• Proceedings of the IEEK Conference
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• 2000.07b
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• pp.945-948
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• 2000

The coupling properties of supermodes guided by grating-assisted directional couplers (GADCs) can be phrased in rigorous modal theory. Such a modal solution for TE modes expressed by simple electrical transmission-line networks is utilized to analyze the power distribution of GADCS with three guiding channels. In particular, the modal transmission-line theory can serve as a template for computational algorithms that systematically evaluate the coupling efficiency that are not readily obtained by other methods.

• Proceedings of the IEEK Conference
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• 1998.06a
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• pp.185-188
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• 1998

A three-waveguide coupler consisted of a central guide and two side guides is theoretically explored by using modal transmission-line theory. The numerical results reveal that the coupling length Lc is different from that calculated by coupled-mode theory and the difference increases gradually as the guiding modes increase.

• Journal of the Optical Society of Korea
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• v.8 no.4
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• pp.149-155
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• 2004

Newly developed modal transmission-line theory(MTLT) is used to analyze rigorously the optical power distribution in grating-assisted directional couplers(GADCs) with three guiding channels. By defining a novel coupling efficiency ${\eta}$ amenable to the rigorous analytical solutions of modal transmission-line theory, we explicitly evaluate the power coupling and distribution of TM modes. The results reveal that the incident power is sensitively partitioned through three output channels in terms of such grating parameters as the grating period, the duty cycle, and the operating wavelength.

• Proceedings of the IEEK Conference
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• 1999.11a
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• pp.917-920
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• 1999

Modal transmission-line theory is described for guided electron waves in quantum-well structures. To demonstrate the validity and usefulness of this approach, we evaluate the propagation characteristics and the coupling properties of electron guiding couplers consisting of double quantum-wells (DQWs).

• Korean Journal of Optics and Photonics
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• v.16 no.2
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• pp.162-167
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• 2005

An optical directional coupler, which consists of quantum wells with nanothickness, is designed by using Modal Transmission Line Theory (MTLT). To demonstrate the validity and usefulness, the propagation characteristics and the coupling efficiencies are rigorously evaluated at nanoscale couplers, which consist of double quantum wells with different effective masses. The numerical result reveals that the coupling efficiency of nanoscale couplers is maximized at a coupling length 2052.3 nm, if the total electron energy is 83.9 meV. Furthermore, the coupler operates as a filter with narrower band as the barrier thickness increases.

• Korean Journal of Optics and Photonics
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• v.17 no.2
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• pp.120-126
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• 2006

A grating-assisted fiber coupler(GAFC), which consists of a thin-film waveguide with grating and circular optical fiber, is proposed and the optimized power coupling is evaluated by using a technique amenable to rigorous longitudinal modal transmission-line theory(L-MTLT). In addition, novel criteria to couple an optical signal incident through the grating waveguide to a single-mode optical fiber are proposed. The numerical result reveals that the optimized power coupling occurs at minimum-gap condition between rigorous modes rather than for the conventional phase-matching condition.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.19 no.5
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• pp.175-180
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• 2019

The optical characteristics and power transfers between guiding channels of blazed grating-assisted directional coupler (B-GADC) are evaluated in detail by using novel and rigorous modal transmission-line theory (MTLT) based on eigenvalue problem. To evaluate the coupling efficiency of B-GADC, the dispersion curves as a function of the grating period and wavelength are analyzed numerically for quasi-TE and quasi-TM modes. Furthermore, symmetric, sawtooth and asymmetric grating profiles are considered to know the effect of blazing characteristics on power transfer of GADC. The numerical results show that the grating period for minimum-gap condition to obtain maximum power transfer decreases gradually as the blazed structure changes from symmetric to asymmetric profile. On the other hand, the coupling length increases reversely.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.9 s.180
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• pp.2302-2312
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• 2000

An active control of the transmission of noise through an aircraft fuselage is investigated numerically. A cylinder-cavity system was used as a model for this study. The fuselage is modeled as a fi nite, thin shel cylinder with constant thickness. The sound field generated by an exterior monopole source is transmitted into the cavity through the cylinder. Point force actuators on the cylinder are driven by error sensor that is placed in 3D cavity. Modal coupling theory is used to formulate the numerical models and describe the system behavior. Minimization of the acoustic potential energy in the fuselage is carried out as a performance index. Continuous parameter genetic algorithm is used to search the optimal actuator position and both results are compared.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.13 no.2
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• pp.149-159
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• 1988

In this paper, the Fourier Transform is employed to solve the coupled differential equations of modal power and three equations of the mode coupling coeficient are dierived using the phasor form trial soluation. The theory of the mode coupling coefficient contains a few theories proposed by earlier authers. Also it is seen that in case the optical source is modulated by a sinusoidal function, this theory is applied as well. In experiment, the mode coupling coefficient is determinded for a multimode graded-index fiber by using the optical source, which modulated by a sinusoidal function.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.19 no.12
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• pp.1244-1251
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• 2009

In this paper the vibrational behavior of a multi-packet blade system having a cracked blade is investigated. Each blade is assumed as a slender cantilever beam. The coupling stiffness effect that originates from either disc flexibility or shroud is considered in the modeling. Hybrid deformation variables are employed to derive the equations of motion. The flexibility due to crack, which is assumed to be open during the vibration, is calculated basing on a fracture mechanics theory. In the paper, the results of the change in modal parameters due to crack appearance are presented. The influence of the crack parameters, especially of the changing location of the crack is examined.