a 3 dB bandwidth of 1.98 nm, insertion loss of approximately 3.5–4.1 dB, and adjacent channel crosstalk of approximately −7.84 dB. • The wavelength resolution of the demodulation system is 1 pm, and the demodulation accuracy is 2.11 pm. Fiber Bragg grating (FBG) sensors have been widely used in various fields. To develop a miniaturized, high-precision, and high-response FBG interrogation system, arrayed waveguide grating (AWG) has been widely used as a key device. In this paper, a 40-channel arrayed waveguide grating based on silica planar lightwave circuits (PLCs) is designed fabricated, coupled to a photodetector array using hybrid integration techniques. The hybrid-integrated demodulation chip enables precise demodulation of the FBG sensor wavelength in the C-band. The test results show that the AWG has a good transmission spectrum with a 3-dB bandwidth of 1.98 nm, insertion loss of about 3.5–4.1 dB, and adjacent channel crosstalk of about −7.84 dB. The established FBG interrogation system can realize continuous interrogation in the dynamic range of 1514.6–1578.6 nm, the wavelength resolution is 1 pm and the demodulation precision is 2.11 pm in the dynamic range of 1555.3–1556.1 nm. [ABSTRACT FROM AUTHOR]

• A wavelength injection locking actively Q-switched wide locking range random fiber laser (RFL) based on single-mode fiber (SMF) is proposed. • A narrow linewidth laser with tunable wavelength and power is injected into the cavity through the wavelength tunable laser (TLS), and the laser mode of RFL is selected by mode resonance. • In the C-band of 1530 to 1565 nm, different laser modes with stable center wavelength and peak power can be selected by changing the wavelength of the injected light. In this paper, a wavelength injection locking actively Q-switched wide locking range random fiber laser (RFL) based on single-mode fiber (SMF) is proposed. Within the C-band range from 1530 nm to 1565 nm, different laser modes can be selected by changing the wavelength of the injected light. Under injection locking state, the power fluctuation within one hour is less than 0.1dBm. When high nonlinear optical fiber (HNLF) is used in the RFL, the pump power is increased from 107 mW to 300 mW, the fixed sine wave modulation signal frequency is 20 kHz, the modulation voltage is 5 V, and the injection power is 15dBm. The RFL is in injection locking state and the output pulse is stable 4 pulses. When HNLF in RFL is replaced by SMF with the same length and the injection locking state is maintained, the output pulse is single pulse. Furthermore, the pump power increases from 107mW to 300mW, the pulse width increase from 1.91 μs to 3.24 μs, and the pulse repetition frequency is 20 kHz. In addition, the laser has wavelength tunable properties in the C-band range and serves as an ideal light source in the fields of laser imaging and pulse coding. [ABSTRACT FROM AUTHOR]

In this paper, we revisit the problem of adjusting transceiver power, amplifier gain, and nodal gain in optical-bypass-enabled networks, taking into account an empirical model of erbium-doped fiber amplifier (EDFA) gain saturation. We assume that network demands have been routed via the shortest possible paths. A heuristic algorithm, which estimates the degradation of the signal-to-noise ratio (SNR) for each demand, is used to assign the modulation level and spectrum slots to the routed demands. Our optimization process aims to maximize the minimum SNR margins of demands, by adjusting EDFA small-signal gain, variable optical attenuator (VOA) attenuation, and transceiver power. Constraints and impairments imposed by the physical-layer include EDFA and VOA gain limits, transceiver power limits, receiver sensitivity, insertion loss of optical switch input ports, EDFA gain saturation, EDFA noise, and fiber non-linear interference. These are modeled using the Gaussian noise model. The proposed optimization problem is formulated as a geometric programming problem and then converted into an equivalent convex problem. Numerical results suggest that in the optimal solution of our optimization, all demands are served with typically low bit error rates (BER) (< 10 − 4). We calculate the operational gains of the EDFA to set the spans to full compensation whenever possible. Pre-amplifiers and line amplifiers do not experience gain saturation due to relatively small input powers, while approximately 10% of boosters undergo more than a 1 dB gain reduction due to high input powers. We observe that overlooking the effect of EDFA gain saturation and physical-layer-imposed constraints such as nodal gain limits or transceiver power limits during network optimization leads to a considerable number of blocked demands due to SNR degradation or high BER (> 10 − 3). [ABSTRACT FROM AUTHOR]

