Optical Principles Research Articles

FDTD method to photonic waveguides for application of optical demultiplexer at 3-communication windows

Present communication manipulates with 1-D photonic crystal waveguide to envisage optical demultiplexer by means of optical principle, which can effectively separate the three communication windows (850 nm, 1310 nm, 1550 nm). The proposed structure is envisaged through three photonic crystal waveguides, comprising of periodic arrangement of silicon (odd layer) and air (even layer). Further, finite difference time domain (FDTD) technique is employed to explore reflectance and absorption loss in the said photonic structures through band gap analysis. Simulation outcomes disclose that demultiplexing application relays on numerous factors such asthickness of various layers, nature of material, structure configuration, lattice constant etc of the proposed photonic waveguide. Moreover, it is seen that thickness of odd as well as even layers regulates band gap of the said waveguides, which leads to allow a particular wavelength and reject other wavelengths. Also, simulation upshots divulged that the first photonic crystal permits wavelength of 850 nm and rejects 1310 nm and 1550 nm for thickness of odd layer and even layer as 930 nm and 70 nm respectively. Similarly, the second photonic structure having odd layer thickness of 300 nm and 700 nm thickness for even layer, permits 1310 nm and rejects 1550 nm signal. Furthermore, for corresponding thickness of 980 nm and 20 nm for odd and even layer respectively, the third photonic structure allows wavelength of 1550 nmto pass through it. The aforementioned results declare that the suggested photonic structure can be apposite candidate for demultiplxer application in photonic integrated circuit.

Optically guided level set for underwater object segmentation.

Combining underwater optical imaging principles and the level set, this paper proposes a novel type of level set method called optically guided level set. This novel method can transform optical challenges in underwater environments (such as the illumination bias and wavelength-selective absorption) into valuable guidance for underwater object segmentation. Using the underwater optical guidance, our novel method can generate accurate object segmentation results by suitable initialization and regular evolving of the level set. The optical guidance core lies in two observations pertaining to the underwater optical imaging process: (i) the overlap between the object region and optical collimation region and (ii) the correspondence between the object structure and irradiation distribution inside the optical collimation. The high accuracy of our proposed method is demonstrated via comparisons to the state-of-the-art level set and salient object detection methods for public underwater images collected in diverse environments. Moreover, by using the work presented in this paper, we plan to demonstrate optical principles' potential for improving computer vision research, which is a promising research topic with many practical applications.

Implicit Structural Modeling by Minimization of the Bending Energy with Moving Least Squares Functions

In this paper, an implicit structural modeling method using locally defined moving least squares shape functions is proposed. The continuous bending energy is minimized to interpolate between data points and approximate geological structures. This method solves a sparse problem without relying on a complex mesh. Discontinuities such as faults and unconformities are handled with minor modifications of the method using meshless optic principles. The method is illustrated on a two-dimensional model with folds, faults and an unconformity. This model is then modified to show the ability of the method to handle sparsity, noise and different reliabilities in the data. Key parameters of the shape functions and the pertinence of the bending energy for structural modeling applications are discussed. The predefined values deduced from these studies for each parameter of the method can also be used to construct other models.

Methane microwave optical master oscillator for fountain references

We have demonstrated a microwave master oscillator operating on optical principles and based on a He – Ne/CH4 optical frequency standard (λ = 3.39 μm) and femtosecond fibre laser system ( λ = 1.54 μm). The output signal spectrum of the oscillator has the form of an equidistant frequency comb in the range 60 MHz to 10 GHz with a 60-MHz step. Comparison of the frequencies of two master oscillators shows that the short-term output frequency instability for the comb components in the range 0.8 – 1.5 GHz is under 1 × 10−14 at an averaging time of 1 s. We have tested microwave signals from the oscillator using apparatus in the reference facility at the State Time and Frequency Service, All-Russia Research Institute of Physical and Radio Engineering Measurements. A signal at a nominal frequency of 100 MHz synthesised from one comb component was compared to signals from two hydrogen masers with enhanced short-term stability in the reference facility. The short-term frequency stability of the synthesised signal has been shown to be twice better than the stability of the masers and to be limited by the intrinsic instability of the commercial synthesiser of a 100-MHz nominal frequency. Our experiments confirm that the proposed microwave optical master oscillator is potentially attractive for use in systems with increased requirements for short-term frequency stability, in particular in time and frequency fountain references.

