Showing papers on "Angular aperture published in 1997"

Scattering losses from dielectric apertures in vertical-cavity lasers

Abstract: In vertical-cavity lasers (VCLs) employing oxide or airgap apertures, the lasing mode typically travels unguided throughout most of the structure. For the aperture to exactly compensate for the diffraction of the mode in these regions, it would need to have a parabolic lateral index profile (i.e. that of an ideal thin lens). Although nonparabolic aperture shapes will partially compensate diffraction losses, some light will be scattered out of the mode. These scattering losses increase as the aperture size is reduced and will limit the performance of the smallest devices. We analyze these losses first using a semianalytic approach which allows us to frame the problem in terms of two parameters of the structure: the Fresnel number and the effective optical path length across the aperture. We compare the estimate with experimental results and with an iterative numerical calculation of the actual mode and losses. Lastly, we compare the loss reduction with different amounts of tapering that provide a better approximation to the ideal parabolic lens.

Combined space and polarization diversity antennas

Abstract: An antenna system with both spatial and polarization diversity having a first antenna aperture and a second antenna aperture, a polarization separation angle formed by the difference between the polarization angle of the first antenna aperture and the polarization angle of the second antenna aperture, and a vertical separation formed by mounting the second antenna aperture a vertical distance above the first antenna aperture, such that diversity gain is achieved by both the polarization angle and the vertical distance. The combination of spatial and polarization diversity allows closer antenna aperture spacing and non-orthogonal polarization angles.

An optical method for direct determination of the radiometric aperture area at high accuracy

Abstract: An optical method for calibration of the aperture area is described and studied both theoretically and experimentally. A spatially uniform, known irradiance is formed over the aperture by overlapping identical, parallel laser beams centred at constant spacing in an orthogonal lattice. The ratio of the throughput power and irradiance gives the area of the aperture. The method has several advantages compared with previous methods: it measures the area of the aperture directly, the shape of the aperture is not limited to a circle, it is relatively inexpensive to establish, it does not damage the edges of the aperture and the calibration set-up is similar to that for the actual use of the aperture. It is estimated that the relative standard uncertainty is in calibration of a circular 3 mm diameter aperture. The results that the present method gave for one aperture have been compared with the result of a mechanical calibration at the National Physical Laboratory (UK). The relative difference between the results was , with a combined standard uncertainty of .

Independently controllable shutters and variable area apertures for off axis illumination

Abstract: Apertures to vary the size and shape of the aperture area without the need to change the whole aperture plate in off axis lithography The off axis illumination apertures allow the size and shape of apertures to be changed without having to change the aperture plates for each step in the lithographic process The aperture plate (40) is fitted with simple shutter mechanisms (41-44) that allow ready adjustment of the aperture openings

Zoom lens having image stabilizing function

Abstract: A zoom lens comprises a plurality of lens units, in which at least one of lens unit separations in the plurality of lens units is varied to vary a focal length, an aperture stop, and a variable angle prism unit disposed on an image side of the aperture stop and having an apex angle varied to refract light, the zoom lens satisfying the following conditions: 1.16

Objective lens system utilizing diffractive optical element

Abstract: A low cost objective lens system that provides complete axial color correction with no substantial residual color dependent aberrations such as spherochromatism or chromatic coma. The objective lens system includes a first lens element having an aspherical lens surface and a second lens element having a diffractive optical surface and an aperture disposed between the first and second lens elements. The axial separation of the aspherical lens surface and the diffractive optical surface may be determined by the condition 0.5

Optical disk having a protective layer of specified thickness relative to the numerical aperture of the objective lens

Abstract: An optical disc system uses an optical disc with a light-transmitting cover and an objective lens for bundling or focusing a light beam on a recording layer of the optical disc in order to perform recording and/or reproducing of information. The thickness of the light-transmitting cover falls within the range of 0.05 mm to 0.6 mm, the numerical aperture (NA) of the objective lens is set to fall within the range of 0.55 to 1.10, and the wavelength of the light beam is selected to be between 100 nm to 780 nm.

