Optical Principles Research Articles

Long Integral Time Continuous Panorama Scanning Imaging Based on Bilateral Control with Image Motion Compensation

Urban remote sensing with moving carriers enables comprehensive monitoring of an urban area. High spatial resolution and wide covering are always required to improve the performance and efficiency of remote sensing. Continuous scanning imaging is a feasible solution. However, imaging motion degrades the performance of a remote sensing system. Rotating motion leads to the loss of key urban morphology information of a panorama imaging. Image translation results in blurry images. For high spatial resolution and high efficiency imaging with low illumination condition, such as imaging at dusk, long-focus lens and long integral time must be further utilized, which makes the problem more severe. In this paper, a novel image motion compensation method is proposed to compensate for image rotation and image translation simultaneously. A quantitative description of image motion, including both image rotation and image translation, is first developed based on the principle of geometrical optics and then analyzed in detail through numerical simulations. Furthermore, a comprehensive image rotation compensation method is developed based on four-channel bilateral control with sliding mode controller, at the same time image translation compensation is performed according to the quantitative relationship of the motion of the scan mirror and image translation compensator. The experimental results show that the proposed method provides effective compensation for image rotation and image translation. This enables acquisition of high spatial resolution urban panoramic images.

Large-scale optical delay line design for axial parameter measurement of the eye

The performance of an optical delay line is important for an accurate and wide-range measurement of the axial parameters of the human eye, in particular in coherence tomography. In order to improve its performance, a rotating optical delay line device based on the equidifference fiber group is proposed by analyzing the optical path delay principle of the rotating mirror type delay line and the optical path multiplication principle of the equidifference fiber group. The delay distance formula is theoretically derived and a self-calibration method for the optical path difference of the fiber group is proposed. Finally, an experiment system was built to test and evaluate the characteristics of the delay distance, delay linearity, and self-calibration repeatability for the optical path difference of the fiber group. The measurement results show that the maximum delay optical path is 128.094 mm and the delay linearity error is 0.17%. The repeatability is better than 0.036 mm. This can meet the requirements of human eye axial parameters for accurate and wide-range measurement.

Optimization of Light Management Layers for Light Harvest of Perovskite Solar Cells

Recently, with rapid development of perovskite solar cells, the record efficiency has exceeded 24.2%. However, the research of efficiency improvement never stops. This work introduces an effective approach to remarkably reduce the device reflection loss by using light management (LM) cover layer. A specific model combined with ray and wave optics was built to numerically optimize the texture of the LM layers for light harvesting in photovoltaics cells and explore the optical principles in the light trapping. The LM layer texture is made of 2D periodic triangle structures. Both symmetric and asymmetric triangle structures were investigated. The results indicate that asymmetric structures possess the close performance compared with symmetric ones, and notably, on contrary to the symmetric structures, the light trapping abilities are much more insensitive to the bottom thicknesses of asymmetric structures. It will benefit the practical fabrication, since the precise bottom thickness control can be avoided. From the optimization results, 3 optimal structures are found. With the optimal LM layers, a thin active layer (165nm) device is able to produce the short circuit current intensities (Jsc) of around 21mA/cm2, which is approximately equivalent to the Jsc of a thick active layer (800nm) device without LM layers. Meanwhile, about 23% power conversion efficiency (PCE) enhancement is achieved. On the other hand, active layer thickness also makes influence on the light trapping abilities. As the active layer thickness is increased from 165nm to 800nm, the Jsc only improves by about 2.4mA/cm2, while the PCE enhancement is dropped from ~23% to ~11%. In consideration of the compromise between total device energy output and PCE enhancement, as well as material cost reduction, the active layer with around 165nm should be an optimal thickness.

Visualization of Light Propagation with Multifocal Intraocular Lenses Using the Ouzo Effect.

