Optical Principles Research Articles

Optical correction principles of accommodative esotropia

Accommodative esotropia is the most common type of esotropia in children. The patients often need to wear hyperopic glasses to correct eye positions and improve vision and binocular function. However, the course of accommodative esotropia is usually long, so it is necessary to monitor the refractive changes for a long time. Maintaining full hyperopic correction will interfere with the emmetropia development of the eyeball, and undercorrection of hyperopia will lead to the risk of esotropia decompensation. These often bring confusion when clinicians prescribe glasses. The benefits of accommodative esotropia with a high accommodation convergence/accommodation ratio from fitting bifocal lenses and the effect of prisms on residual esotropia have also been controversial topics in this field. In this article, we combine the research status and clinical practice to present some points of view for the peer reference. (Chin J Ophthalmol, 2021, 57: 331-335).

Optical Prior-Based Underwater Object Detection with Active Imaging

Underwater object detection plays an important role in research and practice, as it provides condensed and informative content that represents underwater objects. However, detecting objects from underwater images is challenging because underwater environments significantly degenerate image quality and distort the contrast between the object and background. To address this problem, this paper proposes an optical prior-based underwater object detection approach that takes advantage of optical principles to identify optical collimation over underwater images, providing valuable guidance for extracting object features. Unlike data-driven knowledge, the prior in our method is independent of training samples. The fundamental novelty of our approach lies in the integration of an image prior and the object detection task. This novelty is fundamental to the satisfying performance of our approach in underwater environments, which is demonstrated through comparisons with state-of-the-art object detection methods.

DbOBS: dual buffered switch for variable optical bursts in future datacenters

Modern data-driven applications pose stringent requirements of high bandwidth, ultra-low-latency, low-powered, and scalable interconnections among switches and routers in data-centers. To address these demands, electronic switching is not a viable choice due to bandwidth and computing bottlenecks. Thus, researchers explored effective optical switch design principles for next-generation data-centers. In optical switches, data aggregates in the form of optical bursts (OB) at ultra-high speeds. In the case of OB contention, solutions are proposed by researchers to store OB as recirculating patterns in fiber delay lines (FDL) with induced optical delay. However, due to variable burst length, it is not possible to measure slot delay length, thus storage of contending bursts is not possible at intermediate core switches. Motivated from the aforementioned discussions, in this paper, we propose a switch design DbOBS, that is capable to store variable OB during contention slots. DbOBS estimates mean burst length, and possible deviation from mean length to minimize burst loss. The considered switch design is validated through parameters like-burst length estimation, over-reservation, and waiting time. For network-layer simulations, poison arrivals of data bursts are considered as packetized units. The packets are sent through Monte-Carlo arrivals and burst loss probability (BLP) is estimated at various input load conditions and buffer sizes. DbOBS achieves a BLP in order of $$10^{-4}$$ at load $$\approx$$ 0.8, and buffer-size of 50, and burst length of $$L=5$$ , that outperforms the traditional switch designs.

Methods, principles and applications of optical detection of metal ios

• The optical detection methods of 12 common metal ions are reviewed. • The main principles and experimental phenomena of optical detection are summarized. • The development and advantages of optical detection methods are summarized. • The applications of optical detection method are summarized. • The future development and main challenges of optical detection are discussed. Heavy metal elements were widely used in alloy manufacturing, medical treatment, food additive, military industry and other fields, which were harmful to human body. Optical detection was a non-contact nondestructive detection method, which had the advantages of high selectivity, high sensitivity and low cost, and had important applications and prospects in environmental monitoring and biological science. In this paper, the optical detection methods, detection principles and detection methods of 12 kinds of metal ions (Ag + , Al 3+ , Cd 2+ , Co 2+ , Cr 3+ , Cu 2+ , Fe 2+ , Fe 3+ ,Hg 2+ ,Pb 2+ , Pd 2+ ,Zn 2+ ) were reviewed. Fluorescence, colorimetry and spectral change were the main detection methods. Fluorescence detection methods mainly included fluorescence quenching, fluorescence enhancement and fluorescence spectrum changes; The colorimetric method included the change of color and the change of ultraviolet absorption spectrum; The spectral changes mainly included circular dichroism, phosphorescence and surface enhanced Raman scattering, etc. Photoinduced electron transfer, intramolecular charge transfer and fluorescence resonance energy transfer were the primary principles of optical detection. The application prospect and main challenges of optical detection were discussed.