A new architectural paradigm, named, optical-computing-enabled network, is proposed as a potential evolution of the currently used optical-bypass framework. The main idea is to leverage the optical computing capabilities performed on transitional lightpaths at intermediate nodes and such proposal reverses the conventional wisdom in optical-bypass network, that is, separating in-transit lightpaths in avoidance of unwanted interference. In optical-computing-enabled network, the optical nodes are therefore upgraded from conventional functions of add-drop and cross-connect to include optical computing/processing capabilities. This is enabled by exploiting the superposition of in-transit lightpaths for computing purposes to achieve greater capacity efficiency. While traditional network design and planning algorithms have been well-developed for optical-bypass framework in which the routing and resource allocation is dedicated to each optical channel (lightpath), more complicated problems arise in optical-computing-enabled architecture as a consequence of intricate interaction between optical channels and hence resulting into the establishment of the so-called integrated/computed lightpaths. This necessitates for a different framework of network design and planning to maximize the impact of optical computing opportunities. In highlighting this critical point, a detailed case study exploiting the optical aggregation operation to re-design the optical core network is investigated in this paper. Optical aggregation enables the combination of lower-speed and/or lower-order format channels into a single higher-rate and/or higher-order format one for saving spectrum resources and such new perspective give rises to major challenges involving aggregation assignments. Specifically, the determination of demands for aggregation, the nodes at which the optical aggregation takes place and the wavelength selection for aggregated lightpaths constitute a critical issue to be tackled. Numerical results obtained from extensive simulations on the COST239 network are presented to quantify the efficacy of optical-computing-enabled approach versus the conventional optical-bypass-enabled one. [Display omitted] • Optical-computing-enabled network as an evolution of optical-bypass architecture. • In-network optical computing paves the way for era of optical-layer intelligence. • A vision on the integration of optical computing and communications infrastructure. • A new research problem, that is, routing, wavelength and aggregation assigment. • A call for optical network design and planning 2.0 framework. [ABSTRACT FROM AUTHOR]

A highly stable Kerr lens mode locked (KLML) erbium-doped fiber laser (EDFL) modulated by silica tapered fiber is systematically demonstrated for the first time. Compared to usual silica fiber, the prepared silica tapered fiber possesses much larger nonlinear efficiency, and the significant Kerr lens (KL) effect facilitates the generation of conventional solitons (CSs) as well as soliton molecules (SMs) in this paper. In the CSs regime, the system operates at a central wavelength of 1561.5 nm with 3 dB bandwidth of 6.22 nm. The obtained pulse duration is 442 fs with repetition rate of 25.126 MHz and signal-to-noise ratio (SNR) of 72.64 dB. The available maximum output power is 11.788 mW, corresponding to a pulse energy of 0.469 nJ. By finely modulating the orientations of the PC, the system can be switched to the SMs regime. A tight soliton bound states consisting of two CSs is achieved and analyzed in detail. This work extends and enriches the implementing methods of achieving mode-locked fiber lasers. More importantly, due to the low cost, easy processing, and high stability, the silica tapered fibers, are of great significance in reducing the cost as well simplifying the structure of ultrafast fiber lasers, and hence accelerate and promote the practical applications of ultrafast lasers. [ABSTRACT FROM AUTHOR]