The number of presbyopia correcting intraocular lenses (IOLs) is increasing and new technologies are constantly emerging with the aim of correcting the loss of accommodation after cataract surgery. Various optical designs have been proposed to implement multifocality or an extended depth of focus (EDOF). Depending on the optical principle of an implanted lens, the visual performance often is deteriorated by superposition of individual image planes and halos of varying intensity. This experimental study presents a concept to visualize the light fields and especially the halos of mono- and multifocal IOLs using the well known alcoholic beverage “ouzo” in order to obtain qualitative data on the imaging characteristics. We conclude that ouzo is a useful, cost effective, and nonpolluting medium for beam visualization and an alternative to fluorescein or milk, which could find an application for educational purposes.

Optical logic operation via plasmon-exciton interconversion in 2D semiconductors

Nanophotonic devices manipulating light for high-speed computing are a counterpart of speed-limited electronic circuits. Although plasmonic circuits are a promising platform for subwavelength miniaturization, the logic-operation principle is still limited to mimicking those of photonic waveguides using phase shifts, polarization, interference, and resonance. Meanwhile, reconfigurable interconversion between exciton and plasmon engender emerging applications like exciton transistors and multiplexers, exciton amplifiers, chiral valleytronics, and nonlinear excitonics. Here, we propose optical logic principles realized by exciton-plasmon interconversion in Ag-nanowires (NW) overlapped on transition metal dichalcogenides (TMDs) monolayers. Excitons generated from TMDs couple to the Ag-NW plasmons, eventually collected as output signals at the Ag-NW end. Using two lasers, we demonstrate AND gate by modulating single excitons in Ag-NW on MoS2 and a half-adder by modulating dual excitons in lateral WSe2 and WS2. Moreover, a 4-to-2 binary encoder is realized in partially overlapped MoSe2 and MoS2 using four-terminal laser inputs. Our results represent great advances in communication processing for optical photonics integrable with subwavelength architectures.

Material selection for GRIN-based achromatic doublets.

We use first-order optical principles to examine the ability of gradient index (GRIN) lenses to correct chromatic aberrations. We consider radial GRIN lenses with flat surfaces, with a flat diffractive surface, and with curved surfaces. We model the GRIN material system as a locally varying, subwavelength blend of three materials. In this model, we demonstrate that the color-correcting properties of each lens type can be expressed solely in terms of the dispersion properties of the base materials. We find, at this level of approximation, that the material condition for a two-material GRIN achromat with curved surfaces is identical to that for a homogeneous doublet achromat comprised of the same two materials. For the more general case of three-material, ternary GRIN elements, we use the theory to develop a figure-of-merit-based optimization approach. This allows us to identify promising material combinations without first fabricating a GRIN element. The optimization approach can be applied to alternate GRIN geometries and arbitrary glass catalogs. We use our model to search a large, commercial glass catalog to identify the best achromatic glass combinations for the three different GRIN lenses described above. Significant numerical effort was required to identify which glass combinations performed best. Ternary glass combinations are necessary to achieve good achromatic performance for flat geometries. Diffraction combined with a graded-index enables improved color correction for the same optical power or nearly a factor of two increase in power for the same level of color correction. Glass pairs that perform well as an achromatic doublet also perform well chromatically when blended in a GRIN singlet.

Compressive hyperspectral imaging with non-zero mean noise.

Compressive hyperspectral imaging (CHI) has attracted widespread attention due to its advantage of snapshot by encoding the 3D spectral image into a 2D measurement. The bottleneck of CHI for the real application now lies in the limited reconstruction quality, for which one of the fundamental reason is the inaccurate modeling of the measurement noise. Our key observation is that in practical scenarios, the measurement is inevitably contaminated with a positive offset (i.e., noise mean) due to the unideal imaging conditions (e.g. stray light and dark current), resulting in serious degradations of the reconstruction quality. In this paper, we propose to model the real noise with non-zero mean that generalizes the traditional zero mean noise to faithfully characterizing the optical imaging principle, and then introduce a novel reconstruction method with a goal to boost the reconstruction quality. During the reconstruction, the noise mean is estimated gradually to its convergence by measuring the deviation of the intermediate reconstruction result from the system measurement. We demonstrate the superior performance of our method by experiments on synthetic data and real capture data with a hardware prototype.

