Browsing by Subject "Spatial filtering"

Now showing 1 - 6 of 6

Open Access
Convolution and filtering in fractional fourier domains
(Springer-Verlag, 1994) Özaktaş, Haldun M.; Barshan, B.; Mendlovic, D.
Fractional Fourier transforms, which are related to chirp and wavelet transforms, lead to the notion of fractional Fourier domains. The concept of filtering of signals in fractional domains is developed, revealing that under certain conditions one can improve upon the special cases of these operations in the conventional space and frequency domains. Because of the ease of performing the fractional Fourier transform optically, these operations are relevant for optical information processing.
Open Access
Fractional Fourier transforms and their optical implementation. II
(Optical Society of America, 1993) Özaktaş, Haldun M.; Mendlovic, D.
The derivation of a linear transform kernel for fractional Fourier transforms is presented. Discussed in direct relation to fractal Fourier transforms are spatial resolution and the space-bandwidth product for propagation in graded-index media. Results show how fractional Fourier transforms can be made the basis of generalized spatial filtering systems.
Open Access
Graded-index fibers, Wigner-distribution functions, and the fractional Fourier transform
(Optical Society of America, 1994) Mendlovic, D.; Özaktaş, Haldun M.; Lohmann, A. W.
Two definitions of a fractional Fourier transform have been proposed previously. One is based on the propagation of a wave field through a graded-index medium, and the other is based on rotating a function's Wigner distribution. It is shown that both definitions are equivalent. An important result of this equivalency is that the Wigner distribution of a wave field rotates as the wave field propagates through a quadratic graded-index medium. The relation with ray-optics phase space is discussed.
Open Access
Multifrequency spatial filtering: a general property of two-dimensional photonic crystals
(Elsevier, 2016) Serebryannikov, A. E.; Colak, E.; Petrov, A.; Usik, P. V.; Özbay, Ekmel
Spatial filtering, an analog of frequency-domain filtering that can be obtained in the incidence angle domain at a fixed frequency is studied in the transmission mode for slabs of two-dimensional rod-type photonic crystals. In the present paper, the emphasis is put on the demonstration of the possibility to obtain various regimes of spatial filtering, i.e., band-stop, band-pass, and low-pass filtering in different frequency ranges in one simple configuration. The operation is based on the use of several Floquet-Bloch modes with appropriate dispersion properties, so that such one or two co-existing mode(s) contribute to the forming of a proper filter characteristic within each specific frequency range. It is shown that high-efficiency transmission and steep switching between pass and stop bands can be obtained in the angle domain for wide ranges of variation of the problem parameters. In particular, by varying the rod-diameter-to-lattice-constant ratio, one attains lots of freedom in the engineering of spatial filters with desired transmission characteristics.
Open Access
A simple mie-resonator based meta-array with diverse deflection scenarios enabling multifunctional operation at near-infrared
(De Gruyter Open, 2020) Aalizadeh, Majid; Serebryannikov, A. E.; Özbay, Ekmel; Vandenbosch, G. A. E.
Deflection, a basic functionality of wavefront manipulation is usually associated with the phase-gradient metasurfaces and the classical blazed gratings. We numerically and experimentally demonstrate an unusually wideband and simultaneously wide-angle deflection achieved at near-infrared in reflection mode for a periodic (nongradient), ultrathin meta-array comprising only one silicon nanorod (Mie resonator) per period. It occurs in the range where only the first negative diffraction order and zero order may propagate. Deflection serves as the enabler for multifunctional operation. Being designed with the main goal to obtain ultra-wideband and wide-angle deflection, the proposed meta-array is also capable in spatial filtering and wide-angle splitting. Spatial filtering of various types can be obtained in one structure by exploiting either deflection in nonzero diffraction orders, or the specular-reflection (zero-order) regime. Thus, the role of different diffraction orders is clarified. Moreover, on–off switching of deflection and related functionalities is possible by changing polarization state of the incident wave. The suggested device is simple to fabricate and only requires cost-effective materials, so it is particularly appropriate for the large-area fabrication using nanoprint lithography. Ultra-wideband wide-angle and other deflection scenarios, along with the other functionalities, are promising for applications in optical communications, laser optics, sensing, detection, and imaging.
Open Access
Spatial and spatial-frequency filtering using one-dimensional graded-index lattices with defects
(ELSEVIER, 2009) Usik, P. V.; Serebryannikov, A. E.; Özbay, Ekmel
The potential of one-dimensional, periodic, graded-index, isotropic dielectric lattices with defects in multiband spatial and spatial-frequency filtering is studied. It is shown that both narrow- and wide-bandpass filters can be obtained at a proper choice of the number, location, and parameters of the defects placed inside the relatively thin slabs. The peculiarities of achieving multibandness for narrow- and wide-bandpass filters are discussed. Multiband narrow-bandpass filtering is closely related to the transmission features that are associated with Fabry-Pérot resonators with semitransparent planar mirrors. Correspondingly, the observed transmission can be interpreted in terms of the equivalent parameters of such resonators. In particular, it is shown that the resonators filled with an ultralow-index medium can be mimicked, so that defect-mode angle-domain spectrum can be rarefied at large angles of incidence. The obtained results are also expected to be applicable for prediction of the angle-domain behavior of transmission in case of piecewise-homogeneous multilayers.