Optical Principles Research Articles

Anti-crosstalk device based on a Novel Micro-LED structure design

Herein, the crosstalk problem of display pixels and color subpixels is solved according to the optical design requirements of a large half-beam angle and highly uniform far-field light distribution to obtain improved display effects. A new chip micro-light emitting diode (LED) + quantum dot (QD) fluorescence mode is presented. The design optical principle uses the Monte Carlo method to prevent the light emitted from the chip from entering the QD film in adjacent pixels. Implementation is achieved by adjusting the distance between the QD film and the chip. The results are obtained by optimizing the distance between the micro-LED and the QD phosphor. When the distance between the QD fluorescent film and the chip is constant, the intensity of the light received by the QD fluorescent film decreases at increasing distances between the subpixel chips, and its contrast increases. The analyzed results suggest that anti-crosstalk micro-LED optical devices can reduce the illuminance on the receiving surface of adjacent pixels to the original 0%. Thus, the crosstalk between display pixels is effectively addressed.

Fifth-order asymptotic geometric aberrations of electron lenses

In this article the analytical expressions of the fifth-order asymptotic geometric aberrations of electron lenses are derived by Mathematica. The process of the derivation is analogous to the method described in “Principles of Electron Optics” by P.W. Hawkes and E. Kasper. All the analytical formulae for asymptotic aberration coefficients in polynomials in the reciprocal magnification are numerically cross-validated with the differential algebraic (DA) method. The results indicate that the derived formulae are doubtless correct.

Shaped Omnidirectional Reflector Fed by a Dielectric Lens Associated with a Coaxial Feed Horn

The paper explores an omnidirectional antenna configuration composed of a reflector fed by a shaped dielectric lens associated with a coaxial TEM horn. A simple formula describes the lens shape obtained by applying Fermat’s principle to control the rays’ caustic emerging from the dielectric interface. Based on geometrical optics (GO) principles, a synthesis technique defines the reflector shape to control the antenna radiation pattern in the vertical plane. Concatenated conic describes the reflector generatrix. The study employs a full-wave analysis to validate the designs and explores the proposed configuration to attend two distinct far-field specifications.

Partially coherent laser beam shaping in a zoom homogenizer.

This paper proposes a synthesis method including wave optics and geometric optics to design the zoom homogenizer for partially coherent laser beams and discusses the effects of the spatial coherence and system parameters on the beam performance. Based on the principles of pseudo-mode representation and matrix optics, a numerical model for fast simulation has been built and the parameter constraints for avoiding beamlet crosstalk have been presented. The relation of the size and the divergence angle of the highly uniform beams formed in the defocused plane with system parameters has been developed. The variations in the intensity profile and the uniformity of the variable-size beams during zooming have been explored.

Projected feature assisted coarse to fine point cloud registration method for large-size 3D measurement.

Fringe projection profilometry has gained significant interest due to its high precision, enhanced resolution, and simplified design. Typically, the spatial and perspective measurement capability is restricted by the lenses of the camera and projector in accordance with the principles of geometric optics. Therefore, large-size object measurement requires data acquisition from multiple perspectives, followed by point cloud splicing. Current point cloud registration methods usually rely on 2D feature textures, 3D structural elements, or supplementary tools, which will increase costs or limit the scope of the application. To address large-size 3D measurement more efficiently, we propose a low-cost and feasible method that combines active projection textures, color channel multiplexing, image feature matching and coarse-to-fine point registration strategies. Using a composite structured light with red speckle patterns for larger areas and blue sinusoidal fringe patterns for smaller ones, projected onto the surface, which allows us to accomplish simultaneous 3D reconstruction and point cloud registration. Experimental results demonstrate that the proposed method is effective for the 3D measurement of large-size and weak-textured objects.