Opto-Electron Eng, 2019, 46(3)]Development status and prospect of optical storage technology

With the rapid development of internet, internet of things, cloud computing and artificial intelligence, human society has entered the age of Big Data. In the face of such a large amount of data, how to store it safely and reliably, green and energy-saving, long life and low cost has become an important issue. Traditional optical storage technology has been unable to meet the practical requirements, and needs to be modified and upgraded, or even developed a new generation of storage technology. So far, a variety of prototypes based on the optical storage principle have been successfully developed and applied in engineering. The optical storage technology has been improved continuously and is being applied and used gradually. This paper first briefly introduces the development history of optical storage technology, and then lists eight types of optical storage technologies with industrial prospects in detail, summarizes their principles and development status, and discusses their technical features and prospects as Big Data storage media. Finally, the future development trend of optical storage technology is prospected in order to provide technical reference for the development of optical storage technology in the era of Big Data.

Principles of Electron Optics, Volumes 1 & 2, Basic Geometrical Optics and Applied Geometrical Optics, Second Edition P. Hawkes and E. Kasper, Academic Press, Cambridge, MA, 2017. Volume 1: 728 pp. ISBN: 0081022565 Volume 2: 766 pp. ISBN: 0128133694

When Principles of Electron Optics by Hawkes and Kasper first appeared, starting in 1989, it was clear that at last a modern comprehensive treatment of the subject was available for researchers and teachers. This was the first since Glaser's Grundlagen of 1952. The three volumes of Hawkes and Kasper on Basic, Applied, and Wave Optics, have since become the standard reference on the subject. What stood out in these volumes was the astonishingly comprehensive bibliography, and the education young readers obtained on the very complete and fascinating history of the subject, together with rigorous derivations from first principles. Those books complemented the substantial texts by Zworykin, Grivet, Sturrock, Septier, and others in the days when the use of computers was just beginning. Second editions of these hefty volumes are now appearing, more than 25 years later. During that time many excellent texts have appeared, including the books by H. Rose and M. Berz, some of more limited scope, specialized for particular applications such as accelerator physics or low electron energies. But the most important development in that time has been the successful development of aberration correctors, which did not exist in 1989. As Harald Rose once commented, “the aberration corrector became possible (in the 1990s) when the speed of modern computer diagnostics for aberrations and corrective feedback finally became faster than the instability time of the lens electronics.”

Temperature Field Reconstruction of Concrete Dams based on Distributed Optical Fiber Monitoring Data

Mastering the real temperature distribution of the concrete dam is the basis for solving the problem of temperature control and crack prevention. In this paper, Distributed Temperature Sensing (DTS) technology was applied to temperature monitoring of a high-arch dam under construction in southwest China. In order to obtain a more comprehensive temperature distribution of the dam, optical fiber layout principles for arch dams were studied, and horizontal and vertical optical fiber layout schemes were first proposed according to these principles. The real temperature variation processes of the dam were obtained in real time with a line temperature measurement pattern instead of a point temperature measurement pattern. Additionally, a framework of distributed optical fiber data acquisition and remote transmission was proposed. Interconnection of multiple DTS hosts and remote transmission of temperature data were realized. Then, two-dimensional temperature fields of a typical dam block in different ages and longitudinal profiles of dam blocks with embedded fibers were reconstructed based on large amounts of temperature monitoring data and the Kriging difference algorithm. Temperature field reconstruction results showed that the temperature distribution law of the concrete arch dam was in accordance with the actual situation.

