Showing papers on "Angular aperture published in 2017"

Reflective metasurface lens with an elongated needle-shaped focus

Abstract: Novel multifocal flat metasurface (MS) lenses are developed using two techniques: (i) polarization diversity, and (ii) annular segmentation of the lens aperture. The polarization-diversity technique enables overall lens aperture reuse, thus doubling the number of foci through the simultaneous focusing of two orthogonal linearly polarized incident beams at two distinct foci using the lens aperture. The annular-segmentation technique, on the other hand, is independent of incident beam polarization and is only based on dividing the lens aperture into concentric annular segments that converge different portions of the illuminating beam at different foci. The total number of foci can be further increased by combining the polarization-diversity and the annular-segmentation techniques. Subsequently, the concept of multifocality is further extended to design a novel flat lens with an overall single needle-like focal region with elongated depth of focus (DOF) without loss of lateral resolution. To this goal, we design a multifocal lens with overlapping profiles of foci superposed into a single elongated needle-shaped focal region. Using the combination of polarization-diversity and annular-segmentation techniques, we develop a novel MS flat lens made of Y-shaped nanoantennas, whose polarization-dependent reflection phase and amplitude can be controlled independently via their geometrical parameters. Via numerical calculations, we demonstrate that the proposed MS lens has an overall single focal region with an extremely long DOF of about 74.1 λ, a lateral full width at half maximum varying in the range of 1.37 λ to 2.8 λ, and a numerical aperture of about 0.26 (considering the center of the focal region as the effective focal point). Here, the MS lens’s capability to synthesize extremely long DOF is conceptually demonstrated without resorting to time-consuming and complicated wavefront synthesis methods. The engineering of focal intensity profiles with flat MSs may introduce significant advancement in nanoimaging, many areas of microscopy, and ophthalmic applications.

Transient Field Calculation of Aperture Antennas for Various Field Distributions Over the Aperture

Abstract: This letter presents a time-domain method of near-field calculation for circular plane apertures of various field distributions. The method allows getting analytic forms presented in inverse trigonometric functions. New formulas for transient near field are derived in this letter for circular plane apertures of electric field falling down to edges of the aperture. The behavior of the transient near field of a circular aperture with distributions tapered toward the edge is explained.

Fresnel Lens at Millimeter-Wave: Enhancement of Efficiency and Radiation Frequency Bandwidth

Abstract: In this paper, the performance of Fresnel lens antennas is investigated in detail. The performance is evaluated in terms of aperture efficiency and stable radiation pattern over a wide frequency band. This paper proposes an efficient technique for enhancing aperture efficiency by smoothly compensating for the spherical phase front arriving upon the lens surface. The feeder has been optimized to fit an axially symmetric cos n -like radiation pattern. For this, an accurate technological process has been used to manufacture a lens that allows for smooth compensation of the phase shift. The lens is compared with a classic Fresnel lens having the same physical dimensions and feeding system. The improvement is validated by measurement, which has revealed a maximum measured gain of 38.9 dBi corresponding to a maximum measured aperture efficiency of 59% with a −2 dB radiation frequency bandwidth of 29.25 GHz around 90 GHz. This amounts to an aperture efficiency enhancement of 60% and −2 dB radiation frequency bandwidth enhancement of 72% as compared with those of the classic Fresnel lens.

Determination of the paraxial focal length using Zernike polynomials over different apertures

Abstract: The paraxial focal length is still the most important parameter in the design of a lens. As presented at the SPIE Optics + Photonics 2016, the measured focal length is a function of the aperture. The paraxial focal length can be found when the aperture approaches zero. In this work, we investigate the dependency of the Zernike polynomials on the aperture size with respect to 3D space. By this, conventional wavefront measurement systems that apply Zernike polynomial fitting (e.g. Shack-Hartmann-Sensor) can be used to determine the paraxial focal length, too. Since the Zernike polynomials are orthogonal over a unit circle, the aperture used in the measurement has to be normalized. By shrinking the aperture and keeping up with the normalization, the Zernike coefficients change. The relation between these changes and the paraxial focal length are investigated. The dependency of the focal length on the aperture size is derived analytically and evaluated by simulation and measurement of a strong focusing lens. The measurements are performed using experimental ray tracing and a Shack-Hartmann-Sensor. Using experimental ray tracing for the measurements, the aperture can be chosen easily. Regarding the measurements with the Shack-Hartmann- Sensor, the aperture size is fixed. Thus, the Zernike polynomials have to be adapted to use different aperture sizes by the proposed method. By doing this, the paraxial focal length can be determined from the measurements in both cases.

