An Efficient Algorithm for Steady State Analysis of Fibre Lasers Operating under Cascade Pumping Scheme

We derive an efficient algorithm for the steady state analysis of fibre lasers operating under cascade pumping scheme by combining the shooting method with the Newton-Raphson method. We compare the proposed algorithm with the two standard algorithms that have been used so far in the available literature: the relaxation method and the coupled solution method. The results obtained show that the proposed shooting method based algorithm achieves much faster convergence rate at the expense of a moderate increase in the calculation time.  It is found that a further improvement in the computational efficiency can be achieved by using few iterations of the relaxation method to calculate the initial guess for the proposed shooting method based algorithm

Técnicas alternativas para amplificação de Raman em telecomunicações

Doutoramento em FísicaO presente trabalho centra-se no estudo dos amplificadores de Raman em fibra ótica e suas aplicações em sistemas modernos de comunicações óticas. Abordaram-se tópicos específicos como a simulação espacial do amplificador de Raman, a equalização e alargamento do ganho, o uso de abordagens híbridas de amplificação através da associação de amplificadores de Raman em fibra ótica com amplificadores de fibra dopada com Érbio (EDFA) e os efeitos transitórios no ganho dos amplificadores. As actividades realizadas basearam-se em modelos teóricos, sendo os resultados validados experimentalmente. De entre as contribuições mais importantes desta tese, destaca-se (i) o desenvolvimento de um simulador eficiente para amplificadores de Raman que suporta arquitecturas de bombeamento contraprogantes e bidirecionais num contexto com multiplexagem no comprimento de onda (WDM); (ii) a implementação de um algoritmo de alocação de sinais de bombeamento usando a combinação do algoritmo genético com o método de Nelder- Mead; (iii) a apreciação de soluções de amplificação híbridas por associação dos amplificadores de Raman com EDFA em cenários de redes óticas passivas, nomeadamente WDM/TDM-PON com extensão a região espectral C+L; e (iv) a avaliação e caracterização de fenómenos transitórios em amplificadores para tráfego em rajadas/pacotes óticos e consequente desenvolvimento de soluções de mitigação baseadas em técnicas de clamping ótico.The present work is based on Raman Fiber Amplifiers and their applications in modern fiber communication systems. Specific topics were approached, namely the spatial simulation of Raman fiber amplifiers, the gain enlargement and equalization the use of hybrid amplification approaches by association of Raman amplifiers with Erbium doped fiber amplifiers (EDFA) and the transient effect on optical amplifiers gain. The work is based on theoretical models, being the obtained results validated experimentally. Among the main contributions, we remark: (i) the development of an efficient simulator for Raman fiber amplifiers that supports backward and bidirectional pumping architectures in a wavelength division multiplexing (WDM) context; (ii) the implementation of an algorithm to obtain enlargement and equalization of gain by allocation of pumps based on the association of the genetic algorithm with the Nelder-Mead method; (iii) the assessment of hybrid amplification solutions using Raman amplifiers and EDFA in the context of passive optical networks, namely WDM/TDM-PON with extension the C+L spectral bands; (iv) the assessment and characterization of transient effects on optical amplifiers with bursty/packeted traffic and the development of mitigation solutions based on optical clamping

Spatially integrated erbium-doped fiber amplifiers enabling space-division multiplexing

