基于单片集成光谱整形单元的量子点被动锁模激光器机理研究

In recent years, much attention has been attached to the single section quantum-dot passive mode-locked laser, which opens up a potential breakthrough for realizing the integratable femtosecond ultrafast laser with high performance and low power consumption. Currently, among many possible mechanisms that may all lead to the mode locking in quantum dot lasers, the dominant effect(s) is not clear, which makes the effort towards improving the device performance rather inefficient. Moreover, the large high-order dispersion within this device was found to affect pulse generation. With the purpose to remedy the aforementioned problems, this application proposes to explore the dominant effect(s) of the mode locking through analyzing two basic nonlinear effects, i.e. spectrum hole burning and spatial hole burning. And the mode locking features are expected to be enhanced through band structure engineering and a spatial modulation of the dots density. Furthermore, the application also brings up a dispersion compensation mechanism based on the integrated optical spectrum shaper, in order for realizing the Fourier transform limited pulses. The research outcome could lead to the high locking performance, integratable quantum dot passive mode-locked laser with ultra low dispersion, which will be very promising in the applications of future high-capacity optical networks as well as ultra high speed all optical signal processing systems.

近几年来，备受关注的单段量子点被动锁模激光器为高性能、低功耗的可集成飞秒脉冲源的实现方案开启了一个可能的突破方向。目前，对该器件产生被动锁模现象的主导诱发机制尚不明确，因而提高锁模特性的有效方法仍有待研究；此外，该器件腔内存在的较大高阶色散已成为其产生超短脉冲的主要障碍。针对上述问题，本申请提出通过分析“谱域烧孔”和“空域烧孔”这两类基本非线性过程，探索该器件发生锁模的主导机制。并有针对性的提出：通过能带结构的设计以及对量子点密度的空间调制，将有望增强器件的锁模效应。在机理分析的基础之上，本申请进一步提出利用腔内单片集成谱域整形单元的思路，实现对高阶色散的补偿，以形成接近傅里叶变换极限的超短脉冲序列。本研究以期实现的极低色散、高锁模性能、易集成的量子点被动锁模激光器在未来超大容量光网络以及超高速全光信号处理等系统中将有十分良好的应用前景。

本项目首先建立了器件理论模型，并在理论上提出了一种计算本征问题的高效算法。随后，通过理论仿真验证了“谱域烧孔”和“空域烧孔”这两类基本非线性过程均为锁模发生的基本原因。研究了单段量子点被动锁模激光器（不包含色散补偿部分）本身的锁模特性随量子点密度及均匀度在一定范围内的变化。研究了等效的饱和吸收效应对锁模特性的影响。进而根据在腔内单片集成谱域整形单元的思路，用积分剥层算法反推整形单元的光栅结构以期对高阶色散进行补偿，实现超短脉冲。然而在研究过程中，我们发现对于接近傅里叶变换极限的超短脉冲所对应的谱宽，积分剥层算法目前所能实现的补偿范围无法达到，仍有待进一步研究。另一方面，研究还表明，采用单片集成的滤波结构（谱域整形单元）对激光器输出特性的调整在某些应用上成效显著。我们因此在理论上提出了基于本项目基本思路的两种新型单片集成的激光器，并对其中一种结构进行了实验研究。结果表明，这两种结构具有结构紧凑，成本低，与传统结构相比具有更优的传输特性，特别在高速接入系统中具有较高的应用前景。