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Applied Optics

Hira Farooq, Sueli Skinner-Ramos, Hawra Algasham, Ayrton A Bernussi, Luis Grave de Peralta
Scanning the direction of the light that is diffracted by a sample permits the achievement of image diversity, which is necessary for implementing the Fourier ptychographic microscopy technique (FPM) using only perpendicular illumination. We also demonstrated that the same method allows for implementation of the illumination-direction-multiplexing FPM technique when the sample is illuminated using a ring-shaped condenser.
September 1, 2018: Applied Optics
Xingxing Liu, Yun Mou, Hao Wang, Renli Liang, Xinzhong Wang, Yang Peng, Mingxiang Chen
Deep ultraviolet light-emitting diodes (DUV-LEDs) have become a promising UV light source for sterilization, disinfection, and purification. However, the challenge in practical application of DUV-LEDs still remains in their low light efficiency. In this paper, we propose an optimized aluminum (Al) reflector for the light extraction enhancement of DUV-LEDs. The optical model of DUV-LEDs was established, and the optical simulations were performed to achieve the optimized reflector. The DUV-LEDs exhibit the highest light efficiency when the reflector has the optimized feature sizes with an angle of 60°, a height of 2...
September 1, 2018: Applied Optics
Akito Shimomura, Takashi Fukuda, Akira Emoto
As a potential means of measuring birefringence distribution, we analyzed the interference fringes based on three circularly polarized beams: a right-handed signal beam, a left-handed reference beam, and a right-handed reference beam. All beams were crossed at the same angle on the interfering plane, creating a two-dimensional interference fringe with three grating vectors. We proposed that by analyzing the interference fringes, we can measure the anisotropic phase shift in the signal beam. The obtained features of the anisotropic phase shift can be extended to the measurement of two-dimensional birefringence distributions without rotational manipulations of the objectives or polarizers...
September 1, 2018: Applied Optics
Kazuo Hasegawa, Satoru Kato, Tomoya Okazaki, Hiroshi Murotani, Kazuya Saito
We present herein a method to fabricate a higher-order fiber grating (HOFG) for use as a fiber-cavity mirror in a fiber laser. The HOFG was fabricated by irradiating the Yb-doped large core of a double-clad fiber by a femtosecond pulsed laser. The HOFG served as a laser cavity mirror with a reflectance of 13.2% and yielded a laser line with a spectral full width at half-maximum of 0.56 nm.
September 1, 2018: Applied Optics
Elias N Glytsis, Aristeides D Papadopoulos, Theodoros T Koutserimpas
Several known and widely used averaging techniques aiming to improve the accuracy of the two-dimensional finite-difference frequency-domain (FDFD) method, in the presence of material discontinuities, are reviewed, numerically tested, and compared with respect to their accuracies. Furthermore, all averaging techniques are rigorously and efficiently implemented using the Supercover Digital Differential Analyzer algorithm and a modified Liang-Barsky algorithm suitably adapted from computer graphics applications...
September 1, 2018: Applied Optics
Jinfeng Qiu, Mujun Li, Huichun Ye, Chen Yang, Cuicui Shi
We demonstrate a simple, controllable, and stable method for fabricating high fill factor cylindrical microlens array with a novel isolated thermal reflow process. In this method, microstripes with a very small gap were obtained via digital micromirror device-based lithography, then covered with polydimethylsiloxane (PDMS) solution. The prepared microstripes were isolated and were heated and reflowed to a cylindrical microlens array. During the reflow process, the semicross-linked PDMS can serve as a barrier to prevent the diameter change and the bonding of adjacent microlenses...
September 1, 2018: Applied Optics
Yan Yang, Feng Shao, Zhenqi Fu, Randi Fu
Automated retinal blood vessel segmentation is important for the early computer-aided diagnosis of some ophthalmological diseases and cardiovascular disorders. Traditional supervised vessel segmentation methods are usually based on pixel classification, which categorizes all pixels into vessel and non-vessel pixels. In this paper, we propose a new retinal vessel segmentation method with the motivation to extract vessels based on vessel block segmentation via cross-modality dictionary learning. For this, we first enhance the structural information of vessels using multi-scale filtering...