L'augmentation exponentielle de la demande de bande passante pour les communications laisse présager une saturation prochaine de la capacité des réseaux de télécommunications qui devrait se matérialiser au cours de la prochaine décennie. En effet, la théorie de l’information prédit que les effets non linéaires dans les fibres monomodes limite la capacité de transmission de celles-ci et peu de gain à ce niveau peut être espéré des techniques traditionnelles de multiplexage développées et utilisées jusqu’à présent dans les systèmes à haut débit. La dimension spatiale du canal optique est proposée comme un nouveau degré de liberté qui peut être utilisé pour augmenter le nombre de canaux de transmission et, par conséquent, résoudre cette menace de «crise de capacité». Ainsi, inspirée par les techniques micro-ondes, la technique émergente appelée multiplexage spatial (SDM) est une technologie prometteuse pour la création de réseaux optiques de prochaine génération. Pour réaliser le SDM dans les liens de fibres optiques, il faut réexaminer tous les dispositifs intégrés, les équipements et les sous-systèmes. Parmi ces éléments, l'amplificateur optique SDM est critique, en particulier pour les systèmes de transmission pour les longues distances. En raison des excellentes caractéristiques de l'amplificateur à fibre dopée à l'erbium (EDFA) utilisé dans les systèmes actuels de pointe, l'EDFA est à nouveau un candidat de choix pour la mise en œuvre des amplificateurs SDM pratiques. Toutefois, étant donné que le SDM introduit une variation spatiale du champ dans le plan transversal de la fibre, les amplificateurs à fibre dopée à l'erbium spatialement intégrés (SIEDFA) nécessitent une conception soignée. Dans cette thèse, nous examinons tout d'abord les progrès récents du SDM, en particulier les amplificateurs optiques SDM. Ensuite, nous identifions et discutons les principaux enjeux des SIEDFA qui exigent un examen scientifique. Suite à cela, la théorie des EDFA est brièvement présentée et une modélisation numérique pouvant être utilisée pour simuler les SIEDFA est proposée. Sur la base d'un outil de simulation fait maison, nous proposons une nouvelle conception des profils de dopage annulaire des fibres à quelques-modes dopées à l'erbium (ED-FMF) et nous évaluons numériquement la performance d’un amplificateur à un étage, avec fibre à dopage annulaire, à ainsi qu’un amplificateur à double étage pour les communications sur des fibres ne comportant que quelques modes. Par la suite, nous concevons des fibres dopées à l'erbium avec une gaine annulaire et multi-cœurs (ED-MCF). Nous avons évalué numériquement le recouvrement de la pompe avec les multiples cœurs de ces amplificateurs. En plus de la conception, nous fabriquons et caractérisons une fibre multi-cœurs à quelques modes dopées à l'erbium. Nous réalisons la première démonstration des amplificateurs à fibre optique spatialement intégrés incorporant de telles fibres dopées. Enfin, nous présentons les conclusions ainsi que les perspectives de cette recherche. La recherche et le développement des SIEDFA offriront d'énormes avantages non seulement pour les systèmes de transmission future SDM, mais aussi pour les systèmes de transmission monomode sur des fibres standards à un cœur car ils permettent de remplacer plusieurs amplificateurs par un amplificateur intégré.The exponential increase of communication bandwidth demand is giving rise to the so-called ‘capacity crunch’ expected to materialize within the next decade. Due to the nonlinear limit of the single mode fiber predicted by the information theory, all the state-of-the-art techniques which have so far been developed and utilized in order to extend the optical fiber communication capacity are exhausted. The spatial domain of the lightwave links is proposed as a new degree of freedom that can be employed to increase the number of transmission paths and, subsequently, overcome the looming ‘capacity crunch’. Therefore, the emerging technique named space-division multiplexing (SDM) is a promising candidate for creating next-generation optical networks. To realize SDM in optical fiber links, one needs to investigate novel spatially integrated devices, equipment, and subsystems. Among these elements, the SDM amplifier is a critical subsystem, in particular for the long-haul transmission system. Due to the excellent features of the erbium-doped fiber amplifier (EDFA) used in current state-of-the-art systems, the EDFA is again a prime candidate for implementing practical SDM amplifiers. However, since the SDM introduces a spatial variation of the field in the transverse plane of the optical fibers, spatially integrated erbium-doped fiber amplifiers (SIEDFA) require a careful design. In this thesis, we firstly review the recent progress in SDM, in particular, the SDM optical amplifiers. Next, we identify and discuss the key issues of SIEDFA that require scientific investigation. After that, the EDFA theory is briefly introduced and a corresponding numerical modeling that can be used for simulating the SIEDFA is proposed. Based on a home-made simulation tool, we propose a novel design of an annular based doping profile of few-mode erbium-doped fibers (FM-EDF) and numerically evaluate the performance of single stage as well as double-stage few-mode erbium-doped fiber amplifiers (FM-EDFA) based on such fibers. Afterward, we design annular-cladding erbium-doped multicore fibers (MC-EDF) and numerically evaluate the cladding pumped multicore erbium-doped fiber amplifier (MC-EDFA) based on these fibers as well. In addition to fiber design, we fabricate and characterize a multicore few-mode erbium-doped fiber (MC-FM-EDF), and perform the first demonstration of the spatially integrated optical fiber amplifiers incorporating such specialty doped fibers. Finally, we present the conclusions as well as the perspectives of this research. In general, the investigation and development of the SIEDFA will bring tremendous benefits not only for future SDM transmission systems but also for current state-of-the-art single-mode single-core transmission systems by replacing plural amplifiers by one integrated amplifier

