• Journal of the Korea Institute of Information and Communication Engineering
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• v.9 no.1
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• pp.199-203
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• 2005

We present a method to implement a $M{\times}N$ switching system by use of an $M{\times}1$ multimode waveguide and N hologram filters. The pass of optical signals is provided by an $M{\times}1$ multimode waveguide. The complex speckle patterns generated from the multimode waveguide are recorded into the N hologram filters and used as the code for destination. The feasibility of our method is experimentally demonstrated.

• Journal of Institute of Control, Robotics and Systems
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• v.15 no.7
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• pp.683-687
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• 2009

Track jump control is a random access strategy for short distance movement. The most common track jump scheme is a bang-bang control of a kick and brake manner. In a conventional track jump scheme, a track-following compensator is turned off during kick and brake periods, and restarted at a target track for track pull-in. The inevitable controller switching with non-zero initial condition results in undesirable transient response, and excessive overshoot in the transient response causes track pull-in failure. In this paper, a new track jump scheme is proposed for enhancing track jump stability. Instead of control switching, internal states of a track-following controller are artificially manipulated for kick and brake actions in a digital control environment. Experimental results are provided in comparison with conventional track jumps.

• Journal of the Optical Society of Korea
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• v.20 no.1
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• pp.156-164
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• 2016

We demonstrated the pretilt angle effect on the viewing angle properties of a single-domain fringe-field switching (FFS) liquid crystal (LC) mode. By performing the Póincare sphere analysis, we investigated, in detail, the origin of the viewing angle asymmetry that exists in the single-domain FFS LC mode both in the field-on and field-off states. Using this analysis, we confirmed that the pretilt angle reduces the viewing angle symmetry in the single-domain FFS LC mode. Finally, we examined the effect of a zero pretilt angle on the viewing angle symmetry by evaluating real single-domain FFS LC cells.

• Proceedings of the Optical Society of Korea Conference
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• 2009.10a
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• pp.359-360
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• 2009

This paper reports experimental results on temporal characteristics of injection-locked polarization switching of a conventional type 1.55-${\mu}m$ wavelength single-mode vertical-cavity surface-emitting laser (VCSEL). The polarization of external injection beam was kept orthogonal to main mode of VCSEL. The relation for variation of intensity of two polarization modes of VCSEL with wavelength detuning for various repetition rates of injection pulse is reported.

• Journal of the Optical Society of Korea
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• v.18 no.4
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• pp.395-400
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• 2014

We proposed a method for fast turn-off switching of a vertically-aligned liquid crystal cell by low-temperature curing of the polymer structure. We confirmed that the turn-off times of the fabricated cells were reduced significantly as the curing temperature was lowered to $-20^{\circ}C$. We accounted for the effect of low-temperature curing on the turn-off time by using a mathematical model and by observing images obtained via scanning electron microscopy. We also confirmed that low-temperature curing is more effective in reducing the response time when the device is operated at a low temperature.

• Journal of the Optical Society of Korea
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• v.9 no.2
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• pp.64-67
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• 2005

A diode-pumped $Nd:YVO_4$ laser is developed. The laser has a closely folded resonator. The laser beam in two arms of the folded resonator passes the same acousto-optic modulator. The laser output power and pulsewidth dependence on a Q-switching frequency were measured. It is found that the newly proposed geometry provides an effective means for reducing the pulsewidth while maintaining almost the same output power compared with the usual folded resonator, where the beam in one arm of the resonator passes the acousto-optic modulator.

• Proceedings of the Optical Society of Korea Conference
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• 2003.02a
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• pp.160-161
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• 2003

완전 광 3R(Retiming, Reshaping, Reamplification) 재생기는 WDM 시스템과 광 네트워크의 크기를 쉽게 확장시키기 위하여 필요한 매우 중요한 소자이다. 완전 광 3R 재생기의 구현에서 입력 광 신호로부터 광 클락을 추출하는 기술은 매우 중요한 기술이다. 이러한 광 클락 추출기술을 구현하기 위하여 모드락 레이저 다이오드와 다중 전극 OFB 레이저에서 self-pulsation 현상을 이용하는 방법이 많이 연구되고 있다. 모드락 레이저 다이오드를 이용한 방법은 모드 락킹 주파수가 레이저의 공진기의 길이에 의해서 결정되기 때문에 공진기의 길이를 정확하게 조절해야 한다는 단점을 가지고 있는 반면에 다중 전극 DFB 레이저의 경우 self-pulsation 주파수를 전기적으로 튜닝할 수 있다는 장점을 가지고 있다. (중략)

• ETRI Journal
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• v.29 no.1
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• pp.116-119
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• 2007

In this letter, we design a collision resolution protocol for optical burst switching ring networks to avoid burst collision. We define the offset time condition for no burst transmission collision and manage the free time list of nodes for no burst reception collision. In order to improve the throughput, we use a fiber delay line, void-filling, and void-compression. This protocol does not require any additional procedures for bandwidth reservation such as centralized assignment of bandwidth, lightpath setup of WDM ring networks, or token capturing for the burst transmission. The simulation results show that the proposed protocol can achieve high throughput while saving 70% of wavelengths when compared to round robin with random selection, round robin with persistent, and round robin with non-persistent with only destination delay.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.16 no.9
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• pp.833-837
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• 2003

The spectral and temporal characteristics of a V-groove AIGaAs-GaAs quantum wire (QWR) laser were investigated with varying the cavity length. At cavity lengths shorter than 300 ${\mu}{\textrm}{m}$, a discrete shift in tile wavelength occurred from the n=1 to the n=2 subband due to the increased cavity losses. Utilizing this characteristic, ultrafast lasing characteristics at each subband were investigated by tile gain switching method.

• Korean Journal of Optics and Photonics
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• v.18 no.2
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• pp.100-104
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• 2007

We have measured the optical spectra while varying the temperature of photonic crystal fibers (PCFs) with periodic air holes in the cladding. These are liquid crystal infiltrated fibers. For the liquid crystal infiltrated PCFs, we obtained the transmission of several wavelengths at specific temperatures. The transmission power could be reduced by about $10\sim15dB$ by varying the applied temperature in the liquid crystal PCF. We expect that it is applicable as a wavelength switching device in the specific wavelength band.