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    47196 results match your criteria Applied optics[Journal]

    1 OF 944

    Distribution of splice loss in single mode optical fiber.
    Appl Opt 2018 Feb;57(5):1140-1150
    This work investigates a probabilistic model for splice loss in single mode optical fibers. We derive the probability density function for loss values as a function of lateral and angular misalignment. We then use observed data to estimate these model parameters; both Bayesian and maximum likelihood estimation procedures are described. Read More

    Temperature-insensitive sum frequency generation of 355-nm ultraviolet laser radiation in LiBOby compensating thermally induced phase mismatch.
    Appl Opt 2018 Feb;57(5):1134-1139
    A temperature-insensitive sum frequency generation method based on thermally induced phase mismatch compensation is proposed to enhance the thermal stability and scale up the output power of ultraviolet (UV) lasers. In the method, three LiBOcrystals are cascaded for sum frequency generation of a 355-nm UV laser, and the two crystals at the ends are employed for frequency conversion; the middle one, which is not required to be phase matched and has an opposite sign of first temperature derivative of phase mismatch, compensates the thermally induced phase mismatch generated in the first crystal. The temperature acceptance bandwidth of frequency conversion in the three cascaded crystals is about double that in a single long crystal with the same interaction length. Read More

    Wavefront reconstruction of a non-coaxial diffraction model in a lens system.
    Appl Opt 2018 Feb;57(5):1127-1133
    To reconstruct a wavefront in a non-coaxial lens system, we propose a diffraction model using the Fresnel integral. Inclination angle is the newly included parameter in the mathematical formula describing beam propagation. It is determined through two ways in this paper, which are correlation operation and optical flow method. Read More

    Highly amplified light transmission in a parity-time symmetric multilayered structure.
    Appl Opt 2018 Feb;57(5):1119-1126
    We propose a parity-time symmetric dielectric-nano-film-dielectric multilayered structure that could facilitate highly amplified transmission of optical power in the infrared spectrum. We have theoretically studied our model using the transfer-matrix formalism. The reflection and the transmission coefficients of the S-matrix are evaluated. Read More

    Radiometric model for coaxial single- and multimode optical emission from double-clad fiber.
    Appl Opt 2018 Feb;57(5):1110-1118
    Double-clad fibers (DCFs) are versatile waveguides supporting a single-mode core surrounded by a multimode inner cladding. DCFs are increasingly used for multimodal biomedical applications, such as imaging or therapy, for which the core is typically used for coherent illumination and the inner cladding, to support a concurrent modality. Proper optimization is, however, critical to ensure high optical performance and requires accurate modeling of coaxial single- and multimode output beams. Read More

    Weighted spline based integration for reconstruction of freeform wavefront.
    Appl Opt 2018 Feb;57(5):1100-1109
    In the present work, a spline-based integration technique for the reconstruction of a freeform wavefront from the slope data has been implemented. The slope data of a freeform surface contain noise due to their machining process and that introduces reconstruction error. We have proposed a weighted cubic spline based least square integration method (WCSLI) for the faithful reconstruction of a wavefront from noisy slope data. Read More

    Adjustable-focus ultracompact endoscopic lens design with ultrahigh optical performance.
    Appl Opt 2018 Feb;57(5):1091-1099
    An internally focusing design is developed for a compact endoscopic lens to have optical performance close to the diffraction limit. When changing the working distance from infinity to a predetermined short distance, the overall system length and the field of view remain constant. It is numerically demonstrated that the diffraction-limit-like performance is maintained over a wide range of working distances, showing a novel capability of adjustable focuses. Read More

    Effect of angle-of-arrival fluctuation on heterodyne detection in slant atmospheric turbulence.
    Appl Opt 2018 Feb;57(5):1083-1090
    A mathematical model of the effect of random pointing errors on the mixing efficiency of heterodyne detection is established, and the effect of angle-of-arrival fluctuation on the mixing efficiency of heterodyne detection is investigated. The results show that the average mixing efficiency is significantly affected by the angle-of-arrival fluctuation in the outer scale. The larger the obscuration ratio and receiving aperture of the optical system, the lower the average mixing efficiency is. Read More