Investigation of EDFA power transients in circuit-switched and packet-switched optical networks

Erbium-doped fibre amplifiers (EDFA’s) are a key technology for the design of all optical communication systems and networks. The superiority of EDFAs lies in their negligible intermodulation distortion across high speed multichannel signals, low intrinsic losses, slow gain dynamics, and gain in a wide range of optical wavelengths. Due to long lifetime in excited states, EDFAs do not oppose the effect of cross-gain saturation. The time characteristics of the gain saturation and recovery effects are between a few hundred microseconds and 10 milliseconds. However, in wavelength division multiplexed (WDM) optical networks with EDFAs, the number of channels traversing an EDFA can change due to the faulty link of the network or the system reconfiguration. It has been found that, due to the variation in channel number in the EDFAs chain, the output system powers of surviving channels can change in a very short time. Thus, the power transient is one of the problems deteriorating system performance. In this thesis, the transient phenomenon in wavelength routed WDM optical networks with EDFA chains was investigated. The task was performed using different input signal powers for circuit switched networks. A simulator for the EDFA gain dynamicmodel was developed to compute the magnitude and speed of the power transients in the non-self-saturated EDFA both single and chained. The dynamic model of the self-saturated EDFAs chain and its simulator were also developed to compute the magnitude and speed of the power transients and the Optical signal-to-noise ratio (OSNR). We found that the OSNR transient magnitude and speed are a function of both the output power transient and the number of EDFAs in the chain. The OSNR value predicts the level of the quality of service in the related network. It was found that the power transients for both self-saturated and non-self-saturated EDFAs are close in magnitude in the case of gain saturated EDFAs networks. Moreover, the cross-gain saturation also degrades the performance of the packet switching networks due to varying traffic characteristics. The magnitude and the speed of output power transients increase along the EDFAs chain. An investigation was done on the asynchronous transfer mode (ATM) or the WDM Internet protocol (WDM-IP) traffic networks using different traffic patterns based on the Pareto and Poisson distribution. The simulator is used to examine the amount and speed of the power transients in Pareto and Poisson distributed traffic at different bit rates, with specific focus on 2.5 Gb/s. It was found from numerical and statistical analysis that the power swing increases if the time interval of theburst-ON/burst-OFF is long in the packet bursts. This is because the gain dynamics is fast during strong signal pulse or with long duration pulses, which is due to the stimulatedemission avalanche depletion of the excited ions. Thus, an increase in output power levelcould lead to error burst which affects the system performance