Photoacoustic Imaging with a double-Ring Sensor

Abstract: Laser-induced acoustic waves in tissue can be detected by measurement of the pressure transient or displacement at the tissue surface. Measurement of these pressure transients using piezoelectric sensors is the most commonly used method in photoacoustics. Although optical methods for detection of acoustic waves have been developed as well [1-6], piezoelectric sensors have the advantage that broadband sensors are easier to construct and have a slightly better sensitivity than optical detection systems [7]. The shape and size of the piezoelectric element determine the characteristics, such as the directivity pattern and the frequency response of the sensor. Sensors with a small element size (“point sensors”) have a very large angular aperture, and thus are able to detect acoustic signals originating from a large volume in the tissue. As a result, reconstruction algorithms are needed to obtain an image. In contrast, for sensors with a narrow angular aperture, e.g., ring-shaped or annular sensors, the time traces can be regarded as 1D depth images (amplitude (A)-scans) of photoacoustic sources inside the measurement volume. Comparable to an echographic B-scan, imaging with such a ring-shaped sensor is carried out by scanning the sensor over the tissue surface, permitting real-time reconstruction of the corresponding part of the image without the need for information on adjacent sensor positions.

Electrostatic analyzer with a 3-D instantaneous field of view for fast measurements of plasma distribution functions in space

Abstract: We describe the concept and properties of a new electrostatic optic which aims to provide a 2π sr instantaneous field-of-view to characterize space plasmas. It consists of a set of concentric toroidal electrodes that form a number of independent energy selective channels. Charged particles are deflected towards a common imaging planar detector. The full 3D distribution function of charged particles is obtained through a single energy sweep. Angle and energy resolution of the optics depends on the number of toroidal electrodes, on their radii of curvature, on their spacing, and on the angular aperture of the channels. We present the performances, as derived from numerical simulations, of an initial implementation of this concept that would fit the need of many space plasma physics applications. The proposed instrument has 192 entrance windows corresponding to 8 polar channels each with 24 azimuthal sectors. The initial version of this 3D plasma analyzer may cover energies from a few eV up to 30 keV, typically with a channel dependent energy resolution varying from 10% to 7%. The angular acceptance varies with the direction of the incident particle from 3° to 12°. With a total geometric factor of two sensor heads reaching ~ 0.23 cm2 · sr · eV/eV, this “donut” shape analyzer has enough sensitivity to allow very fast measurements of plasma distribution functions in most terrestrial and planetary environments on three-axis stabilized as well as on spinning satellites.

Focusing properties of radially polarized modified Bessel-modulated Gaussian beam by a high numerical aperture objective

Abstract: In this paper, the focusing properties of radially polarized modified Bessel-modulated Gaussian (RPMQBG) beam with quadratic radial dependence through a high numerical aperture (NA) lens are investigated, theoretically and numerically, using the vector diffraction theory model. The tight focusing properties are studied in great detail. The numerical simulation results show that the intensity distribution of the RPMQBG beam at the focal region of the numerical aperture can be changed considerably by the variation of the optical vortex beam topological charge l and by the high numerical aperture angle (NA).

