Refractive Index Matching Material Research Articles

Phase wavefront perturbation calculation model for spectroscopic refractive index matching of hybrid materials.

A low-cost flexible spectroscopic refractive index matching (SRIM) material with bandpass filtering properties without incidence angle and polarization dependence by randomly dispersing inorganic C a F 2 particles in organic polydimethylsiloxane (PDMS) materials was proposed in our previous study. Since the micron size of the dispersed particles is much larger than the visible wavelength, the calculation based on the commonly used finite-difference time-domain (FDTD) method to simulate light propagation through the SRIM material is too bulky; however, on the other hand, the light tracing method based on Monte Carlo theory in our previous study cannot adequately explain the process. Therefore, a novel approximate calculation model, to the best of our knowledge, based on phase wavefront perturbation is proposed that can well explain the propagation of light through this SRIM sample material and can also be used to approximate the soft scattering of light through composite materials with small refractive index differences, such as translucent ceramics. The model simplifies the complex superposition of wavefront phase disturbances and the calculation of scattered light propagation in space. The scattered and nonscattered light ratios; the light intensity distribution after transmission through the spectroscopic material; and the influence of absorption attenuation of the PDMS organic material on the spectroscopic performance are also considered. The simulation results based on the model are in great agreement with the experimental results. This work is important to further improve the performance of SRIM materials.

Understanding migratory flow caused by helicoid wire spacers in rod bundles: An experimental and theoretical study

The core of a Liquid Metal Fast Breeder Reactor (LMFBR) consists of cylindrical fuel rods that are wrapped by a helicoidally-wound wire spacer to enhance mixing and to prevent damage by fretting. It is known that the liquid metal close to the rod is forced to follow the wires, and that liquid metal further away from the rod crosses the wires (called: migratory flow). This work aims at gaining more insight into the physics behind migratory flow and to provide a model for its bending angle. To this purpose, the flow field in a 7-rods, wire-wrapped, hexagonal bundle with water is studied within the Reynolds number range of 4990–16330 by using Particle Image Velocimetry (PIV). Refraction of the light is minimized by using Fluorinated Ethylene Propylene (FEP), which is a refractive index-matching (RIM) material. These measurements confirm that liquid near the rod follows the helicoid path and bends cross-wise with respect to the wire further away from the rod. A theoretical model for the bending angle of the flow is derived from the Euler equations and shows that the bending is primarily caused by the pressure gradient field induced by the wire. The model shows a very good correspondence with the experimentally obtained PIV data. These findings improve our understanding of the physics at play in rod bundle flows with wrapped wires and can be of assistance in developing practical correlations for frictional pressure losses and heat transfer in such bundles.

Experimental investigation on the influence of gap vortex streets on fluid-structure interactions in hexagonal bundle geometries

Gap vortex streets characterise many industrial applications involving rod bundle flows, such as heat exchangers and nuclear reactors. These structures, known as gap vortex streets, may excite the structural components of the bundle to resonance, leading to fretting and fatigue. This work aims to measure these coherent structures and the resulting displacement and oscillation frequency of the neighbouring rod, to provide unique data for fluid-structure interaction studies and to develop a general correlation for estimating the coherent structure’s wavelength. A water loop was built to host a hexagonal rod bundle. Fluorinated Ethylene Prophylene (FEP), a refractive index matching (RIM) material, was used to have undisturbed optical access in the area around the central rod. The flow was measured with Laser Doppler Anemometry (LDA) to detect coherent structures, while the vibrations were measured with a high speed camera. A new correlation for estimating the wavelength of the coherent structures is derived with dimensional analysis based on experimental evidence. The correlation is tested on different geometries: rectangular channels with single or half-rods, and two rod bundles, within the pitch-to-diameter ratio (P/D) range 1.02–1.2. Moreover fluctuations in the flow, given by the detected coherent structures, govern the structural response of the rod. The rod is excited to resonance if these fluctuations match twice the natural frequency of the rod.