광학적 이득이 포함된 비선형 광학적 매질에서의 초연속체 생성 및 펄스 역학에 관한 이론적 연구

학위논문(박사)--서울대학교 대학원 :공과대학 전기·컴퓨터공학부,2020. 2. 정윤찬.In this dissertation, supercontinuum generation (SCG) and related soliton dynamics in gain-embedded highly nonlinear photonic crystal fibers (HNL-PCFs) are numerically and theoretically analyzed in anomalous dispersion (AD) and flattened all-normal dispersion (FAND). The first part of the dissertation introduces the fundamental of fiber optics, fiber lasers, and nonlinear fiber optics. Based on the background knowledge on fiber optics, fiber lasers, and nonlinear fiber optics, the fundamental principle of SCG is briefly overviewed, which is a key basis for this dissertation. Then, a numerical model of dynamics of ultrafast pulses under dispersive, nonlinear, and optical gain effects. First, the well-known numerical model on evolution of ultrafast pulses in HNL-PCFs, nonlinear Schrödinger equation (NLSE), is discussed. Moreover, optical bright solitons (BSs) and dark solitons (DSs), the key elements of the SCG, are introduced briefly. Then, a numerical model of optical gain effects on sub-fs ultrafast pulses is suggested. Especially, a semi-classical numerical model based on the generalized complex Ginzburg-Landau equation (GCGLE) is suggested in order to take account of ultrafast interactions between gain ions and ultrafast solitons. Based on the GCGLE, SCG in a rare-earth doped HNL-PCF with AD in the sub-ps pulse regime is numerically investigated. The SCG characteristics of an active HNL-PCF is compared with a passive-type counterpart, unveiling novel optical gain effects. Moreover, gain-induced soliton dynamics, such as soliton-cascade-like behaviors, soliton-quasi-soliton collisions, and phase-matched dispersive wave generation, is rigorously analyzed, which eventually contributes to enhancement of energy scaling of SC radiation without incurring considerable degradation of its spectral flatness. As a counterpart of SCG in a rare-earth doped HNL-PCF with AD, SCG in a rare-earth doped HNL-PCF with FAND in the sub-picosecond pulse regime is also numerically investigated. In particular, spontaneous generation of DSs in FAND regime and its physical mechanism of the DS generation is discussed. By the combined effect of the optical gain and Raman scattering, Raman-induced oscillatory structure (RIOS) is emitted at the outermost blue-shifted SPM peak, and it develops dark solitons under the optical gain effect. The emitted dark solitons significantly affect SCG characteristics such as spectral bandwidth and shot-to-shot coherence. Consequently, it is proven that the utilization of active fibers for SCG yields bandwidth- or coherence-controllable SCG system. Therefore, this study suggests the possibility of further improvement of SCG by exploiting the novel active-type HNL-PCFs, which is all-in-one structure of a passive-type HNL-PCF and a rare-earth doped fiber. Furthermore, soliton dynamics related to SCG in active HNL-PCFs is drastically different to the conventional soliton dynamics of SCG in passive fibers. The reason is that in active HNL-PCFs, the soliton dynamics correlated with SCG is actually the soliton dynamics in open systems where external energy inflows are present. The energy inflow causes various soliton dynamics, which have not been observed in soliton dynamics in a closed system. For example, soliton clusters, collisions of a soliton and a quasi-soliton, spontaneous and eruptive generation of DSs, and DS-based coherence collapse. Such novel soliton dynamics in an open system will open up new possibilities for extended power-scaling, controlled spectral broadening and shot-to-shot coherence of SCG.본 논문에서, 광학적 이득이 포함된 고-비선형 광 결정 광섬유에서의 초연속체 생성과 관련된 솔리톤 역학을 수치적 및 이론적으로 분석하였다. 특히, 고-비선형 광 결정 광섬유의 전-정상 분산 및 비정상 분산에서의 밝은 솔리톤과 어두운 솔리톤 역학 현상을 조사하였고, 이러한 솔리톤 역학이 초연속체 생성에 미치는 영향을 자세히 분석하였다. 논문의 첫 번째 챕터에서는, 광섬유 광학과 광섬유 레이저, 그리고 광학적 솔리톤 및 초연속체 생성과 같은 비선형 광학 현상을 개괄적으로 소개하였다. 