    Temporal coherence study of four-wave mixing products with and without the laser cavity effect.
    Appl Opt 2018 Feb;57(5):1075-1082
    In this work, we have studied the temporal coherence property of a four-wave mixing (FWM)-assisted continuous-wave erbium-doped fiber ring laser source. To understand the temporal coherence characteristics of FWM, we have analyzed the visibility of their interference pattern with the help of a Mach-Zehnder-based fiber interferometer. The visibility of FWM sidebands is compared with respect to the input pumps, with and without the cavity effect. Read More

    Optimized star sensors laboratory calibration method using a regularization neural network.
    Appl Opt 2018 Feb;57(5):1067-1074
    High-precision ground calibration is essential to ensure the performance of star sensors. However, the complex distortion and multi-error coupling have brought great difficulties to traditional calibration methods, especially for large field of view (FOV) star sensors. Although increasing the complexity of models is an effective way to improve the calibration accuracy, it significantly increases the demand for calibration data. Read More

    Compact optical fiber temperature sensor with high sensitivity based on liquid-filled silica capillary tube.
    Appl Opt 2018 Feb;57(5):1061-1066
    We propose a highly sensitive fiber temperature sensor based on a section of liquid-sealed silica capillary tube inserted in a single-multi-single-mode fiber structure. The liquid polymer is filled into the silica capillary tube through two micro-holes drilled by a femtosecond laser. Then the micro-holes are blocked by UV curable adhesive with ultra-small volume. Read More

    Orbital angular momentum channel monitoring of coaxially multiplexed vortices by diffraction pattern analysis.
    Appl Opt 2018 Feb;57(5):1056-1060
    We theoretically and experimentally demonstrate a scheme to monitor the weight of a single orbital angular momentum (OAM) channel for coaxial multiplexed optical vortices with large mode spacing. A specially designed holographic grating is illuminated by the incident multiplexed vortices first. Then the weight of each single OAM channel is obtained after analyzing the captured diffraction patterns. Read More

    Study on the inversion of doped concentration induced by millisecond pulsed laser irradiation silicon-based avalanche photodiode.
    Appl Opt 2018 Feb;57(5):1051-1055
    In this paper, an experimental study of silicon-based avalanche photodiode (Si-APD) with millisecond pulse laser irradiation was carried out, and the C-V curve of Si-APD was obtained by using a semiconductor analyzer. Based on the single-side abrupt junction character of n+p, combined with the corresponding theoretical derivation, the doping concentration varying with the axial depth of damaged Si-APD was obtained by inverse computation. The lattice dislocation and junction reduction were the fundamental causes of the reduced doping concentration. Read More

    Principal frequency component analysis based on modulate chopper technique used in diffuse reflectance spectroscopy measurement.
    Appl Opt 2018 Feb;57(5):1043-1049
    Diffuse reflectance spectroscopy (DRS) is significantly affected from the interference of the ambient light and dark current of the instrument. Optical choppers, together with lock-in/synchronous amplification, can overcome these interferences. However, in spectral measurement, the sampling rate of the spectrometer is different from the Δ-pulse sampling, which is not high enough because of the integration time. Read More

    Focus detection by shearing interference of vortex beams for non-imaging systems.
    Appl Opt 2018 Feb;57(5):1037-1042
    In focus detection of non-imaging systems, the common image-based methods are not available. Also, interference techniques are seldom used because only the degree with hardly any direction of defocus can be derived from the fringe spacing. In this paper, we propose a vortex-beam-based shearing interference system to do focus detection for a focused laser direct-writing system, where a vortex beam is already involved. Read More

    Microlens array expander with an improved light intensity distribution throughperiodic submicro-scale filling for near-eye displays.
    Appl Opt 2018 Feb;57(5):1026-1036
    A type of microlens array (MLA) expander with an improved light intensity distribution (LID) is designed and fabricated through submicro-scale filling, which could be applied to near-eye displays. Through the reflection of a 0.8-μm-wide metal filling, the light field is split and superimposed only through the microlens. Read More