September 1, 2018: Applied Optics
Roberto Casini, Dennis Gallagher, Anthony Cordova, Matthew Morgan
We measured the efficiency of a reflective echelle grating that was specially coated in order to reduce the polarization of the diffracted light. The standard coated grating can be used between approximately 350 and 1200 nm for diffraction orders between 14 and 5. In these orders, the standard grating can be strongly polarized (up to ∼80%), which impacts its usability in spectro-polarimetric instruments. The adoption of the shadow-cast coating technique, which implies selectively depositing the reflective coating exclusively onto the blazed facets, can significantly reduce the polarization of the grating while preserving its average efficiency...
September 1, 2018: Applied Optics
C Dorrer, A Kalb, P Fiala, S-W Bahk, A Sharma, K Gibney
Quantitative wavefront measurements are demonstrated using a Hartmann mask re-imaged onto a camera. The wavefront is reconstructed using standard algorithms applied to the difference of beamlet centroids determined from fluence distributions obtained for two different longitudinal locations of the mask. The wavefront of the optical wave in the object plane is measured independently of imaging-system collimation. Apodization obtained with spatially dithered distributions of small transparent or opaque pixels improves the measurement accuracy by reducing the spatial-frequency content of the mask holes...
September 1, 2018: Applied Optics
Tianjiao Li, Chuanxin Zhang, Yuan Yuan, Yong Shuai, Heping Tan
We propose a novel flame temperature estimation method based on a flame light field sectioned imaging model of complex temperature distribution in different media. The proposed method relies on multi-pixel reconstruction to improve the resolution of sub-aperture images. In addition, the wavelet transform denoises the flame refocused image, and then the Lucy-Richardson algorithm deconvolves the image. The temperature estimation accuracy using the proposed method is higher than that reported in a previous work, with a larger temperature estimation range from 1250 K to 1800 K...
September 1, 2018: Applied Optics
Junbao Hu, Yan Kong, Zhilong Jiang, Liang Xue, Fei Liu, Cheng Liu, Shouyu Wang
Via the transport of intensity phase microscopy, quantitative phase can be retrieved directly from captured multi-focal intensities. The accuracy of the retrieved phases depends highly on the quality of the recorded images; therefore, the exposure time should be carefully chosen for high-quality intensity captures. However, it is difficult to record well-exposure intensities to maintain rather a high signal to noise ratio and to avoid over-exposure due to the complex samples. In order to simplify the exposure determination, here the adaptive dual-exposure fusion-based transport of intensity phase microscopy is proposed: with captured short- and long-exposure images, the well-exposure multi-focal images can be numerically reconstructed, and then high-accurate phase can be computed from these reconstructed intensities...
September 1, 2018: Applied Optics
Fu-Li Wang, Yue-De Yang, Yong-Zhen Huang, Zhi-Xiong Xiao, Jin-Long Xiao
AlGaInAs/InP waveguide-coupled deformed hexagonal resonator microlasers with enhanced mode quality (Q)-factors are demonstrated for realizing single-transverse-mode operation. A circular hole is introduced to the center of the hexagonal resonators with rounded corners to enhance the mode Q-factors and suppress high-order transverse modes simultaneously. Single-mode lasing with side-mode suppression ratios up to 40 dB is obtained for the 10-μm-sidelength hexagonal microlasers with a center hole. All the lasing spectra demonstrate pure single-transverse-mode properties within the whole tuning range of injection current, and mode hopping with one, two, and three longitudinal-mode intervals is observed due to the mode Q-factor modification by the center holes...
September 1, 2018: Applied Optics
Simone Donadello, Ali Gökhan Demir, Barbara Previtali
In this work, self-mixing interferometry (SMI) is implemented inline to a laser microdrilling system to monitor the machining process by probing the ablation-induced plume. An analytical model based on the Sedov-Taylor blast wave equation is developed for the expansion of the process plume under multiple-pulse laser percussion drilling conditions. Signals were acquired during laser microdrilling of blind holes on stainless steel, copper alloy, pure titanium, and titanium nitride ceramic coating. The maximum optical path difference was measured from the signals to estimate the refractive index changes...