Orbital angular momentum density and spiral spectrum of Lorentz–Gauss vortex beams diffracted by a rectangular aperture

Abstract: Based on the expansions of the Lorentz distribution and the aperture function, an analytical expression of Lorentz–Gauss vortex beams with a topological charge of ±1 diffracted by a rectangular aperture is derived. One can judge the sign of the topological charge from the normalized intensity and the phase distributions. The effects of the rectangular aperture on the orbital angular momentum density and the spiral spectrum are investigated, respectively. When the length and the width of the rectangular aperture are not equal, the orbital angular momentum density distribution becomes twisted and tilted. When the size of the rectangular aperture increases, the magnitude of the orbital angular momentum density and the weight coefficient of the dominant spectrum both increase, while the weight coefficients of other minor spectra decrease. In addition, the expansion of the spiral spectrum in the case of rectangular aperture is smaller than that in the case of the single slit. The difference between the...

Justification and implementation of the coordinate method among potentially possible precise methods for measuring angles between axes of small-angle beams

Abstract: A series of studies devoted to the theoretical justification and development of methods and tools for angular measurements based on the use of multiple sources of optical beams with a small angular aperture is continued. The source used in this study is a holographic prism: a fluorite single crystal with a system of superimposed holograms recorded in its bulk, which generates a series of diffracted small-angle beams in the form of a flat fan under illumination by a reference laser. This fan has a high spatial stability, including constancy of angles between any pair of fan beams in a wide range of external conditions. Based on the previously introduced notion of an effective beam axis, potential exact methods for measuring angles between fan beams are considered, and a coordinate method using a coordinate measuring machine and a CCD recorder is substantiated and implemented. The accuracy of the proposed method is analyzed. It is shown that its errors can potentially be reduced to a level of 1″ or even less.

Wide angle six-piece lens

Abstract: A wide angle six-piece lens includes a first lens having a negative refractive power and an image side as a concave surface, a second lens having a positive refractive power and an object side as a convex surface, an aperture, a third lens having a positive refractive power and an image side as a convex surface, a fourth lens having a positive refractive power and an object surface and an image surface as convex surfaces, a fifth lens having a negative refractive power and an object side as a concave surface, and a sixth lens having a positive refractive power and an object side as a convex surface. The overall effective focal length of the wide angle six-piece lens is f, the focal length of the third lens is f3, and an equation 0.29

New generation of Fourier optics viewing angle measurement systems

Abstract: We explain the technical bases of the Fourier Optics Technology (OFT) for viewing angle measurement of displays and the increasing capacities of the ELDIM systems over the years. A new generation of OFT systems devoted to quality control is introduced. In spite of a more compact size, the optic shows excellent performances in terms of angular aperture, angular resolution and collection efficiency. The detection is made with a new generation high resolution CMOS camera which allows very short measurement times. In addition, the probe can be used on a robotic arm to offer a cost effective solution for quality control of displays with any kind of size and shape.

Indoor Experimental Assessment of the Efficiency and Irradiance Spot of the Achromatic Doublet on Glass (ADG) Fresnel Lens for Concentrating Photovoltaics.

Abstract: We present a method to characterize achromatic Fresnel lenses for photovoltaic applications. The achromatic doublet on glass (ADG) Fresnel lens is composed of two materials, a plastic and an elastomer, whose dispersion characteristics (refractive index variation with wavelength) are different. We first designed the lens geometry and then used ray-tracing simulation, based on the Monte Carlo method, to analyze its performance from the point of view of both optical efficiency and the maximum attainable concentration. Afterwards, ADG Fresnel lens prototypes were manufactured using a simple and reliable method. It consists of a prior injection of plastic parts and a consecutive lamination, together with the elastomer and a glass substrate to fabricate the parquet of ADG Fresnel lenses. The accuracy of the manufactured lens profile is examined using an optical microscope while its optical performance is evaluated using a solar simulator for concentrator photovoltaic systems. The simulator is composed of a xenon flash lamp whose emitted light is reflected by a parabolic mirror. The collimated light has a spectral distribution and an angular aperture similar to the real Sun. We were able to assess the optical performance of the ADG Fresnel lenses by taking photographs of the irradiance spot cast by the lens using a charge-coupled device (CCD) camera and measuring the photocurrent generated by several types of multi junction (MJ) solar cells, which have been previously characterized at a solar simulator for concentrator solar cells. These measurements have demonstrated the achromatic behavior of ADG Fresnel lenses and, as a consequence, the suitability of the modelling and manufacturing methods.

