In this paper, the expression for the SNR has been developed through the imaging model. It is concluded that the image SNR decreases with the increase of the number of light-emitting points of the target under the same hardware conditions and experimental parameters. Using uniform bright squares of different sizes as the target, the SNR of the reconstructed image is calculated. Simulation and prototype

Photometric stereo allows us to estimate the surface normal of an object based on its shading. In uncalibrated photometric stereo, the light source direction is unknown; thus, both the light source direction and surface normal should be estimated, which establishes an ill-posed problem with ambiguity in its solution. Consequently, assumptions should be made to uniquely determine the solution; however

To image distant and dim objects, this paper designs a sparse aperture optical system with a small F number and a large filling factor. The design process is divided into three steps. To start with, the curvature radius and spacing of the primary and secondary mirrors are calculated under the guidance of the paraxial imaging theory. Then, based on the primary aberration theory, the conic coefficients

A gradient-index (GRIN) array is used as an imaging unit in light-emitting diode (LED) printers. In this study, we measure tilts of GRINs in an array and analyze the intensity distribution of the image to clarify the tilting amount and to evaluate the relation between the GRIN tilt and the degradation of the image. The arrangement intervals of the GRINs are measured, and the GRIN tilts are calculated

Up to now, laser self-mixing interferometry (SMI) has been widely applied to numerous scientific and industry fields. A easily negligible parameter, linewidth enhancement factor \(\alpha \), influences the inclination of SMI signals, and larger \(\alpha \) generally indicates more inclined fringes. It is demonstrated in the paper that solid-state lasers (SSL) have smaller linewidth enhancement factors

The radiation force calculated in the Rayleigh regime is investigated by comparison with the generalized Lorenz Mie Theory (GLMT). The basic concepts behind the Rayleigh regime and GLMT are introduced, and a numerical simulation is conducted to analyze the difference between these two methods. Several physical parameters are considered to evaluate their effect on the calculation accuracy of the Rayleigh

The saturated gain performance of the two-pump fiber optical parametric amplifier (2-P FOPA) in the presence of random dispersion fluctuation as well as fourth-order dispersion coefficient are investigated. The gain spectra of the 2-P FOPA is simulated by solving the coupled equations numerically, considering the dispersion fluctuations along the fiber as a stochastic process with a given standard

Multimode fibers (MMF) are enjoying a renewed attention boosted by recent advances in multimode complex nonlinear optics. Reason behind nonlinearity is occurred either due to intensity dependence of the medium refractive index or to inelastic-scattering phenomenon. The most commonly occurred non-linear effects in optical Multiple Input Multiple Output (O-MIMO) are the Kerr, Stimulated Brillouin Scattering

In hyperspectral imaging, the captured signal is often affected by saturation due to specular reflection or a peaky spectrum. In this paper, we propose a restoration method for saturated hyperspectral signals. Our algorithm is based on principal component analysis to obtain the reconstruction basis and then solve a linear constrained least square problem to calculate the coefficients of each basis

An accurate inversion technique in double integrating sphere (DIS) measurement is essential for determining the optical properties of biological tissue. Although there are several established techniques, the computational time and complexity for spectral analysis require some approximations of the anisotropy factor g and refractive index n. We aim to demonstrate an artificial neural network (ANN) based

In this study, we discuss a new method to optimize the design of an omnidirectional gaze optical imaging system with ultrahigh resolution and long focus. An aspheric diffractive optical element is used in the optical system to offer more freedom, simplify the structure, and decrease the chromatic aberration. Owing to large image sensor arrays, the omnidirectional gaze photoelectric imaging system is

Both Fabry–Pérot interferometry and the DC electrochemical method have been simultaneously used for the first time to measure in situ the anodic current density (J) of aluminum oxide films in 0, 2, 4, 5, 6, 8 and 10% sulfuric acid solutions (H2SO4). The calculated values of J by Fabry–Pérot interferometry were verified by the DC electrochemical method, i.e., a potentiostat, and the AC electrochemical

We propose a superimposing interferogram method to enhance the sensitivity and interference definition of spatial-phase-shift interferometers. The proposed method uses a multi-slit array as a redesigned field stop for the spatial-phase-shift interferometer. The widths of the apertural and blocked areas correspond to half the wavelength of the fringe pattern on the imaging plane and determine the wavelength

We live in a colorful world, and it is important for us to receive visual information from colors in situations such as when we read a map. However, such important color-based information cannot be accurately received by some people. These people generally have some type of color vision deficiency such as protanopia or deuteranopia. It is important to realize their difficulties in recognizing differences

Hollow-core photonic crystal fibers (HCPCFs), a form of optical conveyer belts, have been used to guide particles for many years. However, only the translational motions of a guided particle can be manipulated. In contrast to traditional types, we demonstrate a new form of optical conveyor belts based on a polarization-maintaining hollow-core photonic crystal fiber (PMHCPCF). Because of the constant

