• Proceedings of the IEEK Conference
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• 2006.06a
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• pp.203-204
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• 2006

We present and demonstrate a novel method of alternate-phase return-to-zero (RZ) signal generation and pulse-amplitude equalization simultaneously in a rational harmonic mode-locked fiber ring laser, using a dual-drive Mach-Zehnder (MZ) modulator. By adjusting the voltages applied to both arms of the modulator, the rational harmonic mode-locked pulse trains are equalized in their amplitudes. In addition to that, the amplitude-equalized pulse trains multiplying the repetition rate at ${\sim}10\;GHz$ have alternate $\pi$ phase difference between adjacent pulses. The alternate-phase RZ signal generated by the proposed method enhances transmission performance through the single-mode fiber (SMF) links without dispersion compensation.

• Structural Monitoring and Maintenance
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• v.9 no.4
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• pp.373-388
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• 2022

A USW based diagnostic procedure is presented for estimating the depth of surface-breaking cracks. The diagnosis is demonstrated on seven lab-scale SFRC beam specimens, which are subjected to the CMOD controlled three-point bending test to create real bending cracks. Then, the recorded multiple ultrasonic signals are examined with the signal processing techniques, including wavelet transform and two-dimensional Fourier transform, to investigate the relationships between the crack depth and two diagnostic indices, namely the attenuation coefficient and dispersion index (DI). Finally, the reliabilities of these indices for depth estimation are verified with the visually measured crack depths as well as the crack features obtained with a digital image processing algorithm. It is found that the DI outperforms the attenuation coefficient in depth estimation, where this index displays good agreement with the visual inspection for 86% of the inspected specimens.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.34D no.11
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• pp.54-63
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• 1997

The 1-D finite-element mehtod is applied for designing double-clad otpical fibers with dispersion-compensation capability. design parameters allowing only a $LP_{01}$ single mode are treated and macro-bending loss are taken into consideration. Design parameters are extracted to have the compensation ratio $(L_{SMF}/L_{DCF})$ of 6.2 for core structure with step-index profile, and of 5.2 for core with triangular-index profile.

• Journal of Advanced Navigation Technology
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• v.17 no.4
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• pp.413-420
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• 2013

The design rule depending on total transmission length is induced in the optical links with residual dispersion per span (RDPS) of the random distribution, which is adopted for implementing the flexible systems of wavelength division multiplexing (WDM) transmission with dispersion management (DM) and optical phase conjugation. DM parameters used for the analysis of the design rule are the effective net residual dispersion (NRD) and the effective launch power. It is confirmed that the flexible optical network configuration with the total transmission length lower than 1,000 km is possible, because the system performance difference between the randomly distribution and the uniform distribution of RDPS is small. And, in the optical links with the randomly distributed RDPS, the wide NRD can be applied for transmitting WDM channels of the relatively wide launch power.

• Journal of Advanced Navigation Technology
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• v.14 no.6
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• pp.831-837
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• 2010

Optimal conditions of 40 Gbps RZ format for implementation of optical time division multiplexing/wavelength division multiplexing (OTDM/WDM) transmission system are induced by analyzing and comparing performance depending on duty cycle and extinction ratio (ER). Optical phase conjugator (OPC) and inline dispersion management (DM) are applied into optical transmission links for compensating signal distortion due to chromatic dispersion and nonlinearity of fiber. It is confirmed that RZ format of 0.25 duty cycle is less effected by system performance change depending on ER and it is suitable for multiplexing to 160 Gbps signal through OTDM. Also, it is shown that performance improvement of RZ format determined by same net residual dispersion (NRD) is more increased as residual dispersion per span (RDPS) becomes large.

• Proceedings of the Optical Society of Korea Conference
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• 2004.02a
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• pp.280-281
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• 2004

• Korean Journal of Optics and Photonics
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• v.11 no.2
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• pp.135-138
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• 2000

• Proceedings of the Korean Society For Composite Materials Conference
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• 2004.10a
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• pp.272-277
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• 2004

The elastic waves in the plate are dispersive waves with the characteristics of Lamb waves. However, $S_0$ symmetric mode is less dispersive in the frequency region less than first cut-off frequency. And, in anisotropic plates such as CFRP plates, the propagation velocities vary with the direction. So, the wave vector direction to be the phase velocity direction is not accord with the energy flow direction to be the group velocity direction. In this work, the group velocities of the $S_0$ symmetric mode less than the first cut-off frequency was analyzed with the group velocity dispersion curves in unidirectional CFRP plate. And, the group velocity curve obtained by the group velocity dispersion curves are compared with the measured velocities as varied the propagation direction of the Lamb wave. The measured velocities are good agreement with the corrected group velocity curve except near the fiber direction which is called the cusp region. When the propagation direction is not accorded with the principal axis, the direction of the group velocities declines to the fiber direction in the unidirectional CFRP plates. This implies that the energy propagates preferentially toward fiber direction.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.18 no.11
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• pp.1607-1617
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• 1993

The performance of Manchester-coded ASK optical wavelength division multiplexing(WDM) systems is evaluated laking into account the shot noise and the four wave mixing(FWM) caused by fiber nonlinearities. The result is compared to conventional non-return-to-zero(NRZ) systems for ASK modulation formats. Further, the dynamic range, defined as the ratio of the maximum input power(limited by the FWM), to the minimum input power(limited by receiver sensitivity), is evaluated. For 1.55 rm 16 channel WDM systems, the dynamic range of ASK Manchester coded systems shows a 2.0 dB improvement with respect to the NRZ. This result holds true for both dispersion-shifted fiber and conventional fiber it has been obtained for 10 GHz channel spacing, 1 Gbps/channel bit rate.

• Korean Journal of Optics and Photonics
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• v.23 no.6
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• pp.246-250
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• 2012

We derive analytical expressions for the output spectral density and the noise power $P_{\beta}$ in noise loading analysis using Volterra kernels to characterize fiber nonlinearities. The bandwidth of the input noise source has little effect on $P_{\beta}$, but the power of the input noise source and the dispersion parameter value of the fiber have a significant effect on $P_{\beta}$. The Volterra method predicts ${\Delta}P_{\beta}[dB]$ = 30 dB/decade, which agrees very accurately over a wide range of fiber parameters compared with the numerical results by the split-step Fourier method. Therefore the Volterra method could be useful to predict the performance of a dense WDM system when we plan to upgrade fiber or increase signal power.