    Accurate estimation of the illumination pattern's orientation and wavelength in sinusoidal structured illumination microscopy.
    Appl Opt 2018 Feb;57(5):1019-1025
    Structured illumination microscopy is able to improve the spatial resolution of wide-field fluorescence imaging by applying sinusoidal stripe pattern illumination to the sample. The corresponding computational image reconstruction requires precise knowledge of the pattern's parameters, which are its phase (ϕ) and wave vector (p). Here, a computationally inexpensive method for estimation of p from the raw data is proposed and illustrated with simulations. Read More

    Calibration of the degree of linear polarization measurements of the polarized Sun-sky radiometer based on the POLBOX system.
    Appl Opt 2018 Feb;57(5):1011-1018
    Polarization observation of sky radiation is the frontier approach to improve the remote sensing of atmospheric components, e.g., aerosol and clouds. Read More

    Light-absorbing aerosol properties retrieved from the sunphotometer observation over the Yangtze River Delta, China.
    Appl Opt 2018 Feb;57(5):992-1004
    In this study, aerosol optical depth (AOD) and extinction Ångström exponent (EAE) are derived from ground-based sunphotometer observations between 2007 and 2014 at urban sites of Nanjing over the Yangtze River Delta. In addition, the present study aims to investigate aerosol light-absorbing properties such as single-scattering albedo (SSA), absorption Ångström exponent (AAE), and the aerosol-absorbing optical depth (AAOD). The retrieval of aerosol properties is compared with AERONET inversion products. Read More

    Design and analysis of a triple reflection grazing incidence x-ray telescope.
    Appl Opt 2018 Feb;57(5):983-991
    A triple reflection grazing incidence x-ray telescope is proposed and evaluated. This form of an optical system can detect x-ray energy that is close to the optical axis, which solves the problems encountered by traditional Wolter-type systems. In this paper, we also propose a new design method to ensure that the entire telescope structure is compact and integrated. Read More

    Q-plates with a nonlinear azimuthal distribution of the principal axis: application to encoding binary data.
    Appl Opt 2018 Feb;57(5):1005-1010
    We encode q-plates where the angular orientation of the principal axis is varied spatially with a nonstandard distribution. In the usual q-plate design, the orientation of the optical axis depends linearly on the azimuthal angle. In this work, we examine cases where this azimuthal dependence is nonlinear. Read More

    Visible Infrared Imaging Radiometer Suite reflective solar bands on-orbit calibration using solar diffuser illuminated by scattered light through the nadir port.
    Appl Opt 2018 Feb;57(5):1273-1283
    A new variant to the standard on-orbit calibration of the reflective solar bands (RSBs) using a solar diffuser (SD) is formulated. Instead of direct solar exposure through the SD port in the front of the instrument as originally designed, the variant method uses light reflecting off Earth's surface coming through the nadir port as the light source to illuminate the built-in onboard SD. The methodology is applied to the Visible Infrared Imaging Radiometer Suite on board the Suomi National Polar-orbiting Partnership satellite, and is shown to be viable and useful. Read More

    Quantitative detection of oxygen in reduced graphene oxide by femtosecond laser-induced breakdown spectroscopy.
    Appl Opt 2018 Feb;57(5):1267-1272
    This paper proposes a simple, direct, and fast method for the quantitative detection of oxygen in reduced graphene oxide (r-GO) by femtosecond laser-induced breakdown spectroscopy (fs-LIBS). First, GO was reduced by continuous-wave (CW) laser beams with different powers; subsequently, the oxygen content in the r-GO was detected through the intensity of oxygen obtained by fs-LIBS. The fit of the observed data and errors by LIBS was compared with the results of x-ray photoelectron spectroscopy (XPS), and the fs-LIBS results correlate well with the XPS results; it indicated that fs-LIBS can realize quantitative analysis of the GO-reduction degree. Read More

    Temperature-dependent optical constants of highly transparent solids determined by the combined double optical pathlength transmission-ellipsometry method.
    Appl Opt 2018 Feb;57(5):1260-1266
    The optical constants of five highly transparent substrates (polycrystalline BaF, CaF, MgF, ZnSe, and ZnS) were experimentally determined based on a combined technique using both the double optical pathlength transmission method and the ellipsometry method within temperature range 20°C-350°C in the ultraviolet-infrared region (0.2-20 μm). The results show that the refractive index spectra of polycrystalline BaF, CaF, and MgFare similar, but differ from that of polycrystalline ZnSe and ZnS. Read More