Illusion Elastics in a Fluid Background

Applying principles of transformation optics to acoustic systems continues to gain traction. It has been shown that transformation elastics, or $i\phantom{\rule{0}{0ex}}l\phantom{\rule{0}{0ex}}l\phantom{\rule{0}{0ex}}u\phantom{\rule{0}{0ex}}s\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}n$ $e\phantom{\rule{0}{0ex}}l\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}s\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}c\phantom{\rule{0}{0ex}}s$, is challenging, as the elastodynamic wave equation will change its form after coordinate transformation. Here the authors use transformation acoustics based on Fabry-P\'erot (FP) resonances, to obtain an illusion such that an arbitrary solid object sounds like a different object in a fluid background. This elastic illusion is confirmed analytically using Mie theory, for both two and three dimensions. This approach could be important in underwater acoustic communication, $e.g.$ sonar.

Review of Mathematical Equations for the Design of Compound Parabolic Concentrating Solar Energy Collectors

Compound Parabolic Concentrator (CPC) is the most popular static low-concentrating system for solar energy collection. The main advantages of CPCs over other solar collectors include high optical efficiency, elimination of the diurnal tracking requirement at intermediate concentrations and being able to collect both diffuse and direct radiation. The overall performance of CPCs depends on the accurate design of solar radiation reflecting surfaces, which is based on the edge-ray principle and identical optical length principle. However, most students and junior researchers in the field of solar energy find it difficult to design CPCs. The reason is that they cannot fully understand the design principles of CPCs and derive mathematical equations of the reflectors, thus they are only interested in the design equations. In this study, an attempt has been made to review all mathematical equations that have been used to design symmetric and asymmetric CPCs with different receiver configurations. This article offers an opportunity for researchers to obtain accurate information more quickly than going through past publications in the hope of finding something relevant. It is anticipated that the results from this study will increase the application of CPCs to photovoltaics and/or thermal conversions.

Research progress of topological photonics

Inspired by topological phases and phase transitions in condensed matter, a new research field based on topological band theory, topological photonics, has emerged. It breaks through the traditional idea of light regulation by optical superposition principle of real space and energy band theory of solids of reciprocal space, providing a novel mechanism of optical regulation and rich properties of transport and light manipulation. Such as transmission properties of against backscattering and rubout to defects and disorders, selective transports dependent on spin-orbit coupling, and high dimensional manipulation of light. This review paper classifies different topological photonic systems by dimensions, briefly introducing the topological model, the novel physical phenomena, and the corresponding physical picture, such as SSH models, photonic quantum Hall effects, photonic quantum spin Hall effects, photonic Floquet topological insulator, and photonic three-dimensional topological insulator; other advanced platforms such as higher-order, non-Hermitian, and nonlinear topological platforms are also involved; a summary and outlook about the current development, advantages, and challenges of this field are present in the end.

“Light in and Sound Out”: Review of Photoacoustic Imaging in Cardiovascular Medicine

Photoacoustic imaging (PAI) is one of the most recent additions to the expanding armamentarium of diagnostic imaging technologies. Based on the working principles of optics and ultrasound, PAI provides relatively accurate, differential, and comprehensive information for a variety of physiological and pathological conditions in a real-time fashion. PAI was previously put to use in the field clinical oncology and has only recently been attempted in diseases of the heart and vessels. Notwithstanding the fact that it is still in the pre-clinical stage, PAI, with its important advances, has shown considerable potential to make a significant, transformative leap forward in cardiovascular imaging. The applications of PAI-based techniques in cardiovascular medicine include, but are not limited to, the identification and evaluation of atherosclerotic vulnerable plaque (with or without the use of tissue-specific extraneous contrast), the visualization of clots in different thrombosis-related diseases, the detection of myocardial lesions during catheter ablation of cardiac arrhythmias, the real-time monitoring of blood rheology and hemodynamics, and so on. In this contemporary literature review, we have summarized major applications of different PAI-based techniques for various cardiovascular situations, highlighted key innovations, and their respective clinical feasibilities, and then discussed future perspectives of these versatile methodologies in the practice of cardiovascular imaging. In our view, the unique advantages of PAI render it immensely promising to open up new avenues in the study of cardiovascular diseases.

Trash to treasure Retcam.

