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

In this paper, we demonstrate a non-interferometric phase imaging technique based on modified transport of intensity equation (TIE) through a liquid crystal variable retarder (LCVR) and partial coherent illumination. The LCVR has been used in pure phase shifter configuration for creating refractive index variation. The modified TIE eliminates the need of mechanical displacement of camera or object

We propose a virtual camera that can pass through a small hole in an obstruction to capture an image on the other side. Recently, free-viewpoint television technology has enabled the generation of video in which viewpoint images are captured from locations where cameras are not actually placed. However, capturing the images of objects concealed behind obstructions or beyond a camera’s field of view

In this paper, we analyze a machine-learning-based non-iterative phase retrieval method. Phase retrieval and its applications have been attractive research topics in optics and photonics, for example, in biomedical imaging, astronomical imaging, and so on. Most conventional phase retrieval methods have used iterative processes to recover phase information; however, the calculation speed and convergence

This study measured the polarised light reflected from the surface of thermally modified Scots pine (Pinus sylvestris L.) wood using a Stokes imaging polarimeter. The data were analysed using the Mueller matrix method. The Scots pine boards were heat treated in an oven at temperatures of 160 ºC, 200 ºC and 220 ºC, with a heat treatment time of 3 h at the maximum temperature. The results indicated that

The non-contact method is used to detect the physical stress of the human body, thereby providing a good model for practical application. However, the existing method is highly inaccurate and requires people’s background information. This study introduces a new method to detect the physical stress of the human body by maximizing thermal infrared imaging. First, the method of multi-object correlation

A precise and efficient edge-controlled method is of importance to ensure the final performance of the optical system. The authors put forward a novel method to reduce the edge effect in the magnetorheological finishing (MRF) process through further analyzing the stability of the MRF edge tool influence function (TIF) and correcting the post-edge algorithm of dwell time. To demonstrate the feasibility

The stabilization of the laser oscillation frequency of a dual-mode microchip laser was demonstrated by stabilizing the beat frequency generated by the two simultaneously oscillating longitudinal modes. In the experiment, a beat frequency of 101 GHz was stabilized to ± 50 kHz using negative feedback control. As a result, the fluctuation of the laser oscillation frequency was finally stabilized to ± 50 MHz

There are color vision barrier-free conversion algorithms that are used to improve the contrast in images for dichromats. The algorithms focus on whether dichromats can distinguish a combination of colors and often use a simulation model of color appearance for dichromats. To adjust the algorithms for individual dichromats, it is necessary to investigate whether the simulation model used is suitable

Owing to high accuracy in the whole measurement range, the compensator-rotating method is a powerful technique for transmission/reflection ellipsometric measurements. The compensator-rotating imaging ellipsometer, which is a system combing the optical microscope and single measurement point ellipsometer, faces non-ideal measurement conditions involving nonuniformity of the retardation across the compensator

Photonic approach to generating linearly chirped waveforms with large time–bandwidth product (TBWP) is proposed and demonstrated. In the approach, a dual-output dual-parallel Mach–Zehnder modulator (DPMZM) is employed to generate dual-tone wavelengths in the two output ports. The polarization modulator (PolM) is employed to conduct complementary phase modulation of the dual-tone wavelengths. After

As an optical molecular imaging modality, fluorescence molecular tomography (FMT) can monitor the activities of organisms in vivo at the molecular and cellular levels. However, the recovered image quality is affected by mesh voxel when the finite element method is utilized to recover the fluorescence probe. The target localization is likely to deviate from the actual target under the coarse mesh, but

The finite-difference time-domain (FDTD) method, which is often used to solve Maxwell’s equations, has been proposed to solve the optical diffusion equations to simulate light propagation in turbid media such as biological tissue. Finite-difference methods can be numerically unstable and calculation can diverge unless a stability condition is satisfied. Until now, the stability condition for FDTD of

A novel micro-vibration reconstruction method based on inverse Hilbert transform is presented. By inversing either side of the SMI signal after Hilbert transform, micro-vibration can be reconstructed quickly and conveniently. In the paper, the principle of inverse Hilbert transform algorithm is studied. And, the effectiveness of the method is verified through simulated signals, and several experiments

The average bit error rate (BER) and outage probability of circle polarization shift keying (CPOLSK) modulation in free-space optical (FSO) system operating under exponentiated Weibull (EW) distribution are studied. The closed expression of the average BER is derived by generalized Gauss–Laguerre polynomials. The analytical results show the relationship between the average BER and average signal to

In this paper, we proposed a useful calculation method to perform the perception-based selection of lighting position that emphasizes the material appearance of CG object. The proposed method is based on the conventional viewpoint entropy which is used to find an appropriate viewing angle. To find an appropriate shot for material appearance, we first identified the important surface that has information