Fiber Bundle Array Research Articles

Multi-modal imaging using a cascaded microscope design.

We present a multi-modal fiber array snapshot technique (M-FAST) based on an array of 96 compact cameras placed behind a primary objective lens and a fiber bundle array. Our technique is capable of large-area, high-resolution, multi-channel video acquisition. The proposed design provides two key improvements to prior cascaded imaging system approaches: a novel optical arrangement that accommodates the use of planar camera arrays, and a new ability to acquire multi-modal image data acquisition. M-FAST is a multi-modal, scalable imaging system that can acquire snapshot dual-channel fluorescence images as well as differential phase contrast measurements over a large 6.59 mm × 9.74 mm field-of-view at 2.2-μm center full-pitch resolution.

Imaging Dynamics Beneath Turbid Media via Parallelized Single-Photon Detection.

Noninvasive optical imaging through dynamic scattering media has numerous important biomedical applications but still remains a challenging task. While standard diffuse imaging methods measure optical absorption or fluorescent emission, it is also well‐established that the temporal correlation of scattered coherent light diffuses through tissue much like optical intensity. Few works to date, however, have aimed to experimentally measure and process such temporal correlation data to demonstrate deep‐tissue video reconstruction of decorrelation dynamics. In this work, a single‐photon avalanche diode array camera is utilized to simultaneously monitor the temporal dynamics of speckle fluctuations at the single‐photon level from 12 different phantom tissue surface locations delivered via a customized fiber bundle array. Then a deep neural network is applied to convert the acquired single‐photon measurements into video of scattering dynamics beneath rapidly decorrelating tissue phantoms. The ability to reconstruct images of transient (0.1–0.4 s) dynamic events occurring up to 8 mm beneath a decorrelating tissue phantom with millimeter‐scale resolution is demonstrated, and it is highlighted how the model can flexibly extend to monitor flow speed within buried phantom vessels.

High precise time division multiplex UV pulse waveform measurement system for high power laser facility

In high power laser facility, the waveform measurement of UV pulse injected to target is very important for power balanced control and experiment result analysis. A time division multiplex UV frequency modulation pulse waveform measurement system based on fiber bundle and lens array is built for a high precise measurement result as well as low construction and maintaining cost. The system can remarkably improve coupling efficiency inject to fiber contribution to the aperture splicing sampling technology and a 50μm multi-mode UV fiber specially developed with 9.2GHz bandwidth@60m transmission. A “four-in-one” time division multiplex measurement system is built for laser facility and the practical experiment indicated that the system can realize precise waveform measurement within good economy and anti-interference performance.

Measurement of dilation pulses using a pulse-dilation framing camera.

A pulse-dilation framing camera (PFC) and its working principle are introduced. The influence of the dilation pulse on the exposure time is discussed. The measurement of the dilation pulse using the PFC are theoretically analyzed and experimentally verified. The waveform and the entire time history of the potential of the dilation pulse are simulated by the known dilation factors of the PFC in theory, with the potential deviation at the end of the dilation time of pulse being approximately 3.2%. In the experiment, the exposure time and dilation factors of the PFC are measured by using an array of fiber bundles and in taking many measurements, the waveform and the entire time history of the potential of dilation pulse are achieved by the dilation factors, with the potential deviation at the end of the dilation time of pulse being approximately 6.3%. The research results show that the experimental measurement is consistent with theoretical analysis, although there are some deviations, and it is feasible to measure the waveform and the entire time history of the potential of dilation pulse using the PFC. Moreover, the research may provide an idea for new applications of the framing camera.

Conceptual design of JT-60SA edge Thomson scattering diagnostic

JT-60SA will complement ITER in resolving key issues to finally decide an acceptable DEMO design. Diagnostics play a key role in this mission. The electron temperature and density profiles are measured by a core and an edge Thomson scattering (TS) diagnostics with high spatial resolution, needed to identify the pedestal parameters and small profile structures. The two systems use a common tangential Nd:YAG laser beam path in the plasma equatorial plane. The collection optics for the edge system (low field side) is hosted in a lower oblique port and that for the core system in a horizontal port. The optics fit in the port plug tube and image the scattering volumes into an array of fiber bundles. They both are exposed to a high neutron dose of 1016 n/cm2 over 13 years of operation. The optics are supported by a mechanical structure decoupled from the cryostat. A set of filter polychromators with avalanche photodiode (APD) detectors spectrally analyze the scattered radiation. The development of the TS systems is carried out by a joint Japan-EU team. The conceptual design of the edge TS system is presented here. Simulations of the TS signals show acceptable accuracy down to 1 × 1019 m−3 electron density, sufficient to measure the edge gradient and even a small region outside the separatrix.

Three-dimensional ultrastructural imaging and quantitative analysis of the periodontal ligament.

