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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
Norman Nathan Axelrod1
10 Dec 1969
TL;DR: In this article, an optical spatial filtering technique for detecting hole-type defects and excess spot defects in photomasks used in making microcircuits is described, where an approximate form factor intensity filter provides suppression of the regularly shaped mask features.
Abstract: This disclosure describes an optical spatial filtering technique for detecting hole-type defects and excess spot defects in photomasks used in making microcircuits. An approximate form factor intensity filter provides suppression of the regularly shaped mask features. For masks with features whose boundaries are along only the X-Y direction, this filter advantageously is a cross placed in the transform plane. With rectangular features suppressed, only nonrectangular defect data passes. Spots as small as 0.1 mil are detected and displayed on a TV monitor; or, using a photomultiplier tube, signals are stored on an oscilloscope or by a recorder for analysis, or counted with a pulse counter. Masks or circuits on opaque substrates are also inspected by this method.

43 citations

Journal ArticleDOI
TL;DR: A spatial filtering interferometry setup that employs a periodic spatial filter with either cosine transmittance or binary phase modulation to produce an interference pattern of the two input fields at the output plane of the system.
Abstract: We discuss a spatial filtering interferometry setup that employs a periodic spatial filter with either cosine transmittance or binary phase modulation. The setup's input plane is formed by two separate windows, one of which supports a phase object and the other, a reference beam. Using the appropriate frequency and orientation of the filter produces an interference pattern of the two input fields at the output plane of the system. The main attributes and advantages of the setup are discussed and experimentally illustrated with the example of a binary phase periodic filter implemented with a spatial light modulator.

43 citations

Journal ArticleDOI
TL;DR: In this article, the authors proposed to use the time-frequency processing approach, which formulates a spatial filter that can enhance a target direction based on local direction of arrival estimates at individual timefrequency bins.
Abstract: When a micro aerial vehicle (MAV) captures sounds emitted by a ground or aerial source, its motors and propellers are much closer to the microphone(s) than the sound source, thus leading to extremely low signal-to-noise ratios (SNR), e.g., −15 dB. While microphone-array techniques have been investigated intensively, their application to MAV-based ego-noise reduction has been rarely reported in the literature. To fill this gap, we implement and compare three types of microphone-array algorithms to enhance the target sound captured by an MAV. These algorithms include a recently emerged technique, time-frequency spatial filtering, and two well-known techniques, beamforming and blind source separation. In particular, based on the observation that the target sound and the ego-noise usually have concentrated energy at sparsely isolated time-frequency bins, we propose to use the time-frequency processing approach, which formulates a spatial filter that can enhance a target direction based on local direction of arrival estimates at individual time-frequency bins. By exploiting the time-frequency sparsity of the acoustic signal, this spatial filter works robustly for sound enhancement in the presence of strong ego-noise. We analyze in details the three techniques and conduct a comparative evaluation with real-recorded MAV sounds. Experimental results show the superiority of blind source separation and time-frequency filtering in low-SNR scenarios.

43 citations

Journal ArticleDOI
TL;DR: In this paper, the phase-locked mode is demonstrated in fiber-laser arrays coupled to a common resonator containing a spatial filter, and the ability to maintain phase locking is attributed to a self-adjusting process, which can be found only in systems with a combination of high gain, long length, low Q, and broad gain bandwidth.
Abstract: Phase locking has been demonstrated in fiber lasers coupled to a common resonator containing a spatial filter. The phase-locked mode is highly stable despite the phase variations in the individual elements caused by thermal and mechanical effects. The ability to maintain phase locking is attributed to a self-adjusting process, which can be found only in systems with a combination of high gain, long length, low Q, and broad gain bandwidth, all of which can be met in fiber laser arrays.

43 citations

Journal ArticleDOI
TL;DR: This section was established to reduce the lead time for the publication of Letters containing new, significant material in rapidly advancing areas of optics judged compelling in their timeliness.
Abstract: Matched filtering is the key concept in coherent optical pattern recognition. Unfortunately, matched filters are more sensitive to some things (nonconsequential variations in size, rotation angle, etc.) and less sensitive to other things (differences between object classes) than we might desire. The generalized matched filter is a filter tailored to the specific requirements of the task. It contains the matched filter as a special case.

43 citations


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