Fiber Optic Light Guides Research Articles

Determination of refractive indices of materials in modeling multilayer mirrors

Thin-film coatings for optical elements are widely used in various industries. Antireflection coatings are used in display screens, photodetectors, fiber optic light guides, mirror coatings are used for telescopes, medical equipment, etc. One of the main goals in the production of thin-film coatings is to determine the refractive index and the choice of materials applied to optical products. We present the results of determining the refractive indices of materials used for the manufacture of multilayer mirrors with the desired spectral characteristics. In general, light reflection occurs at the interface between two materials, for example, glass and air. Dielectric films were obtained by high-frequency ion-beam sputtering of the target. It is shown that the refractive index of the SiO2 film must be repeatedly corrected to minimize systematic errors. The results obtained can be used in the production of high-precision optical systems for various industries, especially medicine, space instrumentation, aviation and others.

Fiber-optic light guides as secondary sources of light for hen keeping in cage batteries

The method of local illumination of cage batteries with LED lamps, previously developed by us, made it possible to increase the livability and productivity of hens in comparison with the traditional method. In this case, the placement of low-power LED sources directly in each cage requires a large number of rather complex electronic devices across the whole metal structure of the cage battery and extended power transmission lines. This work compares the efficiency of local LED lighting and fiber-optic light guides when keeping hens of the productive flocks of cross SP-789 in traditional cages. The 120-day-old hens were divided by the method of analogs in 2 groups of 100 heads. In the control group, LED lamps were used for local illumination of hens, and in the experimental group, fiber-optic light guides were used with LEDs as the primary source of illumination. The color temperature of light-emitting diodes was 3000 K. Up to 260 days of age, hens were kept in triple-tiered cage batteries, 5 animals per cage. The results of the study showed that in the control and experimental groups, the livability of the livestock was 95.0 and 99.0%, the egg production per initial hen was 99.2 and 102.5 pieces. The weight of eggs was 57.9 and 58.3 g, the yield of the egg weight per initial hen was 5.81 and 5.98 kg, feed consumption for 10 eggs and 1 kg of egg weight were 1.37, 2.35 and 1.30, 2.23 kg, respectively, without significant changes in the morphological and chemical qualities of eggs.

Characterization and Pilot Human Trial of Dedicated Breast Ring Positron Emission Tomography (BRPET) System

We describe the design and performance of BRPET, a novel dedicated breast PET (dbPET) scanner designed to maximize visualization of posterior regions of the breast. BRPET uses prone imaging geometry and a 12-module detector ring built from pixelated LYSO crystals coupled to position sensitive photomultiplier tubes (PSPMTs). Optical coupling via slanted plastic fiber optic light guides permits partial insertion of the crystals into the exam table’s breast aperture. Image quality testing procedures were adapted from the NEMA NU4-2008 protocol. Two additional phantom tests quantified the posterior extent of the usable volume of view (VoV). BRPET axial, radial, and tangential FWHM spatial resolutions at the isocenter were 1.8, 1.7, and 1.9 mm, respectively. The peak absolute system sensitivity was 0.97% using an energy window of 460–562 keV. The peak noise equivalent counting rate was 5.33 kcps at 21.6 MBq. The scanner VoV extends to within ~6 mm of the plane defining the location of the chest wall. A pilot human study (n = 10) compared the diagnostic performance of FDG-BRPET to that of contrast enhanced MRI (CEMRI), with biopsy as ground truth. Averaged over three expert human observers, the sensitivity/specificity for BRPET was 0.93/1.0, compared to 1.0/0.25 for CEMRI.

Application of fiber optic light guides with quartz core and cladding and plastic coating as indicators of the emergence of cracks in brickwork

Fiber optic light guides can be used as indicators (witness devices) of the emergence of cracks in masonry composed of construction-grade ceramic bricks. In this study, we experimentally investigated the relationship between the type and size of the fiber optic light guide and the size of the crack opening that caused fiber breakage by physically modeling a crack opening on a special stand. Two sizes of multimode fiber optic light guides with quartz core and cladding and poly(methyl methacrylate) (acrylic) coating were studied in detail. The results are useful for the practical implementation of the proposed method in automatic optoelectronic crack detection systems for brick buildings and structures.

Three-dimensional beam profiling used to characterize dental light-curing units.