이어 두 번째 챕터에서는, 초고속 광 펄스와 이득 이온 사이의 초고속 상호 작용을 수치적으로 모델링하였다. 특히, 초고속 광 펄스가 겪는 비선형 광학 현상은 비선형 슈뢰딩거 방정식으로 모델링하였으며, 펨토 초 영역에서 이득 이온과 광 펄스의 빠른 상호작용을 모델링하기 위하여 멕스웰-블로흐 방정식을 유도하였다. 특히, 광섬유에 도핑이 되는 이온인 어븀 그리고 이터븀에 대한 멕스웰-블로흐 방정식을 각각 유도하였다. 또한, 일정한 주기를 가지고 반복적으로 입력이 되는 펄스에 의한 이득 이온의 이득 포화 작용을 멕스웰-블로흐 방정식으로부터 유도하여, 해당 작용을 유효 포화 에너지라는 단일 상수로 표현하였다. 이는 세 번째 챕터에서 멕스웰-블로흐 방정식과 비선형 슈뢰딩거 방정식을 결합시키는 열쇠가 된다. 세 번째 챕터에서는, 초고속 광 펄스와 광학적 이득의 상호작용에 의한 초연속체 현상을 모델링하고, 광학적 이득이 초연속체 및 솔리톤 역학에 미치는 영향을 조사하였다. 일반적으로 실제로 피코 초 펄스와 이득 이온의 상호 작용은 종종 잘 알려진 비율식 (rate equation)과 비선형 슈뢰딩거 방정식으로 모델링 되지만, 비정상 분산 영역에서 초연속체 생성 과정 중에 필연적으로 발생하는 100-fs 이하 초고속 펄스와 이득 이온의 상호 작용은 비율식으로 모델링 될 수 없다. 따라서, 본 논문에서는 두 번째 챕터에서 유도한 이터븀 이온에서의 멕스웰-블로흐 방정식과 비선형 슈뢰딩거 방정식을 결합한, 일반화된 긴즈버그-란다우 방정식 모델을 사용하였다. 긴즈버그-란다우 방정식에 기초하여, 피코 초 미만 펄스 영역에서 비정상 분산을 갖는 활동성 광결정 광섬유에서의 초연속체 생성을 수치해석적으로 조사하였다. 이득 효과는 단계적 솔리톤 방출, 솔리톤-준솔리톤 충돌, 및 고주파수의 분산광 생성과 같은, 수동성 광결정 광섬유의 초연속체에서 발견되지 않은 새로운 솔리톤 역학 현상을 야기하였다. 이득에 의해 새로이 발현된 솔리톤 역학은, 초연속체가 평탄성을 잃지 않고 광대역 스펙트럼 성분이 균등하게 증폭시키는데 기여한다. 논문의 네 번째 챕터에서는, 전-정상 분산의 특성을 갖는 이득 광결정 광섬유에서의 초연속체 생성을 분석하였다. 일반적으로 전-정상 분산의 조건에서는 어두운 솔리톤이 자발적으로 생기지 않는다. 하지만, 일정 임계점 이상의 높은 이득을 인가한다면, 자발적으로 어두운 솔리톤이 생성될 수 있다는 사실을 본 수치 해석을 통해 확인하였다. 이득 및 라만 산란 파라미터를 조절하며 비교적 수치 해석을 수행한 결과, 어두운 솔리톤은 광학적 이득과 라만 산란이 동시에 존재하는 경우에만 생성된다는 사실을 확인했다. 높은 광학적 이득은 펄스의 첨두 출력을 상승시키고, 상승된 첨두 출력은 자기-위상 변조에 의해 생성된 청-주파수 쪽 첨두 스펙트럼 파워를 상승시킨다. 첨두 스펙트럼 파워가 일정 문턱 값을 넘어서게 된다면, 청-주파수 첨두 스펙트럼으로부터 라만-유도 진동 구조 (RIOS)가 발생한다. 발생한 RIOS는 시간이 지남에 따라 점점 더 증폭되며, 진동 구조로부터 어두운 솔리톤이 발생한다. 이러한 어두운 솔리톤은 서로 반발적으로 충돌하며 복잡한 역학적 양상을 보인다. 이러한 복잡한 어두운 솔리톤 역학은 초연속체 스펙트럼의 대역폭 및 간섭성에 영향을 준다. 어두운 솔리톤에 의해 초연속체 스펙트럼의 간섭성은 점진적으로 감소하며, 동시에 적-주파수 한계선 너머로 추가적인 스펙트럼의 확장이 발생한다. 이는 곧 펌프 파워와 같은 광학적 이득 파라미터를 조절함으로써 초연속체의 대역폭, 파워, 그리고 간섭성을 조절할 수 있음을 의미한다. 이는 파워 및 간섭성-제어 가능한 초연속체 생성 시스템 개발의 핵심 원리로 적용될 수 있다. 결론적으로, 광학적 이득이 포함된 광 결정 광섬유에서 초연속체를 생성할 때, 광학적 이득을 조절함으로써 초연속체의 파워 스케일링을 할 수 있으며, 동시에 대역폭 및 간섭성 특성을 제어할 수 있다는 사실을 본 연구를 통해 규명하였다. 이는 곧 입력 초연속체의 특성을 조절할 수 있는 기존의 파라미터인 펄스 폭과 첨두 출력 이외에 펌프 파워라는 추가적인 제어 파라미터의 획득을 의미한다. 펄스 폭이나 첨두 출력을 증가시키면 초연속체 스펙트럼의 파워보다는 대역폭이 증가하는 경향이 컸던 반면, 이득을 증가시키면 스펙트럼의 대역폭보다는 파워가 증가하는 경향이 크기 때문에 초연속체의 파워 스케일링에 용이하다. 이에 더하여, 전-정상 분산 영역에서는 이득에 따라 shot-to-shot 간섭성이 달라지기 때문에, 단순히 펌프 파워만을 조절하여 저-간섭성에서부터 고-간섭성 초연속체 광원을 모두 생성할 수 있다. 따라서, 본 연구의 결과는 다양한 광 응용 분야에서 요구하는 특성의 초연속체 광원을 맞춤형으로 생성할 수 있는 종합적 초연속체 광원 생성 시스템 개발의 기반 원리로서 응용될 수 있다. 또한, 본 연구에서 관찰된 솔리톤 역학은 기존의 닫힌 계 솔리톤 역학이 아닌 에너지가 출입하는 열린 계에서의 솔리톤 역학으로, 닫힌 계에서는 볼 수 없었던 흥미로운 현상들이 다수 관찰되었다. 열린 계에서의 집단적 솔리톤 상호작용은 아직 활발히 연구되지 않은 새로운 비선형 광학 연구 분야이다. 이에, 본 논문을 통해 보고되는 연구 성과가 앞으로 이득이 결합된 비선형 매질에서의 솔리톤 역학 및 응용에 관한 후속 연구에 도움이 될 것을 희망한다.1. Introduction 1 1.1 Fiber optics 1 1.2 Fiber laser 9 1.3 Nonlinear fiber optics 13 1.4 Supercontinuum generation 14 1.5 Motivation 17 1.6 Scope of the study 21 2. Numerical model of ultrafast optics active and nonlinear media 22 2.1 Numerical model of ultrafast optics 22 2.2 Semiclassical model of light-matter interactions 30 2.3 Gain saturation effect by an ultrafast pulse train 44 3. Superconitnuum generation and bright soliton dynamics in gain-embedded highly nonlinear photonic crystal fibers with anomalous dispersion 50 3.1 Background of the study 50 3.2 Numerical model and methods 54 3.3 Gain effects and soliton dynamics on SCG in the AD regime 61 3.4 Comparative analysis of energy-scaling scheme for SCG 72 3.5 Direct amplification of SC radiation 76 4. Superconitnuum generation and dark soliton dynamics in gain embedded highly nonlinear photonic crystal fibers with flattend all-normal dispersion 79 4.1 Background of the study 79 4.2 Numerical model 84 4.3 Review of SCG in active FAND-PCFs in low gain regime 87 4.4 Eruptive generation of Dss on SCG in active FAND-PCFs 91 4.5 Raman-induced oscillatory structure 100 4.6 DS dynamics and its impact on SCG in active FAND-PCFs 109 5. Concluding remarks 120 Appendix A. Derivation of Maxwell-Bloch equation in two-level and the saturation energy 125 Bibliography 131 Abstract in Korean 141Docto

