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Elastic optical networks (EONs) using optical orthogonal frequency division multiplexing (O-OFDM) technique are considered to be promising optical networks due to their ability to achieve flexible spectrum management. This paper studies dynamic anycast in EONs. The rapid growth of service demand has brought enormous challenges to the network environment, resulting in the increase of blocking rate. In order to reduce the traffic blocking rate, we propose a spectrum-aware ant colony optimization (S A − A C O) algorithm to optimize the anycast transmission problem in EONs and improve the spectrum utilization in the network. Different from the traditional anycast allocation algorithm, the proposed S A − A C O algorithm can adapt to the real-time changes of the system. We add bandwidth factor into the node pseudo-random selection rule, and add a weight factor to weigh the impact of bandwidth on the system. In the found candidate path set, the link distance and link spectrum availability are processed to find the optimal path suitable for the current service transmission. In terms of pheromone update, we delay the secretion of ant pheromone, and secrete pheromone on the path where the relatively optimal solution is located in the solution space found by the ant colony. Through extensive simulation experiments, we evaluate the performance of the algorithm. By comparing with the reference algorithms in previous literature, our proposed algorithm significantly outperforms other methods in reducing bandwidth blocking probability performance. • ACO is applied to dynamic anycast transmission in elastic optical network. • Bandwidth factor is added to the pseudo-random selection rule. • Pheromone secretion of the ant colony is delayed in terms of pheromone renewal. [ABSTRACT FROM AUTHOR]

• The first real time experimental demonstration of a hybrid OFDM DFMA PON. • The DSP complexity is reduced leading to a cost effective system-on-chip device. • A joint sideband processing technique improves the transmission performance. • The system is robust to symbol timing offset. • The clock requirement can be drastically reduced translating to lower power consumption. This paper presents the first real-time experimental demonstration of a hybrid OFDM DFMA PON. The presented PON is validated for two channels (I or Q) occupying two subwavelength bands. The hybrid OFDM DFMA PON eliminates the need for a dedicated matching filter at the receiver for each individual channel, by employing a single FFT operation to recover all channels, thereby achieving lower computational complexity. The hybrid OFDM DFMA PON used in conjunction with a joint sideband processing technique, when compared to a DFMA PON under the exact same operating conditions, is shown to offer increased performance, including a lower received optical power of up to 1.2 dB for the adopted FEC limit at a given bit rate. The experimentally demonstrated PON is also proven to be significantly more tolerant to the symbol timing offset effect at the OLT receiver. Furthermore, compared to the DFMA PON's OLT receiver, the implemented FFT-based receiver is shown to operate at a drastically reduced logic clock rate and with significantly lower DSP complexity. The hybrid OFDM DFMA PON is thus shown to have numerous advantages over the DFMA PON. [ABSTRACT FROM AUTHOR]

• A gain saturation theoretical model was constructed and simulated. • Gain saturation in MDM-EDFA of 1550 nm with scaling mode number of signal up to 60-mode group with the energy conversion efficiency up to 18.58% was analyzed. Saturation occurs at short EDF length and high pump power as the number of modes growth. • Variation of gain saturation with number of modes in "WDM + MDM" systems provides a reliable solution for the implementation of high-capacity, high-quality "WDM + MDM" communication systems. Gain saturation in a mode-division-multiplexed erbium-doped fiber amplifier (MDM-EDFA) has a significant impact on system capacity due to complex mode competition. In this paper, the gain saturation of MDM-EDFA at single and multiple wavelengths is investigated. The gain saturation occurs as a certain negative linear correlation between EDF length and pump power. The saturation performance tends to be flat beyond 49 mode groups transmission. In a "WDM + MDM" system with 36 × 36 channels, the normalized root mean square value of the saturation gain is lower than 3. The results provide a theoretical basis for the application of the upcoming "WDM + MDM" system. [ABSTRACT FROM AUTHOR]

• A large bandwidth optical fiber magnetic field sensor based on Sagnac interferometer for weak alternating magnetic fields measurement is proposed. • The sensing mechanism of this magnetic field sensor under an alternating magnetic field is theoretically derived and simulated. • The experimental system is built to verify the simulation results, and the magnetic field sensitivity is optimized by increasing the length of the delayed fiber ring. • The magnetic field sensor performances, such as frequency response, linear range, and noise, are analyzed theoretically and demonstrated experimentally. In this paper, a fiber magnetic field sensor is proposed based on Terfenol-D and Sagnac interferometer. The mechanism of the sensor is deduced theoretically. As the frequency of the magnetic field increases, on the one hand, the sensitivity is enhanced because the response to the high-frequency non-reciprocal phase differences is intensified in the Sagnac interferometer. On the other hand, the sensitivity is suppressed by the eddy current effect. Then it exhibits significant linear response to alternating magnetic field in a certain frequency range. The sensor performances, such as frequency response, linear range, and noise, are analyzed theoretically and demonstrated experimentally. Experimental results show that the sensor has a 3 dB bandwidth from 100 Hz to 2500 Hz, and the excellent linearity and reversibility from 0 to 274.05 μT (rms). The high sensitivity of 1.34 mV/μT (rms) and minimum detectable magnetic field of 25 nT/√Hz (rms) are achieved at 500 Hz. The sensor with large bandwidth and wide measuring range is suitable for detecting weak alternating magnetic field. [ABSTRACT FROM AUTHOR]

• Designed a reliable self-healing communication integrated with a sensor network for the function of fault protection. • Design a cost-effective and flexible network, and increase the coverage of transmission distance. • Designed communication integrated with a sensor network for simultaneous transmission of communication and sensing signals. • Proposed machine learning algorithm to predict the wavelength of sensors. In this paper, we proposed a novel self-healing fiber/free-space optics (FSO) communication integrated with a sensor network for simultaneous transmission of optical communication signal and sensing signal as well as a function of fault protection by using a coarse wavelength-division multiplexer (CWDM). The combination of CWDM and fiber integrated with FSO transmission channel is incorporated to design a cost-effective, flexible network and increase the coverage of transmission distance. The experiment result proves that the fiber integrated with an FSO transmission channel achieves a clear constellation diagram and best error vector magnitude (EVM) value. On the other hand, the scanning-laser interrogation system is used for data acquisition in the strain-based fiber Bragg grating (FBG) sensor system. Moreover, the radial basis function neural network (RBFNN) algorithm is used to estimate the central wavelength of FBGs. [ABSTRACT FROM AUTHOR]

• Both directions outside the main vibration direction have excellent anti-interference ability. • Extending the base to reduce the effective length of the fiber plays a role in improving the sensitivity. • In the beam type FBG accelerometer, the accelerometer in this paper has the characteristics of small volume and easy processing. A Fiber Bragg Grating (FBG) accelerometer with cantilever beam is presented and experimentally demonstrated. The effective length of the optical fiber is reduced by changing the base of the accelerometer, so as to increase the sensitivity. The resonant frequency and the sensitivity of the accelerometer are deduced theoretically. The structural parameters were optimized by numerical simulations and the characteristics of the accelerometer were simulated by finite element simulations. The experimental results show that the resonant frequency of the accelerometer is 119 Hz, the sensitivity (the main direction z) is 134.29 pm/g within 2–60 Hz flat region. It also designed with good immunity to interference, the cross sensitivity in the x and the y directions are 3.86 % and 2.97 %, respectively. In addition, the accelerometer has the characteristics of small volume and easy processing. In general, this accelerometer has a research significance in the field of oil and gas exploration. [ABSTRACT FROM AUTHOR]

• PCF-based sensors have been investigated for biomedical applications. • Various novel PCF-based structures have been also investigated. • Various novel nanomaterials used with PCF have been tested. • Several diseases diagnosis can be also perform with PCF. • Sensing performance of PCF-based sensors are high. Nowadays, the usage of photonic crystal fibers (PCF) has become a very quick and prevalent innovation in sensor implementation. PCFs have unique features and capabilities due to their geometric design, which makes them ideal choice for sensing applications. In this study, various simulations of biomedical sensors are analyzed. A biosensor is a type of an analytical device that analyses a biological system using either chemical or biological components. By filling the solutions into PCF shows good results in diagnosing disease, malignancies, hemoglobin concentrations and antibodies. PCF type biosensors are widely used in biological research, clinical trials, medication development and other applications. This research proposes a survey for different shapes of PCFs in biomedical sensors. This research paper main objective is to describe the numerous applications of biomedical sensors like glucose, blood, protein, and DNA sensors. The sensitivity and confinement loss are compared using this different-shaped PCF with different background materials. [ABSTRACT FROM AUTHOR]