Recent advances in artificial intelligence (AI) have inspired researchers to explore machine learning (ML)-based optimization and reverse design techniques for photonic crystal fibers (PCFs). These studies often seek to improve model generalization, particularly for data that the model has not previously encountered. Traditional centralized training methods are challenging for devices with limited resources, as they rely on aggregating expansive datasets, which is hindered by constraints in storage capacity and communication efficiency. This paper introduces an innovative distributed framework for optimizing PCF parameters, utilizing decentralized training to amalgamate knowledge across various institutions while maintaining data privacy. Each institution develops a lightweight neural network using a small subset of local data, contributing to the construction of a collective and robust global model. This approach is advantageous for both internal and external applications in PCF engineering. Rigorous empirical experiments conducted with real-world PCF optimization data substantiate the efficacy and benefits of the proposed framework. This framework shows promise in achieving an equilibrium between data protection and resource efficiency, offering a novel platform for the reverse design of microstructured optical fibers. [ABSTRACT FROM AUTHOR]

In this paper, we propose two novel architectures for the short-reach optical access network (SR-OAN) and long-reach optical access network (LR-OAN) to provide high bandwidth and high connection availability to the users in wireless and fiber-to-the-x networks. The proposed architectures are referred to as network congestion alleviating architecture with partial protection (NCAA-PP) and network congestion alleviating architecture with full protection (NCAA-FP). Both the proposed NCAA-PP and NCAA-FP architectures utilize the idle backup optical line terminals and dark fibers efficiently to develop the integrated mechanisms for alleviating network congestion and providing protection against failures of the optical resources in the network. We also propose a dynamic bandwidth allocation scheme, referred to as a surplus bandwidth allocation scheme, at medium access control layer to allocate surplus bandwidths to the users in the SR-OAN and LR-OAN during the network congestion periods. For the practical network scenarios, the simulation and analytical outcomes reveal that the proposed NCAA-PP and NCAA-FP architectures can reduce up to 82% average packet delay during the network congestion periods. Moreover, the proposed architectures offer high connection availabilities to the users and are very cost-efficient. [ABSTRACT FROM AUTHOR]

In this paper we studied thermal-lens effect on transverse modes in the confined-gain Yb-doped fiber for the first time, to the best of our knowledge. It is found that the thermal-lens effect is enhanced with the reduction of doped area due to the higher thermal density in the doped area. Then, the variations of three low-order transverse modes (i.e., fundamental, LP 11 and LP 02 modes) with the heat load and doped diameter are studied, and the mode areas and overlapping factors with the doped area of these transverse modes are also discussed. The gain competition of these transverse modes is also investigated by calculating the differential-gain ratio with the purpose of achieving the single-mode operating. It is found that the stronger thermal-lens effect will result in the reduction of optimum doped diameter for suppressing high-order modes. This study can provide significant guidance for designing the confined-gain Yb-doped fibers for the applications in high-power fiber lasers and amplifiers. [ABSTRACT FROM AUTHOR]

• Underwater acoustic sensor based on microfiber knot resonator. • The microfiber knot hydrophone has a simple fabrication. • The feasibility of the hydrophone is proved with theory and experiment. • The hydrophone has the high sensitivity and wide working bandwidth. In this paper, a water acoustic sensor based on a microfiber knot resonator is proposed. It utilizes microfiber technology, resulting in a smaller sensor size and excellent detection capability for low-frequency signals. By developing suitable packaging techniques to protect the sensor, it becomes more suitable for underwater detection environments and increases the stability of the device. Polydimethylsiloxane (PDMS) has a lower refractive index than silicon dioxide and exhibits good transmission performance. PDMS is used for encapsulation on both the top and bottom of the fabricated microfiber knot resonator, which improves its Q-factor and provides better protection for the resonator underwater. We employ filtering and amplification techniques to demodulate the received sound signals. The test results demonstrate that the sensor has an average sensitivity of −135.8 dB within the frequency range of 10 Hz to 2 kHz and an average signal-to-noise ratio of 53.2 dB. At 400 Hz, the sensitivity reaches −113.6 dB, with a signal-to-noise ratio of 80 dB. [ABSTRACT FROM AUTHOR]

