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An analytical approach about the general type of step-index optical fiber modes and their variations is presented in this paper. The theoretical model is solved through our analytical method. With the boundary conditions, a composite equation set is established and solved. The precise results of all modes are achieved with a high-precision numerical solution. The modal characteristic contains the distributions of electromagnetic fields, the effective refractive index, and its tendencies. The modal sensitivity is based on the former and the partial derivative of the effective refractive index (neff/ni and neff/ri). The derivative rule of implicit functions and determinant function allows our method to analyze the sensitivity of modes. Furthermore, four qualitative deductions are derived during the process, including the qualitative analysis of modes and their constraints, supporting previous experiments. Our work is beneficial for exploiting new fiber and researching relative fiber sensors.

We give sufficient conditions for the tautness of a transversely homogenous foliation defined on a compact manifold, by computing its base-like cohomology. As an application, we prove that if the foliation is non-unimodular then either the ambient manifold, the closure of the leaves or the total space of an associated principal bundle fiber over $S^1$.

In infrared optical wireless communications, narrow beams require the perfect calibration of the base station (BS) and user terminal (UT), which cannot support multiple moving users. This paper proposes a fiber lens based optical antenna, which employs a fiber unit array and a transmit lens to generate multiple beams, achieving full beam coverage. Specifically, we first design a fiber lens to extend the spreading angle of the emitted lights. We employ the wave optics to analyze the characteristic of the fiber lens and use the geometric optics to design the parameters of the lens. With the fiber lens, we then design the optical antenna consisting of a hexagonal fiber unit array and a transmit lens. Each fiber unit generates a beam to a specific direction and different fiber units irradiate different directions. All the generated beams can fully cover the communication area. Thus, the BS has the potential to support multi-user communication via multiple beams. Simulation results verify the performance of the designed fiber lens and the optical antenna achieving full beam coverage.

In this paper, the Sagnac interferometer with a one-way optical fiber ring and a novel dual Sagnac distributed fiber vibration sensor with an asymmetrical structure for disturbance localization is proposed. The two Sagnac interferometers in this system are asymmetrical and equal in the lengths of optical paths. Using time delay estimation based on cross-correlation, the disturbance localization can be calculated from the two demodulated phase signals. The localization precision is ±10 m with a 50 km sensing fiber and the overall localization error is 0.02%. The time error problem possibly existing in the fiber sensing systems based on time delay estimation is firstly studied. Due to the design of equal optical path lengths, the time error problem does not exist in this system, which is a possible reason for high localization precision. The system has application potential in long-distance perimeter security and many other fields.

An accurate power map is mandatory to evaluate the performance of optical fiber transmissions in the nonlinear transmission region. In this letter, we discuss the performance variation in dispersion unmanaged fiber links due to power excursions, overarching the fiber nonlinearity that imposes a fundamental limit on the capacity of optical fiber transmissions. After using digital back-propagation (DBP) in optical fiber transmissions, the performance degradation due to power excursions shows different characteristics, depending on the location of the power excursion. Further, due to the cascading effect of the nonlinear signal-noise interaction (NSNI), the power excursion on the latter spans exerts a greater impact than that on the front spans. We implement a polarization-multiplexed 16-QAM over 12 spans of standard single-mode fiber (SSMF) experiment. The experimental results verify our theoretical analyses that the received SNRs after DBP can be sensitive to the power excursion and its location.

Equivalent-graded-index photonic-crystal fiber (EGI-PCF) is a modified photonic-crystal fiber (PCF) where the cladding is not required to be periodic. A radial gradient of the equivalent refractive index distribution provides extra freedom to efficiently tailor the dispersion of EGI-PCF. However, such additional complexity makes the manual fiber design much more challenging where the time consumption becomes too much to be afforded eventually. In this paper, we for the first time propose the method of computer-aided inverse fiber design (CAFD) based on empirical dispersion formula to circumvent this hurdle. We apply the differential evolution (DE) genetic algorithm to seek for the optimized EGI-PCF design with a target of specific dispersion profile. In the dispersion oriented EGI-PCF design, the use of empirical formula instead of numerical simulation (e.g., finite-element method) is proved to greatly reduce the run-time of CAFD and simplifies the fitness function evaluation as much as possible. We adopt our method and demonstrate a design of EGI-PCF with a near-zero ultra-flattened dispersion in the whole S+C+L band, which merely costs a few seconds of a laptop to return an optimized fiber design. Thus improvement of efficiency is about three orders of magnitude faster than any previous CAFD attempts as far as we learn. In the end, we use our method to explore an EGI-PCF design with a unique dispersion profile of all-normal dispersion-decreasing along the fiber length centered around 1 μm that plays a key role for the self-similar pulse evolution in a fiber laser/amplifier.

