基于冰刻纳米金棒可饱和吸收体的飞秒孤子锁模与调控

Saturable absorber (SA) is one of the most important components in an ultrafast pulse laser system. Gold nanorod (GNR), as one of the most common plasmonic SAs, becomes a great potential to generate laser pulses with high integration, short recovery time and tunable soliton properties. GNR SAs, however, are all fabricated by chemical synthesis as reported, which makes the orientation and the gap of GNRs out of precise controls during the integration on the fiber. Therefore, the efficiency of resonant absorption is low and the dependence of solitons on plasmons can not be quantified. In this study, a novel approach which is based on an ice lithographical GNR SA is proposed. Focusing on the efficient excitation of linear and nonlinear plasmons and coupling mechanism between plasmons and solitons, GNRs with different dimensions are numerically designed, in-situ fabricated, optically characterized and passively mode-locked. It is aimed to clarify the dependences of plasmons on the polarization and GNR dimensions, and realize an all-fiber femtosecond soliton mode-locking, which has a central wavelength of 1550 nm. The ultimate goal of this proposal is to reveal the mechanisms of plasmon modulated soliton properties, including pulse width, central wavelength and nonlinear dynamics. The study opens an avenue for advanced applications of plasmonics on the ultrafast optics, fiber optics and other interdisciplines in the field of optics.

可饱和吸收体是超快光纤激光器实现被动锁模的关键器件。纳米金棒作为最常用的等离激元可饱和吸收体之一，有望产生集成度高、恢复时间短、孤子特性可调控的超短激光脉冲。针对现有化学法制备的纳米金棒可饱和吸收体，存在因均匀性较差导致的共振吸收效率较低及等离激元对孤子特性难以定量调控的问题，本项目拟采用冰刻法实现纳米金棒在光纤上的均匀加工，并作为可饱和吸收体进行孤子的飞秒锁模与定量调控。围绕高效激发纳米金棒线性和非线性共振吸收及等离激元定量调控孤子特性两个关键科学问题，通过对纳米金棒进行结构设计、原位加工、线性和非线性光学表征及被动锁模，以阐明纳米金棒尺寸和偏振对等离激元共振的影响规律，进而实现全光纤化的工作波长在1550nm的飞秒孤子锁模，最终揭示等离激元对脉冲宽度、工作波长和动态相位等孤子特性的定量调控机理，为发展具有自主知识产权的超短、超强脉冲激光技术和前沿基础学科之间的交叉融合提供理论依据。

可饱和吸收体是超快激光器实现被动锁模的关键器件。针对现有化学法制备的纳米金棒可饱和吸收体，存在因均匀性较差导致的共振吸收效率较低以及等离激元对孤子特性难以定量调控的问题，本项目采用了多种微纳加工方法实现了纳米金棒在光纤端面上的均匀加工，并作为可饱和吸收体实现了孤子锁模和中心波长的定量调控。通过对纳米金棒进行结构设计、原位加工、线性和非线性光学表征及被动锁模，本研究可以得到如下几个结论：.（1）通过冰刻或标准平面技术可以将等离激元纳米结构或超构表面原位集成在光纤端面上，前者设备独有，适用于在裸线上加工；后者方法具有一般性，可以大规模推广；.（2）等离激元谐振波长（纵向偶极子模式）可以通过控制纳米金棒的长轴来定量调节，通信波段均可覆盖；.（3）等离激元超构表面具有一定的可饱和吸收特性，调制深度在平面衬底可最大达到60%，在光纤端面调制深度有所降低（~30%），其饱和吸收的内在机理可以理解为由于非线性效应而导致的等离激元谐振峰的蓝移；.（4）利用等离激元超构表面的作为可饱和吸收体，实现了最短脉宽513 fs的孤子锁模脉冲。.在取得成果方面，发表SCI论文8篇，其中，第一/通讯作者（含共同一作1篇）论文7篇，光学专业顶刊2篇（Light: Science & Application和Optica各1篇），包含一篇ESI高被引论文。申请发明专利5项，获得软件著作权3项，参加国内外学术会议4次，协助培养博士研究生3名。.本研究首次利用等离激元超构表面实现了全光纤化的工作波长在1.5 μm和2 μm波段的、脉宽为亚皮秒量级的孤子锁模，并揭示了等离激元可饱和吸收的物理机理以及对孤子脉冲宽度、工作波长的调控机制，为发展具有自主知识产权的超短、超强脉冲激光技术和前沿基础学科之间的交叉融合提供了可靠的理论依据。