使用有限差分時域法模擬分析光學吸收體

Abstract

吸收邊界條件最初廣泛的應用在模擬邊界的吸收以避免誤差來自邊界的反射，本篇論文中，利用有限差分時域法(FDTD)，以摺積完美匹配層(CPML)的基本概念去創造出圓形的光學靶，並且分析其解析度對應所造成的誤差及不同頻率對應的吸收效率，光源將使用高斯光束、環形高斯分佈場來分析其吸收效率，最後的結果得出吸收效率與解析度有關，但和頻率無關。 由於電磁波在如生物組織等強散射介質中，造成電磁波從四面八方而來，利用圓形光學吸收體的特性，能夠有效的吸收各方向的入射光，以應用在模擬光學現象在生物組織中的情形。

Absorbing boundary conditions (ABCs) are widely used for boundary absorbing which can reduce the error from the boundary reflection in simulation space. In the thesis, we explore and analyze the absorption of a convolutional perfectly matched layer (CPML) optical target under the condition of different resolutions, and different frequencies Gaussian beam source in the Finite-Difference Time-Domain (FDTD) simulations. We show the performance of CPML optical target that eliminates the impinging wave and analyze the absorption efficiency of CPML optical target with different resolutions and the influence by different frequencies source. Specific simulation results show that the absorption of the CPML optical target is dependent upon its resolution, but independent upon the source frequency. In turbid media such as biological tissue, electromagnetic (EM) wave would be scattered strongly so that makes the light come from any direction possibly. By using the optical target to absorb the impinging wave from arbitrary direction, we can model light propagation through biological tissue to a specific target posistion.