Calculation of the geometrical point-spread function from wavefront aberrations.

This report uses the principles of geometrical optics to compute the optical point-spread function (PSF) from the wavefront error function. Step 1 uses Prentice's rule to determine the spatial form of the PSF established by tracing a field of rays from the eye's exit pupil to the retina. Ray vergence is related to the slope of the wavefront error function, which enables the mapping of light rays to produce a retinal 'spot diagram'. Step 2 completes the PSF by assigning an irradiance value to each ray in the spot diagram. Spot irradiance is inversely proportional to the Gaussian curvature (i.e. the product of principal curvatures) of each local region of wavefront error surface centered on the corresponding ray. The Gaussian curvature, in turn, may be computed as the determinant of the vergence error matrix associated with each point on the wavefront error surface. Elements of the vergence error matrix consist of sums and differences of the local power vector components M, J0 and J45 . This method is shown to be equivalent to published derivations of the geometric PSF using the Jacobian of the ray mapping function and equivalent also to the Hessian of the wavefront error function. Examples are presented for the familiar cases of spherical and astigmatic blur as well as for higher order aberrations and the formation of caustics in the retinal image.

Method for Vertical Calibration of Laser-Projection Transnasal Fiberoptic High-Speed Videoendoscopy

The ability to provide absolute calibrated measurement of the laryngeal structures during phonation is of paramount importance to voice science and clinical practice. Calibrated three-dimensional measurement could provide essential information for modeling purposes, for studying the developmental aspects of vocal fold vibration, for refining functional voice assessment and treatment outcomes evaluation, and for more accurate staging and grading of laryngeal disease. Recently, a laser-calibrated transnasal fiberoptic endoscope compatible with high-speed videoendoscopy (HSV) and capable of providing three-dimensional measurements was developed. The optical principle employed is to project a grid of 7 × 7 green laser points across the field of view (FOV) at an angle relative to the imaging axis, such that (after calibration) the position of each laser point within the FOV encodes the vertical distance from the tip of the endoscope to the laryngeal tissues. The purpose of this study was to develop a precise method for vertical calibration of the endoscope. Investigating the position of the laser points showed that, besides the vertical distance, they also depend on the parameters of the lens coupler, including the FOV position within the image frame and the rotation angle of the endoscope. The presented automatic calibration method was developed to compensate for the effect of these parameters. Statistical image processing and pattern recognition were used to detect the FOV, the center of FOV, and the fiducial marker. This step normalizes the HSV frames to a standard coordinate system and removes the dependence of the laser-point positions on the parameters of the lens coupler. Then, using a statistical learning technique, a calibration protocol was developed to model the trajectories of all laser points as the working distance was varied. Finally, a set of experiments was conducted to measure the accuracy and reliability of every step of the procedure. The system was able to measure absolute vertical distance with mean percent error in the range of 1.7% to 4.7%, depending on the working distance.

Three-Dimensional Microtubular Devices for Lab-on-a-Chip Sensing Applications.

The rapid advance of micro-/nanofabrication technologies opens up new opportunities for miniaturized sensing devices based on novel three-dimensional (3D) architectures. Notably, microtubular geometry exhibits natural advantages for sensing applications due to its unique properties including the hollow sensing channel, high surface-volume ratio, well-controlled shape parameters and compatibility to on-chip integration. Here the state-of-the-art sensing techniques based on microtubular devices are reviewed. The developed microtubular sensors cover microcapillaries, rolled-up nanomembranes, chemically synthesized tubular arrays, and photoresist-based tubular structures via 3D printing. Various types of microtubular sensors working in optical, electrical, and magnetic principles exhibit an extremely broad scope of sensing targets including liquids, biomolecules, micrometer-sized/nanosized objects, and gases. Moreover, they have also been applied for the detection of mechanical, acoustic, and magnetic fields as well as fluorescence signals in labeling-based analyses. At last, a comprehensive outlook of future research on microtubular sensors is discussed on pushing the detection limit, extending the functionality, and taking a step forward to a compact and integrable core module in a lab-on-a-chip analytical system for understanding fundamental biological events or performing accurate point-of-care diagnostics.

