초단 펄스 영역에서 비선형 광섬유 레이저 시스템의 수치해석 연구

학위논문 (박사)-- 서울대학교 대학원 공과대학 전기·컴퓨터공학부, 2017. 8. 정윤찬.In this dissertation, nonlinear fiber laser systems in the sub-ps pulse regime are numerically investigated. The main research subjects of this dissertation are categorized into two groups: (1) nonlinear effects in noncavity configurations, e.g. nonlinear fiber sections pumped by ultrashort pulses and (2) nonlinear effects in cavity configurations, e.g. mode-locked fiber ring lasers. When the systems accompany large amount of nonlinearity, the nonlinear effects result in extreme spectral broadening, called supercontinuum generation (SCG) for the former case and multi-pulse operation for the latter case. By exploiting the master equations based on the nonlinear Schrödinger equation (NLSE), I numerically simulate the ultrashort-pulse evolution in the nonlinear fiber laser systems. By analyzing the simulation results, I optimize the system performance or verify unclarified phenomenon in the investigated systems. In the first two parts of the dissertation, I focus on studying the SCG in noncavity configurations. First, I numerically study the dynamics of SCG for a variety of possible combinations of photonic crystal fibers (PCFs) and ultrafast fiber laser pulses that current technologies offer. Three types of PCFs typically used in SCG and four representative types of ultrafast fiber laser pulses are considered for this combinatorial study. I numerically model and qualitatively discuss the nonlinear evolution of the pulses for their 12 combinatorial cases. I also quantitatively analyze their output spectra and organize a performance chart for them in terms of spectral bandwidth, flatness, and degree of spectral coherence. Through these works, I suggest the most viable combinations among the given PCFs and ultrafast fiber laser pulses in order to generate a target SC spectrum for various specific cases. In the second part of this dissertation, I numerically study the dynamics of SCG in a ytterbium-doped highly nonlinear PCF (HNL-PCF) in the sub-ps regime. I disucss the enhancement of the energy spectral density and the recovery of the peak power depletion in the SCG process through the fiber in comparison with the SCG based on a passive-type fiber. As a unique application of the novel characteristics of the active HNL-PCF, I also analyze the direct amplification of a SC pulse through it, showing that the incident SC pulse can be amplified by 10 dB without undergoing significant degradations in terms of spectral bandwidth and flatness. These numerical investigations on the active HNL-PCF will be helpful for opening up new opportunities for fiber-based SCG technology in the sub-ps pulse regime. In the third part of this dissertation, I focus on the nonlinear effects in cavity configurations. I numerically investigate quasi-mode-locked (QML) multi-pulse dynamics in a fiber ring laser in the anomalous dispersion (AD) regime. I show that the laser cavity can operate in five constitutively different QML regimes, depending on the saturation power of the saturable absorber element and the length of the passive fiber section that parameterize the overall nonlinearity and dispersion characteristics of the laser cavity. I classify them into the incoherent noise-like pulse (NLP), partially-coherent NLP, symbiotic, partially-coherent multi-soliton, and coherent multi-soliton regimes, accounting for their coherence and multi-pulse formation features. In particular, I numerically clarify and confirm the symbiotic regime for the first time to the best our knowledge, in which NLP and multi-solitons coexist stably in the cavity that has recently been observed experimentally. Furthermore, I analyze the shot-to-shot coherence characteristics of the individual QML regimes relative to the amount of the nonlinear-phase shift per roundtrip, and verify a strong correlation between them. I also show that the net-cavity dispersion plays a critical role in determining the multi-pulse dynamics out of the partially-coherent NLP, symbiotic, and partially-coherent multi-soliton regimes, when the cavity bears moderate nonlinearity. I quantify and visualize all those characteristics onto contour maps, which will be very useful and helpful in discussing and clarifying the complex QML dynamics. In the fourth part of this dissertation, I extend the analysis of the AD QML cavity into the normal-dispersion (ND) QML cavity. While adjusting two chosen cavity parameters: saturation power of the SA and the length of the ND passive fiber, I verify three distinctive QML operation regimes. Accounting for the temporal dynamics in three QML regimes, I classify them into the NLP, transient, and symbiotic regimes. In each regime, I quantitatively analyze the shot-to-shot stability of the QML pulse and its relation with the cavity nonlinearity by visualizing the results on contour maps. Finally, I discuss the origin of the degradation of the shot-to-shot stability in the ND QML cavity.Chapter 1 Introduction. 1 1.1 Overview on fiber optics 1 1.2 Motivation of this dissertation 6 1.3 Scope and organization. 10 Chapter 2 Nonlinear dynamics in noncavity configurations: supercontinuum generation. 12 2.1 Passive supercontinuum generation in the sub-ps regime. 12 2.2 Active Supercontinuum generation in the sub-ps regime 45 Chapter 3 Nonlinear dynamics in cavity configurations: quasi-mode-locked operation. 67 3.1 Quasi-mode-locked operation in an anomalous dispersion cavity. 67 3.2 Quasi-mode-locked operation in a normal dispersion cavity 92 Chapter 4 Conclusion. 106 Bibliography. 112 한글 초록. 120Docto

The Effects of Sulfur on Welding Properties in Silicon Added Heat-Resistant Stainless Steel