The periodontal ligament (PDL) is a unique connective tissue mainly comprising collagen fiber bundles and cells between the roots of teeth and inner walls of the alveolar-bone socket. PDL fiber bundles are arrayed between teeth and bone, with both ends embedded in the cementum or alveolar bone as Sharpey's fiber. These bundles, synthesized by PDL fibroblasts (PDLFs), form several distinct groups within the PDL which has important functions besides tooth anchoring including tooth nutrition, proprioception, sensory detection, homoeostasis, and repair of damaged tissue. However, little is known about how the regular-PDL fiber bundle arrays are formed, maintained, and remodeled over large distances from cementum to alveolar bone. Recently, novel instruments and 3D-imaging methods have been developed that have been applied to the investigation of hard tissues including the PDL. Work from our laboratory has revealed the three-dimensional (3D) ultrastructure of PDLFs and PDL collagen bundles by focused ion beam/scanning electron microscope tomography. We have shown that PDLFs have a flat shape with long processes or a wing-like shape, while PDL bundles are a multiple-branched structure wrapped in thin sheets of PDLF cytoplasm. Furthermore, PDLFs form an extensive cellular network between the cementum and alveolar bone. The PDL cellular network is presumed to synchronize PDL fiber bundles and regulate arrays of PDL fiber bundles via gap junctions. In this review, we summarize and discuss our current 3D-histomorphometric studies of the PDL at the mesoscale level.

Optical Diagnostics of Multi-Gap Gas Switches for Linear Transformer Drivers

The trigger characteristics of a multi-gap gas switch with double insulating layers, a square-groove electrode supporter and a UV pre-ionizing structure are investigated aided by a high sensitivity fiber-bundle array detector, a UV fiber detector, and a framing camera, in addition to standard electrical diagnostics. The fiber-bundle-array detector is used to track the turn-on sequence of each electrode gap at a timing precision of 0.6 ns. Each fiber bundle, including five fibers with different azimuth angles, aims at the whole emitting area of each electrode gap and is fed to a photomultiplier tube. The UV fiber detector with a spectrum response of 260-320 nm, including a fused-quartz fiber of 200 μm in diameter and a solar-blinded photomultiplier tube, is adopted to study the effect of UV pre-ionizing on trigger characteristics. The framing camera, with a capacity of 4 frames per shot and an exposure time of 5 ns, is employed to capture the evolution of channel arcs. Based on the turn-on light signal of each electrode gap, the breakdown delay is divided into statistical delay and formative delay. A decrease in both of them, a smaller switch jitter and more channel arcs are observed with lower gas pressure. An increase in trigger voltage can reduce the statistical delay and its jitter, while higher trigger voltage has a relatively small influence on the formative delay and the number of channel arcs. With the UV pre-ionizing structure at 0.24 MPa gas pressure and 60 kV trigger voltage, the statistical delay and its jitter can be reduced by 1.8 ns and 0.67 ns, while the formative delay and its jitter can only be reduced by 0.5 ns and 0.25 ns.

Comparison of BCF-10, BCF-12, and BCF-20 Scintillating Fibers for Use in a 1-Dimensional Linear Sensor

One-dimensional fiber-bundle arrays may prove useful in a number of radiation sensing applications where radiation detection over large areas is needed. Tests have been performed to evaluate the light generation and transmission characteristics of 15-meter long, 10-fiber bundles of BCF-10, BCF-12, and BCF-20 scintillating fibers (Saint Gobain) exposed to collimated gamma-ray sources. The test set-up used one R9800 (Hamamatsu) photomultiplier tube (PMT) at each end, with a high-speed waveform digitizer to collect data. Time constraints were imposed on the waveform data to perform time-of-flight analysis of the events in the fiber bundles, eliminating spurious noise pulses in the high gain PMTs and also allowing 1-dimensional localization of interactions along the lengths of the fiber bundles. Measurements show that the spatial response of these three fibers is linear over at least 15-m lengths and that, with the equipment used here, the spatial resolution for events irradiating 1 cm of fiber (using a collimated source) ranges from 50 cm to 60 cm over the entire length of the bundles. The efficiency for detecting events varies along the length of the arrays, with the sensitivity at the midpoint (half of the distance) of an array ranging from ~ 2X to ~ 3X the efficiency at the ends, depending on the length of the fiber-bundle array and the self-absorption factor for each fiber's scintillation light. Compared to prior work, a 20-fold improvement in detection sensitivity has been shown for this technique, most likely due to improved optical coupling and improved signal analysis.