Two-dimensional (2D) beam profiling is an emerging technique used to characterize the beam homogeneity in dental light-curing units (LCUs). This project developed a method to combine multiple 2D beam profiles that had been measured along the beam path to create a 3D profile of the beam. This allowed a quantitative investigation of beam divergence and homogeneity at different distances from the source. To illustrate the use of this technique, four representative dental LCUs were measured. In addition, the selected dental LCUs demonstrated the effects of LCU design, particularly that of fiber optic light guides, on beam quality. The results show the value of a program that can recombine multiple beam profile images made at different distances from the source to create a 3D beam profile of a light beam.

An adaptive-coherence light source for hyperspectral, topographic, and flow-contrast imaging.

Colorectal cancer accounts for an estimated 8% of cancer deaths in the United States with a five-year survival rate of 55-75%. The early detection and removal of precancerous lesions is critical for reducing mortality, but subtle neoplastic growths, such as non-polypoid lesions, often go undetected during routine colonoscopy. Current approaches to flat or depressed lesion detection are ineffective due to the poor contrast of subtle features in white light endoscopy. Towards improving colorectal lesion contrast, we present an endoscopic light source with custom laser channels for multimodal color, topographic, and speckle contrast flow imaging. Three red-green-blue laser units, paired with laser speckle reducers, are coupled into endoscopic fiber optic light guides in a benchtop endoscope. Tissue phantom topography is reconstructed using alternating illumination of the laser units and a photometric stereo endoscopy algorithm. The contrast of flow regions is enhanced in an optical flow phantom using laser speckle contrast imaging. Further, the system retains the ability to offer white light and narrow band illumination modes with improved power efficiency, a reduced size, and longer lifetimes compared to conventional endoscopic arc lamp sources. This novel endoscopic light source design shows promise for increasing the detection of subtle lesions in routine colonoscopy screening.

Решение для фундаментальной моды ступенчатого оптического волоконного волновода с керровской нелинейностью

Решение для фундаментальной моды ступенчатого оптического волоконного волновода с керровской нелинейностью

Applying the autosynchronization of waves to amplify laser radiation in waveguides

The possibility of applying the phenomenon of autosynchronization of waves in tunnel-coupled optical waveguides to amplify the laser radiation is considered. An optical amplification method of high-power laser radiation, which includes division, amplification in each channel, and the addition of amplified waves, is proposed. It increases the formation rate of the amplified directed radiation. In the proposed method, the optical waves propagate along optical waveguides made so that the tunnel optical coupling occurs between them, and these waveguides are nonlinear-optical. This method is applicable for the synchronization (phasing) of waves in fiber-optic light guides with many cores in conditions of amplifying these waves. For example, this method can be applied in erbium amplifiers with many cores.

LC(Liquid crystal)-광섬유를 이용한 최소 침습적 레이저 온열 치료용 온도 측정 센서의 개발을 위한 기초 연구

최근 최소 침습적 수술(minimal invasive surgery)방법에 대한 관심이 높아지면서 인체 내부의 악성 종양을 치료하는 방법 중의 하나로 레이저를 이용한 온열 치료법(laserthermia)이 사용되고 있다. 인체 심부의 암세포에 대한 레이저 열 치료는 레이저를 조직에 흡수시키면서 발생되는 열을 이용하여 암세포를 제거하는 방법이다. 본 시스템은 레이저 전달용 광섬유, 영상 획득용 내시경, 온도 측정 센서 등으로 구성된다. 온열 요법은 치료할 암세포를 적절한 온도(<TEX>$42{\sim}43^{\circ}C$</TEX>)로 유지시켜주면서 정상 세포는 레이저의 조사에 의한 열 발생을 최소화시키는 것이 중요한데 이러한 온도 유지를 위해서는 신속 정착한 온도 측정이 요구되고 있다. 본 연구에서는 새로운 형태의 LC(liquid crystal)-광섬유 온도 측정 센서를 개발하기 위해 온도 변화에 따른 LC물질의 색 변화 정도를 수광-발광 광섬유로서 측정하였고 측정된 수광량과 온도 변화 사이의 관계식을 도출하였다. 그리고 광섬유와 LC물질간의 복잡한 거리 문제를 해결하고, 보다 향상된 실험 결과를 얻기 위해 Y-coupler를 제작하여 LC물질의 반사 광량과 온도 사이의 관계도 알아보았다. Nowadays, laserthermia is widely used to treat malignant tumors with generating heat as the one of minimal invasive surgeries. Generally, the laserthermia probe system consists of the fiber-optic laser and light guides, image guide and temperature sensor. It is very important to measure the temperature of treating tumor and make a stable temperature (<TEX>$42{\sim}43^{\circ}C$</TEX>) during the treating time. Therefore, laserthermia probe needs temperature sensor which can measure it exactly and fast. In this study, to develop a new type of temperature sensor with LC(liquid crystal) and optical fiber, the reflectivity of LC according to the temperature changes are measured. Also, the relationships are derived from the results.

