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• An intelligent wearable plastic optical fiber (POF) integrated sensor system. • Video image sampling greatly improves system integration and sampling frequency. • Radial basis function neural network (RBF-NN) accurately recognizes human motion patterns. In recent years, the development of flexible bend sensors and their detection devices has attracted great interest. In this paper, an intelligent wearable plastic optical fiber (POF) integrated sensing system for human motion detection is presented. The system consists of POF bend sensors and a wearable fiber bend detection meter (WFBDM). By capturing the POF array image from the video stream, it realizes a sampling frequency of 91.7 times/s. It also greatly increases the integration of multiple sensors, with an integrated sensing area of only 0.35*0.35 mm2 for a single sensor. POF bending sensors with a diameter of 0.25 mm were tested using this system with a linear range of −40° to 90°, an accuracy of up to 0.4°, and a response time of 26.2 ms. The system has been successfully applied to human joint and muscle motion monitoring, and combined with machine learning to realize the intelligent recognition of human motion state. The sensing system is small in size, large in sensing range, high in sensitivity and good in stability, and has the ability of intelligent recognition and highly integrated multi-channel bend signals sensing. [ABSTRACT FROM AUTHOR]

• A numerical model of a dual-pass bismuth-doped fiber amplifier is established. • By analyzing the loss of the reflection module of the bismuth-doped fiber amplifier in a dual-pass configuration versus the gain of the amplifier, a reflector-based signal and pump dual-pass bismuth-doped fiber amplifier is designed. • The amplifier experimentally obtained a maximum net gain of 41.8 dB at 1325 nm with a noise figure of 5.8 dB. Due to the tendency of data traffic approaching the current capacity limit, the development of a high-performance o-band amplifier has become an important topic. In this paper, we construct a model of the dual-pass BDFA and compare it with the single-pass BDFA. In addition, the effect of the loss of the reflected part of the dual-pass structure on the gain is analyzed by numerical simulation. Utilizing the theory to guide the experiment, a reflector-based signal and pump dual-pass O-band bismuth-doped phosphosilicate fiber amplifier is proposed. The amplifier experimentally obtained a maximum net gain of 41.8 dB at 1325 nm with a noise figure (NF) of 5.8 dB under the total pump power of 1050 mW and the input signal power of −34 dBm. The 3 dB saturation output signal power of the BDFA is 16.8 dBm at a total pump power of 1050 mW, at which point the signal input power is –22 dBm and the NF is 6.6 dB. The gain coefficient is 0.064 dB/mW at the input signal power of −30 dBm. The measured 3 dB and 10 dB net gain bandwidths of this amplifier are 30 nm (1312–1342 nm) and 58 nm (1300–1358 nm), respectively. [ABSTRACT FROM AUTHOR]

• A broadband mid-infrared supercontinuum of OAM modes is numerically generated. • The generated supercontinuum covers a band with >3100 nm at low input pulse power of 1000 W. • Six supported OAM modes exhibits highly robust propagation for supercontinuum generation. In this paper, a wide supercontinuum of multi-order orbital angular momentum (OAM) modes is generated theoretically in the mid-infrared region based on a ring-core As 2 S 3 -based photonic crystal fiber (PCF). This PCF supports six OAM modes with two orders and exhibits an ultra-high effective refractive index difference of 10-2 between the vortex modes. After customizing the nonlinear coefficient and dispersion, all the supported OAM modes can be used for wide-band supercontinuum (>3100 nm) generation at low input pulse power of 1000 W. In particular, the supercontinuum of OAM 1,1 mode covers a wavelength range from 2860 nm to 6120 nm at −40 dB level. This work has great potentials in the OAM-based mid-infrared source in optical communication and sensor systems. [ABSTRACT FROM AUTHOR]

• Novel acetone gas optical sensor using ZnO-TiO 2 nanorod on tapered multimode fiber. • Present the influence of titanium dioxide (TiO 2) as a catalyst to the zinc oxide (ZnO) nanorods. • Low-temperature detection of acetone gas at 87 °C for the acetone concentrations of 1000, 5000 and 10,000 ppm. • Notable output intensity responses were observed for ZnO-TiO 2 nanorods decorated with Au-Pd thin films (ZTNAP). This paper presents the influence of titanium dioxide (TiO 2) as a catalyst to the zinc oxide (ZnO) nanorods coated on the tapered MMF fiber utilized as a sensing layer for the detection of acetone gas at low temperatures. To enhance the sensitivity of the sensor ZnO-TiO 2 nanorods were decorated with Au-Pd film. Hydrothermal method was used to synthesize the ZnO nanorods while TiO 2 powder was incorporated by using a simple doping procedure during fabrication. The decoration of the Au-Pd thin films is integrated with the ZnO-TiO 2 by using DC sputtering method. The ZnO doped with 15 mM TiO 2 shows a strong and significant peak based on XRD analysis which can be indexed to the hexagonal phase of ZnO. A few globular structures of TiO 2 were randomly distributed as observed by the SEM image. Four different fiber sensing layers were prepared with respect to 10 mM ZnO precursor; ZnO nanorods (ZN), ZnO nanorods decorated with Au-Pd thin films (ZNAP), ZnO-15 mM TiO 2 nanorods (ZTN) and ZnO-15 mM TiO 2 nanorods decorated with Au-Pd thin films (ZTNAP). The spectrometry setup was used to measure the response of the sensor toward different concentrations of acetone gas in terms of intensity with respect to its wavelength. Notable output intensity responses were observed for ZTNAP in terms of sensitivity and standard deviation towards various acetone concentrations while the repeatability curve showed a high response of acetone gas at 10,000 ppm. All experiments were performed at the low temperature of 87 °C. [ABSTRACT FROM AUTHOR]

• This accelerometer principally consists of a pair of identical mass blocks, a pair of identical inclined cantilever beams, a pair of identical fixing blocks, a pair of identical columns, and a base. • The natural frequency of this accelerometer is 46 Hz, which has good flatness in the frequency range of 0.1 to 28 Hz. • Static stress analysis and modal simulation analysis using ANSYS. • Built a low-frequency vibration testing system consisting of a low-frequency vibration system and an optical fiber sensing system. • The signal of the time series is transformed into a fast Fourier transform using the periodogram method. The low-frequency vibration measurement technology is significant in energy exploration, aerospace, geophysical activities, health monitoring of large engineering structures, etc. A low-frequency FBG accelerometer based on a dual oblique wing is proposed to address the issue of difficulty in accurately measuring low-frequency vibration signals in current fiber Bragg grating accelerometers. Firstly, the structure of this accelerometer was theoretically analyzed and dimension-optimized. Secondly, the static stress analysis and modal simulation analysis are carried out, and the accelerometer is developed. Finally, it is fixed on the vibration table, and the low-frequency vibration test system is built to test the performance. The experimental results show that the natural frequency of the accelerometer is 46 Hz, the working frequency band is 0.1–28 Hz, the sensitivity is 55.6 pm/g, the dynamic range is 48.94 dB, and the resistance to transverse interference of less than 5.62 %. The accelerometer designed in this paper provides a new idea for low-frequency vibration signal measurement. [ABSTRACT FROM AUTHOR]

• Stress field distribution characteristics in the three-core optical fiber are analyzed. • Effective method to extract stress induced birefringence in the fiber is acquired. • Three-core optical fiber with ultra-low PMD is found and its parameter is present. This paper investigates the stress field distribution characteristics in the three-core optical fiber. Utilizing Fourier transform analysis of the stress tensor components, it is shown that the constant part in the stress tensor, or the overall elevated value of the oscillation curve, is directly related to the stress induced birefringence. So, an effective method to extract information about stress induced birefringence is acquired. The polarization mode dispersion (PMD) and the relationship between stress induced birefringence and the structural parameter of the optical fiber are investigated by numerical simulation. It is found that the PMD usually decreases with the increase of the distance from the core to the fiber center. And it even reaches zero at a certain distance; while increases again thereafter. Some three-core optical fibers with ultra-low PMD and high transmission rates are designed based on these results. [ABSTRACT FROM AUTHOR]