Scanless optical feedback imaging principle by single-pixel compressed sensing.

Optical feedback in lasers is being used for unconventional imaging of fluid dynamics, pressure fields, material properties, and free-carrier distribution, especially in spectral regions where two-dimensional detectors are not yet available. As this technique requires scanning the laser spot across the target, the resulting image contrast is often hampered by the speckle effect. Compressed sensing is becoming a workhorse technique for signal analysis, allowing the reconstruction of complex images from a relatively small number of integrated (single-pixel) measurements, and is being efficiently adapted to a number of single-pixel detector cameras. We applied compressed sensing algorithms to the inherently single-pixel optical feedback in a semiconductor diode laser, demonstrating for the first time, to the best of our knowledge, scanless and detectorless speckle-free imaging of a simple binary object.

Detection of Scots Pine Single Seed in Optoelectronic System of Mobile Grader: Mathematical Modeling

The development of mobile optoelectronic graders for separating viable seeds by spectrometric properties with high detection accuracy represents a very relevant direction of development for seed handling operations. Here, the main parameters of the radiation source and receiver for detecting a single seed in the diagnostic system of a mobile grader were modeled based on the principles of technical optics using Scots pine (Pinus sylvestris L.) seeds as a case study. Among the pine seeds in the seed batch, there are fossilized and empty seeds that are exactly the same in geometric and gravitational parameters as live seeds. For their separation from the seed batch, data from spectrometric studies in the near-infrared (980 nm) region can be used. To substantiate the parameters of the light source, a geometric optical model of optical beam formation was considered, while the energy model of optical beam formation was considered to substantiate the parameters of the light detector. The results of this study show that the signal value depended on the orientation of a single seed relative to the recording window. The beam angle from the radiation source should be within 45 degrees. The difference between the optical streams should be 50 microns, which made it possible to clearly detect the signal at a standard noise level of 15 microns and signal-to-noise detection accuracy ratio of 56.3 dB. This study expands theoretical knowledge in the field of the spectrometric properties of a single seed, considering the cases of its orientation relative to the optical beam, which affected the effective area of detection of the seed. The obtained data on the location of the main elements of the diagnostic system will speed up the design of mobile optoelectronic graders, and the development of a contemporary protocol for improving Scots pine seed quality.

Generation of anomalous vector Bessel beams with varying polarization order along the propagation direction

Vector Bessel beams (VBBs) contain non-uniform polarization distributions on the cross-section and non-diffraction characteristics, have been widely used in many fields, including optical trapping, optical microscope, optical communication, etc. Here, we propose a theoretical model to obtain anomalous-VBBs with polarization order dependent on propagation distance. Based on geometrical optics principle, the designed spiral slit allows the introduction of a continuous phase delay, which is used to generate two Bessel vortex beams with opposite chirality and topological charges. Then, by coherently superimposing these two Bessel vortex beams, an anomalous-VBB is generated and shows the polarization order dependent on the propagation distance. Arbitrary polarization orders including integers and fractions can be generated by manipulating the propagation distance. The simulation results show that the local polarization distribution measured at different distances is in good agreement with the polarization distribution of theoretical VBBs, and the local polarization order of anomalous-VBBs is inversely proportional to the propagation distance. The characteristic of this anomalous beam may intrigue the applications of VBBs in light-matter interaction, microscopy and quantum information.

Experimental test of the geometric model of image formation in bright-field microscopy.

