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Spatial filter

About: Spatial filter is a research topic. Over the lifetime, 6170 publications have been published within this topic receiving 100451 citations.


Papers
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Patent
30 Apr 2001
TL;DR: In this paper, the shape of a correlation surface used in the navigation process is tested for the presence of a transverse ridge in the correlation surface, and two spatial filters have been developed that are respectively effective about the 45° and 135° inclinations of the Standard filter.
Abstract: Optical navigation upon grainy surfaces whose orientation is inclined at about 45° to the X and Y axes of the navigation mechanism is enhanced by: First, detect that a spatial filter in use is inappropriate for the orientation presently occurring, and; Second, employ a different and more appropriate spatial filter subsequent to such detection. Two spatial filters have been developed that are respectively effective about the 45° and 135° inclinations of the Standard filter. The shape of a correlation surface used in the navigation process is tested for the presence of a transverse ridge in the correlation surface. This generates control metrics whose filtered excursions are tracked by a control system that changes the spatial filter in use. The control system incorporates a time constant to prevent thrashing and excessive sensitivity to isolated random variations. The direction from which illumination arrives relative to the X and Y axes affects the range of angles (relative to, say, the Y axis) that a filter is effective, by changing the apparent size and proportions of the highlights and shadows that are the perceived features ultimately navigated upon. Stable operation of the control system can be enhanced by ensuring overlap of the filters' ranges, and can be promoted by dynamically altering the direction from which illumination reaches the navigation surface, so that it corresponds to, or varies in relation with, the filter in use.

48 citations

Journal ArticleDOI
TL;DR: A prototype semiautomatic optical processor has been developed that utilizes the Vander Lugt type complex spatial filters and the optical filter averaging technique employed is described.
Abstract: Presented are some results obtained from the application of matched spatial filtering techniques to the identification of biological specimens called diatoms (i.e., water algae). A prototype semiautomatic optical processor has been developed that utilizes the Vander Lugt type complex spatial filters. We describe the optical filter averaging technique employed and discuss our semi in situ developing method for the filters. The advantage of this method with regards to the critical position requirements for time sharing optical filters is also presented. The filter holder is mounted on X, Y stages and precision positioned under the control of a PDP-11-40 computer.

48 citations

Journal ArticleDOI
TL;DR: A study is presented of a Mach-Zehnder interferometer for the measurement of phasing errors of the type found in segmented telescopes and shows that with a pinhole much larger than the Airy disk and an optical path difference between the arms equal to a quarter of the wavelength, the interferometric signal is related to the second derivative of the wave front.
Abstract: A study is presented of a Mach-Zehnder interferometer for the measurement of phasing errors of the type found in segmented telescopes. We show that with a pinhole much larger than the Airy disk and an optical path difference between the arms equal to a quarter of the wavelength, the interferometric signal is related to the second derivative of the wave front. In this condition the signal is produced mostly by the segmentation errors and is marginally sensitive to other aberrations including atmospheric turbulence. The signal has distinguishable symmetric and antisymmetric properties that are related to segment aberrations. We suggest using the antisymmetric component of the signal to retrieve piston, tip, and tilt. The symmetric component of the signal serves as an estimate of the measurement error. In this way we proceed with a study of the errors associated with the misalignment of the interferometer, the segment edge imperfections, and the nonaveraged atmospheric perturbations. The entire study is performed on a theoretical basis, and numerical simulations are used to cross check the analytical results.

48 citations

Journal ArticleDOI
TL;DR: In this paper, a superpixel method for full spatial phase and amplitude control of a light beam using a digital micromirror device (DMD) combined with a spatial filter is presented.
Abstract: We present a superpixel method for full spatial phase and amplitude control of a light beam using a digital micromirror device (DMD) combined with a spatial filter. We combine square regions of nearby micromirrors into superpixels by low pass filtering in a Fourier plane of the DMD. At each superpixel we are able to independently modulate the phase and the amplitude of light, while retaining a high resolution and the very high speed of a DMD. The method achieves a measured fidelity $F=0.98$ for a target field with fully independent phase and amplitude at a resolution of $8\times 8$ pixels per diffraction limited spot. For the LG$_{10}$ orbital angular momentum mode the calculated fidelity is $F=0.99993$, using $768\times 768$ DMD pixels. The superpixel method reduces the errors when compared to the state of the art Lee holography method for these test fields by $50\%$ and $18\%$, with a comparable light efficiency of around $5\%$. Our control software is publicly available.

48 citations

Journal ArticleDOI
TL;DR: In this article, a radial birefringent crystal with a surface curvature ρ provides a radial variation of polarization retardation, and one or more of these radial elements in combination with a polarizer form a radial intensity filter (RIF).
Abstract: A birefringent crystal with a surface curvature ρ provides a radial variation of polarization retardation. One or more such radial birefringent elements in combination with a polarizer form a radial intensity filter (RIF). RIF’s permit the generation of a variety of radial transmittance and reflectance profiles that are useful in resonator and spatial filter applications.

48 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202321
202265
202181
2020144
2019180
2018179