Purpose Seepage of the dam is an important safety problem, which may cause internal erosion of the structure. In the field of seepage monitoring in civil engineering, the distributed optical fiber sensing technology based on the temperature tracing method has been paid more attention due to its unique advantages of high sensitivity, good stability and high resolution. The purpose of this paper is to make a review of the existing related research, so as to facilitate the later scholars to understand and further study more systematically. Design/methodology/approach In this paper, three kinds of commonly used distributed fiber temperature measurement technologies are introduced. Based on the working principle, monitoring system, theoretical analysis, experimental research and engineering application of the fiber seepage monitoring technology, the present situation of dam seepage monitoring based on distributed fiber is reviewed in detail and their advantages and disadvantages are compared. Findings The thermal monitoring technology of seepage measurement depends on the accuracy of optical fiber temperature measurement (including the accuracy of the system and the rationality of the discrimination method), the correct installation of optical fiber and the quantitative analysis of temperature data. The accuracy of the current monitoring system can basically meet the existing measurement requirements, but the correct installation of optical fiber and the calibration of temperature data need to be further studied for different discrimination methods, and this field has great research value. Originality/value At present, there are many applications and research studies of optical fiber sensing in the field of structural health monitoring, and there are also reviews of related aspects. However, there is little or no review only in the field of seepage monitoring. This paper summarizes the research and application of optical fiber sensing in the field of seepage monitoring. The possibility of the gradient method to find its new prospect with the development of monitoring systems and the improvement of temperature resolution is discussed. The idea of extending the seepage monitoring method based on distributed optical fiber thermal monitoring technology to other monitoring fields is also given in the paper.

In this letter, we propose a novel 3D shape sensing algorithm for flexible endoscopic surgery using multi-core fiber Bragg grating (FBG) sensors. Considering the signal noises and environmental perturbations, the direct use of FBG measurements for shape sensing and position estimation is regarded as far from accurate and stable, especially when utilized in the sensing of long and flexible surgical instruments. To solve this problem, a novel and generic model-based filtering technique for the iterative curvature/twist estimation by taking advantage of the configurations of the multi-core FBGs in the optical fiber is introduced to remedy the sensory noises. Besides, we introduce an enhanced moving average approach to smooth the estimated curvatures and twists spatially on the fiber. We extensively validate our algorithm by conducting shape sensing tasks in simulations under varying conditions, and in experiments using a robotic-assisted colonoscope system integrated with a multi-core FBG fiber. The results prove our method substantially outperforms the conventional approach in the aspect of estimation accuracy and robustness, showing the superiority and application feasibility.

Optical communication either in free space wireless mode or optical fiber mode is much preferred for high data transmission rate in the range of 100 GHz or few THz. Implementation of OFDM in fiber helps to simplify the dispersion compensation but nonlinearity in fiber material will become a major challenge. This Chapter is review and literature survey about the development and possibilities for OFDM in optical fiber communication systems. It presents the basic features of OFDM and its impact on the mitigation of optical fiber impairments.

Optical fiber sensing technology has developed rapidly since the 1980s with the development of the optical fiber and fiber optical communication technology. It is a new type of sensing technology that uses light as a carrier and optical fiber as a medium to sense and transmit external signals (measurands). Distributed fiber optical sensors (DFOS) can continuously measure the external physical parameters distributed along the geometric path of the optical fiber. Meanwhile, the spatial distribution and change information of the measured physical parameters over time can be obtained. This technology has unmatched advantages over traditional point-wise and electrical measurement monitoring technologies. This paper summarizes the state-of-the-art research of the application of the distributed optical fiber sensing technology in geo-engineering in the past 10 years, mainly including the advantages of DFOS, the challenges in geo-engineering monitoring, related fundamental theoretical issues, sensing performance of the optical sensing cables, distributed optical fiber monitoring system for geo-engineering, and applications of optical fiber sensing technology in geo-engineering.

A module has been designed for automated acquisition and preliminary processing of optical signals from devices based on a fiber laser with frequency self-sweeping. The primary processing, i.e., pulse-by-pulse data normalization, is performed using a microcontroller. Signals are then transmitted to a personal computer for further processing in the form of the dependence of the signal amplitude on the pulse number. The optimal characteristics of the used analog-to-digital converter are as follows: the sampling rate is 5 MHz and the bit depth is at least 8 bits. The operation of the module was tested in an optical frequency reflectometer for interrogating fiber sensors.

