以有限時域差分法模擬分析數位光學相位共軛現象

當光穿過紊亂介質,與介質接觸時,產生的繞射與散射將嚴重影響觀測的影像,但若利用非線性光學中的相位共軛特性: 當光的相位改變,與原入射波為共軛之關係,光將自行回溯至波源。數位光學共軛鏡(Digital Optical Phase Conjugation)結合了電光調製器(Electro Optical modulator)及空間光調製器(Spatial light modulator),經由此儀器我們可以成功的產生相位共軛的光波,藉以達到光學回溯的效果。本論文使用有限時域差分法(Finite-Difference Time-Domain technique), 並搭配此方法的額外技術, 針對數位光學相位共軛鏡進行一連串數值模擬與研究。我們在空間中擺放物質, 觀測電磁波經光學相位共軛鏡讀取資訊後之光回溯場型, 並更改模擬區域的寬度, 觀察光學相位共軛鏡與入射波在入射波波源處的能量場型, 企圖藉由此類數值模擬來了解數位光學相位共軛鏡之基本性質。此外, 我們更改變數位光學相位共軛鏡接收向前傳播散射波(Forward scattering wave) 之頻率以及共軛鏡的解析度, 試圖找出最有效率的組合, 並進一步利用此一組合, 模擬數位光學共軛鏡在穿透不同濃度的紊亂介質(turbid medium)時之光學回溯效果。

關鍵字

有限時域差分法；數位光學相位共軛鏡；紊亂介質

並列摘要

Due to the complex structure of biological tissues, wave propagateing through turbid medium generates interference and diffraction, generally the image is scattered and blurred. However, in nonlinear optics, with the technique of optical phase conjugation (OPC), for wave propagating through OPC, the wave refocuses to initial emanating point. Digital optical phase conjugation (DOPC) combines electro optical modulator (EOM) and spatial light modulator (SLM), which records forward scattering wave information and digitally reverses the phase information. In this thesis, we apply the Finite-Difference Time-Domain (FDTD) technique, with additional techniques, to simulate DOPC refocusing phenomenon. Not only we simulate the basic property of DOPC, like placing an object in the simulation area to observe DOPC refocusing phenomenon, altering the width of simulation area to compare the profile of DOPC wave and the profile of incident wave; we also alter the DOPC recording time interval and spatial resolution to find the most efficient wave for DOPC refocusing. Moreover, we make use of these results to simulate DOPC refocusing through turbid medium.

並列關鍵字

Finite-Different Time-Domain Method (FDTD) ； Digital Optical Phase Conjugation (DOPC) ； Turbid Medium

參考文獻

[1] H. Eichler and O. Mehl, “Phase conjugate mirrors,” Journal of Nonlinear Optical Physics andMaterials, vol. 10, pp. 43–52, 2001.

[2] J. Schmitt, “Optical coherence tomography (OCT): a review,” IEEE Journal of selected topics in quantum electronics, vol. 5, no. 4, pp. 1205–1215, 1999.

[3] M. Fink, “Time reversal of ultrasonic fields—Part I: Basic principles,” IEEE Trans. Ultrason. Ferroelectr. Freq. Control, vol. 39, no. 5, pp. 555–566, 1992.

[4] P. Kosmas and C. Rappaport, “Use of the FDTD method for time reversal: Application to microwave breast cancer detection,” in Proceedings of SPIE, vol. 5299, p. 1, 2004.

[5] S. Yang, “2-D PSTD Simulation of optical phase conjugation for turbidity suppression,”Opt. Express, vol. 15, pp. 16005–16016, 2007.

國際替代計量

以有限時域差分法模擬分析數位光學相位共軛現象

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