In Won Lee

Half-aperture shearing interferometer for collimation testing

A half-aperture shearing interferometer for collimation testing is proposed. It consists of a wedge plate, two plane mirrors, and two baffles. Detailed analyses for three configurations of this system are presented.

Fast ray-tracing methods for LCD backlight simulation using the characteristics of the pattern

We develop fast ray-tracing methods for LCD backlight simulation. In general, the LCD backlight uses the light guide plate (LGP) to deliver the lights from the side of backlight to the viewing surface. The printed pattern, which consists of many scattering elements (dots), makes the uniform light distribution on the viewing surface. These dots are distributed in a certain regular array at the bottom of the LGP. Since there are too many dots to be handled, it takes a long time for nonsequential Monte Carlo ray-tracing simulations. To speed up the simulation of the backlight with a printed pattern we use a restricted condition and two fast calculation algorithms for the pattern. From the restricted condition, the ray tracing for pattern is performed only when the ray meets the pattern surface. We use two different fast calculation algorithms to verify whether or not a ray meets the pattern. In the first one, since the probability that a ray meets the pattern is the same as the pattern density at the meeting position, we use the pattern density function as a probability function of meeting. This method makes it possible to speed up the simulation and has another merit that the simulation can be processed without using the pattern data: positions, sizes, and the shape of the pattern elements. In the second one, instead of the great number of dots, we determine four dots that can possibly meet a ray. This method gives faster simulation speed and the same result as that from the calculation with all the dots.

Ellipsometric examination of optical property of the Si–SiO2 interface using the s-wave antireflection

Using variable-angle spectroscopic ellipsometry and introducing two models (a three-phase and a two-film model), we examined the optical properties of thermally grown SiO2 layers on Si, with special focus on phase difference Δ and amplitude ratio tanu200aψ for the s and p waves. We found an abrupt flip of the cosu200aΔ curve from which the s and p-wave antireflection conditions were determined and evaluated the interface sensitivities for cosu200aΔ and tanu200aψ based on the three-phase (ambient-oxide substrate) and the two-film (ambient-oxide-interlayer substrate) model. The sensitivities for cosu200aΔ and tanu200aψ were shown to have maximum values at the same angle of incidence and photon energy in the s-wave antireflection condition. By fitting the variable-angle spectroscopic ellipsometry data measured in the s-wave antireflection condition, the thickness of the Si–SiO2 interface was determined as 0.784±0.003 nm for a 52-nm thick oxide sample and 0.764±0.002 nm for a 150-nm-thick oxide one. We also found that the effective ...

Measurement of a long radius of curvature using a half-aperture bidirectional shearing interferometer

We describe a simple method for measuring the long radiusnof curvature by using a half-aperture bidirectional shearing interferometer.nThe method is based on the direct comparison of the fringe widthsnin the two fields. This is very convenient for quantitative interpretation ofnthe fringes. Detailed analyses for optical arrangements and achievablenaccuracy are presented.

Testing of steep convex aspheric surface with a Hartmann sensor by using a CGH

Most aspheric surfaces have been tested by interferometer with some null correctors. This approach, however, often fails when there are many aspherical terms or test surface is very steep because it is not easy to design the conventional null lens or CGH (Computer Generated Hologram). On the other hand, 3-D profilometer can measure aspheric surfaces without any null correctors; however, it takes some time to measure, which makes it unsuitable for the production line in the factory. In this paper, we apply the Hartmann test to the measurement of steep convex aspheric surfaces of which diameter is about 16 mm. In order to increase the measurement accuracy, we calibrated the test setup using a CGH that simulates the ideal test surface. We demonstrated that the significant amount of error in the test setup could be removed by this calibration process. The test results showed only 2 nm rms WFE (wave front error) difference even though the WFE of test setup was worsened by more than 0.13 mum rms. Since this method makes it possible to measure highly aspheric surface quickly and accurately, it can be used in the production line.

Null Hartmann test for the fabrication of large aspheric surfaces

Most aspheric mirrors have been tested by the null lens or computer-generated hologram method. This approach, however, requires that the shape of the surface be similar to the target shape; otherwise testing may not be possible or correct. The Hartmann test has an advantage in that it has a larger dynamic range than a general interferometer, which means that the surface can be tested beginning at an early stage of the polishing process. We suggest use of the null Hartmann test in conjunction with a phase-shifting interferometer for the measurement of a 0.9-m aspheric concave mirror. This setup was able to measure the surface with a large surface form error as well as with a small error without sacrificing any measurement accuracy. Using this setup, we have successfully polished a surface to remove approximately 1 microm of peak-to-valley wave-front error of a total of 39 microm of error during 1 month of polishing.

Optimization of resolution and color reproduction by controlling luminance and contrast levels of a liquid-crystal display monitor

The image quality of a color liquid-crystal display monitor is studied by changing the contrast and the luminance levels. The resolution is assessed with modulation transfer function area (MTFA) that is measured at nine different combinations of the luminance and contrast. At these combinations, we measure the chromaticity coordinates and luminance of red-green-blue channels as a function of the digital-analog convert value. We analyze the relations among MTFA value, constant-channel chromaticity, color gamut, and maximum luminance of a white pattern. From the results, the combination of levels is found that provides both high resolution and good color reproduction.

Optical characterization of silicon dioxide layers grown on silicon under different growth conditions

Abstract Silicon dioxide layers on crystalline silicon substrates were thermally grown under different oxidation conditions. The ellipsometric functions (ψ and Δ) of the silicon dioxide layers were measured by using variable-angle spectroscopic ellipsometry (VASE). The effective refractive index of the silicon dioxide layer decreases from 1.544 to 1.458 as the layer thickness increases from 12 to 150 nm. The critical behavior of the s- and the p-wave antireflection condition has been observed from the experimental VASE data in accordance with the predicted sensitivity graphs based on an interface layer between the crystalline silicon substrate and the oxide.

Noncollimated bidirectional shearing interferometer for measuring a long radius of curvature

A method for measuring a long radius of curvature with a modified half-aperture bidirectional shearing interferometer is described. A plane mirror of the interferometer is replaced with a test mirror, and the incident beam is decollimated by shifting of the source to equalize the widths of the bidirectional shearing fringes reflected from the plane and test mirrors. This method can be applied to concave and convex surfaces.

Development of an Equipment for measuring the MTF of Camera Phone Lenses

직경과 초점거리가 수 ㎜인 카메라폰 렌즈의 성능을 평가하는 변조전달함수(Modulation Transfer Function: MTF) 측정장치를 개발하였다 전체 측정장치는 물체부, 상분석부, 렌즈 마운터로 구성되며, 물체부는 비축상 측정을 위하여 회전한다. 렌즈의 정밀한 정렬을 위하여 정밀한 수평형 거치대를 제작하였으며 광축 조정과 렌즈의 기울어짐 등의 문제를 매우 효과적으로 개선하였다. 시험렌즈의 초기정렬이 끝나면 자동으로 MTF를 측정하며 측정시간은 10초 이내이다.