LDA measurements of coherent flow structures and cross-flow across the gap of a compound channel with two half-rods

The enhancement of heat transfer from fuel rods to coolant of a Liquid Metal Fast Reactor (LMFR) decreases the fuel temperature and, thus, improves the safety margin of the reactor. One of the mechanisms that increases heat transfer consists of large coherent structures that can occur across the gap between adjacent rods. This work investigates the flow between two curved surfaces, representing the gap between two adjacent fuel rods. The aim is to investigate the presence of the aforementioned structures and to provide, as partners in the EU SESAME project, an experimental benchmark for numerical validation to reproduce the thermal hydraulics of Gen-IV LMFRs. The work investigates also the applicability of Fluorinated Ethylene Propylene (FEP) as Refractive Index Matching (RIM) material for optical measurements.The experiments are conducted on two half-rods of 15 mm diameter opposing each other inside a Perspex box with Laser Doppler Anemometry (LDA). Different channel Reynolds numbers between Re = 600 and Re = 30,000 are considered for each P/D (pitch-to-diameter ratio).For high Re, the stream wise velocity root mean square vrms between the two half rods is higher near the walls, similar to common channel flow. As Re decreases, however, an additional central peak in vrms appears at the gap centre, away from the walls. The peak becomes clearer at lower P/D ratios and it also occurs at higher flow rates. Periodical behaviour of the span wise velocity across the gap is revealed by the frequency spectrum and the frequency varies with P/D and decreases with Re. The study of the stream wise velocity component reveals that the structures become longer with decreasing Re. As Re increases, these structures are carried along the flow closer to the gap centre, whereas at low flow rates they are spread over a wider region. This becomes even clearer with smaller gaps.

High reliability solid refractive index matching materials for field installable connections in FTTH network

We performed environmental and accelerated aging tests to ensure the long-term reliability of solid type refractive index matching material at a splice point. Stable optical characteristics were confirmed in environmental tests based on an IEC standard. In an accelerated aging test at 140°C, which is very much higher than the specification test temperature, the index matching material itself and spliced fibers passing through it had steady optical characteristics. Then we performed an accelerated aging test on an index matching material attached to a built-in fiber before splicing it in the worst condition, which is different from the normal use configuration. As a result, we confirmed that the repeated insertion and removal of fiber for splicing resulted in failure. We consider that the repetition of adhesion between index matching material and fibers causes the splice to degrade. With this result, we used the Arrhenius model to estimate a median lifetime of about 68years in a high temperature environment of 60°C. Thus solid type index matching material at a splice point is highly reliable over long periods under normal conditions of use.

Extratympanic observation of middle ear structure using a refractive index matching material (glycerol) and an infrared camera

High-resolution computed tomography has been used mainly in the diagnosis of middle ear disease, such as high-jugular bulb, congenital cholesteatoma, and ossicular disruption. However, certain diagnoses are confirmed through exploratory tympanotomy. There are few noninvasive methods available to observe the middle ear. The purpose of this study was to investigate the effect of glycerol as a refractive index matching material and an infrared (IR) camera system for extratympanic observation. 30% glycerol was used as a refractive index matching material in five fresh cadavers. Each material was divided into four subgroups; GN (glycerol no) group, GO (glycerol out) group, GI (glycerol in) group, and GB (glycerol both) group. A printed letter and middle ear structures on the inside tympanic membrane were observed using a visible and IR ray camera system. In the GB group, there were marked a transilluminated letter or an ossicle on the inside tympanic membrane. In particular, a footplate of stapes was even transilluminated using the IR camera system in the GB group. This method can be useful in the diagnosis of diseases of the middle ear if it is clinically applied through further studies.

Field Assembly Splice Technique With Solid Refractive Index Matching Material

Solid refractive index matching material enables us to splice fiber with air holes as well as conventional single-mode fiber. In this paper, we report our study of the applicability of solid refractive index matching material to a field assembly splice technique. We investigate pressing force and bending loss characteristics as a function of fiber buckling experimentally. We also investigate the impact of the hardness of the solid material on the splice loss characteristics of the field assembly splice technique. Then we derive appropriate splice conditions for both the hardness of the solid material and fiber buckling. Finally, we confirm the validity of the derived splice condition by using a single-mode hole assisted fiber.

