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Applied Optics

M A Bisyarin, O I Kotov, A H Hartog, L B Liokumovich, N A Ushakov
The Rayleigh backscattering produced by an incident fundamental mode in a multimode step-index optical fiber was analyzed using a recently developed diffraction technique. The complete set of backward propagating modes, both radial and azimuthal, was determined and regarded. For this type of fiber, normalized mode functions were constructed in an explicit form, thus providing a unified power scale to characterize the relationships between various excited modes. The dependencies of the mode excitation efficiencies on the technical parameters of the fiber and the frequency of the launched radiation were studied...
January 10, 2017: Applied Optics
Syed Azer Reza, Arslan Anjum
This paper presents a motion-free technique to characterize the focal length of any spherical convex or concave lens. The measurement test-bench uses a Gaussian laser beam, an electronically controlled variable focus lens (ECVFL), a digital micro-mirror device (DMD), and a standard photo-detector (PD). The method requires measuring beam spot sizes for different focal length settings of the ECVFL and using the measurement data to obtain a focal length estimate through an iterative least-squares-based curve-fitting algorithm...
January 10, 2017: Applied Optics
M H M Passos, M R Lemos, S R Almeida, W F Balthazar, L da Silva, J A O Huguenin
In this work, we report on the analysis of speckle patterns produced by illuminating different rough surfaces with an optical vortex, a first-order (l=1) Laguerre-Gaussian beam. The generated speckle patterns were observed in the normal direction exploring four different planes: the diffraction plane, image plane, focal plane, and exact Fourier transform plane. The digital speckle patterns were analyzed using the Hurst exponent of digital images, an interesting tool used to study surface roughness. We show a proof of principle that the Hurst exponent of a digital speckle pattern is more sensitive with respect to the surface roughness when the speckle pattern is produced by an optical vortex and observed at a focal plane...
January 10, 2017: Applied Optics
Jiri Libich, Joaquin Perez, Stanislav Zvanovec, Zabih Ghassemlooy, Roberto Nebuloni, Carlo Capsoni
Despite the benefits of free-space optical (FSO) communications, their full utilization is limited by the influence of atmospheric weather conditions, such as fog, turbulence, smoke, snow, etc. In urban environments, additional environmental factors such as smog and dust particles due to air pollution caused by industry and motor vehicles may affect FSO link performance, which has not been investigated in detail yet. Both smog and dust particles cause absorption and scattering of the propagating optical signal, thus resulting in high attenuation...
January 10, 2017: Applied Optics
Katayoon Samavati, M Taghi Tavassoly, Hamid Ghomi
When a grating is imaged by an optical imaging system, due to the aberrations of the system, the parameters of the image grating suffer minute gradual changes across the image. Superimposing an ideal grating image over the real grating image at the phase singularity state of the two gratings leads to phase contours, special Moiré fringes, which directly represent the distortions over the image. In this report, after a brief review of the required theoretical bases, we show when the parameters of a grating change linearly the corresponding Moiré fringes at the singularity state are represented by quadratic functions, and for nonlinear changes higher order functions are involved...
January 10, 2017: Applied Optics
Ziba Saleki, Samad Roshan Entezar, Amir Madani
The transmission properties of a one-dimensional defective photonic crystal have been investigated using the transfer matrix method. A layer of graphene-based hyperbolic metamaterial whose optical axis is tilted with respect to the interface is taken as a defect. It is shown that two kinds of the defect modes can be found in the band gaps of the structure for TM-polarized waves. One kind is created at the frequency range in which the principle elements of the effective permittivity tensor of the defect layer have the same signs...