Optical soft aperture and use thereof

Abstract: A soft aperture allows gradual attenuation of a light beam dependent upon its location away from the center of a diffractive optical element. Such an optical element may be provided by decreasing a number of phase levels, increasing a number of phase levels, increasing a density of metal patches or diffractive gratings, or decreasing a blaze height and/or duty cycle, all radially from the center. Alternatively, the soft aperture may be defined by a photolithographic process. Such a soft aperture is particularly useful in aiding circularizing of an elliptical light beam. The soft aperture may be used alone or integrated with other optical elements.

Measurement optimization in speckle interferometry: the influence of the imaging lens aperture

Abstract: Speckle interferometry has long proven its usefulness for measuring the deformation and contours of objects with rough surfaces. Nevertheless, the influence of a parameter as important as the lens aperture of the imaging system on the result of the measurement is still not precisely known. Generally, it is stated that the speckles must be resolved by the camera and that therefore the lens aperture number should be large enough (e.g., f /11 or f /16 for typical applications with a standard CCD). It is shown, theoretically as well as experimentally, that it is not necessary to resolve the speckles when making measurements in speckle interferometry. The joint probability distribution of the pixel modulation and the pixel background intensity, which determines the percentage of valid pixels, is investigated for different lens aperture numbers, i.e., for different numbers of speckles per pixel. The comparison between theory and the experimental counterpart enables a number of speckles per pixel to be determined for any given aperture number and pixel size. It appears that the average pixel modulation remains high enough even with a relatively large number of speckles per pixel. The results lead to the conclusion that, especially when the total camera noise is low enough, lens apertures up to f /2 can be used. Thus, measurements are less constrained by limited laser power and decorrelation effects.

Ionospheric effects on synthetic aperture radar at VHF

Abstract: Synthetic aperture radars (SAR) operated from airplanes have been used at very high frequency (VHF) because of their enhanced foliage and ground penetration compared to radars operated at higher frequencies. A satellite-borne VHF SAR would have considerable utility but in order to operate with high resolution it would have to use both a large relative bandwidth and a large aperture. The presence of the ionosphere in the propagation path of the radar will cause a deterioration of the imaging because of dispersion over the bandwidth. In this paper we present calculations of the effects of a deterministic ionosphere on SAR imaging for a radar operated with a 100 MHz bandwidth centered at 250 MHz and over an angular aperture of 23/spl deg/. A daytime ionosphere induces a point spread function with an approximate width of 100 m in slant-range compared to the nominal resolution of 1.5 m.

Optimum lens aperture in phase-shifting speckle interferometric setups for maximum accuracy of phase measurement.

Abstract: Negative exponentially distributed intensities of speckle fields seem unfavorable in terms of precision metrology, if interferometric setups are involved with a saturable photodetector and an analog-to-digital converter that imposes a finite resolution. By spatial integration, extended detector apertures modify the intensity distribution toward a less awkward function. However, because the detector aperture also integrates over points of rapidly changing speckle phases, this is done at the expense of a lower modulation of measured intensity during phase shift. An optimum set of parameters is calculated here, consisting of values for the lens aperture, the mean speckle intensity, and the beam ratio. The remaining phase-measurement error assumes its minimum of 10.6 mrad when the space–bandwidth product of the lens–detector system (thus concerning the lens aperture) is 0.31, the mean speckle intensity is 1/11 of the saturation intensity, and the reference intensity is four times higher than the mean speckle intensity. The 90° phase-shift algorithms with either three, four, or five frames turned out to be quite powerful, even with interference signals of rather poor modulation. Not needing a very small lens aperture is interesting, because stopping down the lens is a trade-off with the limited power of the laser.

Objective lens having a doublet lens with high numerical aperture

Abstract: An objective lens having a doublet structure and a number of apertures of 0.7 or more and an optical pickup apparatus having the objective lens to be adaptable to a optical recording medium having a high information recording density, the objective lens being structured such that at least one side is formed into a aspheric surface and the lens elements are made of low-diffusion glass having an Abbe's number of 40 or greater.