September 1, 2018: Applied Optics
Islam Samir El-Sayed, Yasser M Sabry, Walid ElSayd ElZeiny, Niveen Badra, Diaa A Khalil
The Fourier transform spectrometer based on cascaded Fabry-Perot interferometers is analyzed, where one of the interferometers has a fixed length, while the other is scanning. We propose a method to reconstruct the spectrum correctly based on solving the integral equation of the overall response of the cascaded interferometers. The method is tested for different design parameters and noise conditions. Low reconstruction error below -80  dB is found to be achievable.
September 1, 2018: Applied Optics
Warlley H Campos, Jakson M Fonseca, Joaquim B S Mendes, Márcio S Rocha, Winder A Moura-Melo
Reflection and refraction of light can be used to trap small dielectric particles in the geometrical optics regime. Absorption of light is usually neglected in theoretical calculations, but it is known that it occurs in the optical trapping of semi-transparent particles. Here, we propose a generalization of Ashkin's model for the radiative force exerted on a spherical bead, including the contribution due to attenuation/absorption of light in the bulk of the particle. We discuss in detail the balance between refraction, reflection, and absorption for different optical parameters and particle sizes...
September 1, 2018: Applied Optics
Zhimin Rao, Tingyao He, Dengxin Hua, Yunlong Wang, Xusheng Wang, Yingying Chen, Jing Le
A laser-induced fluorescence lidar has been developed for detecting the concentration of fluorescent aerosols in the air. The fluorescence lidar was constructed with a pulsed fourth-harmonic Nd:YAG laser at the ultraviolet wavelength of 266 nm with a repetition rate of 10 Hz. A 250 mm diameter custom telescope was used to collect optical spectra ranging from 260 to 560 nm. Fluorescence signals with wavelengths ranging from 310-440 nm were extracted, exploring a filter with a bandwidth of 130 nm. The preliminary experiments were conducted at the campus of Xi'an University of Technology, in which the fluorescence signals of atmospheric fluorescent aerosols were continuously collected from 20:00 to 23:00 CST on 13 December 2017...
September 1, 2018: Applied Optics
F Guillou-Camargo, V Ménoret, E Cantin, O Lopez, N Quintin, E Camisard, V Salmon, J-M Le Merdy, G Santarelli, A Amy-Klein, P-E Pottie, B Desruelle, C Chardonnet
We report on a fully bidirectional 680 km fiber link connecting two cities for which the equipment, the setup, and the characterization are managed for the first time by an industrial consortium. The link uses an active telecommunication fiber network with parallel data traffic and is equipped with three repeater laser stations and four remote double bidirectional erbium-doped fiber amplifiers. We report a short-term stability at 1 s integration time of 5.4×10-16 in 0.5 Hz bandwidth and a long-term stability of 1...
September 1, 2018: Applied Optics
Nurmemet Abdukerim, M Imrul Kayes, Alexandre Rekik, Martin Rochette
We report a bidirectional mode-locked thulium-doped fiber laser. Mode-locking is enabled by the combination of semiconductor saturable absorption and nonlinear polarization rotation. Two stable mode-locked picosecond pulse trains in opposite directions are generated with a fundamental repetition rate of ∼16.57  MHz. Output wavelengths are tunable over 35 nm.
September 1, 2018: Applied Optics
Tatiana Latychevskaia
In this work, issues in phase retrieval in the coherent diffractive imaging (CDI) technique, from discussion on parameters for setting up a CDI experiment to evaluation of the goodness of the final reconstruction, are discussed. The distribution of objects under study by CDI often cannot be cross-validated by another imaging technique. It is therefore important to make sure that the developed CDI procedure delivers an artifact-free object reconstruction. Critical issues that can lead to artifacts are presented and recipes on how to avoid them are provided...
September 1, 2018: Applied Optics
Chenchun Shi, Yunfeng Peng, Liang Hou, Zhenzhong Wang, Yinbiao Guo
Bonnet polishing technology has been widely applied in precision optical machining. Until now, most of the research concerning the modeling for material removal mechanisms of bonnet polishing have been presented based on the well-known Preston model. However, the various parameters involved in the bonnet polishing process are not formulated into that model, such as slurry characteristics, pad properties, bonnet sizes, processing conditions, etc. Recently, several analysis models capturing those various parameters have been developed and are even capable of interpreting non-Prestonian behaviors, but the pad wear effect has still not been taken into account...
September 1, 2018: Applied Optics
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