At present days, metropolitan and access communication networks are markedly developing utilizing a variety of technologies. Their bearer communication infrastructures will be mostly exploiting the optical transmission medium where wavelength division multiplexing techniques will play a key role. Wavelength-Division Multiplexed Passive Optical Networks (WDM-PON) attract considerable attention for the next generation optical metropolitan and access networked systems. Simultaneously, the utilization of common optical network resources in wavelength domains will be more important. The main purpose of this paper is presented by the evaluation of resource efficiencies for the non-symmetric dynamic wavelength allocation method applied in the WDM-PON network design with a conventional topology. This contribution introduces a novel non-symmetric Dynamic Wavelength Allocation (DWA) method for a selected network design with the utilization only passive optical splitters in remote nodes. This novel wavelength allocation method is oriented on minimizing a number of working wavelengths that will be used for compliance of customers' requests for data transmitting in the common point-to-multipoint WDM–PON network design. For evaluation of wavelength scheduling, a simulation model related to the conventional WDM-PON network design is realized in the MATLAB programming environment is presented with results. Finally, different traffic loading scenarios are determined and, subsequently, resource efficiencies of the presented non-symmetric DWA method are evaluated from a viewpoint of application in future WDM-PON network designs. [ABSTRACT FROM AUTHOR]

Network function virtualization (NFV) uses virtual network functions (VNFs) and VNF service chains (VNF-SCs) as a flexible and cost-efficient way of providing network services. This new backbone plays a vital role in dealing with the outbreak of traffic patterns generated by diverse services. Elastic optical networks (EONs) can be used for maximum flexibility to interconnect the computing infrastructure and data centers (DCs) required to host these VNFs and effectively transport the heterogeneous traffic flowing through the VNF-SC. The aim of the paper is to provide a complete mixed integer linear programming (MILP) formulation for the problem of VNF-SC deployment with survivability to minimize the total number of functions, balance the load utilization through grooming, and avoid spectrum fragmentation in EONs. In addition, we propose an efficient heuristic solution in dealing with the problem of large networks. The performance of the proposed strategies is evaluated based on the availability of resources (function computing capability). Simulation results show that the proposed MILP and heuristic can reduce the total amount of allocated VNFs, thereby, allowing for a certain level of resilience. [ABSTRACT FROM AUTHOR]

• A compact concentration sensor based on the modified thin-diameter polarization-maintaining fiber is demonstrated. • The relationship between the measurement sensitivity and the length and corroded time of the TDPMF is discussed. • The SC concentration sensor exhibits a high linear sensitivity response up to 4.65 nm/%, and the temperature sensitivity is 0.08179 nm/°C. • The MMF-MTDPMF-MMF structure sensor has excellent repeatability and stability in SC concentration sensing. Sodium citrate, as strong alkali and weak acid salt, play an essential role in the food and pharmaceutical industries. However, lack of detection method selectivity, limited biocompatibility and complexity of the manufacturing process are challenges that hinder the practical application of the sensors. In this paper, a improved-sensitivity sodium citrate concentration sensor with simple and compact interrogation setup is proposed. The sensor is fabricated by fusion splicing the sandwich structure of modified thin-diameter polarization-maintaining fiber, two pieces of multimode fiber, and single-mode fiber. In theoretical modeling, the properties of the structure are investigated. In the experiment, the evanescent field generated by the modified thin-diameter polarization-maintaining fiber plays a vital role in the detection of different sodium citrate concentrations. The sodium citrate concentration sensor exhibits a high linear sensitivity response up to 4.65 nm/%. The sensor provided refractive index sensitivity of 3173.2 nm/RIU. In addition, the response, repeatability, and stability are also evaluated by the experiments. Our results show that the sodium citrate concentration sensor holds great promise for serving as a soft and biocompatible probe for monitoring sodium citrate in situ. [ABSTRACT FROM AUTHOR]

• A method to solve the lack of multiplexed ability for fiber sensor based on specklegrams. • A specklegram can be decomposed spatially according to different incident angle. • The annular specklegram can be formed by the incident of side-coupling light. • Transfer learning technology is employed to improve the accuracy of multiplexed sensor based on specklegram recognition. With the advancement of image processing and artificial intelligence technology, Fiber Specklegram Sensors (FSS) based on specklegram recognition have emerged as a novel sensing technology. The output speckles represent the interference between different transmission modes in the fiber, which vary with changes in fiber fluctuations such as the pressure on the fiber or ambient temperature. This sensor boasts high precision and low cost. However, when the optical fiber is required to perform multi-parameter or multi-position sensing simultaneously, the variety of specklegrams counterpart to external stimuli has become very large, significantly limiting the application scenarios of FSS. In this paper, a new structure based on side-coupling theory is proposed, where the output specklegram comprises a circular specklegram and an annular specklegram formed by end-coupling light and side-coupling light respectively. In this manner, the circular specklegram and annular specklegram can represent different sensing parameters, and the circular specklegram is completely unaffected by the annular specklegram, enabling multiplexed sensing. Multiplexed experiments for pressure and temperature sensing are conducted utilizing this structure, and deep learning technology is employed to process the different sets of specklegrams for regression prediction. The accuracy of pressure and temperature sensing tests reached 98.62% and 95.31% respectively, verifying the feasibility of this method for multiplexed sensing. [ABSTRACT FROM AUTHOR]

• In terms of adjusting the splitting ratio f and cavity length L of the NOLM, self-similar pulse (SSP), soliton molecule (SM), DSR, DS and dissipative soliton pair (DSP) can be obtained in such fiber laser system. • Found that the parameter P max defined by us is the main factor that determines the type of solitons generated in the laser. • Investigated the nonlinear dynamics in the process of the transformation between these solitons. • Discussed the mechanisms and characteristics of these solitons. The properties of the saturable absorber are critical to the soliton dynamics in the all-normal dispersion Yb-doped mode-locked fiber laser based on the nonlinear optical loop mirror (NOLM). In this paper, it is found that by adjusting the splitting ratio f and cavity length L of the NOLM, self-similar pulse (SSP), soliton molecule (SM), dissipative soliton resonance (DSR), dissipative soliton (DS) and dissipative soliton pair (DSP) can be obtained in such fiber laser system. In addition, the mechanisms and characteristics of these solitons are discussed. These findings will facilitate the in-depth understanding of the characteristics of nonlinear pulses generated by NOLM-based all-normal dispersion Yb-doped mode-locked fiber laser. [ABSTRACT FROM AUTHOR]

• Mode-locked erbium-doped all-fiber laser using Mo 2 Ti 2 AlC 3 saturable absorber. • Mo 2 Ti 2 AlC 3 was drop-casted onto a side-polished fiber. • The laser produced a soliton pulse train at 1561.3 nm. • The repetition rate and pulse duration are 1.8 MHz and 1.2 ps, respectively. We developed an ultrafast fiber laser using MAX phase material, Mo 2 Ti 2 AlC 3 , as a saturable absorber (SA). Mo 2 Ti 2 AlC 3 was drop casted onto a side-polished fiber to act as a SA in an erbium-doped fiber laser cavity. A soliton pulse train was successfully obtained via a mode-locking mechanism. It operated at 1561.3 nm with a repetition rate of 1.8 MHz and a pulse duration of 1.2 ps when a pump light was launched into the cavity at a range between 14.8 mW and 106.4 mW. The signal-background noise ratio of the laser was extremely high at 72.9 dB. We believe that this paper is the first that demonstrates the novel application of Mo 2 Ti 2 AlC 3 as a promising SA. [ABSTRACT FROM AUTHOR]

Optical Fiber Communication is known for its extremely high data-carrying capacity among all the existing transmission technologies. However, its capacity to the fullest is restrained by the effects of nonlinearity, thereby urging nonlinear compensation. In this paper, we have attempted to enhance the performance of Nonlinear Frequency Division multiplexing (NFDM) based nonlinearity compensation, a recent attraction due to its high throughput nature. Here, we design optimal transmit signals, emphasizing lowering the Peak to Average Ratio (PAPR). With appropriate investigation, optimal eigenvalue and Quadrature Amplitude Modulation (QAM) constellations for encoding have been procured that aid in constructing low PAPR NFDM signals. To upgrade the optimal QAM design, two novel Spiral QAM models, Model I and Model II are proposed that diversify signal envelopes in addition to lowering the PAPR. This improves the overall fault tolerance of the NFDM system. For a 2-eigenvalue NFDM system, using the proposed constellations, the PAPR is reduced by 0.24 dB (Model I) and 1.42 dB (Model II), compared to the conventional scheme. Thus, we have designed optimum NFDM transmit pulses and subsequently accomplished a high performing 10 Gbps NFDM system using the proposed constellation models. • Realized an enhanced 10 Gbps NFDM transmission system. • Designed optimal NFDM transmit signals with low Peak to Average Ratio. • Proposed novel Spiral QAM constellation models to diversify signal envelopes. • Improvement in the overall fault tolerance of the NFDM system. • Achieved better transmission reach. [ABSTRACT FROM AUTHOR]

