• Current Optics and Photonics
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• v.1 no.2
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• pp.150-156
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• 2017

A diffraction limited optical system for head mounted displays (HMDs) was designed. This optical system consists of four modules, including 1:5 mm and 5:30 mm beam expanders, polarization grating-polarization conversion system (PG-PCS) and refractive/diffractive projection optical module. The PG-PCS module transforms the unpolarized Gaussian beam to a linearly polarized beam and it simultaneously homogenizes the spatial intensity profile. The optical projector module has a $30^{\circ}$ field of view, a 22 mm eye relief, and a 10 mm exit pupil diameter with a compact structure. Common acrylic materials were utilized in the optical design process; therefore, the final optical system was lightweight. The whole optical system is suitable for a 0.7 inch liquid crystal on silicon microdisplay (LCOS) with HDTV resolution ($1920{\times}1080$) and $8.0{\mu}m$ pixel pitch.

• Proceedings of the Optical Society of Korea Conference
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• 2008.02a
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• pp.283-284
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• 2008

In this paper, we report a broadband circular polarization reflectors and color separators realized as cascades of helical films with different pitch thickness. These helical films were prepared by glancing angle deposition technique.

• Journal of the Optical Society of Korea
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• v.16 no.1
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• pp.29-35
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• 2012

We propose a subpixel scale elemental image generation method to correct the errors created by finite display pixel size in integral imaging. In this paper, two errors are mainly discussed: pickup-and-display mismatch error and mismatch error between pixel pitch and lens pitch. The proposed method considers the relative positions between lenses and pixels in subpixel scale. Our proposed pickup method calculates the position parameters, generates an elemental image with pixels completely inside the lens, and generates an elemental image with border pixels using a weighted sum method. Appropriate experiments are presented to verify the validity of the proposed method.

• Journal of the Optical Society of Korea
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• v.9 no.4
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• pp.140-144
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• 2005

In this paper we have investigated the guiding properties of photonic crystal fibers (PCFs) with a square-lattice of air-holes in the cladding. We have shown numerical results of PCFs with various air hole sizes and hole-to-hole spacings over a wide wavelength range. The group velocity dispersion, effective area and effective refractive index of PCF have been calculated numerically. The waveguide dispersion has greatly affected the group velocity dispersion when hole-to-hole spacing is about $1{\mu}m$. The effective area is quite flat over the wide spectral range whether the hole-to-hole spacing is large or ratio of diameter to pitch is large. From the field distribution, we found that the field is tightly confined within the core region of PCF when the pitch is $3{\mu}m$ and the air-filling fraction is 0.9.

• Journal of the Optical Society of Korea
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• v.9 no.3
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• pp.92-94
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• 2005

We present a novel method for three-dimensional optical memory and microchannel embedded in fused silica glass. Three-dimensional dot patterning with a femtosecond laser pulse and observation with optical microscope are performed. Dot patterns are created by use of a 0.42 N.A. objective to focus 100 fs laser pulses inside the material. We demonstrate data storage with $2{\mu}m$ dot pitch and $7{\mu}m$layer spacing $(36 Gbit/cm^3)$. A three-dimensional microchannel acting as microfluidic and microoptical components is directly fabricated inside a silica glass. The optical micrographs of the microchannel are obtained by a digital camera of a microscope.

• JSTS:Journal of Semiconductor Technology and Science
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• v.4 no.3
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• pp.189-195
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• 2004

