• Title/Summary/Keyword: Apodization function

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Point Spread Function of Optical Systems Apodized by Semicircular Array of 2D Aperture Functions with Asymmetric Apodization

  • Reddy, Andra Naresh Kumar;Sagar, Dasari Karuna
    • Journal of information and communication convergence engineering
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    • v.12 no.2
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    • pp.83-88
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    • 2014
  • The simultaneous suppression of sidelobes and the sharpening of the central peak in the process of diffraction pattern detection based on asymmetric apodization have been investigated. Asymmetric apodization is applied to a semicircular array of two-dimensional (2D) aperture functions, which is a series of 'coded-phase arrays of semicircular rings randomly distributed over the central circular region of a pupil function' and is similar to that used in the field of diffractive optics. The point spread function (PSF) of an imaging system with asymmetric apodization of the discrete type has been found to possess a good side with suppressed sidelobes, whereas its bad side contains enhanced sidelobes. Further, the diffracted field characteristics are obtained in the presence of these aperture functions. Asymmetric apodization is helpful in improving the performance of the optical gratings or 2D arrays used in real-time imaging techniques.

Characteristics of dispersion compensation for apodized linearly-chirped optical fiber gratings (Apoidzed 선형처프된 광섬유 grating의 분산보상특성에 대한 연구)

  • 조상연;이경식
    • Journal of the Korean Institute of Telematics and Electronics S
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    • v.35S no.1
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    • pp.23-28
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    • 1998
  • A linearly-chirped fiber grating for the dispersion compensation over 520km of 1.3.mu.m single mode fiber is designed. The compensation characteristics of the gratings apodized each with Gaussian and hyperbolic tangent function are studied. the ripples in reflection and delay curves are coniderably reduced for both cases, but the reflection bandwidth for the hyperbolic tangent apodization is much less shrinked than that of the Gaussian apodization.

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Design of Diffractive Optical Element for Improving Jitter Characteristics of Optical Pickup (광 픽업 장치에서의 지-터 특성개선을 위한 회절 광학소자의 설계)

  • Lee Gun-Ki;Jung Won-Geun;Lee Ju-Won;Kim Young-Il;Jun Jae-Chul
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.8 no.8
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    • pp.1810-1817
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    • 2004
  • A diffractive optical element(DOE) for an optical pickup system is proposed in this thesis. Optimization algorithms are used to synthesise the DOE to meet a detailed specification of the two kind of cost function. The one isso called as apodization which refers to the process of suppressing the secondary maxima and the other is so called as sharpness which refers to the process of reducing the size of primary maxima. The result obtained by simplex optimization method is that the apodization and sharpness are well achieved separately. In apodization, the secondary maxima is reduced up to 39%. And in sharpness, the size of first maxima is reduced to 95.2%.

SIR analysis for Enhancing Image Quality in Underwater Acoustic Lens System (수중음향렌즈 카메라에서 영상 품질 향상을 위한 SIR 분석)

  • Lee, Jieun;Im, Sungbin;Shim, Taebo
    • Journal of the Institute of Electronics and Information Engineers
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    • v.51 no.4
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    • pp.181-190
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    • 2014
  • The underwater acoustic lens system is one of the systems getting high-resolution images on the seafloor by the beam forming method using acoustic lens. The beam forming using acoustic lenses reduces complexity and driving power. When receiving an incoming beam with the acoustic lens array, beam pattern analysis and arrangement problem of the array sensor must be addressed. Introducing SIR (Signal to Interference Ratio), the relationship among sensor interval, beam pattern and image quality would be analyzed. Generally if the sensor interval getting wider, the less effect of the side lobes makes SIR high. If the amplitude of a side lobe is high, SIR is generally getting low. The type of the apodization function changes the width, shape and amplitude of both main lobe and side lobes. Thus an appropriate apodization function can improve SIR. In this paper, SIR is stable at the sensor interval of 13mm with 0-10dB, which is not high relatively. By applying the Chebyshev function, the SIR becomes 80dB over the sensor interval of 37 mm or higher. The Hann and triangular functions demonstrate better SIR when the sensor interval becomes narrower.

A New Tailored Sinc Pulse and Its Use for Multiband Pulse Design

  • Park, Jinil;Park, Jang-Yeon
    • Investigative Magnetic Resonance Imaging
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    • v.20 no.1
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    • pp.27-35
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    • 2016
  • Purpose: Among RF pulses, a sinc pulse is typically used for slice selection due to its frequency-selective feature. When a sinc pulse is implemented in practice, it needs to be apodized to avoid truncation artifacts at the expense of broadening the transition region of the excited-band profile. Here a sinc pulse tailored by a new apodization function is proposed that produces a sharper transition region with well suppression of truncation artifacts in comparison with conventional tailored sinc pulses. A multiband pulse designed using this newly apodized sinc pulse is also suggested inheriting the better performance of the newly apodized sinc pulse. Materials and Methods: A new apodization function is introduced to taper a sinc pulse, playing a role to slightly shift the first zero-crossing of a tailored sinc pulse from the peak of the main lobe and thereby producing a narrower bandwidth as well as a sharper pass-band in the excitation profile. The newly apodized sinc pulse was also utilized to design a multiband pulse which inherits the performance of its constituent. Performances of the proposed sinc pulse and the multiband pulse generated with it were demonstrated by Bloch simulation and phantom imaging. Results: In both simulations and experiments, the newly apodized sinc pulse yielded a narrower bandwidth and a sharper transition of the pass-band profile with a desirable degree of side-lobe suppression than the commonly used Hanning-windowed sinc pulse. The multiband pulse designed using the newly apodized sinc pulse also showed the better performance in multi-slice excitation than the one designed with the Hanning-windowed sinc pulse. Conclusion: The new tailored sinc pulse proposed here provides a better performance in slice (or slab) selection than conventional tailored sinc pulses. Thanks to the availability of analytical expression, it can also be utilized for multiband pulse design with great flexibility and readiness in implementation, transferring its better performance.

