Mo Chen, Liu Jingbo, Wei Dongshan, Wu Honglei, Wen Qiye, Ling Dongxiong
School of Electrical Engineering and Intelligentization, Dongguan University of Technology, Dongguan 523808, China.
College of Physics and Optoelectronic Engineering, Shenzhen University, Shenzhen 518061, China.
Sensors (Basel). 2020 Apr 13;20(8):2198. doi: 10.3390/s20082198.
Nanostructures can induce light multireflection, enabling strong light absorption and efficient photocarrier generation. In this work, silicon nanostructures, including nanocylinders, nanotips, and nanoholes, were proposed as all-optical broadband THz modulators. The modulation properties of these modulators were simulated and compared with finite element method calculations. It is interesting to note that the light reflectance values from all nanostructure were greatly suppressed, showing values of 26.22%, 21.04%, and 0.63% for nanocylinder, nanohole, and nanotip structures, respectively, at 2 THz. The calculated results show that under 808 nm illumination light, the best modulation performance is achieved in the nanotip modulator, which displays a modulation depth of 91.63% with a pumping power of 60 mW/mm at 2 THz. However, under shorter illumination wavelengths, such as 532 nm, the modulation performance for all modulators deteriorates and the best performance is found with the nanohole-based modulator rather than the nanotip-based one. To further clarify the effects of the nanostructure and wavelength on the THz modulation, a graded index layer model was established and the simulation results were explained. This work may provide a further theoretical guide for the design of optically tunable broadband THz modulators.
纳米结构可引发光的多次反射，从而实现强光吸收和高效光载流子生成。在这项工作中，提出了包括纳米圆柱体、纳米尖端和纳米孔在内的硅纳米结构作为全光宽带太赫兹调制器。对这些调制器的调制特性进行了模拟，并与有限元方法计算结果进行了比较。值得注意的是，所有纳米结构的光反射率值都被大大抑制，在2太赫兹时，纳米圆柱体、纳米孔和纳米尖端结构的反射率值分别为26.22%、21.04%和0.63%。计算结果表明，在808纳米照明光下，纳米尖端调制器实现了最佳调制性能，在2太赫兹时，泵浦功率为60毫瓦/平方毫米时，其调制深度为91.63%。然而，在较短的照明波长下，如532纳米，所有调制器的调制性能都会下降，基于纳米孔的调制器比基于纳米尖端的调制器具有最佳性能。为了进一步阐明纳米结构和波长对太赫兹调制的影响，建立了渐变折射率层模型并对模拟结果进行了解释。这项工作可能为光学可调谐宽带太赫兹调制器的设计提供进一步的理论指导。