Optical Grating Diffraction and Optical Beat Frequency Principle-Based Ultrahigh Resolution Displacement Measurement System

This research presents a novel displacement measurement system that combines optical grating diffraction, the optical Doppler principle, and the optical beat frequency principle. The system utilizes a double-frequency laser device, an interferometer, a measuring grating, and an electrical signal processing unit. By dividing the laser into reference light and measuring light and analyzing the beat frequency signal generated by the interaction of the measuring light and the reference light, the system achieves precise linear displacement measurements in two directions. The system offers sub-nanometer-grade or even higher resolution and accuracy, simultaneous measurement of horizontal large-stroke displacement and horizontal displacement, and exhibits advantages such as environmental insensitivity, high measurement accuracy, compact size, and lightweight. The proposed system finds potential applications in ultraprecise workpiece platform position measurement systems, contributing to the overall performance improvement of lithography machines.

Fabrication and characterization of electro-optic polymer/silicon hybrid MZI for interrogating small signals from an ECG

A Mach–Zehnder interferometer (MZI) composed of electro-optical polymer/silicon hybrid slot waveguides is reported. The device is designed to be asymmetrical so that the modulator is in a linear workspace when no electric field is applied to the initial operating state. We rely on the fast and strong nonlinearities of CLD-1/PMMA that infiltrates silicon rather than on the slower free-carrier effect in silicon. The modulated arm waveguides are designed in the shape of silicon/polymer hybrid slot waveguides to increase the interaction of the polymer material with the light field. The results show that the loss of the proposed MZI is 3.51 dB with a core size of 420μm × 160μm, and the half-wave voltage of the MZI is 2.1 V at 1550 nm, which provides the possibility of application in measuring small signals from an electrocardiogram with the optical principle.

50.3: Main Optical Performance Measurement Method of Near‐Eye‐Display Device Based on Binocular Camera

Optical measurement of display equipment has always been the most important means to evaluate its performance, and AR/VR and other Near‐Eye‐Display (NED) is a new type of display equipment. In recent years, its optical performance measurement methods and measuring equipment have been introduced, but the operation is complicated, the cycle is long and the cost is expensive. Therefore, this paper designs a method of measuring the main optical performance parameters of near eye display device based on binocular camera. According to the optical correlation principle of the display device, the derivation modeling, system design and calibration experiments were carried out, so as to realize the convenient, rapid and low‐cost measurement of the main optical performance parameters of the NED device.

Phase Contrast Image Restoration by Formulating Its Imaging Principle and Reversing the Formulation With Deep Neural Networks.

Phase contrast microscopy, as a noninvasive imaging technique, has been widely used to monitor the behavior of transparent cells without staining or altering them. Due to the optical principle of the specifically-designed microscope, phase contrast microscopy images contain artifacts such as halo and shade-off which hinder the cell segmentation and detection tasks. Some previous works developed simplified computational imaging models for phase contrast microscopes by linear approximations and convolutions. The approximated models do not exactly reflect the imaging principle of the phase contrast microscope and accordingly the image restoration by solving the corresponding deconvolution process is not perfect. In this paper, we revisit the optical principle of the phase contrast microscope to precisely formulate its imaging model without any approximation. Based on this model, we propose an image restoration procedure by reversing this imaging model with a deep neural network, instead of mathematically deriving the inverse operator of the model which is technically impossible. Extensive experiments are conducted to demonstrate the superiority of the newly derived phase contrast microscopy imaging model and the power of the deep neural network on modeling the inverse imaging procedure. Moreover, the restored images enable that high quality cell segmentation task can be easily achieved by simply thresholding methods. Implementations of this work are publicly available at https://github.com/LiangHann/Phase-Contrast-Microscopy-Image-Restoration.

How Reliable Is Pyramidal Wavefront-Based Sensor Aberrometry in Measuring the In Vivo Optical Behaviour of Multifocal IOLs?

