• Current Optics and Photonics
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• v.3 no.5
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• pp.451-457
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• 2019

Laser processing using holograms can greatly improve processing speed, by spatially distributing the laser energy on the target material. However, it is difficult to reconstruct an image with arrays of closely spaced spots for laser processing, because the specklelike interference pattern prevents the spots from getting close to each other. To resolve this problem, a line target was divided in two, reconstructed with orthogonally polarized beams, and then superposed. Their optical reconstruction was performed by computer-generated holograms and a pulsed laser. With this method, we performed two-dimensional (2D) laser drilling of polyimide film, with a kerf width of $20{\mu}m$ and a total processing length of 20 mm.

• Current Optics and Photonics
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• v.2 no.5
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• pp.431-435
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• 2018

A modified setup of a CMD technique for high power coherent beam combining was presented to address an issue of low damage threshold of electro-optic modulators. The feasibility of the modified setup was demonstrated by combining eight fiber beams, and it was successfully performed with ${\lambda}/44$ of residual phase error and 100 Hz of control bandwidth. It is expected that the modified CMD setup facilitates ultra-high power coherent beam combination without a limitation caused by the low damage threshold of electro-optic modulators.

• Current Optics and Photonics
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• v.3 no.5
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• pp.365-373
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• 2019

This paper investigates the performance of a hybrid single input multiple output radio frequency/free-space optics (SIMO-RF/FSO) communication system. Each SIMO-RF link is modeled as an independent and identically distributed (i.i.d.) Rayleigh distribution, while the FSO link follows a generalized $M{\acute{a}}laga$ (M) distribution. Considering the fixed gain amplify-and-forward (AF) relay and misalignment errors, novel expressions for the outage probability (OP), average bit error rate (ABER) and average capacity are derived. Numerical results show that atmospheric turbulence and misalignment errors can seriously impair the system performance, and the hybrid RF/FSO communication system using SIMO-RF links can greatly improve system performance. We also analyze system performance under different types of modulation schemes. Numerical results are verified by Monte Carlo simulations.

• Current Optics and Photonics
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• v.5 no.6
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• pp.641-651
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• 2021

To handle the servo delay in a real-time adaptive optics system, a linear subspace system identification algorithm was employed to model the system, and the accuracy of the system identification was verified by numerical calculation. Experimental verification was conducted in a real test bed system. Through analysis and comparison of the experimental results, the convergence can be achieved only 200 times with prediction and 300 times without prediction. After the wavefront peak-to-valley value converges, its mean values are 0.27, 4.27, and 10.14 ㎛ when the communication distances are 1.2, 4.5, and 10.2 km, respectively. The prediction algorithm can effectively improve the convergence speed of the peak-to-valley value and improve the free-space optical communication performance.

• Journal of the Korean Society for Precision Engineering
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• v.33 no.3
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• pp.167-172
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• 2016

The computer controlled optical surfacing (CCOS) technique provides superior fabrication performance for optical mirrors when compared to the conventional method, which relies heavily on the skill of the optician. The CCOS technique provides improvements in terms of mass production, low cost, and short polishing time, and are achieved by estimating and controlling the moving speed of the tool and toolpath through a numerical analysis of the tool influence function (TIF). Hence, the exact estimation of various TIFs is critical for high convergence rates and high form accuracy in the CCOS process. In this paper, we suggest a new model for TIFs, which can be applied for various tool shapes, different velocity distributions, and non-uniform tool pressure distributions. Our proposed TIFs were also verified by comparisons with experimental results. We anticipate that these new TIFs will have a major role in improving the form accuracy and shortening the polishing time by increasing the accuracy of the material removal rate.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.11
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• pp.1023-1026
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• 2016

We calculate the propagation characteristic of antennas considering refractive indices of space environments. The effective indices of troposphere, stratosphere, and inonshpere are computed and the ray tracing method, geometrical optics, and Huygens' principle are used to estimate refracted and attenuated electromagnetic wave of space environment.

• Journal of Korean Ophthalmic Optics Society
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• v.4 no.1
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• pp.63-68
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• 1999

It was made of a chart by new method to be measured the contrast sensitivity for a spatial frequency, and the mean luminance of a lattice frequency was made to three forms of 25, 50, 75% and let it to be ready a CS value from 0 to $10^3$. As a result of measuring of the CS value for a spatial frequency on a target of 12 year old students, CS value decreased of according to down the average luminance value and also the peak position shift to low spatial frequency. The low visioned person decreased the CS value in side of high frequency or in space of total frequency. By the lattice adaptation, a measured CS value was decreased in circumstance regions of adapted space frequency.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.10
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• pp.93-97
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• 2005

We have developed the FDSS (Fine Digital Sun Sensor) for the space technology of the STSAT-2 (Seience & Technology Satellite 2). The FDSS is firstly developed by using CMOS image sensor(CIS) in South Korea. The FDSS consists of the optics part, FPGA(Field Programable Gate Array) part, and MCU(Micro controller unit)part. This paper will focus on the optical characteristics of the optics part and describe the configuration of FDSS with the design of aperture. We also analyze the characteristic of optics about the pixel of the CMOS image sensor.

• Journal of the Optical Society of Korea
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• v.20 no.1
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• pp.150-155
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• 2016

To evaluate the autofocusing performance of recent mobile phone cameras, it is necessary to determine the peak position of the center field MTF (Modulation Transfer Function), -known as the through focus MTF- of the module. However, the MTF peak position found by conventional methods deviates from the ideal position due to the focus scanning resolution of mobile phone cameras. This inaccurate peak position results in false judgements of the optical performance, leading to yield losses or customer complaints. An increase in the focus scanning resolution can address this problem, but the manufacturing UPH (Unit per Hour) level will also unfortunately increase as well, resulting in a loss of manufacturing capabilities. In this paper, several fitting models are studied to find an accurate MTF peak position within a short period of time. With an analysis of a large amount of manufacturing data, it is demonstrated that the fitting methods can reduce false judgements and simultaneously increase the capabilities of the manufacturing system.

• Journal of the Optical Society of Korea
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• v.17 no.6
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• pp.525-532
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• 2013

Contrary to the academic interests of other existing studies elsewhere, this study deals with how the alignment algorithms such as sensitivity or Differential Wavefront Sampling (DWS) can be better used under effects from field, compensator positioning and environmental errors unavoidable from the shop-floor alignment work. First, the influences of aforementioned errors to the alignment state estimation was investigated with the algorithms. The environmental error was then found to be the dominant factor influencing the alignment state prediction accuracy. Having understood such relationship between the distorted system wavefront caused by the error sources and the alignment state prediction, we used it for simulated and experimental alignment runs for Infrared Optical System (IROS). The difference between trial alignment runs and experiment was quite close, independent of alignment methods; 6 nm rms for sensitivity method and 13 nm rms for DWS. This demonstrates the practical usefulness and importance of the prior error analysis using the alignment algorithms before the actual alignment runs begin. The error analysis methodology, its application to the actual alignment of IROS and their results are described together with their implications.