• The geometric dimension of the package shell of the sensing unit are studied by theory and experiment, and improper design of the package housing may degrade the frequency response characteristics of the sensing unit. • The influence of prestress on the frequency response characteristic of sensor is studied. • The geometric dimension of the package shell and the prestress of the sensing unit are reasonably optimized to make the working frequency of the sensor avoid the resonant frequency of the shell. • The paper provides a theoretical basis for the design and manufacture of the sensors with wide frequency response and high sensitivity in different engineering applications, such as high frequency small amplitude and low frequency large amplitude. In coal mine, military, oil well monitoring and other fields, the traditional electrical accelerometers based on piezoelectric and capacitive can not meet the needs of high-performance applications. The optical fiber acceleration sensor with high precision, large dynamic, wide frequency response, anti-electromagnetic interference and other unique advantages, can meet a variety of applications. The complete optical fiber acceleration sensor consists of a package housing and an internal sensing unit. Some factors, including the vibration and deformation of the housing itself, and the prestress of the sensing unit will directly affect the frequency response characteristics of the sensor. The experimental results show that the resonant frequency of the package housing is outside the operating frequency band of the sensor through reasonable design of shell parameters; in a certain torque range (0.2 N . m ∼ 0.8 N . m), the resonant frequency increases with the increase of the torque. The research provides a theoretical basis for the design and manufacture of the sensors with wide frequency response and high sensitivity in different engineering applications, such as high frequency small amplitude and low frequency large amplitude. [ABSTRACT FROM AUTHOR]

• We build a system to sense the micro-deformation of connecting rods. • We design a connecting rod sensing network based on FBG. It not only detects the deformation of the connecting rod after compression but also detects the deformation of the connecting rod in the tensile state. • The work provides a new detection scheme to ensure the machining quality of connecting rods. As a key component of the ship power equipment, the deformation of the connecting rod directly affects its performance and life. Therefore, the deformation detection of the connecting rod plays an important role in ensuring the service life of the power equipment. In this paper, we propose a deformation perception and reconstruction method based on fiber Bragg grating (FBG) for the connecting rod of the marine diesel engine. According to the deformation characteristics under loads of different sizes and directions obtained from the finite element, a sensing distribution FBG-based is designed for the connecting rod. On this basis, we establish the FBG-based deformation sensing system and develop a three-dimensional deformation reconstruction model, which can realize the real-time monitoring of the deformation during the processing of the connecting rod. The experiments show that the deformation trends obtained by FBG and finite element are consistent. Therefore, the FBG-based deformation perception and reconstruction method is feasible. It provides a new and accurate detection scheme to ensure the processing quality of the connecting rod and a new idea for the deformation detection of other key parts of the ship power equipment. [ABSTRACT FROM AUTHOR]

• In this paper, we propose a distorted pulse detection method based on odd function for pulse decomposition, to solve the problem of optical path mismatch in UWFBG array. • In theory, we build a mathematical model of the distortion pulse and derive the corresponding odd function. • Then, we analyze the peak trajectory obtained by the difference curve by simulation, and determine the optimal interference position of the distorted pulse. • Finally, we use the vibrating liquid column method to carry out underwater acoustic sensing experiments, under different conditions of optical path mismatch. • The results show that, when the distance between adjacent UWFBGs is 50 m and pulse width with 100 ns, the gain of harmonic SNR and average PSD is improved from 2.3 dB and 1.8 dB to 11.2 dB and 10.0 dB respectively, under different circumstances with length difference for 1 m, 1.5 m, and 2 m respectively. In this paper, we propose a distorted pulse detection method based on odd function for pulse decomposition, to solve the problem of optical path mismatch in UWFBG array. In theory, we build a mathematical model of the distortion pulse and derive the corresponding odd function. Then, we analyze the peak trajectory obtained by the difference curve by simulation, and determine the optimal interference position of the distorted pulse. Finally, we use the vibrating liquid column method to carry out underwater acoustic sensing experiments, under different conditions of optical path mismatch. The results show that, when the distance between adjacent UWFBGs is 50 m and pulse width with 100 ns, the gain of harmonic SNR and average PSD is improved from 2.3 dB and 1.8 dB to 11.2 dB and 10.0 dB respectively, under different circumstances with length difference for 1 m, 1.5 m, and 2 m respectively. So, the algorithm is more robust to length mismatch, and verifies the effectiveness of the algorithm, and has potential significance for reducing the difficulty of designing the UWFBG array interferometer. [ABSTRACT FROM AUTHOR]