Wide field-of-view imaging spectrometer using imaging fiber bundles

A field-of-view-folding approach is proposed to extend the field of view (FOV) of a dispersive imaging spectrometer after introducing several linear arrays of imaging fiber bundles to which to replace the slit. The fiber bundles can flexibly connect fore-optics with a spectrometer to yield an imaging fiber-optic spectrometer (IFOS). The technology of FOV segmenting and folding, which can decrease simultaneously the dimension and spectral distortion of the imaging spectrometer, is described in detail. Because of the sampling function of the fiber bundles, the IFOS is a double-sampling imaging system. We analyze the effect of fiber coupling on the modulation transfer function (MTF) and then develop a cascade MTF model to estimate the imaging performance of the IFOS. A spaceborne IFOS example is presented to describe how the method can be used.

Numerical modeling and optimization of bundled fiber optic FTIR probes for spectroscopy of small targets

Fiber optic probes coupled to a Fourier Transform Infrared (FTIR) spectrometer allow sample analysis without the need to place the sample directly into the instrument. This is particularly attractive for spacecraft lander/rover applications where the additional mechanics, mass and cost associated with excavating and placing a small sample in a sample bay is not desirable. This paper uses numerical modeling to analyze fiber bundle array configurations and fiber numerical apertures to determine their light gathering efficiency and sample size as a function of probe-to-sample distance. The model was validated against experimental measurements for a selection of off the shelf fiber optic probes. The collection efficiency of a probe can be optimized by using a hexagonal packing method, and by using fibers with high numerical apertures. By increasing the numerical aperture of the fibers used in our model probes from 0.2 to 0.5, we were able to increase the collection efficiency of a seven fiber probe from 4.5% to 9.5%, with the peak collection efficiency corresponding to a spot size of diameter 3 mm.

The Effect of Certain Morphological Features on the Permeability of Clustered Fibrous Media

A good understanding of the microscopic details of flow through fiber preforms remains a critical step in the design and optimization of composite liquid molding processes such as Resin Transfer Molding (RTM) and its variants. However, the measurement of the key relevant property, namely the permeability of the preform, is still not standardized and remains difficult to perform as well as to interpret. In this paper, numerical results are presented for boundary element simulations of creeping flow through model fibrous media made up of parallel fiber bundles. Starting from ordered arrays of fiber bundles, several types of microstructural variations are introduced, and their effect on permeability is examined and quantified. It is shown that deviations from regular arrays cause substantial scatter in the corresponding permeability values. These results help to understand the large data scatter typically observed in permeability measurements.

Imaging interferometers for analysis of Thomson scattered spectra

Polarization interferometers have some potential efficiency advantages for imaging Thomson scattering spectral analysis. In this article we present a number of designs for high-efficiency imaging polarization interferometers for Thomson scattering spectral analysis. The use of high-efficiency crystal polarizing beamsplitters (both displacement and angle) results in low-loss complementary passbands (no edge losses), simple imaging systems, and wide field of view. The efficiency and relative merits of both multiple-filter and dispersive-type configurations are being assessed before installation on the JT-60U ruby-laser Thomson scattering system. Light is transferred from the viewing port via a linear array of optical fiber bundles which will be imaged through the interferometer onto the photocathode of an intensified charge coupled device camera. Because of the broadband nature of the Thomson light, the optical delays required to Fourier analyze the spectrum are quite small. This leads to compact multicolor or dispersive systems based on combinations of Wollaston and Savart splitters and traditional waveplates.

Non‐Isotropic structured fibrous media: The permeability of arrays of fiber bundles of elliptical cross section

AbstractA computational analysis of viscous flow across hexagonal arrays of fiber bundles of elliptical cross section, each consisting of up to 350 individual filaments, is carried out using the Boundary Element Method. Such arrays are non‐isotropic dualporosity systems, characterized by the aspect ratio (λ) of the fiber bundles, their inter‐ (ϕi) and intra‐tow (ϕt) porosities as well as by the number (Nf) of filaments within each bundle. The results, in terms of the hyraulic permeability (K) of these arrays, are compared to earlier analytical models and a good agreement is found. A dimensionless correlation, earlier proposed for arrays of circular cross section, is used to reduce the computed permeabilities for bundles of aspect ratio λ = 2 and λ = 3 on a single master curve. This correlation offers a simple model for the calculation of the permeability of such dual porosity systems form knowledge of ϕi, ϕt, λ and Nf. By considering bulk flow along the two principal directions of the fiber bundle, we also compare the two principal permeabilities of such arrays.

Intense electron emission from carbon fiber cathodes

We studied the emission properties of carbon fiber cathodes. These cathodes were made either of a single carbon fiber or of carbon fabric, or of an array of carbon fiber bundles. It was found that an intense emission of electrons occurs from a plasma which is formed on the carbon fiber surface as a result of a flashover process. In addition, the time delay in the appearance of the electron emission with respect to the start of the accelerating voltage pulse was found to depend strongly on the voltage growth rate. A simple model of the plasma formation is suggested.