Cataract or refractive lens surgery, along with the implantation of multifocal intraocular lenses (MF-IOL), enables a complete range of functional far, near and intermediate vision. Refractive, diffractive and extended depth of focus (EDoF) or combination of these principles represent the technology used to obtain this multifocality. Aberrometry makes it possible to study the aberrations induced by MF-IOLs. Among the different optical principles available to measure ocular aberrations, pyramidal wavefront-based sensor (PWS) aberrometry shows the highest resolution with MF-IOLs. Retinal image quality measured by a PWS aberrometer differed significantly according to the technology of the implanted lens. Monofocal and diffractive lenses showed the highest values of far-distance retinal image quality, followed by refractive and EDoF lenses; however, retinal image quality analysed in diffractive lenses appears to be more dependent on residual refractive error. Considering this limitation, PWS-aberrometry could be used to compare diffractive lenses. Nevertheless, further studies are needed to provide additional information about the clinical retinal image quality of MF-IOLs and to help surgeons in the important preoperative selection of IOLs.

Effects of Medium Density Fiberboards (MDF) Recycling Methods on Fiber Dimensions and Some Reconstructed Board Properties

In this study, different methods, including acid hydrolysis (phosphoric and formic acid), thermohydrolysis, and microwave methods were tested for recycling of fiberboards made of 100 % beech and 70 % beech + 30 % pine wood fibers, which are widely sold in the market. The impacts of the using methods on the fibers were investigated with the help of a device that determines the fiber dimensions according to optical principles. In a laboratory setting, test boards were constructed using recycled fibers, and the changes in certain physical and mechanical qualities were studied. As a result, it was determined that recycled fibers obtained from microwave and thermo-hydrolysis fibers could be effectively used in fiberboard production. However, the proportion of fibers, longer than 1.24 mm, was decreased by about 30 % with the phosphoric acid method for MDF samples composed of 100 % beech fiber. The fiberboards could not be obtained from fibers recycled through acid hydrolysis except for phosphoric acid method with 100 % beech fibers.

Design and fabrication method of holographic waveguide near-eye display with 2D eye box expansion.

Augmented reality near-eye display (AR-NED) technology has attracted enormous interests for its widespread potential applications. In this paper, two-dimensional (2D) holographic waveguide integrated simulation design and analysis, holographic optical elements (HOEs) exposure fabrication, prototype performance evaluation and imaging analysis are completed. In the system design, a 2D holographic waveguide AR-NED integrated with a miniature projection optical system is presented to achieve a larger 2D eye box expansion (EBE). A design method for controlling the luminance uniformity of 2D-EPE holographic waveguide by dividing the two thicknesses of HOEs is proposed, which is easy to fabricate. The optical principle and design method of the HOE-based 2D-EBE holographic waveguide are described in detail. In the system fabrication, laser exposure fabrication method of eliminating stray light for HOEs is proposed, and a prototype system is fabricated and demonstrated. The properties of the fabricated HOEs and the prototype are analyzed in detail. The experimental results verified that the 2D-EBE holographic waveguide has a diagonal field of view (FOV) of 45°, an ultra-thin thickness of 1 mm, and an eye box of 16 mm × 13 mm at an eye relief (ERF) of 18 mm, the MTF values of different FOVs at different 2D-EPE positions can be better than 0.2 at 20 lp/mm, and the whole luminance uniformity is 58%.

Resolution analysis on light-field particle image velocimetry.

With rapid developments in light-field particle image velocimetry (LF-PIV) based on single-camera, dual-camera, and dual-camera with Scheimpflug lenses, comprehensive quantitative analysis and careful evaluation of their theoretical spatial resolutions are essential to guide their practical applications. This work presents a framework for and better understanding of the theoretical resolution distribution of various optical field cameras with different amounts and different optical settings in PIV. Based on Gaussian optics principles, a forward ray-tracing method is applied to define the spatial resolution and provides the basis of a volumetric calculation method. Such a method requires a relatively low and acceptable computational cost, and can easily be applied in dual-camera/Scheimpflug LF-PIV configuration, which has hardly been calculated and discussed previously. By varying key optical parameters such as magnification, camera separation angle, and tilt angle, a series of volume depth resolution distributions is presented and discussed. By taking advantage of volume data distributions, a universal evaluation criterion based on statistics that is suitable for all three LF-PIV configurations is hereby proposed. With such a criterion, the pros and cons of the three configurations, as well as the effects of key optical parameters, can then be quantitatively illustrated and compared, thus providing useful guidance on the configuration and optical parameter selections in practical implementations of LF-PIV.

