• Journal of electromagnetic engineering and science
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• v.12 no.2
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• pp.171-175
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• 2012

In this work, a new microstrip-to-substrate integrated waveguide (SIW) transition using the parallel half-mode substrate integrated waveguide (HMSIW) is proposed. The proposed transition consists of three sections : a microstrip, parallel HMSIWs, and an SIW. By inserting the parallel HMSIWs section between the microstrip section and the SIW section, the proposed transition can improve the return loss characteristics of the near cut-off frequency because the HMSIWs section has a lower cut-off frequency than the SIW section (8.6 GHz). The lower cut-off frequency is achieved through gradual electromagnetic field mode changes for a low reflection. The measured return loss is less than 20 dB in the of 9.1~16.28 GHz freqeuncy range for the back-to-back transition. The measured insertion loss is within 1.6 dB for the back-to-back transition. The proposed transition is expected to play an important role in wideband SIW circuits fed by a microstrip.

• Journal of the Optical Society of Korea
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• v.14 no.1
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• pp.38-41
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• 2010

We design and fabricate a widely tunable laser diode made of InGaAsP-InP. The diode is monolithically integrated with a wavelength-selective coupled-ring reflector and semiconductor amplifiers. For realization of a compact size device, deeply etched multi-mode interference couplers and square ring resonators composed of total-internal-reflection mirrors are adopted and fabricated using a self-aligned process. It is demonstrated that the laser diode exhibits single mode operation and 16 nm tuning range with side-mode-suppression-ratio exceeding 20 dB.

• International Journal of Highway Engineering
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• v.2 no.4 s.6
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• pp.101-109
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• 2000

This study was performed to estimate fatigue life of polymer-modified and reinforced overlay asphalt mixtures with respect to reflection cracking in asphalt overlay pavement. In order to achieve the goal, the expedited reflection cracking test method was developed and applied to various mixtures and the results were compared one another with respect to the resistant characteristics of reflection cracking. The theoretical prediction equation of fatigue life for each mixture was suggested based on statistical analysis of experimental test results in the flexural failure mode. Since coefficients of correlation between estimated values and measured values were very high ($r^2=0.95$ or higher), the prediction model can be used for relative comparison of various pavement overlay choices to be used in the field.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.9
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• pp.1113-1118
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• 2011

In order to evaluate the characteristics of solid-solid contact interfaces, reflection or transmission techniques involving normal-incidence longitudinal waves are generally used. However, these normal-incidence techniques are of limited use in field applications such as in the inspection of welded parts. The oblique-incidence ultrasonic technique may be an alternative for overcoming these problems. However, in this technique, the mode conversion at the contact interfaces should be taken into account along with the normal and tangential interface stiffness. In this study, we have suggested a theoretical model for obliqueincidence ultrasonic waves at the contact interfaces and analyzed their reflection and transmission characteristics. Experimental results showed that the measured reflection coefficient and second harmonic wave agreed well with the suggested theoretical model. Consequently, the oblique-incidence technique can be a promising method for evaluating the characteristics of the contact interfaces.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.6B
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• pp.1123-1133
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• 1999

In this paper, we applied mode matching and generalized scattering matrix methods to three plane mode matching method for analyzing T-junctions. We calculated all scattering matrix elements by only three times and considered several incident modes. By proposed analysis method, we could analyze various waveguide discontinuity structures more conveniently and accurately. Using the stepped T-junction, we would be able to reduce the reflection coefficient at an input port and use it over wider band. Simulated and HFSS data of T-junctions are compared, showing good agreement for scattering matrix elements. Considering step numbers, height, length and position, we extracted for optimum dimensions and equivalent circuit parameters.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.21 no.11
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• pp.1029-1035
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• 2011