    Calculation model of the scattering polarization coherency matrix for a detection system of oil spills at sea.
    Appl Opt 2018 Feb;57(5):1254-1259
    As a new analytical method to identify oil spills at sea, the main effect of a polarization measurement system is the scattering polarization information of different measured parts. To improve measurement accuracy, the scattering polarization characteristics of oil film and seawater were observed in this paper. A useful computational model, the scattering polarization coherency matrix (SPCM), was derived, which is a probabilistic mixture of the polarization coherency matrix. Read More

    Compact optical multipass matrix system design based on slicer mirrors.
    Appl Opt 2018 Feb;57(5):1174-1181
    High path-to-volume ratio (PVR) and low-aberration-output beams are the two main criteria to assess the performance of multipass absorption cells. However, no substantial progress has been reported for large-numerical-aperture-coupled multipass cells, which is due to the accumulated aberrations caused by a large number of off-axis reflections. Based on Chernin's design, in this study, we modified Chernin's four-objective multipass matrix cell by using slicer mirrors to eliminate alignment difficulty and decrease the system volume. Read More

    Comb-referenced frequency-sweeping interferometry for precisely measuring large stepped structures.
    Appl Opt 2018 Feb;57(5):1247-1253
    A precise 3D surface measurement method for large stepped structures without height ambiguity is proposed based on optical-frequency-comb-referenced frequency-sweeping interferometry and Fourier-transformed fractional phase retrieval. Unlike other interferometry that depends on the absolute phase value for several certain wavelengths, this method obtains results from the phase change during frequency sweeping and thus remains free from the confined non-ambiguity range. By reference to an optical frequency comb, the relative uncertainty from the tunable laser frequency was reduced by three orders of magnitude, and the sweeping frequency range can be precisely determined. Read More

    Real-time identification of the singleness of a trapped bead in optical tweezers.
    Appl Opt 2018 Feb;57(5):1241-1246
    Beads trapped in optical tweezers are aligned along the optical propagation direction, which makes it difficult to determine the number of beads with bright-field microscopy. This problem also dramatically influences the measurement of the optical trapping based single-molecule force spectroscopy. Here, we propose a video processing approach to count the number of trapped micro-objects in real time. Read More

    Nondestructive evaluation of demineralized enamel in a human incisor and molar using laser ultrasonics.
    Appl Opt 2018 Feb;57(5):1231-1240
    This study aims to evaluate early caries in human teeth with different geometry structures by using the dispersion curves of a surface acoustic wave (SAW) generated by a pulsed laser. Through the finite element method, SAWs propagating on teeth models with different enamel thickness and curvature radius were simulated, and the influence of the geometry difference on the dispersion curves of SAWs was discussed. Laser ultrasonic experiments were performed on an extracted human incisor and molar with different demineralization conditions. Read More

    Diverse mode of operation of an all-normal-dispersion mode-locked fiber laser employing two nonlinear loop mirrors.
    Appl Opt 2018 Feb;57(5):1225-1230
    In this paper, we propose an all-normal-dispersion ytterbium-fiber laser with a novel ring cavity architecture having two nonlinear amplifying loop mirrors (NALM) as saturable absorbers, capable of delivering distinctly different pulses with adjustable features. By optimizing the loop lengths of the individual NALMs, the cavity can be operated to deliver Q-switched mode-locked (Q-ML) pulse bunches with adjustable repetition rates, mode-locked pulses in dissipative soliton resonance (DSR) regime or noise-like pulse (NLP) regime with tunable pulse width. The DSR pulses exhibit characteristic narrowband spectrum, while the NLPs exhibit large broadband spectrum. Read More