A 10 Gb/s limiting amplifier IC with the emitter area of $1.5{\times}10{\mu}m^2$ for optical transmission system was designed and fabricated with a AIGaAs/GaAs HBTs technology. In this stud)', we evaluated fine pitch bump using WL-CSP (Wafer Level-Chip Scale Packaging) instead of conventional wire bonding for interconnection. For this we developed WL-CSP process and formed fine pitch solder bump with the $40{\mu}m$ diameter and $100{\mu}m$ pitch on bonding pad. To study the effect of WL-CSP, electrical performance was measured and analyzed in wafer and package module using WL-CSP. In a package module, clear and wide eye diagram openings were observed and the riselfall times were about 100ps, and the output" oltage swing was limited to $600mV_{p-p}$ with input voltage ranging from 50 to 500m V. The Small signal gains in wafer and package module were 15.56dB and 14.99dB respectively. It was found that the difference of small signal gain in wafer and package module was less then 0.57dB up to 10GHz and the characteristics of return loss was improved by 5dB in package module. This is due to the short interconnection length by WL-CSP. So, WL-CSP process can be used for millimeter wave GaAs MMIC with the fine pitch pad.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.4
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• pp.342-351
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• 2010

UAV (Unmanned Aerial Vehicle) have an INS(Inertial Navigation System) equipment and also have an electro-optical Equipment for mission. This paper proposes the vision based attitude estimation algorithm using Kalman Filter and Optical flow for UAV. Optical flow is acquired from the movie of camera which is equipped on UAV and UAV's attitude is measured from optical flow. In this paper, Kalman Filter has been used for the settlement of the low reliability and estimation of UAV's attitude. Algorithm verification was performed through experiments. The experiment has been used rate table and real flight video. Then, this paper shows the verification result of UAV's attitude estimation algorithm. When the rate table was tested, the error was in 2 degree and the tendency was similar with AHRS measurement states. However, on the experiment of real flight movie, maximum yaw error was 21 degree and Maximum pitch error was 7.8 degree.

• Transactions of the Society of Information Storage Systems
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• v.1 no.1
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• pp.67-72
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• 2005

This study proposes a design methodology to determine the optimum configurations of the optical flying head (OFH) for near-field recording systems. Since the OFH requires stricter static and dynamic characteristics of slider air-bearings within an optical tilt tolerance over the entire recording band, an optimum design to keep the focusing and tracking ability stable is essential. The desired flying characteristics considered in this study are to minimize the variation in flying height between the SIL and the disk from a target value, satisfying the restriction of the minimum flying height, to keep the pitch and roll angles within an optical tilt tolerance, and to ensure a higher air-bearing stiffness. Simulation results demonstrate the effectiveness of the proposed design methodology by showing that the static and dynamic flying characteristics of the optimally designed OFH are enhanced in comparison with those of the initial. The gap between the SIL and the disk can be kept at less than 100 nm even if the optical tilt tolerance of the SIL is considered.

• Journal of Information Display
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• v.7 no.4
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• pp.1-4
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• 2006

The optical performances of rounded prism films were investigated using a ray tracing technique. The angular distribution of the luminous intensity was obtained as functions of the prism pitch and the curvature of rounded apex and valley of prism arrays. The gain of the on-axis luminance decreased with decreasing curvature (increasing diameter) and pitch. The existence of the curved area on the prism film decreased the recycling efficiency of the prism film, i.e., the rays which would otherwise have been recycled through total internal reflections via the prism surfaces were refracted on the curved regions and redirected toward directions other than the on-axis direction. Quantitative correlation between the luminance gain and the curvature in addition to the prism pitch was obtained, which might serve as basic data for the optimization of prism films and the manufacturing processes.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.16 no.5
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• pp.7-13
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• 2007

This study proposes a new screw measurement system that is capable of measuring the pitch or lead of a screw, which is one of the most important parameters representing the screw quality. There are various conventional methods for screw measurement including some mechanical and optical ones, but they can not be applied to measure the lead except the profiles or sizes. The newly suggested method is able to measure the pitch or lead directly. This is executed by scanning the thread with a digital probe while the target screw rotates. The devised measurement system is a integrated computer system which is composed of a stepping motor, a digital linear gauge and a chuck device for holding the measured screw. In order to operate the system effectively and conveniently, a computer program having graphical user interface facility is developed. Some experiments were done to prove the effectiveness of the system.