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.

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.

Integrated dynamic wet spinning of core-sheath hydrogel fibers for optical-to-brain/tissue communications.

Hydrogel optical light-guides have received substantial interest for applications such as deep-tissue biosensors, optogenetic stimulation and photomedicine due to their biocompatibility, (micro)structure control and tissue-like Young's modulus. However, despite recent developments, large-scale fabrication with a continuous synthetic methodology, which could produce core-sheath hydrogel fibers with the desired optical and mechanical properties suitable for deep-tissue applications, has yet to be achieved. In this study, we report a versatile concept of integrated light-triggered dynamic wet spinning capable of continuously producing core-sheath hydrogel optical fibers with tunable fiber diameters, and mechanical and optical propagation properties. Furthermore, this concept also exhibited versatility for various kinds of core-sheath functional fibers. The wet spinning synthetic procedure and fabrication process were optimized with the rational design of the core/sheath material interface compatibility [core = poly(ethylene glycol diacrylate-co-acrylamide); sheath = Ca-alginate], optical transparency, refractive index and spinning solution viscosity. The resulting hydrogel optical fibers exhibited desirable low optical attenuation (0.18 ± 0.01 dB cm−1 with 650 nm laser light), excellent biocompatibility and tissue-like Young's modulus (<2.60 MPa). The optical waveguide hydrogel fibers were successfully employed for deep-tissue cancer therapy and brain optogenetic stimulation, confirming that they could serve as an efficient versatile tool for diverse deep-tissue therapy and brain optogenetic applications.

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.

Coherent propagation of laser beams in a small-sized system of weakly coupled optical light guides

The features of the self-action of a wave field in a small-sized optical system consisting of $2N$ identical light guides, which are disposed equidistantly along a ring, and an isolated fiber in the center are studied analytically and numerically. Stable exact solutions are found for intense wave beams in such a system, allowing long-distance coherent transport of radiation in a set of optical fibers. The total beam power in this case can exceed several times the critical power of self-focusing in the continuous medium. This is clearly manifested for the out-of-phase spatial distribution of ${u}_{n}={(\ensuremath{-}1)}^{n}f$, which is stable at arbitrary powers. Direct numerical simulation of the nonlinear unidirectional wave propagation equation confirms the stability of found wave field distributions.

Решение для фундаментальной моды ступенчатого оптического волоконного волновода с керровской нелинейностью

Решение для фундаментальной моды ступенчатого оптического волоконного волновода с керровской нелинейностью

Tolerancing the alignment of large-core optical fibers, fiber bundles and light guides using a Fourier approach.

Optical fiber technology is found in a wide variety of applications to flexibly relay light between two points, enabling information transfer across long distances and allowing access to hard-to-reach areas. Large-core optical fibers and light guides find frequent use in illumination and spectroscopic applications, for example, endoscopy and high-resolution astronomical spectroscopy. Proper alignment is critical for maximizing throughput in optical fiber coupling systems; however, there currently are no formal approaches to tolerancing the alignment of a light-guide coupling system. Here, we propose a Fourier alignment sensitivity (FAS) algorithm to determine the optimal tolerances on the alignment of a light guide by computing the alignment sensitivity. The algorithm shows excellent agreement with both simulated and experimentally measured values and improves on the computation time of equivalent ray-tracing simulations by two orders of magnitude. We then apply FAS to tolerance and fabricate a coupling system, which is shown to meet specifications, thus validating FAS as a tolerancing technique. These results indicate that FAS is a flexible and rapid means to quantify the alignment sensitivity of a light guide, widely informing the design and tolerancing of coupling systems.

Structural Color for Additive Manufacturing: 3D-Printed Photonic Crystals from Block Copolymers.

The incorporation of structural color into 3D printed parts is reported, presenting an alternative to the need for pigments or dyes for colored parts produced through additive manufacturing. Thermoplastic build materials composed of dendritic block copolymers were designed, synthesized, and used to additively manufacture plastic parts exhibiting structural color. The reflection properties of the photonic crystals arise from the periodic nanostructure formed through block copolymer self-assembly during polymer processing. The wavelength of reflected light could be tuned across the visible spectrum by synthetically controlling the block copolymer molecular weight and manufacture parts that reflected violet, green, or orange light with the capacity to serve as selective optical filters and light guides.