• In view of the lack of online damage detection of CFRP driveshaft, this paper aims to establish a damage detection system for CFRP driveshaft and establishes a damage identification model for CFRP driveshaft based on strain and damage mechanism. • Considering the shortcomings of the existing research, this paper makes full use of the unique advantages of FBG sensors, combined with GWO-BP neural network, constructs a CFRP driveshaft damage identification system, and realizes the damage identification and localization of the CFRP driveshaft. • Combining theoretical methods, simulation calculations and experimental studies, torsion experiments were carried out on CFRP driveshafts, and damage identification was carried out by using the identification and localization system constructed in this paper to compare the actual damage and damage identification. Carbon Fiber Reinforced Plastic (CFRP) has the advantages of light weight, high strength, small coefficient of thermal expansion, good vibration damping performance, etc., the use of its production drive shaft can reduce weight, improve the intrinsic frequency, transmission efficiency and precision, and has been used in helicopters, heavy duty machine tools, wind turbines, ships and other high-end equipment. Once the damage occurs, it will cause adverse effects such as reduction of mechanical efficiency of the system, degradation of transmission system performance, and decrease of reliability and safety. The existing non-destructive testing technology for carbon fiber reinforced plastic has limitations such as inconvenient use, complex equipment, and no real-time online monitoring. To address this problem, this paper adopts Fiber Bragg Gratings (FBG) sensors to obtain real-time strain field data of CFRP drive shaft, and uses the linear and nonlinear mapping ability of Back Propagation Neural Network (BP neural network) to identify and locate the damage of CFRP drive shaft. At the same time, the GWO optimization algorithm is used to optimize the BP neural network to construct a CFRP drive shaft damage identification and localization system based on FBG sensing network and GWO-BP neural network. The experiments show that the CFRP drive shaft damage identification and localization system constructed in this paper can obtain the CFRP drive shaft strain field information in real time and accurately identify the damage and its location. [ABSTRACT FROM AUTHOR]

• This paper aims to predict resource allocation accurately and efficiently based on historical requests. Artificial neural networks (ANN) with historically allocated bandwidth from different time series are used to build the prediction model. • This model is constructed by the normal equation method. • The proposed model needs a small dataset for its training phase, while its accuracy is higher than other models. • The discrete dynamical system builds to find an equilibrium point, which is a stable point in the system. • The results show that the system throughput improves by up to 5%, and packet loss improves by up to 15%. Moreover, the prediction accuracy of the system reached 99.48%. Resource allocation is one of the challenges in the time division multiple access (TDM) passive optical network (PON) area. Much research has been done to find an efficient resource allocation method. Using machine learning (ML) and finding proper ML algorithms in predictive dynamic bandwidth allocation remains an open research question. This paper aims to predict resource allocation accurately and efficiently based on historical requests. Artificial neural networks (ANN) with historically allocated bandwidth from different time series are used to build the prediction model. This model is constructed by the normal equation method. The proposed model needs a small dataset for its training phase, while its accuracy is higher than other models. The discrete dynamical system builds to find an equilibrium point, which is a stable point in the system. The proposed model can be implemented as a pre-training, or it can be dynamically refined when the model is running by using some of its output as feedback. The system evaluation verifies that the proposed DBA (EQ-ANN) elevates the quality of service (QoS) metrics, such as system throughput, packet drop probability, and packet means delay. The results show that the system throughput improves by up to 5%, and packet loss improves by up to 15%. Moreover, the prediction accuracy of the system reached 99.48%. [ABSTRACT FROM AUTHOR]

