Optical Concept Research Articles

Tracking movements: Black activism, aerial surveillance, and transparency optics

This article examines the 2015 Baltimore uprisings that emerged in the wake of Freddie Gray’s death and the Federal Bureau of Investigation’s (FBI) covert aerial surveillance of the protesters. It does so by investigating the records that the American Civil Liberties Union (ACLU) extracted from the government agency through the Freedom of Information Act (FOIA). The article first traces the process of discovering and circulating this corpus of information. It then considers what the digital disclosures, including 18-plus hours of aerial surveillance footage, can reveal about the racial and technological dimensions of contemporary state surveillance. In considering the agency’s strategies of public admission, I develop the concept of transparency optics and identify some of its potential logics at work. I then discuss these records’ epistemological limits, such as the shortcomings of analyzing digital processes through ocularcentric approaches. Finally, this article contrasts the FBI videos’ panoptic vantage of the protests with the embodied, ground-level perspective of a local participant’s documentary film.

Broadband Achromatic Metasurface-Refractive Optics.

Existing methods of correcting for chromatic aberrations in optical systems are limited to two approaches: varying the material dispersion in refractive lenses or incorporating grating dispersion via diffractive optical elements. Recently, single-layer broadband achromatic metasurface lenses have been demonstrated but are limited to diameters on the order of 100 μm due to thelarge requiredgroup delays. Here, we circumvent this limitation and design a metacorrector bycombininga tunable phase and artificial dispersion to correct spherical and chromatic aberrations in a large spherical plano-convex lens. The tunability results from a variationin light confinement in sub-wavelength waveguides by locally tailoring the effective refractive index. The effectiveness of this approach is further validated by designing a metacorrector, which greatly increases the bandwidth of a state-of-the-art immersion objective (composed of 14 lenses and 7 types of glasses) from violet to near-infrared wavelengths. This concept of hybrid metasurface-refractive optics combines the advantages of both technologies in terms of size, scalability, complexity, and functionality.

Diffraction-Beam Optics of Filamentation: I–Formalism of Diffraction Beams and Light Tubes

The concept of nonstationary diffraction-beam optics of high-power femtosecond laser pulses is presented. According to the concept, the power of a beam propagates along specific light structures—diffraction- beam tubes. These tubes do not intersect and do not exchange energy, but changes in their shape and cross sections during propagation show the effect of physical processes that occur with radiation in the medium. The nonstationary theory is supplemented with evolutionary equations for time-averaged diffraction rays and effective squared radii of diffraction tubes.

Multimodal Optical Medical Imaging Concepts Based on Optical Coherence Tomography

Optical medical imaging techniques in general exhibit outstanding resolution and molecule-specific contrast. They come however with a limited penetration in depth and small field of view. Multimodal concepts help to combine complementary strengths of different imaging technologies. The present article reviews the advantages of optical multimodal imaging concepts using optical coherence tomography (OCT) as core technology. In particular we first discuss polarization sensitive OCT, Doppler OCT and OCT angiography, OCT elastography and spectroscopic OCT as intramodal concepts. To highlight intermodal imaging concepts, we then chose the combination of OCT with photoacoustics, and with non-linear optical microscopy. The selected multimodal concepts and their particular complementary strengths and applications are discussed in detail. The article concludes with notes on standardization of OCT imaging and multimodal extensions.

Facilitating understanding of image formation through the luminous ray model mediated by virtual simulation

The ray model is usually applied to explain optical phenomena involving light propagation through an optical system and the formation of an image. However, students have difficulties understanding the image formation in some cases because the traditional ray model only represents special light rays. In the present study, we replaced the traditional ray model with the luminous ray model (LRM) to help students understand image formation. In addition, the positive impact of virtual simulation (VS) in the learning process has been documented over the past few decades. The purposes of this study were to investigate high school students' conceptual change in learning image formation through the LRM, and to explore the learning effectiveness of VS on learning different optical concepts. The results indicated that the LRM is helpful in improving students' conceptual understanding. A further analysis showed that VS+LRM was more beneficial than other groups regarding the concept that the object lying on the horizontal central axis could form a real image. These results will help science teachers develop an instructional module to facilitate students' learning of image formation.

