• Title/Summary/Keyword: Annular grating

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Spatial Frequency Filtering Characteristics of Annular Phase Gratings (고리형 위상 격자의 공간 주파수 필터 효과)

  • 김인길;고춘수;임성우;오용호;이재철
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.17 no.9
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    • pp.994-1000
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    • 2004
  • We studied the characteristics of annular phase gratings as spatial frequency filters. We first calculated the Fraunhofer diffraction patterns of annular gratings and then got the modulation transfer function (MTF) from the zeroth order Hankel transform of the intensity distribution function. Binaryphase annular grating shows higher diffraction efficiency than binary phase rectangular grating. But the MTF decreases linearly in the low-frequency region as that of rectangular grating does. The diffraction pattern of 4-phase annular grating is similar to that of 2-phase grating and hence MTFs of the two are much alike. For 8-phase annular grating, the 7th order diffracted beam is the lowest one next to the first. Consequently, the diffraction efficiency is very high and the MTF graph is curved upward. The diffracted beams except the first order are negligible and hence the MTF characteristics are more improved in the case of 16-phase grating. But the degree of improvement becomes lowered c(Impaled with 8-phase grating. We made a 16-phase annular grating and measured its MTF. The experimental result agrees well with the calculated one.

Modified Illumination with a Concentric Circular Grating at the Backside of a Photomask (마스크 뒷면에 동심원 격자를 사용한 변형조명 방법)

  • Oh, Yong-Ho;Go, Chun-Soo;Lim, Sungwoo;Lee, Jai-Cheol
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.18 no.3
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    • pp.212-215
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    • 2005
  • Modified illumination techniques have been used to enhance the resolution of the sub-wavelength lithography. But, since they shield the central part of incident light, the light efficiency is seriously degraded, which in turn reduces the throughput of a lithography process. In this research, we introduced an annular illumination structure that enhances the light efficiency with a concentric circular grating at the backside of a photomask. The efficiency of the structure was theoretically analyzed.

Modified Illumination by Binary Phase Diffractive Patterns on the Backside of a Photomask (마스크 뒷면에 2 위상 회절 격자를 구현한 변형 조명 방법)

  • 이재철;오용호;고춘수
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.17 no.7
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    • pp.697-700
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    • 2004
  • We propose a method that realizes the modified illumination by implementing a binary phase grating at the backside of a photomask. By modeling the relationship between the shape of a grating on the photomask and the light intensity at the pupil plane, we developed a program named MIDAS that finds the optimum grating pattern with a stochastic approach. After applying the program to several examples, we found that the program finds the grating pattern for the modified illumination that we want. By applying the grating at the backside of a photomask, the light efficiency of modified illumination may be improved.

Optimal design of a concave annular array transducer to generate high intensity focused ultrasound (고강도 집속 초음파 발생용 오목한 환상형 배열 트랜스듀서의 최적설계)

  • Choi, Euna;Roh, Yongrae
    • The Journal of the Acoustical Society of Korea
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    • v.35 no.6
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    • pp.452-465
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    • 2016
  • In this study, the structure of a concave annular array transducer was optimized to generate high intensity focused ultrasound for medical therapeutic application. The transducer has a phased array structure composed of several concentric channels that have 40 mm as the radius of curvature. We derived theoretical equations to analyze the sound field of the transducer and verified the validity of the equations by comparing the results calculated by the equations with those from finite element analyses. We also checked the possibility of dynamic focusing at around the geometric focal point. Further, the level of a grating lobe occurring at an unwanted position in the transducer sound field was confirmed to be reducible through the relation between the number of channels and the frequency of the transducer. Hence, the structure of the transducer was optimized to place the main lobe within a specific range from the zenith while systematically reducing the level of the maximum sidelobe including the grating lobe. The designed structure showed the performance better than that targeted at all the focal points.

The analysis of grating lines' reformation replication using fraunhofer approximation (Fraunhofer 근사로 해석한 회절격자 무늬의 복제에 관한 연구)

  • 전영석;이성묵;신희명;정해빈
    • Korean Journal of Optics and Photonics
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    • v.3 no.3
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    • pp.155-160
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    • 1992
  • 1)iscussed in this paper are the effects of phase modulation on the line spread functions (LSF) and MTFs of ;I binocular objective system. The binocular objective lens is made in Korea. It has rotationally symmetric aberrations. The LSFs and MTFs are measured experimentally. The phase modulation is carried out by applying phase retardation n on the aperture. The area where the phase is not retarded presents a double annular type. The OTF curves of phase modulated aperture are compared with that of unmodulated aperture. The comparison shows that there is the aberration compensation effect in aberration loaded system. Therefore the performance of many optical system can be improved without any loss of light energy by properly modulating the phase on the aperture.

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