• Novel bidirectional full-duplex transmitting WDM-PON over single SSMF is proposed. • SRS + FWM impact on the proposed system performance is evaluated. • SXR-input power, SXR-channel spacing, SXR-channel length variations are simulated. • Results show a reliable communication with the system under SRS + FWM impact. • Proposed system and analyses are important for 5G and beyond fronthaul networks. Wavelength division multiplexing (WDM) is an important method in modern optical communication systems for both long-haul and access networks. Particularly, after being standardized by Telecommunication Standardization Sector of International Telecommunication Union (ITU-T), WDM passive optical network (WDM-PON) becomes a considerable choice for fronthaul implementations of 5G networks. Stimulated Raman scattering (SRS) and four-wave mixing (FWM) are crucial nonlinear impacts that significantly limit the performance of WDM-based optical fiber communication systems. In this paper, an ultra-dense/dense WDM-PON (UDWDM/DWDM-PON) architecture has been proposed and combined dual impact of SRS and FWM on performances of upstream channels (USCs) and downstream channels (DSCs) of the proposed UDWDM/DWDM-PON has been numerically analyzed. USCs have been assumed to operate in 1310 nm region while operating wavelength region of DSCs has been taken as 1550 nm. Simulations have been performed on both UDWDM-PON architectures with 3.125 GHz and 6.25 GHz channel spacings and DWDM-PON architectures with channel spacings between 12.5 GHz and 100 GHz. 2x15-channel and 2x63-channel system structures have been considered in simulations. Signal-to-crosstalk ratio (SXR) has been chosen as performance parameter and its variation with channel input powers, channel spacings and channel lengths have been simulated for both USCs and DSCs of 2x15- and 2x63-channel UDWDM/DWDM-PONs. Results show that the proposed UDWDM/DWDM-PONs using single G.652 fiber can exhibit a reliable communication with minimum 23 dB SXR performance under combined dual impact of SRS and FWM unless some highlights about input powers and channel lengths mentioned in the paper are neglected. [ABSTRACT FROM AUTHOR]

• This paper presents a systematic discussion of the frequency-domain channel transmission model for PDM CO-OFDM/OQAM systems. • Through a thorough analysis of ASE noise correlation, we introduce a novel approach, Combined Intra Symbol Frequency-Domain Averaging (CISFDA) channel estimation method for PDM OFDM/OQAM systems. • In comparison to the Full-Loaded Frequency-Domain (FL-FD) method, CISFDA enhances system robustness against ASE noise and fiber nonlinear effects significantly. Intrinsic imaginary interference (IMI) induced by chromatic dispersion (CD) and polarization mode dispersion (PMD) seriously degrades the performance of optical orthogonal frequency division multiplexing offset-quadrature amplitude modulation (O-OFDM/OQAM) systems. Therefore, effective channel estimations are required for such systems to maintain good transmission performance. In the previous publications, both the full loaded (FL) and the half loaded (HL) frequency-domain channel estimation methods for polarization-division-multiplexed (PDM) coherent optical OFDM/OQAM (CO-OFDM/OQAM) systems have been proposed. However, for these frequency-domain methods, the channel frequency-domain responses caused by the correlation of the amplified spontaneous emission (ASE) noise are not considered. In this paper, we systematically discuss the frequency-domain channel transmission model for PDM CO-OFDM/OQAM systems. With the analysis of the correlation of the ASE noise, we propose a combined intra symbol frequency-domain averaging (CISFDA) channel estimation method for PDM OFDM/OQAM systems. Compared with the full-loaded frequency-domain channel estimation (FL-FD) method, the CISFDA method promotes the system robustness against the ASE noise and fiber nonlinear effect significantly. The proposed method is validated by numerical Monte Carlo simulations of the PDM CO-OFDM/OQAM system. Our new algorithm outperforms the FL-FD method in the 36 Gb/s PDM OFDM CO-OFDM/OQAM system, and the transmission distance is improved by 500 km with the bit-error-rate (BER) target at 3.8 × 10 - 3 . [ABSTRACT FROM AUTHOR]