We demonstrate distributed measurement of the polarization beat length along single-mode optical fibers (SMFs) using slope-assisted Brillouin optical correlation-domain reflectometry (BOCDR) with high spatial resolution, long measurement range, high sampling rate, and single-end accessibility. The beat lengths of SMFs wound on mandrels with radii of 10.5, 7.5, and 3.4 cm are measured to be 36.0, 18

Two-point resolution for ordinary microscopy was studied in a bright background under partially coherent light. The basic equation was derived from the unified theory of image intensity for two point-like objects for bright and dark backgrounds. For an extended Rayleigh’s criterion, it is shown that the two-point resolution in a bright background is noticeably different from that in a dark background

The optical three-dimensional (3D) measurement technique based on the laser stripe has become increasingly important in additive manufacturing, which is necessary to extract the laser stripe accurately. In welding, the wrong laser stripe centers due to the high-brightness noise are usually extracted, which causes serious measurement error. In this paper, a laser stripe extraction algorithm based on

Applications of digital micromirror device for lidar are overviewed. A large Lagrange invariant value makes DMD as one of the attractive beam steering transmitter and receiver solutions for a time-of-flight lidar, especially with its an extended angular throw by synchronized pulsed laser illumination.

We have established a holographic particle tracking velocimetry (HPTV) technique based on compressed sensing (CS) for measurement of the velocity field of microflows in this study. In conventional HPTV, where the scattered light field is reconstructed via backpropagation calculations, the particle image spreads greatly in the depth direction and it is then difficult to perform three-dimensional three-component

In the astronomical speckle interferometry, low-light CCD cameras such as the electron bombarded/multiplying CCDs (EB/EMCCDs) are being widely used for taking the faint speckle images. The detector noise affects the power spectral estimate of the astronomical object as well as the speckle noise does. The estimation errors of the object power spectrum are results of the propagation of the random fluctuations

We report on a high-power continuous-wave (CW) intracavity frequency-doubled laser at 670.8 nm, which is produced by the second-harmonic generation of a diode side-pumped Nd:YAP crystal laser with a type-II noncritically phase-matched LBO crystal. A maximum output power up to 13 W at 670.8 nm is obtained with an optical-to-optical \((808\mathrm{ nm}\to 671\mathrm{ nm})\) efficiency of 2.4%. The beam

We propose an image reconstruction technique of a color 3-D object to perform image refocusing by combining information from bright-field image and digital holography. The key concept is first to reconstruct the 3-D object using compressive holography. Next, a binary mask is created to separate objects and transparent voxels. Then, the mask is used to assist the 3-D color object reconstruction from

For images with insufficient visibility, image processing is required. Retinex theory is often implemented for image contrast enhancement for images with this characteristic. This paper proposes a multi-scale retinex-based contrast enhancement method using the illumination component; this method could preserve the naturalness of color images. In the proposed method, illumination was first modified

Plasmonic nanostructures or metasurfaces have recently been actively researched for structural color generation. Controlling the plasmonic resonant wavelengths of surface plasmon polaritons excited along the metal dielectric interfaces, arising from the resonant interaction with incident electromagnetic waves, reflection or transmission color can be effectively tuned in the visible wavelength region

Fluorescent diffuse optical tomography (FDOT) is an emerging imaging modality, with great prospects in areas such as biology and medicine. However, current FDOT encounters difficulty in simulating photon propagation in biological tissue, i.e., the forward problem, which limits its further application in biomedical research. This paper presents a lattice Boltzmann method (LBM) on the GPU to greatly

Heat-assisted magnetic recording (HAMR) is a promising technology for achieving more than 10 Tbit/inch2 recording density. A near-field transducer (NFT), which forms a small light spot on a recording medium, is necessary in HAMR. However, the heat generated by the NFT would melt the NFT itself. To solve this problem, the authors have proposed a novel device, in which a metal nano-antenna is attached

Optical discs are being sought as low-cost, earth-friendly storage candidates in response to increasing data volumes. To increase the recording density of optical disc, analog recording technique such as the Orthogonal Frequency Division Multiplexing (OFDM) method has been investigated. Since bitwise information is recorded on optical discs, it is necessary to create a column of marks corresponding

Because of its simple optical system setup and robust noise tolerance, non-interferometric phase retrieval is an important technique for phase-modulated holographic data storage. Usually, the iterative algorithm of non-interferometry needs hundreds of iteration numbers to retrieve phase accurately, the data transfer rate decreases severely. Strong constraints such as adding embedded data into the phase

Point ahead angle (PAA) prediction is important in space laser communication, but the existing methods have low accuracy and complicated calculation processes. In this paper, a new PAA prediction method is proposed based on Kalman filtering of the optical axis pointing trajectory. The proposed method uses the high precision of fine tracking to improve the accuracy of predictive filtering. Taking ground-satellite