January 10, 2017: Applied Optics
Xiaofeng Liu, Yanqi Gao, Jian Sun, Dawei Li, Meiping Zhu, Guohang Hu, Weili Zhang, Yuan'an Zhao, Jianda Shao
The active-mirror architecture is widely used in high-power laser systems. In this study, the laser-damage characteristics of Nd:glass active mirrors are investigated. They are exposed to nanosecond 1064 nm laser incident from the Nd:glass. The laser-induced damage thresholds (LIDTs) of the coated sides are lower than those of the uncoated sides. The LIDT of the active mirror whose substrate is manually scrubbed is lower than that of one whose substrate is ultrasonically cleaned. Analysis shows that the absorbing surface defects on the manually scrubbed Nd:glass surface are responsible for the lower LIDT of the active mirror prepared via manual scrubbing, while the subsurface defects in the ultrasonically cleaned Nd:glass substrate are the main reason for the damage of the active mirror prepared via ultrasonic cleaning...
January 10, 2017: Applied Optics
Yihan Wang, Jiao Li, Tong Lu, Limin Zhang, Zhongxing Zhou, Huijuan Zhao, Feng Gao
Hybrid imaging methods combining diffuse optical tomography (DOT) and other anatomical or nonoptical functional modalities have been widely investigated to improve imaging performance degraded by the strong optical scattering of biological tissues, through constraining the reconstruction process by prior structures. However, these modalities with different contrast mechanisms may be ineffective in revealing early-staged lesions with high optical contrast but no morphological changes. Photoacoustic tomography (PAT) is particularly useful for visualizing light-absorbing structures embedded in soft tissues with high spatial resolution...
January 10, 2017: Applied Optics
Xinghui Li, Kai Ni, Qian Zhou, Peng Yan, Jinchao Pang, Xiaohao Wang
An imprinting process that enables fabrication of blazed concave gratings with small radius and large curvature is presented. In this process, a combination-type convex grating substrate is used as a master to replace the single part used in the traditional process. The two parts of the combined convex grating are independently separated from the resist layer. In this manner, the concave blazed grating pattern in the resist can maintain maximum consistency with that on the combined convex grating. Experiments are conducted to demonstrate the feasibility of a two-step fabrication technology...
January 10, 2017: Applied Optics
Ming Li, Wenbo Gao, Milorad Cvijetic
As a continuation of our previous work [Appl. Opt.54, 1453 (2015)APOPAI0003-693510.1364/AO.54.001453] in which we have studied the performance of coherent free space optical (FSO) communication systems operating over a horizontal path, in this paper we study the coherent FSO system operating over a general slant path. We evaluated system bit-error-rate (BER) in the case when the quadrature phase-shift keying (QPSK) modulation format is applied and when an adaptive optics (AO) system is employed to mitigate the air turbulence effects for both maritime and terrestrial air transmission scenarios...
January 10, 2017: Applied Optics
Ying Lu, Xuhui Xie, Lin Zhou, Zuocai Dai, Guiyang Chen
An ion beam with high removal rate and small diameter is expected in ion beam figuring. For an ion beam figuring tool, reducing the extraction grid opening is a feasible method to decrease the ion beam diameter, but the ion beam removal rate decreases at the same time. The ion beam removal rate depends much on the ion density in the ion source discharge room. The plasma in a hollow cathode (HC) ion source and a radio frequency (RF) ion source was simulated. The simulations suggested that the ion density in the RF ion source is higher than that of the HC one...
January 10, 2017: Applied Optics
Felipe Aquino, Wojciech M Jadwisienczak, Faiz Rahman
Laser diode (LD) pumped white light sources are being developed as an alternative to light-emitting diode-pumped sources for high efficiency and/or high brightness applications. While several performance metrics of laser-pumped phosphor-converted light sources have been investigated, the effect of laser speckle has not been sufficiently explored. This paper describes our experimental studies on how laser speckle affects the behavior of light from laser-excited phosphor lamps. A single LD pumping a phosphor plate was the geometry explored in this work...
January 10, 2017: Applied Optics
Yunhao Zhang, Yonggang Zhang, Zhongxing Gao
As a high-precision angular sensor, the fiber-optic gyroscope (FOG) usually shows high sensitivity to disturbances of the environmental temperature. Research on thermal-induced error of the FOG is meaningful to improve its robust performance and reliability in practical applications. In this paper, thermal-induced nonreciprocal phase-shift error of the FOG due to asymmetric fiber tail length is discussed in detail, based on temperature diffusion theory. Theoretical analysis shows that the increase of thermal-induced nonreciprocal phase shift of the FOG is proportional to the asymmetric tail length...