Compound lens body and optical pickup

Abstract: PROBLEM TO BE SOLVED: To provide the compound lens body which can be made small-sized and thin and has high precision and the optical pickup which is equipped with the compound lens body and can be made small-sized by uniting a lens, an aperture stop, and a flange part by using an aspherical surface shape body formed on the lens. SOLUTION: The aspherical surface shape part 5 made of an optical material is formed on the incidence surface 4c of a spherical glass lens 4a integrally with the spherical glass lens 4a. This aspherical surface shape part 5 consists of the aperture stop 5a, aberration compensating lens shape part 5b, and flange part 5c. The aperture stop 5a consists of a convex light diffusion part which emits incident light so that the light is diffused form the focus of the spherical glass lens 4a. Further, the flange part 5c is formed at the outer peripheral part of the spherical glass lens 4a. COPYRIGHT: (C)1998,JPO

Image-forming lens having four lens elements

Abstract: An image-forming lens having four lens elements of refractive power, in order from the object side, of: negative, positive, positive, and negative. By making the distance from image-side surface of the first element to the image-side surface of the second lens element to be greater than or equal to 0.3 f and less than or equal to 1.5 f, where f is the focal length of the image-forming lens, an image-forming lens having an F# of approximately 2.8 and a picture angle of about 60 degrees is obtained. A diaphragm may be positioned such that the distance along the optical axis from the diaphragm to the object side of the fourth lens is less than or equal to the focal length of the image-forming lens.

Theoretical and experimental results for focusing of two-dimensional scalar waves

Abstract: We compare theoretical and experimental results for focusing of two-dimensional scalar waves in the presence of cylindrical aberration and coma and show that good agreement can be obtained by a proper choice of the aberration coefficients. Therefore, such comparisons can be used to obtained an accurate estimate of both first-order and higher-order aberrations. We restrict our attention to systems of sufficiently low angular aperture that a scalar theory is adequate.

Electron optical lens system with a slot-shaped aperture cross section

Abstract: This invention concerns a lens system, particularly for focusing electrons, with a cylindrical lens with pole shoes or electrodes, between which an aperture is located. This aperture has a slot-shaped cross section perpendicular to the optical axis of the lens. The cylindrical lens (4) is combined with a magnetic lens (1) with which a quadripole field can be produced. The lenses are arranged with little or no distance between them and their optical axes run parallel to one another. The quadripole lens (1) has a slot-shaped aperture (10) which is oriented parallel to the opening (9-11) of the cylindrical lens (4). The focusing plane of the quadripole lens (1), which comprises the optical axis (19), is oriented parallel to the longitudinal axes of the apertures (9-11) and its defocusing plane perpendicular to the longitudinal axes. The refractive power of the cylindrical lens (4) can be set at twice that of the quadripole lens (1).

Photographic lens system

Abstract: A photographic lens system which is composed, in order from the object side, of a first lens element having a positive refractive power, a second lens element having a negative refractive power, a third lens element having a positive refractive power, and a fourth lens element which has an aspherical surface on the image side and a negative refractive powers. An aperture stop is disposed between the second lens element and the third lens element or between the third lens element and the fourth lens element. This photographic lens system has a large aperture, favorable optical performance within a photographing range from infinite distance to an extremely short distance, a compact size and a simple composition, and can be manufactured at a low cost.

Bar code reading optical apparatus

Abstract: In a bar code reading optical apparatus including a semiconductor laser and a prism both mounted on a photodiode IC so that emitted light from a semiconductor laser is reflected by a reflective plane of a prism and signal light from a bar code to be read out enters in and detected by a photodiode, a numerical aperture conversion hologram is provided in a light path of the emitted light reflected by the reflective plane of the prism to adjust the numerical aperture of a converging lens so that the numerical aperture for the emitted light be smaller than the numerical aperture for the signal light. The numerical aperture conversion hologram may be omitted by shaping the reflective plane of the prism into a concave plane to adjust the numerical value for the emitted light smaller than the numerical value for the signal light.

Holographic Diffraction Image Velocimetry for Measurement of Three-Dimensional Velocity Fields

Abstract: A new optical nonintrusive method for the gross-field measurement of three-dimensional (3-D) three-component (3-C) flows has been developed and tested. Termed Holographic Diffraction Image Velocimetry (HDIV), it is based on double-exposure dual-reference-beam holographic capture of particle-seeded flow fields and the subsequent processing of time-sequence image data obtained from a single observation direction. The technique uses variable-size transplacing-window cross-correlation (VS-TW-CC) together with an image cross-product (CP) method to extract inand out-of-plane particle displacements from the particle diffraction images. Preliminary experiments have shown that the method can resolve fine in-plane motions limited only by the finite pixel size of the image digitizer and the magnification of the imaging system used. For out-of-plane motions, resolutions measured with a relatively crude setup have been shown to be on the order of two tenths of the illumination wavelength divided by the square of the effective angular aperture of the system, which represents the image decorrelation distance. (Author)

