• The Science & Technology
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• no.1 s.404
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• pp.50-51
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• 2003

'양자 초단면 이론' 으로 거울 대칭현상 해결/ '1조분의 1초'의 '초고속 현상' 연구 탁월/ 극미세 나노물질의 형성 원리 밝혀/ 인체 면역시스템을 분자적 수준서 규명/

• The Transactions of the Korea Information Processing Society
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• v.4 no.12
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• pp.3063-3068
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• 1997

In this paper, we have extended the generalization back-propagation algorithm to multi-layer polynomial higher order neural networks. The purpose of this paper is to describe various pattern recognition using polynomial higher-order neural network. And we have applied shift position T-C test pattern for invariant pattern recognition and measured generalization by mirror symmetry problem. simulation result shows that the ability for invariant pattern recognition increase with the proposed technique. Recognition rate of invariant T-C pattern is 90% effective and of mirror symmetry problem is 70% effective when the proposed technique is utilized. These results are much better than those by the conventional methods.

• The Mathematical Education
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• v.46 no.3
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• pp.273-292
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• 2007

The purpose of this study was to find out how second, fourth and sixth graders understood the main contents related to spatial sense in the Seventh National Mathematics Curriculum. For this purpose, this study examined students' understanding of the main contents of congruence transformation (slide, flip, turn), mirror symmetry, cubes, congruence and symmetry. An investigation was conducted and the subjects included 483 students. The main results are as follows. First, with regards to congruence transformation, whereas students had high percentages of correct answers on questions concerning slide, they had lower percentages on questions concerning turn. Percentages of correct answers on flip questions had significant differences among the three grades. In addition, most students experienced difficulties in describing the changes of shapes. Second, students understood the fact that the right and the left of an image in a mirror are exchanged, but they had poor overall understanding of mirror symmetry. The more complicated the cubes, the lower percentages of correct answers. Third, students had a good understanding of congruences, but they had difficulties in finding out congruent figures. Lastly, they had a poor understanding of symmetry and, in particular, didn't distinguish a symmetric figure of a line from a symmetric figure of a point.

• Korean Journal of Optics and Photonics
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• v.31 no.6
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• pp.304-313
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• 2020

By using an off-axial field with an inverse Cassegrain system where the aperture stop is at the secondary mirror, the two-mirror system can be used for a wide-field objective. However, aberration corrections in conventional two-mirror systems are limited because the design parameters are too small. In this study, we present a new improved design of the off-axial-field two-mirror system. The new design has an independently displaced aperture stop and a secondary mirror. The new design parameters yield more improvement in correction for 5th-order coma and astigmatism, and better aberration balancing for the whole off-axial field. The spot sizes of the new design system are reduced to half of those for a conventional reference design, and the improvement effects are shown for the whole field evenly.

• Korean Journal of Optics and Photonics
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• v.4 no.4
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• pp.420-427
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• 1993

Dielectric thin film mirrors are embedded in multimode and single-mode fibers by a fusion splicing technique. The fibers with $45{\circ}$ angled embedded mirrors serve as ultra-compact directional couplers with low excess optical loss of 0.2 dB for multimode and 0.5 dB for single mode at 1.3 ${\mu}m$ and excellent mechanical properties. The reflectance is wavelength dependent and strongly polarization depencient. Far-field scans of the reflected output power measured with a white-light source show a pattern which is almost circularly symmetric with aspect ratio of 1.09 at 5% of the peak power. The splitting ratio in a multimode coupler measured with a diode laser source is much less dependent on input coupling conditions than in conventional fused biconical-taper couplers, indicating that these couplers are less susceptible to modal noise occuring in optical fiber communication systems. Spectral properties of multilayer internal mirrors normal to the fiber axis have been investigated experimentally, and a matrix analysis has been used to explain the results.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.37 no.8
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• pp.76-85
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• 2000

Effects of the random fluctuation in grating half-period have been studied by an effective index transfer matrix method in DFB lasers. The laser facets are assumed to be perfectly antireflection coated, and the period fluctuation is modeled as a Gaussian random variable. The random fluctuation breaks spectral symmetry in both uniform-grating and quarter-wavelength -shifted(QWS) DFB lasers, and decreases the effective coupling coefficient. This leads to increased average mirror loss of ${\pm}$1 modes and reduced stopband width in uniform grating DFB lasers, and degradation in the wavelength accuracy and the single mode stability in QWS-DFB lasers. Threshold gain difference decreases with increasing period fluctuation irrespective of grating coupling coefficient in QWS-DFB lasers, while spatial hole-burning effect is exacerbated or alleviated when the normalized coupling coefficient is lower and higher than 1.5, respectively.

• Korean Journal of Optics and Photonics
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• v.17 no.2
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• pp.198-202
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• 2006

Resonator stability condition, $M^2$ beam quality factor, and laser output power are analyzed for two types of two-rod Nd:YAC lasers with rod-end curvatures. Two laser rods with rod-end curvatures are positioned closely to each other or placed separately near each resonator mirror. Experimentally, the output powers and $M^2$ beam quality factors of those lasers are measured with and without thermal birefringence compensation, and compared to numerical analyses.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.6
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• pp.1025-1031
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• 2006

In this paper, a deconvolution filtering method for all-pass systems based on FIR approximation is proposed. The proposed method enables us to obtain a causal stable deconvolution filter by FIR approximating a non-causal stable deconvolution filter to a causal stable one. As we can see in this paper, the impulse response of the deconvolution filter for all-pass system is simply the mirror image of the impulse response for all-pass system itself. Due to this symmetric property between all-pass system itself and its deconvolution Inter, this method can be applied to all-pass systems without special limitation of the system's order. In order to verify the performance of the proposed method. computer simulation results for 1st-, 2nd- and 400th-order all-pass systems are included.

• Korean Journal of Optics and Photonics
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• v.14 no.5
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• pp.555-564
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• 2003

WDM thin film filters for fiber optical communication were designed using Fabry-Prot type multiple cavity filters and an equivalent thin film technique. As the number of cavities in multiple cavity filters increases, it becomes difficult to design the filters due to a great number of variables (the number of cavities, period of reflectors, order of spacers). To solve the problem of design, we treated the fewest variables, regarding symmetrical thin films as equivalent layers, and we applied structural and numerical formulas based on an analysis method of multiple cavity filters. The equivalent thin film technique was able to provide systematic and quantitative design of the WDM thin film filters.

• Journal of the Institute of Convergence Signal Processing
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• v.5 no.2
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• pp.151-158
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• 2004

In this paper, an inverse filtering technique for the digital filter model is proposed. This technique enables us to obtain a stable non-causal m inverse filter by transforming (approximating) it to a causal stable inverse system. In practice, a causal FIR approximation to this inverse filter is proposed. It can be shown that the impulse response of the inverse filter for all-pass systems is simply the mirror image of the impulse response for the system. Specially, due to this symmetric property of the impulse response of all-pass systems, the proposed technique is more useful for all-pass systems than other systems. In order to illustrate the proposed inverse filtering technique, four examples are presented. Two of them are for all-pass filters. The other two examples are for IIR and FIR filters. Also, computer simulations demonstrate that the proposed technique works very well.