Color holographic display system based on utilization of effective viewing area

AbstractIn this paper, a color holographic display system based on the utilization of effective viewing area (EVA) is proposed. Color reconstruction is achieved by using a single spatial light modulator (SLM). The EVA of three color reconstructed images is analyzed based on the holographic diffraction theory and the principle of geometrical optics. Then, the effective holograms of three colors are calculated based on the EVA of the system. When three color lasers are used to collimate the SLM, three color reconstructed images can be coincided in the same position with a fast speed of calculation. Moreover, the chromatic aberration can be eliminated and the experimental results verify the feasibility of the proposed system.

Time-Domain Characterization of the Radiation Pattern of the Terahertz Photoconductive Antennas

We present a novel method to characterize the radiation pattern of the terahertz photoconductive antennas in time-domain. The method uses a modified version of the terahertz time-domain spectroscopy system, where we use the basics of physical optics and the optical path compensation principle using the delay line in the system in order to detect the spatial distribution of the terahertz radiation of the photoconductive antennas in two major planes. Using this method, we investigate two terahertz photoconductive antennas, namely dipole and spiral antennas, and compare the measurement results with simulations in time-domain. The comparison of the calculation and measurement results shows good agreement, where we measure an average and maximum optical path difference error of 4.7 and 8%, which results in an average and maximum half-power beam width error of 1.87 and 3.2°, respectively. We believe that the proposed method will be useful for predicting the system level performance of the terahertz time-domain spectroscopy systems in real-life applications.

Influence of MoS2 and PTFE in oil film characteristics and tribological performance in EHL point contacts

ABSTRACTThe use of improvers of viscosity index mixed with engine oil to enhance film thickness of lubricant, have been tribologically studied by the optical interferometry technique. The viscosity index improvers (PTFE and MoS2) effect on the mixed engine oil, were experimentally studied and compared with benchmark engine oil without added viscosity improvers. The outcome of the improvers, rolling velocity and contact pressure on the engine oil film formation in a steel ball, loaded on a flat glass surface in point contact, was investigated. The two-beam light source optical interferometry principle was used in this experiment. The Hamrock and Dowson's numerical methods for EHL film formation was compared with the tribo-test results. The base engine oil for this study is SAE 30 while PTFE and MoS2 powdered lubricants were blended with the engine oil. The viscosities of the lubricants ranged from 0.0109 Pa s to 0.255 Pa s. The rolling speed and the loads were distinctly selected between 0.189 m/s to 0.641 m/s and 1 N to 2.6 N, respectively. The steady and rolling state was used to evaluate the stability of the film thickness at contact point. The viscosity improvers were observed to have significant positive influence on the film thickness behaviour.

Multiband notch filter based guided-mode resonance for mid-infrared spectroscopy

A dielectric guided-mode resonance (GMR) notch filter with multiple channels was designed to operate in the mid-wave infrared (MWIR, 3∼4μm). The transmission characteristics of filters were analyzed using a finite difference time domain (FDTD) method. In the structure of notch filter, two different periodic (p1=1.6μm and p2=2.0μm) silicon (Si) grating waveguide layers (GWLs) are constructed on the CaF2 substrate. Si waveguide layer thickness and CaF2 cladding layer thickness were designed based on optical interference principle to give maximum transmission across the MWIR. The transmission spectrum presents two narrow band located at 3.410μm and 3.833μm with not only a high bandstop coefficient (>99%), but also a broadband high transmission (>90%) off-resonance. The resonant wavelengths can be flexible modulated in wide range by changing grating periods or filling factors, and it is proved that filter is stable and useful in actual atmospheric conditions. Because of the good performance in the bandstop features, the multiband GMR notch filter designed in this method may have a potential for a variety of imaging or detection applications.