Finite element time-domain body-of-revolution Maxwell solver based on discrete exterior calculus

We present a finite-element time-domain (FETD) Maxwell solver for the analysis of body-of-revolution (BOR) geometries based on discrete exterior calculus (DEC) of differential forms and transformation optics (TO) concepts. We explore TO principles to map the original 3-D BOR problem to a 2-D one in the meridian ρz-plane based on a Cartesian coordinate system where the cylindrical metric is fully embedded into the constitutive properties of an effective inhomogeneous and anisotropic medium that fills the domain. The proposed solver uses a (TEϕ,TMϕ) field decomposition and an appropriate set of DEC-based basis functions on an irregular grid discretizing the meridian plane. A symplectic time discretization based on a leap-frog scheme is applied to obtain the full-discrete marching-on-time algorithm. We validate the algorithm by comparing the numerical results against analytical solutions for resonant fields in cylindrical cavities and against pseudo-analytical solutions for fields radiated by cylindrically symmetric antennas in layered media. We also illustrate the application of the algorithm for a particle-in-cell (PIC) simulation of beam-wave interactions inside a high-power backward-wave oscillator.

Feature issue introduction: Topological Photonics and Materials.

Photonic crystals have become a very common and powerful concept in optics since its introduction in the 1980s by Eli Yablonovitch and Sajeev John. It is in fact a concept borrowed from condensed matter physics. The discussion of photonic bands and bandgaps allows us to manipulate light on an optical chip, along a photonic crystal fiber and even in the quantum optics regime. Now, we are witnessing another round of concept translation again from condensed matter physics to optics about topology. Describing photonic bands by using their topology in the reciprocal space gives us a new tool to understand wave propagation and to design optical components. Topology is also an important aspect in light-matter interaction in the field of metamaterials and 2D materials.

Particle emission from open quantum systems

In this work, we discuss connections between different theoretical physics communities and their works, all related to systems that act as sources of particles such as photons, phonons, or electrons. Our interest is to understand how a low-dimensional quantum system driven by coherent fields, e.g. a two-level system, Jaynes-Cummings system, or photon pair source driven by a laser pulse, emits photons into a waveguide. Of particular relevance to solid-state sources is that we provide a way to include dissipation into the formalism for temporal-mode quantum optics. We will discuss the connections between temporal-mode quantum optics, scattering matrices, quantum stochastic calculus, continuous matrix product states and operators, and very traditional quantum optical concepts such as the Mandel photon counting formula and the Lindblad form of the quantum-optical master equation. We close with an example of how our formalism relates to single-photon sources with dephasing.

Optically Graded Ultra Dark Absorber for Visible and Near-infrared Wavelength Range

Near perfect absorbers find application in many areas including solar cells, energy harvesting and antireflection coatings for space applications. Here we report the use of optical gradation concept to fabricate a near perfect absorber on etched Si wafer. As a proof of concept, 99.4% absorption is achieved in the broad range of 300 nm to 2000 nm. Moreover, absorption capacity of optically graded surface remains higher than 99% up to beam incident angle of 50°. While carbon nanotubes (index ~1.1) are used as top layer, subsequent layers with increasing optical index across the thickness are chosen so as to satisfy zero reflection condition on multilayered assembly. Inward bending of incident beam and total internal reflection of reflected beam caused due to optical index gradient contributes to absorb the incident beam more efficiently. In addition, multiple scattering of incident beam due to the presence of multiscale feature size in graded assembly helps to absorb shorter as well as longer wavelengths of incident light. The graded assembly shows contact angle of 160° with roll-off angle equal to 5° implying that the graded absorber is not only super black but also superhydrophobic and self-cleaning in nature. The combination of properties shown by the super absorber makes it very attractive, especially for next generation solar cells to harness energy in the wavelength range of 1000 nm to 2000 nm.

New Concepts for 3D Optics in X-ray Microscopy

New Concepts for 3D Optics in X-ray Microscopy

RELATIVE EFFECTIVENESS OF CASE-BASED AND COLLABORATIVE LEARNING STRATEGIES ON STUDENTS’ ACHIEVEMENT AND RETENTION IN SENIOR SECONDARY SCHOOL PHYSICS