• Paper proposes a FiWi network planning for creating the WiFi enabled villages (Gram Panchayats) of India. • The proposed planning provides the optimized position of wireless routers and ONUs in terms of latitude and longitude. • For optimizing position of wireless routers and ONUs, we propose to use customized SMA algorithm. • Simulation has been performed for four gram panchayats of Indore region of India to make them WiFi enabled. • Cost estimation has been given to create the complete network. Fiber Wireless (FiWi) access network consists of high speed passive optical network (PON) at back end and wireless mesh network at front end. It is emerging as the most prominent access network due to its inherent feature. It may provide fast Internet services at minimum possible cost. Many of the villages of the India are still not connected with high speed network hence the present paper provides FiWi network planning for creating the Wireless Fidelity (WiFi) enabled villages (Gram Panchayats) of India. The main aim of the paper is to deploy the cost effective FiWi network to provide the faster internet services at reasonable prices to the users of the gram panchayat (GP) in India. The area of the GP and the user's location in particular GP is taken as input for network planning. The proposed planning provides the optimized position of wireless routers and Optical Network Units (ONUs) in terms of latitude and longitude. For optimizing position of wireless router and ONUs, we propose to use customized Slime Mould algorithm (SMA). We considered four gram panchayats of Indore region of India to make them WiFi enabled using FiWi access network. The customized SMA algorithm provides the best possible position and number of wireless routers and ONUs to connect all the users of gram panchayat. Beside, the total fiber length from the Optical Line Terminal (OLT) to all the ONUs and total cost estimation is also given to create the complete network. [ABSTRACT FROM AUTHOR]

• The paper proposes a new topology for a B5G WDM-PON fronthaul. • The topology employs tunable VCSELs as colorless sources for downstream transmission, as well as data erasure and wavelength reuse for upstream. • Radio-over-fiber transmission performance is evaluated for 1.25 Gbps at the RF carrier frequency of 3.5 GHz and 10 Gbps at 26 GHz, over a 20 km optical link. • The simulation setup is validated by direct comparison against available experimental data.The results comply to 3GPP requirements. The 5G/6G fronthaul link is one of the main drivers for the rising of new passive optical network (PON) standards. Among the possible technologies, wavelength division multiplexing (WDM) is likely the most suitable to meet the stringent performance requirements of fronthaul applications. However, to reduce the implementation and operation costs of WDM-PONs, one of the main issues is the availability of colorless optical sources, in which the same optical hardware can be used to generate any wavelength required by the network. In order to address these needs, in this paper, we propose and analyze a bidirectional colorless WDM-PON topology serving as an analog fronthaul for a 5G and Beyond scenario, comprising the use of recently demonstrated tunable VCSEL lasers for the downlink and the carrier reuse technique for the uplink. We numerically evaluated radio-over-fiber transmission performance when transmitting 1.25 Gbps at the RF carrier frequency of 3.5 GHz and 10 Gbps at the RF carrier frequency of 26 GHz, over a 20 km optical link. The simulation setup is validated by direct comparison against available experimental results, and the obtained results fall within the 3GPP requirements, demonstrating that the proposed topology is a suitable candidate for a future fronthaul configuration. [ABSTRACT FROM AUTHOR]

• Our sensor has a significant intensity response of torsion in the range from −200° to 200°. • The sensitivity of ∼1.1 dB/(rad/m) is achieved with the maximum of 1.17 dB/(rad/m) and the measured error of less than 0.03 rad/m. • Our sensor has the ultra-low cross-sensitivities of 4.7 × 10−2 (rad/m)/m−1 and 1.2 × 10−2 (rad/m)/℃. • Our sensor has the merits of ease of fabrication and cost-efficiency. In this paper, a few-mode-fiber based in-line Mach-Zehnder interferometer is proposed and completed for directional torsion sensing by core-offset splicing technique. The optimal offset and fiber length for fabrication are gained and the comprehensive tests are conducted in terms of torsion, bending and temperature. The experimental results show that our sensor has obvious intensity variation with the applied shear strain. The torsion sensitivity reaches ∼1.1 dB/(rad/m) in the range from −13.08 rad/m to 13.08 rad/m, but with the wavelength shift of 0.102 nm/(rad/m). In addition, thanks for the tiny bending and temperature responses of −0.055 dB/m−1 and 0.014 dB/℃, the ultra-low cross-sensitivities of 4.7 × 10−2 (rad/m)/m−1 and 1.2 × 10−2 (rad/m)/℃ are gained simultaneously, which dramatically improves the practicality of fiber-optic torsion sensor. [ABSTRACT FROM AUTHOR]

• A overlapping spectral demodulation method based on OTDR and 1-DDCNN was proposed. • Real time monitoring of small fire sources in subway tunnels is realized. • The determination of peak wavelengths of four highly overlapping sensing signals realizes that the RMSE is less than 1.5 pm and the average demodulation time is less than 30 ms. To improve the rapidity and reliability of the subway tunnel fire monitoring system and realize the monitoring of small fire sources, the method of regional subsection demodulation is used to group several adjacent nearly identical ultra-weak fiber Bragg gratings (UWFBGs) sensors into a group, and the 1-D dilated convolutional neural network (1-DDCNN) is used to demodulate the same group of highly overlapping sensing signals. The well-trained 1-DDCNN model can achieve extremely low signal demodulation error. The experiment shows that the UWFBG demodulation scheme proposed in this paper improves the detection accuracy of the subway tunnel fire monitoring system and shortens the detection time. The root-mean-square error (RMSE) of four highly overlapping peak wavelengths of sensing signals is less than 1.5 pm, and the average demodulation time is less than 30 ms. [ABSTRACT FROM AUTHOR]

• An optical fiber device for detecting gas ethanol is proposed. • Gas detector based on surface plasmon resonance. • The device has a high repeatability and durability. • The device has a large detectable concentration range and an acceptable response time. Ethanol is an important material in for chemical, pharmaceutical or food industry. But ethanol gas in the air induces health danger and explosion risk. Therefore, the concentration of ethanol gas must be monitored. In this paper, an optical fiber device for ethanol gas detection is demonstrated. Glycerol aqueous solution is taken as the ethanol absorbent, a Teflon capillary is used as the gas permeable cell and a surface plasmon resonance (SPR) fiber sensor is employed as the receiver. When ethanol gas permeates into the capillary and be absorbed by the absorbent, the refractive index of the absorbent is modulated and then detected by the SPR sensor. With this principle, sensing devices were fabricated and tested. Within the range of 0–7534 ppm, the limit of detection (LOD) is obtained as 38.31 ppm. In cycle test, the excellent reusability, repeatability and durability are testified. In addition, with the large detectable range and low cost, the proposed device may realize wide applications in industrial process. [ABSTRACT FROM AUTHOR]

• Improved ADTP-based direct detection OPM monitoring scheme. • The key is the linear mapping of lightness channel values and R,G,B channel values. • The scheme shows the superiority of single channel convolutional neural network and grayscale map. • The feasibility of the three mapping methods is verified by simulation experiments. For the first time, a combination of grayscale maps and single-channel convolutional neural networks (CNN) is used in the direct detection optical performance monitoring (OPM) technique. Due to the faster monitoring speed of the direct detection OPM technique, it is very suitable for intermediate nodes of optical networks. The OPM technique proposed in this paper is an improvement based on the previous asynchronous delay-tap plot (ADTP) techniques. By reducing the redundant color channel information, the training process of the ADTP feature-based monitoring model is improved. In the simulation stage, three high-order modulated signals, 16quadrature amplitude modulation (QAM), 32QAM and 64QAM, are used as sample signals. The ADTP color maps, ADTP pseudo-color maps and ADTP grayscale maps generated by these three modulated signals with different signal-to-noise ratios and cumulative dispersion (CD) are collected. The accuracy of the monitoring model based on these three feature maps is close to 100% for both cumulative dispersion identification and signal modulation formats identification (MFI). However, the monitoring models based on grayscale maps and pseudo-color maps perform slightly better in estimating optical signal-to-noise ratio (OSNR) compared to the monitoring models based on color maps. And the grayscale map-based model slightly outperforms the other two models in terms of training complexity and monitoring speed. The superiority of grayscale maps and single-channel convolutional neural networks compared to previous ADTP-based OPM techniques is demonstrated. [ABSTRACT FROM AUTHOR]

