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Higher order optical resonant filters based on coupled defect resonators in photonic crystals
Park, Dongsoo,Kim, Sangin,Park, Ikmo,Lim, Hanjo IEEE 2005 Journal of Lightwave Technology Vol.23 No.5
In this paper, a general methodology for the design of higher order coupled resonator filters in photonic crystals (PCs) is presented. In the proposed approach, the coupling between resonators is treated as though it occurs through a waveguide with an arbitrary phase shift. The coupling through the waveguide is analyzed theoretically, based on the coupled-mode theory in time. The derived theoretical model suggests a way to extend an equivalent circuit approach, previously demonstrated with a certain value of a phase shift, to the higher order filter design with an arbitrary phase shift. The validity of the proposed approach is confirmed by the design of a third-order Chebyshev filter having a center frequency of 193.55 THz, a flat bandwidth of 50 GHz, and ripples of 0.3 dB in the passband. The characteristics of the designed filter are suitable for wavelength-division-multiplexed (WDM) optical communication systems with a 100-GHz channel spacing. The performance of the designed filter is numerically calculated using the two-dimensional (2-D) finite-difference time-domain (FDTD) method.
InGaAs/GaAs 양자우물 표면발광레이저 설계에 관한 연구
박승환,정원국,김인,최병두,임한조 대구효성가톨릭대학교 자연과학연구소 1993 基礎科學硏究論集 Vol.1993 No.1
InGaAs/GaAs 양자우물 표면발광레이저(0.98㎛)의 문턱전류밀도에 대한 최적화 조건을 이론적으로 조사 연구하였다. Material gain은 strain과 band-mixing을 고려하여 계산하였고, 이것으로부터 active layer내 최적의 양자우물 수 그리고 최적의 active layer 수를 결정하고자 하였다. 반사율 R=0.95에 대해,periodic gain structure(PGS)는 한 개의 active layer를 가진 uniform gain structure(UGS)에 비해 3배정도로 문턱전류가 낮았으며, PGS의 최적 양자우물 수는 2, 그리고 최적의 cavity length는 반파장의 17배 정도로 나타났다. 또한, UGS는 4개의 양자우물에서 최소의 문턱전류밀도를 보여주었다. Optimization conditions of the threshold current density in InGaAs/GaAs quantum well(QW)surface-emitting laser(SEL)(0.98㎛)are studied theoretically. Material gain is caculated by considering strain and band-mixing effects. From this, QW number in active layer and numbers of active layer are optimized. It is found that the periodic gain structure(PGS) can provide a factor of three reduction in threshold current density comparing to the uniform gain structure(UGS) with a single active layer. For PGS, the optimum QW number is two, and the optimum cavity length is 17 half wavelengths. Also, UGS shows that the optimum QW number is four.
정한조(Hanjo Jeong),박병화(Byeonghwa Park) 한국지능정보시스템학회 2015 지능정보연구 Vol.21 No.1
As opinion mining in big data applications has been highlighted, a lot of research on unstructured data has made. Lots of social media on the Internet generate unstructured or semi-structured data every second and they are often made by natural or human languages we use in daily life. Many words in human languages have multiple meanings or senses. In this result, it is very difficult for computers to extract useful information from these datasets. Traditional web search engines are usually based on keyword search, resulting in incorrect search results which are far from users’ intentions. Even though a lot of progress in enhancing the performance of search engines has made over the last years in order to provide users with appropriate results, there is still so much to improve it. Word sense disambiguation can play a very important role in dealing with natural language processing and is considered as one of the most difficult problems in this area. Major approaches to word sense disambiguation can be classified as knowledge-base, supervised corpus-based, and unsupervised corpus-based approaches. This paper presents a method which automatically generates a corpus for word sense disambiguation by taking advantage of examples in existing dictionaries and avoids expensive sense tagging processes. It experiments the effectiveness of the method based on Naive Bayes Model, which is one of supervised learning algorithms, by using Korean standard unabridged dictionary and Sejong Corpus. Korean standard unabridged dictionary has approximately 57,000 sentences. Sejong Corpus has about 790,000 sentences tagged with part-of-speech and senses all together. For the experiment of this study, Korean standard unabridged dictionary and Sejong Corpus were experimented as a combination and separate entities using cross validation. Only nouns, target subjects in word sense disambiguation, were selected. 