以時域擬譜法分析光通過散射介質及改變光學相位共軛技術之張角的回聚效果

Abstract

在本篇論文中，我們將探討在不同條件下的光回聚情形。我們建立了一個圓形散射介質隨機分佈的空間，並利用時域擬譜法（PSTD）來模擬大尺度的電磁波傳遞，透過此種方法相對於時間有限差分法更有效率。在論文中更詳細推導介紹了時域擬譜法、Nyquist Theorem、單軸完美吸收邊界及光學相位共軛的技術，我們利用這些方法相互搭配，進而模擬電磁波在真空中、散射介質中及HT-29二維虛擬組織中的傳遞情形。從模擬結果來看，我們得知波長與回聚效果呈現反比關係；張角與回聚效果成正比關係；介質數則會與張角設置方向不同呈現不同的關係，最後透過虛擬組織的模擬得到了和散射介質相似的結果，為後續的研究訂下基礎。

We investigate the phenomena of light focusing effect under different conditions. We construct a simulation space with randomly distributed circular scattering medium and employ the pseudospectral time-domain (PSTD) method to simulate large-scale electromagnetic wave propagation, which is more efficient than finite-difference time-domain (FDTD) method. Detailed derivation of the PSTD method, the Nyquist theorem, the uniaxial perfectly matched layer absorbing boundary condition, and the optical phase conjugation (OPC) are provided. We utilize these methods to simulate the propagation of electromagnetic waves in different circumstances, such as vacuum, scattering medium, and two-dimensional virtual tissues (HT-29). Our findings indicate that the focusing effect is inversely proportional to the wavelength of the light and is proportional to the angular span of the phase conjugate mirror (PCM). Furthermore, the relation between the light focusing effect and the number of medium numbers depends on whether the PCM is located in the forward direction or sideway. Finally, the results utilizing HT-29 are similar to those of scattering medium, which very helpful for the future research.