    Freeform lens design to eliminate retroreflection for optical systems.
    Appl Opt 2018 Feb;57(5):1218-1224
    This paper presents an effective approach to alleviate the cat-eye effect by inserting a freeform single lens into the original optical system. By shifting the image of the given optical system transversely on the original image plane, the reflected beams originating from the sensor are subsequently blocked by the optical aperture, substantially eliminating retroreflections from the system. The influence of incident angle on retroreflected beams is analyzed in detail, and the optimal image translation distance for completely eliminating the cat-eye effect is also proposed via numerical simulations. Read More

    Design of an optical trap for storing femtosecond laser pulses.
    Appl Opt 2018 Feb;57(5):1212-1217
    An optical trap for storing femtosecond laser pulses to enhance the interaction effectiveness with optically thin targets is being proposed and investigated. Presently, we studied the trapping of 10-200 fs laser pulses of wavelength 800 nm, 1 μJ energy per pulse, and 10 Hz repetition rate. To compensate the optical losses in the trap, a Ti: Sapphire crystal as an amplifying medium is being considered, which should be synchronously pumped by the second harmonic of the Nd: YAG laser. Read More

    Cost-effective plane-grating monochromator design for extreme-ultraviolet application.
    Appl Opt 2018 Feb;57(5):1202-1211
    The optical design of a plane-grating monochromator mainly intended for high resolution in the extreme ultraviolet and soft x-ray is presented. The configuration has three optical elements. It uses a uniform line-spaced plane grating illuminated in the converging light coming from a focusing concave mirror and an additional plane mirror that is needed to change the grating subtended angle to keep the system in focus on a fixed slit. Read More

    Scattering characteristics of a cylindrical reflector covered with a general bi-isotropic layer.
    Appl Opt 2018 Feb;57(5):1188-1195
    The scattering characteristics of an electric line source radiating in the presence of a bi-isotropic coated circular cylindrical reflector have been investigated using numerical calculations. The analytic expressions of the electric and magnetic fields in the bi-isotropic coating and the background medium have been found using the wave-field decomposition approach. It is studied that a bi-isotropic coating enhances the gain in the forward direction as compared to chiral, Tellegen, and dielectric coatings. Read More

    Tunable spectral and spatial filters for the mid-infrared based on hyperbolic metamaterials.
    Appl Opt 2018 Feb;57(5):1182-1187
    In this paper we present the possibility of shaping the reflectivity characteristics of tunable hyperbolic metamaterials (THMMs). Using the example of voltage-sensitive graphene-based structures, we demonstrate the existence of spectral and spatial functionalities of edge and narrowband filters, controlled dynamically over a 3-5 μm spectral range, that are important for both civilian and military applications. We also demonstrate that the adoption of apodization techniques in the THMM design leads to a reduction in the sidelobe's parasitic effect in edge filters, as well as providing the means to reshape the overall reflectivity characteristics, which not only unveiled the tunable angle aperture functionality but also significantly increased the potential for tailoring optical properties of THMM nanostructures in general. Read More

    Five-step phase-shifting white-light interferometry for the measurement of fiber optic extrinsic Fabry-Perot interferometers.
    Appl Opt 2018 Feb;57(5):1168-1173
    Five-step phase-shifting white-light interferometry is presented for interrogating the absolute cavity length of the fiber optic extrinsic Fabry-Perot interferometer (EFPI). It combines ideas of phase-shifting interferometry and white-light interferometry (WLI) to extend the measurement range of fiber optic WLI. Five sub-interferograms intercepted from the white-light optical spectrum are used to recover the optical path difference (OPD) of the EFPI. Read More

    Symmetric decomposition of experimental depolarizing Mueller matrices in the degenerate case.
    Appl Opt 2018 Feb;57(5):1159-1167
    We propose a detailed procedure to determine the two retardance matrix factors entering the symmetric decomposition of Mueller matrices when the depolarizer matrix is partially degenerate (i.e., two out of three of its depolarization coefficients are equal), which is a common occurrence. Read More

    "Achromatic limits" of Pancharatnam phase lenses.
    Appl Opt 2018 Feb;57(5):1151-1158
    Lenses based on the Pancharatnam phase have the advantage of being thin and inexpensive. Unfortunately, their optical effect is strongly wavelength dependent, and their applications generally are limited by the requirement of a monochromatic source. However, low-power lenses based on the Pancharatnam phase can be considered for applications over the visible range. Read More

