LC-R2500液晶空間光調變器之測定研究

Characteristics measurement of the liquid crystal spatial light modulator LC-R2500

施嘉博(Jia-Bo Shih)

指導教授 ： 徐巍峰

國立臺北科技大學/電資學院/光電工程系研究所/碩士(2008年)

https://doi.org/10.6841/NTUT.2008.00207

摘要

液晶空間光調變器(Liquid-crystal spatial light modulator, LC-SLM)是本實驗室用來實現繞射光學元件(Diffractive optical element)的主要元件之一，其原理為利用液晶加電壓後，會使光發生相位延遲並產生相位差分佈函數。本研究檢測之液晶空間光調變器為Holoeyes公司製造的LC-R2500，其特性為反射式、液晶扭轉角為45度。
在使用液晶空間光學調變器作為繞射光學元件前，我們需先對它進行振幅與相位光波調制特性的量測。本論文在振幅調變(反射率)量測方面，我們直接量取入射與反射光功率以計算其反射率特性曲線；相位量測是利用麥克森干涉儀的架構進行量測，藉由改變LC-SLM半邊的灰階值來改變相位延遲，使干涉條紋產生位移，再經由相關性(correlation)運算可計算出實際的相位延遲量。由於不同偏振方向的光波入射至LC-R2500所產生的相位延遲、反射光強均有所不同，因此，針對不同應用的課題，我們對偏振角和液晶分子的光軸夾約正負20度以內的情況做量測。量測後的相位曲線尾端皆有非線性上升的現象，我們以多項式曲線來擬合量測曲線前半段線性的部分，並依其公式修正尾端的曲線，最後經由實驗證明修正後的相位曲線較接近LC-R2500的相位曲線。

關鍵字

液晶空間光調變器 ； 繞射光學元件 ； 麥克森干涉儀

並列摘要

Liquid-crystal spatial light modulator (LC-SLM) will be used in replace of phase-only diffractive optical elements in our laboratory. It provides a corresponding phase delay to the incident light depending on the external electrical field. The LC-SLM used in our lab is LC-R2500, made by Holoeyes Co., in which the twist angle of liquid crystal is 45° and light operation is in reflective mode.
Before using LC-SLM for the diffraction optical elements, we first measured the amplitude and phase modulation of LC-R2500. We used the Michelson interferometer to produce the interference fringes. By changing the applied voltage of one half the corresponding interference fringes have a certain displacement, which was calculated by a correlation operation. The phase delay of the applied voltage was than obtained as the ratio of the interference displacement to the period of the interference fringes. Because the incident light is different polarized directions might result in different measurement results of the reflectivity and the phase delay, the angle of the polarizer was changed every 10 degrees from -20 to +20 degrees to obtain experiential data to characterize the LC-SLM. The measured characteristic of the phase delay to the gray scale (the applied voltage) are nonlinear, and are used a polynomial of order to fit the measured data. Finally, the phase delays calculated from the polynomial were used in the design of diffractive optical elements which were implemented by LC-R2500.

並列關鍵字

LC-SLM ； DOE ； Michelson interferometer

參考文獻

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