The Hydraulic Permeability of Dual Porosity Fibrous Media

We present a computational analysis of viscous flow through arrays of fiber bundles using the Boundary Element Method (BEM) implemented on a multi-processor computer. Up to 700 individual fibers are included in each simulation. These are simple but not trivial models for fibrous preforms used in composites manufacturing-dual porosity systems characterized by different inter- and intra-tow porosities. The way these porosities affect the hydraulic permeability of a preform is currently unknown and is elucidated through our simulations. Numerical results are compared to analytical models. Through a large number of simulations we construct a master curve for the permeability of arrays of fiber bundles for various packing arrangements.

The Hydraulic Permeability of Dual Porosity Fibrous Media

We present a computational analysis of viscous flow through arrays of fiber bundles using the Boundary Element Method (BEM) implemented on a multi-processor computer. Up to 700 individual fibers are included in each simulation. These are simple but not trivial models for fibrous preforms used in composites manufacturing-dual porosity systems characterized by different inter- and intra-tow porosities. The way these porosities affect the hydraulic permeability of a preform is currently unknown and is elucidated through our simulations. Numerical results are compared to analytical models. Through a large number of simulations we construct a master curve for the permeability of arrays of fiber bundles for various packing arrangements.

Flow across structured fiber bundles: a dimensionless correlation

We present a computational analysis of viscous flow across unidirectional arrays of fiber bundles using the boundary element method (BEM). We consider hexagonal arrays of fiber bundles in which the individual filaments are packed in hexagonal or square arrangements. Up to 300 individual filaments are included in each simulation. These are simple but not trivial models for dual porosity fibrous media (such as the preforms used in composites manufacturing or fiber bundles used in hollow membrane oxygenators) characterized by different inter- and intra-tow porosities. The way these porosities interact to determine the hydraulic permeability of such media is not well understood. Numerical solution of the flow problem yields the flowrate through the unit cell, from which the hydraulic permeability ( K p) of the dual porosity medium is computed. Through a large number of simulations we determine K p for a range of inter- and intra-tow porosities and for a range of fiber sizes. A semi-empirical correlation is proposed which collapses all the numerical data (a total of 380 data points) on a single curve, for both, hexagonal and square intra-tow fiber arrangements. This correlation allows prediction of the permeability of hexagonal arrays of fiber bundles from a knowledge of their inter- and intra-tow porosities, the type of intra-tow packing and the size (or number) of the intra-tow filaments.

Demonstration of Primary and Secondary Muscle Fiber Architecture of the Bovine Tongue by Diffusion Tensor Magnetic Resonance Imaging

The myoarchitecture of the tongue is comprised of a complex array of muscle fiber bundles, which form the structural basis for lingual deformations during speech and swallowing. We used magnetic resonance imaging of the water diffusion tensor to display the primary and secondary fiber architectural attributes of the excised bovine tongue. Fiber orientation mapping provides a subdivision of the tongue into its principal intrinsic and extrinsic muscular components. The anterior tongue consists of a central region of orthogonally oriented intrinsic fibers surrounded by an axially oriented muscular sheath. The posterior tongue consists principally of a central region of extrinsic fibers, originating at the inferior surface and projecting in a fan-like manner in the superior, lateral, and posterior directions, and lateral populations of extrinsic fibers directed posterior-inferior and posterior-superior. Analysis of cross-fiber anisotropy indicates a basic contrast of design between the extrinsic and the intrinsic fibers. Whereas the extrinsic muscles exhibit a uniaxial architecture typical of skeletal muscle, the intrinsic core muscles, comprised of the verticalis and the transversus muscles, show strong cross-fiber anisotropy. This pattern is consistent with the theory that the tongue's core functions as a muscular hydrostat in that conjoint contraction of the transverse and vertical fibers enable the tissue to expand at right angles to these fibers. These findings suggest that three-dimensional analysis of diffusion tensor magnetic resonance imaging provides a structural basis for understanding the micromechanics of the mammalian tongue.

Coherent radiative transfer through multi-layer fibrous media

This paper presents the theoretical formulation for the propagation of coherent radiation through multiple fibrous layers. Each fibrous layer contains a periodic array of parallel fiber bundles which consist of a large number of closely-spaced aligned Rayleigh limit fibers. The alignment and optical properties of the fibers can be different in each layer. The time-averaged Poynting vector for the coherent scattered radiation is developed by a rigorous solution of Maxwell's equations.

Fabrication of fiber bundle arrays for free-space photonic switching systems

We describe a technique for assembling fiber bundle arrays as needed in optical computing and photonic switching systems. Two 4 x 4 arrays with single-mode and multimode optical fibers were manufactured. Fiber ends were located to within 3 μm of their ideal position and to a pointing precision of 30 arcmin. A third 4 x 8 array was manufactured with single-mode fibers, and fiber ends were located to within 1.5 μm of their ideal position.