Sub-femtosecond precision timing distribution, synchronization and coherent synthesis of ultrafast lasers

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 180-189).In this thesis, we present a complete set of techniques for sub-femtosecond measurement, control and distribution of ultrafast optical pulse trains, with respect to pulse timing and phase. First, analytical analysis of the balanced optical cross-correlator (BOC) for attosecond precision pulse timing measurement is presented for both short and long crystal devices. It is found that the sensitivity of the long crystal BOC is independent of pulse duration, to first order. In addition, analytical noise models predict 13 as rms resolution, within a 1 MHz bandwidth, for optical pulses consistent with a practical fiber optic timing link. This analysis aids the widespread adoption of the BOC technique for other wavelengths and implementations. Secondly, long term timing distribution of a 200 MHz ultrafast optical pulse train over 340 m of single mode optical fiber is demonstrated, using the BOC. In this way, the group delay of the fiber link is directly stabilized with unprecedented precision and longterm stability. In addition, by distributing the entire optical pulse train, all optical and RF harmonics are provided at the remote location for direct synchronization of remote ultrafast lasers and microwave electronics. Over 168 hours of continuous, unaided operation, a drift of 5 fs rms is achieved, with less than 1.5 fs rms drift at timescales up to 10,000 seconds. Additional analysis of factors effecting performance, such as polarization mode dispersion and fiber nonlinearity is studied through experiment and simulations. It is found that nonlinear-origin drifts can be avoided for pulse energies below 40 pJ. A chirped pulse method could be implemented to distribute pulses of higher energy. Thirdly, the first quantum-resolution timing jitter measurement of ultrafast laser timing jitter for passively mode-locked lasers up to the Nyquist frequency is presented. The total jitter from for a 79.4 MHz stretched pulse erbium fiber laser is found to be 2.6 fs rms [10 kHz, 39.7 MHz]. It is found that the timing jitter power spectral density scales with frequency according to that expected for a white noise source, in agreement with theory. However, unexpected spurious jitter at high frequencies can occur for some mode-locked states, adding up to 5.5 fs rms jitter. Similar measurements of a 200 MHz erbium fiber soliton laser reveal the decay time of center frequency fluctuations to be 17 ns, with a predicted excess noise of approximately ten. These measurements suggest that timing jitter can be decreased through improved amplifier design. Finally, the synchronization of a 8 fs fiber supercontinuum at 1200 nm to a 7 fs Ti:Sapphire laser pulse train at 800 nm is achieved for both pulse timing and phase with attosecond precision. This achievement is enabled by the development of a novel scheme for stabilization of the carrier envelope offset of the entire optical bandwidth of an octave spanning supercontinuum, without introducing excess timing jitter. In particular, by implementing an acousto-optic frequency shifting (AOFS) feedback system within a fiber supercontinuum source, carrier envelope phase locking, to the Ti:Sapphire laser, is demonstrated to within 200 mrad rms [100 Hz, 5 MHz]. Previous techniques lack the high-speed, orthogonal control of CEP and pulse timing and broad optical bandwidth for synthesizing few-cycle optical pulses. Furthermore, timing synchronization of 280 as rms is achieved through combined piezoelectric and electro-optic feedback on the fiber supercontinuum, as measured with the BOC. This work enables the synthesis of a frequency comb spanning 650 to 1400 nm, resulting in a 3.5 fs transform limited pulse duration-assuming ideal spectral phase compression. To date, the spectrum has been successfully compressed to 4.7 fs, as measured with two-dimensional spectral shearing interferometry (2DSI). Moreover, by stabilizing a fiber supercontinuum source to a low-noise Ti:Sapphire laser, the ultra-high stability of the Ti:Sapphire laser is fully transferred to the octave spanning supercontinuum.by Jonathan A. Cox.Ph.D