• Traffic balancing and crosstalk aware resource provisioning strategies for scheduled traffic in MCF based EONs are proposed. • The proposed strategies utilize traffic characteristics, SLA conditions and network features to balance the traffic. • A crosstalk aware core prioritization and allocation method is proposed to efficiently allocate the spectral resources. • The performance superiority of the proposed strategies is validated through numerical simulations. Elastic optical networks technology in combination with space division multiplexing is playing a major role to fulfil the need of increasing internet traffic. However, it suffers from resource sub-utilization due to the traffic heterogeneity in time and bandwidth domains, and the crosstalk between the adjacent cores in a multi-core fiber link. In this paper, we propose time and bandwidth aware traffic balancing strategies with crosstalk consideration to efficiently utilize the spectral resources in MCF based EONs. To this end, we utilize network features and SLA conditions to balance the traffic, in both, the time and the bandwidth domains. In bandwidth domain, we utilize squeezing and splitting with multipath routing, and in time domain, we use sliding and shifting. To further enhance the performance, we use a MCF structure dependent prioritized core allocation based RMCSA strategy. Simulation results indicate superiority of the proposed strategies in terms of different parameters of interest as compared to the benchmark strategies. [ABSTRACT FROM AUTHOR]

Bidirectional recurrent neural networks (bi-RNNs), in particular bidirectional long short term memory (bi-LSTM), bidirectional gated recurrent unit, and convolutional bi-LSTM models, have recently attracted attention for nonlinearity mitigation in fiber-optic communication. The recently adopted approaches based on these models, however, incur a high computational complexity which may impede their real-time functioning. In this paper, by addressing the sources of complexity in these methods, we propose a more efficient network architecture, where a convolutional neural network encoder and a unidirectional many-to-one vanilla RNN operate in tandem, each best capturing one set of channel impairments while compensating for the shortcomings of the other. We deploy this model in two different receiver configurations. In one, the neural network is placed after a linear equalization chain and is merely responsible for nonlinearity mitigation; in the other, the neural network is directly placed after the chromatic dispersion compensation and is responsible for joint nonlinearity and polarization mode dispersion compensation. For a 16-QAM 64 GBd dual-polarization optical transmission over 14 × 80 km standard single-mode fiber, we demonstrate that the proposed hybrid model achieves the bit error probability of the state-of-the-art bi-RNN-based methods with greater than 50% lower complexity, in both receiver configurations. • Fiber nonlinearities can be mitigated in optical communication using low-complexity neural networks. • Neural networks outperform digital back-propagation for equalization in dual-polarization long haul optical fiber transmission. • Hybrid convolutional recurrent neural networks outperform CNN and pure RNN models for mitigation of PMD and Kerr nonlinearity. [ABSTRACT FROM AUTHOR]

The distributed sub-tree (DST) scheme in the elastic optical datacenter network (EODN) can use multiple datacenters (DCs) to jointly serve a multicast request. By allocating some suitable DCs to the multicast request, the route length can be reduced, thereby reducing resource consumption and decreasing blocking probability. However, DST scheme also has a defect that, all source nodes of multicast requests are hosted in the DCs, which leads to that links connecting the DCs nodes have higher usage than other links, and the resulting network bottleneck makes the network performance declines sharply. In this paper, we propose a link-aware cost calculation (LA-CC) formula and a link-aware distributed steiner sub-tree (LA-DSST) algorithm to make the usage of all links as balanced as possible, thus reducing the blocking probability caused by network bottlenecks. Simulation results show that our proposed algorithm significantly improves performance with the lowest blocking probability compared to existing well-performing algorithms. • A link-aware cost calculation formula for different kinds of links is presented. • A link-aware distributed steiner sub-tree algorithm is presented. • Reduce the blocking probability of multicast requests due to network bottlenecks. [ABSTRACT FROM AUTHOR]

• A temperature measurement method with error suppression is performed by a dual-wavelength FRL with an intracavity Sagnac interferometer. • A dual-wavelength filter is formed by cascading two DWDMs. • The intensity difference of two peaks is measured by difference method. • Compared with single-wavelength configuration, the measurement error of dual-wavelength is reduced from 0.443% to 0.066%. The sensors based on intracavity intensity modulation of fiber ring laser (FRL) have shown excellent performance in sensing resolution and detection limit, but suffer from large measurement errors. The measurement errors mainly result from the power fluctuation of pump source and environmental interference. Therefore, the methods of error suppression are of great significance for FRL sensors. In this paper, a temperature measurement method with error suppression is performed by a dual-wavelength FRL with an intracavity Sagnac interferometer. The sensing principle of single- and dual-wavelength FRL sensors have been analyzed. By the sensing manner of intensity difference of two excited wavelengths, the measurement error has been decreased from 0.443% to 0.066% compared with the single-wavelength configuration. The temperature sensitivity and measurement stability have been further discussed. This method can be extended to similar FRL sensors to suppress measurement errors. [ABSTRACT FROM AUTHOR]

• An MZI fiber optic temperature sensor was designed with a new structure of TCF-NCF-TCF (thin-core optical fiber, abbreviated to TCF; and no-core optical fiber, abbreviated to TNT) • The fiber optic sensor has been sensitized with PDMS, a material with high thermo-optical coefficient and thermal expansion coefficient, which increases the sensitivity from 57.14 pm/°C to 130 pm/°C. • The sensor exhibits high sensitivity and accuracy in temperature sensing, which has good stability in the range of 50 °C to 80 °C. • The MZI in this paper is simple to manufacture, low cost and easy to produce. It has great advantages for forming large-scale industrial production. A novel fiber optic sensor based on the Mach-Zender interference (MZI) principle and sensitized with polydimethylsiloxane (PDMS) is proposed. This sensor is primarily a sandwich structure with TCF-NCF-TCF (thin-core optical fiber, abbreviated to TCF; and no-core optical fiber, abbreviated to TNT) fused together sequentially, and its overall length is 3 cm. The TNT structure can effectively excite the cladding mode due to the fiber-core mismatch, which produces a significant interference spectrum. Because no-core optical fibers lack a core and cladding structure, they are equivalent to direct contact between the optical waveguide and the external environment, which is extremely sensitive to the variations in the external environment. The experimental results show the highest temperature sensitivity of 57.14 pm/°C ranges from 45 °C to 80 °C. PDMS, a material with high thermo-optical and thermal expansion coefficients, is coated on the surface of the fiber optic sensing zone. And the temperature sensitivity is effectively improved up to 130 pm/°C. Due to the small shape, compact structure, easy production, and steady mechanical strength, the sensor offers significant promise for temperature sensing applications. [ABSTRACT FROM AUTHOR]

• An improved distributed vibration sensing scheme is proposed. • The multiple vibrations with high frequency can be accurately demodulated. • A spatial resolution of ∼20 m is achieved in a 4.95 km sensing fiber link. • A maximum frequency response of 45 kHz is achieved. Distributed multiple vibrations detection with high frequency response is still a challenging task in distributed optical fiber vibration sensors. In terms of optical interferometer based vibration sensors, the location information can not be directly demodulated. Moreover, the detectable frequency response in the optical reflectometer based vibration sensors is limited by the repetition frequency of the modulated optical pulse. In this paper, an integrated vibration sensing scheme based on two dual narrow line-width laser (NLL) sources with different wavelengths has been theoretically proposed and experimentally demonstrated. In the scheme, one NLL source is used for constructing the phase sensitive optical time domain reflectometry (Φ-OTDR), and the other one is used to build the Michelson interferometer. These two vibration sensors are integrated by using a dense wavelength division multiplexer. Based on the sensing mechanism of the integrated vibration sensor, the multiple simultaneous vibration points can be located by the Φ-OTDR sensing part, meanwhile its corresponding frequencies information can be fully acquired by the Michelson part. Experiments on detection of the piezolelectric transducer (PZT) show that a spatial resolution of ∼20 m is achieved in a 4.95 km sensing fiber link based on the width of the modulated optical pulse in Φ-OTDR part was set as 200 ns. And a maximum frequency response can reach 45 kHz restricted by the vibration source of the PZT. Compared to conventional vibration structure, the proposed vibration sensing scheme can offer a series of unique advantages, such as simple signal demodulation process, high signal to noise ratio of the demodulated frequency spectrum, no high order harmonics in the frequency spectrum, no dead zone in the detectable frequency range and it can be achieved with a common sensing fiber. [ABSTRACT FROM AUTHOR]

