• Journal of the Optical Society of Korea
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• 제13권1호
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• pp.42-47
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• 2009

The propagation of an intense laser pulse through an upward density-gradient plasma in a self-modulated laser wakefield acceleration (SM-LWFA) is investigated by using particle-in-cell (PIC) simulations. In the fully relativistic and kinetic PIC simulations, the relativistic and kinetic effects including Landau damping enhance the electron dephasing. This electron dephasing is the most important factor for limiting the energy of accelerated electrons. However, the electron dephasing, which is enhanced by relativistic and kinetic effects in the homogeneous plasma, can be forestalled through the detuning process arising from the longitudinal density gradient. Simulation results show that the detuning process can effectively maintain the coherence of the laser wake wave in the spatiotemporal wakefield pattern, hence considerable energy enhancement is achievable. The spatiotemporal profiles are analyzed for the detailed study on the relativistic and kinetic effects. In this paper, the optimum slope of the density gradient for increasing electron energy is presented for various laser intensities.

• 지구물리
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• 제3권4호
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• pp.227-234
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• 2000

진폭이상이나 브라이트 스팟은 종종 탄화수소(가스, 석유)의 집적과 관계 있지만 또한 가까이 있는 두개의 반사면 때문에 생기는 튜닝효과에 의해서도 나타날 수 있다. 탄화수소의 가채매장량을 계산하기 위해서 탄성파 진폭과 저류암의 두께를 계산할 때 탄성파 진폭도로부터 튜닝효과를 제거할 수 있다. 가장 손쉬운 튜닝효과제거(디튜닝) 방법은 탄성파자료의 저류암 진폭을 쐐기모델로부터 얻어진 튜닝반응곡선을 이용하여 보정해 주는 것이다. 진폭이상과 관련된 탄화수소의 집적은 퓨닝효과가 제거된 자료를 이용해야 보다 정확하게 예측할 수 있다.

• ETRI Journal
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• 제45권2호
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• pp.193-202
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• 2023

We demonstrate the transmission of uncompressed 4K videos over the photonics-based terahertz (THz) wireless link using a directly modulated distributed feedback laser diode (DFB-LD). For optical heterodyne mixing and data modulation, a DFB-LD was employed and directly modulated with a 5.94-Gb/s non-return-to-zero signal, which is related to a 6G-serial digital interface standard to support ultra-high-definition video resolution. We derived the optimal frequency of the THz carrier by varying the wavelength difference between DFB-LD output and Tunable LD output in the THz signal transmitter to obtain the best transmission performances of the uncompressed 4K video signals. Furthermore, we exploited the negative laser-to-filter detuning for the adiabatic chirp management of the DFB-LD by the intentional discrepancy between the center wavelength of the optical band-pass filter and the output wavelength of the DFB-LD. With the help of the abovementioned methods, we successfully transmitted uncompressed 4K video signals over the 2.3-m wireless transmission distance without black frames induced by time synchronization error.

• 대한전자공학회논문지
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• 제25권3호
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• pp.238-242
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• 1988

It is analyzed how performance of phase-locked loop driven by photodetector current in optical receiver will be changed under the condition that Gaussian thermal noise, pattern noise and shot noise are present and the loop has the nonzero detuning frequency. The phase error variance cahnges with the circuit configuration and the produced noise models. The analyzed results are applied to the previously implemented 90.194Mbps optic system whose loop filter is the improved active noninverting 1-st order lag-lead type.

• 한국광학회:학술대회논문집
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• 한국광학회 2001년도 제12회 정기총회 및 01년도 동계학술발표회
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• pp.52-53
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• 2001

지속적인 발전을 거듭해 온 초고속 분광학으로 인해, 반도체(semiconductor) 또는 반도체 양자 구조(quantum structure)와 같은 물질에서 결맞는(coherent) 시간 내에 일어나는 다양하고 흥미로운 광학적 특성들의 관찰이 가능해졌다 대부분의 펨토초(femtosecond) 광학 실험이 공명여기(resonant excitation)에 국한되어왔던 반면 최근엔 비공명(off-resonant) 흡수에 의한 가상 여기(virtual excitation)에 대한 관심이 증대되고 있다[1, 2]. (중략)

• Journal of information and communication convergence engineering
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• 제8권4호
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• pp.457-460
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• 2010

we have analyzed tens of Giga pulse signal generation using sideband injection locking scheme. The numerical model for semiconductor lasers under the strong optical injection is based on the Lang's equation and has been extended in order to take into account the simultaneous injection of the multiple sidebands of the current-modulated laser. The numerical simulation results show that the unselected sidebands will affect the optical and RF-spectral characteristics even though the semiconductor laser is locked to the target sidebands.