Holographic data storage (HDS) based on a computer-generated hologram (CGH) technique has been proposed as a promising approach to realize an in-line and simple HDS system. This work focuses on multiplexed recording for CGH-based HDS, and the approach based on the reference wave correlation is introduced to the HDS. For the proposed method, the processes for a CGH design are modified to generate reference

Bidirectional reflectance distribution function (BRDF) offers complete description of the visual appearance properties of materials including the spectral and spatial characteristics. Numerous studies on BRDF have been performed for its important role in computer graphics, remote sensing, object characteristics analysis, and other fields. A few of these studies focus on the spectral polarized BRDF

In general, as people age the functions of their sensory organs deteriorate. For example, in the eye of an elderly person, the visual field becomes dark owing to a decrease in the amount of light reaching the retina. Moreover, objects appear blurred due to a decrease in contrast sensitivity. In particular, the contrast sensitivity decreases remarkably as the spatial frequency increases. In this study

A novel method for analyzing a rotating target by an orthogonal-beam Doppler velocity measurement system on the basis of a single laser diode is presented. Using the method of fast Fourier transform after smoothing filter, we can obtain two groups of Doppler frequency shifts in the spectrum to calculate the velocity of a rotating target. A theoretical analysis and an experimental setup have been implemented

High-dynamic range image reproduction using tone-mapping algorithms are used for image processing to reduce the dynamic range of a real scene to be displayed on low-dynamic range devices. General tone-mapping methods are associated with the determination of local parameters for tone compression and the halo artifact connected to detail enhancements. This paper proposes a lightness-preserved tone-mapping

We present a polarization-manipulated multispectral perfect absorber based on a 2D metal/insulator/metal nanocavity array, in which a periodic structure of stacked Au–Al2O3 elliptical nanodisk is deposited on a bulk flat Au substrate. Theoretical analysis of the electromagnetic property showed that both the dipolar plasmon resonance and the plasmon cavity mode are the physical origins of the near-perfect

To achieve quick-response Electrowetting displays with an accurate gray level performance for image applications, oil-splitting is an important issue which needs to be optimized. The study found that oil patterns affect the pixel aperture ratio. This paper proposes a novel driving waveform that can suppress an oil-splitting phenomenon without affecting the refresh rate. The experimental results show

In order to understand the physical meaning of the best-fitting sphere of aspheric surface, based on the optical design idea of the aberration theory, the relationship between the curvature radius of the best-fitting sphere and the spherical aberration for the full aperture aspheric surface is set. The result is consistent with the traditional calculation method, which gets mainly from the geometric

In this paper, a novel phase demodulation method for multiple self-mixing interferometry (MSMI) is proposed, which can improve the resolution and accuracy of vibration measurement in laser self-mixing interferometry (SMI). The sinusoidal phase modulation of the beam is obtained by an electro-optic modulator (EOM), and phase demodulation is performed by a lock-in amplifier analysis method. The phase

Scattering problem by one cylinder whose radius is comparable to incident wavelength can be solved by Mie theorem. Due to complicated multiple scattering, scattering characteristics by two adjacent cylinders cannot be easily expounded. In this paper, high-accuracy non-standard finite-difference time domain (NS-FDTD) method is utilized to simulate electromagnetic field scattered by two nano-sized circular

We propose two mid-infrared photonic crystal fibers with an elliptical As2S3 core and a dual-cladding structure with high birefringence and high nonlinearity. The cladding filling material is silica and the core material is As2S3. The full vector finite-element method is used to study the birefringence, and nonlinear coefficient of the structure in the 3–5 μm band. The Simulation results show that

A novel method of gas concentration calibration for tunable diode laser absorption spectroscopy, in which spectral analysis and harmonic signal intensity ratio measurement are combined, is proposed in this study. A harmonic signal is extracted from a transmitted light intensity by spectral analysis. The ratio of the second harmonic to the first harmonic is proportional to the gas concentration. The

The macro-bending loss of multimode step-index helical, s-shaped, and figure-of-eight-shaped optical fibers is investigated by ray-tracing simulation. In particular, fibers with the same radius of curvature having the three different configurations are compared. It is found that macro-bending loss strongly depends on the configuration as well as the bending curvature of the fibers. For the same curvature

This paper proposes a 3D reconstruction scheme for monocular cameras based on an improved line structure cursor positioning method and the Scheimpflug principle to overcome the limitations of current calibration methods for line-structured light 3D reconstruction and binocular stereo vision matching. Unlike the traditional line structure cursor positioning method, the line-structured light is projected

An optical cloud droplet and ice crystal measurement system ICEMET (icing condition evaluation method), designed for present icing condition monitoring in field conditions, is presented. The aim in this work has been to develop a simple but precise imaging technique to measure the two often missing parameters needed in icing rate calculations caused by icing clouds—the droplet size distribution (DSD)