X=ray examination or diagnostic device with two adjustable apertures

Abstract: The device has an x-ray emitter (1) to generate an x-ray beam bundle which passes through a first aperture arrangement with adjustable aperture plates (10) to an examination region. After passing through a second aperture arrangement (20) with adjustable plates (21,23) the beam bundle is incident on a unit (5) to display an x-ray recording. The aperture plates of at least one of the two aperture arrangements (10,20) are provided with markings (25). These are shown in the x-ray recording at least when the radiation field from the first aperture arrangement (10) deviates from that of the second (20).

In-line SB electron gun with large and deep main lens apertures

Abstract: An in-line electron gun includes a main lens having G3 and G4 three aperture electrodes and corresponding chain link (extended aperture) electrodes. The outer apertures in each of the G3 and G4 electrodes are barrel shaped and the middle aperture is elliptical. This construction maximizes the aperture area. The spacings between the G3 and G4 electrodes and their corresponding chain link electrodes are maximized within the existing size constraints of the gun. The combined effect weakens the electric field of the main lens which reduces spherical aberration.

Laser diode-lens alignment with 0.09 or less numerical aperture

Abstract: A light-emitting module includes a laser diode, a laser diode holder, a lens, and a lens barrel. The laser diode is supported by the laser diode holder, and both the lens 2 and the lens barrel are supported by the lens holder. The laser diode and the lens holder engage with each other to be fixed so that the optical axes of the laser diode and the lens agree with each other. The lens holder has an optical fiber fixed in the emergent direction. The lens holder further has an opening to set the numerical aperture for the lens to the laser diode to 0.09 or less.

Acousto-optic tunable filter system which radiates a source light beam incident on a surface of the crystal filter body at an oblique angle

Abstract: In a non-collinear type acousto-optic tunable filter, a source light beam is made off-perpendicularly incident on a crystal body, so that the cross section of the source light beam is narrowed within the crystal body. As a result, the receiving angular aperture becomes large to increase the amount of light collected into the crystal body. Consequently, highly accurate spectrometry can be performed even if the intensity of the source light beam is low. Further, the non-diffraction part of the crystal body can be eliminated by the off-perpendicular incidence of the source light beam, so that the sufficient diffraction length of acoustic and optic waves can be obtained.

Effects of Fresnel diffraction on confocal imaging with an annular lens

Abstract: yOptoelectronic Imaging Group, Department of Applied Physics, Victoria Universityof Technology, PO Box 14428, MCMC, VIC 8001, AustraliazDepartment of Physical Optics, University of Sydney, NSW 2006, AustraliaSubmitted 9 January 1997, accepted 26 June 1997Abstract. The effect of the Fresnel diffraction on the imaging properties of confocalmicroscopy with one circular aperture and one annular aperture is investigated. Theresults show that the Fresnel diffraction patterns alter the axial imaging properties moreseriously than the transverse imaging properties. The axial response of such a confocalmicroscope is sharpened, but severely distorted.Keywords: Fresnel diffraction, annular pupil, confocal microscopy1. IntroductionAnnular aperture is a widely used spatial filter in confocalmicroscopy. It gives some improvement in transverseresolution, but a degradation in axial resolution appears ina confocal system with an annular structure [1,2]. Recentresearch suggests that the use of annular apertures as spatialfilters can suppress the scattered photons [3]. For example,a reflection-mode confocal system with an annular aperturein the illumination path is reported to show a significantenhancement in signal-to-noise ratio for imaging through ahighly scattering medium [4].In practice, an annular aperture cannot be placed exactlyat the back focal plane of an objective. In this case,Fresnel diffraction by the annular aperture exists. Fresneldiffraction of a finite-sized aperture can produce bright anddark fringes because of the interference of the waveletscontributed from points over the aperture [5,6]. Theintensity modulation caused by the interference fringes canalter the imaging properties of confocal microscopy, sincethe effective pupil function of the objective illuminatedby the Fresnel patterns changes accordingly, resulting inthe alteration of the intensity in the focal region [7–10].Therefore, it is important to investigate the effect of Fresneldiffraction on the imaging performance of a confocalsystem with an annular aperture.This paper is organized as follows. Section 2 presentsthe Fresnel diffraction of an annular aperture. The effectof Fresnel diffraction patterns of an annular aperture on theimaging properties of confocal microscopy is discussed insection 3.2. Fresnel diffraction of an annular apertureIf an aperture is placed in the back focal plane of anobjective then focusing is described by Debye theory. TheFresnel number is infinity in this situation. However, ifthe aperture is placed away from the back focal plane by adistance