• The crosstalk influence between the different cores in MCF on IFOG is analyzed and relevant experiment is designed. • By connecting four cores of a 300-m long MCF as fiber coil of IFOG, the ARW is 0.006°∕√h and the drift is 0.01°∕h, which is close to the performance of SCF with the same length. • Closed-loop scheme and DSP are used. This scheme is expected to put MCF into the products of IFOG in the foreseeable future. In this paper, multi-core fiber (MCF) is integrated in interferometric fiber optic gyroscope (IFOG) as the sensing coil to improve its sensitivity without increasing the fiber length or Shupe error. We have used a 300-m long 7-core fiber and connected 4 cores of MCF to each other by fan-in and fan-out (FIFO) devices of fused taper in closed-loop IFOG to replace the traditional single-core fiber (SCF). Before experiment, the main benefits and certain possible problems of using MCF are explained and analyzed. The angular random walk (ARW) of 0.006°/√h and drift of 0.01°/h have been achieved, which is close to the performance of IFOG using the 1200-m long SCF. Besides having a lower Shupe sensitivity, the MCF-IFOG also has small crosstalk effect when using broadband light source. The results show that the scheme of MCF for IFOG is expected to be used in practical application in the foreseeable future. [ABSTRACT FROM AUTHOR]

• A highly sensitive temperature and strain sensor based on Lyot filter with Vernier effect has been demonstrated. • Because the interference spectra of the Lyot filter and fiber Sagnac interferometer are both relatively uniform, it is easy to achieve the Vernier effect. • The FSRs of the Lyot filter and fiber Sagnac interferometer can be regulated conveniently, it is easy to achieve higher magnification based on Vernier effect. • Compared with the sensors based on Lyot structure with Vernier effect, the sensor in this work realized highest magnification and sensitivity. A highly sensitive temperature and strain sensor cascaded with a fiber Lyot filter (FLF) and a fiber Sagnac interferometer (FSI) is proposed in this paper. The temperature and strain characteristics of Lyot filter without and with Vernier effect are experimentally studied. Because the free spectral ranges (FSRs) of the two interferometers can be controlled simply by adjusting the length of polarization-maintaining fiber (PMF), the Vernier effect can be realized conveniently. High temperature and strain sensitivity measurement is obtained by this structure for the first time. The experimental results indicate that the temperature and strain sensitivity of the cascade structure can reach −61.52 nm/°C and 58.63 pm/με respectively, which is about 50 times higher than that of a single FLF whose temperature and strain sensitivity is 1.23 nm/°C and 1.21 pm/με. By carefully optimizing the structural parameter, the sensitivity can be further improved, which provides a new choice for temperature and strain detection. [ABSTRACT FROM AUTHOR]

• Ring based Hybrid FSO- Fiber Optic Architecture. • Same wavelength transmission for downstream and upstream Transmission. • A reliable hybrid 4 × 10 Gbps fiber optic-FSO based ring architecture. • Backup protection at CO side as well as at user side. This paper proposes a reliable hybrid 4 × 10 Gbps fiber optic-FSO based ring architecture. The proposed architecture aims to provide reliable and bandwidth-efficient transmission. The proposed architecture has a fault protection capability in presence of the link failure occurring at the feeder network (FN) and distribution network (DN) towards the central office (CO) and optical networking unit (ONU) respectively. To avail the benefits of free space optics (FSO), it is integrated with the optical fiber at the user end. The architecture transmits the data on the ring in only a clockwise direction for both downstream and upstream transmission and therefore enables the utilization of the same wavelengths without any interference. i.e. the proposed architecture improves the bandwidth utilization and needs only half of the spectrum. In the proposed architecture, four 10 Gbps signals are propagated through a 20 km single-mode fiber (SMF) and a 200 m length of free-space/optical fiber link for the downstream and upstream transmissions. We also compared the signal transmission performance of architecture in terms of bit error rate (BER) for different weather conditions of the FSO link at the user side. The architecture works well for the different weather conditions and can transmit data through the FSO link for upto 700 m and 200 m for clear and heavy rain weather conditions respectively. Protection against faults in the fiber links; improves the survivability and reliability of the network. The proposed architecture is useful in rural and urban hilly areas where signal transmission interrupts frequently due to various geographical challenges. [ABSTRACT FROM AUTHOR]

• A novel compound-ring resonator of an optical fiber laser configurated with two interleaved sub-ring resonators has been developed. • Single-longitudinal-mode laser has been emitted from the optical fiber laser. • A Fabry-Perot etalon has been designed as a criterion to which the frequency of the laser has been locked. • The frequency of the laser has been stabilized by the Fabry-Perot etalon and an active feedback controlling circuit. In this paper we report the development of a robust highly stable frequency single-longitudinal-mode optical fiber laser based on a Fabry-Perot etalon and an active feedback controlling system. The laser is fundamentally structured on an all-fiber compound-ring resonator which is configurated with two interleaved and optical-path-overlapped sub-ring resonators. By employing a length of erbium-doped fiber as the gain medium and a FBG as a reflector, the effective linewidth of the gain spectrum of the compound-ring resonator is restricted to be as narrow as the reflected spectrum of the FBG, which is about 0.043 nm. Because of the vernier effect between the two interleaved sub-ring resonators, the longitudinal mode spacing of the compound-ring resonator can be expanded to be as wide as the effective linewidth of the gain spectrum of it, which permits only one longitudinal mode oscillating. By employing an external Fabry-Perot etalon as a criterion and using an active feedback controlling system to tune the length of the cavity of the compound-ring resonator, the ambiance disturbances to the cavity can be compensated and the frequency of the emitted laser is locked to the offset frequency of the Fabry-Perot etalon. Therefore the frequency of the emitted laser has been stabilized to be 10−8. [ABSTRACT FROM AUTHOR]

• A compact, high-sensitivity fiber laser sensing system is experimentally demonstrated. • Chirped FBG converts the change of dispersion into the shift of longitudinal mode beat frequency in a fiber laser system. • Experimental results show that a linear sensitivity of 3.17 MHz/nm is reached. • Higher sensitivity is achieved compared with conventional fiber laser sensors. In this paper, a multi-longitudinal mode fiber laser (MMFL) sensing system is proposed and experimentally demonstrated. The longitudinal mode beat frequency (LMBF) of the MMFL is related to the effective optical path length of the laser's resonant cavity, which is determined not only by the physical length of the resonant cavity but also by its dispersion characteristic. Thus, when the total dispersion of the resonant cavity varies with the disturbance caused by external physical factors, the LMBF of the laser would shift and can be used for sensing applications. A chirped FBG was induced in the MMFL to enable such dispersion-frequency mapping. The model of such MMFL system is proposed and verified theoretically and experimentally. Experimental result shows that the proposed sensing system has a more compact size and higher resolution compared to conventional configure. [ABSTRACT FROM AUTHOR]

Single-mode-no-core-single-mode (SNS) optical fiber structures have valuable potential to encapsulate as high-precision temperature sensors, due to their great sensitivity. This paper is to improve the temperature sensitivity of SNS fibers by studying the parameters of fiber length, diameter, and refractive index of the seal liquid. Transmission spectra of the fibers are given in both aspects of experiment and numerical simulation. We find that using a slim no-core fiber section sealed with liquid of high refractive index can effectively improve the sensitivity, while the choice of fiber length mainly affects the width of transmission peak. The results may contribute to the development of high-sensitivity optic temperature sensor. [ABSTRACT FROM AUTHOR]