• The prepared biosensor has the advantages of good bio-sensing performance, short measurement time and low limit of detection. • The RI sensitivity can reach 2427.68 nm/RIU, showing a superior performance compared to the raw sensors coated by Au film. • The sensor was used to detect the concentration of CRP, with the bio-sensitivity of 0.09 nm/(µg/mL) and LOD of 0.22 µg/mL. C-reactive protein (CRP) is a vital inflammatory marker in humans and a key single marker of cardiovascular diseases. In this paper, the concentration of CRP was specifically detected by a polydopamine nanospheres (PDA-NPs) developed surface plasmon resonance (SPR) sensor with high accuracy. PDA-NPs is a self-polymerizing material that can be obtained from dopamine through the mussel adhesion effect. The PDA-NPs (diameter ≈ 100 nm) modified SPR sensor exhibits enhanced refractive index (RI) sensitivity and bio-sensitivity attributed to the large specific surface area and high surface reactivity of the PDA-NPs. The developed sensor demonstrates a RI sensitivity of 2427.68 nm/RIU, presenting a 55.7% increase compared to the raw sensor (RI sensitivity was 1559.08 nm/RIU). Moreover, the developed biosensor is used to detect CRP specifically. The bio-sensitivity reaches 0.09 nm/(µg/mL), while the limit of detection (LOD) reaches 0.22 µg/mL. These findings indicate that the developed biosensor can specifically detect CRP with a low LOD. Therefore, this PDA-NPs modified biosensor has great potential in clinical detection and other bio-detection filed. [ABSTRACT FROM AUTHOR]

• A highly sensitive MZI microstructured fiber optic temperature sensing unit based on SNMNS was designed and fabricated by combining simulation analysis. • The novel intrinsic MXene-Ti 3 C 2 T x material was prepared by water bath method, and the preparation was verified by SEM and XRD characterization, and the temperature sensing properties were experimentally verified by combining with microstructure sensing units. • The effects of the length of MMF and whether or not to coat MXene-Ti3C2Tx material on the sensing performance were investigated in depth, and it was concluded that for the designed sensor intrinsic MXene-Ti3C2Tx has a sensitizing effect. • The superior sensitivity and repeatability of the designed temperature sensor is achieved over a temperature range of 30 to 80 degreesC. A temperature sensing method with simple fabrication, real-time detection, and high sensitivity is proposed, and the feasibility of the method is experimentally verified. The sensing unit uses a single-no-multi-no-single (SNMNS) Mach-Zehnder Interferometric (MZI) structure to excite a stronger evanescent field and compares the effect of two different lengths of multimode fibers on the temperature sensing performance. To enhance the sensor sensitivity, a novel 2D material with superior photothermal, optoelectronic, and structural properties, MXene-Ti 3 C 2 T x , was innovatively coated on the optical fiber surface. The intrinsic MXene-Ti 3 C 2 T x material was prepared by the water bath method and characterized by scanning electron microscopy (SEM) and X-ray diffraction spectroscopy (XRD). The same temperature sensing experiments were carried out on uncoated and coated material fibers respectively, and the results showed that the temperature sensitivity improved from a minimum of 61.97 pm/℃ to 120.71 pm/℃ over the temperature range of 30℃∼80℃, an improvement of 94.7 % in sensitivity, with linearity all above 0.98. This paper combines for the first time the sensitive 2D material MXene-Ti 3 C 2 T x with a microstructured fiber-optic temperature-sensing unit, providing a new way of thinking in the field of temperature detection and showing great promise in the field of fiber-optic sensing. [ABSTRACT FROM AUTHOR]

• The localization of low velocity impact on CFRP laminate was conducted by using a normalized error outlier-based algorithm. • An experimental system for low-velocity impact monitoring of CFRP laminates based on FBG sensing network was constructed. • A reference database of impact location-impact response normalized characteristics quantities was constructed. • The low velocity impact on CFRP plate was successfully located with an average localization error of 8.19 mm. • The algorithm used in this paper is better than that of the PCA and BP neural network-based localization algorithms. This study conducted the localization of low velocity impact on Carbon Fiber Reinforced Plastic (CFRP) laminate using a normalized error outlier-based algorithm cooperating with Daubechies3 (Db3)-wavelet threshold noise reduction. The monitoring of CFRP plate impact was conducted by multiplex Fiber Bragg Grating (FBG) sensors connected to its upper surface, and the impact response signal was collected using an interrogator at a frequency of 2 kHz. Results showed that the Db3-wavelet threshold noise reduction algorithm could improve the impact localization performance of CFRP plate structure. By setting an appropriate outlier threshold and using a normalized error outlier-based algorithm, the low velocity impact on CFRP plate was successfully located with a maximum localization error of 21.35 mm and an average localization error of 8.19 mm. [ABSTRACT FROM AUTHOR]

• High accuracy and good generalization ability. • Easy saturation and unable to perceive continuous variation of parameters are solved. • The relationship between the specklegram and the accuracy is analyzed. • Analytical process is conductive to the selection of dataset. • Transfer learning is used to tackle the poor portability and reusability. A novel fiber specklegram torsion sensor based on multimode fiber (MMF) is proposed and experimentally demonstrated in this paper. The Residual Network (ResNet) is used to establish the relationship between the changing process of the specklegram and the torsion angle of the MMF. The experimental results indicate that the sensor exhibits the advantages of high accuracy and large measurement range. Within a torsion angle range of 0–360°, the prediction error is within ±2° for 99.1% of the specklegrams in test set. By analyzing the decorrelation process of the specklegrams from different kinds of MMFs, we find that the difference in torsion angle prediction accuracy of different MMFs stems from the decorrelation angle of the specklegram, and the larger decorrelation angle of specklegram holds higher torsion angle sensing accuracy of the trained ResNet. Meanwhile, the difference of the decorrelation angle of specklegram is attributed to the difference of the fiber normalized frequency. This analytical process may be applicable to the analysis of other specklegram based sensing schemes and the selection of dataset for fiber specklegram sensor. The possibility of transfer learning is also investigated to show an improved portability and reusability. In addition, the fiber specklegram torsion sensor owns other merits such as easy fabrication and good robustness, which shows its wide range of potential applications. [ABSTRACT FROM AUTHOR]

This paper presents and experimentally validates a highly sensitive fiber-optic Fabry-Perot interferometer sound sensor based on a fiber-optic spherical structure. The Fabry-Perot interferometer comprises an aluminum foil diaphragm and a fused fiber-optic microsphere end face, both sealed in a structure made of a glass tube. An optical fiber microsphere structure is used for the first time in acoustic sensing. Based on the strong focusing capability of the microsphere, the high coupling efficiency to the reflected beam, and the extensive range of the focused convergent optical field formed, the focused convergent optical fields facilitate the sensing of an extensive range of motion or deformation of the cavity compared to the divergent optical field of a flat fiber end face, i.e., the acoustic signals at more minor sound pressures can also be well sensed, thus compared to a flat fiber end face fiber The acoustic sensor can monitor acoustic signals over a more extensive frequency range and a larger range of acoustic pressure variations, and the output voltage signal is of a larger amplitude at the same acoustic signal, which allows the monitoring of acoustic signals at acoustic frequencies within the hearing range of the human ear. Experimental results show that the sensor shows a flat frequency response in the range of 20 Hz–20 kHz, covering all frequency components of the human ear hearing range, and the signal-to-noise ratio of the proposed acoustic sensor in the range of 20 Hz–20 kHz is greater than that of the flat fiber end-surface based acoustic sensor and the reference electroacoustic sensor, especially The sensor has the advantages of good high sensitivity, excellent linearity, wide planar response range, and simple manufacturing process. It can potentially be used as a highly sensitive, high acoustic quality fiber optic microphone in practical applications. [ABSTRACT FROM AUTHOR]

The polarization characteristics of the optical fiber have spurred interest in a plethora of smart fiber optic sensors with extremely compact structures due to the capability of in-line configuration, except that the sensing sensitivity remains too low to meet the practical requirements. In this paper, fiber Lyot filter (FLF) is leveraged to generate Vernier effect for sensitivity enhancement of birefringence-based and versatile fiber optic sensor. The proposed sensing structure is composed of two sections of polarization maintaining fibers (PMF) with the reflective scheme, which can be applied to birefringence sensing scenarios such as strain and temperature measurement. The working principle analysis derived from Jones matrix indicates that the combination of Vernier effect and the reflective structure catalyzes a significant improvement in sensitivity. The length of the PMF used in this sensor, the fusing angle between two PMFs, and the birefringence properties of the PMF are all numerically investigated to generate better Vernier performance. Also, experiments are carried out for validation, and sensitivity as high as −12.96 nm/rad is achieved. The compact and in-line structure of the proposed sensor can enable itself to perform excellent and versatile sensing on various occasions. • Fiber birefringence sensors are widely used in many applications. Low sensitivity due to the slight birefringence change of the polarization maintaining fiber hinder their development, and the practicality and stability of existing structures (core-offset fiber, tapered fiber, etc.) used to generate Vernier effect are unsatisfactory. Therefore, we investigate the Lyot filter-induced Vernier effect for sensitivity improvement of fiber birefringence sensor. • The Lyot filter is used to generate Vernier effect for sensitivity improvement of fiber birefringence sensor. • This approach provides a practical and stable structure with high sensitivity and easy packaging. • Simulations and experiments show that the sensor is stable with high sensitivity, providing more opportunities for versatile sensing in various occasions. [ABSTRACT FROM AUTHOR]

