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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 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.

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.

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.

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.

Built on the hybrid immersed boundary/finite element (IB/FE) method, fluid–structure interaction (FSI) simulations of aortic valve (AV) dynamics are performed with three different constitutive laws and two different fiber architectures for the AV leaflets. An idealized AV model is used and mounted in a straight tube, and a three-element Windkessel model is further attached to the aorta. After obtaining ex vivo biaxial tensile testing of porcine AV leaflets, we first determine the constitutive parameters of the selected three constitutive laws by matching the analytical stretch–stress relations derived from constitutive laws to the experimentally measured data. Both the average error and relevant R-squared value reveal that the anisotropic non-linear constitutive law with exponential terms for both the fiber and cross-fiber directions could be more suitable for characterizing the mechanical behaviors of the AV leaflets. We then thoroughly compare the simulation results from both structural mechanics and hemodynamics. Compared to the other two constitutive laws, the anisotropic non-linear constitutive law with exponential terms for both the fiber and cross-fiber directions shows the larger leaflet displacements at the opened state, the largest forward jet flow, the smaller regurgitant flow. We further analyze hemodynamic parameters of the six different cases, including the regurgitant fraction, the mean transvalvular pressure gradient, the effective orifice area, and the energy loss of the left ventricle. We find that the fiber architecture with body-fitted orientation shows better dynamic behaviors in the leaflets, especially with the constitutive law using exponential terms for both the fiber and cross-fiber directions. In conclusion, both constitutive laws and fiber architectures can affect AV dynamics. Our results further suggest that the strain energy function with exponential terms for both the fiber and cross-fiber directions could be more suitable for describing the AV leaflet mechanical behaviors. Future experimental studies are needed to identify competent constitutive laws for the AV leaflets and their associated fiber orientations with controlled experiments. Although limitations exist in the present AV model, our results provide important information for selecting appropriate constitutive laws and fiber architectures when modeling AV dynamics.

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.

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.

The work presents modeling results of the fiber-optic multi-sensory strain measurement system for load sensing wheel hub bearings based on the addressed fiber Bragg structures (AFBS) with two symmetrical phase shifts. The system includes six strain sensors attached to the outer ring of the bearing and one senor isolated from strain for temperature compensation. The results of the numerical modeling are presented, as well as the simulation results of a complete optoelectronic interrogation scheme, which confirm the high accuracy of the AFBS central wavelengths determination by means of the microwave-photonic interrogation approach. The proposed load-sensing bearings can be used to estimate of the loads acting on the wheels of the vehicle, which serve as input parameters for active safety systems or fully automated driving, in order to enhance their effectiveness and safety of the vehicle.

Fiber positioning technology is widely used in spectroscopic telescopes, and the accurate identification of the fiber position on the focal plane directly affects the efficiency of the astronomical spectrum. At present, fiber positioning usually uses the “back-illuminate” technique to illuminate one end of the fiber. The other end of the fiber is used for detection. The fiber could be stressed or twisted during locator motion, resulting in a difference between the detected fiber position and the actual fiber core. However, the fiber-optic back-illuminated device in the spectrometer system increases the complexity of the system and the time loss of fiber positioning. This paper attempts to use a new method combining image processing with deep learning to identify the fiber ferrule by the front-illuminated method. We built an experimental platform in the lab and experimented with a CMOS camera and telecentric lens. We tested the repeated errors and displacement measurement errors of the two methods. A series of comparative experimental results show that the final detection accuracy of this method can meet the needs of optical fiber positioning in the laboratory, although it has not yet reached the accuracy of the back-illuminated approach. In the future, if the light source and fiber ferrule were specifically designed for the front-illuminated method, its accuracy could be further improved.

The paper presents the prerequisites for the use of polyharmonic microwave photonic vector analyzers for probing multiplicative sensors based on fiber Bragg structures in order to improve the metrological characteristics of systems for complex monitoring of technically complex objects.

This article presents the results of modeling and comparative analysis of the real-time efficiency of the microwave photonic measurement system for assessing the angular velocity of a vehicle tire for two types of addressed fiber Bragg structures. The relevance of this research is due to the development of active vehicle safety and fiber-optic measuring devices. Since knowledge of the change in adhesion properties of the tire is the most important information for the active vehicle safety systems. This fact is forcing engineers to create measuring devices capable of measuring at a high sampling rate, which can be achieved using the technology of polling addressed fiber Bragg structures.

