Optical Guides Research Articles

Instruments and methods for coating of wavelength-shifting materials used for noble liquid technology

The use of wavelength-shifting coatings is of primary interest in the area of liquified noble gases detectors. Argon and xenon are used as active medium in the neutrino physics and dark matter experiments, because charged particles crossing the noble liquid volume produce excitation and ionization followed by recombination and both the processes lead to the emission of VUV light. Noble liquid scintillation light emitted in the VUV range needs to be converted to be detected by conventional photosensors. Wavelength-shifting materials, such as TetraPhenyl-Butadiene and p-TerPhenyl, are used for this conversion to the visible range. The wavelength-shifters are particularly important in the case of large area detectors since only a fraction of the surface can be instrumented. To this purpose dedicated set-ups have been built and specific techniques have been adopted to produce and characterize very uniform wavelength-shifting coatings on highly reflecting material substrates, optical filters and optical guides. Some type of the facilities used to this task, with particular attention to the vacuum deposition systems, will be described, operations for production of the coatings will be reported, methods for the characterization of the samples will be briefly presented.

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.

Multi-feature round silicon membrane filters enable fractionation and analysis of small micro- and nanoplastics with Raman spectroscopy and nano-FTIR.

Visualization of small micro-(20-1 μm) and nanoplastics (<1 μm) combined with chemical identification is still a challenge. To address this, we designed and manufactured easy-to-handle silicon membrane filters with a standard round filter geometry of 25 mm in diameter and a 10 mm diameter filtration area, holding hexagonal sections with periodically arranged pores of either 250 nm or 1 μm. Due to their flat and reflective surface, the filters serve as a versatile substrate for spectroscopic identification of particles. Optical markers at different levels of magnification, including the bare eye, allow for an easy transfer and repositioning of samples between instruments and methods as well as for a re-measurement of nanoscale particles. We demonstrate how nanoscale particles of weakly absorbing polymers such as polyethylene and polystyrene are analyzed on these filters by nano-FTIR, a combination of atomic force microscopy and Fourier transform infrared spectroscopy. By sequential filtration we separated the fractions of small micro and nanoplastics from a degraded polylactic acid coffee cup lid and achieved subsequent identification by Raman and nano-FTIR spectroscopy. The applications presented in this study will enable future research regarding the identification of small polymer particles difficult to access by other methods.

Simple Visualization of Universal Ferroelastic Domain Walls in Lead Halide Perovskites.

Domain features and domain walls in lead halide perovskites (LHPs) have attracted broad interest due to their potential impact on optoelectronic properties of this unique class of solution-processable semiconductors. Using nonpolarized light and simple imaging configurations, ferroelastic twin domains and their switchings through multiple consecutive phase transitions are directly visualized. This direct optical contrast originates from finite optical reflections at the wall interface between two compositionally identical, orientationally different, optically anisotropic domains inside the material bulk. The findings show these domain walls serve as internal reflectors and steer energy transport inside halide perovskites optically. First-principles calculations show universal low domain-wall energies and modest energy barriers of domain switching, confirming their prevalent appearance, stable presence, and facile moving observed in the experiments. The generality of ferroelasticity in halide perovskites stems from their soft bonding characteristics. This work shows the feasibility of using LHP twin domain walls as optical guides of internal photoexcitations, capable of nonvolatile on-off switching and tunable positioning endowed by their universal ferroelasticity.

Highly Integrated Multi-Material Fibers for Soft Robotics.

Soft robots are envisioned as the next generation of safe biomedical devices in minimally invasive procedures. Yet, the difficulty of processing soft materials currently limits the size, aspect-ratio, manufacturing throughput, as well as, the design complexity and hence capabilities of soft robots. Multi-material thermal drawing is introduced as a material and processing platform to create soft robotic fibers imparted with multiple actuations and sensing modalities. Several thermoplastic and elastomeric material options for the fibers are presented, which all exhibit the rheological processing attributes for thermal drawing but varying mechanical properties, resulting in adaptable actuation performance. Moreover, numerous different fiber designs with intricate internal architectures, outer diameters of 700µm, aspect ratios of 103 , and a fabrication at a scale of 10s of meters of length are demonstrated. A modular tendon-driven mechanism enables 3-dimensional (3D) motion, and embedded optical guides, electrical wires, and microfluidic channels give rise to multifunctionality. The fibers can perceive and autonomously adapt to their environments, as well as, probe electrical properties, and deliver fluids and mechanical tools to spatially distributed targets.