Preparation and optical properties of composite materials based on polybenzimidazole and silver nanoparticles

Rigid-chain heat resistant polymers (with poly-2,2'-p-oxydiphenylene-5,5′-bisbenzimidazole as example) were impregnated for the first time with a silver-containing precursor in formic acid and in supercritical carbon dioxide. A procedure allowing the precursor reduction to silver nanoparticles both throughout the volume by thermal annealing of the films in the temperature interval 100–150°С and in the targeted mode using lasers operating at 405 and 532 nm was developed. It opens prospects for developing a process for production of heatresistant optical gratings and light guides. The reduces nanoparticles and their agglomerates have the size in the interval 50–200 nm and give a plasmon band in the range 450–460 nm.

Parallel fluorescence and phosphorescence monitoring of singlet oxygen photosensitization in rats

The time- and spectral-resolved set-up for measurements of weak infrared luminescence of photosensitizers (PSs) and singlet oxygen using optical lightguides was used on skin of laboratory animals in vivo. Wistar rats with abdominal incisions treated by methylis aminolevulinitis (MAL) were used as a model. A control group of animals with abdominal incisions was also tested. Spectrally resolved fluorescence of the PS was acquired during the treatment from the same spot. The intensity and spectral profile of the fluorescence signal from the skin can be used to guide the detection setup to the investigated spots in the lesion. The rate of bleaching of Protoporphyrin IX band and appearance of a band of its photoproducts during the treatment can be characterized by the exposition ED, under which the latter becomes dominant feature in fluorescence spectrum. ED value differs statistically significantly between the normal skin and the lesion treated by MAL. No direct proportionality was found between the fluorescence signal and singlet oxygen production. Nevertheless, the strong fluorescence signal is necessary but not a sufficient condition for higher singlet oxygen production in vivo. ED value correlates rather well with production of singlet oxygen, but differently in lesion and normal skin. Lifetimes of singlet oxygen differ between spots outside and in the lesion. PS triplet state lifetimes exhibit weak difference between spots treated and untreated by MAL.

Study of scintillation in natural and synthetic quartz and methacrylate

Samples from different materials typically used as optical windows or light guides in scintillation detectors were studied in a very low background environment, at the Canfranc Underground Laboratory, searching for scintillation. A positive result can be confirmed for natural quartz: two distinct scintillation components have been identified, not being excited by an external gamma source. Although similar effect has not been observed neither for synthetic quartz nor for methacrylate, a fast light emission excited by intense gamma flux is evidenced for all the samples in our measurements. These results could affect the use of these materials in low energy applications of scintillation detectors requiring low radioactive background conditions, as they entail a source of background.

A charged particle detector array for detection of light charged particles from nuclear reactions

A 4π charged particle detector array (CPDA), for detecting low-Z charged particles from nuclear reactions, was built to improve selection of fusion evaporation channels for in-beam gamma spectroscopy measurements at Inter University Accelerator Centre, New Delhi. The array consists of fourteen fast–slow plastic phoswich detectors coupled to photomultiplier tubes through indigenously developed optical light guides. This paper describes design of optical light guide, target chamber, front-end electronics and presents in-beam performance of the array. Custom made analogue electronic device enables online selection of nuclear reaction channel. The charged particle detection efficiency and improvement in peak to background ratio obtained using CPDA in conjunction with a gamma-detector array demonstrates its usefulness in selection of specific nuclear reaction channel. This array has been used in a number of nuclear spectroscopic and reaction investigations.

Monolithic crystals for PET devices: Optical coupling optimization

In this work we present a method to efficiently collect scintillation light when using monolithic scintillator crystals. The acceptance angle of the scintillation light has been reduced by means of optical devices reducing the border effect which typically affects continuous crystals. We have applied this procedure on gamma detectors for PET systems using both position sensitive PMTs and arrays of SiPMs. In the case of using SiPMs, this approach also helps to reduce the photosensor active area.We evaluated the method using PMTs with a variety of different crystals with thicknesses ranging from 10 to 24mm. We found that our design allows the use of crystal blocks with a thickness of up to 18mm without degrading the spatial resolution caused by edge effects and without a significant detriment to the energy resolution. These results were compared with simulated data. The first results of monolithic LYSO crystals coupled to an array of 256 SiPMs by means of individual optical light guides are also presented.