93,522 word senses among 265,655 nouns and 56,914 sentences from related proverbs and examples were additionally combined in the corpus. Sejong Corpus was easily merged with Korean standard unabridged dictionary because Sejong Corpus was tagged based on sense indices defined by Korean standard unabridged dictionary. Sense vectors were formed after the merged corpus was created. Terms used in creating sense vectors were added in the named entity dictionary of Korean morphological analyzer. By using the extended named entity dictionary, term vectors were extracted from the input sentences and then term vectors for the sentences were created. Given the extracted term vector and the sense vector model made during the pre-processing stage, the sense-tagged terms were determined by the vector space model based word sense disambiguation. In addition, this study shows the effectiveness of merged corpus from examples in Korean standard unabridged dictionary and Sejong Corpus. The experiment shows the better results in precision and recall are found with the merged corpus. This study suggests it can practically enhance the performance of internet search engines and help us to understand more accurate meaning of a sentence in natural language processing pertinent to search engines, opinion mining, and text mining. Naive Bayes classifier used in this study represents a supervised learning algorithm and uses Bayes theorem. Naive Bayes classifier has an assumption that all senses are independent. Even though the assumption of Naive Bayes classifier is not realistic and ignores the correlation between attributes, Naive Bayes classifier is widely used because of its simplicity and in practice it is known to be very effective in many applications such as text classification and medical diagnosis. However, further research need to be carried out to consider all possible combinations and/or partial combinations of all senses in a sentence. Also, the effectiveness of word sense disambiguation may be improved if rhetorical structures or morphological dependenc
박은경(Eunkyung Park),유동호(Dongho Yoo),조정연(Jungyon Cho),정한조(Hanjo Jung),김장선(Jangsun Kim),맹승렬(Seungryoul Maeng),조정완(Jungwan Cho) 한국정보과학회 1996 한국정보과학회 학술발표논문집 Vol.23 No.1A
고성능의 다중처리기 시스템에 대한 요구가 증가됨에 따라 최근에 LAMP(Local Area MultiProcessor)라고 불리는 새로운 다중처리기 시스템이 제안되었다. 본 논문에서는 SCI를 기반으로 하는 고성능 LAMP 환경을 구축하기 위하여 PCI 버스와 SCI를 연결하는 SCI 버스 브리지를 설계하고 구현하였다. SCI는 다중처리기 시스템에서 노드간의 연결에 관한 IEEE의 표준(P1596)이다. 본 논문에서 설계한 SCI/버스 브리지는 처리기 모듈과 SCI의 주소 변환을 위해 주소 변환 테이블을 사용하며, 각 처리기간의 인터럽트 전송을 위하여 메일박스를 사용한다. 또한, 많은 양의 자료를 빠르게 전송하기 위하여 DMA 방식을 사용하고 있으며, 동기화 문제를 해결하기 위하여 SCI 프로토콜에 적합한 하드웨어 단위명령 메카니즘을 지원한다. 본 논문에서는 설계된 SCI 버스 브리지를 VHDL을 사용하여 구현 및 검증하였다.
Proposal for ideal 3-dB splitters-combiners in photonic crystals.
Kim, Sangin,Park, Ikmo,Lim, Hanjo Optical Society of America 2005 Optics letters Vol.30 No.3
<P>We propose a structure for ideal 3-dB splitters (1 x 2)-combiners (2 x 1) in photonic crystals. In photonic crystals, ideal 3-dB splitters based on a three-port system are achievable in principle, but it is impossible to achieve ideal 3-dB combiners based on the three-port system because there is no path for a loss, owing to strong confinement of photons. The proposed structure is based on a four-port system in which the concept of a microwave circuit, the so-called rat-race circuit is adopted. Design conditions for two-dimensional photonic-crystal-based rat-race circuits have been investigated by use of the coupled-mode theory in time. With the proposed structure, a 3-dB splitter-combiner has been designed. The performance of the device was numerically calculated by the finite-difference time-domain method.</P>
Photonic crystal multi-channel drop filters based on microstrip lines
Kee, Chul-Sik,Park, Ikmo,Lim, Hanjo Institute of Physics [etc.] 2006 Journal of Physics. D, Applied Physics Vol.39 No.14
<P>We propose photonic crystal (PC) multi-channel drop filters implemented using microstrip lines. Their performance is based on coupling between the cavity modes of microstrip PC cavities and the guiding modes of microstrip waveguides. The dropping frequency can be controlled by correct design of the cavity. The proposed multi-channel drop filter can be useful for implementing new types of functional microwave filters.</P>