Real-time edge detection by cyclic-path polarization interferometer
TL;DR: In a triangular path cyclic interferometer employing a polarizing beam splitter, using a linear polarizer in the path of the orthogonally polarized imaging beams, it is possible to achieve amplitude subtraction between the two images, resulting in an edge-enhanced image of the sample.
Abstract: In a triangular path cyclic interferometer employing a polarizing beam splitter (PBS), the two counterpropagating beams are orthogonally polarized. A sample placed almost equidistant from the PBS is imaged by a lens placed in the path of the emerging beams so that two defocused images of the sample are recorded on a CCD. Using a linear polarizer in the path of the orthogonally polarized imaging beams, it is possible to achieve amplitude subtraction between the two images, resulting in an edge-enhanced image of the sample. The proposed real-time edge-enhancement technique is experimentally demonstrated.
Citations
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TL;DR: It is shown that either isotropic or anisotropic edge enhancement in any desired orientation can be performed by operating the same spatial filter setup in different illuminating polarization states.
Abstract: Using polarization as an additional parameter apart from amplitude and phase in spatial filtering experiments offers additional advantages and possibilities. An S-waveplate that can convert a linearly polarized light into radially or azimuthally polarized light can also be used for isotropic edge enhancement. For anisotropic edge enhancement, introduction of a polarizer at the output was recommended and edge selection was done by orientation of the polarizer. But the full potential of the S-waveplate as a spatial filter has not been exploited so far. Unlike the standard amplitude and phase-based Fourier filters, which are independent to the state of polarization of the illuminating beam, the S-waveplate acts in a different way depending on the state of polarization. The edge selection does not need to be carried out by changing the orientation of the polarizer. With a fixed polarizer at the output, we show that either isotropic or anisotropic edge enhancement in any desired orientation can be performed by operating the same spatial filter setup in different illuminating polarization states.
41 citations
Cites methods from "Real-time edge detection by cyclic-..."
...Among the polarization-based filtering methods, image subtraction is one of the methods to extract the edges [27]....
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TL;DR: In this article, a method for generating carrier fringes and a nonconventional rotational shear in a triangular cyclic-path interferometer, while simultaneously suppressing the presence of typical lateral and radial shearing, is presented.
Abstract: This work presents a method for generating carrier fringes and a nonconventional rotational shear in a triangular cyclic-path interferometer, while simultaneously suppressing the presence of typical lateral and radial shearing. To carry out this method, a 4f optical system is implemented into the cyclic interferometer. The most important contributions of this paper are its demonstration of the linear dependence of the movable mirror displacement with the carrier frequency introduced, and the realization of a nonconventional rotational shearing interferometer. Additionally, we think that one of its possible potential applications is the observation of the angular derivative of parallel projections of a phase object placed at the output plane, generating a great advantage in edge-enhancement optical tomography. In this paper, we develop a theoretical model and show experimental results.
6 citations
Cites methods from "Real-time edge detection by cyclic-..."
...Introduction A cyclic path optical configuration (CPOC) has been used extensively to measure many physical quantities in many fields in science and technology [1-21]....
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TL;DR: Experimental results presented in this Letter could provide an insight into the momentum change associated with the energy redistribution in the fundamental phenomenon of optical interference.
Abstract: A scheme to study the effect of residual phase gradients in an optical interference between two out-of-phase Gaussian beams is proposed. In a Sagnac interferometer configured to provide a null output, a variable linear phase swept across the null point unfolds an optical field rotation due to an apparently negligible residual phase gradient present orthogonal to the linear phase sweep. As the optical beam that rotates around its propagation axis carries orbital angular momentum, the experimental results presented in this Letter could provide an insight into the momentum change associated with the energy redistribution in the fundamental phenomenon of optical interference.
5 citations
TL;DR: In this article, a cyclic interferometric configuration is chosen to maintain the stability of the operation against external vibrations, and a wave plate is inserted into the common paths to introduce an intrinsic phase difference between the orthogonal polarized beams.