On the nature of the light produced within PMMA optical light guides in scintillation fiber-optic dosimetry

The goal of this study was to evaluate the nature of the stem effect light produced within an optical fiber, to quantify its composition, and to evaluate the efficiency of the chromatic technique to remove the stem effect. Spectrometry studies were performed during irradiations of a bare PMMA optical fiber with kilovoltage x-rays from a superficial therapy unit, an Ir-192 high-dose-rate brachytherapy source, a Co-60 external-therapy unit, and megavoltage electrons and x-rays from a linear accelerator. Stem effect spectra can be accurately modeled by a linear combination of the Cerenkov light and fluorescence emitted spectra. Fluorescence light contributes more for lower-energy modalities. Cerenkov light contributes more as the energy increases above the threshold for its production. The chromatic stem effect removal technique is accurate in most of the situations. However, noticeable differences were obtained between very specific high-energy irradiation conditions. It would be advantageous to implement an additional channel in the chromatic stem effect removal chain or implement a spectral approach to independently remove the Cerenkov and the fluorescence components from the signal of interest. This would increase the accuracy and versatility of the actual chromatic stem effect removal technique.

Biosensors for Brain Trauma and Dual Laser Doppler Flowmetry: Enoxaparin Simultaneously Reduces Stroke-Induced Dopamine and Blood Flow while Enhancing Serotonin and Blood Flow in Motor Neurons of Brain, In Vivo

Neuromolecular Imaging (NMI) based on adsorptive electrochemistry, combined with Dual Laser Doppler Flowmetry (LDF) is presented herein to investigate the brain neurochemistry affected by enoxaparin (Lovenox®), an antiplatelet/antithrombotic medication for stroke victims. NMI with miniature biosensors enables neurotransmitter and neuropeptide (NT) imaging; each NT is imaged with a response time in milliseconds. A semiderivative electronic reduction circuit images several NT’s selectively and separately within a response time of minutes. Spatial resolution of NMI biosensors is in the range of nanomicrons and electrochemically-induced current ranges are in pico- and nano-amperes. Simultaneously with NMI, the LDF technology presented herein operates on line by illuminating the living brain, in this example, in dorso-striatal neuroanatomic substrates via a laser sensor with low power laser light containing optical fiber light guides. NMI biotechnology with BRODERICK PROBE® biosensors has a distinct advantage over conventional electrochemical methodologies both in novelty of biosensor formulations and on-line imaging capabilities in the biosensor field. NMI with unique biocompatible biosensors precisely images NT in the body, blood and brain of animals and humans using characteristic experimentally derived half-wave potentials driven by oxidative electron transfer. Enoxaparin is a first line clinical treatment prescribed to halt the progression of acute ischemic stroke (AIS). In the present studies, BRODERICK PROBE® laurate biosensors and LDF laser sensors are placed in dorsal striatum (DStr) dopaminergic motor neurons in basal ganglia of brain in living animals; basal ganglia influence movement disorders such as those correlated with AIS. The purpose of these studies is to understand what is happening in brain neurochemistry and cerebral blood perfusion after causal AIS by middle cerebral artery occlusion in vivo as well as to understand consequent enoxaparin and reperfusion effects actually while enoxaparin is inhibiting blood clots to alleviate AIS symptomatology. This research is directly correlated with the medical and clinical needs of stroke victims. The data are clinically relevant, not only to movement dysfunction but also to the depressive mood that stroke patients often endure. These are the first studies to image brain neurotransmitters while any stroke medications, such as anti-platelet/anti-thrombotic and/or anti-glycoprotein are working in organ systems to alleviate the debilitating consequences of brain trauma and stroke/brain attacks.