This study investigated the relative effectiveness of case-based and collaborative learning strategies on students’ achievement and retention in senior secondary school physics. The study adopted pretest, posttest control group design. Simple random sampling technique was used to select three schools used for the study. The sample used for the study was eighty five (85) senior secondary two (SS 2) physics students randomly selected from the three schools in Ileoluji/Okeigbo Local Government Area of Ondo State, Nigeria. The study made use of Physics Achievement Test (PAT) with internal consistency of 0.84 using Kuder Richardson Formular 21. The data collected were analysed using Analysis of Covariance and Scheffe post hoc analysis was used to obtain the direction of significance. From the findings, it was observed that, learning strategies had significant main effect on students’ achievement (F (2,82) = 134.97, p = 0.000) and retention (F (2,82) = 20.67, p = .000) in the concept of optics in physics. The results of the Scheffe post hoc analysis indicated that, case-based learning strategy was the most effective in facilitating students’ achievement and retention in the concept of optics. This was followed by collaborative learning strategy while conventional learning strategy was found to be the least facilitative. Conclusion from the findings led to the recommendation that, teachers should be encouraged to adopt the use of case-based and collaborative learning strategy in teaching the concept of optics in physics in order for the students to develop problem solving skills, construction of knowledge and student-centred activities. Article visualizations:

Beamforming Networks for antenna array, useful inWiFi applications

In this paper several types of beamforming networks have been presented, this proposal can be used for an array antenna, which are used in several types of WiFi applications, IEEE 802.11b/g/draft-n. The first design corresponds to a 4x4 Butler Matrix for a resonance frequency at 2.45 GHz, depending on the port through which the signal is excited, it will be possible to obtain several variations in phase at the output ports (45°, 135°, -45° and -135°), the proposed Butler matrix has been optimized from a generalized matrix scheme, reducing the size through a simple overlap of multiple transmission lines to l/4 at the central frequency. The second design corresponds to a Rotman lens with a characteristic resonance frequency of 5.8 GHz, with a maximum focal angle of 30°, for this design has been used geometric optics concept, and the last design has been made for a frequency of 5.8 GHz using a slot array designed with Substrate Integrated Waveguide technology.

Nonimaging optics: a tutorial

Nonimaging optics is the theory of thermodynamically efficient optics and as such, depends more on thermodynamics than on optics. Historically, nonimaging optics that work as ideal concentrators have been discovered through such heuristic ideas as “edge ray involutes,” “string method,” “simultaneous multiple surface,” and “tailored edge ray concentrator,” without a consistent theoretical definition of what “ideal” means. In this tutorial, we provide a thermodynamic perspective of nonimaging optical designs to shine light on the commonality of all these designing ideas, or what “ideal” nonimaging design means. Hence, in this paper, a condition for the “best” design is proposed based purely on thermodynamic arguments, which we believe have profound consequences. Thermodynamics may also be the most intuitive way for a reader who is new to this subject to understand or study it within a certain framework, instead of learning from sporadic designing methodologies. This way of looking at the problem of efficient concentration and illumination depends on probabilities, the ingredients of entropy, and information theory, while “optics” in the conventional sense recedes into the background. We attempt to link the key concept of nonimaging optics, etendue, with the radiative heat transfer concept of view factor, which may be more familiar to some readers. However, we do not want to limit the readers to a single thermodynamic understanding of this subject. Therefore, two alternative perspectives of nonimaging optics will also be introduced and used throughout the tutorial: the definition of a nonimaging optics design according to the Hilbert integral, and the phase space analysis of the ideal design. The tutorial will be organized as follows: Section 1 highlights the difference between nonimaging and imaging optics, Section 2 describes the thermodynamic understanding of nonimaging optics, Section 3 presents the alternative phase space representation of nonimaging optics, Section 4 describes the most basic nonimaging designs using Hottel’s strings, Section 5 discusses the geometric flow line designing method, and Section 6 summarizes the various concepts of nonimaging optics.

G-index: A new metric to describe dynamic refractive index effects in HPLC absorbance detection

High performance liquid chromatography (HPLC) with a solvent gradient and absorbance detection is one of the most widely used methods in analytical chemistry. The observed absorbance baseline is affected by the changes in the refractive index (RI) of the mobile phase. Near the limited of detection, this complicates peak quantitation. The general aspects of these RI-induced apparent absorbance effects are discussed. Two different detectors with fundamentally different optics and flow cell concepts, a variable-wavelength detector equipped with a conventional flow cell and a diode-array detector equipped with a liquid core waveguide flow cell, are compared with respect to their RI behavior. A simple method to separate static – partly unavoidable – RI effects from dynamic RI effects is presented. It is shown that the dynamic RI behavior of an absorbance detector can be well described using a single, relatively easy-to-determine metric called the G-index. The G-index is typically in the order of a few seconds and its sign depends on the optical flow cell concept.