In the geometric optics approximation, an image formed by an objective lens replicates the distribution of intensity at the front focal plane of the objective. Although this fact represents a fundamental optical principle, its application to analysis of bright-field microscopic images was developed only recently and has not been tested experimentally. In this paper, we applied simple ray tracing to compute an image of a glass cylinder at various positions of the objective and to compare it to the experiment. We obtained a close match between theory and observation, except for a slight underestimation of the intensity in the middle part of the cylinder. The likely reason for this minor difference was constructive interference due to lens-like properties of a cylinder, which could not be accounted for by geometric approximation. We expect that such artefacts would be negligible in imaging of live cells, and the geometric approach would successfully complement the existing quantitative phase methods.

Pinhole-imaging-based learning butterfly optimization algorithm for global optimization and feature selection

Butterfly optimization algorithm (BOA), as a recently proposed meta-heuristic optimization technique, performs competitively in solving numerical optimization problems as well as real-world applications. However, BOA has low precision, slow convergence and may be prone to local optimum, when solving complex or high-dimensional optimization problems. To overcome these defects, a modified BOA (called PIL-BOA) with adaptive gbest-guided search strategy and pinhole-imaging-based learning is proposed. Firstly, a modified position updated equation by introducing the global best (gbest) solution and the inertia weight is designed to efficiently improve the exploitation capability and the solution precision. Secondly, a novel pinhole-imaging learning strategy based on the principle of optics is presented to effectively search the unknown regions and avoid premature convergence. 23 classical problems and 60 complex optimization tasks from CEC 2014 and CEC 2017 are used to further investigate the effectiveness of PIL-BOA. The comparison results demonstrate that PIL-BOA has better performance than most compared algorithms on benchmark test functions. Finally, PIL-BOA is applied to solve feature selection problems and fault diagnosis in real-world wind turbine. The results show that PIL-BOA is superior to other competitors in term of classification accuracy.

Optical Screening Methods for Pesticide Residue Detection in Food Matrices: Advances and Emerging Analytical Trends.

Pesticides have been extensively used in agriculture to protect crops and enhance their yields, indicating the need to monitor for their toxic residues in foodstuff. To achieve that, chromatographic methods coupled to mass spectrometry is the common analytical approach, combining low limits of detection, wide linear ranges, and high accuracy. However, these methods are also quite expensive, time-consuming, and require highly skilled personnel, indicating the need to seek for alternatives providing simple, low-cost, rapid, and on-site results. In this study, we critically review the available screening methods for pesticide residues on the basis of optical detection during the period 2016–2020. Optical biosensors are commonly miniaturized analytical platforms introducing the point-of-care (POC) era in the field. Various optical detection principles have been utilized, namely, colorimetry, fluorescence (FL), surface plasmon resonance (SPR), and surface enhanced Raman spectroscopy (SERS). Nanomaterials can significantly enhance optical detection performance and handheld platforms, for example, handheld SERS devices can revolutionize testing. The hyphenation of optical assays to smartphones is also underlined as it enables unprecedented features such as one-click results using smartphone apps or online result communication. All in all, despite being in an early stage facing several challenges, i.e., long sample preparation protocols or interphone variation results, such POC diagnostics pave a new road into the food safety field in which analysis cost will be reduced and a more intensive testing will be achieved.

Optical Remote Sensing of Oil Spills in the Ocean: What Is Really Possible?

Optical remote sensing (ORS) of reflected sun light has been used to assess oil spills in the ocean for several decades. While most applications are toward simple presence/absence detections based on the spatial contrast between oiled water and oil-free water, recent advances indicate the possibility of classifying oil types and quantifying oil volumes based on their spectral contrasts with oil-free water. However, a review of the current literature suggests that there is still confusion on whether this is possible and, if so, how. Here, based on the recent findings from numerical models, laboratory measurements, and applications to satellite or airborne imagery, we attempt to clarify this situation by summarizing (1) the optics behind oil spill remote sensing, and in turn, (2) how to interpret optical remote sensing imagery based on optical principles. In the end, we discuss the existing limitations and challenges as well as pathways forward to advance ORS of oil spills.