January 10, 2017: Applied Optics
Dar Dahlen, Russell Wilcox, Wim Leemans
We demonstrate a new way to analyze stable, multipass optical cavities (Herriott cells), using the linear canonical transform formalism, showing that re-entrant designs reproduce an arbitrary input field at the output, resulting in useful symmetries. We use this analysis to predict the stability of cavities used in interferometric delay lines for temporal pulse addition.
January 10, 2017: Applied Optics
Zhangwen Liu, Xueguang Qiao, Ruohui Wang
A microminiaturized all-fiber Fabry-Perot interferometer (FPI) for high-temperature sensing has been proposed and experimentally demonstrated. The FPI is composed of a micro-air bubble and a taper probe with a tip less than 2 μm in diameter as reflected interfaces. A temperature sensitivity of 14.68 pm/°C near the wavelength of 1550 nm is obtained. The sensor, with its miniature size, can work in an ultra-small space with a large range of temperature variation.
January 10, 2017: Applied Optics
Jin Yang, Rui Zhang, Lu Yin, Ci Sun, Tianjiao Li
Stray light is one of the important factors for evaluating the quality of gratings. Therefore, it has become an important problem in the field of grating development to measure the stray light of planar diffraction gratings accurately. For that reason, a planar grating stray light testing instrument based on a Czerny-Turner (C-T) structure has been studied. On the premise of the low stray light of the instrument itself, the instrument is capable of measuring wideband, variable aperture, and high resolution stray light for planar gratings...
January 10, 2017: Applied Optics
Teemu Tomberg, Thomas Fordell, Jorma Jokela, Mikko Merimaa, Tuomas Hieta
Electronic distance meters are routinely used to accurately determine the distance between two points. To reach relative measurement uncertainties of 10<sup>-7</sup>, the average temperature along the beam has to be known within 100 mK since it is a key component in determining the refractive index of air. Temperature measurements at this level are extremely challenging over long distances and especially in an outdoor environment. This paper presents a thermometer for accurate temperature measurements over distances up to a few km...
January 10, 2017: Applied Optics
Jian Ren
Electro-optic crystals, such as potassium tantalate niobate [KTa<sub>1-x</sub>Nb<sub>x</sub>O<sub>3</sub>(KTN)], are enabling materials for many optical devices. Their utility in broadband applications heavily depends on their dispersion property. To this end, an analysis of dispersion mismatch in broadband optical interferometers is first presented. Then a method utilizing polynomial phase fitting to measure the dispersion property of materials composing the arms of an interferometer is introduced...
January 10, 2017: Applied Optics
Edoardo Rubino, Tindaro Ioppolo
This paper describes a non-contact transduction mechanism for the measurement of linear displacements that is based on the electrostrictive properties of a polymeric optical resonator. The spherical resonators, with a diameter of ∼1  mm and an average optical quality factor of ∼10<sup>6</sup>, are made using a commercially available polymer (Super Soft Plastic-Manufacturing Company). The spherical resonator is immersed in a homogeneous electric field that is generated by applying a voltage difference between two metallic plates...
January 10, 2017: Applied Optics
Ninik Irawati, Nur Atiqah M Yusuf, Husna A Rahman, Moh Yasin, Harith Ahmad, Sulaiman W Harun
Two straight microfiber sensors are proposed and demonstrated for the detection of various concentrations of a potassium permanganate (KMnO<sub>4</sub>) solution. Two types of straight microfibers, namely, silica microfiber and poly(methyl methacrylate) microfiber, have been fabricated by using the flame brushing technique and the direct drawing technique, respectively. Based on the varied KMnO<sub>4</sub> concentrations of the solution from 1% to 6%, the measurement of the peak voltage of the transmission power was made...
January 10, 2017: Applied Optics
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