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.
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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.
30 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: 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
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.
5 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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01 Dec 2015
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
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.
2 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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References
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Abstract: The second edition of this respected text considerably expands the original and reflects the tremendous advances made in the discipline since 1968. All material has been thoroughly updated and several new sections explore recent progress in important areas, such as wavelength modulation, analog information processing, and holography. Fourier analysis is a ubiquitous tool with applications in diverse areas of physics and engineering. This book explores these applications in the field of optics with a special emphasis on applications to diffraction, imaging, optical data processing, and holography. This book can be used as a textbook to satisfy the needs of several different types of courses, and it is directed toward both engineers ad physicists. By varying the emphasis on different topics and specific applications, the book can be used successfully in a wide range of basic Fourier Optics or Optical Signal Processing courses.
12,152 citations
Book•
01 Jan 1968
Abstract: The second edition of this respected text considerably expands the original and reflects the tremendous advances made in the discipline since 1968. All material has been thoroughly updated and several new sections explore recent progress in important areas, such as wavelength modulation, analog information processing, and holography. Fourier analysis is a ubiquitous tool with applications in diverse areas of physics and engineering. This book explores these applications in the field of optics with a special emphasis on applications to diffraction, imaging, optical data processing, and holography. This book can be used as a textbook to satisfy the needs of several different types of courses, and it is directed toward both engineers ad physicists. By varying the emphasis on different topics and specific applications, the book can be used successfully in a wide range of basic Fourier Optics or Optical Signal Processing courses.
9,252 citations
Abstract: There are several methods for optically subtracting one image from another in order to detect differences between scenes or between photographs of scenes. There are many applications for such a technology, including earth resource studies, meteorology, automatic surveillance and/or inspection, pattern recognition, urban growth studies, and bandwidth compression. This paper presents an overview of several techniques for obtaining optical image subtraction, including holographic, interferometric, coding, and positive-negative superposition methods. As part of this review, a table is presented summa-rizing and comparing the characteristics of more than twenty-five approaches. An extensive bibliography is also given.
80 citations
42 citations
TL;DR: Improvement of microcalcifications in a mammogram for early diagnosis of breast cancer is the main focus and the intensity dependent refractive index can be exploited as a phase filter for phase contrast imaging with a coherent source.
Abstract: This paper briefly reviews the basics of optical Fourier techniques (OFT) and applications for medical image processing as well as phase contrast imaging of live biological specimens. Enhancement of microcalcifications in a mammogram for early diagnosis of breast cancer is the main focus. Various spatial filtering techniques such as conventional 4f filtering using a spatial mask, photoinduced polarization rotation in photosensitive materials, Fourier holography, and nonlinear transmission characteristics of optical materials are discussed for processing mammograms. We also reviewed how the intensity dependent refractive index can be exploited as a phase filter for phase contrast imaging with a coherent source. This novel approach represents a significant advance in phase contrast microscopy.
36 citations
"Real-time edge detection by cyclic-..." refers background in this paper
...A comprehensive review of several of these Fourier plane techniques is found in [6]....
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