以二階光柵的一階繞射光強來量測空間光調變器特性之研究

The study of characterization of spatial light modulator using the first-order diffraction of binary phase grating

陳建宏(Chien-Hong Chen)

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(2013年)

https://doi.org/10.6841/NTUT.2013.00268

摘要

液晶空間光調變器(Liquid-crystal spatial light modulator, LC-SLM)為本實驗室用來實現繞射光學元件(Diffractive optical elements, DOEs)的主要元件之一，其運作原理是利用液晶對其施加電壓後，會使光波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Holoeye公司製造的LC-R2500，其為反射式、液晶扭轉角為45度。而實驗所用之方法與結果做為其它空間光調變器特性量測之參考依據。

使用液晶空間光學調變器作為繞射元件前，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，我們先使用偏振分光鏡(Polarizer beam spliter)來確定此元件液晶的原始配置方向，在量取元件對不同的灰階的反射率時，我們使用兩個光功率計，分別作為監控光與反射光以計算其反射率特性曲線，所量得的反射率並用於相位量測。相位量測方面是利用二階光柵在其一階繞射點的光強變化，可計算出實際的相位延遲量。接著，不同的雷射入射角度對空間光調變特性的影響，以提供一個比較完整的數據，除了綠光(532nm)的雷射以外，SLM對紅光(638nm)和藍光(457nm)的特性示於本文中有完整之量測分析。

關鍵字

液晶空間光調變器 ； 繞射光學元件 ； 相位延遲

並列摘要

The liquid-crystal spatial light modulator (LC-SLM), LC-R2500 by (Holoeye Photonics, AG), is used to implement phase-only diffractive optical elements in our laboratory. LC-R2500 provides a corresponding phase delay to the incident light depending on the applied voltage which is controlled by gray level displayed by a computer. It is therefore important to correctly characterize the relationship between gray levels and the phase delays. In this thesis, we proposed a method to measure the reflectivity and phase delay of a LC-SLM. The measurement results were need to characterize LC-R2500 for designing diffractive optical elements, and the method can be applied for other LC-SLMs.

Prior to using LC-R2500 as the diffraction optical elements, we developed a fast and reliable method to standardize the intensity and phase modulations of LC-R2500. We used a PBS (polarizer beam splitter) to identify the original configuration direction of liquid crystal. To measure different the reflectance of the gray levels, we used two power meters to obtain the power of intensity the reference beam and the reflective beam, and calculated the reflectance curve. To measure the phase delay, we measured the first-order intensity by using the binary complex-valued grating patterns, with a fixed gray level and a varying gray level. Owing to the change of the second gray level, the first-order intensity is changed. Using the measured intensity (power) and the reflectance obtained previously, We calculated the phase delay of the two gray levels. In addition, the reflectance and the phase delay of the LC-SLM need with incident beam at different angles were obtained using the same method. The complete measurement and the characteristics of LC-SLM for green (532nm) , red (638nm) and blue (457nm) were also characterized in this thesis.

並列關鍵字

LC-SLM ； Fraunhoffer diffractions ； DOES

參考文獻

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