Polar nephelometer for light-scattering measurements of ice crystals

We report on a small, lightweight polar nephelometer for the measurement of the light-scattering properties of cloud particles, specifically designed for use on a balloonborne platform in cirrus cloud conditions. The instrument consists of 33 fiber-optic light guides positioned in a two-dimensional plane from 5 degrees to 175 degrees that direct the scattered light to photodiode detectors-amplifier units. The system uses an onboard computer and data acquisition card to collect and store the measured signals. The instrument's calibration is tested by measurement of light scattered into a two-dimensional plane from small water droplets generated by an ultrasonic humidifier. Excellent comparisons between the measured water-droplet scattering properties and expectations generated by Mie calculation are shown. The measured scattering properties of ice crystals generated in a cold chamber also compare reasonably well with the theoretical results based on calculations from a unified theory of light scattering by ice crystals that use the particle size distribution measured in the chamber.

Sensing of Volatile Organic Compounds Using a Simplified Reflectometric Interference Spectroscopy Setup

We present a simplified optical sensor system using the principle of reflectometric interference spectroscopy (RIfS) for monitoring organic solvent vapors in air. The shift of the interference pattern caused by a change of the optical thickness of a sensitive layer, due to the influence of analyte, is investigated. The interference pattern is detected by only four wavelengths, in contrast to the system described formerly, which detects the same spectral range with a diode-array spectrometer. With the use of a direct light path between the light-emitting diodes (LEDs), transducer, and detector, no fiber-optic light guides are required. The advantages and requirements of the new optical and electronic setup as well as several applications in gas sensing are discussed with respect to the limits of detection for some analytes.

White-light fiber-optic intermode interferometer

An interferometric system with a low-coherence light source and two multimode fiber-optic light guides operating in an intermode interference regime is considered theoretically. It is shown that the employment of fiber-optic intermode interferometers significantly expands the range of permissible mismatch between the lengths of the reference and signal interferometers. Mismatch up to a few centimeters is possible for light-emitting diodes (LED’s). The use of multimode light guides and intermode interference facilitates the construction of systems with fibers of great length and matching to an optical source.

Cumulation jets in microchannels inside explosive materials

Fiber optic light guides with diameters of 0.125 mm are used to measure the velocity of jets formed in microchannels inside plastic explosives. The velocity of the head of a jet can exceed the normal detonation velocity by a factor of two in air-filled microchannels with axes perpendicular to the detonation front.

Photostimulation with caged neurotransmitters using fiber optic lightguides

`Caged' neurotransmitters are molecules that are transformed to a neuroactive state by exposure to light of an appropriate wavelength and intensity. Use of these substances has centered on in vitro bath application and subsequent activation using light from lasers or flashlamps that is delivered into the preparation through microscope optics. We have tested a new and simpler method, using finely tapered fiberoptic lightguides, that promises to expand the use of caged compounds for in vitro and in vivo experimentation. We demonstrated the feasibility and flexibility of this method for caged neurotransmitter delivery using a range of ex vitro, in vitro and in vivo approaches. The degree and timing of uncaging could be controlled by manipulating the wavelength, intensity and timing of the light projected into the optical fiber. Because of the small size of the light guide and the ability to control light exposure at the source, this new method promises greater control over the spatial and temporal delivery of neuroactive substances than simple bath or iontophoretic application, and enables delivery of conventional neurotransmitters with a spatial and temporal resolution closer to that of the natural neuronal circuitry. In addition, this new method allows the application of normally labile substances, such as the free radical gas nitric oxide, by the photoconversion of photosensitive precursors.