• In this paper, a new feature extraction and recognition method for perimeter intrusion vibration signals is proposed, using msCNN to extract multi-scale structural features of the signal, and combining features of different scales at the end of each convolutional block. • Before entering into the next convolutional block, the attention mechanism is used to recalibrate the combined features to enhance the expression ability of the features. • Finally, the time dependence is analyzed by LSTM, so that the characteristics of the signal are richer and more comprehensive, so as to obtain a higher recognition rate. To improve the recognition rate of ultra-weak fiber Bragg grating (UWFBG) arrays in perimeter security monitoring, this paper proposes a msCNN-LSTM combinatorial model recognition method, which combines an improved multi-scale convolutional neural network (msCNN) and a long short-term memory neural network (LSTM) to identify intrusion behaviors more accurately by synchronously extracting the multi-scale structural features and time-dependent relationships of vibration signals. Using msCNN to cross-learn multi-layer features, the hidden information between features at different scales can be obtained. The attention mechanism was applied to recalibrate the combined features extracted from the shallower layers, which enhanced the expression ability of features. Finally, the time dependence is analyzed by LSTM. Experimental results show that the scheme can effectively distinguish five typical intrusion behaviors, and the average recognition rate can reach 97.84%. [ABSTRACT FROM AUTHOR]

Semi-filterless optical networks (semi-FONs), a novel passive wide area network (WAN) solution, have attracted considerable attention. This paper investigates the dynamic routing, modulation and spectrum assignment (RMSA) problem in semi-FONs, where requests may propagate on unnecessary links due to the broadcast characteristics of semi-FONs, resulting in wastage of spectrum resources. Moreover, the dynamically setup and torn down of requests can lead to significant spectrum fragments. To address these issues, this paper studies semi-FONs based on two metrics: resource consumption M and fragmentation degree N. Resource consumption M refers to reducing spectrum wastage caused by broadcasting and establishing requests using minimal resources, while fragmentation degree N refers to the situation where the remaining available resources after establishing a request are more concentrated. Based on these metrics, we propose the Minimum Resource Consumption and Fragmentation Degree (Min-RCF) algorithm. We conduct simulation experiments on the German-Net and China's Henan-Net network topologies, and the results demonstrate that the proposed Min-RCF algorithm achieves lower blocking probability and spectrum waste rate than the compared algorithms. • In the routing phase, resource consumption and spectrum wastage are reduced. • In the spectrum assignment phase, the spectrum fragmentation is reduced. • Reduced blocking probability and spectrum waste rate in the semi-filterless network. [ABSTRACT FROM AUTHOR]

• To convert the measured strain of the optical fibre into ground subsidence: 1. this paper proposes a strain–displacement conversion method based on the sequence-to-sequence (Seq2Seq) model. 2. The method is validated using data from indoor model experiments. The research results indicate that distributed optical fibre sensing technology can effectively monitor the strain distribution of soil during the subsidence process. It can identify the development location of ground subsidence and reveal the deformation evolution patterns. The strain–displacement intelligent conversion model based on Seq2Seq can convert the strain monitored by the optical fibre during the ground subsidence process into ground subsidence. Compared to traditional methods, this conversion model exhibits higher accuracy. After a water supply pipeline experiences leakage due to damage, the surrounding soil is prone to erosion, leading to the formation of underground voids. As the voids gradually expand, there is a high possibility of triggering ground subsidence accidents. Monitoring ground deformation is the simplest and most effective method for capturing the process of ground subsidence development. Among various methods of ground deformation monitoring, distributed optical fibre sensing has advantages such as real-time performance, distributed measurement, and ease of networking. This paper investigates the monitoring effectiveness of distributed optical fibre strain sensing technology on ground subsidence induced by underground voids under different conditions through indoor model experiments. To convert the measured strain of the optical fibre into ground subsidence, this paper proposes a strain–displacement conversion method based on the sequence-to-sequence (Seq2Seq) model. The method is validated using data from indoor model experiments. The research results indicate that distributed optical fibre sensing technology can effectively monitor the strain distribution of soil during the subsidence process. It can identify the development location of ground subsidence and reveal the deformation evolution patterns. The strain–displacement intelligent conversion model based on Seq2Seq can convert the strain monitored by the optical fibre during the ground subsidence process into ground subsidence. Compared to traditional methods, this conversion model exhibits higher accuracy. [ABSTRACT FROM AUTHOR]

