Hyun-Jun Kim

Bio: Hyun-Jun Kim is an academic researcher from Inha University. The author has contributed to research in topics: Photonic crystal & Photonic integrated circuit. The author has an hindex of 8, co-authored 22 publications receiving 297 citations.

Photonic crystal power-splitter based on directional coupling.

Abstract: We propose a new power-splitting scheme in two-dimensional photonic crystals that can be applicable to photonic integrated circuits. The proposed power-splitting mechanism is analogous to that of conventional three-waveguide directional couplers, utilizing coupling between guided modes supported by line-defect waveguides. Through the analysis of dispersion curve and field patterns of modes, the position in propagation direction, where an input field is split into a two-folded image, is determined by simple mode analysis. Based on the calculated position, a photonic crystal power-splitter is designed and verified by finite-difference time-domain computation

Self-imaging phenomena in multi-mode photonic crystal line-defect waveguides: application to wavelength de-multiplexing

Abstract: We show that the self-imaging principle still holds true in multimode photonic crystal (PhC) line-defect waveguides just as it does in conventional multi-mode waveguides. To observe the images reproduced by this self-imaging phenomenon, the finite-difference time-domain computation is performed on a multi-mode PhC line-defect waveguide that supports five guided modes. From the computed result, the reproduced images are identified and their positions along the propagation axis are theoretically described by self-imaging conditions which are derived from guided mode propagation analysis. We report a good agreement between the computational simulation and the theoretical description. As a possible application of our work, a photonic crystal 1-to-2 wavelength demultiplexer is designed and its performance is numerically verified. This approach can be extended to novel designs of PhC devices.

Conceptual Framework for Recommendation System Based on Distributed User Ratings

Abstract: A recommender system is an automated collaborative filtering system that helps users to decide what they are interested in by extracting their own preferences. Most studies related to recommendation system have focused on centralized environment causing several serious problems such as fraud rating and privacy issues. In this paper, however, we propose the distributed recommender system with FOAF on P2P environment. This system can recommend users without the centralized server, which keeps updating their profiles. In order to find out the most eligible users to be recommended, user grouping (selecting objects) is one of the most important processes in the whole recommendation. Thereby, we have exploited cosine-based similarity method to cluster the users in the same level. More importantly, RFR (Recommend-Feedback-Re-recommend) algorithm is suggested to improve the confidence of recommendation. For the experiment, we have used the MovieLens datasets and have tested the performance by using “F1-measure” and Mean Absolute Error (MAE). As a conclusion, we have improved the robustness of the system. Also, we have shown the possibility of distributed recommender system on semantic web.

Affective social network--happiness inducing social media platform

Abstract: We propose a human emotion regarding social network, namely, the Affective Social Network. Our suggestion firstly builds a user's emotion profile in terms of the personality, mood and emotion by analysing the user's activities in social network. This subsequently builds an Emotional Relationship Matrix (ERM) which represents the depth of the emotional relationship based on the emotion profile. From our proposal, the more elaborate services based on the current user's emotional state can be provided to users. By considering emotional aspects in a social network, we can effectively answer which users or media contents will show the best results for inducing users' emotional states. From the experiments, we verified that message containing emotional words and users' relationship in a social network has significant correlations.

Design of ultra compact all-optical XOR, XNOR, NAND and OR gates using photonic crystal multi-mode interference waveguides

Abstract: We propose ultra compact all-optical XOR, XNOR, NAND and OR gates based on photonic crystal multi-mode interference waveguides for binary-phase-shift-keyed signals. The logic gates have been simulated and analyzed by finite difference time domain method. The extinction ratio between the ON state and the OFF state for XOR, XNOR, NAND and OR gates are more than 28.6 dB, 28.6 dB, 25 dB and 26.6 dB in the whole C-band, respectively. The proposed structure can achieve logical function when the radius of all rods is fabricated with relaxed error tolerance within −10% to 30% from designed parameters. The device possesses ultra compact size with approximately 6.9 μm×6.7 μm. The proposed logic gates may potentially be used as key components in all-optical information networks for processing binary-phase-shift-keyed signals.