Recognizing objects directly from optical fiber output images is useful in endoscopic applications when forming a clear image of the object is unnecessary or rather difficult. Conventional fiber-optic systems, such as multicore-fiber-based and multimode-fiber-based systems, suffer from the sensitivity of the fiber to external perturbations. For example, a slight movement of the fiber (a-few-millimeters translation of the tip for meter-long multicore fibers or multimode fibers) can greatly change the output images of the system. In this work, we utilize the light guidance stability of recently proposed glass-air Anderson localizing optical fiber (GALOF) to achieve robust imaging-free objection recognition. We transport five classes of cell images through an 80-cm straight GALOF. A deep convolutional neural network is trained to classify the output images and tested on images never seen, namely, images collected when the fiber is bent or when the fiber facet is placed several millimeters away from the object without any distal optics. Bending-invariant high classification accuracy (86.8% on average) is observed all the way to the maximum bending offset distance of 45 cm (∼74thinsp;° bending angle). High classification accuracy (91.2%) is also preserved when the fiber facet is 0.5 mm away from the object.

As we all know, the change of mode interference caused by the curvature change in multi-mode fiber (MMF) can be well represented as a fiber specklegram recorded by CCD (Charge-coupled Device). However, it's difficult to identify the different bending occurred in several points in short distance. The paper proposes plastic fiber bending sensors can be used to detect the multi-point bending without adding any hardware. The convolutional neural network was used to classify the output speckles under different bending states. Specklegrams from fiber with three sensitization areas can be recognized by the neural network with a bending interval of 15°,10° and 5° with an accuracy rate of 99.2%, 96.1% and 93.5% respectively. Compared with traditional multi-point distributed sensors, this method is lower cost and easier to operate. The method proposed in this paper can find applications in distinguishing the status of certain structures, such as robotic arms and some disabled auxiliary equipment.

In this paper, we propose a distributed optical fiber vibration sensing system based on Φ-OTDR and Michelson interferometer. It can detect multiple vibrations simultaneously along a sensing fiber, and the vibration waveform, frequency, position and amplitude could be demodulated correctly using our proposed PGC demodulation algorithm. The experimental results show, a SNR of 34.86 dB is achieved with the background noise level of − 37 dB at the 1000 m, and the SNR is 28.09 dB with the background noise level of − 32 dB at the 6000 m.

Cosmic ray muons are widely used to study the internal structure of different large-scale natural and artificial objects. The technique is called muonography in analogy with radiography. In this work, results are presented from tests of different elements of the detecting system of the muon hodoscope under development at MEPhI.

The problem of information protection against unauthorized access is considered and the results of a comparative analysis of methods for extracting information from an optical fiber are presented. A method for detecting the formation of channels of information leakage, which is performed in various ways, is proposed for the successful struggle against unauthorized access. Among the analyzed methods for forming information leakage channels in a fiber-optic communication line, the simplest method involves bending the optical fiber to disturb the conditions for the total internal reflection. In this case, the monitoring system must track the introduced losses made in order to detect fiber bends.

A recent topic of considerable interest in the "smart building" community involves building interactive devices using sensors, and rapidly creating these objects using new fabrication methods. However, much of this work has been done at what might be called hand scale, with less attention paid to larger objects and structures (at furniture or room scales) despite the fact that we are very often literally surrounded by such objects. In this work, we present a new set of techniques for creating interactive objects at these scales. We demonstrate fabrication of both input sensors and displays directly into cast materials -those formed from a liquid or paste which solidifies in a mold; including, for example: concrete, plaster, polymer resins, and composites. Through our novel set of sensing and fabrication techniques, we enable human activity recognition at room scale and across a variety of materials. Our techniques create objects that appear the same as typical passive objects, but contain internal fiber optics for both input sensing and simple displays. We use a new fabrication device to inject optical fibers into CNC milled molds. Fiber Bragg Grating optical sensors configured as very sensitive vibration sensors are embedded in these objects. These require no internal power, can be placed at multiple locations along a single fiber, and can be interrogated from the end of the fiber. We evaluate the performance of our system by creating two full-scale application prototypes: an interactive wall, and an interactive table. With these prototypes, we demonstrate the ability of our system to sense a variety of human activities across eight different users. Our tests show that with suitable materials these sensors can detect and classify both direct interactions (such as tapping) and more subtle vibrations caused by activities such as walking across the floor nearby.

A novel chaotic optical time-domain reflectometry (OTDR)-based approach was proposed for monitoring long-haul fiber communication systems with multiple fiber segments. The self-phase modulation and group velocity dispersion effects of the optical cable was considered in demonstrating the proof-of-concept experiment and simulation. In experiments, the correlation peaks are clearly obtained from the correlation trace between the reference and reflected (or scattered) light signals propagating in three optical-fiber segments. The technique affords a high spatial resolution of 2 m, and further long-haul fiber simulations indicate that the sensing distance can be more than 3300 km. Thus, the new proposed technique can be effectively applied for health monitoring of long-haul fiber communication systems.