Gas monitoring instrument utilising fibre optic, piezoelectric and gas-sensitive polymer techniques

The most usual form of instrument for the monitoring of gases such as carbon dioxide involves absorption bands in the infra-red spectrum, which in turn mandates the use of infra-red optics and sensors. The present instrument dispenses with the use of infra-red by employing visible light along with a gas-sensitive polymer which changes colour in the presence of CO 2, this being a reversible process. The instrument itself also utilises a novel realisation of the well-known double-beam-in-time principle in which fibre-optic light guides replace lens systems. The mechanical beam splitting is performed by a piezoelectric bimorph cantilever.

Optical sensing of oxygen using phosphorescence quenching

Optical measurements that exploit the ability of oxygen to quench the photoexcited states of other molecules provide an alternative to the standard electrochemical and paramagnetic methods of measuring molecular oxygen concentration. In the present work we have re-examined the phosphorescence quenching technique as a means of monitoring oxygen concentrations in a gas stream at room temperature. Camphorquinone (CQ) is selected because it has strong absorption and emission bands in the visible region, enabling the use of inexpensive silica fibre-optic light guides. Determination of oxygen in the range 0.1–25% is easily achievable and, for a 10 μm thick PVC film containing CQ, the time to attain 90% response is of the order of 10 s. Photooxidation and photoreduction account for a significant loss of material under certain conditions of illumination and film composition. The use of triplet lifetime as a measure of oxygen concentration offers several advantages. In particular, by using an intrinsic property of the sensing molecule, variations in lamp intensity and photomultiplier sensitivity are avoided and the effects of photobleaching reactions are minimized.

A new technique for in situ measurements of erosion and redeposition in a single discharge

Based on the very different refractive constants of quartz substrates (∼1.5) and of amorphous deposits (>1.7) collected in the scrape-off layer of TEXTOR, in situ reflectometry has been developed in order to determine the growth rates. Laboratory experiments comparing the light intensities reflected from the rear side of the system glass/deposit to the theoretically calculated reflectivity demonstrate the feasibility of the technique. The optical constants needed are determined ex situ by ellipsometry. For the application to TEXTOR, the Stockholm TEXTOR collector probe system has been equipped with fibre optic light guides which end behind quartz substrates carried by a replaceable graphite head. This arrangement avoids disturbance due to vibrations or due to observation over long distances.

Optical readout performance and phototubes testing for an internal tagging system

We describe the performance of the readout of the Jet-Target internal tagging system. The apparatus and methods to test signal transmission and time dispersion of 3.5 m fiber optic light guides, and time drift, gain measurement and rate effect of the phototubes are presented.

Phagocytosis by Kupffer cells predominates in pericentral regions of the liver lobule

These studies were designed to determine whether particle phagocytosis could be monitored from the surface of the perfused liver. To achieve this goal, decreases in reflected light were measured during phagocytosis of colloidal carbon particles. Livers were illuminated with 623-nm light via a relatively large fiber-optic light guide (tip diam 2 mm), and reflected light was monitored continuously. A decrease in reflected light was observed when carbon was infused that was proportional to the influent carbon concentration. Initial changes in reflected light were linearly related to rates of carbon uptake by Kupffer cells. Subsequently, rates of carbon uptake were determined from changes in reflected light in periportal and pericentral regions of the liver lobule with miniature fiber-optic light guides. In perfusions in the anterograde direction, rates of carbon uptake were approximately 80% higher in pericentral than periportal regions of the liver lobule. This pattern was reversed when livers were perfused in the retrograde direction. Thus particle phagocytosis predominates in downstream regions of the liver lobule. Because decreasing the pH of the influent perfusate increased carbon uptake, the pH gradient over the liver lobule may be involved in the regulation of particle uptake at the sublobular level.

Optics

Schott is pleased to announce the launch of its new cold light source, the KL 1500 electronic. The light source is used in the field of microscopy and also when photographing heat-sensitive objects to produce intense yet ‘cold’ illumination. After passing through a Schott KG1 heat filter the light from the 150W halogen bulb is directed to the object via flexible or semi-rigid fibre-optic light guides. These light guides are available in a variety of configurations with up to three branches with a maximum length of 1600 mm. Accessories for the KL 1500 electronic include a range of filters such as daylight conversion, neutral density and a variety of colours. In addition, a focusing lens can be fitted to the individual fibreoptic output beam to produce a spotlight effect. Polarising and coloured-glass filters are also available to fit directly into the focusing lens. The light source has a variable brightness control and a sliding bulb housing which permits quick and easy bulb replacement.