Performance Evaluation of the Inveon Dedicated PET Preclinical Tomograph Based on the NEMA NU-4 Standards

The Inveon dedicated PET (DPET) scanner is the latest generation of preclinical PET systems devoted to high-resolution and high-sensitivity murine model imaging. In this study, we report on its performance based on the National Electrical Manufacturers Association (NEMA) NU-4 standards. The Inveon DPET consists of 64 lutetium oxyorthosilicate block detectors arranged in 4 contiguous rings, with a 16.1-cm ring diameter and a 12.7-cm axial length. Each detector block consists of a 20 x 20 lutetium oxyorthosilicate crystal array of 1.51 x 1.51 x 10.0 mm elements. The scintillation light is transmitted to position-sensitive photomultiplier tubes via optical light guides. Energy resolution, spatial resolution, sensitivity, scatter fraction, and counting-rate performance were evaluated. The NEMA NU-4 image-quality phantom and a healthy mouse injected with (18)F-FDG and (18)F(-) were scanned to evaluate the imaging capability of the Inveon DPET. The energy resolution at 511 keV was 14.6% on average for the entire system. In-plane radial and tangential resolutions reconstructed with Fourier rebinning and filtered backprojection algorithms were below 1.8-mm full width at half maximum (FWHM) at the center of the field of view. The radial and tangential resolution remained under 2.0 mm, and the axial resolution remained under 2.5-mm FWHM within the central 4-cm diameter of the field of view. The absolute sensitivity of the system was 9.3% for an energy window of 250-625 keV and a timing window of 3.432 ns. At a 350- to 625-keV energy window and a 3.432-ns timing window, the peak noise equivalent counting rate was 1,670 kcps at 130 MBq for the mouse-sized phantom and 590 kcps at 110 MBq for the rat-sized phantom. The scatter fractions at the same acquisition settings were 7.8% and 17.2% for the mouse- and rat-sized phantoms, respectively. The mouse image-quality phantom results demonstrate that for typical mouse acquisitions, the image quality correlates well with the measured performance parameters in terms of image uniformity, recovery coefficients, attenuation, and scatter corrections. The Inveon system, compared with previous generations of preclinical PET systems from the same manufacturer, shows significantly improved energy resolution, sensitivity, axial coverage, and counting-rate capabilities. The performance of the Inveon is suitable for successful murine model imaging experiments.

SU-EE-A2-01: Proton Dose Deposition in Water-Equivalent Plastic Scintillation Detectors

Purpose: Designing a scintillation detector for proton radiotherapy requires careful considerations. Most scintillators exhibit some energy dependence due to quenching under proton irradiation. Water equivalence, one of the main advantages of plastic scintillators for photon measurement has yet to be validated for the wide range of proton energies used for proton therapy. In this work, we studied the most important factors that would affect the performance of a scintillation detector. Method and Materials: Experimental measurements were used to study quenching effect in scintillators and the amount of the spurious light produced in the optical light guides. Monte Carlo simulations were performed with GEANT4. Proton beams between 50 and 250 MeV were simulated to study the water equivalence, the optimal size, the optimal coating of plastic and inorganic scintillators. Results: We found that the dose deposited in a plastic scintillator was within 2% of the dose deposited in a similar volume of water on the whole depth dose curve for protons with energies higher than 50 MeV. Inorganic scintillators received a dose 5 to 10% lower than the dose in a similar volume of water. The main disadvantage of plastic scintillators is the quenching effect that reduces the amount of scintillation and result in 26% and 14% underestimation at the Bragg peak of 50 MeV and 250 MeV, respectively. To avoid the averaging effect, the radius of the scintillation detector should be 0.25 mm or less. To improve the signal of such small volume detector the scintillator can be coated with a diffuse reflector. Conclusion: According to our experimental and Monte Carlo analysis of scintillation detection in the higher energy range for proton therapy, it is possible to construct an effective detector that would overcome the problems traditionally encountered in proton dosimetry.

59.5L: Late‐News Paper: A 68‐inch SVGA 4×4 Tiled Display

AbstractIn this paper, we describe recent advances in the production and performance of a seamless tiled display technology. A new automated method to produce arrays of optical light guides has been implemented in the development of a 68‐inch 16‐tile SVGA (800×600) display.