Direct Comparison of PdAu Alloy Thin Films and Nanoparticles upon Hydrogen Exposure.

Nanostructured metal hydrides are able to efficiently detect hydrogen in optical sensors. In the literature, two nanostructured systems based on metal hydrides have been proposed for this purpose each with its own detection principle: continuous sub-100 nm thin films read out via optical reflectance/transmittance changes and nanoparticle arrays for which the detection relies on localized surface plasmon resonance. Despite their apparent similarities, their optical and structural response to hydrogen has never been directly compared. In response, for the case of Pd1–yAuy (y = 0.15–0.30) alloys, we directly compare these two systems and establish that they are distinctively different. We show that the dissimilar optical response is not caused by the different optical readout principles but results from a fundamentally different structural response to hydrogen due to the different nanostructurings. The measurements empirically suggest that these differences cannot be fully accounted by surface effects but that the nature of the film–substrate interaction plays an important role and affects both the hydrogen solubility and the metal-to-metal hydride transition. In a broader perspective, our results establish that the specifics of nanoconfinement dictate the structural properties of metal hydrides, which in turn control the properties of nanostructured devices including the sensing characteristics of optical hydrogen sensors and hydride-based active plasmonic systems.

An experimental method for quantitative analysis of real contact area based on the total reflection optical principle**Project supported by the National Natural Science Foundation of China (Grant No. 11872033) and the Beijing Natural Science Foundation, China (Grant No. 3172017).

The simulation of real contact area between materials is foundationally important for the contact mechanics of mechanical structures. The Greenwood and Williamson (GW) model and the Majumdar (MB) model are the basic models in this field, which are widely accepted and proven to be valid in many experiments and engineering. Although the contact models have evolved considerably in recent years, the verifications of the models are most based on the indirect methods such as electrical conductivity and contact stiffness, because of the lack of effective methods to directly measure the variation of contact surface. In this paper, the total reflection (TR) method is introduced into the verification of contact models. An experiment system based on TR method is constructed to measure the real contact area of two PMMA specimens. The comparison analysis between the results of experiment and models suggests that the experiment result has the same trend with simulation, the MB model has better agreement with the experimental result because this method can take into account the variation of radius and the merging of asperities, while the GW model has a huge deviation because of the dependence on resolution and the lack of considering the variation of radius and asperity’s merging process. Taking the interaction of asperities into account could give a better result that is closer to the experiment. Our results and analysis prove that the experimental methods in this paper could be used as a more direct and valid method to quantitatively measure the real contact area and to verify the contact models.

Fermat et le principe du moindre temps

The principle of least time was first conceived by mathematicians-physicists, such as Ibn al-Haytham (Alhazen), as the principle of the easiest way followed by the light ray. It was not until the invention of the maximum and minimum method by Pierre de Fermat that this principle, stated in the Book of Optics of Ibn al-Haytham, became the principle of least time. This article examines the history of this principle in ancient and classical optics.

The Relationship between Safety of Night Voyage and Light Pollution at Sea

In order to study the relationship between the safety of night voyage and the light pollution at sea, based on the theory of system engineering, the safety of night voyage of ships affected by light pollution at sea is analysed from two aspects: the recognisability of ship lights and navigation aids and the visual effect of human body. The following conclusions are drawn: Marine light pollution does exist in China, and its pollution sources include at least glare of urban landscape lighting, evanescent light of fishing lighting at sea, direct light of harbour wharf operation area, and intensive mooring lights of ships in harbour and colour highlight lights of bridges. Based on the analysis of optical principle, the brightness contrast and colour contrast of ship lights and navigation aids are reduced by light pollution at sea, which has an impact on the safety of night voyage. Analysing by using visual ergonomics principle, light pollution at sea weakens the contrast sensitivity, colour vision function and stereo vision function of the driver’s visual effect, and affects the safety of ship’s night voyage.

