• Current Optics and Photonics
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• 제2권5호
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• pp.407-412
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• 2018

An optimal matching approach is proposed to maximally ensure the output power uniformity of the cascaded encoder in the passive optical network (PON) monitoring system based on a remote coding scheme. The calculation results show that the optimum arrangement can effectively reduce the difference of the total insertion loss in comparison to the random arrangement (i.e., 0.07 dB vs 2.67 dB in the cascaded encoder with 16 output ports). The proposed approach realizes the optimum configuration for the $1{\times}2$ optical splitters used without adding any extra components. The test results of the fabricated cascaded encoder with 32 output ports prove the feasibility of the proposed approach.

• Journal of the Optical Society of Korea
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• 제19권5호
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• pp.503-507
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• 2015

Using the reflectivity mode of an optical microscope, we analyzed the optical contrast to identify the layer number of flakes of hexagonal boron nitride on a $SiO_2$/Si substrate. Overall optical contrast in the visible range varies with the thickness of flakes. However, the wavelength of zero contrast exhibits a linear redshift of 0.53 nm per layer, independent of the $SiO_2$ thickness, and increases proportionally with $SiO_2$thickness. Experiments show good agreement with calculations and the results of AFM measurements. These results show that this zero-contrast approach is more accurate and easier than the reflectivity-contrast approach using the overall optical contrast.

• Current Optics and Photonics
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• 제7권5호
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• pp.545-556
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• 2023

This paper introduces volume-sharing multi-aperture imaging (VMAI), a potential approach proposed for volume reduction in space-borne imagers, with the aim of achieving high-resolution ground spatial imagery using deep learning methods, with reduced volume compared to conventional approaches. As an intermediate step in the VMAI payload development, we present a phase-1 design targeting a 1-meter ground sampling distance (GSD) at 500 km altitude. Although its optical imaging capability does not surpass conventional approaches, it remains attractive for specific applications on small satellite platforms, particularly surveillance missions. The design integrates one wide-field and three narrow-field cameras with volume sharing and no optical interference. Capturing independent images from the four cameras, the payload emulates a large circular aperture to address diffraction and synthesizes high-resolution images using deep learning. Computational simulations validated the VMAI approach, while addressing challenges like lower signal-to-noise (SNR) values resulting from aperture segmentation. Future work will focus on further reducing the volume and refining SNR management.

• Current Optics and Photonics
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• 제4권4호
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• pp.361-367
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• 2020

An approach based on an integrated photonic Ti:LiNbO₃ Y branch has been proposed, designed, and analyzed for the microwave instantaneous frequency measurement (IFM). By designing the Y branch with length L = 6545 ㎛ and refractive index N_TE - N_TM = 0.0764, a complementary optical filter with free spectral range (FSR) of 600 GHz is constituted, which results in a maximum measureable frequency of 300 GHz being obtained. Theoretical analysis on the temperature stability of the Ti:LiNbO₃ Y branch shows that the FSR variation of the complementary filter is 0.3% for the temperature change of 100 K, which indicates that the IFM approach will have a better stability. All these results demonstrate that the proposed IFM approach has potential capability to be used for the increasingly higher microwave IFM with better stability.

• Journal of Communications and Networks
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• 제8권2호
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• pp.234-240
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• 2006

We study the dynamic burst assembly based on traffic prediction and offset and delay differentiation in optical burst switching network. To improve existing burst assembly mechanism and build an adaptive flexible optical burst switching network, an approach called quality of service (QoS) based adaptive dynamic assembly (QADA) is proposed in this paper. QADA method takes into account current arrival traffic in prediction time adequately and performs adaptive dynamic assembly in limited burst assembly time (BAT) range. By the simulation of burst length error, the QADA method is proved better than the existing method and can achieve the small enough predictive error for real scenarios. Then the different dynamic ranges of BAT for four traffic classes are introduced to make delay differentiation. According to the limitation of BAT range, the burst assembly is classified into one-dimension limit and two-dimension limit. We draw a comparison between one-dimension and two-dimension limit with different prediction time under QoS based offset time and find that the one-dimensional approach offers better network performance, while the two-dimensional approach provides strict inter-class differentiation. Furthermore, the final simulation results in our network condition show that QADA can execute adaptive flexible burst assembly with dynamic BAT and achieve a latency reduction, delay fairness, and offset time QoS guarantee for different traffic classes.

