标题: 光纤雷射混合式主动及被动锁模与同步机制 之理论建模研究
Modeling of Hybrid Active/Passive Fiber Laser Mode-locking and Synchronization
作者: 吴尚颖
Wu, Shang-Ying
赖暎杰
Lai,Yin-chieh
光电工程研究所
关键字: 光纤;雷射;锁模;同步;建模;Fiber;Laser;Mode-locking;Synchronization;Modeling
公开日期: 2015
摘要: 超快光纤雷射是应用于许多科学研究和产业研发之光电整合系统中的基本构建模组,有很好的研究价值。在本研究中,我们发展合适的理论模拟模型来具体地探讨双波长锁模光纤雷射系统的被动式时序同步技术以及混合式(主动/被动)锁模光纤雷射系统中从同步到非同步的不同锁模操作态转换现象。
关于双波长锁模光纤雷射时序同步技术之研究,掺铒(Er-doped)和掺镱(Yb-doped)锁模光纤雷射可以藉由所提出的主附式(master-slave)架构来达到被动式同步的效果。我们利用数值计算来探讨此被动同步系统中的光脉冲非线性动力学特性,藉由脉冲传播模型来处理在共同传播光纤部分中的脉冲碰撞状况,并且使用锁模雷射的Master equation模型来探讨掺铒雷射共振腔中脉冲的动力学演变。当此两雷射的共振腔长度有些微不匹配时,我们根据计算结果指出Er雷射的光脉冲中心波长会经由在共同传播光纤中两种不同波段脉冲互相作用所产生的交叉相位调变(XPM)效应而产生改变,进而与注入的Yb光脉冲保持相同的光脉冲重复率。此外,由于光纤中色散作用所造成之脉冲宽度变化会导致XPM效应所产生的频率调变函数对不同的起始碰撞相对时间位置变数的反对称性特征被改变,非线性脉冲传播的准确数值模拟更显必需。我们进一步藉由所发展的理论模型来探讨分析此双波长被动同步锁模光纤雷射系统的相对时序杂讯特性,发现经由适当地调整两脉冲的相对时间位置,相对时序杂讯抖动可以被有效率地抑制,并且所预测的物理特性也在实验系统中得到验证。在这里所发展出的超低时序同步技术能用来获得低于飞秒尺度的脉冲相对时序杂讯,提供了一个新方法能用来发展多种重要应用,包括同调脉冲合成技术与精确时序分配技术等。
在关于混合式(主动/被动)锁模光纤雷射锁模特性之研究中,我们理论性地探讨混合式(主动/被动)锁模光纤雷射在相位调变器的调变频率被稍微错开时所会产生的不同锁模操作态转换现象,此现象也可以广义地视为雷射光脉冲序列与光调变讯号的时序同步效应。基于所使用的混合式锁模雷射Master equation模型,在不同程度之错开调变频率与调变强度下,我们发现有三种截然不同的锁模操作态,它们的状态转移图也被首次准确计算与画出。除此之外,我们也藉由变分法和单一高斯脉冲解的假设来解此Master equation模型,重要脉冲参数的演变方程式可被推导出,此变分模型可以用来与直接数值模拟所获得的结果作比较以便厘清阐明关键的物理机制。我们更进一步透过计算不同锁模操作态在稳态结果下的雷射增益,厘清了雷射在接近过度点的不稳定现象原因以及非线性饱和吸收效应对于稳定非同步锁模操作态的重要性。这些发展出的分析方法可以示范出一套有效理论工具来解释说明非线性混合式锁模光纤雷射在调变频率错开效应下的动力学变化,并能准确预测此种雷射系统在不同操作条件下的运作性能。
Ultrafast fiber lasers can be employed as fundamental building blocks in many photonic systems for scientific research and industrial development. In this study, we develop appropriate simulation models to specifically investigate the essential properties of passive timing synchronization between two color mode-locked fiber lasers and the synchronous to asynchronous mode-locking state transition in hybrid (passive/active) mode-locked fiber laser systems.
For the first objective of the research, the passive synchronization between the Er-doped and Yb-doped mode-locked fiber lasers is studied under the master-slave configuration. We numerically investigate the nonlinear optical dynamics of the passive synchronization system based on the pulse propagation model for the pulse collision in the common fiber section and the master equation model for modelling the dynamics of the Er laser cavity. When there is some mismatch of the cavity length, the computational results indicate that the central optical frequency of Er laser pulses may be shifted through the significant cross phase modulation (XPM) effect of the two color pulses interacted in the shared fiber section so as to maintain the same repetition rate with injecting Yb laser pulses. Additionally, since the pulse duration change by fiber dispersion can distort the anti-symmetric characteristics of the frequency modulation function caused by the XPM effect with respect to the relative timing position, accurate numerical simulation of the nonlinear pulse propagation effects will be critical. Furthermore, the relative timing jitters between the two passively synchronized mode-locked fiber lasers are analyzed based on the developed theoretical model. The relative timing jitter noises of the two synchronized lasers can be minimized by adjusting the relative pulse timing position and the predicted dependence agrees well with experimental observation. The presented ultra-low timing (< ~fs) synchronization technique provides an alternative approach to the development of many applications including the coherent pulse synthesis and precision timing distribution.
For the second objective of the research, we theoretically investigate the different mode-locking operation states of a hybrid (active/passive) mode-locked fiber laser system with frequency detuning effects of active phase modulation. This may also be viewed as a timing synchronization problem between the laser pulse train and the optical modulation signal. Based on the master equation model of this hybrid mode-locked laser, we find three distinct mode-locking states and also determine their transition diagram under varying detuning frequency and modulation strength. Additionally, the evolution equations of essential pulse parameters are derived from the variational solution of the master equation under the single Gaussian pulse solution ansatz for the comparison of results and clarification of key physical mechanisms. The occurrence of laser instability near the transition points, and the importance of the nonlinear saturable absorption effect for stable asynchronous mode-locking operation are further clarified by examining the steady-state lasing gain as a function of the detuning modulation frequency. These presented analyses demonstrate an effective approach for the elucidation of the nonlinear mode-locked laser dynamics caused by the detuning effects and for the performance prediction of the studied laser system under different operation conditions.
URI: http://140.113.39.130/cdrfb3/record/nctu/#GT079924831
http://hdl.handle.net/11536/126679
显示于类别:Thesis