• 대한전기학회논문지
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• 제37권4호
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• pp.220-225
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• 1988

A class of adaptive controllers with integral action is proposed, which may riject the offset due to any load disturbance on the plant. Effective integral action and robust identification against the offset can be achieved via the zero-gain predictor. The system is improved, in this paper, to be of more generalized structure, and the detuning control weight which can cope with nonminimum-phase systems is tuned on-line. Discrete-time versions of the improved system are developed, which may be more flexible for the choice of the design parameters. The resulting control systems may also be shown to be robust to the unmodelled dynamics.

• 한국광학회지
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• 제12권1호
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• pp.40-47
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• 2001

초고속 디지털 광통신용 $1.55{\mu}m$ InGaAsP/InGaAsP MQW 광흡수 변조기에서 각종 구조변수들이 광흡수변조기 성능에 미치는 영향을 체계적으로 조사분석하였다. 일반적으로 행하여지는 양자우물 수 $N_w$, 양자우물 두께 $t_w$, detuning 양 $\Delta\lambda$, 소자길이 L과 같은 구조 파라미터들에 더불어 본 연구에서 새롭게 제안한 SCH 영역내에 n형으로 도핑된 길이 $t_n$가 소자 성능에 미치는 영향을 해석하였다 이를 통해 소자길이 L=$100{\mu}m$의 광흡수변조기에서 구동 전압 $V_{\alpha}$=0~-2V 영역에서 동작하고 기초흡수 -1.5dB 이하, -1V에서 -2.92dB 및 -2V에서 -10.0dB 이상의 소광비를 주는 우수한 성능을 갖는 초고속 광흡수 변조기 설계가 가능하였다.

• 전자공학회논문지D
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• 제34D권3호
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• pp.60-73
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• 1997

By introducing a compressive-strained quanternary InGaAsP quantum-wells instead of a conventional ternary InGaAs quantum-wells in 1.55.mu.m DFB-LD, the lasing performances canb e improved and the problems caused by the thickness non-uniformity and the compositional abruptness among the hetero-interpaces canb e relaxed. In this paper, we investigated an iptimum InGaAsP/InGaAsP multiple-quantum-well(MQW) structure as an active layer in a direct-modulated 1.55.mu. DFB-LD from the view point of threshold current, chirping charcteristics, and resonance frequency. The optimum compressive-strained MQW structure was revealed as InGaAsP/InGaAsP structure with strain amount of about 1.2%, number of wells $N_{w}$ of 7, well width $L_{w}$ of 58.agns.. The threshold current density J of 500A/c $m^{2}$, the linewidth enhancement factor a of 1.8, and differential resonance frequency of d $f_{r}$/d(I-I)$^{1}$2/=2GHz/(mA)$^{1}$2/(atI=2 $I_{th}$) were expected in 1.55.mu.m .gamma./4-shifted DFB-LD with the cavity length of 400.mu.m long and kL value of 1.25. These values are considerably improved ones compared to those of 1.55um DFB-LD with InGaAs/InGaAsP MQW which have enhancement factor and the resonance frequence frequency by the detuning of lasing wavelength and gain-peak wavelength. It was found that the linewidth enhancement factor of 20% and differential resonance frequency of 35% without the degradation of the threshold current density could be enhanced in the range of -15nm~-20nm detuning which can be realized by controlling the thickness and Incomposition of InGaAsP well. well.and Incomposition of InGaAsP well. well.

• 한국광학회지
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• 제21권2호
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• pp.74-81
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• 2010

WDM-PON 용 저가형 광원으로 유망한 주입 잠금 패브리-페롯 레이저 다이오드의 특성 해석을 위한 모델링 방법을 제시하였다. 해석 방법으로는 시영역 대신호 모델을 이용하였으며, 계산 결과는 기존의 실험 결과와 유사한 경향을 보임을 확인하였다. 이를 토대로 특정한 파라미터를 가지는 레이저 다이오드 구조에서의 단면 반사율에 따른 동작 특성과 디튜닝, 아이 다이어그램등을 모델링 하였다. 특히 단면 반사율의 값에 따른 부모드 억제율 특성 및 디튜닝의 영향을 살펴보았으며, 주입되는 단면의 반사율이 1% 미만으로 유지되어야 안정된 특성을 얻을 수 있음을 확인하였다. 아이 다이어그램의 경우 155 Mbps 급에서는 손쉽게 아이 열림을 얻을 수 있지만, 1.25 Gbps 급에서는 레이저 다이오드의 활성층 두께 등의 파라미터를 적정화해야 적정한 아이특성을 얻을 수 있음을 보였다.