Spatial dispersion of index components required for building invisibility cloak medium from photonic crystals

The opportunities to use dielectric photonic crystals (PhCs) as the media of cylindrical invisibility cloaks, designed using transformation optics (TO) concepts, are investigated. It is shown that TO-based prescriptions for radial index dispersion, responsible for turning waves around hidden objects, can be dropped if the PhC media support self-collimation of waves in bent crystals. Otherwise, to provide prescribed anisotropy of index dispersion, it is possible to employ PhCs with rectangular lattices. It is found, however, that at acceptable cloak thicknesses, modifications of crystal parameters do not allow for achieving the prescribed level of index anisotropy. This problem is solved by finding the reduced spatial dispersion law for the radial index component, which is characterized by decreased against TO-prescriptions values near the target and increased values in outer layers of the cloak. The cloak utilizing reduced prescriptions for indices is shown to perform almost as efficiently as a TO-based cloak, in terms of both wave front restoration behind the target and reducing the total scattering cross-width of the target.

Optimization of Digital Image Processing Method to Improve Smoke Opacity Meter Accuracy

One of the parameters of exhaust emission testing on diesel engines is the level of smoke opacity. If the opacity is high then the emission quality is bad. The instrument for measuring smoke opacity is called Smoke Opacity Meter. The commonly used basic concept to measure smoke density is by utilizing a light sensor (optical sensor). Development of Smoke Opacity Meter applies the concept of Digital Image Processing. Even though it has initially begun, the measurement result is yet as perfect as Optical Sensor Concept. Therefore, this paper describes on how to implement the Digital Image Processing Method in processing the smoke opacity video data.

A compact disc under skimming light rays

The optical properties of a compact disc (CD) under “skimming” light rays have been analyzed. We have noticed that a clear green line can be detected when the disc is irradiated with light rays coming from a lamp in such a way that only those skimming the CD, held horizontally, are selected. We provide a physical interpretation of this phenomenon on the basis of elementary optics concepts. Extension of these concepts to digital versatile discs (DVDs) is given.

Entanglement indicators for quantum optical fields: three-mode multiport beamsplitters EPR interference experiments

We generalize a new approach to entanglement conditions for light of undefined photons numbers given in Żukowski et al (2017 Phys. Rev. A 95 042113) for polarization correlations to a broader family of interferometric phenomena. Integrated optics allows one to perform experiments based upon multiport beamsplitters. To observe entanglement effects one can use multi-mode parametric down-conversion emissions. When the structure of the Hamiltonian governing the emissions has (infinitely) many equivalent Schmidt decompositions into modes (beams), one can have perfect EPR-like correlations of numbers of photons emitted into ‘conjugate modes’ which can be monitored at spatially separated detection stations. We provide entanglement conditions for experiments involving three modes on each side, and three-input-three-output multiport beamsplitters, and show their violations by bright squeezed vacuum states. We show that a condition expressed in terms of averages of observed rates is a much better entanglement indicator than a related one for the usual intensity variables. Thus, the rates seem to emerge as a powerful concept in quantum optics, especially for fields of undefined intensities.

Stepwise Luneburg Lens for Bloch Surface Waves

In order to enlarge the capability for in-plane manipulation of the Bloch surface wave (BSW), we investigate 2D gradient index (GRIN) optical components using a finite-difference time-domain (FDTD) numerical method. To ease difficulties in fabrication to acquire a continuous index profile of GRIN optical components, we propose a stepwise index profile. For 2D surface wave devices, such discrete index steps can be achieved by stepwise structuring of the top layer, also called the device layer. For the demonstration of the stepwise GRIN optics concept, we consider a Luneburg lens, which is a good example of the GRIN optical component that produces a strong focal spot on the shadow-side curvature of the lens. The limited index contrast of the BSW systems loosens the confinement of the focal spot. A mitigation plan is to elongate the circular geometry to the prolate ellipse. BSW-based Luneburg lenses with a relatively small number of steps and an elliptical geometry are demonstrated with comparable performances to a standard Luneburg lens.

Rosalind Franklin's X-ray photo of DNA as an undergraduate optical diffraction experiment

Rosalind Franklin's X-ray diffraction patterns of DNA molecules rendered the important clue that DNA has the structure of a double helix. The most famous X-ray photograph, Photo 51, is still printed in most Biology textbooks. We suggest two optical experiments for undergraduates that make this historic achievement comprehensible for students by using macromodels of DNA and visible light to recreate a diffraction pattern similar to Photo 51. In these macromodels, we replace the double helix both mathematically and experimentally with its two-dimensional (flat) projection and explain why this is permissible. Basic optical concepts are used to infer certain well-known characteristics of DNA from the diffraction pattern.