Study on Silicon Optical Modulator on Insulator

本研究旨在实现一种基于自由载流子吸收的硅光调制器。实现该调制器最重要的关键因素之一是为载流子与红外光之间的相互作用提供多少自由载流子。因此，梳状MOS晶体管得到了发展和评价。在第一次试验中，由于入射的红外光（波长λ=1.55μm）滑入硅衬底，被重掺杂的多晶硅栅极吸收，在高度为1 μm、长度为1 mm的SOI（绝缘体上硅）上的硅光调制器无法观测到光调制。然而，多通道MOS晶体管已被成功地开发并在学术上提出。第二次试验计划解决上述问题并未带来调制成功。主要原因是通过硅衬底的噪声光的强度比通过硅波导内部的信号光的强度大1000倍以上，导致致命的信噪比。通过对实验结果的分析，估计在很大程度上需要降低噪声光。因此，提出了一种在硅衬底上具有红外光吸收区的器件结构。在衬底上填充炭黑沟槽，有效地降低了噪声光。另一种实现结构改进的硅光调制器的试验也已进行。

This research is aiming to realize a silicon optical modulator based on free-carrier absorption. One of the most important key factors to realize the modulator is how much free carriers can be provided for interaction between carriers and infrared light. Thus, comb-shaped MOS transistors were developed and evaluated.In a first trial, the optical modulation for a silicon optical modulator on SOI (silicon-on-insulator) of 1 μm in height and 1 mm in length could not be observed because that incident infrared light (wavelength, λ=1.55μm) slipped out into silicon substrate and heavily-doped polysilicon gate absorbed the light. However, multi-channel MOS transistors were successfully developed and academically proposed.The second trial planning to solve the above issues has not brought about a successful modulation. The main cause is that the strength of noise light running through silicon substrate is more than 1000 times greater than that of signal light coming through inside silicon waveguide causing fatally bad signal-to-noise ratio.Analyzing the experimental, it is estimated that the noise light has to be reduced to great extent. Thus, a device structure with infrared light absorption region in silicon substrate has been proposed. A trench in the substrate filled with carbon black has reduced the noise light efficiently. Another trial to realize the silicon optical modulator with improved structure has been carried out to date.