Digital fundus imaging is being used in diagnosis, documentation, and sharing of many retinal diseases and hence forms an essential part of ophthalmology. The use of smartphones for the same has been ever increasing. There is a need for simpler devices to couple the 20D lens and smartphone so as to take fundus photographs which can help in fundus documentation. This article describes a simple inexpensive technique of preparing a smartphone fundus photography device (Trash To Treasure (T3) Retcam) from the used materials in the clinics within minutes. This article will also review the optical principles of the T3 Retcam and describe the step–by–step method to record good-quality retinal image/videos. This inexpensive device is made by recycling and modifying the plastic hand sanitizer bottle in the clinics/hospitals which can be used for documenting, diagnosing, screening, and academic purposes.

Super-resolution enhancement by quantum image scanning microscopy

The principles of quantum optics have yielded a plethora of ideas to surpass the classical limitations of sensitivity and resolution in optical microscopy. While some ideas have been applied in proof-of-principle experiments, imaging a biological sample has remained challenging mainly due to the inherently weak signal measured and the fragility of quantum states of light. In principle, however, these quantum protocols can add new information without sacrificing the classical information and can therefore enhance the capabilities of existing super-resolution techniques. Image scanning microscopy (ISM), a recent addition to the family of super-resolution methods, generates a robust resolution enhancement without sacrificing the signal level. Here we introduce quantum image scanning microscopy (Q-ISM): combining ISM with the measurement of quantum photon correlation allows increasing the resolution of ISM up to two-fold, four times beyond the diffraction limit. We introduce the Q-ISM principle and obtain super-resolved optical images of a biological sample stained with fluorescent quantum dots using photon antibunching, a quantum effect, as a resolution enhancing contrast mechanism.

High-Sensitivity “Hot-Wire”-Based Gas Velocity Sensor for Safe Monitoring in Mining Applications

In this paper, building on a design developed from an advanced mathematical model, a practical fiber optic sensor, which is an analog of the familiar “hot-wire” wind velocity monitor, has been developed, as an intrinsically safe sensor device for use on coal mining monitoring applications. The device response time, the dynamic measurement range, the sensitivity, the sensor probe surface heat transfer coefficient, and the effect of the wind (gas) velocity have been investigated in the laboratory and in situ and results reported, enabling the mathematical model used in the design process to be validated. The underpinning optical fiber-based principle used is the shift in the center wavelength of a fiber Bragg grating which is cooled by the gas flowing over it, and the device sensitivity found was determined to be ~1500 pm per unit m/s wind velocity in the range of 0–0.5 m/s, ~330 pm per unit m/s in the range 0.5–2 m/s, and ~50 pm per unit m/s in the range of 2–4.5 m/s. In the “proof of concept” tests carried out, it was found that the greater the surface dissipation factor of the sensor, the shorter was its response time. Furthermore, the response time was seen to decrease as the wind velocity increased, showing a typical value of 6 s, which is suitable for the mining applications envisaged.

Tunable Luminescent A-SiNxOy Films with High Internal Quantum Efficiency and Fast Radiative Recombination Rates.

In this work, we systematically investigated the Nx bonding defects that induced high photoluminescence internal quantum efficiencies (PL IQEs) and very fast radiative recombination processes in amorphous silicon oxynitride (a-SiNxOy) systems. The luminescent N‒Si‒O bonding-related defect states were checked for the XPS, EPR, and temperature-dependent steady-state PL (TD-SSPL) properties. The PL IQEs were calculated from PL quantum yields through the principle of planar geometry optics, and then confirmed by the TD-SSPL properties. The radiative recombination rates [kr(R)] were determined by combining the PL IQE values and ns-PL lifetimes obtained from time-resolved PL measurements. Both the PL IQE, exceeding 72%, and the fast kr(R) (~108 s−1) are proportional to the concentration of Nx defects, which can be explained by N‒Si‒O bonding states related to the quasi-three-level model, suggesting the possible realization of stimulated light emission in a-SiNxOy systems.

DNA-Assisted Assembly of Gold Nanostructures and Their Induced Optical Properties.

