具有缓变折射率的太赫兹宽带增透器件

Terahertz broadband antireflection photonic device with graded refractive indices

用高阻硅制作的光学元件是太赫兹系统里常用的器件,但是其高达3.42的相对折射率所引起的阻抗失配严重影响了太赫兹系统的功率,因此研究人员尝试了各种各样的方式在高阻硅表面镀上有效的增透膜.在太赫兹波段,缺乏合适的材料是增透研究中亟需解决的一个重要问题.介绍一种结构新颖的硅材料增透器件—三维光子倒置光栅.与普通高阻硅片相比,当结构周期为15μm时,该器件在0.2—7.3 THz范围内对太赫兹波具有明显的增透作用,且覆盖了大部分太赫兹波段.此外,该器件的使用不受太赫兹偏振方向限制,适用于大入射角情形,并具有高达116.3%的相对3 dB带宽.

High resistivity silicon is a very common optical component in a terahertz system. However, its high relative refractive index of 3.42 causes a large impedance mismatch at the silicon-to-air interface. This severely reduces the available power in a terahertz system which motivates researchers to find a good anti-reflection solution. In the terahertz region, the lack of proper materials for broadband anti-reflection severely hinders such a research development. A photonic grating with graded refractive indices is demonstrated on silicon. Compared wich the case of planar silicon wafer, the transmission is observed to increase from 0.2 THz to over 7.3 THz for a device with 15 μm period, which covers most of the terahertz band. With a striking relative 3 dB bandwidth of 116.3%, the device is polarizationindependent and can be used under a wide incidence angle.