激光诱导载流子信号处理光栅研究

Modern communication and electronic countermeasure are constantly posing severe technical challenges to digital receivers and signal processing systems. Acousto-optic receiver, which has the ability of real-time and concurrent optical signal processing, is confronted with the technical bottleneck of device machining and thus its bandwidth is strongly limited. Inspired by the methodology of Bragg device which uses sound to control light, we propose a laser-induced photocarrier grating (PCG) technology in this project, which uses one light beam to control another light beam. This technology not only keeps the advantages of the acousto-optic device but also can overcome the machining difficulties and break through the bottleneck of the bandwidth for signal processing. The steady-state PCG, the traveling-wave PCG, and their applications to the signal spectral analysis and correlation operation will be studied both theoretically and experimentally. Our concentration will mainly focus on: 1) the microscopic mechanism of the grating formation due to carrier-induced refractive index change; 2) how to make the carrier density wave (parabolic diffusion field) behave as a traveling wave (hyperbolic wave field); 3) how to deal with the distortion of the signal during the spatial expansion. The all-optical signal processing technology based on the PCG is expected to overtake and replace the traditional acousto-optic Bragg device in military radar. Furthermore, it is easy to be integrated and thus having an excellent prospect in civilian application.

现代通信与电子对抗正在不断向数字化接收机和信号处理系统提出严峻的技术挑战。基于光信号处理的声光接收机虽然具有实时、并行处理信号的能力，但其带宽受器件工艺限制仍难以满足需求。受声光布拉格器件的声控光原理的启发，本项目提出一种光控光的过剩光载流子光栅技术，在保留声光器件优点的同时，克服其工艺困难，突破时间带宽积的瓶颈，实现全光信号处理。主要开展（1）载流子静态衍射光栅、（2）行波衍射光栅、（3）信号谱分析及相关运算等方面的理论与实验研究；重点攻克（1）载流子致折射率改变的光栅形成微观机理、（2）如何使载流子密度波（抛物型扩散场）呈现出行波（双曲型波动场）特性、（3）如何克服载流子扩散和复合过程带来的信号空间展开畸变等关键科学问题。基于载流子光栅的全光信号处理技术不仅有望超越和取代传统声光布拉格器件在军用雷达中的关键作用，同时其易于集成的特点也保证了在民用领域的广阔发展前景。

受声光布拉格器件的声控光原理的启发，本项目提出一种光控光的过剩光载流子光栅技术，在保留声光器件优点的同时，克服其工艺困难、突破时间带宽积的瓶颈，目标为全光信号处理。主要开展了（1）过剩光载流子光栅的产生机理分析以及衍射效率计算，建立了稳态载流子光栅的理论模型，分析了能带填充效应、带隙收缩效应和自由载流子吸收效应三种物理机制决定的载流子浓度致折射率改变，利用严格耦合波方法数值计算了TE偏振光在布拉格衍射条件下的光载流子光栅衍射效率，找到了载流子光栅的最佳构造参数结构；（2）建立了周期性光激励下的非线性载流子动力学理论模型，分析了双分子辐射复合、俄歇复合等非线性载流子复合效应对载流子光栅衍射特性的影响，并找到了激励光强同衍射效率呈线性关系的载流子注入浓度区间；（3）建立了载流子输运参数空间分布的全光定量表征和成像方法，实现了半导体基底材料的载流子输运参数（等效载流子寿命、扩散长度等）空间分布的定量成像，为表征载流子光栅特性以及光栅核心参数优化提供了表征手段；（4）完成了约束性周期离散化结构的设计和加工，通过掺杂生成的PN结周期性分布以及外加交变电场控制结构，来抑制扩散过程对载流子光栅强度的影响，并维持相应的载流子浓度空间分布、避免畸变；（5）发展了基于自由载流子吸收技术、光热辐射技术等的半导体载流子全光定量表征手段，为电子信息和无损检测领域的创新研究提供先进的表征手段。后续研究将聚焦在场维持系统和行波光栅的衍射瞬态特征两方面，努力完成外加交变约束电场的最佳参数研究和行波光栅的谱分析及相关运算。