• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.1A
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• pp.16-23
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• 2008

In this paper, we propose a new code grouping interference cancellation(IC) receiver for multirate wideband code division multiple access(WCDMA) system based on orthogonal variable spreading factor(OVSF) code. The users are assigned different lengths of OVSF codes as a spreading code according to their data rates and divide the active users having same representative code split into a group for effective cancellation. The code grouping IC receiver performs cancellation between the groups first and cancellation within group. This proposed IC receiver can cancel the interferences using desired user's code information and then desired signals are detected. The results show that the large improvement in performance can be attained by groupwise IC scheme and we can make the effective systems compare to conventional ones.

• Korean Journal of Optics and Photonics
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• v.3 no.4
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• pp.239-243
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• 1992

We have investigeted the interference phenomena of the second harmonic waves of Nd:YAG laser generated at KDP single crystals and the nitrogen CARS signals. To get the phase difference between the successively generated nonlinear optical signals, a phase shifting unit made of BK-7 glass and a high pressure gas cell are used. Coherence lengths of several samples for the nonlinear signals are measured. Adjusting the thickness of the phase shifting unit where the CARS signals make destructive interference completely, the CARS spectrum of nitrogen suppressed over wide wavelength range is obtained. Also, we have observed the change in degree of suppression of the spectrum for the variation of the thickeness of the phase shifting unit.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.44 no.2
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• pp.46-54
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• 2007

We have fabricated and characterized MMI (Multimode Interference) coupled ring resonator with the total internal reflection mirrors and the semiconductor optical amplifier for the integration of the WDM (Wavelength Division Multiplexing) system. The TIR (Total Internal Reflection) mirrors were fabricated by self-aligned process and had losses of about 0.71 dB per mirror. Coupling in and out of a resonator was achieved using the extremely small MMI couplers. The MMI length and width used in the experiment were $119{\mu}m$ and $9{\mu}m$, respectively. The resulting FSR (Free Spectral Range) and on-off ratio were approximately 1.333 nm (162 GHz) and 13 dB, respectively.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.22 no.4
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• pp.367-374
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• 2004

In order for the measurement results of an electro-optical distance meter(EDM), which is widely used in surveying, to be reliable, an EDM should be calibrated. For the calibration of an EDM, we have settled a traceability chain, which connects the EDM under calibration to the definition of metre. The chain starts from the iodine stabilized He-Ne laser which realizes the definition of metre, and then connected to a stabilized laser interferometer, a standard EDM, and finally to the EDM under calibration through the baseline. We achieved the expanded calibration uncertainties of the scale and length measurement of an EDM being evaluated to be 6$\times$10$^{-6}$ and 0.2 mm, respectively. Two different calibration methods, and their results are compared.

• The Journal of the Acoustical Society of Korea
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• v.29 no.5
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• pp.339-346
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• 2010

For the implementation of the crosstalk canceller, the filters with large length are needed, which is because that the length of the filters greatly depends on the length of the head-related impulse responses. In order to reduce the length of the crosstalk cancellation filters, many methods such as frequency warping, common acoustical pole and zero (CAPZ) modeling have been researched. In this paper, we propose a new method combining these two methods. To accomplish this, we design the filters using the CAPZ modeling on the warped domain, and then, we implement the filters using the poles and zeros de-warped to the linear domain. The proposed method provides improved channel separation performance through the frequency warping and significant reduction of the complexity through the CAPZ modeling. These are confirmed through various computer simulations.

• Korean Journal of Optics and Photonics
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• v.17 no.2
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• pp.159-164
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• 2006

We demonstrate a compact optical coherence tomography(OCT) system based on the optical fiber delay line controlled by a cylindrical piezo-electric transducer(PZT). An 18-m length of single mode fiber is wrapped under constant tension around a PZT. Approximately 134 windings are used. Wraps of the long length of fiber allow the small expansion of the PZT to be magnified to an optical path length delay of 0.78 m. The OCT system shows characteristics for 2-dimensional imaging, exhibiting 96.9dB of signal-to-noise ratio(SNR), $18.6{\pm}0.5\;{\mu}m$ of axial resolution, and $5\;{\mu}m$ of lateral resolution with samples.

• Proceedings of the Korea Institute of Convergence Signal Processing
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• 2001.06a
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• pp.33-36
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• 2001

In MC-CDMA systems effects of delay spread of the channel are reduced with increased symbol duration by simultaneously transmitting data symbols on the parallel subcarriers. However, the increased symbol duration causes the system to be more vulnerable to time selective fading. In this paper, we investigate the effects of time selective fading characteristics of the mobile channel from the viewpoint of desired signal power to inter-carrier interference power ratio at the combiner output of the MC-CDMA receiver.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.11 no.1
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• pp.47-52
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• 2011

In this paper, to evaluate the design properties of 3D optical multimode interference (MMI) couplers with ultracompact width, modal transmission line theory and effective dielectric method are combined with together. A coupling efficiency based on the composed approach is defined, and the coupling length is numerically determined for the design of 3 dB coupler, cross coupler and bar coupler. The simulation result shows that the designed MMI coupler has a low insertion loss and a high splitting ratio.

• Proceedings of the Optical Society of Korea Conference
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• 2006.07a
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• pp.409-410
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• 2006

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.04a
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• pp.513-517
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• 1997

수중음향 센서로서 감도가 높고 제작이 비교적 용이한 광섬유 하이드로폰은 근래에 미국 및 유럽 등지에서 활발히 연구 개발되고 있다. 본 논문에서는 알루미늄 맨드릴에 150 m 길이의 광섬유를 감아 광섬유 하이드로폰을 제작하였다. 광섬유 하이드로폰의 음향 감지 성능을 보기 위하여 Mach-Zehnder형 광간섭계를 구성하고 신호 안정화를 위하여 3 * 3 광결합기를 이용하였으며 이것을 음향수조에서 실험을 하였다. 음향신호의 주파수를 2kHz로 구동하였을 때 제작된 광섬유 하이드로폰은 음향신호를 안정적으로 감지함을 확인하였다.