基于氧化物简并半导体的红外光学非线性和超快光调制

Nonlinear optical (NLO) processes are ubiquitous in the interaction of intense laser with different materials. Many semiconductors and their nanostructures exhibit prominent resonant optical nonlinearity associated with inter-band transitions, while the nonlinearity becomes rather weak at photon energies smaller than the optical bandgap. In heavily doped degenerate semiconductors, however, the high plasmon frequency results in strong broadband absorption and optical nonlinearity at infrared frequencies far lower than the bandgap, making them highly attractive in diverse photonic applications, such as pulse lasers, optical switches and integrated optical devices. In the present project we will focus on the degenerate oxide semiconductors and their nanostructures with high stability and laser damage threshold and investigate the material design and fabrication oriented for nonlinear optical properties. We will unravel the involved mechanisms in the ultrafast optical nonlinearity through systematically investigation on the interplay of intrinsic and extrinsic properties on the optical nonlinearity of these materials. Based on these materials, we will further develop series of saturable absorbers with their working bandwidth covering the entire near infrared and part of mid-infrared region. The developed devices will enable pulse Q-switched and mode-locked pulse generation based on fiber and solid state lasers, as well as ultrafast optical switches with high efficiency operating at the same spectral region. The results of this project will have strong implications for the development of novel nonlinear optical materials and relevant photonics devices operating in the infrared region.

非线性光学现象普遍存在于激光与材料相互作用的过程中。半导体材料及其纳米结构常表现出源于带间跃迁的显著的共振非线性，而对能量小于带隙的光子往往非线性响应极弱。但在重掺的简并半导体中，较高等离子频率使其在能量远小于带隙的红外波段出现宽带吸收以及超快非线性响应，因此在近/中红外波段的脉冲激光器、光开关以及集成光子器件中有巨大的应用前景。本项目将围绕具有高稳定性和高损伤阈值的氧化物简并半导体及其纳米结构，研究其面向光学非线性的材料设计、制备手段以及源于自由载流子的超快非线性及产生机制，系统阐明其非线性光学性质和材料本征特性以及非本征特性的关系。在此基础上基于这类半导体，开发工作波段覆盖近红外以及部分中红外光区的饱和吸收体，在光纤和固体激光器中实现调-Q和锁模脉冲激光输出；并研制相应波段的光调制器，实现超快且高效的光开关。本项目的研究成果将推动红外波段新型非线性光学材料和相关光子器件的开发和应用。

金属氧化物半导体广泛应用于液晶显示、光催化以及太阳能电池等邻域。其电学性质主要取决于其中掺杂产生的自由载流子的类型、浓度以及有效质量等参数。根据特鲁德模型及非线性光学原理，这些参数也同样影响着金属氧化物半导体材料的线性和非线性光学性质， 因此，金属氧化物半导体可通过掺杂来方便实现对光学性质的调控。近年来在光子学以及非线性光学领域引起广泛的研究兴趣。.本项目围绕氧化铟锡（ITO）、氧化钛等代表性金属氧化物的制备、非线性光学性质以及超快光子学应用展开研究。通过湿化学法、拓补化学法以及磁控溅射等不同工艺手段制备了ITO、TiO2-x、MoO3-x、TiON等不同的金属氧化物纳米颗粒、纳米片以及薄膜，通过Z-扫描以及超快瞬态吸收等手段研究了这些材料在红外波段的非线性光学性质以及超快载流子弛豫等过程，实现了通过化学计量来调控材料的非线性响应，观察到了由于绝缘体-金属相转变而导致的非线性吸收吸收的反转，并结合理论计算提出了简并半导体材料非线性响应调控的基本策略。在以上研究的基础上，本项目基于这些氧化物半导体材料的可饱和吸收效应，开发了工作于红外波段的超快光开关，在1.0 m和1.5m波段的光纤和固体激光器中实现了锁模和调Q脉冲输出。本项目还基于所开发了氧化物半导体的非线性效应，演示了光通讯波段的全光调制。.本项目的研究成果证实了传统氧化物半导体在红外波段具有可调谐的强非线性响应、将有力推动这类材料在光子学器件尤其是超快激光相关器件的应用，此外，由于这些氧化物半导体材料（如ITO）薄膜的制备和CMOS工艺兼容，本项目关于全光调制方面的研究成果也表明氧化物半导体材料在集成光电子器件领域有巨大的应用前景。