Abstract: An alternative polarization phase-shifting technique is proposed to determine the thickness of transparent thin-films. In this study, the cyclic interferometric configuration is chosen to maintain the stability of the operation against external vibrations. The incident light is simply split by a non-polarizing beam splitter cube to generate test and reference beams, which are subsequently polarized by a polarizing beam splitter. Both linearly polarized beams are orthogonal and counter -propagating within the interferometer. A wave plate is inserted into the common paths to introduce an intrinsic phase difference between the orthogonal polarized beams. A transparent thin-film sample, placed in one of the beam tracks, modifies the output signal in terms of the phase retardation in comparison with the reference beam. The proposed phase-shifting technique uses a moving mirror with a set of “fixed” polarizing elements, namely, a quarter-wave retarder and a polarizer, to facilitate phase extraction without rotating any polarizing devices. The measured thicknesses are compared with the measurements of the same films acquired using standard equipment such as the field-emission scanning electron microscope and spectroscopic ellipsometer. Experimental results with the corresponding measured values are in good agreement with commercial measurements. The system can be reliably utilized for non-destructive thickness measurements of transparent thin -films.
3 citations
Additional excerpts
...In this study, a cyclic interferometric configuration, which is less prone to the instability due to environmental disturbances, is chosen [16, 17]....
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01 Dec 2015
TL;DR: In this paper, a scheme to sense the residual phase gradients in an optical interference of two out-of-phase Gaussian beams is proposed, which is implemented using a Sagnac interferometer configured to provide a null output.
Abstract: A scheme to sense the residual phase gradients in an optical interference of two out-of-phase Gaussian beams is proposed. Its implementation by detecting the residual phase gradient as an optical field rotation in a Sagnac interferometer, configured to provide a null output is presented.
3 citations
References
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TL;DR: The method is based on the capability of twisted-nematic liquid-crystal displays to traduce the image information in changes of the state of polarization of the light to generate simultaneously a "positive" and a "negative" replica of the digital image displayed on the LCD.
Abstract: We present an image processing method for nondirectional edge extraction/enhancement. The method is based on the capability of twisted-nematic liquid-crystal displays (LCDs) to traduce the image information in changes of the state of polarization of the light, which allows us to generate simultaneously a "positive" and a "negative" (i.e., contrast-reversed) replica of the digital image displayed on the LCD. The negative image is low-pass filtered in a novel polarization-selective 4f optical processor. When the smoothed negative image is imagined together with the original image, an image with nondirectional edge enhancement is obtained. Unlike other Fourier methods presented in the literature, the proposed technique provides a simple way to control the relative amount of high frequencies present in the final image. The proposed method does not involve numerical processing, and, thus, it could be a useful tool for edge extraction/enhancement in large images in real-time applications. Validation experiments are presented.
11 citations
TL;DR: In this paper, the authors explored the possibility of using a biconvex quartz lens as a spatial frequency filter for real-time edge enhancement and periodic noise removal, and experimental results were also presented.
Abstract: It is well known that a suitably shaped birefringent material, placed between two polarizers, exhibits a spatial variation in amplitude transmittance. The present article explores the possibility of using such an arrangement as a spatial frequency filter. The advantage of such filters is that the nature of filtering achievable can be changed by rotating any of the two polarizers. The specific case of a biconvex quartz lens as a spatial frequency filter is considered and techniques for real-time edge enhancement and periodic noise removal are discussed. Experimental results are also presented.
10 citations
TL;DR: A programmable spatial-filtering system using bacteriorhodopsin (BR) film as a programmable, optically addressed spatial light modulator illuminated by a single wavelength of light is described.
Abstract: We describe a programmable spatial-filtering system using bacteriorhodopsin (BR) film as a programmable, optically addressed spatial light modulator illuminated by a single wavelength of light. We use a computer-controlled mirror scanning system to write time-varying filter functions to the BR film and present proof-of-principle experimental results that demonstrate several elementary filtering operations.
9 citations
"Real-time edge detection by cyclic-..." refers background in this paper
...A real-time, selfadaptive spatial plane filter using the photoinduced anisotropy of Bacterio-Rhodopsin films placed on the Fourier plane and illuminated by a polarized actinic beam has also been demonstrated [5]....
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TL;DR: A modified sinogram able to reconstruct edge-enhanced phase slices is obtained and it is proved that they share two properties with the Radon transform: its symmetry property and its zeroth-moment conservation.
Abstract: In optical tomography, isotropic edge-enhancement of phase-object slices under the refractionless limit approximation can be reconstructed using spatial filtering techniques The optical Hilbert-transform of the transmittance function leaving the object at projection angles ϕ∈(00,3600), is one of these techniques with some advantages The corresponding irradiance of the so modified transmittance is considered as projection data, and is proved that they share two properties with the Radon transform: its symmetry property and its zeroth-moment conservation Accordingly, a modified sinogram able to reconstruct edge-enhanced phase slices is obtained In this paper, the theoretical model is amply discussed and illustrated both with numerical and experimental results
5 citations