Design of narrow band-pass filter using two fiber bragg gratings (광섬유 격자소자를 이용한 협대역 투과 필터의 설계)

  • 임종훈;이경식
    • Journal of the Korean Institute of Telematics and Electronics D
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    • v.35D no.8
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    • pp.82-88
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    • 1998
  • We propose and design a new type of anrrow band-pass optical filter based on two fiber gratings with different reflection wavelength. The ripples occur in the spectra of the filter with two uniform fiber gratings. Our simulation results also show that the ripples disappear with the fiber gratings apodized to both gaussian and hyperbolic tangent function. The hyperbolic tangent function seems to be a better apodization function for improving the filter's performance in terms of narrow pass bandwidth and high transmission.

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A Study on Sidelobe Reduction Using Kaiser Window in Ultrasonic Imaging System (초음파 영상시스템에서 카이저 윈도우를 이용한 사이드 로브 감축에 관한 연구)

  • Na, Byeong-Yoon;Ahn, Young-Bok;Jeong, Mok-Kun
    • Journal of Biomedical Engineering Research
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    • v.17 no.2
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    • pp.189-200
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    • 1996
  • In this paper, we compared the performance of the Kaiser window with those of others as a weight function of well known anodization technique for regression of side lobe in a field pattern resulted from focusing of transducer array. The Kaiser window is an window providing many types of curve with several variables. In order to compare performance of the Kaiser window as the weight function, anodization results of the previously used Hamming window function and the Matched Gaussian function are compared Result of computer simulation, the pertormance of Kaiser window with $\delta$=0.0025 in side lobe regression was better than that of Hamming window or Matched Gausian function.

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SAW Filter Transmission Characteristics Design with Genetic Algorithm

  • Park, Kyu­-Chil;Kim, Seok­-Jae
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.7 no.8
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    • pp.1767-1775
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    • 2003
  • The SAW device is extensively used as a electro$.$mechanical band­pass filter in which a two­pairs of interdigital transducers are provided over the surface of the piezoelectric substrate. For the design requirement, the central frequency and the bandwidth of the passband, and the attenuation level of the stopband region are specified. The configuration is made so as to satisfy the specification given. The central frequency is mainly determined by the distance between the pair of the finger electrodes. The design is considered as an optimization problem with which the error norm, the distance between the desired characteristics and the calculated for a given model is to be minimized. The delta function model and the electrical equivalent circuit model are utilized to represent the SAW filter characteristics. Genetic algorithm is used for optimization in which apodization of the transducer fingers is chosen as a design variable.

SAR IMAGE ENHANCEMENT BASED ON THE PHASE EXTENSION DECONVOLUTION METHOD (위상 확장 디콘볼루션 방식을 이용한 SAR 영상 향상)

  • Do, Dae-Won;Song, Woo-Jin;Kwon, Jun-Chan
    • Proceedings of the IEEK Conference
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    • 2000.09a
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    • pp.389-392
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    • 2000
  • In this paper, we propose a novel post processing method of deconvolution for SAR images based on phase extension inverse filtering, which improves spatial resolution as well as effectively eliminates sidelobes with low computational complexity. It extends the bandwidth only to control the magnitude of the processed SAR data without distortions of the phase in frequency domain unlike the other techniques such as spatially variant apodization (SVA), and other deconvolution techniques. We compare the image processed by the proposed method with images processed by uniform weighting function, Hamming weighting function whose coefficient is 0.75, and SVA.

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Gaussian apodization for annular pupil (윤대 동구에 대한 Gaussian Apodization)

  • 송영란;이민희;이상수
    • Korean Journal of Optics and Photonics
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    • v.7 no.3
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    • pp.196-199
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    • 1996
  • The amplitude LSF(Line spread function, $C_1e^{{o^2}{x^2}}$ or amplitude impulse) of the Gaussian apodized annular pupil is found to be same to that of the full aperture LSF($C_0e^{{o^2}{x^2}}$). $C_0$ and $C_1$ depending on $\sigma$, ${\omega}_0=\frac{2{\pi}}{\lambda}\;\frac{a_0}{l}$ and ${\omega}_0'=\frac{2{\pi}}{\lambda}\;\frac{a_0'}{l}$ which are the geometric parameter and pupil coordinates of the annular pupil. The important inequality relation among ${\omega}_0,\;{\omega}_0'$, a (fraction of diffraction amplitude) and $\sigma$ is obtained. It is $\frac{{\omega}_0}{\sqrt{2}}<{\sigma}{\le}(\frac{1-a}{2a})^{1/2}\;{\omega}_0$, and in the case of $a=e^{-1},\;a_0'{\le}0.34a_0$. The case of λ=0.013${\mu}{\textrm}{m}$, l=20 cm, $a_0=5cm$ and $a_0=0.34a_0=1.7cm$ give a Gaussian apodized superresolution ${\Delta}=\frac{\sqrt{log2}}{\sigma}=0.008{\mu}m$ annular pupil with the intensity signal equal to $e_{-2}$ times the signal obtainable by using the full aperture system(a=1)

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