• PDMS is introduced to fiber-optic Fabry-Perot interferometer for sensitization. • The sensor has a wide range of temperature measurement from −30 °C to 85 °C and has high temperature sensitivity. • The sensor's specifications are tested to prove its excellent performance. • The sensor is simple to make and has the potential for mass production. In this paper, a highly sensitive temperature sensor based on polymer-coated Fabry-Perot interferometer (FPI) is proposed and demonstrated. The FPI temperature sensor consists of the end face of single-mode fiber (SMF) and the Polydimethylsiloxane (PDMS) cap on the end face. By varying the number of coatings, the thickness of the PDMS cap can be flexibly controlled to obtain FPI sensors with different cavity lengths. The temperature sensitivity is studied experimentally from −30 °C to 85 °C, and it is found that the sensor shows different sensitivity in different temperature intervals, up to 0.698 nm/°C. Compared to similarly constructed sensors, the sensor in this paper has a large temperature range while maintaining a high sensitivity. In addition, the performance of the sensor is tested by experiments and the results show that the sensor possesses the advantages of good stability, fast response time and good repeatability. [ABSTRACT FROM AUTHOR]

• A nonlinear compensation scheme for FMF MDM-WDM using PNN is proposed for the first time. • This scheme has a good benefit to fiber nonlinear compensation and device nonlinear compensation. • Its effectiveness is verified by simulation system. • The complexity of this scheme is lower than that of DBP under comparable performance. In this paper, we propose for the first time to apply probabilistic neural network (PNN) to fiber nonlinear compensation (NLC) in a high-speed coherent optical communication system that combines few-mode fiber (FMF) mode division multiplexing (MDM) with wavelength division multiplexing (WDM). By training on a small number of symbols, the PNN equalizer can compute the statistical distribution of the signal nonlinearity, make decisions on test symbols, and thereby compensate for the nonlinear impairments of the signals. To verify the effectiveness of the proposed scheme, we construct a MDM-WDM simulation system with 28 GBaud polarization division multiplexing (PDM) 16-quadrature amplitude modulation(QAM) and 64 GBaud PDM-64QAM, 6 spatial mode signals are transmitted over 11 wavelength channels with link lengths of 1500 km and 400 km, respectively. The results show that the PNN equalizer can make nonlinear judgments on received signals and effectively compensate the signal impairments caused by Kerr nonlinearity and device nonlinearity in a large launch power range after undergoing carrier phase recovery (CPR). Meanwhile, this scheme exhibits strong robustness against residual linear mode coupling (LMC), differential mode group delay (DMGD), and amplified spontaneous emission (ASE) noise. Finally, by the computational complexity comparison, it is proved that the complexity of the probabilistic neural network nonlinear compensation (PNN NLC) scheme is lower than that of digital back propagation (DBP) with comparable performance, which is on the order O(N). [ABSTRACT FROM AUTHOR]

• An adjustable Tm-doped gain-switched fiber laser with variable repetition frequency and pulse duration by implementing an adjustable QML self-pulsing fiber laser as the pumping laser for the first time. • A QML pulse with a maximum repetition frequency of 72.5 kHz is generated due to the weak NPR effect. • A stable gain-switched pulse with a minimum duration of 366.2 ns, and an adjustable repetition frequency of 37–73 kHz is generated. • Simulation agrees with the experimental results for the gain-switched fiber laser. This paper reports on the first gain-switched fiber laser in the 2 μm region that uses an adjustable self-pulsing Er-doped QML fiber laser as a pumping source. By adjusting the output of the self-pulsing laser, a stable gain-switched pulse with a minimum duration of 366.2 ns and an adjustable repetition frequency of 37–73 kHz at 1959 nm is generated. The maximum output power achieved is 26.5 mW, with a pulse energy of 0.35 μJ and a slope efficiency relative to the pumping power of 4.6 %. Our study demonstrates the potential of an adjustable self-pulsing fiber laser as an effective pumping source for gain-switched fiber lasers. [ABSTRACT FROM AUTHOR]