Simulating the Action Principle in Optics

Light has a fascinating property: it always travels the path that takes the least time between any two points. This is the motivating property behind optical phenomena such as reflection and refraction. The unreasonable economic efficiency of light is captured by a single proposition: the principle of least action (PLA) in optics. Unlike reflection and refraction, which emerge from optimizing a one-dimensional function, the PLA emerges from optimizing an infinite-dimensional functional. The PLA can be difficult for students to comprehend, as the formulation of the Lagrangian is often left unexplained. To this end, this paper presents various simulations to demonstrate the action principle, including a numerical solution to a generalization of the brachistochrone problem to an arbitrary refractive profile. The interactive simulations discussed in the paper are available at Ref. 1.

An analytical approach to assess the interrelation of surface properties and softness of tissue paper

The tissue industry constantly strives for improving the overall quality of tissue paper, as customers pay more attention to special quality features when it comes to a purchase decision between different products. As producers need to optimize their processes and furnish mixtures to keep production costs low, accurate and fast methods are crucial for characterization of important tissue properties. Here, we present a method for the characterization of the tissue surface regarding roughness and describe its relation to the tissue surface softness properties, based on a sample set of dry-creped bath tissue (DCT) with different amounts of softwood (SW), hardwood (HW), and nonwood pulp (NWP). The surface of tissue is complex and consists of several overlying structural features; thus, the optical non-contact measurement principle of focus variation was used to provide robust and reliable topographical surface information. Based on the obtained 3D data, areal surface analysis was performed to determine the surface roughness of the tissue samples, which is described by the developed interfacial areal ratio (Sdr) and the power spectral density (PSD). To determine the surface softness properties (TS7) of the tissue, a widely-used tissue softness analyzer (TSA) in the industry was employed. The surface softness (TS7) and the stiffness (D) parameters of this instrument were considered for surface and structural characterization. The results of the surface roughness (Sdr and PSD) and surface softness TS7 measurements show a good linear correlation, with higher surface roughness implying a higher TS7. The presented evaluation of these aspects of tissue softness allows an objective, fast, and accurate assessment of the relevant properties in addition to standard panel tests and is also applicable to other hygiene products.

Did Christiaan Huygens need glasses? A study of Huygens' telescope equations and tables

In the later stages of his life, Christiaan Huygens semi-empirically derived a set of relations between the objective focus and diameter, the eyepiece focus, and the magnification that resulted from combining the two lenses. These relations were used by him and his brother to build what he believed were optimized telescopes. When comparing these equations to the ones derived from modern optical principles, Huygens' telescopes were in fact far from optimal. While there are several potential reasons for this discrepancy, one possible reason, explored in this work, is that Huygens might have suffered from a mild case of myopia (or near-sightedness) and that he compensated this condition by building telescopes that overmagnified by a factor of 3.5. Based on this hypothesis, Huygens' visual acuity is estimated to be around 20/70, which on average corresponds to an optical prescription of −1.5 diopters.

Refractometric Imaging and Biodetection Empowered by Nanophotonics

AbstractAdvancing clinical and nonclinical diagnostic technologies is particularly crucial for improved preparedness for the next pandemic and other global healthcare challenges. To this end, marrying advanced microscopic imaging with chip‐scale bioanalytical systems provides fresh modalities by analyzing signals of transmitted, reflected, or scattered light waves. This review brings clarity to the latest progress of refractometric imaging and biodetections on a chip, in which interferences and resonances as cornerstones of optics and plasmonics are breaking new ground. A vast range of nanophotonic and plasmonic transducers are discussed, ranging from planar films, nanoarrays, and waveguiding resonators to holistic designs. The augmented bioanalyses cover immunoassays, single‐molecule analysis, and motion tracking of bacterial pathogens and cells. Compared to single‐point spectroscopic measurements, imaging‐empowered approaches are rapidly evolving with greatly promoted signal‐noise ratio, spatial‐temporal resolutions, multiplexability, and throughput, which can be accomplished in a compact cradle system with minimized bulky components in a spectrometer‐free manner. Besides, advances in machine learning technologies applied for data analytics and transducer designs are highlighted. All in all, there are unlimited opportunities for new optical structures, principles, and ways of data retrieval to tap in, which will raise technological impacts on unveiling fundamental issues in life science and advancing global healthcare technologies.