This paper studies optical soliton pulses. The Kundu–Mukherjee–Naskar equation is considered because this model describes the propagation of soliton dynamics in optical fiber communication system. Bright, dark, singular, combo bright-dark solitons are emerged from the Riccati function, sine-Gordon function, F-expansion and functional variable principles.

We consider threefold del Pezzo fibrations over a curve germ whose central fiber is nonrational. Under the additional assumption that the singularities of the total space are at worst ordinary double points, we apply a suitable base change and show that there is a one-to-one correspondence between such fibrations and certain nonsingular del Pezzo fibrations equipped with a cyclic group action.

Fiber reinforced concrete is an emerging material in civil engineering with many desirable properties. However, material model for this material has not been yet firmly established. Failure model has a particular property: fibers do not break in failure, they got pulled-out of the concrete matrix. Accordingly, the bond between the fiber and the matrix (bond-slip law) strongly influences material behavior in failure. In attempts to experimentally determine the bond-slip law rather large spread in results becomes evident. This variance in results can be simulated by replacing the deterministic model with the stochastic description based on the idea from the fiber bundle model. Stochastic parameters are difficult to guess so mathematical procedure based on inverse analysis has been devised. The inverse model relies on the non-linear least squares approach combined with order statistics. This novel procedure successfully extracts stochastic bond-slip parameters from experimental results.

An optical fiber sensing sensor based on modified generalized cross-correlation algorithm is proposed, which could be used for distributed vibration detection. This sensor consists of double Sagnac interferometers connected by sensing fiber, which has a higher accuracy with the help of digital filtering and a simpler calculation because of conjugate multiplication. The impact, narrowband and broadband vibrations could be located, by means of the extraction of time delay between output signals. In this system, the positioning error on the sensing fiber of 5 km in length is stable less than 100 m.

A deep-learning-based time–frequency domain signal recovery method is proposed to deal with the signal distortion in fiber-connected radar networks. In this method, the deteriorated signal is converted to the time–frequency domain, and a two-dimensional convolutional neural network is used to conduct signal recovery before inverse conversion to the time domain. This method can achieve high-accuracy signal recovery by learning the complete features in both time and frequency domains. In the experiment, distorted linear frequency modulated radar signals with a bandwidth of 2 GHz after 8-km fiber transmission are recovered with the noise effectively suppressed. The proposed signal recovery method works well under different input signal-to-noise ratios. Specially, the average peak to floor ratio after radar pulse compression is improved by 25.5 dB. In addition, the method is proved to be able to recover radar signals of multiple targets.

The integration of quantum key distribution (QKD) devices with the existing optical fiber networks is of great significance in reducing the deployment costs and saving fiber resources. Wavelength division multiplexing (WDM) is expected to be a desirable approach to fulfill this ultimate task. In this paper, we analyze the dominant noises in WDM-based QKD system and optimize the key parameters based on a modified model with 200 GHz channel spacing. Then, an appropriate decoy-state method is adopted to estimate the system performance considering statistical fluctuations. Finally, a three-layer artificial neural network is used to train and predict the optimal mean photon numbers within different situations. Our work provides a useful method for the parameters optimization of WDM-QKD system and accelerates the practical development of QKD that coexists with the current backbone fiber infrastructure.

Femtosecond point-by-point inscription through protective plastic coating is a modern method of inscription of gratings, grating complexes, and other complex fiber devices. By using this inscription method, fiber devices with unique characteristics can be obtained. For the output parameters of the products to meet the requirements, a control system for the inscription was developed. A method for optical control of the fiber position during inscription, a method for determining the position of the core, and an auto-alignment system are proposed. All this made it possible to create not only simple, but also apodized FBG with arbitrary apodization profile. Through the automation of the inscription process of fiber devices, it was possible to achieve good results, both in the quality of the output products, and in the speed of inscription. This article describes the implementation of the proposed methods, the problems that had to be faced when building a control system and analyzes the results of the proposed control system. The results show that the use of the auto-alignment of a transparent ferrule with fiber by piezoceramic stage with feedback through the processed image of the fiber core in this ferrule makes it possible to inscript various FBG and FBG complexes that are competitive and in demand on the market.

