螺旋环绕式饱和吸收体及其脉宽可调被动锁模机理分析与实现

Recently, passive mode-locking fiber lasers with pulse-width tunability have attracted remarkable research interests, because of their excellent advantages such as ultrafast temporal resolution, ultra-high peak power, and pulse width tunability for potential applications on optical communications, biological imaging and diagnostics, laser-machining and so on. It is a great challenge to develop a large tuning range of the pulse width for the passive mode-locking fiber laser. This project proposes a novel saturable absorber, which involves polarizing, coupling, and modulating technology. It is composed with a polarization-dependent micro/nano waveguide with 2D nanomaterials surround by spiral microfiber coils. In this project, in order to enlarge the saturable absorption difference of two orthogonal linearly polarized modes, the interaction between 2D nanomaterials and evanescent fields of the polarized lights in the microfiber and polarization-dependent micro/nano waveguide to realize the polarized absorption modulation would be investigated. Such saturable absorber can be employed by fiber laser to realize passive mode-locking. An ultrafast dynamic model is established and used for improving a large tuning range of pulse-width in the passive mode-locking, in order to meet urgent needs of optical communications, biological imaging and diagnostics, laser-machining. Our research could enrich the application of 2D nanomaterials and provide a theory and research method for photonic devices based on 2D nanomaterials. Our research is combined with many theory and technology such as optical information, material, and laser technology for exploring the future of laser field, which is related to multidisciplinary development.

脉宽可调锁模光纤激光器具有超快时间分辨率、高瞬时功率、脉宽可调等诸多优点，近年来成为备受瞩目的国际前沿和研究热点。如何对其输出激光脉冲宽度进行大范围调节是摆在研究人员面前的一道难题。基于此，本项目拟将偏振、耦合及调制三种光信息技术与二维纳米材料相融合，研制一种新型饱和吸收体。其原理为：将微纳光纤螺旋环绕于偏振相关的二维纳米材料微纳光波导表面，利用偏振相关微纳光波导及螺旋状微纳光纤的偏振消逝场与二维纳米材料之间的相互作用来实现偏振吸收调制，从而扩大两束线偏振光之间的饱和吸收深度差值。将其放置于光纤激光器中，并构建超快动力学模型分析其锁模机理，实现被动锁模以大幅提升锁模脉宽的调节范围来满足光通信、生物成像、加工等领域的迫切需求。本项目交叉融合了光信息、新材料与激光技术等多个领域，为二维纳米材料光子器件的研制及脉宽可调被动锁模机理的分析提供理论参考和研究方法，为未来激光技术的发展提供新思路。

脉宽可调锁模光纤激光器具有超快时间分辨率、高瞬时功率、脉宽可调等诸多优点，近年来成为备受瞩目的国际前沿和研究热点。如何调控锁模光纤激光器的脉冲宽度和光谱宽度是摆在研究人员面前的一道难题。基于此，本项目拟将偏振、耦合及调制三种光信息技术与二维纳米材料相融合，研制新型饱和吸收体，并将研制的饱和吸收体用于锁模光纤激光器系统中实现脉宽可调控、光谱可调控的被动锁模。基于此展开了以下研究：（1）为了研制新型饱和吸收体，提出了高双折射双零色散点光纤结构，提出了堆叠结构设计提升石墨烯与光场之间相互作用来提升偏振消光比，设计并制备了基于表面波导石墨烯饱和吸收体，实现了调制深度可调控，非饱和吸收损耗可调控。TE偏振光调制深度从43%到33.78%；TM偏振光的调制深度从50%到20%，非饱和吸收损耗29.21%~50%。（2）采用分步傅里叶-龙格库达法建立了饱和吸收体的光脉冲调制模型，分析了泵浦光和信号光通过饱和吸收体后被调制的情况，还建立掺铒光纤和单模光纤的传输模型，分析高能脉冲的传播情况。（3）采用分步傅里叶-龙格库达法建立了基于饱和吸收体的锁模光纤激光器的理论模型，分析了光脉冲和光谱的形成过程。搭建了饱和吸收体可调的锁模光纤激光器系统，获得了脉宽可调控、谱宽可调控的被动锁模，锁模脉冲宽度从780fs到1.2ps可调控，光谱宽度从~33nm到~50nm。（4）提出了基于氮化硅波导的石墨烯调制器，获得了80GHz的调制带宽和2dB插入损耗；还基于新型饱和吸收体的电学测试获得了兴奋性突触后电位双脉冲易化效应，与人类神经突触的短时程突触可塑性相似，上述工作为脉宽可调控的锁模光纤激光器、高速调制器、新型神经突触器件提供了参考。