數位光學相位共軛現象的模擬分析

Simulation and Analysis of Digital Optical Phase Conjugation

丁偉倫(Wei-Lun Ting)

指導教授 ： 曾雪峰

國立臺灣大學/電機資訊學院/光電工程學研究所/碩士(2013年)

https://doi.org/10.6342/NTU.2013.02669

摘要

散射現象描述了光波在經過紊亂介質時，其波前因紊亂介質而產生扭曲變形的情形，因為散射現象的存在，在紊亂介質後方的成像技術具有相當的挑戰。為了克服上述的困難，此篇論文中介紹了光學相位共軛 (optical phase conjugation)的理論以及實驗設計 ，吾人可以利用光學相位共軛抑制散射現象。然而光學相位共軛在真實的實驗環境中受到相位共軛反射率(phase conjugation reflectivity)太小以及需要特定光源種類、非線性材料的限制，為了改善這些缺點，吾人決定採用數位光學相位共軛 (digital optical phase conjugation) 技術來模擬散射現象的抑制。
在本篇論文中，吾人利用有限時域差分法 (finite-difference time-domain method) 以及全場散射場技術 (total-field / scattered-field technique) 進行一系列二維空間中的數位相位共軛現象的模擬，並且分析各種不同的變因對於相位共軛波重建的波前造成的影響。本篇論文所提供的模擬結果兼具定性以及定量的特性，期許對於未來各項運用到數位光學共軛現象的技術可以提供足夠的資訊供以改善其效能，另外也期許本論文提供的資訊能夠更進一步拓展非侵入式生醫顯影技術的精進。

關鍵字

有限時域差分法 ； 數位光學相位共軛 ； 全場散射場技術

並列摘要

Wavefront of the light propagating through a turbid medium would be distorted severely due to the scattering phenomenon and hence we can barely see objects behind the turbid medium. To overcome that challenge, we introduce the optical phase conjugation (OPC) to suppress the distortion caused by incoherent scattering of a turbid medium. However, conventional OPC is limited due to its minute phase conjugation reflectivity, which is defined as the power ratio of the phase conjugate signal to the input signal, and the requirements of specialized light sources and nonlinear materials. To improve the conventional OPC, digital optical phase conjugation (DOPC) proposed by Yang’s research team is applied. Basically, DOPC is identical with DOPC except it utilizes digital signal processing to generate the phase-conjugate wave to modify the performance of its phase conjugation reflectivity.
In this thesis, we simulate the macroscopic light scattering phenomenon of the DOPC phenomena in two-dimensional cases by using the finite-difference time-domain (FDTD) method and total-field / scattered-field (TF / SF) technique. Also, we analyze our DOPC simulation results and investigate the factors to optimize the reconstruction efficiency. The reported simulation results enable qualitative and quantitative characterization that can provide important information for further improvement of the DOPC technique and explore the possibility in noninvasive biomedical imaging approaches.

並列關鍵字

Digital Optical Phase Conjugation (DOPC) ； Finite-Difference Time-Domain Method (FDTD) ； Total-Field / Scattered-Field technique (TF / SF technique)

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