SUMMARY The image processing of muscular fibers has seen significant improvements over the last decades, from light microscopy acquisition to virtual microscopy and from manual segmentation and fiber typing to automatic. The present study aims to discuss the main tools employed in different histo-enzymological image processing phases applied to muscle fibers, which are respectively: the acquisition, segmentation and fiber typing as well as their efficiency in the determination of morphometric parameters. First, the acquisition: to count the cell numbers within the muscle fiber sections, optical microscopic images with different magnifications (x100, x200, x250, and x400) were compared with virtual slides digitized by Slide Scanner. Second, the segmentation: Three softwares (Fiji “Digitizing pen, Mouse”, Image Pro Plus 10 [semi-automatic], and Cytoinformatics LLC [automatic]) were compared for image segmentation quality and the determining of fiber numbers. Third, manual fiber typing: employing Fiji of segmented images using the 3 previously mentioned softwares were performed to calculate the accuracy of the morphometric parameter (Cross sectional Area [CSA], perimeter and Minimal Feret's Diameter [MFD]). The results of the acquisition showed that the scanner slides have a better resolution and detected a higher number of cells than when optical microscopes with different magnifications were used; with the latter, the processing can be performed only with an acceptable resolution, where the number of cells is lesser, which unfortunately requires several repetitions and exhausting work. Our findings regarding segmentation indicate that the Cytoinformatics LLC showed the best processing time and the highest quality followed by IP and Fiji. Finally and for the ultimate step, the morphometric parameter calculation: showed that the best accuracy was attained by using Fiji followed by Cytoinformatics and finally by IP. The findings of this study suggest that Fiji (semi-automatic) showed the best quality/price ratio (open access software) for segmentation and fiber typing, but it proved to be time consuming when compared to Image Pro Plus 10 (semi-automatic) and Cytoinformatics LLC (automatic).

In the framework of radio astronomic systems, and in particular in the realization of the Aperture Array Verification Systems of the low frequency part of the Square Kilometre Array project, a monitoring of the delay introduced by the fiber optic cable of the antenna downlink is necessary in order to properly calibrate the receiver chain. A simple and relatively low-cost system is here proposed, which can directly provide such measurement without the use of complex post-processing systems, with precision estimated in 60ps for 6Km of fiber length.

A flexible fiber acoustic transducer is created by designing a parallel configuration of a Rubidium iron boron (NdFeB) magnet fiber and an aluminum fiber. The former provides a stable magnet field, while the latter vibrates to phonate upon applying alternating current or generates alternating voltage in the sound field. This single device exhibits dual functions as a loudspeaker or a microphone. As a fiber loudspeaker, it can generate 40-60 dB of audible (20 Hz-20 kHz) and directional sounds which can be used for blind navigation and controllable sound field distribution. The fiber acoustic transducer functions as a microphone when external sound waves force the aluminum fiber to vibrate. After the fiber microphones are woven into several different positions of a piece of clothing, the sound source can be accurately located based on the time differences reaching different microphones. This wearable fiber acoustic transducer is promising to be used to quickly search people in trouble during emergency rescue activities such as earthquakes or fires.

We experimentally demonstrate a high-precision time synchronization system over a fiber-optic network with an equivalent 2400 km backbone link and a 60 km urban access link. Time signals aligned with the master station can be available at arbitrary station over the backbone and access links. Moreover, link calibrations are not required, which decreases the operation and maintenance cost significantly. The high-precision, easy-to-implement and telecom-network-compatible time synchronization system demonstrated here opens up a possibility to providing synchronized time signals to multiple users over the public telecom fiber networks.

For flow-enhanced crystallization in fiber spinning, the viscoelastic two-phase fiber models by Doufas et al. (J. Non-Newton. Fluid Mech., 2000) and Shrikhande et al. (J. Appl. Polym. Sci., 2006) are state of the art. However, the boundary conditions associated to the onset of crystallization are still under discussion, as their choice might cause artificial boundary layers and numerical difficulties. In this paper we show that the model class of ordinary differential equations is singularly perturbed in a small parameter belonging to the semi-crystalline relaxation time and derive asymptotically justified boundary conditions. Their effect on the overall solution behavior is restricted to a small region near the onset of crystallization. But their impact on the performance of the numerical solvers is huge, since artificial layering, ambiguities and parameter tunings are avoided. The numerics becomes fast and robust and opens the field for simulation-based process design and material optimization.

When light with object information passes through a multi-core fiber, the speckle pattern is obtained. The reconstruction of the original image from the speckle pattern is crucial. In this paper, we propose a lightweight adversarial network for reconstruct image from the speckle pattern. Combining the characteristics of U-Net network and Mobile-Net, a lightweight Mobile-U-Net network is formed to reduce the number of network parameters by using deep separable convolution to realize fast reconstructing image. The adversarial network is also introduced to restrain the quality of the restored image and solve the quality problem of the restored image further. Thus, a high-quality reconstructing image can be achieved.