Unusual fault detection and loss analysis in optical fiber connections with refractive index matching material

We investigated and analyzed an unusual fault that occurs in optical access fiber networks, which is caused by a defective fiber connection. We developed a fault-detection system to locate such a fault by using both optical power level and optical pulse measurement methods. We investigated a defective mechanical splice in three laboratory tests: outward appearance, non-destructive, and dismantled. As a result, we confirmed that the defective mechanical splice had large gaps of more than 10μm. We also analyzed the unusual fault that occurs from such a defective mechanical splice in mechanically transferrable (MT) connector experiments. The experimental results revealed that the optical performance of fiber connections with a mixture of refractive index matching material and air-filled gaps was extremely unstable and varied widely. In the worst case, the insertion loss worsened to more than 30dB. The case of the fault caused by a mixture of refractive index matching material and air-filled gaps between the ends of optical fibers is thought to occur independently of the sorts or structures of optical fiber connectors and could be a characteristic peculiar to optical fiber connections using refractive index matching material. These findings can be applied to optical fiber connections that use refractive index matching material, such as MT connectors in outside underground facilities, mechanical splices, or field assembly connectors at aerial and home sites in optical access networks. These findings also support the practical construction and operation of optical network systems.

Mechanical Splice Characteristics of a Hole-Assisted Fiber

The mechanical splice characteristics of a single-mode hole-assisted fiber (SM-HAF) are investigated both numerically and experimentally. Mode-coupling theory is used to investigate the mechanical splice loss characteristic of the HAF. We introduced an air filling fraction and a \bm V-parameter to allow us to consider an HAF with arbitrary structural parameters. We derive the optimum conditions (e.g., refractive index and temperature coefficient) of a solid-type refractive index matching material to realize good splice and return loss characteristics simultaneously. The validity of the derived conditions is investigated experimentally. Finally, we confirm that we can achieve comparable splice characteristics to those of conventional single-mode fiber splices by using the optimized refractive index matching material independent of the structural parameters of the SM-HAF.

Visualization of ripples on the surface of a rising bubble through an immiscible oil/water interface

AbstractThis paper visually demonstrates instantaneous behavior of ripples propagating on the surface of a rising bubble through an oil/water interface. This experiment uses potassium iodide (KI) 31 wt% as refractive index matching material which makes the water phase invisible. As a result, the generated micro droplets, which are shown in the preceding paper (Uemura et al. in Europhys Lett 92:34004, 2010), cannot be visible in the present results, and therefore the droplets are positively confirmed to be made of water.Graphical Abstract[IMAGE]

Optical Characteristics and Reliability of Mechanical Splice Utilizing Solid Refractive Index Matching Material for Hole-Assisted Fiber Connection

We demonstrated that a mechanical splice utilizing solid refractive index matching material enables us to connect hole-assisted fibers with the same optical characteristics as the mechanical splice used with single-mode fibers. The optical characteristics remained stable in environmental and mechanical tests.

Temperature dependence of return loss for optical fiber connectors with refractive index-matching material

This letter describes the temperature dependence of return loss for optical fiber connectors with refractive index-matching material. We have performed return loss calculations and experiments for mated flat endface plugs whose fiber endfaces had a high index layer. We used index-matching material with a refractive index of 1.467 at 20/spl deg/C and a thermal coefficient of -2.9/spl times/10/sup -4///spl deg/C. We confirmed that almost all the connectors with a return loss of /spl ges/40 dB at 20/spl deg/C had return loss values of /spl ges/35 dB between -40/spl deg/C and 80/spl deg/C. >

Laser-based refractive-index detection for capillary electrophoresis: ray-tracing interference theory

The fringe pattern observed in a far field after a laser beam illuminates a fused silica capillary immersed in a refractive-index matching material and filled with an analyte fluid is exploited to develop a sensitive optical detector for capillary chemical analysis. The inner capillary interface splits the laser beam into a reflected beam fan and a refracted beam fan, which, on overlapping in the far field, lead to interferences. The intensity and the position of the fringes for capillaries with 250 microm >/= i.d. (inner diameter) >/= 25 microm are well reproduced by the presented model. The calculation predicts the fringe pattern for various beam/i.d. geometric configurations and is used to optimize the performance of the nanoliter-picoliter refractive-index on-column detection studied. It is found that the best contrast corresponds to a capillary that is illuminated with a beam waist of omega(0) ~ i.d./12, which is off-center focused with an offset of s ~ i.d./2. For a given interference pattern, the fringes that are found to be more sensitive to Deltan are those that appear near the optical axis but still retain high intensity and contrast. The sensitivity increases approximately linearly with the fringe number, and the maximal fringe number increases proportionally with the i.d.