착시의 원리를 이용한 스캐니메이션의 색의 차이에 따른 시인성 평가

본 연구의 목적은 산업디자인 분야에서 스캐니메이션을 효과적으로 사용하기 위한 색의 적용 방법을 찾는 것이다. 스캐니메이션이란 Scan과 Animation의 조합어로서 잔상의 원리를 이용한 운동성 착시의 한 종류이다. 최근 산업디자인 분야에서 시각적인 즐거움을 주는 요소로 많이 활용되고 있으나 그것에 관한 체계적인 연구는 아직 부족한 실정이다. 스캐니메이션에 대한 선행연구가 아직 부족하고, 지금까지의 연구는 마스킹 레이어의 마스킹 면적과 투명한 슬릿의 면적, 이미지 레이어의 이미지 분할 등 스캐니메이션의 구동 원리에 초점이 맞추어져 있다. 인간의 시·지각에 있어 70% 이상을 색이 차지하므로 효과적인 스캐니메이션의 사용에 있어 색에 관한 연구는 필수적이다. 배색에 관한 선행연구가 있지만, 이는 PCCS 색체계를 이용한 일부 색상의 배색에 국한되었다. 본 연구는 2010년 한국산업표준으로 지정된 KS 표준색을 기준으로 한 스캐니메이션의 연구라는 점에서 선행연구와의 차별성을 가지며, 스캐니메이션을 산업디자인 분야에 효과적으로 적용하기 위한 색의 적용 방법을 알아보는 것을 목적으로 한다. 연구를 통해 검은색 마스킹 레이어를 기준으로 색의 시인성 지수를 알 수 있었다. 또한, 색상의 상관계수 분석을 통해 색상환을 기준으로 인접한 색상일수록 유사한 시인성 지수를 가진다는 것을 발견했다. 명도와 채도를 기준으로 하는 분석 실험을 통해서는 명도와 채도가 동일하게 유지되더라도 시인성을 결정짓는 유일한 색의 속성으로 작용할 수 없다는 것을 파악했다. 따라서 스캐니메이션을 산업디자인 분야에 적용할 시에는 기준이 되는 마스킹 레이어의 색을 중심으로 이미지 레이어 색의 시인성 지수를 개별적으로 참조하여 적용해야 할 필요성이 있으며 목적에 맞는 스캐니메이션의 색을 적용하기 위해서는 다른 색의 마스킹 레이어를 기준으로 한 후속 연구가 이루어질 필요성이 있다.

Modeling the interaction of light and nutrients as factors driving lake eutrophication

Eutrophication is a major problem in the field of water environments at present, and its main driving factors are light and nutrients. In this paper, the process of eutrophication in small artificial lake is studied, according to the principle of water optics and conservation of mass, the light and the nitrogen and phosphorus in water nutrients were selected as influencing factors, and 16 different scenarios of light-nutrients interaction conditions were designed by orthogonal experiment. Then water eutrophication model was used to analyze the process of eutrophication under different light-nutrient scenarios. According to the comparison of simulation results, if the concentration of nutrients is increased under low light conditions, the growth of algae will be inhibited; And if the light condition is set to a fixed value, the simulation results under different nitrogen and phosphorus concentrations in the water show that the effect of phosphorus on algae growth is greater than that of nitrogen; In addition, comparing the growth of algae under different light and phosphorus scenarios, it can be seen that the light-driven effect is more significant than that of phosphorus. By simulating all the design scenarios and analyzing the results, it can be found that the algae growth rate reaches a maximum when the light intensity and the nitrogen and phosphorus concentration increase to a certain range; while continuing to increase the light and nutrient concentration exceeds a certain threshold range, the rate of algae growth will be inhibited.