• To survive impact the contact radius between the fiber and impactor must be increased. • Silicone was chosen due to its high strain to failure and elastic properties. • In situ silicone sensors have shown to minimally effect back face deformation depth. • Silicone sensing mats are able to protect optical fibers during impact. The authors previously demonstrated the use of FBG sensors in Kevlar mats behind body armor to measure the transient back face deformation (BFD) during ballistic testing. This paper presents a novel sensor system based on a Fiber Bragg Grating embedded in silicone mats to improve the survivability of the body armor in-situ strain sensing layers. Due to the large amount of deformation, a relative slip between the optical fibers and the supporting structure is needed to maintain the performance of the sensors and determine the relationship between the measured strain and deformation shape. Two silicone materials were tested, Smooth-Sil 950 and Sorta-Clear 40, in both 1 mm and 2 mm thicknesses to evaluate their survivability and impact on BFD. To enhance slipping between the fibers and surrounding silicone a thin layer of petroleum jelly was placed on the fibers prior to being cast in the silicone mats. The 1 mm Sorta-Clear 40 mats performed best in silicone survivability, FBG survivability and minimal impact on the BFD. The new system improves on key deficiencies that were found from inserting the fibers directly into the Kevlar with minimal to no impact on the back face deformation. [ABSTRACT FROM AUTHOR]

• In this paper, a high-sensitivity surface plasmon resonance (SPR) sensor based on photonic crystal fibre (PCF) is designed and simulated for a wide range of applications involving refractive index (RI) sensing. • The outside surface of PCF is coated with gold (Au), and a small layer of titanium dioxide acts as an adhesive between the gold and silica. • Wavelength sensitivity of 10000 nm/RIU, sensor resolution of 2 × 10−5 RIU and amplitude sensitivity of 1115 RIU−1 are achieved. • In the operating wavelength between 0.5 µm and 1.35 µm, the proposed sensor can detect the RI of the analyte from 1.35 to 1.40. • The proposed sensor is exceptional for biochemical sensing, medical testing, and environmental monitoring due to its extensive range of RI detection and sensing. Until now, the use of photonic crystal fiber (PCF) based sensors has been limited. Environmental monitoring, the chemical industry, the food industry, and biomedicine are merely some of the fields. In this work, a surface plasmon resonance (SPR) sensor based on PCF is designed and simulated for a wide range of refractive index (RI) sensing applications with high sensitivity. The outer surface of PCF is coated with gold (Au), and a thin coating of titanium dioxide serves as an adhesive between the Au and silica. Using the SPR interaction between the core mode and Surface Plasmon Polariton mode of the proposed sensor, the RI of the analyte is detected. The simulated sensor has shown wavelength sensitivity of 10000 nm/RIU, sensor resolution of 2 × 10−5 RIU and amplitude sensitivity of 1115 RIU−1. Its operating wavelength ranges from 0.5 µm to 1.35 µm and it can detect the RI ranges from 1.35 to 1.40. The proposed sensor is exceptional for biochemical sensing, medical testing, and environmental monitoring due to its extensive range of RI detection and sensing. [ABSTRACT FROM AUTHOR]

• We propose a Adaptive larm rediction (AAP) for optical transport networks. • We use real network data for verification. • We explore the performance of AAP at different feature selection. The experimental results show that even when the features differ between source and target domain, the method can still work. Artificial intelligence (AI) applications about optical network management are increasing, especially in fault diagnosis. When the network fault or alarm occurs, the equipment running status and performance parameters are changing. AI algorithms can extract the internal relationship from the data and it is proved that the alarm prediction method based on AI is effective. However, the performance of AI models, especially supervised learning, rely on large data sets. These training sets with only a small number of samples are usually unavailable due to the lack of historical data. How to improve the generalization ability of AI models is still a key problem to be solved in the intelligent maintenance of optical networks. In optical network alarm prediction, performance data of devices have different degrees of relationship to alarms and the generalization performance of models is limited by the data structure. In this paper, we propose a method to optimize the model generalization ability in alarm prediction, i.e., the training of a small sample model is solved through parameter transfer in the training process. We verify the generalization effect of the models by using real data of a commercial optical network. Experimental results show that the models achieve significant performance improvement in the data set with a high correlation between performance and alarm. [ABSTRACT FROM AUTHOR]

• Enhanced Mach-Zehnder interferometer multimode–single-mode–multimode fiber optic refractive index sensor based on surface plasmon resonance is proposed and experimentally demonstrated. • Simultaneous using of SPR effect and chemical etching provides a high-performance Mach-Zehnder RI sensor. • Reducing the waist of the sensing head of the SPR-MZI sensor results in the improvement of sensitivity (about 50%) in a wide range of RI near to 1.333. • High sensitivity, simple fabrication, and reproducibility make these sensors promising devices for chemical and biosensing applications. In this paper, an all-fiber Mach-Zehnder interferometer (MZI) sensor for refractive index (RI) measuring is presented, which is based on Multimode–Single-mode–Multimode (MSM) fiber. The effects of both reducing the radius of the sensing part and the surface plasmon resonance (SPR) on its efficiency are investigated. Increasing the interaction of high-order modes with external media, caused by etching the cladding layer of the single-mode fiber part, significantly improves the sensitivity. Both wavelength and intensity interrogation approaches are employed to study the Multimode–etched Single-mode–Multimode (MESM) fiber sensor. The intensity and the wavelength sensitivities for the RI measurement in the range of 1.428–1.458 are obtained as −2306.754 %/RIU and 1315.74 nm/RIU, respectively. Finally, the MESM-SPR sensor is proposed and characterized. Results exhibit high performance in the RI range of 1.333 to 1.357, in which the sensitivity of 1437.056 nm/RIU is achieved. The advantages like low cost, high sensitivity, and simple fabrication methods make these sensors promising devices for chemical, food industry, and biosensing applications. [ABSTRACT FROM AUTHOR]

• The VMD algorithm is improved by optimizing the number of decompositions K; • A high-sensitivity flexible FBG packaging structure is designed; • Constructed a mapping algorithm with inversion of respiratory wave and ECG characteristics; • The accuracy rate of the mapping algorithm is as high as 99.28 %, and the error is only 0.2 bpm. We propose a pulse and respiration monitoring system based on fiber optic sensing, to achieve accurate monitoring of human pulse and respiration rate with wearable and high comfort. We designed a flexible packaging structure -- to embed the fiber Bragg grating sensors (FBGs) fiber optic sensor into a nylon bandage, which constitutes a wearable real-time monitoring system that can acquire pulse and respiration rates simultaneously. The system uses the Variational Mode Decomposition - Feature Point Recognition (VMD-FPR) signal processing algorithm to demodulate and analyze the FBG echo signal to invert the pulse and respiration rate. The experiments were conducted on human heart rate and respiration rate in different states. The experimental results showed that the error range of respiration rate was within ±0.2 bpm, and the accuracy of the respiration experiment feature point recognition algorithm was 93.29 %. The error range of heart rate was within ±2 bpm, and the accuracy of the pulse experiment main wave feature point recognition algorithm was 99.28 %. Thus, the system can accurately collect and analyze the feature points in the respiratory and pulse wave signals. The information obtained from the experiments is used to build an information base, which provides data support for establishing the analysis model of pulse characteristics and respiratory characteristics of the detectors, and to achieve the function of real-time monitoring of human physiological parameters. [ABSTRACT FROM AUTHOR]

• Having established a simulation model, the spectrum broadening characteristics of the narrow-linewidth FBG-based amplifier were analyzed based on multiple factors. • A plum-shaped coiling design for the gain fiber was used to filter out high-order modes thus obtaining a beam quality m2 of 1.32 at the maximum output power of 3.3 kW. • A Raman suppression ratio of 26.3 dB was obtained at the maximum output power of 3.3 kW. • To the best of our knowledge, this is the highest record of narrow-linewidth fiber laser based on one stage MOPA configuration with normal commercial narrow-bandwidth fiber gratings and non-wavelength-locked laser diodes. This paper demonstrates a narrow-linewidth fiber laser with near-diffraction-limited beam quality and high Raman suppression ratio by utilizing Master Oscillator Power-Amplifier structure based on narrow-bandwidth fiber Bragg gratings. The output power reaches 3.31 kW with a slope efficiency of 85.0 %. At the maximum output power, the 3 dB, 10 dB, and 20 dB linewidths are 0.40 nm, 1.20 nm, and 3.09 nm, respectively. The beam quality M2 factor is 1.32 and the Raman suppression ratio reaches 26.3 dB. A pair of narrow-bandwidth fiber gratings were used in the oscillator to compress the linewidth of the seed laser. We used backward-pumping configuration and plum-coiled gain fiber in the amplification stage to suppress the Raman effect and select transverse mode by fiber-bending. Finally, a compact all-fiber laser was obtained with narrow-linewidth, high beam quality, and effective suppression of the Raman effect. To the best of our knowledge, this is the highest output power for a sub-nanometer-linewidth laser using narrow-bandwidth fiber gratings and none-wavelength-locked laser diodes, which achieves near-diffraction-limit beam quality. This provides a solution for high-power narrow-linewidth laser sources with high beam quality. [ABSTRACT FROM AUTHOR]