This paper presents a sharp review of the current state-of-the-art related to the fiber optic sensors with (i) gratings (namely, fiber Bragg gratings, i.e., FBG and long period fiber gratings, i.e., LPG) and (ii) plasmonic nanostructures (metallic/non-metallic gratings, corrugations, and arrays). The objective of this review is to highlight the importance of these areas in terms of their high sensing performance and the great potential they possess for developing plasmonics-based fiber optic chemical and biosensors with even higher levels of performance in the future. In line with the above objectives, the selected salient works are revisited while beginning with the earliest works on general fiber SPR sensors as well as both the above-mentioned areas. In this process, the review makes a thoughtful attempt to spot the possible future scope and emergent themes in these research areas. The review will be able to provide adequate directives to the researchers willing to take up these areas as their future endeavors.

The design idea and complete system design scheme of crack monitoring system based on fiber micro-bending principle are proposed. The simulation test platform of crack monitoring system is constructed, which provides theoretical and technical guarantee for crack monitoring test based on fiber sensing. A crack monitoring technique based on oblique fiber optic sensing network is proposed, and the angle of skew between the fiber and the crack is equal to 60. Time is the best sensor network deployment solution. The technical method has the advantages of simple process, low cost, easy implementation, and ability to realize distributed measurement. A crack monitoring technology based on microbend sensitized fiber sensor head is proposed. The quantitative relationship between optical loss and crack width of sensitized fiber sensor network is established, and microbend sensitized fiber sensor head is designed and fabricated. The technical method can accurately locate and accurately measure concrete cracks under the condition of unknown crack direction, and the test precision reaches 0.05 mm, which is completely suitable for high-precision and distributed monitoring of concrete cracks, and can be used in concrete bridges and dams. Widely promoted and applied in crack monitoring such as tunnels.

Inspired by the outstanding performance of artificial intelligence for various tasks, in this work we explore a new method for the fiber modal demodulation based on convolutional neural networks (CNN). The neural network is trained by using a self-made data set and is utilized to obtain the rough modal information. Based on this initial information, the interior point (IP) algorithm is afterward used to explore the precise optimal value. Simulation results indicate that this approach has stable performance and excellent accuracy. In addition, the method also has a satisfactory real-time characteristic.

An optical fiber acoustic sensor based on the combination of generalized cross-correlation and improved minimum control recursive average algorithms is proposed. The sensing system consists of a double Sagnac interference structure that picks up acoustic signals along the sensing fiber. The improved minimum control recursive average algorithm is used to preprocess the acquired signal to improve the signal-to-noise ratio, then the time-delay information is obtained through the correlation operation on the processed signal, and the acoustic source is located through the time delay information. Experiments show that under the condition of high signal-to-noise ratio of the acquired signal, the accuracy of acoustic source localization can be improved.

This paper proposes an endpoint detection method based on short-time Fourier transform (STFT), which can be applied to fiber optic interferometric vibration sensing systems. This scheme consists of time-frequency analysis, feature extraction and thresholds judgment. Field experimental results demonstrate that the average error of 100 experiments of the proposed scheme is lower than the error of the short-time zero-crossing ratio method. The mean processing time (0.149 s) is lower than the sampling time (0.3 s), which allows the system to perform continuous in-field intrusion detection related applications.

In this letter, we present a new soft and flexible sensor which can reconstruct its surface shape in real time. A single-core optical fiber with fiber Bragg gratings (FBGs) is capable of detecting sparse local strains at high bandwidth using wavelength-division multiplexing. The fiber was embedded into an elastomeric substrate to reconstruct its global surface morphology. Finite element analysis was used to determine the design parameters, and also to validate the unique mapping from sparse strain measurements to the continuum shape of the sensor. To simplify the fabrication and error compensation process without precise/prior knowledge of the FBG locations in the sensor, machine learning-based modeling was applied. This enables real time, robust and reliable shape reconstruction. It is demonstrated to outperform various applications of electronics-based sensors, which require sophisticated electrode wiring and noise reduction. Experiments were performed to evaluate the sensing accuracy and repeatability.

Let P(G) denotes the set of sizes of fibers of nontrivial commutators of the commutator word map. Here, we prove that |P(G)|=1, for any finite group G of nilpotency class 3 with exactly two conjuga...

The state of a soliton is characterized by the eigenvalues of the Zakharov–Shabat problem. The data transfer rate in the fiber-optic communication lines that use eigenvalues for coding signals can be significantly increased only by developing optical eigenvalue control methods. We propose to use optical fibers with a sinusoidally changing dispersion to generate given sets of complex eigenvalues and to detect soliton states. Under the action of a periodic change in dispersion, multisoliton pulses divide into several solitons moving at different group velocities. This effect can be used to prepare fixed sets of eigenvalues. A soliton signal can be recognized by analyzing pulses and their spectra at the exit from a fiber with a periodically changing dispersion. Using the solitons specified by sets of four eigenvalues, we show that the field at the exit from a fiber corresponds to a unique combination of the spectrum and the number of pulses determined by initial eigenvalues.