Design of Adjustable Liquid Simulated Eye for Spherical Power Detection of Eccentric Photographic Vision Screening Instrument

A liquid simulated eye was designed to detect different spherical diopter indexes in the type inspection of medical equipment vision screening instrument. This liquid test simulation eye design is composed of three parts: lens, cavity and retina-imitation piston. By using the principle of geometric optics and the optical scattering effect of human retina, the relationship between the accommodation displacement of the designed adjustable liquid simulated eye and the spherical mirror power was calculated and analyzed. The designed liquid test simulated eye can be applied to vision screening instruments, computer refractometers and other optometry equipments based on photography principle in spherical lens measurement and so on.

Optical characterisation of two novel myopia control spectacle lenses.

To quantify the amount of myopic defocus, contrast modulation and other optical characteristics of two novel spectacle lenses (MiYOSMART by Hoya and Stellest by Essilor) with the inclusion of lenslets in their designs were investigated computationally and experimentally. This paper examined the hypothesis that despite the non-coaxial nature of the optics, image degradation will exist due to the fragmented nature of the base optic when imaging through the lens regions populated by lenslets. Optical power was evaluated by computing wavefront vergence and curvature from wavefront slope measured with the Optocraft aberrometer within 1.0 and 6.0 mm apertures across MiYOSMART hexagons and Stellest rings. Point-spread functions (PSFs) were computed using physical (wave) optics and geometrical ray optics principles, and compared with experimental measurements using a 4f optical system. Simulated retinal images and modulation transfer functions (MTFs) were computed from PSF-derived optical transfer functions (OTFs). Mean lenslet power in MiYOSMART was +3.95 ± 0.10 D through the hexagons and +6.00 ± 0.15 D in Stellest in rings 1-5 and decreased by 0.42 D/ring reaching 3.50 D in the final one. Stellest lenslets included up to -0.015 microns of primary spherical aberration. PSFs and retinal images revealed simultaneous contributions of the base optic and lenslets. MTFs showed a decrease in contrast at low (1-10 c/deg) spatial frequencies (SFs) comparable to 0.25 D of defocus, and retention of diminished levels of contrast at higher SFs. Varying sagittal power and consistent curvature power across the lenslets is an identifying signature of the novel non-coaxial lens design included in both spectacle lenses. Lenslet array structure itself plays a significant role in determining image characteristics. For both lenses, the blur created by the fragmented base optic contributes to the image quality. The reduced MTFs over a wide range of spatial frequencies result in lowered image contrast.

Stand-alone optical spinning tweezers with tunable rotation frequency.

Advances in optical trapping design principles have led to tremendous progress in manipulating nanoparticles (NPs) with diverse functionalities in different environments using bulky systems. However, efficient control and manipulation of NPs in harsh environments require a careful design of contactless optical tweezers. Here, we propose a simple design of a fibered optical probe allowing the trapping of dielectric NP as well as a transfer of the angular momentum of light to the NP inducing its mechanical rotation. A polarization conversion from linearly-polarized incident guided to circularly transmitted beam is provoked geometrically by breaking the cylindrical symmetry of a coaxial nano-aperture that is engraved at the apex of a tapered metal coated optical fiber. Numerical simulations show that this simple geometry tip allows powerful light transmission together with efficient polarization conversion. This guarantees very stable trapping of quasi spherical NPs in a non-contact regime as well as potentially very tunable and reversible rotation frequencies in both directions (up to 45 Hz in water and 5.3 MHz in air for 10 mW injected power in the fiber). This type of fiber probe opens the way to a new generation of miniaturized tools for total manipulation (trapping, sorting, spinning) of NPs.