    High-performance color sequence particle streak velocimetry for 3D airflow measurement.
    Appl Opt 2018 Feb;57(6):1518-1523
    In this paper, a high-performance color sequence particle streak velocimetry (CSPSV) technique is proposed to measure the air velocity in a large three-dimensional (3D) space. Based on the basic principle of CSPSV, a new color sequence illumination pattern is designed to mark seeding bubbles for better imaging performance. Synchronized with the illumination system, cameras record the targets' paths at the start, middle, and end points with different color information more clearly. Read More

    Design of a gradient-index lens with a compound parabolic concentrator shape as a visible light communication receiving antenna.
    Appl Opt 2018 Feb;57(6):1510-1517
    We propose a design for a gradient lens that can extend the field of view and receive higher optical power for indoor visible light communication systems. The proposed structure is an axially symmetric lens with a refractive index gradient distribution in the axial direction and a slight gradient in the radial direction, and with a spherical top surface and side surface in a compound parabolic concentrator (CPC) shape. The radius of the outlet of the CPC is 3 mm, and the inlet radius is 6. Read More

    Spatially incoherent common-path off-axis color digital holography.
    Appl Opt 2018 Feb;57(6):1504-1509
    We describe a new method for recording spatially incoherent common-path off-axis color digital holograms. We present the theoretical and experimental evidence to demonstrate an incoherent common-path off-axis color digital holographic (ICOCH) system capable of capturing information from three-dimensional color objects under incoherent illumination, both in transmission and reflection modes. Fresnel incoherent correlation holography (FINCH), a common-path system, is a frequently used incoherent holography technique. Read More

    All-fiber polarization-maintaining erbium-doped dispersion-managed fiber laser based on a nonlinear amplifying loop mirror.
    Appl Opt 2018 Feb;57(6):1492-1496
    In this paper, we build a mode-locked all-polarization-maintaining figure-of-8 erbium-doped fiber oscillator based on a nonlinear amplifying loop mirror. The fiber oscillator can generate 1.6 ps chirped pulses that can be de-chirped to 500 fs at 1550 nm with a pulse energy of 0. Read More

    Improvement of Scheimpflug systems with freeform surfaces.
    Appl Opt 2018 Feb;57(6):1482-1491
    It is well known that freeform surfaces are used to improve the resolution in systems without rotational symmetry. For Scheimpflug systems, the tilted object plane leads to variant magnification in the system imaging. Thus, the system suffers from non-rotationally symmetric aberrations, non-uniform resolution, and non-uniform intensity distribution. Read More

    Air wedge with variable refractive index for precise laser beam steering in a small range.
    Appl Opt 2018 Feb;57(6):1417-1423
    This paper provides the results of work on a new method for metrological laser beam steering for the purpose of angular stabilization. Frequency stabilized metrological lasers are used for interference measurements of length and angle. Angular deviation of the beam may cause cosine errors when measuring displacements. Read More

    Desensitization design method of unobscured three-mirror anastigmatic optical systems with an adjustment-optimization-evaluation process.
    Appl Opt 2018 Feb;57(6):1472-1481
    An off-axis three-mirror anastigmatic optical system with the offset apertures configuration as a typical unobscured optical system is frequently used in various optical instruments. The practical applications show that this type of system has a higher sensitivity in alignment. To reduce the alignment sensitivity of the unobscured optical systems, a desensitization design method with an adjustment-optimization-evaluation process is proposed. Read More

    Highly thermal-stable heterodyne interferometer with minimized periodic nonlinearity.
    Appl Opt 2018 Feb;57(6):1463-1467
    Heterodyne interferometers suffer from thermal drift of optics (TDO), which may introduce error even up to several micrometers. In this paper, we propose a symmetric heterodyne interferometer with spatially separated beams, which realizes completely balanced optical paths between probe and reference beams and simultaneously avoids the optical mixing, and thereby is theoretically capable of eliminating TDO and the periodic nonlinearity (PNL). To validate the performance of the proposed interferometer, first a special experimental setup is constructed, with which the TDO test can be conducted in vacuum, and the result shows that a thermal coefficient of 1. Read More

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