Maste

Effects of MgOon HOt Metal Composition of Blast Furnace Slag

Maste

3-D LDV 시스템을 이용한 3차원 난류구조 해석

2

이동객체 데이타베이스에서 TP 최근접쌍 질의의 처리

학위논문(석사)--서울대학교 대학원 :전기·컴퓨터공학부,2004.Maste

Experimental investigation on the turbulent structure of elliptic jets by using a 3-D LDV system

Maste

3-D LDV 시스템을 이용한 타원제트의 난류특성에 관한 연구

2

Plasma Arc Curing light 으로 광조사한 상아질 접착제의 전단접착강도

Thesis(master`s)--서울대학교 대학원 :치의학과 치과보존학전공,2007.Maste

복합레진의 충전방법이 중합수축응력에 미치는 영향

Objective: The aim of this study was to investigate the effect of layering methods using a methacrylate-based composite, a flowable composite liner and a low shrinkage silorane-based composite on the polymerization shrinkage stress of light cured composites. Methods: Twenty four aluminum blocks were used to prepare MOD cavities and divided into four groups. A universal hybrid methacrylate-based Filtek Z250 composite (Z250), a Filtek Z350 flowable composite (Z350 flowable), and a silorane-based Filtek P90 composite (P90) were used to fill the cavities. Cavities were restored using four different filling protocols. Group 1 was filled in bulk with Z250, group 2 was restored by an increment technique with the same composite, group 3 by an increment technique with Z250 after lining with a Z350 flowable, and group 4 by an increment technique with P90. The axial shrinkage strain and flexural modulus of the three composites were determined, and cuspal deflection of each group was measured with LVDT probes and compared among groups using ANOVA and Tukeys post hoc test (α=0.05). Results: The axial shrinkage strains of P90, Z250, and Z350 flowable were 1.05 (0.09), 2.28 (0.04), and 4.12 (0.09)%, respectively. The flexural modulus of P90 was 10.1 (0.9), Z250 was 13.6 (2.0), and Z350 was 7.6 (0.9) GPa. The cuspal deflections at 33 minutes in groups 1-4 were 18.2 (1.54), 14.5 (0.47), 16.2 (1.10), and 6.6 (0.44) ㎛, respectively. The increment technique yielded significantly lower cuspal deflection than the bulk technique. Flowable composite lining under incrementally filled universal composite (Z250) showed higher cuspal deflection than that without flowable composite lining. Silorane-based (P90) composite exhibited lower cuspal deflection than methacrylate-based (Z250) composite. Significance: Cuspal deflection resulting from polymerization shrinkage stress can be reduced by the increment technique and low shrinking composite to obtain optimal clinical outcomes. Flowable composite lining under incrementally filled universal composite did not reduce polymerization shrinkage stress in terms of cuspal deflection.목적: 본 연구의 목적은 적층충전 방법, flowable 복합레진 이장재의 사용 및 저수축 silorane-based 복합레진 사용이 광중합 복합레진의 중합수축응력에 미치는 영향을 조사하기 위함이다. 재료 및 사용방법: MOD 와동이 형성된 24개의 알루미늄 블록을 제작하여 네 군으로 분류하였다. 충전에 사용된 복합레진은 methacrylate-based 전구치 범용 복합레진 (Z250), flowable 복합레진 (Z350 flowable), silorane-based 복합레진 (P90) 이었고, 형성된 와동은 군별로 네 가지 각기 다른 충전방법으로 충전되었다. 1군은 Z250 복합레진으로 한 번에 충전하였고, 2군은 Z250 복합레진으로 적층 충전하였다. 3군은 Z350 flowable 복합레진으로 이장 후 Z250으로 적층 충전하였고 4군은 P90으로 적층 충전하였다. 세 종의 복합레진의 axial 중합수축률과 굴곡 탄성계수를 측정하였고, LVDT probe를 사용하여 각 군에서 교두굴곡을 측정하였으며, ANOVA와 Tukeys post hoc test로 분석하였다 (α=0.05). 결과: P90, Z250, 그리고 Z350 flowable 의 axial 중합수축률은 각각 1.05 (0.09), 2.28 (0.04), 4.12 (0.09)% 였다. P90의 굴곡 탄성계수는 10.1 (0.9), Z250은 13.6 (2.0), 그리고 Z350은 7.6(0.9) GPa 로 가장 낮았다. 1군에서 4군의 평균 교두굴곡은 광조사 시작 후 33분에서 각각 18.2 (1.54), 14.5 (0.47), 16.2 (1.10), 6.6 (0.44) ㎛ 이었다. 적층 충전이 한 번에 충전보다 현저히 적은 교두굴곡을 보였다. Z250 복합레진으로 적층 충전 하기 전에 flowable 복합레진을 이용하여 이장한 경우, flowable 복합레진 이장재 없이 Z250 으로만 적층 충전 한 경우보다 더 큰 교두굴곡을 보였다. Silorane-based 복합레진 (P90) 이 methacrylate-based 복합레진의 경우 (Z250) 보다 더 적은 교두굴곡을 나타냈다. 고찰: 중합수축응력에 의해 발생되는 교두굴곡은 적층 충전법이나 저수축 복합레진을 사용하여 줄일 수 있었다. 범용 복합레진으로 적층 충전하기 전에 flowable 복합레진 이장재를 사용하는 것은 중합수축응력에 의한 교두굴곡을 감소시키지 못하였다.Docto

전기장을 이용한 핵비등 열전달 촉진과 기포의 동적거동에 관한 연구

Docto