Microwave hologram reconstruction for cylindrical geometry

Microwave imaging is a technique for evaluation of hidden or embedded objects in an optically opaque structure (or media) using electromagnetic waves in microwave regime. The result of the study is a microwave image of the internal structure of the investigated object, which is built by reconstructing the electromagnetic field scattered by the object (microwave hologram), recorded using some radar system at some aperture. Along with the widespread flat aperture, a cylindrical aperture is often used in personnel screening systems, microwave system for automated body measurement for apparel fitting, and medical tomographic scanners. Cylindrical geometry requires special holograms reconstruction methods. The work is dedicated to comparison of three hologram reconstruction methods: №1 – back projection, №2 – back propagation and №3 – Gauss–Newton, and identifying the advantages and disadvantages of each method. All methods were adopted to cylindrical geometry, software implemented using Python programming language and compared. Comparison was performed by reconstruction of microwave holograms of the same objects. Microwave holograms for comparison were calculated in accordance with the principles of physical optics for point scatterers and using the computational electromagnetics software product FEKO for solid objects. Comparison criteria were: speed of calculations, quality of obtained microwave images, required random access memory (RAM) of the computer. Based on the results of numerical experiments, the following conclusions can be made. For both point and solid objects, all methods have showed a similar quality of the obtained microwave images, the difference turned out to be minimal both in visual and numerical estimation. The advantage of method №1 is the simplicity of its software implementation. In addition, using the first method, you can easily do reconstruction for any area (line, surface, volume), the position of which can be arbitrary in relation to the positions of the samples of the radar signal. Method №2 is the fastest method. With the parameters considered in the article, it is two orders of magnitude faster than method №1, and its performance can be easily increased by parallelizing calculations for different radii. Among the shortcomings, one can note the complexity of its software implementation and the dependence of the position and size of the reconstructed area on the location and number of samples of the radar signal. A significant drawback of method №3 is its high requirements to the RAM of the computer, as well as low speed of calculations. When processing microwave holograms with a large number of samples, calculations may require more memory than is installed in the computer, and the calculation time will increase many times due to the continuous exchange of data with the hard disk, or it will be impossible to do the calculations at all.

Comparison of areal and profile surface measurement methods for evaluating surface properties of machined components

The surface properties of machined components not only affect their optical but also functional behaviour, which makes information about waviness and roughness an important basis for optimization approaches. Therefore the still often used tactile measurement principles in industrial applications are continuously replaced by non-destructive optical measurement principles enabling faster and more flexible measuring. This paper discusses the comparability of different surface parameters, which were generated by profile or areal measurement using both the tactile and the stripe light projection principle. Based on the results the validity of the investigated parameters for different applications and materials can be increased.

Review of micromachined optical accelerometers: from m<i>g</i> to sub-μ<i>g</i>

Micro-Opto-Electro-Mechanical Systems (MOEMS) accelerometer is a new type of accelerometer which combines the merits of optical measurement and Micro-Electro-Mechanical Systems (MEMS) to enable high precision, small volume and anti-electromagnetic disturbance measurement of acceleration. In recent years, with the in-depth research and development of MOEMS accelerometers, the community is flourishing with the possible applications in seismic monitoring, inertial navigation, aerospace and other industrial and military fields. There have been a variety of schemes of MOEMS accelerometers, whereas the performances differ greatly due to different measurement principles and corresponding application requirements. This paper aims to address the pressing issue of the current lack of systematic review of MOEMS accelerometers. According to the optical measurement principle, we divide the MOEMS accelerometers into three categories: the geometric optics based, the wave optics based, and the new optomechanical accelerometers. Regarding the most widely studied category, the wave optics based accelerometers are further divided into four sub-categories, which is based on grating interferometric cavity, Fiber Bragg Grating (FBG), Fabry-Perot cavity, and photonic crystal, respectively. Following a brief introduction to the measurement principles, the typical performances, advantages and disadvantages as well as the potential application scenarios of all kinds of MOEMS accelerometers are discussed on the basis of typical demonstrations. This paper also presents the status and development tendency of MOEMS accelerometers to meet the ever-increasing demand for high-precision acceleration measurement.