Spatiotemporal analysis of high-performance military aircraft noise during ground run-up

Abstract: Recent measurements of high-performance military aircraft noise have revealed that full-scale jet noise has features and structures that are still only partly understood, such as the presence of multiple acoustic radiation lobes in the aft direction at certain frequencies. Spatiotemporal analyses of a ground-based microphone array measurement of the noise from a tethered F-35 at various engine conditions are used to investigate these features of the sound field. The ground array covered an angular aperture of 35–152 degrees relative to the front of the aircraft. The large angular aperture allows for a detailed investigation of the correlation and coherence at frequencies exhibiting multi-lobe behavior. This spatiotemporal analysis yields further evidence of the characteristics of multi-lobe behavior in high-performance, full-scale jet noise. [Work supported by an Office of Naval Research grant, a USAFRL SBIR, and the F-35 JPO. Distribution A: Approved for public release; distribution unlimited. Cleared 07...

Acousto-optic filter angular aperture measuring device and measuring method

Abstract: The invention discloses an acousto-optic filter angular aperture measuring device and measuring method. The device comprises a white light source, a light beam collimation system, an acousto-optic filtering system, an angle adjusting turntable, a spectrum detection system and a computer control and analysis system which are arranged sequentially; the spectrum detection system is connected with the computer control and analysis system; a light beam from the white light source passes through the beam collimation system and the acousto-optic filtering system in turn and enters the spectrum detection system; spectrum information acquisition and analysis are performed under the control of the computer control and analysis system; a complete optical path connection is formed; and the computer control and analysis system analyzes spectrum data obtained in an angular aperture measurement process and calculates a corresponding angular aperture. Based on the device, the test method of the present invention is adopted to measure the angular aperture of an acousto-optic filter and can accurately measure the angular aperture of the acousto-optic filter under different light transmission wavelengths. The acousto-optic filter angular aperture measuring device and measuring method have the advantages of high measurement precision, high stability, simplicity and operational easiness.

Periodic aperture imaging

Abstract: We studied periodic aperture imaging with various subaperture configurations in terms of their point spread functions, optical transfer functions, and imaging quality A circular-shaped unit cell provides the best performance compared to square- and cross-shaped unit cells when the total aperture size and collection area are kept the same Moreover, decreasing the separation among the unit cells or the number of subapertures also improve the imaging performance Results have potential applications in optical periodic aperture telescopes, diffraction masks, and coded aperture imaging

A study on phase improvement of focusing dielectric lens horn antenna using dielectric slab

Abstract: The uniform phase planes of the radiated beam in the E- and H-planes are located at different distances from the lens horn aperture due to its asymmetric TE 11 mode aperture distribution. A new method by attaching a simple dielectric slab on the lens surface is proposed for matching the distances. The both uniform phase planes are formed 55 mm away from an antenna aperture with the dielectric slab with thickness of 13 mm for 60 mm antenna aperture at 50 GHz. As a result, the slab improves the phase deviation in the H-plane by 12 degree, and the validity of the proposed method is indicated.

Active liquid-crystal deflector and lens with Fresnel structure

Abstract: A new type of tunable Fresnel deflector and lens composed of liquid crystal was developed. Combined structure of multiple interdigitated electrodes and the high-resistivity (HR) layer implements the saw-tooth distribution of electrical potential with only the planar surfaces of the transparent substrates. According to the numerical calculation and design, experimental devices were manufactured with the liquid crystal (LC) material sealed into the sandwiched flat glass plates of 0.7 mm thickness with rubbed alignment layers set to an anti-parallel configuration. Fabricated beam deflector with no moving parts shows the maximum tilt angle of ±1.3 deg which can apply for optical image stabilizer (OIS) of micro camera. We also discussed and verified their lens characteristics to be extended more advanced applications. Transparent interdigitated electrodes were concentrically aligned on the lens aperture with the insulator gaps under their boundary area. The diameter of the lens aperture was 30 mm and the total number of Fresnel zone was 100. Phase retardation of the beam wavefront irradiated from the LC lens device can be evaluated by polarizing microscope images with a monochromatic filter. Radial positions of each observed fringe are plotted and fitted with 2nd degree polynomial approximation. The number of appeared fringes is over 600 in whole lens aperture area and the correlation coefficients of all approximations are over 0.993 that seems enough ideal optical wavefront. The obtained maximum lens powers from the approximations are about ±4 m-1 which was satisfied both convex and concave lens characteristics; and their practical use for the tunable lens grade eyeglasses became more prospective.

