基于连续波注入的被动谐波锁模光纤激光器特性研究

Passively harmonic mode locking (PHML) is an efficient method to get high repetition frequency ultrashort pulse in fiber laser. This technique not only gets rid of restriction of the cavity length, but also omits the active modulation device and filter elements. However, the formation mechanism of PHML is still unclear and the operation of PHML is unstable which greatly limit the practical application. Recent studies have shown that continuous wave can cause soliton interactions and induce the formation of PHML. In this project, the effect of continuous wave on multi-soliton operation would be studied using the continuous wave injection method with graphene mode-locked erbium-doped fiber laser as the carrier, and the method to obtain high repetition frequency optical pulse would also be explored. The following issues will be addressed: 1. Through experimental research of single continuous wave injection, to find the forming conditions of the PHML; 2. Through theoretical and experimental research, to study the effects of multiple continuous wave injection on the multiple soliton operation, and to find the forming conditions of the PHML with multiple continuous wave injection; 3. By increasing the nonlinear coefficient of the cavity and increasing the frequency spacing of the injected continuous waves, to achieve ultrahigh-order PHML. The project will further reveal the mechanisms of interaction between soliton and continuous wave, and promote the development of high repetition frequency ultrashort pulse source.

被动谐波锁模是光纤激光器获得高重复频率超短光脉冲的有效方法。其不受激光器腔长限制也无需主动调制设备和滤波元件。然而被动谐波锁模的形成机制尚不明确，运行亦不够稳定，这极大限制了其实际应用。最近的研究表明，连续波可引起孤子间的相互作用，诱发被动谐波锁模的形成。本项目拟以石墨烯锁模掺铒光纤激光器为载体，通过外部连续波注入，研究连续波对多孤子运行的影响，探索利用连续波注入获得稳定高重复频率光脉冲的方法。主要内容有：1. 实验研究利用单个连续波注入获得被动谐波锁模所需条件；2. 理论和实验研究多个连续波注入对多孤子运行的影响，以及利用多个连续波注入获得被动谐波锁模所需条件；3. 通过增强激光腔的非线性和增大注入连续波频率间隔的方法，实现超高阶被动谐波锁模。本项目的开展将进一步揭示孤子与连续波相互作用机理，促进高重复频率超短光脉冲源的发展。

本项目以锁模掺铒光纤激光器为载体，通过外部连续波注入，研究连续波对多孤子运行的影响，探索利用连续波注入获得稳定高重复频率光脉冲的方法。在本项目的资助下，我们围绕着可饱和吸收材料锁模、非线性偏振旋转锁模（NPR）光纤激光器开展了研究工作。所取得的主要成果可以概括为以下几方面：1. 在可饱和吸收材料锁模光纤激光器方面：我们研究了石墨烯及拓扑绝缘体锁模元件的特性，搭建了基于石墨烯等可饱和吸收材料的锁模光纤激光器，获得了高输出功率、高重复频率脉冲输出。2. 在连续波注入产生高重复频率脉冲方面：通过连续波注入，在高功率铒镱共掺双包层光纤激光器中获得了高重复频率谐波锁模激光脉冲输出。3. 在基于NPR锁模的高能量激光脉冲方面：我们实验研究了光纤激光器中的高能量矩形脉冲现象；我们通过数值模拟和实验研究了光纤激光器中的双波长阶梯状脉冲现象。4. 在多波长锁模光脉冲研究方面：在负色散激光腔中发现了多波长光畴现象，我们将其命名为“color domians （CDs）”，CDs是由与波长相关的孤子凝相组成，实验中我们观察到了充满整个激光腔的单波长、双波长及三波长CDs，CDs具有可调的占空比、波长及波长间隔；CDs的形成源于激光腔中波长相关的慢变增益，其中多波长CDs的形成原理源于多波长交叉增益饱和。