We propose and discuss a compact and tunable plasmonic terahertz (THz) metamaterial switch based on graphene microcavity. Due to the joint effect of graphene plasmon resonances and Fabry–Perot oscillations, this metamaterial structure can be switched from the ON state to OFF state with the maximum intensity attenuation larger than 95% (ON–OFF ratio larger than 30 dB). The central frequency of the switch

We have demonstrated the design of two types of on-chip optical logic gates in 2D silicon PC slab, which can support AND and XOR logic gate functions at different input frequencies. Different shapes of the center directional emitting cavity and different input/output directions can lead to different logic operations without nonlinearity or magnetism. More complicated logic networks can be built based

Visualization of an electromagnetic field distribution is helpful for spatial evaluation of field leakage and can aid in solving inverse problems of signal-source estimation. Optical detection is more accurate and less invasive than other methods owing to a low metal content in the sensing probes and signal wires. We have previously reported optical detection of alternating magnetic fields using an

PurposeOptical wireless power transmission (OWPT), a new WPT alternative, is a promising solution to tackle the challenges like providing over watt-level power over meter-level distance that conventional WPT technologies face, to provide convenient and perpetual energy supply to the internet of things (IoT), mobile devices, and other various electrical equipments. In the OWPT system, in a room which

Quantum dots (QDs) have a great potential for realizing information processing because of their signal-modulation capability based on energy transfer. We present a method for generating diverse temporal and spectral signals based on the energy transfer between multiple QDs. The method uses randomly distributed QDs, so it is not necessary to precisely arrange a QD network. With multiple energy transfers

It is well known that the performance of orthogonal frequency division multiplexing (OFDM) is limited by phase noise, which depends on the laser linewidths for coherent-detection radio over fiber (RoF) systems. In this manuscript, we present numerical and theoretical results to analyze the combined effects of phase and additive white Gaussian noises in the performance of RoF-OFDM schemes with the feasible

This paper presents the spectral responsivity calibrations of two indium gallium arsenide (InGaAs) and one germanium based near-infrared photovoltaic detectors using a wavelength tunable laser source based on a supercontinuum laser developed at the Metrology Research Institute, Aalto University. The setup consists of a supercontinuum laser based on a photonic crystal fiber as the light source, a laser

We developed a low-coherence interference measurement system using the time-stretch dispersive Fourier transformation technique and demonstrated 10 MHz measurements of the interference signal. We estimated the path length distribution by performing Fourier transformation of the interference signal. The estimated path length difference agreed with the set value. However, as the path length increased

We have developed a setup for measuring differential spectral responsivities of unifacial and bifacial solar cells under bias light conditions. The setup uses 30 high-brightness LEDs for generating a quasi-monochromatic light source covering the wavelength range 290–1300 nm. Halogen lamps are used to generate bias-lighting conditions up to the irradiance level of 1000 W/m2. The setup has been fully

A single-pixel camera is composed of optical coding masks, a photo detector, and a computational decoder as the important feature that it requires no image sensor for imaging, and therefore has very simple optical and electrical architectures. The optical coding masks, the implementation of which is a novel point of our research, are composed of holes on a substrate and are arranged on the circumference

The predictable quantum efficient detector (PQED) is a primary standard of optical power, which utilizes two custom-made induced-junction photodiodes that are mounted in a wedged trap configuration for the reduction of reflectance losses. PQED photodiodes of p-type and n-type were characterized for their dark current dependence on reverse bias voltage at room temperature. As simulations predict that

Scattering of visible light by micrometer-scale natural wood fibers is usually treated by assuming fibers to be perfect long cylindrical scatterers. In industrial processes, however, fibers experience deformations and are far from ideal cylinders. Variation in fiber morphology affects their scattering properties and it poses a challenge for reliable process measurements. In this paper, we have studied

Microplastic (MP) pollution is alarming and poses an imminent threat to the environment with a direct impact on our health and that of fauna in natural water bodies. The understanding of light–MP interactions in water as well as the need for low-cost and robust optical sensors for the detection of MPs that appear everywhere is, therefore, necessary. We have demonstrated the use of a prototype optical

This paper presents a numerical study on simulated spectra and point spread functions in the database that we constructed by moderate grouping of nine layers in a skin model. The database is used for identification of a simulated skin reflectance spectrum which seems most closed to a certain target spectrum or a measured spectrum. On the basis of the properties of absorption and scattering coefficients

During the measurement of spectral luminous efficiency function \(V\left( \lambda \right)\), monochromatic visual stimuli of higher luminance can be obtained by narrow band optical filters with broad band light sources, compared to monochromators. However, the distortion of \(V\left( \lambda \right)\) is inevitably caused due to the bandwidth of the optical filters. In this paper, the effect of optical