This paper presents the experimental analysis of the vulcanisation process of nitrile rubbers for the manufacture of diaphragms used in pressure sensors based on fibre Bragg gratings (FBGs). To investigate the chemical degradation of the vulcanisation process, diaphragms were created utilising various vulcanisation parameters such as temperature, curing time, and rubber thickness. Subsequently, the diaphragm surfaces were analysed by digital macrography, quantifying the degraded area and loading tests to verify the rigidity of vulcanised diaphragms. Also, FBG sensors were incorporated into the diaphragms using different thickness parameters to analyse the sensitivity through pressure tests. Diaphragms vulcanised at 125 °C showed smaller areas of average degradation, 17.5%, 14.5% and 11.0% for diaphragms with rubber thicknesses of 0.5 mm, 1.0 mm and 1.5 mm, respectively. The stiffness of diaphragms vulcanised at 150 °C was higher than that of diaphragms vulcanised at 125 °C, corresponding to 36.69N/mm, 45.25N/mm and 78.29N/mm for rubber thicknesses of 0.5 mm, 1.0 mm and 1.5 mm, concluding that diaphragms with the greater degraded area have less elasticity. Pressure tests with FBGs built into the diaphragms showed high wavelength sensitivity in diaphragms vulcanised at 125 °C and with thicknesses of 0.5 mm, corresponding to 39.08 pm/kPa. Finally, it is possible to have the impact of variables in the vulcanisation processes. In addition, it is possible to align the sensitivity of pressure sensors with FBGs with the vulcanisation parameters, allowing for a more accurate choice of process variables with better responses. • Analysis of optical fibre sensors integration in rubber structures. • Vulcanisation method for optical fibre pressure sensors development. • Comparison of vulcanisation parameters in the optical fibre sensor performance. [ABSTRACT FROM AUTHOR]

• implement all-optical neural networks by combining the techniques of time-stretching and time-division multiplexing. • enabling classification of different datasets. • this architecture is fast, operates efficiently, and achieves pleasing accuracy rates. As factors such as power consumption and bandwidth constrain the development of electronic computing in deep learning, optical neuromorphic computing has the potential to meet the growing computational demands of artificial intelligence, presenting various opportunities and challenges. In this paper, we propose an all-optical neural network through a combination of time-stretching and time-division multiplexing that can be used for the classification of multiple datasets. The system modulates a large number of parameters into chirp optical pulses by time-stretching and increases operational efficiency in conjunction with time-division multiplexing. This all-optical neural network system proposed is capable of operating at the speed of 1 Tera-OPS/s and can achieve data transfer rate in excess of 800 Gbit/s. The system is tested by the feedforward neural network, and the computational simulation realized very encouraging and considerable results. [ABSTRACT FROM AUTHOR]

• An optical band-pass filter-assisted offset DSB direct-detection receiver is proposed for low-cost data center interconnect applications. • The proposed scheme uses an OBPF to filter out the optical carrier as the local oscillator for the receiver. As such, signal-signal beat interference can be eliminated. • Compared with the previous offset DSB CADD scheme, the optimal CSPR of the proposed scheme can be reduced to less than 0 dB, and the OSNR sensitivity can be significantly improved. • The effectiveness of the proposed offset DSB self-coherent detection is fully verified by simulation. The numerical results show the potential of proposed scheme. The offset double-sideband (DSB) scheme has attracted attention because it can achieve field recovery at low carrier-to-signal power ratio (CSPR) and improve the spectral efficiency (SE) of self-coherent detection. In this paper, an offset DSB filter-assisted direct detection (FADD) scheme is proposed and studied for the first time, which uses an optical bandpass filter (OBPF) to filter out the optical carrier as the local oscillator for the receiver. As such, signal-signal beat interference (SSBI) can be eliminated. Since the offset DSB signal has a large frequency gap, the requirement for the bandwidth of the OBPF is not high. The performance of the proposed offset DSB FADD scheme is evaluated for 16-QAM signals. It is comprehensively compared with offset DSB carrier-assisted differential detection (CADD) scheme in terms of OSNR sensitivity, optimal CSPR, and receiver power sensitivity. In addition, the effect of frequency gap compression is significant as SSBI is completely eliminated from the system, thereby utilizing as many low-frequency resources as possible and improving SE. Finally, the proposed offset DSB FADD scheme is resilient to the wavelength offset up to several GHz between the transmitter laser and the center wavelength of the OBPF. [ABSTRACT FROM AUTHOR]

This paper presents a novel design of an optical fiber sensor (OFS) utilizing a single-mode-coreless-multimode-single-mode (SCMS) fiber coated with Poly-Vinyl Acetate (PVAc) for humidity and moisture detection. PVAc, a highly sensitive synthetic polymer, exhibits changes in refractive index (RI) based on relative humidity (RH) variations in the surrounding medium, thereby affecting the output power of SCMS. Numerical analysis using COMSOL Multiphysics determined the optimal coating thickness. The fabricated PVAc-coated SCMS sensor enables RH measurement in air and moisture measurement in oil. The sensor demonstrated a sensitivity of 0.19 dBm/%RH and 0.16 dBm/%RH for increasing and decreasing humidity rates, respectively, within an RH range of 60–85% in air media. Additionally, the sensor achieved a sensitivity of 0.15 dBm/ppm for moisture measurement in oil media. [ABSTRACT FROM AUTHOR]

• An efficient hybrid design method for fiber polarization filters is proposed. • Data-driven feed-forward neural network predicts fiber characteristics fastly. • Genetic algorithm selects structural parameters with optimal performance. • Designed PCF filter exhibits high performance with significant confinement loss. In this paper, we proposed a design method for photonic crystal fiber polarization filters incorporating the artificial neural network (ANN) and the genetic algorithm (GA) to achieve high-performance polarization filters. The ANN is trained to accurately learn the relationship between the structure parameter and polarization properties of PCFs, and GA is utilized to select the structural parameters with optimal performance. Confinement loss, bandwidth, and resonance wavelength of the polarization filter serve as parameters in the multi-objective optimization process performed by the GA. Numerical results demonstrate that the designed PCF filter has high performance, with a confinement loss of 1995.75 dB/cm for the y polarization core mode at 1.55 μm, and crosstalk and bandwidth of 1720.15 dB and 932 nm, respectively. It indicates that the hybrid design method is a promising and viable approach for the development of optical applications. [ABSTRACT FROM AUTHOR]

• Line-coded payload with PolSK overlay is proposed in optical label switching. • Two novel codes (PCC and AVLC) are proposed to provide 75% and 80% code efficiency. • Simulation test is conducted to evaluate the performance under different bit rate ratio. • The tested results show the feasibility of the proposal. Optical label switching (OLS) is an attractive solution for the packet-based optical switching. A novel OLS method applying spectrum shaping line-coding (SSLC) is proposed in this paper. The label signal is superimposed on the amplitude shift keying (ASK) payload signal by polarization shift keying (PolSK) modulation. The low-frequency component of the payload signal is suppressed by line-coding to reduce the induced crosstalk to the label signal. The payload signal and the label signal could be received separately and directly by an ASK receiver and a PolSK receiver, respectively. The performance of the proposed scheme is tested by simulation. Several line-codes are proposed and compared in the simulation. The results of the simulation test show the feasibility of the proposal. Compared with previous OLS methods, the proposed method increases the code efficiency of the payload signal (from 50% to 75% and 80%) without reducing its extinction ratio (ER). So its effective bit rate is increased while its quality is not sacrificed. [ABSTRACT FROM AUTHOR]