Effects of lens aberrations on critical dimension control in optical lithography

Abstract: For sub half-micron lithography, control of the Critical Dimension, represents the key to a robust and manufacturable process. The lithographer must understand and tune the exposure system for critical dimension performance using variables such as Numerical Aperture (NA), Partial Coherence (PC), position of the Focal Plane. Exposure tool must be characterized for its lens signature and the tools must be matched for their CD variation within the optical field In a previous study, we demonstrated that the phase-shift focal plane monitor, PSFM accurately measures focal plane variations when appropriate calibrations are employed. That paper also described the development of a model to determine lens classic aberrations such as Coma, Astigmatism and Field Curvature. The publication correlated the results to an approximation of the stepper's Critical Dimension (CD) behavior for a matrix of NA and PC settings. The present study, continues to study CD uniformity through examination of the lens aberrations and field focal signature of optical steppers in a 0.35 um process. We describe a method of measuring the uniformity of numerical aperture (NA) and partial coherence (PC) across the exposure field this new tool is then applied as an aid in optical lens characterization and tool-to-tool matching. The information gathered is thereupon applied to measure lens aberrations and predict CD variation across the field under various settings of the lens focal plane, the predictions are validated by a comparison against CD uniformity as measured by an advanced critical dimension metrology system.

Electron beam projection optical system

Abstract: PROBLEM TO BE SOLVED: To provide an electron beam projection optical system which does not cause large abberation, does not make a beam largely out of focus, and does not cause large distortion even at a large angular aperture. SOLUTION: An electron beam projection optical system is provided with a first projection lens 2 positioned on a reticle 1 side, a second projection lens 3 positioned on a sample 4 side, a crossover 8 positioned to a point which internally divides the positions of the reticle 1 and sample 4 at a reduction ratio, deflectors 6 and 10 for moving axis, etc., which move the electrooptic axis of each lens. A main beam 12 which passes through a representative point 1a in a sub-visual field separated from the optical axis on the reticle 1 is made to intersect the optical axis of a second deflector 7' at the center of the deflector 7' by means of a first deflector 5' which deflects the beam 12, and to advance along the optical axis of the first projection lens 2 by means of a second deflector 7' which deflects the major beam 12. COPYRIGHT: (C)1998,JPO

Method of using a parallax scanning lens aperture in a range-finding application

Abstract: A lens aperture of an autostereoscopic camera is moved in a parallax scanning pattern through a plurality of disparity positions offset from the optical axis of the camera lens. Images of a scene being photographed, as viewed through the lens aperture in its various disparity positions, are recorded for subsequent display in three dimensional illusion when viewed with the unaided eye. The size of the lens aperture and the parallax scanning pattern are adjustable to suit conditions. The lens aperture may be defined as a through-hole in an opaque card or a planar array of cells switched between transparent and opaque states. In addition to stereoscopic imaging, the moving lens aperture principle of the present invention may be utilized in range-finding and camera image stabilization applications.

Projection display apparatus and spatial light modulation device applied to the same

Abstract: A projection display apparatus includes a light source, a spatial light modulation device, a condenser lens, an aperture stop, and a projecting lens. When the spatial period of complex amplitude modulation in the spatial light modulation device is represented by p, the center wavelength of the incident light is represented by λ, and a half angle subtended by an area around an opening edge of the aperture stop at the condenser lens along the first direction is represented by θasx, parameters of the light source, the spatial light modulation device, the condenser lens, the screen, the aperture stop and the projecting lens and a relative positional relationship therebetween are defined such that the following condition is satisfied: 0.35<θasx/arcsin(λ/p)<0.6.