[Display omitted] • ROFDTS deployed successfully in Indus-2 synchrotron radiation source. • ROFDTS measures the temperature profile of a 160 m long power supply cable (current 760 A, DC) of dipole magnets. • ROFDTS can also detect the progress of unforeseen fire events anywhere in the cable. • The sensing fiber of ROFDTS could survive in the harsh environment of Indus-2. • Mapping of various dipoles is provided on the temperature profile curve. The paper presents the work on development and application of Raman optical fiber distributed temperature sensor (ROFDTS). ROFDTS has been used for monitoring the temperature profile and detecting the progress of unforeseen fire events anywhere in a 160 m long power supply cable (current 760 A, DC) of dipole magnets in the Indus-2 synchrotron radiation source (SRS). Indus-2 is a national facility and is being operated in round the clock mode. The sensing fiber could survive in the harsh environment of Indus-2 SRS that consists of bremsstrahlung radiation of 6.7 Rad/h, high magnetic field of 1.5 T and radio frequency (RF) field of 1.27 MV at 505.812 MHz. The fire detecting capability of ROFDTS was first tested on the mock test setup in the laboratory by artificially creating the four hot zones. Each hot zone has the width of 1.0 m in the sensing fiber at the spatial locations of 26 m, 48 m, 70 m and 92 m respectively. An audio-visual alarm was generated when the temperature of the hot zones exceeded the set temperature limit of 50 °C within 30 s of the start of the fire. Finally, ROFDTS system was deployed to measure the temperature profile of power supply cable during 'no operation', 'injection' of the electron beam current (109 mA with the energy of electrons @ 550 MeV) and at 'normal operation' of the electron beam current (145 mA with the energy of electrons @ 2.5 GeV) in Indus-2 SRS. The peak temperature of power cable reached from 26 °C to 44 °C from 'no operation' to during the 'normal operation' condition of the Indus-2 SRS. [ABSTRACT FROM AUTHOR]

• This novel structure is fabricated only by using ordinary single mode fiber (SMF) and a fiber fusion splicer. • A high strain sensitivity of −34.61 pm/με is obtained, which is 10 times higher than that (3 pm/με) of common inline optic-fiber MZI and 6 times higher than that (6 pm/με) of common inline optic-fiber Fabry-Perot interferometer (FPI). • The length (∼490 μm) of this novel MZI is much smaller than that of an ordinary inline optic-fiber MZI (∼2 cm) with advantages of high sensitivity, low-cost, and easy fabrication. A novel offset-core single micro-tapered fiber-optic Mach-Zehnder interferometer (MZI) with high strain sensitivity is proposed and experimentally demonstrated. This novel structure is fabricated only by using ordinary single mode fiber (SMF) and a fiber fusion splicer, of which the offset-core distance is about 12 μm and micro-tapered fiber length is about 490 μm. A high strain sensitivity of −34.61 pm/με is obtained, which is 10 times higher than that (3 pm/με) of common inline optic-fiber MZI and 6 times higher than that (6 pm/με) of common inline optic-fiber Fabry-Perot interferometer (FPI). In addition, the length (∼490 μm) of this novel MZI is much smaller than that of an ordinary inline optic-fiber MZI (∼2 cm) with advantages of high sensitivity, low-cost, and easy fabrication. The novel optic-fiber MZI proposed in this paper enriches the manufacturing methods for fiber-optic MZIs, which has a good application prospect for strain sensing. [ABSTRACT FROM AUTHOR]

• Chromatic dispersion causes power fading in mm-wave radio-over-fiber links. • Power fading techniques resulting in OSSB-C signal prove to be most universal. • Simple MRR on a PIC promises competitive results in power fading mitigation. • OSSB-C by MRR proves to be an effective solution for carrier distribution in PON of arbitrary topology. • Simple MRR in an integrated RoF transmitter enables power-penalty free transmission. In this paper we address the limiting effect of power fading (PF) in fiber optic communication links, due to the fiber's dispersive properties, and suggest a mitigation approach in intensity-modulated radio-over-fiber (RoF) applications. The proposed method is independent of the length of the optical transmission path. PF is mitigated by employing a simple integrated photonic structure, i.e., a single micro-ring resonator. The latter features a periodic notch-filter response, employed to suppress one of the sidebands in an optical double sideband (ODSB) modulation, reducing the PF of the received RF signal. The suppression ratio measured by the optical spectrum analyzer is 24 dB. In this way we succeeded in reducing the RF signal's power ripple at the receiving end to 3 dB. The proposed approach promises an economic yet effective solution to overcoming the PF in point-to-multipoint-topology optical networks. [ABSTRACT FROM AUTHOR]

• A hundred-Watt 980-nm MOPA fiber laser is demonstrated with the 20/125-μm DCYF. • In-band ASE limits the power up-scaling of the MOPA fiber laser. • Increasing seed power is beneficial to suppress the in-band ASE. • Split-step seed loading method is presented, with which 109-W output power is achieved. • The fiber laser provides a cost-effective solution for high-power core-pumping source. In this paper, a hundred-watt monolithic fiber laser operating near 980 nm is demonstrated by using a double-cladding Yb-doped fiber (DCYF) with 20-μm core and 125-μm inner-cladding diameter. The fiber laser is fabricated with the master oscillator power amplifier (MOPA) configuration to scale up the output power. In our experiment, it is found that the power scalability of the fiber laser is limited by the in-band amplified spontaneous emission (ASE) which can be effectively suppressed by increasing the seed power. Then, with the split-step seed loading method, 109-W output power around 980 nm has been achieved with in-band and 1030-nm ASE suppressed to 17.1 and 40.6 dB, respectively. The beam quality has also been measured, and the M2 factor is about 1.9 at the maximum output power. Our work provides a cost-effective solution to achieve hundred-Watt fiber lasers operating near 980 nm. [ABSTRACT FROM AUTHOR]

• We demonstrate a passively mode-locked laser operating at 2 um region based on a saturable absorber (SA) of FONPs deposited on the D-shaped fiber (DF). This is the first use of FONPs to achieve mode-locking at 2um. • The mode-locking operates in 1931 nm, the 3 dB bandwidth is 5.9 nm, the repetition frequency is 24 MHz, and the pulse width is 1.29 ps. In addition, the signal-to-noise ratio is ∼67 dB, indicating the stability of the output spectrum. As a unique type of transition metal oxides, ferroferric-oxide nanoparticles (FONPs) have attracted much attention due to their outstanding physical and chemical properties. In this paper, we demonstrate a passively mode-locked laser operating at 2 um region based on a saturable absorber (SA) of FONPs deposited on the D-shaped fiber (DF). FONPs were deposited on DF to form FONP-DF SA devices. As inserted into the thulium-doped fiber laser (TDFL), a mode-locked pulse was realized at 1931 nm. For all we know, this is the first demonstration of FONP-DF SA in fiber lasers at 2 um region. This work fills the gap of FNOP in the realization of 2 um mode-locking and lays the foundation for us to use FNOP-DF for magnetic field sensing in the future. [ABSTRACT FROM AUTHOR]