• Compared with ordinary cantilever beam structures with equal cross-section, the lever amplification structure can further increase the axial strain of the FBG, thereby improving the response sensitivity of the accelerometer; • While ensuring the high sensitivity of the accelerometer, the thickness of the cantilever beam has been increased to improve its lateral anti-interference ability. • Its structure is simple and easy to package, and changing the thickness of the beam or the length of the rod can further expand the measurement range of the accelerometer. Combined with the lever amplification principle, this paper designed a fiber Bragg grating (FBG) accelerometer based on the structure of an equal-section cantilever beam, which can weaken the contradiction between the lateral immunity and sensitivity of the equal-section cantilever beam. Increasing the thickness of the beam increases its stiffness, thus improving the lateral immunity of the beam; at the same time, the lever structure increases the axial strain of the FBG, further enhancing the sensitivity of the accelerometer. The experimental study and theoretical analysis of the accelerometer show that the accelerometer response sensitivity is 239.12 pm/G with a good fit of R2 = 0.995 for frequencies varying from 5 to 90 Hz and accelerations varying from 0.1 to 1G; the lateral anti-interference degree is less than 6.27%. It shows that the accelerometer has good sensing performance. And the structure is simple and easy to package. The thickness of the beam or the length of the lever can be changed to further extend the measurement range of the accelerometer. [ABSTRACT FROM AUTHOR]

• A new nanocomposite material (CS/α-Fe 2 O 3) is proposed for the specific identification and detection of copper ions. • The specificity of the CS/α-Fe 2 O 3 nano-composite and the response performance of the fabricated interference fiber sensor were explored and analysed. • High sensitivity measurement of Cu2+ concentration (0–1 μM) was achieved. Instrument methods are essential for simple and rapid detection of copper(II) (Cu2+) in drinking water and healthcare. However, these methods suffer from complex sample pretreatment and long detection time. This paper proposed a highly sensitive fiber optic sensor for trace Cu2+ detection in aqueous solutions. Based on the principle of modal interference, by surface functionalization, a uniform chitosan (CS)/α-Fe 2 O 3 nanocomposite material was coated on a structure of no-core fiber–multimode fiber–no-core fiber (NCF1-MMF-NCF2). The amino and hydroxyl groups in the material have a specific recognition function for Cu2+, which can chelate with Cu2+ and change the refractive index of the material, leading to the shift of interference spectrum. Trace Cu2+ detection can be achieved by monitoring the displacement of the interference spectrum. The results revealed that within the range of 0–1 μM Cu2+ concentrations, with increasing Cu2+ concentration, the interference spectrum underwent a red shift and the maximum detection sensitivity of Cu2+ ions reached 456.69 nm/μM, with a good linearity of 0.989. Also, the sensor has the advantages of high stability, good repeatability, simple fabrication, and low cost. [ABSTRACT FROM AUTHOR]

Filterless optical networks (FON) are attracting attention because of their low-cost characteristics. However, removing active devices forces the signal to be broadcast on all output ports, wasting a significant amount of spectrum resources. In order to maintain the low-cost advantage and save more spectrum resources, this paper studies the routing, modulation, and spectrum assignment (RMSA) problem in semi-filterless optical networks. For this problem, we propose a spectrum assignment algorithm based on adaptive modulation scheme with minimum link and boundary distance (ML-M-MTBD). The algorithm selects the path that occupies the minimal number of links (ML) for spectrum assignment during the routing process and combines it with a variable adaptive modulation scheme (VAMS) between fiber trees. During the spectrum assignment process, the algorithm divides the frequency spectrum resources into two regions, calculates the distance from the frequency spectrum block to the two boundaries of the spectrum resources to be assigned, and selects the position corresponding to the shorter distance to the boundary for spectrum assignment. We conducted simulations on German-Net and Henan-Net, and compared our algorithm with two existing algorithms, the first-fit algorithm and the best-fit algorithm. The simulation results show that the proposed algorithm has a lower blocking probability. • Combining two optimization metrics of routing and spectrum assignment: (1) L: Link occupancy; (2) BD: Boundary distance of the spectrum block, we propose an algorithm for minimum link and boundary distance spectrum assignment. • Reduced the request blocking probability in the semi-filterless network. [ABSTRACT FROM AUTHOR]

• A novel FBG-based sensor for vector displacement measurement has been presented. • The sensor shows high linearity with the R2 of 0.998, large measurement range of 140 mm, high sensitivity of 4.362 pm/mm, maximum hysteresis error of 3.25% and maximum repeatability error of 6.62%, respectively. • A series of sensor calibrations and performance tests of the sensor are conducted. This paper presents a novel fiber Bragg grating (FBG)-based displacement sensor with simple construction for vector deformation monitoring of slope surface. The interesting structure design and sensing principle of determining the displacement direction and amplitude simultaneously are reported. Calibration tests of six different auxiliary structures (namely core sensing elements) of the sensor are reported, which demonstrates that they are characterized by a superb linearity with an R2 of over 0.998, large measurement range of 140 mm, high sensitivity of 4.362 pm/mm, maximum hysteresis error of 3.25% and maximum repeatability error of 6.62%, respectively. A simulated rock slope test of the sensor is conducted to investigate the performance for determining the progressive sliding process of sliding mass. Additionally, a homogeneous soil slope model test is further conducted and the vector deformation of slope surface is accurately captured by three proposed FBG-based displacement sensors. This capability in identifying two-dimensional displacement can provide a bright application prospect in intelligent monitoring field. [ABSTRACT FROM AUTHOR]

• A novel wide dynamic range of temperature sensors based on a Fiber Bragg Grating (FBG) is presented and demonstrated. • The FBG sensor head is reinforced with borosilicate glass wool fiber (BGWF) and housed in a 4 mm quartz tube. • BGWF-reinforced FBG sensors with a dynamic temperature range of 1270 °C from −170 °C to 1100 °C have been demonstrated. • In the 12 Hr stability test, BGWF-reinforced FBG sensors show excellent stability. A novel wide dynamic range of temperature sensors based on a Fiber Bragg Grating (FBG) is presented and experimentally demonstrated. The FBG sensor head is reinforced with borosilicate glass wool fiber (BGWF) and housed in a 4 mm quartz tube. BGWF-reinforced FBG sensors with a dynamic temperature range of 1270 °C from −170 °C to 1100 °C have been demonstrated. Further, the thermal expansion and correlation coefficients are calculated from high-temperature measurements to be 11.46 pm/°C and 0.99677, respectively. In the 12 Hr stability test, BGWF-reinforced FBG sensors show excellent stability, the same as thermocouples. We believe this paper will lay a foundation for researching and designing new FBG sensors to measure extreme temperature conditions. [ABSTRACT FROM AUTHOR]

• Optimized surface bonding configuration for FBG sensors in extreme environment. • Excellent signal is observed in FemtoSecond Grating with polyimide coating at cryogenic temperatures. • Bonding FBG using cryogenic bonding agent Stycast and vacuum grease Apiezon N have been investigated. Optical fibre Bragg grating (FBG) sensors have been used for cryogenic temperature and strain measurements in a variety of applications, e.g., hotspot detection in high-temperature superconductor magnets. In such application, the sensitivity of the FBG and its reflection spectrum strongly depend on the methods of application, chiefly the adhesion and the elasticity of the bond, and the birefringence effect. To investigate those features, Draw Tower Gratings (DTG®) with Ormocer coating and FemtoSecond Gratings (FSG) with polyimide coating are mounted in the V-shaped grooves and on the surface of copper substrates using Stycast and Apiezon N. Their performance is investigated between 293 K and 77 K. The FBG sensors mounted in the V-grooves can achieve higher temperature sensitivities than those on the surface of the copper due to enhanced thermal strain transfer. It is found that although there is no obvious difference between the temperature sensitivity of the Ormocer and polyimide coated FBGs at cryogenic temperatures, the polyimide coated FBGs show superior reflection spectra, whose peak intensity remains strong at 77 K. Cryogenic vacuum grease Apiezon N is shown to bond the fibre well to the copper at cryogenic temperatures, which also reduces the birefringence effect induced from the non-uniform strain across the FBG. This paper provides practical knowledge of bonding FBG sensors in cryogenic environments for temperature and/or strain measurements. [ABSTRACT FROM AUTHOR]

• A transverse pressure sensor based on Sagnac cascaded FBG is proposed. • Based on PMF birefringence effect. • FBG structure is introduced to improve sensitivity. • Finite element method combined with experiment. In the field of engineering, the deformation and lateral stress in structural health detection have attracted extensive attention to obtain the structural health information of building objects in time. Based on the birefringence effect of polarization maintaining fiber (PMF), a transverse pressure sensor based on Sagnac cascade fiber bragg grating (FBG) was proposed and prepared. The performance of the sensor is analyzed by the combination of the finite element method and experiment. The simulation results show that the cross section of PMF is deformed under the pressure along the fast axis and the slow axis and then modulates the refractive index. The experimental results show that by adding FBG structure, the lateral pressure sensitivity of the sensor is 408.7 pm/N, and the linear fit is 98.3%. The lateral pressure sensitivity of the structure without FBG is 281.7 pm/N, and the linear fit is 99.3%. That is to say, the FBG structure increases the sensitivity of the sensor by 45.1%. The experimental results are in full agreement with the theoretical derivation. The optical fiber lateral pressure sensor proposed in this paper has the characteristics of simple fabrication, low cost, and high repeatability. It plays an important role in the field of structural stress monitoring. [ABSTRACT FROM AUTHOR]