In recent years, advanced optical methods combined with genetically encoded indicators has gradually become a helpful solution for monitoring neural activities in behaving animals. Among various optical methods, fiber-based ones have become increasingly versatile as they have declined in size but gained in functionality. We developed a nonlinear optical fiber-based endoscope with single-cell resolution, which enables investigating neural activities within single nucleus in freely behaving mice. To further understand how neural activities are coordinated in the complex circuits over different brain regions, we implemented two multichannel fiber photometry systems for multi-site population neural activity recording in head-restrained mice.

Dual-clad fiber couplers allow combining coherent imaging and diffuse sensing within the same instrument. Since the technology's lab-to-market transfer, several groups reported on its application to OCT, confocal microscopy, and hyperspectral imaging, to name a few. From this initial design, our group has focused on other dedicated optical fiber couplers for biomedical imaging, namely: multimode circulators, bi-directional couplers, and modally-specific photonic lanterns. This presentation will review the application of these recent innovations in the context of biomedical imaging and sensing.

Optical fiber specklegrams originate from the interference between several guided light modes. Since these granular patterns are sensitive to changes in the fiber status, it is possible to retrieve an external stimulus by analyzing their morphology and spatial distribution. This paper evaluates the first and second-order entropies as metrics to interrogate fiber specklegram sensors. Firstly, the refractive index surrounding a no-core fiber is varied to modulate the number and average size of speckles. Secondly, a microbending transducer driven with controlled displacements creates deviations in the output speckle field. Then, the entropy data for each case is compared with Law's energy texture and the zero-mean cross-correlation analyses, respectively. Conversely to the Shannon entropy, the joint and relative entropies process the spatial information of the image and corroborate the theoretical and experimental speckle count, yielding ~0.02 refractive index resolution. Moreover, the relative entropy of the ratio between test and reference speckle field images agrees with the correlation coefficient, achieving ~0.5 µm resolution. The results show that the second-order entropy is effective for interrogating fiber specklegrams, figuring as a straightforward alternative to the widespread texture processing and deep learning approaches FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES Aberto

With ground truths only at 0 imaging depth, we reconstruct high-quality cell images through disordered optical fiber system up to 3mm imaging depth by tracing the state of the system using cycle-consistent adversarial networks.

Optical fiber is the basis of communication network, carrying a huge network traffic, the impact of the cable failure is significant. As a result, the fiber fault prediction is a hot research topic. In this paper, based on the basic parameters and fault information of optical fiber, Support Vector Machine (SVM) model is adopted to classify the faults. Since the cable fault is a small probability event, there is an imbalance in the distribution of the data sample. Use Synthetic Minority Oversampling Technique (SMOTE) algorithm to treat the imbalance data, and then analyze and study by using the SVM classification model.

There exists an increasing interest in monitoring low concentrations of biochemical species, as they allow the early-stage detection of illnesses or the monitoring of the environment quality. Thus, both companies and research groups are focused on the development of accurate, fast and highly sensitive biosensors. Optical fiber sensors have been widely employed for these purposes because they provide several advantages for their use in point-of-care and real-time applications. In particular, this review is focused on optical fiber biosensors based on luminescence and absorption. Apart from the key parameters that determine the performance of a sensor (limit of detection, sensibility, cross-sensibility, etc.), other features are analyzed, such as the optical fiber dimensions, the sensing set ups and the fiber functionalization. The aim of this review is to have a comprehensive insight of the different aspects that must be taken into account when working with this kind of sensors. This research was funded by the Spanish AGENCIA ESTATAL DE INVESTIGACIÓN (AEI), through the project with reference PID2019-106231RB-I00—ESPADA and also by the Regional Government of Navarra, through the project with reference 0011-1365-2020-000061–BREATHALYSER (FEDER).

The design of a digital optical link involves many interrelated operating characteristics of the fiber, source, photodetector, and other components in the link. In carrying out an optical fiber link analysis, several iterations with different device characteristics may be required before the analysis is completed satisfactorily. The two basic analyses that usually are carried out to ensure that the desired system performance can be met are the link power budget and the system rise-time analysis. In addition to discussing these two analyses, this chapter addresses procedures for detecting and controlling errors in a digital data stream in order to improve the reliability of a communication link.