• A hollow-core PCF composed of magnesium fluoride was proposed to identify toxic and hazardous gases. • The structure is based on the quasi-crystal arrangement of air holes. • Numerical simulation results showed that the fiber proposed in this study has a sensitivity coefficient above 50%, relatively low loss, and low dispersion. • The device is suitable for identifying toxic and dangerous gases. • The detection of which using this tool prevents combustion and explosion in the drilling process. In this paper, a hollow-core photonic crystal fiber (PCF) composed of magnesium fluoride is designed to identify toxic and hazardous gases. Its band structure is calculated using the well-known plane wave expansion method. The numerical results show that the proposed structure has a relatively wide photonic bandgap (PBG) in the wavelength range of 1 to 3.3 μm covering the near- and mid-infrared wavelength ranges. Then, by applying optical pulses with a wavelength in the range of the PBG to the proposed PCF, its propagation behavior is calculated by solving the nonlinear Schrödinger equation using the split-step Fourier method. The type of gas can be identified by observing and comparing the frequency responses of the gas-filled PCF with the absence of gas injection. Simulation results show that the fiber proposed in this study has a sensitivity coefficient of more than 50%. The low loss, low dispersion, and high accuracy of the proposed fiber make it a suitable tool for identifying toxic and dangerous gases such as methane and hydrogen sulfide in the drilling and oil exploration industry. Identifying them using this tool prevents combustion and explosion in the drilling process. [ABSTRACT FROM AUTHOR]

• The cross-correlation between short and long pulses in BOTDR results in a narrow Brillouin spectrum width. • The subtraction between two optical pulses with slightly different duration offers sub-meter spatial resolution measurement. • The DCS-BOTDR technique offers a potential application for long distance fiber measurement with high measurement accuracy. In this paper, we report the effect of pulse duration on the Brillouin frequency shift (BFS) accuracy measurement in our previously proposed differential cross-spectrum Brillouin optical time domain reflectometry (DCS-BOTDR) fiber sensing technique. The DCS-BOTDR uses a pair of optical pulsed probes generated via intensity modulation scheme, in which the first probe consists of a long- and short duration of pulses separated by a short interval, while the second probe only has the long pulse with the same duration as the first one. From the experimental analysis, by varying the duration of the long pulse between 6 and 60 ns, we found that an optimum range of the long pulse duration between 14 and 22 ns provided good measurement of BFS accuracy around 5.3 MHz. Furthermore, by heating up a 2 m fiber section at the end of a 4 km test fiber, by using long- and short pulse durations of 18 ns and 4 ns respectively, we have successfully demonstrated 40 cm spatial resolution and 4 °C of temperature resolution measurement. [ABSTRACT FROM AUTHOR]

• Flexible and energy efficient TWDM PON architecture. • Capable of direct inter and intra Optical distribution network (ODN) communication. • Capable of direct inter-optical networking unit (ONU) communication. • Latency-aware and reliable optical network architecture for smart rural and urban communities. Nowadays, service reliability, operation cost, transmission latency of optical access networks are the major challenging issues that need to be addressed while planning and developing the next-generation passive optical networks (NG-PONs). This paper proposes a flexible, energy-efficient, time and wavelength division multiplexed (TWDM) PON architecture that has the capability of centralized optical line terminal (OLT) resource sharing with multiple optical networks. The architecture has the point-to-point direct inter-optical networking unit (dedicated inter-ONU) transmission capability among the various ONUs located within the same optical distribution network (ODN). Such transmission may also be referred to as direct intra-ODN communication. The architecture also has the potential of transmitting an inter-ONU signal to the ONUs residing in the different ODNs (inter-ODN) belonging to the same optical network (OPN). Such transmission may be referred as the direct inter-ODN or intra-OPN transmission. The architecture reduces the normalized energy consumption of approximately 2.21875 Wh per hour, normalized transmission latency of approximately 148 µs for the direct inter-ONU transmission. This is achieved by diverting the inter-ONU signal from the remote nodes (RNs) itself towards the intended ONUs. The percentage energy saving of the proposed architecture is approximately 74 % as compared to the conventional architecture. The proposed architecture is suitable for strengthening the existing information and communication technology (ICT) infrastructures and can be implemented in next-generation flexible, energy-efficient, latency-aware, and reliable optical networks for developing smart rural and urban communities. [ABSTRACT FROM AUTHOR]

In this paper, a Mach-Zehnder interference (MZI) based on asymmetric taper-shaped ultraviolet glue is proposed for highly sensitive temperature sensing. Due to the small diameter and the deflected two ends of the tapered UV glue, part of the light leaked into the air during the propagation of the UV glue taper, resulting in interference. We tested the temperature sensing of several samples with different parameters. Experimental results show that with the increase of temperature, the wavelength moves linearly to a shorter wavelength. The highest temperature sensitivity can reach −15 nm/℃, and the linear correlation coefficient is 0.995. The sensor has the advantages of low cost, simple manufacture and higher temperature sensitivity is suitable for temperature measurement. [ABSTRACT FROM AUTHOR]

• An unclosed fiber optic current sensor based on the helically wound spun highly birefringent fiber half waveplate on the tunnel boring machine is proposed and experimentally demonstrated. • The unclosed fiber optic current sensor is designed to coil the spun highly birefringent fiber around the measured current clockwise and counter clockwise alternately in order to be mounted on the measured object with large diameter easily. • The helically wound spun highly birefringent fiber half waveplate is proposed to accumulate the Faraday effect. • The good performance of the unclosed fiber optic current sensor is confirmed by the laboratory experiment. In the application of the fiber optic current sensor that is mounted on tunnel boring machine (TBM) for measuring the probe current in tunnel geological prediction, the field installation and the influence of the linear birefringence caused by external perturbations are problems needing to be solved. In this paper, an unclosed fiber optic current sensor (UFOCS) based on the helically wound spun highly birefringent (SHB) fiber half waveplate is proposed and demonstrated. The UFOCS is designed to coil the fiber around the measured current clockwise and counter clockwise alternately in order to be mounted on the measured object with large diameter easily. The all-fiber half waveplate made by the helically wound SHB fiber is used to accumulate the Faraday effect. The simulation is carried out based on the polarization model and a linear response is obtained. The laboratory experiment is conducted and the results confirm the good performance of the UFOCS. [ABSTRACT FROM AUTHOR]

• This paper proposes a high sensitivity fiber optic acceleration sensor based on Fabry-Perot interference. • The sensitivity of the sensor is 3.81 nm/g at 300 Hz, and the resonance frequency of the sensor is 800 Hz. • The sensor has a simple structure, low cost and easy to fabricate. A high sensitivity fiber optic acceleration sensor based on Fabry-Perot interferometer is proposed and experimentally demonstrated. The proposed sensor is composed of a sensor pedestal, a mass block, elastic diaphragm and two reflectors, wherein the collimating reflector 1 and the reflector 2 constitute a fiber Fabry-Perot (F-P) interference cavity. By analyzing the relevant parameters of F-P interference theory, we modulate the F-P reflection spectrum with high finesse, and demodulate the F-P reflection spectrum by wavelength demodulation method to obtain the acceleration signal. Through simulation analysis and experimental verification, the resonant frequency, sensitivity and lateral anti-interference ability of the sensor have been investigated. The experimental results show that the resonant frequency of the sensor is 800 Hz, the sensitivity is 3.81 nm/g when the frequency is 300 Hz, the resolution is 0.263 mg, and the lateral anti-interference degree is less than 5 %. Furthermore, the proposed acceleration sensor exhibits the advantages of simple structure and low cost, and has great application prospects in the vibration monitoring of the pitch bearing of wind power generation. [ABSTRACT FROM AUTHOR]

• Temperature effects of fiber-based luminescent solar concentrators. • Effect of thermal cycling on the luminescence of POFs doped with Lumogen dyes. • Almost full recovery in the output intensity of Lumogen red fiber in thermal cycles. • Temperature sensitivities of 0.07 nm/°C in this doped fibers was revealed. In this paper, we report the temperature effects on the luminescence of polymer optical fibers doped with Lumogen dyes (red and orange). Specifically, we have analyzed the intensity and the average wavelength of the spectra emitted by both fibers when they are heated from 30 °C to 90 °C. An almost full self–recovery of the signal in the fiber doped with Lumogen red has been observed when the fiber is subjected to thermal cycles with oscillating temperature variations between 30 °C and 90 °C. The emitted spectra are red/blue shifted when the fiber sample is heated/cooled with a final temperature sensitivity around 0.07 nm/°C when a stationary situation is reached. [ABSTRACT FROM AUTHOR]

