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Improved QS-MMI' 1.31/1.55μm 파장분리기의 최적화 설계 및 제작
김남국,김장겸,최철현,오범환,이승걸,박세근,이일항,Kim, Nam-Kook,Kim, Jang-Kyum,Choi, Chul-Hyun,O, Beom-Hoan,Lee, Seung-Gol,Park, Se-Gun,Lee, El-Hang 한국광학회 2005 한국광학회지 Vol.16 No.3
다중모드간섭 기반의 $1.31/1.55{\mu}m$ 파장분리기의 크기 및 성능개선을 위해 'Improved Quasi-State' 불완전 단일상 개념을 설계에 도입하였다. 코어와 클래딩의 굴절률 차이가 작은 경우의 모드간 위상오차를 역이용 하도록 설계하여 'Quasi-State'의 출력 파워와 소멸비를 월등히 개선하였다. 다중모드간섭기의 폭이 $14.4{\mu}m$, 입력도파로의 수평 이동이 $5.3{\mu}m$가 되도록 설계한 구조를 유효굴절률법과 MPA를 사용하여 분석한 결과 최대 소멸비는 양 파장대역 모두 -25dB 이하로 나타났다. 설계된 파장분리기는 일반적인 다중 모드간섭기의 길이의 1/5정도에 불과한 $2620{\mu}m$의 간섭길이를 가진다. 소프트 리소그래피 공정을 통해 설계된 파장분리기를 제작하였으며, $1.31{\mu}m$와 $1.5{\mu}m$의 성공적인 파장분리를 확인하였다. We designed and fabricated a compact multi-mode interference (MMI) wavelength demultiplexer using the concept of 'Improved Quasi-State' modes. The output power and extinction ratio were improved by utilizing modal phase error which is specially occurred in low-index contrast. For a designed demultiplexer, the mode propagation analysis with effective index approximation shows significant improvement of extinction ratio to -25 dB for both $1.31{\mu}m\;and\;1.51{\mu}m$ wavelength region and the split-length was reduced about 1/5 of other MMI devices. The fabricated device shows successful characteristics for both 1.31 and $1.55{\mu}m$ wavelengths. These results demonstrate the potential of low-index materials system and the embossing process for photonic integrated circuits.
하나님과 악의 인과성 문제 -아퀴나스의 인과성 이론을 중심으로-
김남국 ( Nam Kook Kim ) 한국기독교철학회 2012 기독교철학 Vol.15 No.-
The purpose of this essay is to study that the Aquinas`s attempt to solve the problem of evil can be logically valid and efficacious even today. Aquinas finds out that the problem of evil proposed by Epicurus is the causality problem of evil and also seeks to solve out the problem on the basis of the traditional causality. That is Aquinas`s concept of evil. He follows faithfully after Augustinus`s and uses Aristotle`s causality and theory of four causes to offer persuasively that God, Cause of all beings, is not the cause of evil. According to Aquinas`s theory of four causes, evil has the material cause and efficient cause by way of good, not formal cause and final cause. Aquinas`s concept of evil as privatio boni(privation of good) means lack of a particular good or perfection which a good subject ought to have. If evil is substance then it has the positive nature which can produce something out of itself, and then its cause can`t but be attributed to God, who is the first cause of every substance. And if one denies the concept of evil as privation then he has to approve either that evil is substance, or that evil is illusion. Aquinas`s concept of evil as privation is well defending the classical theodicy by at once evading the above two positions and holding that evil exists enough to be lack of good