• Proceedings of the IEEK Conference
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• 대한전자공학회 2001년도 하계종합학술대회 논문집(4)
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• pp.89-92
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• 2001

In this paper, we propose a new approach for tracking a moving object in moving image sequences using active contour models and optical flow. In our approach object segmentation is achieved by active contours, and object tracking is done by motion estimation based on optical flow. To get more dynamic characteristics, Lagrangian dynamics combined to the active contour models. For the optical flow computation, a method, which is based on Spatiotempo-ral Energy Models, is employed to perform robust tracking under poor environments. A prototype real tracking system has been developed and applied to a contents-based video retrieval systems.

• Journal of the Korean Society for Precision Engineering
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• 제15권7호
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• pp.98-103
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• 1998

Recently, DVD/CD compatible driver is needed for DVD and CD is widely used as a new optical data restoring device. The optical systems of DVD and CD driver are different because they have different optical feature. If only one objective lens is used, the change of an aperture or a dual focal length of the lens is required. This method, however, increases the number of parts and results in loss of the power of laser light. Hence, we propose a dual lens actuator design that can read DVD and CD respectively. Albeit magnetic spring is important mechanism in the dual lens actuator design, there has not been the systematic approach to design the mechanism in the preceding researches. In this article. the guideway to design magnetic spring is presented by using the qualitative theoretical approach and the finite element analysis.

• Journal of the Optical Society of Korea
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• 제9권1호
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• pp.6-12
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• 2005

The perturbation approach is applied to solve the nonlinear Schrodinger equation, and its valid range has been determined by comparing with the results of the split-step Fourier method over a wide range of parameter values. With γ= 2㎞/sup -1/mW/sup -1/, the critical distance for the first order perturbation approach is estimated to be(equation omitted). The critical distance, Z/sub c/, is defined as the distance at which the normalized square deviation compared to the split-step Fourier method reaches 10/sup -3/. Including the second order perturbation will increase Z/sub c/ more than a factor of two, but the increased computation load makes the perturbation approach less attractive. In addition, it is shown mathematically that the perturbation approach is equivalent to the Volterra series approach, which can be used to design a nonlinear equalizer (or compensator). Finally, the perturbation approach is applied to obtain the sinusoidal response of the fiber, and its range of validity has been studied.

• Journal of the Korea Institute of Information and Communication Engineering
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• 제5권7호
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• pp.1257-1262
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• 2001

In recent years there has been a lot of interest in carrying IP over WDM networks in an efficient manner. The benefits here include larger bandwidth capacities, better network scalability, and more efficient operation. W based approach, termed "lambda-labeling" is presented for direct If over WDM integration. In this paper, we study on architecture approach method consider of optical Internet evolution that based on MPLamdaS conception of IETF. Label stack conception collect electronic LSP of optical LSP. This paper is proposed method of co-operation between MPLS domain and MPLambdaS domain. Additionally, proposed architecture of Edge Optical LSR.tical LSR.

• Journal of the Optical Society of Korea
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• 제16권3호
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• pp.247-255
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• 2012

Daylighting has a very effective role in reducing power consumption and improving indoor environments in office buildings. Previously, it was not under consideration as a major source of renewable energy due to poor reliability in the design. Optical fiber as a transmission medium in the daylighting system demands uniform distribution of light to solve cost, heat, and efficiency issues. Therefore, this study focuses on the uniform distribution of sunlight through the fiber bundle and to the interior of the building. To this end, two efficient approaches for the fiber-based daylighting system are presented. The first approach consists of a parabolic mirror, and the second approach contains a Fresnel lens. Sunlight is captured, guided, and distributed through the concentrator, optical fibers, and lenses, respectively. At the capturing stage, uniform illumination solves the heat problem, which has critical importance in making the system cost-effective by introducing plastic optical fibers. The efficiency of the system is increased by collimated light, which helps to insert maximum light into the optical fibers. Furthermore, we find that the hybrid system of combining sunlight and light emitting diode light gives better illumination levels than that of traditional lighting systems. Simulation and experimental results have shown that the efficiency of the system is better than previous fiber-based daylighting systems.