Universal fiber is an optical fiber that supports both multimode and single-mode transmission. It is a multimode fiber with a mode field diameter of the fundamental mode roughly matching that of a standard single-mode fiber. In today's short-distance communications, both multimode fiber and single-mode fiber are used. Universal fiber can accommodate the needs of single-mode and multimode transmission so that end users can take advantage of the cost and performance benefits of each transmission type. In this paper, we present the design and properties of universal fiber, as well as its transmission performance for 100G systems. We also explore several application scenarios where the fiber can be utilized. In particular, we illustrate how the fiber can be used in 5G wireless fronthaul applications to meet the current needs while providing a path for future upgrades. Testing results and discussions of practical issues are also presented.

When developing the Fiber Optics Gyro Astrix™ family, Airbus and Ixblue faced the problematics of the possible radiation effects on optical and opto-electronics parts. After bibliographic research on the subject, selection of parts was made according to existing knowledge, and batch qualification tests performed to quantify the radiation effects. On-ground test results were introduced in worst case optical budget for the optical loop dimensioning. Several years later, following consequent in-orbit data gathering, we can assess that radiation effect are barely noticeable and that inertial performances remain tremendously stable. The careful design of the Astrix optical loop and the proper selection of opto parts were mastered key factor for such an in-flight success.

We propose a novel fiber-optic auditory nerve of ground (FANG) in the suburb based on the fiber-optic distributed vibration sensor (DVS). The feasibility and effectiveness of the principle prototype FANG for traffic flow monitoring are proved and investigated by the field experiment. One of the 31.8 km-long redundant optical fiber of the buried optical-fiber cable for data transmission is utilized as the sensing fiber. Then, the phase-sensitive optical time-domain reflectometer (φ-OTDR) based DVS is realized and regarded as the FANG. The vibration events at 9 observation points with different ground conditions along the sensing fiber are detected by a threshold algorithm during 6.5 hours from 8:00 am. Then, the vibration events are analyzed in combination with the ground conditions to recognize the machine working in the factory, rammer working and the vehicles passed through near different areas and roads. The traffic flow is estimated by the vibration-counting with a counting error that is believed to be in an acceptable range. The distribution and the fluctuation trends of the estimated traffic flow are useful and enlightening for the traffic monitoring and pre-warning of special events, such as an accident. The accuracy can be improved by artificial intelligence methods in the future. It seems that our proposed FANG can be a potential and effective tool for the internet of things, smart ground and smart traffic in the suburb where the video and other information collection methods are not available.

The new piezoelectroluminescent optical fiber sensors are developed for integration into composite structures for the purpose of specified diagnosing and monitoring spatial distributed scalar and tensor physical and mechanical fields, in particular, the temperature, pressure and volumetric deformed state in the loaded composite designs by processing results of intensities for integrated mono or multi-colour light signals at the exit of the sensor fiber. New schemes of the functioning and numerical processing algorithms of informative integrated light signals at the exit of optical fiber sensors were developed. The informative light signal appears as a result of «mechanoluminescent effect» by interaction of piezoelectric and electroluminescent of the sensor layers. Light signals are transmitted via optical fiber to a «receiver analyzer»; control electric signals on the electrodes allow to find locations of heterogeneities of diagnosed fields along the length of the sensor. Results of numerical modeling the «scanned» real distributions and its density functions of the diagnosed fields along the length of sensors are presented; density functions are solutions of the Fredholm integral equation of the 1st kind with the use of the new developed processing algorithms of informative integrated light signals at the exit of the optical fiber.

In article was consider the latest approaches to using the moder up to date technologies in the organization of knowledge bases witch basis on modern information data base technologies (POSTGRESQL, MONGO {DB}) focused on working with Big Data in multicomponent fiber optic information networks (MCFON). The proposed approaches and architecture can be used to create new generation optical distributed networks (such GRID architecture) using high-speed channels (Fiber Optical 5NGi Internet) and parallel GRID based architectural with artificial intelligence algorithms (AIs).

[EN] This paper describes a study of the influence of strain measurement uncertainty on sensing curvature and bending direction, considering one of the most widely used fiber geometries for sensing applications (7-core Multicore Fiber) with different core spacings (distance between outer cores and fiber axis). The Monte Carlo method was proposed to simulate the real measurement process and 33 simulations with 106 iterations were performed to determine the laws of propagation of strain measurement uncertainty in calculating curvature and bending direction. The outcomes, which show the strong influence of strain uncertainty and core spacing on the precision of Multicore Fiber sensors, can be used to support the design of new sensors or new fiber geometry and to predict their achievable performance., This work was carried out within the ITN-FINESSE framework, funded by the European Union's Horizon 2020 Research and Innovation Program under the Marie Sklodowska-Curie Action Grant Agreement No 722509. It was also supported by the Ministry of Economy and Competitiveness of Spain under the project DIMENSION TEC-2017-88029-R.