Best Practices for Germicidal Ultraviolet-C Dose Measurement for N95 Respirator Decontamination.

Ultraviolet-C (UV-C) decontamination holds promise in combating the coronavirus disease 2019 pandemic, particularly with its potential to mitigate the N95 respirator shortage. Safe, effective, and reproducible decontamination depends critically on UV-C dose, yet dose is frequently measured and reported incorrectly, which results in misleading and potentially harmful protocols. Understanding best practices in UV-C dose measurement for N95 respirator decontamination is essential to the safety of medical professionals, researchers, and the public. Here, we outline the fundamental optical principles governing UV-C irradiation and detection, as well as the key metrics of UV-C wavelength and dose. In particular, we discuss the technical and regulatory distinctions between UV-C N95 respirator decontamination and other applications of germicidal UV-C, and we highlight the unique considerations required for UV-C N95 respirator decontamination. Together, this discussion will inform best practices for UV-C dose measurement for N95 respirator decontamination during crisis-capacity conditions.

Comparison of central corneal thickness measurements with three different optical devices.

Purpose:The purpose of this study was to compare and evaluate the agreement of central corneal thickness (CCT) values obtained with three different devices working according to optical principle in healthy eyes.Methods:60 eyes of 60 individuals (30 men and 30 women) were enrolled in this study. CCT measurements performed with Scheimpflug–Placido topographer (Sirius), spectral-domain optical coherence tomography (RTVue) with an anterior segment module, and optical biometer (AL-Scan) were compared. Bland–Altman analysis was used to demonstrate agreement between methods.Results:The mean age was 30.07 ± 7.313 years (range, 18–47 years). The mean CCT values obtained by RTVue, Sirius, and AL-Scan were 518.25 ± 36.38 µm, 526.08 ± 36.33 µm, and 513.50 ± 39.09 µm, respectively. The mean differences in CCT were 7.83 ± 14.15 µm between Sirius and RTVue, 12.58 ± 11.87 µm between Sirius and AL-Scan, and 4.75 ± 4.50 µm between RTVue and AL-Scan. The mean CCT was statistically different among the three groups (p < 0.05). All three modalities of CCT measurements correlated closely with each other, with Pearson’s correlation coefficients ranging from 0.924 to 0.961. The 95% limits of agreement were −19.90 to 35.56 µm between Sirius and RTVue, −10.69 to 35.85 µm between Sirius and AL-Scan, and −4.07 to 13.58 µm between RTVue and AL-Scan.Conclusion:Different results could be obtained through different noncontact devices in CCT measurements. Although the measurement values obtained by these devices show a high level of correlation, it would be a more correct approach to not use them directly interchangeably in clinical practice. Evaluation and follow-up of CCT should be performed using the same device.