Design and Simulation of the Solar Optical Guide Lighting and Ventilation System in a Building

With the continuous development of society, power consumption for the lighting and the ventilation in buildings accounts for more and more proportion of the total energy supply. With the aim of relieving the conflict between the fast-growing urbanization and power limitation, a solar optical guide lighting and ventilation (SOGLV) system combining natural lighting and natural ventilation is proposed in this study. The simulations are carried out to analyze the performance of optical guiding at different times by Monte Carlo method. Meanwhile, the performance of ventilation is simulated under different absorbed heat fluxes by Fluent. It is found from the research that the SOGLV system can achieve the goal of lighting and ventilation. The average indoor illumination intensity on the ground floor first increases then decreases within a day. The heat flux on the optical guide pipe wall appears in a block pattern. The maximum velocity is linearly correlated with the average absorbed heat flux on the optical guide wall, ranging from 0.90 m/s to 1.02 m/s.

An Optical Tool to Optimize the Output of a Photonic Integrated Chip Architecture

Photonic Integrated Chips (PICs) are an up-and-coming solution for base building blocks of quantum computers. The ready accessibility of photonics integrated systems and the fact that they allow for direct monolithic integration with electronics in a compact architecture have pushed the academic community to inspect their capabilities further. Still, at this stage, their characterization, control, and fine-tuning is an open issue for which this work aims to provide a viable solution. In this paper we present a method for an easy setup and an efficient architecture to simultaneously optimize multiple outputs of a PIC. The proposed solution can be embedded in an automation tool for tuning and verifying output on- and off-chip detectors. We fabricated a Silicon Oxynitride (SiON)-based PIC featuring a network of Mach-Zehnder interferometers (MZI) arranged in Clements architecture driven by Titanium-Titanium Nitride (TiTiN) thermistors. We interfaced the chip electronically through commercial driver modules and optically through optical guides and controlled it through a Python optimization algorithm. Finally, we retrieved the feedback of the control both by sensing it through integrated silicon photodetectors and by an image processing algorithm capable of inspecting the light intensity scattered by the waveguides in a custom region.

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.

High-performance 4096× ultra-high CPV module based on multiple concentrator units and optical guides.

Ultra-high concentrator photovoltaic systems aim to enhance the conversion efficiency of sunlight and to reduce the cost of electricity. However, it is still necessary to develop optical systems with higher efficiencies and angular tolerances for them to become a reality. This Letter proposes a novel design that is able to achieve a geometric concentration of 4096×. The system consists of four concentrator units based on parabolic mirrors and optical guides that concentrate the sunlight onto a single cell. Additionally, a preliminary proof-of-concept module has been assembled for validation purposes. The novel design exceeds the optical efficiency of the existing systems, ≈84%, and offers almost double acceptance angles, ≈0.6∘.

Genetic network regulating visual acuity makes limited contribution to visually guided eye emmetropization

During postnatal development, the eye undergoes a refinement process whereby optical defocus guides eye growth towards sharp vision in a process of emmetropization. Optical defocus activates a signaling cascade originating in the retina and propagating across the back of the eye to the sclera. Several observations suggest that visual acuity might be important for optical defocus detection and processing in the retina; however, direct experimental evidence supporting or refuting the role of visual acuity in refractive eye development is lacking. Here, we used genome-wide transcriptomics to determine the relative contribution of the retinal genetic network regulating visual acuity to the signaling cascade underlying visually guided eye emmetropization.Our results provide evidence that visual acuity is regulated at the level of molecular signaling in the retina by an extensive genetic network. The genetic network regulating visual acuity makes relatively small contribution to the signaling cascade underlying refractive eye development. This genetic network primarily affects baseline refractive eye development and this influence is primarily facilitated by the biological processes related to melatonin signaling, nitric oxide signaling, phototransduction, synaptic transmission, and dopamine signaling. We also observed that the visual-acuity-related genes associated with the development of human myopia are chiefly involved in light perception and phototransduction. Our results suggest that the visual-acuity-related genetic network primarily contributes to the signaling underlying baseline refractive eye development, whereas its impact on visually guided eye emmetropization is modest.

Next Generation Monitoring of SiC mosfets Via Spectral Electroluminescence Sensing

This article presents a new methodology for monitoring next generation SiC <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet</small> -based converters. The methodology uses the spectral distribution of electroluminescence that is emitted by the body diodes of SiC <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet</small> s and includes information on device current as well as the junction temperature. Intelligent estimation algorithms based on artificial neural networks allow processing the extracted information to separately estimate device current and junction temperature with high bandwidth. The resulting unified monitoring of device current and junction temperature galvanically isolates the sensors via optical guides from the power module. Thus, it can be effectively integrated into future power electronic modules to replace external temperature and current sensors and enable monitoring for safe and reliable long-term operation. Previous publications successfully investigated how either temperature or current information can be extracted from the intensity of the emitted light if the other variable is known. However, they did not aim to extract both variables at the same time from one measurement. This work presents how multiple optical sensors with different wavelength sensitivities and artificial-intelligence techniques can separately extract both variables. The proposed technology is evaluated using an automotive-grade SiC power module. Its utilization for monitoring future SiC-based converters allows reducing converter size and cost while increasing reliability.