33 Femtosecond Yb-doped optical frequency comb for frequency metrology applications

Ankara : The Department of Physics and the Graduate School of Engineering and Science of Bilkent University, 2013.Thesis (Master's) -- Bilkent University, 2013.Includes bibliographical references leaves 76-87.Optical frequency combs have enabled many applications (high precision spectroscopy, table-top optical frequency metrology, optical atomic clocks, etc.), received considerable attention and a Nobel Prize. In this thesis, the development of a stabilized Yb-doped femtosecond optical frequency comb is presented. As a starting point in the development of the frequency comb, a new type of fiber laser has been designed using numerical simulations and realized experimentally. The developed laser is able to produce pulses that can be compressed to 33 fs without higher-order dispersion compensation. After realization of the laser, a new type of fiber amplifier has been developed to be used for supercontinuum generation. The amplifier produces 6.8 nJ pulses that can be compressed to 36 fs without higher-order dispersion compensation. The dynamics of supercontinuum generation have been studied by developing a separate simulation program which solves the generalized nonlinear Schr¨odinger equation. Using the simulation results, appropriate photonic crystal fiber was chosen and octave-spanning supercontinuum was generated. Carrier-envelope-offset frequency of the laser has been obtained by building an f-2f interferometer. Repetition rate and carrier-envelope offset frequency of the laser have been locked to Cs atomic clock using electronic feedback circuits, resulting in a fully stabilized optical frequency comb. The noise performance and stability of the system have been characterized. Absolute frequency measurement of an Nd:YAG laser, which was stabilized using iodine gas, has been performed using the developed optical frequency comb.Şenel, ÇağrıM.S

Energy recycling versus lifetime quenching in erbium-doped 3-µm fiber lasers

Based on recently published spectroscopic measurements of the relevant energy-transfer parameters, we performed a detailed analysis of the population mechanisms and the characteristics of the output from Er3+-singly-doped and Er3+, Pr3+-codoped ZBLAN fiber lasers operating at 3 um, for various Er3+ concentrations and pump powers. Whereas both approaches resulted in similar laser performance at Er3+ concentrations 4 mol.% and pump powers 10 W absorbed, it is theoretically shown here that the Er3+-singly-doped system will be advantageous for higher Er3+ concentrations and pump powers. In this case, energy recycling by energy-transfer upconversion from the lower to the upper laser level can increase the slope efficiency to values greater than the Stokes efficiency, as is associated with a number of Er3+-doped crystal lasers. Output powers at 3 um on the order of 10 W are predicted

Wavelength-division-multiplexed Transmission Using Semiconductor Optical Amplifiers And Electronic Impairment Compensation