DEVELOPMENT TRENDS IN OPTICAL TECHNOLOGY OF MIRROR ANASTIGMATIC SYSTEMS

The results of the analysis of the design features of mirror anastigmatic systems were given in this article. Such systems can correct three third-order aberrations; they provide a convenient placement of the image plane, protected from stray light by special hoods. Mirror anastigmatic systems make it possible to find research areas of schematic solutions, archiving systems with an increased field of view and a high luminosity, qualities required for registering the radiation of weak and rather extended objects. We established perspective options, with aligned vertices of even and odd mirrors; additionally, identified a group of systems based on the two-stage optic principle. We notice the development trends of compact systems, with a monoblock of two mirrors, including three-mirror schemes with double reflection from the first mirror, and schemes with a monolith of the first and fourth mirrors, they are more technologically advanced than staggered vertex designs. The small aberration values obtained and the presence of high resolution opens up wide possibilities for the use of mirror anastigmatic systems. They can be used in optical devices operating in a wide range of the spectrum: in satellite scanning systems (photographing) of the earth's surface and thermal scanning systems. The variety of application is limited by the range sensitivity of the photodetector and the operation range, of reflective optical coatings. The disadvantages of anastigmatic mirror systems can be large dimensions and technological difficulties in complex aspherical surface manufacturing, besides a significant central obstruction and vignetting when increasing the field of view. The recent works on the calculation of mirror systems show that some traditional theoretical concepts are insufficient for solving modern optical engineering problems. Therefore, research in the mirror anastigmatic systems field of varying degrees of complexity; in the first place, systems with more than three mirrors, the search for original off-axis schemes that improve optical characteristics have received a significant place in the computational optics.

Ultrasensitive Materials for Electrochemical Biosensor Labels.

Since the fabrication of the first electrochemical biosensor by Leland C. Clark in 1956, various labeled and label-free sensors have been reported for the detection of biomolecules. Labels such as nanoparticles, enzymes, Quantum dots, redox-active molecules, low dimensional carbon materials, etc. have been employed for the detection of biomolecules. Because of the absence of cross-reaction and highly selective detection, labeled biosensors are advantageous and preferred over label-free biosensors. The biosensors with labels depend mainly on optical, magnetic, electrical, and mechanical principles. Labels combined with electrochemical techniques resulted in the selective and sensitive determination of biomolecules. The present review focuses on categorizing the advancement and advantages of different labeling methods applied simultaneously with the electrochemical techniques in the past few decades.

Launcher of high-order Bessel vortex beam carrying orbital angular momentum by designing anisotropic holographic metasurface

In this paper, an ultra-low profile anisotropic holographic metasurface is proposed to generate a linearly polarized high-order Bessel vortex beam carrying orbital angular momentum with predesigned topological charge. Based on the leaky-wave theory and optical holographic principle, the anisotropic impedance pattern can be properly mapped by shaping the quasi-periodic metasurface with different meta-atom sizes. Compared with the prevalent spatial wave-modulated metasurface, this surface wave-modulated holographic metasurface effectively transforms a reference wave excited by a feeding source in a single point at the center of the antenna to a leaky high-order Bessel vortex beam without any extra air feeding, which enables a unique characteristic of error-free alignment between the air feeding and designed metasurface. The good agreement between the numerical simulation and the measured result demonstrates that the proposed approach can be employed to launch a linearly polarized high-order Bessel vortex beam with an arbitrary topological mode of interest.

Growth of sillenite Bi12FeO20 single crystals: structural, thermal, optical, photocatalytic features and first principle calculations

Ideal sillenite type Bi12FeO20 (BFO) micron sized single crystals have been successfully grown via inexpensive hydrothermal method. The refined single crystal X-ray diffraction data reveals cubic Bi12FeO20 structure with single crystal parameters. Occurrence of rare Fe4+ state is identified via X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). The lattice parameter (a) and corresponding molar volume (Vm) of Bi12FeO20 have been measured in the temperature range of 30–700 °C by the X-ray diffraction method. The thermal expansion coefficient (α) 3.93 × 10–5 K−1 was calculated from the measured values of the parameters. Electronic structure and density of states are investigated by first principle calculations. Photoelectrochemical measurements on single crystals with bandgap of 2 eV reveal significant photo response. The photoactivity of as grown crystals were further investigated by degrading organic effluents such as Methylene blue (MB) and Congo red (CR) under natural sunlight. BFO showed photodegradation efficiency about 74.23% and 32.10% for degrading MB and CR respectively. Interesting morphology and microstructure of pointed spearhead like BFO crystals provide a new insight in designing and synthesizing multifunctional single crystals.