• ROTDR can be used to quantify the leakage channel outlet diameter in earth-rock dam. • A method for estimating the outlet diameter of leakage channel was proposed. • A practical deployment method of sensing fiber for leakage detection was designed. • The effectiveness of the proposed method was validated through outdoor model test. In the early stage of leakage in earth-rock dam, detection and quantification of the leakage channel outlet can provide an important reference for leakage hazard assessment and emergency response. In this paper, Raman Optical Time Domain Reflectometry (ROTDR) is used to detect the leakage point and a leakage channel outlet diameter estimation method is proposed. Firstly, the variation law between the sensing fiber of different length and ROTDR measurement results under the condition of different temperature difference is explored. Then, a model is constructed to simulate the leakage of earth-rock dam. The sensing fiber is deployed on the shallow layer of downstream slope and cushion of earth-rock dam to detect leakage. Finally, according to the measurement results, the leakage point is located and the diameter of leakage channel outlet is estimated. The estimated value is very close to the measured value. This study provides a useful reference for promoting the quantitative research of ROTDR in leakage detection. [ABSTRACT FROM AUTHOR]

The Quality of Service (QoS) requirements for 5G are very strict in terms of latency of Fifth Generation (5G) traffic. 5G fronthaul networks between the baseband unit and remote radio heads are planned to use Next Generation - Passive Optical Networks 2 (NG-PON2) to carry their traffic. However, these Time Wavelength Division Multiplexing (TWDM) PON based networks also provide service to other traffic such as residential and corporate users. Therefore, it is crucial to provide QoS guarantees to 5G traffic. The main issue includes allocating transmission over multiple wavelengths while maintaining QoS. Although using all the available wavelengths all the time may seem to be the simple solution, each active wavelength increases the cost of operation. To solve these issues, this paper proposes a technique using fuzzy logic to dynamically allocate wavelength and bandwidth for 5G fronthaul networks. Two types of traffic, i.e., 5G traffic and normal traffic are considered while the problem of Dynamic Wavelength and Bandwidth Allocation (DWBA) is formulated as a queueing theory problem using penalties and a cost function. Penalties are assigned for waiting packets as well as each active wavelength. Then, modeling the number of active wavelengths, the number of packets in the system, the total cost, and the traffic intensity as input fuzzy variables while modeling the change in the number of active wavelengths as the fuzzy output variable. The Mamdani implication is used for the fuzzy inference engine and the height method is used for defuzzification of the output variable. Simulations in MATLAB show that the proposed technique can maintain the latency of 5G traffic lower than the defined threshold while also significantly reducing the number of active wavelengths. A comparison with the existing state-of-the-art techniques shows that the proposed technique results in an improvement of at least 46% and 29% in terms of the average number of active wavelengths and the average latency for 5G traffic, respectively. • Dynamic Wavelength and Bandwidth allocation algorithm for 5G fronthaul networks. • Fuzzy logic based controller to dynamically allocate wavelength and bandwidth. • Significant reduction in the average number of active wavelengths and the average latency for 5G as well as non-5G traffic. [ABSTRACT FROM AUTHOR]

• The high-temperature resistance wFBGA based on PI-wFBGA fabricated online by drawing tower. • Post hydrogen-loading and low-temperature annealing to improve its high-temperature resistance. • Optimal annealing of post-hydrogen-loaded PI-wFBG at 200℃ for 120 min. • Operating at 350℃ for more than 40 days and have good temperature consistency. Polyimide coated weak fiber Bragg grating array (PI-wFBGA) fabricated online by drawing tower overcomes the temperature limitation of conventional acrylate coating, and has broad application prospects in high-temperature environments. However, the periodic refractive index modulation of PI-wFBG is weak and rapidly decays or even erases in high temperature, indicating poor high-temperature resistance. In this paper, we report the design of a high-temperature resistance wFBGA based on PI-wFBGA fabricated online by drawing tower, which uses post hydrogen-loading and low-temperature annealing to improve its high-temperature resistance. Activated by thermal energy, hydrogen molecules react chemically with the germanium or silicon-related defects in the glass structure of the optical fiber to produce hydroxyl groups. When two hydroxyl groups combine, they form molecular water, which is a key factor in enhancing the high-temperature resistance of PI-wFBG due to its high stability and low diffusion. After annealing the post-hydrogen-loaded PI-wFBGA at 200℃ for 180 min and then removing the residual hydrogen molecules inside the fiber, the mechanical strength of the fiber remains unchanged. The high-temperature resistance PI-wFBG can operate at 350℃ for more than 40 days and have good temperature consistency in the high and low temperature cycle at 400℃. Changing the temperature and time of annealing, the experimental results show that the annealing of post-hydrogen-loaded PI-wFBG at 200℃ for 120 min is an optimal annealing method considering both the high-temperature resistance and mechanical property of high-temperature resistance PI-wFBG, which can realize the reliable use of PI-wFBGA in the temperature resistance range of polyimide coating. [ABSTRACT FROM AUTHOR]

• Based on EFPI sensor, PB-AOF and wavelength division multiplexing technology, the system realizes one-way four-channel passive audio parallel transmission. • Achieve 20 km long distance optical fiber audio communication. • No difference between the EFPI sensors used by each channel. • Be used in scenarios with special requirements, such as security monitoring and mines. To meet sound transmission requirements in complex work environments, this paper constructs a passive audio pickup sensor based on an extrinsic Fabry-Perot interferometer (EFPI) and develops a one-way four-channel passive audio parallel transmission system based on a passive bidirectional audio over fiber(PB-AOF) transmission system and wavelength division multiplexing technology. The system realizes optical fiber audio transmission over a distance of 20 km. The experimental results show that the signal-to-noise ratio (SNR) is greater than 64 dB, and the highest sensitivity of the four channels in the proposed system is 1.06 V/Pa. Thus, the proposed long-distance terminal passive audio communication network is ideally suited for applications in certain fields. [ABSTRACT FROM AUTHOR]

• An ameliorated PGC demodulation scheme using Taubin least squares (LS) fitting of ellipse is proposed. • A combined internal modulation is used and optimized to guarantee the effectiveness of the ellipse fitting algorithm. • Compare with LS, Taubin LS has a high fitting accuracy, thereby reducing the extra low frequency modulation amplitude. • Quadrature signals are extracted from 0th and 1st harmonics of the interference signal, reducing the system complexity. • The scheme has a phase resolution of 3.16 μrad/√Hz, a dynamic range of 120 dB @ 1 KHz and a linearity of 99.996%. In this paper, we propose an ameliorated phase generated carrier (PGC) demodulation scheme using Taubin least squares (LS) fitting of ellipse to eliminate the nonlinear errors. Taubin LS has carefully chosen a normalization matrix and the ellipse fitting parameters are directly obtained by solving the generalized eigenvector problem, leading to a high accuracy result. Quadrature signals are extracted from the signal fundamental and the sidebands of the fundamental of the carrier, and then corrected by the ellipse fitting algorithm (EFA) based on Taubin LS. A combined internal modulation is used to ensure the proper operation of the EFA under small signals. And the desired phase signal is extracted from the corrected quadrature signals by the differential-cross-multiplying method and evaluated by the total harmonic distortion. Experimental results show that the proposed scheme is superior and highly stable, it has a phase resolution of 3.16 μrad/√Hz, a large dynamic range of 120 dB @ 1 KHz and a good linearity of better than 99.99%. [ABSTRACT FROM AUTHOR]