• A convenient and effective representation method of crosstalk is introduced. • An aligned-prime-partition (APP) algorithm for the RMSCA problem is proposed by jointly considering crosstalk and fragmentation. • Performance of the APP-RMSCA algorithm is evaluated by simulations. Space division multiplexing elastic optical networks (SDM-EONs) have become a promising technology for the next generation of optical backbone networks. Routing, modulation, spectrum and core assignment (RMSCA) problem is one of the key issues in SDM-EONs. In the RMSCA problem, spectrum fragmentation and inter-core crosstalk are two main disadvantages. In this paper, a convenient and effective representation method of crosstalk is introduced first; then an aligned-prime-partition (APP) algorithm for the RMSCA problem is proposed by jointly considering crosstalk and fragmentation. The algorithm adopts three innovational measures: partition spectrum resources into prime blocks and align the prime blocks in all cores, relax usage condition of prime blocks to increase generality of prime blocks and, define two indexes to increase continuity and contiguity of spectrum resources. Simulation results show that the proposed APP-RMSCA algorithm has a lower bandwidth blocking probability than the existing well-performed RMSCA algorithm. [ABSTRACT FROM AUTHOR]

• Low-cost and high-reliability laser cooling optical bench solution. • Free-space fiber coupling structure with extremely high thermal stability using traditional material. • The thermal deformation simulation results of opto-mechanical structure are in good agreement with the experimental results. High-reliability optical systems play an essential role in the wide application of precision cold atom quantum sensors such as cold atom clocks, cold atomic magnetometers and cold atom interferometers. Achieving thermal stability performance is especially critical because the long-term performance of a cold atom system is often ultimately limited by the thermal stability of the optical system. In this paper, we find that the material consistency of the parts on the optical bench is more important for the thermal stability of the optical system than reducing the expansion coefficient of the parts. On several optical benches with the same architecture but different fiber coupler material combinations, the minimum fiber coupling efficiency change reached approximately 3.5% in the variation range of ambient temperature from 8℃ to 43℃, and the coupling efficiency change was less than 0.3% before and after thermal cycling. In addition, a full-function optical bench for rubidium atom laser cooling was developed based on the assembly procedure of the test optical bench. In the multiple output fibers on the bench, the maximal coupling efficiency variation was less than 19% in the range of 8℃∼43℃, and the output laser power change was less than 2% in the bench before and after thermal cycling. [ABSTRACT FROM AUTHOR]

• A fiber SPR refractive index sensor with a tapered arm and U-shaped structure is proposed to increase the optical field intensity while reducing the number of higher-order modes in the cladding. • SPR sensor refractive index test with a FOM of 49.37 /RIU. • The proposed surface plasmon resonance sensor combines high sensitivity (4816 nm/RIU) and narrow full width at half maxima (97.54 nm). The figure of merit (FOM) of conventional surface plasmon resonance (SPR) sensors is low due to the low sensitivity and wide full width at half maxima (FWHM) caused by many low-intensity high-order cladding modes. To address this problem, this paper proposes a SPR sensor based on U-shaped tapered arm cascade of multimode fiber (TUMMF). The U-shaped macro-bend increases the intensity of the light field leaking into the cladding, and the tapered area makes the number of higher-order modes smaller to achieve high sensitivity and narrow FWMH sensing performance. Through simulation and experimental verification, the sensitivity of the sensor is proportional to the fiber curvature and taper ratio, and the FWMH is inversely proportional. Therefore, the parameters of the sensor are optimized by integrating the FOM and the mechanical strength of the sensor. The optimized sensor parameters are 3 mm bending diameter, 0.85 taper ratio, and 152 nm gold film thickness. The sensor was tested in the refractive index (RI) sensing range of 1.3324–1.3731 and showed a sensitivity of 4816.092 nm/RIU and a FWMH of 97.54 nm. The FOM of the proposed sensor is 49.37 /RIU, which is 3.18 times higher than that of the U-shaped multimode fiber SPR sensor. The probe has the advantages of simple fabrication, high environmental stability and easy modification, and has a wide range of applications in bioenvironmental and other fields. [ABSTRACT FROM AUTHOR]

• Minimalistic single-mode fiber biosensors are reviewed; • The fabrication methods for express, minimalistic biosensors are outlined; • A comparison between traditional and minimalistic biosensors paves the road for novel applications; • Minimalistic biosensors require the handling of quasi-random optical spectra. Optical fiber biosensors are receiving significant interest, as they allow real-time, low-limit, and high precision detection of biological analytes such as biomarkers, proteins, and small cells. Classical biosensor designs include gratings, interferometers, and plasmonic structures; however, these systems require a complex design, hard to manufacture on high volumes. Recently, several biosensors having a minimalistic design, rapid and suitable to be automated, have been proposed; the key asset is the scalability potential, in view of fabricating numerous devices for disposable use or for large parallel immunoassays. This new sensor class features reflector-less sensors, shallow tapers, and ball resonators; a pseudo-random spectrum characterizes all these biosensors. In this paper, we provide a bird-eye view of these minimalistic designs and a perspective of their use in advanced biosensing applications. [ABSTRACT FROM AUTHOR]

• Proposed a long-reach optical access network architecture (LCQ-LR-OAN) that utilizes backup resources for providing the protection and alleviating network congestion. The LCQ-LR-OAN can simultaneously support different types of users with different QoS requirements. • Proposed a partial protection strategy that provides protection to all shared optical resources while keeping the unshared optical resources unprotected. We also developed survivability and network congestion alleviating mechanisms using a single set of optical resources. • Considered user priority (e.g., FTTH, FTTC, FTTB and FTTO) with reference to providing the protection. • Proposed a novel DBA scheme (EBA) to allocate the bandwidth of the backup OLT to the LR-PONs during the network congestion periods. • The LCQ-LR-OAN requires lower cost compared to that of the other existing LR-OAN architectures. The LCQ-LR-OAN architecture does not depend on any specific PON standard, viz., EPON, GPON. Thus, it can be used with all the PON standards. In this paper, we explore a low-cost and quality-of-service (QoS)-aware long-reach optical backhaul for the wireless and fiber-to-the-x (FTTx) networks. We exploit the reserved and idle optical resources to provide protection against failures and offer extra bandwidth to the users in the network congestion hours. We use a single set of optical resources to both provide protection and reduce network congestion, thereby incurring the minimum total expenditure. For the practical network scenarios, the simulation outcomes reveal that the proposed architecture can reduce 11 - 79 % average packet delay in the network congestion hours. It offers higher connection availabilities, i.e., five-nine availability (∼ 0.99999) with full protection and four-nine availability (∼ 0.9999) with partial protection. Meantime, it requires ∼ 30 % less capital expenditure cost than the other existing benchmark and state-of-the-art long-reach optical backhaul architectures. The proposed architecture is validated by simulation studies and practical data. [ABSTRACT FROM AUTHOR]

• Using optical fiber sensing system dimensional signals in the space–time domain, a novel signal recognition method based on object detection is proposed. • The signal processing mode and the recognition results of object detection(yolov4) are discussed. • Examined the proposed method on actual pipeline. This method can significantly improves the signal recognition rate(98%), and provides good adaptability under various interference. The total length of the global oil and gas pipelines has increased rapidly during the last decades. Subsequently, prewarning systems for pipeline intrusion damage incidents have become significantly important. The traditional remote optical fiber prewarning systems however often have high false-alarm and missing alarm rates due to the complex environment that reduces signal recognition accuracy. To address this issue, in this paper we analyze the signal characteristics of various dangerous events and then use dimensional signals in the space-time domain to develop a novel signal recognition method based on object detection. Our objective is to improve recognition accuracy and reduce the false alarm rate. Our experiments and test scenarios confirm that the recognition accuracy of this method is greater than 98%. We also examined the proposed method on Pipechina MaFang to MiYun with a total length of 41 km, and show that it significantly improves signal recognition and further provides good adaptability under various interferences. [ABSTRACT FROM AUTHOR]

