• Journal of the Optical Society of Korea
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• v.10 no.4
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• pp.145-156
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• 2006

In the field of ophthalmology, many diagnostic instruments based on optical technology have been developed, such as refractometer, keratometer, corneal mapper, tonometer, fundus camera, slit lamp, laser scan ophthalmoscope and optical coherence tomography. Among them, the refractometer that is used for measuring the refractive power of the human eye has the long research history and various types have been developed. However the efforts to realize more accurate and precise measurement are still in progress. The wavefront analyzer commercialized in recent years is an excellent outcome of such efforts. In this paper, a brief account of the developmental history of various refractometers including the wavefront analyzer is summarized, and the underlying measurement principle is introduced in the view of optics. Finally, the technical issues that should be solved for getting better performance are discussed.

• Korean Journal of Optics and Photonics
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• v.8 no.1
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• pp.73-79
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• 1997

We analyzed the variation of the focus error signal with the effect of land and groove, wavefront error, and optical system parameter variation for the knife-edge and astigmatism methods on the Land/Groove recordable optical disc, using a numerical simulation method. We verified causes of the zero-cross-shift that took place by the effect of land and groove by analyzing the diffraction beam including defocus wavefront errors. We also found that the sensitivty of the focus error signal was reduced by the effect of land and groove in the astigmatism method, as in the analysis of the focus error signal with the each order of the diffraction beam.

• Proceedings of the KIEE Conference
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• 1987.07a
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• pp.101-104
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• 1987

The problem considered is that of calculating the angles of arrival of a multimoded signal at an antenna array from simultaneous measurements of the amplitude and the phase of the signal in each element of the array. The method of wavefront analysis 15 applied to a 4-element direction finder of the Adcock type. A simulated problem is constructed with the aid of suitable computer programs developed here.

• Proceedings of the KIEE Conference
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• 2007.11a
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• pp.138-139
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• 2007

The use of conventional Twyman and Fizeau interferometers inevitably fails in testing high precision optics because of errors always existing in reference elements producing the reference wavefront. Therefore it is necessary to apply to this task the interferometers of a radically new type, which are able to produce perfect reference wavefront with the help of light diffraction by a small obstacle or pinhole. In this paper new theoretical approaches and schematics of point diffraction interferometers are considered in detail with paying attention to constructive reliability. Such interferometers do not use reference optical surfaces and readily provide adequate estimation of errors and aberrations value of 0.01 wavelengths.

• Proceedings of the Optical Society of Korea Conference
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• 2000.08a
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• pp.44-45
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• 2000

Shack-Hartmann 센서로부터 얻어진 기울기 정보로부터 파면을 재구성하고 분석하기 위해서는 각각의 점 영상에 대한 위상 구배로부터 파면의 위상을 재구성할 수 있는 수학적인 알고리즘이 필요하다. 파면의 위상을 재구성하기 위한 알고리즘은 Hudgin, Fried, Southwell이 제시한 세 가지 방법에 대한 연구결과가 가장 많이 알려져 있다. 본 연구에서는 CCD 카메라로부터 전송된 디지털 영상에서 각각의 점 영상의 중심점을 추출하여 점 영상의 이동정보로부터 수평과 수직방향의 기울기를 계산하고, 이를 바탕으로 최소제곱법(least-square fitting)을 사용하여 위상을 재구성하였다. 파면의 기울기 정보로부터 파면을 재구성하기 위해 기존의 이론을 바탕으로 행렬계산법을 사용하여 각각의 경우를 일반화하였고, 위상의 복구와 파면의 보정에 따른 해석적인 오차의 관계를 논의하였다. (중략)

• Current Optics and Photonics
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• v.4 no.4
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• pp.277-285
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• 2020

Computer-generated holograms (CGH) are the core devices to solve the problem of freeform surface measurement. In view of the overlay error introduced in the manufacturing process of CGH, this paper proposes an evaluation model for analyzing the overlay error of CGH. The detection method of extracting CGH profile information by an ultra-depth of field micro-measurement system is presented. Furthermore, based on the detection method and technical scheme, the effect of overlay error on the wavefront accuracy of CGH can be evaluated.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.2
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• pp.56.2-56.2
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• 2018

Ronchi test is an optical test to check the quality of an imaging system. Wavefront of the optical system can be obtained from the Ronchi patterns. In this poster, we present the Ronchi test module and the optical quality evaluation results. The test module consists of a light source, a pinhole, a beam splitter, a Ronchi ruling and a flat mirror. The test module can be simply adapted to any optical systems. We compare measured surface data for both aluminum and glass parabolic mirrors by analyzing the Ronchi patterns.

• Journal of the Korean Physical Society
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• v.73 no.11
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• pp.1657-1662
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• 2018

A null test method which relies on a computer generated hologram (CGH) is widely used to measure a large aspheric surface. For precise measurements of the surface shape of an aspheric optics, the CGH must precisely generate a wavefront that can fit on the ideal surface shape of the aspheric optics. If fabrication errors arise in the CGH, an unwanted wavefront will be generated and the measuring result will lack trustworthiness. Thus far, there has been limited research on wavefronts generated by CGH using only linear-type binary grating models. In this study, a theoretical error model of a circular-type zone plate, the most commonly used types for CGH patterns, is suggested. The proposed error model is checked by simulations and experiments.

• Proceedings of the Optical Society of Korea Conference
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• 2005.02a
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• pp.336-337
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• 2005

• Proceedings of the Optical Society of Korea Conference
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• 2007.07a
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• pp.29-30
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• 2007