Lens with ultra-wide field and large aperture

Abstract: Disclosed is a lens with an ultra-wide field and a large aperture, relating to digital cameras and camera lenses, constituted by at least three parts of a first lens group G1, a second lens group G2 and a third lens group G3 arranged in sequence from an article side to an image side. When an article moves from infinity to a close range, the first lens group G1 is fixed and the second lens group G2 and the third lens group G3 move so as to focus. The following conditions are satisfied: 1.2≤(|F12|+S)/LB≤2.5(1); 0.8≤(|F12|+S)/(tanω×LB)≤1.3(2), wherein F12 is the resulting focal length of the first lens group G1 and the second lens group G2 when the article is at infinity; S is the distance between the frontmost end face of the first lens group on the article side and the diaphragm in the infinity state; LB is the distance between a face closest to an image plane and the image plane in the infinity state; and ω is the angle of the half-angle of view of the optical system. Provided is an ultra-wide field lens having an angle of view of over 110 degrees, being small in size, high in performance and low in costs.

An Accurate Electromagnetic Model of a Circular Aperture With Analytical Solution for On-Axis Near Field

Abstract: This paper presents an accurate model of a circular aperture with full parabolic-in-square aperture distribution that can be applied to reflectors, antenna arrays, microwave lenses, or other aperture antennas. The proposed aperture distribution is a weighted sum of the parabolic in square on a pedestal and parabolic tapered distributions. It permits the analysis and design of efficient aperture antennas with a low sidelobe level. The main far-field parameters of antenna radiation, aperture taper efficiency, directivity, radiated power, half-power beamwidth, and sidelobe level can be determined with simple formulas. Additionally, the applied aperture distribution permits accurate near-field estimation. A new analytical solution of the Helmholtz equations for an on-axis near field is derived. A comparison of the obtained solution with known analytical results based on the Fresnel approximation is presented. Verification of the new near-field formula favorably coincides with near-field numerical simulations using electromagnetic software FEKO.

Diffracted optical vortices by an angular aperture

Abstract: The measurement of the topological charge of laser beams with orbital angular momentum (OAM) is key to many applications like deciphering information encoded in several channels. Current techniques useful for that purpose are interferometry, diffraction through different poligonal apertures like triangular or pentagonal and, azimuthal and radial decomposition. A less explored issue is the diffraction of OAM beams through circular sectors. Jack et al. studied the angular diffraction of Gaussian beams (whose OAM is null) through a circular sector. By means of a Fourier transform of the truncated Gaussian beam they showed that the orbital angular momentum spectrum of the transmitted beam has a sinc-shaped envelope centered at zero orbital angular momentum, the width of which increases as the central angle of the circular sector decreases. We analyze here the spectrum of a laser beam with integer OAM that has been diffracted by a circular sector. We present results for circular sectors of different central angles. For circular π-sector, we also study the influence of the transmittance in the OAM spectra of the transmitted beam, using straight borders of nanometric thin films of titanium oxide with different thicknesses. We use a spatial light modulator with a fork hologram placed on to generate the incoming OAM beam and measure the evolution of the intensity profile of the diffracted beam as it propagates away from the circular sector. The spectra of the diffracted OAM beams are shown numerically and experimentally to have a sinc shaped envelope centered at the OAM value of the incoming OAM wave.