Gold nanocrystals have attracted considerable attention due to their excellent physical and chemical properties and their extensive applications in plasmonics, spectroscopy, biological detection, and nanoelectronics. Gold nanoparticles are able to be readily modified and arranged with DNA materials and protein molecules, as well as viruses. Particularly DNA materials with the advantages endowed by programmability, stability, specificity, and the capability to adapt to functionalization, have become the most promising candidates that are widely utilized for building plenty of discrete gold nanoarchitectures. This review highlights recent advances on the DNA-based assembly of gold nanostructures and especially emphasizes their resulted superior optical properties and principles, including plasmonic extinction, plasmonic chirality, surface enhanced fluorescence (SEF), and surface-enhanced Raman scattering (SERS).

Grundlagen der Optik

As an ophthalmologist, it is very important to know whether limited vision is caused by refractive problems or whether there is another pathology behind it. That's why refraction plays a key role at the beginning of every eye examination. Therefore, it is important to know the basic principles of optics. When fitting spherical and cylindrical lenses, it is interesting to know which properties the respective lenses have. One should also be aware of the optical paths and refraction laws when fitting spectacle lenses and prisms. In addition, when prescribing spectacle lenses, one should consider changes in the distance between corneal apex and spectacle lens and know conversions for the strength of contact lenses. Only if you have a deeper understanding of refraction and correction of refractive errors you will be able to adjust optimal vision aids for more difficult refraction conditions.

Effects of near-field electromagnetic coupling in dimers of nanoparticles with a silver core and a J-aggregate dye shell

We report a theoretical study of the plasmon-exciton coupling effect on the absorption spectra of pairs of closely spaced double-layer hybrid nanoparticles consisting of a metallic core and a J-aggregate dye shell. The effect of frequency conversion of plasmonic lines due to the near-field interaction between plasmons and Frenkel excitons of the organic shell is demonstrated. The effect leads to the appearance of additional spectral lines in the long-wavelength part of the spectrum of the system of hybrid particles. The shapes and the relative intensities of the additional lines exactly reproduce the specific features of the original spectrum of plasmonic absorption bands in uncoated metallic nanoparticles. The discovered phenomenon can be used to design new types of high-sensitivity nanosensors, based on plasmon-exciton effects and principles of near-field optics.

Measurement of Free-Form Curved Surfaces Using Laser Triangulation.

Laser triangulation (LT) is widely used in many fields due to its good stability, high resolution and fast speed. However, the accuracy in these applications suffers from severe constraints on the data acquisition accuracy of LT. To solve this problem, the optical triangulation principle, the object equation of the optical path relationship and the deviation of the laser spot centroid are applied to deduce a mathematical model. Therefore, the image sensor inclination errors can be quantitatively calculated, and the collected data are compensated in real time. Further, a threshold sub-pixel gray-gravity (GG) extraction algorithm is proposed; the gradient function and Gaussian fit algorithm are used to set thresholds to remove the impact of the spot edge noise area on the center location; and polynomial interpolation is employed to enhance the data density of the traditional GG method, thus improving the data acquisition accuracy of LT. Finally, the above methods are applied to on-machine measurement of the American Petroleum Institute (API) thread and the screw rotor, respectively. The experimental results prove that the proposed method can significantly improve the measurement accuracy of free-form curved surfaces using LT and that the improved laser spot center extraction algorithm is more suitable for free-form curved surfaces with smaller curvature and more uniform curvature changes.

A computational approach for engineering optical properties of multilayer thin films: Particle swarm optimization applied to Bruggeman homogenization formalism

An algorithm based on Particle Swarm Optimization (PSO) and Bruggeman Homogenization Formalism was presented to design a model structure for a thin film with various sublayers to obtain a desired optical reflectance/transmittance spectrum. In principle, the results showed that the designed structure is strongly affected by the input parameters of the algorithm such as film thickness, number of sublayers, incident light characteristic wavelength and utilized materials, and the method has its ability to find the best optimized structure based on desired optical properties. The results of calculations were in good agreement with the physical principles of classical optics and the method could be useful in both design and characterization purposes.