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.

Artificial Optic Flow Guides Visual Attention in a Driving Scene.

The objective of this study was to investigate whether an artificial optic flow created by dot motion guides attention in a driving scene. To achieve safe driving, it is essential to understand the characteristics of human visual information processing as well as to provide appropriate support for drivers. Past research has demonstrated that expanding optic flow guides visual attention to the focus of expansion. Optic flow is an attractive candidate for use as a cue to direct drivers' attention toward the significant information. The question addressed concerns whether an artificial optic flow can successfully guide attention even in a traffic situation involving the optic flow that naturally occurs while driving. We developed a visual search paradigm embedded in a video of a driving scene. Participants first observed an optic flow motion pattern superimposed on the video for brief period; next, when the optic flow and video ceased, they searched a static display for a target among multiple distractors. The target detection was faster when a target's locus coincided with the implied focus of expansion from the preceding optic flow (vs. other loci). The artificial optic flow guides attention and facilitates searching objects at the focus of expansion even when the optic flow was superimposed on a driving scene. Optic flow can be an effective cue for guiding drivers' attention in a traffic situation. This finding contributes to the understanding of visual attention in moving space and helps develop technology for traffic safety.

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.

Task-irrelevant optic flow guides attention in visual search.

Motion is an important factor in visual information processing. Studies have shown that global optic flow guides attention, but it remains unclear whether this attentional guidance occurs regardless of top-down attentional control settings for another endogenous cue. To address this issue, we developed a visual search paradigm in which a task-irrelevant optic flow starts and stops prior to a visual search task itself. Participants first observed an initial optic flow motion pattern for a brief period; next, they searched a static display for a target amongst multiple distractors. Results showed faster target detection when a target's locus coincided with the implied focus of expansion (FOE) from the preceding optic flow (vs. other loci). Eye-movement analyses revealed that initial saccades were drawn to the FOE during optic flow exposures and that relatively few saccades were needed to find targets contingent to the preceding FOE. The advantage of FOE for finding target occurred even when a salient feature singleton captured attention or when a task-relevant feature singleton was prioritized. Results of six experiments suggest that attentional control settings for a feature singleton do not over-ride a sustained influence of optic flow on attentional guidance.

Comparison of Optical Surface Guide System and ConeBeamCT Scans in Patient Positioning in Breast CA Radiotherapy

Comparison of Optical Surface Guide System and ConeBeamCT Scans in Patient Positioning in Breast CA Radiotherapy

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.

Generation of propagation-invariant and intensity-controlled dark hollow beams by a refractive beam shaping system.

Dark hollow beams (DHBs) have great potential in the applications of optical manipulation, and the generation of DHBs is still a challenging and rewarding issue. In this paper, we present a beam shaping system for generating DHBs. The proposed system is composed of a freeform lens array and a non-classical zoom system which has a constant focal length but various image locations. The DHBs with a well-controlled intensity profile generated by the proposed system is not sensitive to the change of the intensity distribution of the incident beam, which allows flexible choices of light sources. Moreover, the annular pattern produced by the DHB remains unchanged when the image plane is moved a long distance of 17mm, and the energy efficiency of the beam shaping system is greater than 90% when Fresnel loss is considered. The proposed beam shaping system endows the generated DHBs with new properties and may have great potential in the field of optical tweezers and atom guides.

Complex-structured liquid crystal clad elliptical guides – the cases of with and without conducting sheath helix loadings

Electromagnetic (EM) wave propagation through three-layer liquid crystal clad elliptical optical guides was investigated under the situations when those were loaded with and without conducting sheath helix structures. Due to exceptional features of liquid crystals, such as durable electro-optic behaviour as well as optical anisotropy, the presence of these greatly affects wave propagation, thereby controlling the confinement of power in guides. The present work was aimed to investigate the comparison between three-layer elliptical optical guide having radially anisotropic liquid crystal as its outer clad, and loaded with and without conducting sheath helix structure at the core-inner (dielectric) clad interface. The results reveal prudent use of the former kind (of guide) over the latter one owing to its having on-demand control over the propagation of power, and also, enhanced confinement in the outermost section for the guide. These features allow such sheath helix-loaded guides to be useful in optical sensing applications.