Pressure pulsation of exciting sources that generally occurs on the piping system connected to the discharge of BFP(boiler feed water pump) in power plants causes wave reflection, wave interference, resonance, standing wave and so on. But if the operating speed of the pump is changed, the state of the noise and vibration can be done because characteristics of the exciting source are changed. This paper is to investigate the cause of the noise and vibration occurring on the piping system when the operating speed of BFP is down in accordance with lowering of the power generation. It is approached to two points of view ; Firstly, it is examined whether the pulsation source impacts on the shell mode vibration that vibrates radially across the cross-section of the pipe. But it doesn't affect the shell mode as much as the resonance occurs. Secondly, to find the relation between the pulsation source and the acoustic mode of the piping system, analysis for the piping system by indirect BEM(boundary element method) is carried out. Therefore it is investigated that the mechanism of the noise and vibration relates with acoustic mode of the piping system.

• Korean Journal of Optics and Photonics
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• v.6 no.4
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• pp.296-301
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• 1995

A single-mode erbium-doped fiber laser is constructed by using a intracore fiber Bragg grating and a unidirectional fiber loop mirror. The laser cavity is designed in such a way that the laser beam forms a travelling wave in the gain medium by placing the erbium-doped fiber inside the unidirectional loop and that the wavelength-selective feedback is made from the outside of the loop by a fiber grating with 0.2 nm reflection linewidth. An additional fiber ring resonator is constructed and used as an optical spectrum analyzer to observe the variation of the laser mode spectra. As the result, relatively stable single mode, single polarization output is observed for the most of the time except some mode hoppings in minute scale due to enviommental temperature variations. tions.

• Korean Journal of Optics and Photonics
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• v.15 no.5
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• pp.415-422
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• 2004

We propose and present a new multiplexed bend loss type single-mode fiber-optic sensor system for displacement measurement in order to measure the displacement of several mm of civil engineering structures such as bridges and buildings. We make a bend loss type fiber-optic sensor for measuring displacements using the signal difference between two reflection signals due to various bend losses generating at a pair of optical connectors by using the optical time domain reflectometer. And we fabricate a multiplexed bend loss type fiber-optic sensor detecting linear displacements of 4 measuring positions of an object by setting these new 4 fiber-optic sensors on a single mode fiber simultaneously. We find that the multiplexed fiber-optics displacement sensor has linearity of 0.9942, maximum displacement of 6 mm, and accuracy of 6% for 4 measuring points.

• The Journal of the Convergence on Culture Technology
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• v.6 no.4
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• pp.727-732
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• 2020

In this paper, when a refractive index grating and a gain grating were simultaneously present in a DFB laser having a wavelength of 1.55 ㎛, a dielectric film coating was applied so that reflection did not occur on the right mirror surface, so that 𝜌_r=0. In case of δL > 0, the threshold gain and the beam distribution in the longitudinal direction and the radiated power ratio P_l/P_r of the oscillation mode were compared for the cases of the phase of 𝜌_l=π and π/2. If the phase of 𝜌_l=π, in order to obtain a low threshold current and high frequency stability, κL should be greater than 8. In the case of the phase of 𝜌_l= π/2, when κL is larger than 4.0, the oscillation gain starts to be lower than when the phase of 𝜌_l=π. In order to lower the threshold current of a oscillation mode and enhance the frequency stability, κL should be greater than 8.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.30 no.2
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• pp.11-19
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• 2016

By incorporating a polarization-diversity loop configuration, we have demonstrated the inline switching of transmission and reflection spectra of one of two short-period fiber gratings (SPFGs) with different resonance wavelengths without reconfiguring the filter structure. The proposed filtering apparatus consists of a fiber-pigtailed polarization beam splitter, two SPFGs, and three quarter-wave plates (QWPs). The proposed filter can independently choose the transmission or reflection spectrum of each SPFG through the appropriate adjustment of the orientation angles of the QWPs within the filter without additional optical switches and couplers. The average insertion loss, band rejection ratio, and side-mode suppression ratio of the fabricated filter were measured as ~4.59, ~17.88, and ~19.67dB, respectively.