Three-component geophone rotates randomly during oil and gas exploration, which is difficult to orient. There is a severe impact on the subsequent stratigraphic inversion. By fixing the fiber Bragg grating (FBG) sensor to the three-component geophone, the twist angle is the same. The rotation angle of the three-component geophone can be obtained by measuring the twist angle of the FBG sensor. However, the three-component geophone below the FBG sensor stretches the FBG sensor. Therefore, avoiding the effect of tensile strain on the torsional strain, requires simultaneous inversion of the twist angle and stretch length of the FBG sensor. This paper introduces an FBG sensor with simultaneous inversion of torsion angle and tensile length. The sensor consists of two FBGs embedded in the spiral groove of the compliant cylinder. Firstly, the sensing principle of the FBG sensor is analyzed, and developed FBG sensing model for tensile–torsional strain, including FBG by tilting arrangement, the extension of the tensile strain range of the FBG sensor was realized. Secondly, it describes the fabrication process of the FBG sensor, including loading the FBG with pre-stress, making the FBG sensor realize the extension of the torsion angle range. Next, the convenience of inversion is realized by averaging the calibrated strain transfer coefficients. Finally, to verify the effectiveness of this bidirectional helical fiber design and sensing technology, simultaneous torsion and tension tests were conducted on FBG sensors. The experimental results show that the sensor achieves simultaneous torsion angle and tensile length inversion. The maximum torsion angle of the inversion is 180°. The maximum stretch length of the inversion is 10 mm. • The first application of FBG sensor based on a bi-directional helix structure for identification of three-component geophone orientation, and the simultaneous inversion of FBG sensor torsion angle and tensile length is realized. • The strain range is 6000 μ ϵ for axially arranged FBG. In tilt arrangement FBG, where the helical angle is 45°, the tilted FBG strain range is 4 times higher than the axial FBG strain range, and the extension of the tensile strain range has been realized. • The twist angle measured by the four-core FBG sensor is 78° (Modes et al., 2020). By loading pre-stress, the FBG sensor based on a bi-directional helical arrangement measures a torsion angle of 180°. In contrast, an expansion of the torsional angle range has been achieved. [ABSTRACT FROM AUTHOR]

• A self-assembled whispering gallery mode microbottle resonator was fabricated. • The proposed microbottle resonator can be used for acetone gas sensing. • The sensor has merits of small size, low cost, and simple manufacture using non-toxic materials. In this paper, an acetone gas sensor based on a polyvinyl alcohol (PVA) self-assembled whispering gallery mode (WGM) microbottle resonator coated with polydimethylsiloxane (PDMS) is proposed and demonstrated. The preparation of the PVA self-assembled microresonator and the coating of PDMS are all finished by employing a dip coater. Compared with the PVA microresonator and the PDMS microresonator, the PVA microresonator coated with PDMS shows the highest acetone gas sensitivity, which is up to −6.34 pm/ppm. Besides, it can effectively reduce the effects of humidity on the detection of acetone gas compared to the PVA microresonator. Since the concentration of acetone in breathing gas is an indicator of diabetes, the proposed sensor with the benefits of small size, low cost, and simple manufacture using non-toxic materials presents promising applications for painless and non-invasive diagnosis of diabetes. [ABSTRACT FROM AUTHOR]

The Structural Health Monitoring (SHM) of large civil infrastructures has become a priority due to economic advantages and early detection of structural failure. Distributed Fiber Optics (DFO) sensors are becoming widely used for SHM due to their immunity to Electromagnetic interference and the ability to collect multiple data points from a single fiber cable. However, its reliability for a long monitoring period is still an area of interest. This paper studied the long-term performance of DFO embedded into textiles for faster installation procedures. The aim was to understand if the textile distributed fiber sensor experience any signal degradation after multiple weather seasons. To perform this investigation a railway bridge was used as a case study. The data was collected using Brillouin Optical Time Domain Reflectometry (BOTDR) and Brillouin Optical Time Domain Amplification (BOTDA). Additionally, a temperature compensation technique was investigated to remove the cross-relation between temperature and strain. The final results show the sensor's effectiveness for long-term monitoring, where the data quality remained constant with an average standard deviation of 0.455 for the BOTDR and 0.208 for the BOTDA approaches. • Developed a Smart textile for Structural Health Monitoring (SHM). • Performed long-term monitoring of a Railway bridge under different weather conditions. • Utilized Brillouin Optical Time Domain Reflectometry (BOTDA) in combination with the smart textile to determine changes in the fiber strain distribution. • Determined the survivability of the Smart Textile under New England's harsh conditions. [ABSTRACT FROM AUTHOR]

• We propose and demonstrate a delta-sigma modulator (DSM) based radio-over-fiber (RoF) system for MMW indoor communication. • In the experiment, 2-bit DSMs are used to quantize the high-order QAM orthogonal frequency division multiplexing (OFDM) signal into the 16QAM signal. • We have successfully achieved the transmission of up to 16,384 QAM signals on a DSM based RoF system without significantly reducing performance. When the received optical power is high enough, the corresponding error vector magnitude (EVM) and bit error rate (BER) are 0.53% and 7 × 10−3, respectively. In this paper, we propose and demonstrate a delta-sigma modulator (DSM) based radio-over-fiber (RoF) system for MMW indoor communication. In the experiment, 2-bit DSMs are used to quantize the high-order QAM orthogonal frequency division multiplexing (OFDM) signal into the 16QAM signal. At the receiver, the original high-order signal can be recovered by the low pass filter (LPF) and down-sampling operation. Based on the experimental results, up to 16,384 QAM signals can be transmitted over the DSM-based RoF system without noticeable performance degradation. When the received optical power is high enough, the corresponding error vector magnitude (EVM) and bit error rate (BER) are 0.53% and 7 × 10−3, respectively. [ABSTRACT FROM AUTHOR]

• Through PRBS phase modulation, a narrow-linewidth linearly polarized pulsed laser output with an average power of 30 W, a peak power of 376 kW(repeat frequency of 10 kHz, pulse width of 7.5 ns). • This peak power is the highest index obtained by the reported pulsed fiber laser. The peak power and average power can be further increased by adding an amplifier stage. When designing a fiber laser, it is difficult to achieve both narrow linewidth and high power due to nonlinear effects, especially stimulated Brillouin scattering (SBS). However, using the pseudo-random binary sequence (PRBS) phase modulation technique, SBS can be effectively suppressed in narrow-linewidth fiber lasers during amplification. In light of this, we carried out the experimental research described in this paper. First, based on a theoretical analysis, a narrow-linewidth linearly polarized pulsed fiber laser system was designed; then, an experimental platform of a multistage master-oscillator power amplifier (MOPA) structure was constructed, including one-stage continuous optical amplification and four-stage pulsed optical amplification. In our experiments, without phase modulation, a linearly polarized narrow-linewidth fiber laser achieved an average power output of 17 W and a peak power of 188 kW (repetition frequency of 10 kHz, pulse width of 8.5 ns). At this level of power, the spectral signal-to-noise ratio was about 40 dB, and the beam transmission factors in the X and Y directions were 1.14 and 1.11, respectively. Using PRBS phase modulation, a linearly polarized narrow-linewidth pulsed laser achieved an average power output of 30 W and a peak power of 376 kW (repetition frequency of 10 kHz, pulse width of 7.5 ns) at a clock rate of 1.25 GHz. The polarization extinction ratio was greater than 15 dB, the spectral signal-to-noise ratio was greater than 40 dB, and the beam transmission factors in the X and Y directions were 1.18 and 1.12, respectively. [ABSTRACT FROM AUTHOR]

• Due to the production process, the refractive index of the fiber is different from the ideal refractive index. We studied the effect of this difference on the performance of the separating vector mode of the ring fiber. • Established a model to simulate how impact the ring thickness, the maximum refractive index of the ring and curve steepness have on the mode separation. • Fabricated two ring-core fiber and compared their performances. In this paper, the influences of the ring thickness, the maximum refractive index of the ring and curve steepness on the mode separation are analyzed. The model is established with considering the actual fiber fabrication, especially the transition range between two adjacent layers are studied. Then we manufacture the ring-core fiber with central air hole. This study has reference significance for the structure design of vortex optical fibers. [ABSTRACT FROM AUTHOR]

• A RI sensor was researched on eliminating the influence of ambient temperature. • A F-P interferometer based on PVC film is used to demodulate temperature shift. • The accuracy of the sensor is high and it has good repeatability. An optical fiber sensor based on a gradually hot-pressed flatted plastic optical fiber (POF) and F-P interference structure is proposed to eliminate the effect of ambient temperature drift in the refractive index (RI) detection of glucose concentration. Based on the analysis of the influence of the sensor itself and the RI change of solution on the transmitted light intensity under the effect of temperature, a self-calibration formula was established by means of the peak wavelength and the transmitted light intensity of interference peak were used as information carriers to calibrate the parameters. The results of the validation show that the temperature drift compensation method proposed in this paper is feasible. The maximum relative error between the measured RI after compensation and actual value is only 0.032%, and it has good repeatability. The precision to the RI with temperature compensation of the gradually hot-pressed flatted POF and F-P interference structure has potential applications in the biochemistry, medical diagnosis, and environmental monitoring. [ABSTRACT FROM AUTHOR]