• An actively heated fiber optics method is proposed to monitor the grout diffusion range in goaf. • The grid installation method of AHFO is designed, and the calculation formula of grid size is deduced. • The two-dimensional positioning of optical fiber is realized, the grouting diffusion range is quantified, and the measurement accuracy is improved. • The visualization of slurry diffusion morphology is realized. The invisibility of grouting has always been one of the most challenging problems related to the research of grouting theory, but it has not been solved. An actively heated fiber optics (AHFO) method is proposed in this paper to realize the visualization of slurry diffusion morphology. The grid installation method of AHFO is designed, and the calculation formula of grid size is deduced. Based on the self-developed spatial positioning algorithm and Kriging spatial interpolation algorithm, the temperature anomaly in the AHFO temperature profile is used to locate and quantify the range of grouting diffusion in goaf. To verify the applicability of this method, a large-scale three-dimensional grouting model test was carried out. The test results show that the grouting diffusion mode is elliptical, consistent with the previous research results. Compared with the theoretical calculation results, the maximum relative error of the monitored grouting diffusion radius is 18 %. Therefore, the monitoring method can monitor the grouting diffusion. [ABSTRACT FROM AUTHOR]

• Investigated POF integrated with smartphone for HR and BR monitoring. • The performance of the POF sensor with different sensitivity zone is analyzed. • The shutter speed of the smartphone is optimized. • Investigated the POF sensor under different motion states. Human physiological signal monitoring is a key factor in diagnosing health conditions, such as monitoring heart rate and respiration. To meet the increasing monitoring requirements, such as safety, economy, and equipment miniaturization, it is necessary to optimize and improve the monitoring device. Polymer optical fiber sensor has great potential in human physiological monitoring because of their inherent safety, compactness, electrical isolation, and flexibility. In this paper, we report the integration of low-cost plastic optical fibers in smartphones for the measurement of respiratory rate and heart rate in human physiological monitoring. The performance of the plastic optical fiber (POF) sensor with different sensitivity zone is analyzed. With three sensitivity zones, the respiratory rate and heart rate can be displayed in the power spectral density simultaneously. For improving the POF sensor performance, the shutter speed of the smartphone is also optimized to 30 s−1. Finally, the POF sensor is tested under different motion states indicate that the sensor can monitor the heart rate and breathing rate under different postures (running, walking, standing, squatting and lying), where the spectral energy is 2.8 ± 0.11 × 108 pt during running and is 1.4 ± 0.55 × 107 pt in the supine state. And it also can be used to assess the dynamic posture, which is important for some potential sensory applications in clinical and home settings. [ABSTRACT FROM AUTHOR]

• The sensor can be used to monitor crack growth at structural joints. • Equal-strength beam is used to realize the desensitization mechanism of the sensor. • The sensor shows good linearity and repeatability in calibration tests. • The sensor is used in model experiments and shows good consistency with simulation. Monitoring of cracks on offshore platforms is necessary to ensure the safe operation and prolong their service life. The crack extension width is of great significance for the calculation of stress intensity factor (SIF). This paper developed a measuring device for crack extension width based on Fiber Bragg Grating (FBG) sensing technique. The designing principle was detailed introduced upon which a sensor with measuring range of 0–5 mm and sensitivity of 0.4 nm/mm was encapsulated according to engineering requirements. The calibration results indicated that the sensor has good linearity and repeatability within the design range. Based on local model experiment with prefabricated crack, results demonstrated that the sensor has high precision and feasibility for different crack damage conditions as well as good stability towards cyclic loading tests, showing potential prospective for offshore platform crack monitoring. [ABSTRACT FROM AUTHOR]

• A simple modification to the passive RDSHI to separately control the reference beam and loop feedback power. • Equal power split for the reference beam confirmed best to enhance the detectable beat order number. • Influence of the loop coupler's coefficient upon maximal beat notes studied experimentally. • Larger number of beats and better performance confirmed for the improved RDSHI scheme. This paper presents an improved scheme of a passive recirculating delayed self-heterodyne interferometer (RDSHI) for laser linewidth measurement. The proposed scheme includes two additional fiber couplers in a regular RDSHI to independently control the reference beam and the loop signal for best system performance. The analysis and experimental results have confirmed that an initial equal power split for the reference beam is best suited to enhance the maximal number of detectable beat notes. The output coupling coefficient of the fiber loop has also been experimentally studied for system optimization. The experimental results have confirmed that the proposed modification to a basic RDSHI can achieve more detectable beat notes (14 vs. 12) and finer linewidth resolution (∼14% improvement) than a basic RDSHI in our test setup of 2-km-long delay line. [ABSTRACT FROM AUTHOR]

• All fiber-optic sensor based on a Balloon-like interferometer for pH measurement was demonstrated. • The Mach-Zehnder interferometer was fabricated by bending standard single-mode fiber into a Balloon shape. • In addition to the high sensitivity, the proposed sensor exhibits a fast response time with excellent stability. In this paper, we present the fabrication of a new fiber-optic pH sensor based on the macro-bending loss properties in a droplet-shaped single-mode fiber (SMF) bending structure for the first time. To form the droplet-shaped probe, a segment of straight SMF is properly bent into a droplet shape using a short length of a thin silica capillary tube and without any splicing. By gradually varying the bending diameter of the droplet-shaped structure, interference results between the core and cladding modes, and a Mach–Zehnder interferometer (MZI) is effectively introduced within the bending section. Sodium hydroxide (NaOH) or hydrochloric acid (HCl) were added to the pH indicator utilizing buffers solution to achieve a wide pH range from 1 to 14. Experimental results show that the proposed sensor exhibits maximum sensitivity of 3.264 nm/pH and 5.336 nm/pH for acidic and alkaline solutions, respectively. In addition to the high sensitivity, the proposed sensor structure provides high sensitivity with a high linear response and good repeatability. [ABSTRACT FROM AUTHOR]

• A Gaussian mixture model (GMM) based nonuniform quantization scheme with low-bit resolution is proposed. • Our scheme can directly obtain the optimal quantized levels and has no requirement of PDF estimation. • This scheme achieves better performance compared with uniform quantization. • The performance comparison of the proposed scheme with the non-uniform quantization scheme (the Non-Parametric Histogram estimation, NPHE) based on PDF estimation is discussed. • It can be applied to use in some transmission systems with irregular signal distribution. In this paper, a Gaussian mixture model (GMM) based nonuniform quantization scheme with low-bit resolution is firstly presented in optical intensity-modulated direct detection universal filter multicarrier (IMDD-UFMC) system for increasing system performance. By utilizing the Expectation-Maximum (EM) iterative algorithm of GMM model, the optimal quantized level can be directly obtained, and then is used to realize the nonuniform quantization for reducing the digital-to-analog converter (DAC) bit resolution of UFMC signals. In this processing, the extra estimation operation of signals' probability density distribution (PDF) is not involved, which can reduce the complexity of the common non-uniform quantization scheme compared to the method based on the PDF estimation. And, the proposed scheme is further validated in a 10 Gb/s IMDD-UFMC transmission system through a 20 km fiber based the commercially OptiSystem15.0 software. And, all the results are obtained by this numerical simulation. Results verified that, in the cases of 3 ∼ 5 bit, 2.7%∼7.8% the error vector magnitude (EVM) and at least 1-dB received sensitivity improvements can be achieved compared to the uniform quantization schemes. [ABSTRACT FROM AUTHOR]

• Single edge filter LPFG sensor interrogation. • Well stablished FBG modulation technique to obtain signal related to LPFG resonance. • Data-driven approach to process frequency domain signal with simple model. • ∼5 times more precise than the traditional edge-filtering interrogation method. • ∼5 times more accurate than the traditional edge-filtering interrogation method. Optical fiber sensors have been used in several applications due to their unique advantages, such as immunity to electromagnetic interference, small size, light-weight, and robustness, for example. Long-period fiber grating (LPFG) is a type of fiber sensor with great sensitivity to several parameters, including the surrounding refractive index. However, the challenge in using LPFGs lies in their interrogation, which relates the change in optical characteristics with the measurand. This paper presents a novel method for the interrogation of LPFG sensors. This method uses a single FBG attached to a vibrating piezoelectric component and harmonic analysis of the optical power reflected by the FBG filter to estimate the resonant wavelength of an LPFG. The method was simulated to process several arc-induced LPFG spectra and achieved results comparable to the baseline method for half of the test set and improved by roughly 5 times the accuracy and precision by limiting the dynamic range. [ABSTRACT FROM AUTHOR]