Neurological and psychiatric conditions pose an increasing socioeconomic burden on our aging society. Our ability to understand and treat these conditions relies on the development of reliable tools to study the dynamics of the underlying neural circuits. Despite significant progress in approaches and devices to sense and modulate neural activity, further refinement is required on the spatiotemporal resolution, cell-type selectivity, and long-term stability of neural interfaces. Guided by the principles of neural transduction and by the materials properties of the neural tissue, recent advances in neural interrogation approaches rely on flexible and multifunctional devices. Among these approaches, multimaterial fibers have emerged as integrated tools for sensing and delivering of multiple signals to and from the neural tissue. Fiber-based neural probes are produced by thermal drawing process, which is the manufacturing approach used in optical fiber fabrication. This technology allows straightforward incorporation of multiple functional components into microstructured fibers at the level of their macroscale models, preforms, with a wide range of geometries. Here we will introduce the multimaterial fiber technology, its applications in engineering fields, and its adoption for the design of multifunctional and flexible neural interfaces. We will discuss examples of fiber-based neural probes tailored to the electrophysiological recording, optical neuromodulation, and delivery of drugs and genes into the rodent brain and spinal cord, as well as their emerging use for studies of nerve growth and repair.

This paper presents a topology optimization method for the sequential design of material layout and fiber orientation in functionally graded fiber-reinforced composite structures. Specifically, the proposed method can find the optimal structural layout of matrix and fiber materials together with optimal discrete fiber orientations. In this method, an orientation design variable in the Cartesian coordinate system is employed with a conventional density design variable. The orientation design variable controls not only the fiber orientation, but also fiber volume fraction. The fiber volume fraction control can be used to relax the orientation design problem and simultaneously design a functionally graded structural layout of fiber material. To avoid intermediate fiber orientations and achieve discrete fiber orientation design, a penalization scheme is applied to the orientation design variable. For solving the optimization problem which involves multiple design variables such as the density variable, fiber orientation variable, and target discrete orientation set, a three-step sequential optimization procedure is proposed. In this procedure, the result for each step provides the isotropic design, continuous fiber orientation design, and functionally graded discrete orientation design, respectively. To validate the effectiveness of the proposed approach, numerical examples for structural compliance minimization and compliant mechanism design are provided.

Virtual and augmented reality are rapidly developing technologies, but their large-scale penetration will require breakthroughs in the optical architecture. Unlike electronics that has rapidly evolved and shrunk in size following Moore’s law, the appearance and the underlying physics of lenses have not changed much. In this talk, we would like to show a path to a future VR/AR platform based on the meta-optics. We show millimeter-scale-diameter, high-NA, sub-micron thin, metasurface-based lenses that achieve diffraction-limited achromatic focusing of the primary colors by exploiting constructive interference of light from multiple zones and dispersion engineering meta-atoms. We further demonstrate a VR system based on a home-built fiber scanning near-eye display..

PURPOSE Fiber Optic RealShape (FORS) is a new technology that visualizes the full three-dimensional shape of medical devices, such as catheters and guidewires, using an optical fiber embedded in the device. This three-dimensional shape provides guidance to clinicians during minimally invasive procedures, and enables intuitive navigation. The objective of this paper is to assess the accuracy of the FORS technology, as implemented in the current state-of-the-art Philips FORS system. The FORS system provides the shape of the entire device, including tip location and orientation. We consider all three aspects. METHODS In bench experiments, we determined the accuracy of the location and orientation of the tip by displacing and rotating the fiber end, while allowing the rest of the fiber to change shape freely. To test the accuracy of the full shape, we have placed the fiber in a groove, which was accurately machined in a thick, stiff metal "path plate." We then compared the reconstructed shape with the known shape of the groove. RESULTS The tip location is found with submillimeter accuracy, and the orientation is sensed with milliradian accuracy. The shape of a fiber in the path plate faithfully follows the known shape of the groove, with typical deviation less than 0.5 mm in the plane of the plate. Out of plane accuracy, perhaps slightly less relevant clinically, is more challenging, due to the influence of twist; yet even out of the plane, the deviation is only submillimeter. CONCLUSION The technology achieves submillimeter precision and provides full three-dimensional shape, surpassing the reported precision of other navigation and tracking technologies, and therefore may potentially alleviate the need for fluoroscopy.