Over the last decade, rapid growth of broadband services necessitated research aimed at increasing transmission capacity in fiber-optic communication systems. Wavelength division multiplexing (WDM) technology has been widely used in fiber-optic systems to fully utilize fiber transmission bandwidth. Among optical amplifiers for WDM transmission, semiconductor optical amplifier (SOA) is a promising candidate, thanks to its broad bandwidth, compact size, and low cost. In transmission systems using SOAs, due to their large noise figures, high signal launching powers are required to ensure reasonable optical signal-to-noise ratio of the received signals. Hence the SOAs are operated in the saturation region and the signals will suffer from SOA impairments including self-gain modulation, self-phase modulation, and inter channel crosstalk effects such as cross-gain modulation, cross-phase modulation, and four-wave mixing in WDM. One possibility to circumvent these nonlinear impairments is to use constant-intensity modulation format in the 1310 nm window where dispersion is also negligible. In this dissertation, differential phase-shift keying (DPSK) WDM transmission in the 1310 nm window using SOAs was first considered to increase the capacity of existing telecommunication network. A WDM transmission of 4 x 10 Gbit/s DPSK signals over 540 km standard single mode fiber (SSMF) using cascaded SOAs was demonstrated in a recirculating loop. In order to increase the transmission reach of such WDM systems, those SOA impairments must be compensated. To do so, an accurate model for quantum-dot (QD) SOA must be established. In this dissertation, the QD-SOA was modeled with the assumption of overall charge neutrality. Static gain was calculated. Optical modulation response and nonlinear phase noise were studied semi-analytically based on small-signal analysis. The quantitative studies show that an ultrafast gain recovery time of ~0.1 ps can be achieved when QD-SOAs are under high current injection, which leads to high saturation output power. However more nonlinear phase noise is induced when the QD-SOAs are used in the transmission systems operating at 10 Gbit/s or 40 Gbit/s. Electronic post-compensation for SOA impairments using coherent detection and digital signal processing (DSP) was investigated next in this dissertation. An on-off keying transmission over 100 km SSMF using three SOAs at 1.3 [micrometer] were demonstrated experimentally with direct detection and SOA impairment compensation. The data pattern effect of the signal was compensated effectively. Both optimum launching power and Q-factor were improved by 8 dB. For advanced modulation formats involving phase modulation or in transmission windows with large dispersion, coherent detection must be used and fiber impairments in WDM systems need to be compensated as well. The proposed fiber impairment compensation is based on digital backward propagation. The corresponding DSP implementation was described and the required calculations as well as system latency were derived. Finally joint SOA and fiber impairment compensations were experimentally demonstrated for an amplitude-phase-shift keying transmission

Versatile short-wave and mid-infrared sources based on wideband parametric conversion

The mid-infrared part of the optical spectrum is of high interest in a wide range of applications such as environmental gas monitoring, contaminant detection in the chemical, food or pharmaceutical industry, medical diagnosis, or defense and security. Relevant molecules can readily be identified through their mid-infrared absorption spectra, as the latter contains the fundamental resonances of a number of pollutant and toxic gases. Consequently, spectroscopic apparatus, light detection and ranging systems or free-space communication links all benefit from the progress accomplished by mid-infrared technologies over the last years. However some shortcomings in the light emitters capabilities are still to be addressed. In this research work, we aim at designing a mid-infrared laser as versatile as possible and based on nonlinear wavelength conversion. The conversion relies on third-order parametric effects in waveguides such as optical fibers made of various types of glass, or integrated semiconductor chips. The objective is to leverage mature communication-band components to generate and shape the seed optical signals, then mixed in the abovementioned waveguides to down-convert them towards midinfrared. The wavelength conversion is performed in two stages, and the first stage consists of a parametric source emitting in the short-wave infrared range. This thesis mostly focuses on the design and realization of this stage. As such, it is closely linked to the field of nonlinear fiber optics, where the use of silica is preponderant. We build on the research performed over the last years on parametric amplifiers, initially used for the re-amplification of communication signals, and we combine it with technologies dedicated to short-wave infrared fiber lasers. As such, we are able to build wavelength tunable and modulation-capable short-wave infrared sources, significantly more powerful and versatile than previous broadband parametric converter designs. The end of the dissertation is then dedicated to the solutions that are then envisioned to realize the second conversion stage, towards mid-infrared. Very promising numerical and experimental results indicate a successful outcome to the project, confirming the validity of the laser concept