Simulation of the influence of line edge roughness on the performance of deep ultraviolet wire grid polarizers
Simulation of the influence of line edge roughness on the performance of deep ultraviolet wire grid polarizers
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DOI：
10.1117/12.2269602
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发表时间：
2017-06
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影响因子：
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通讯作者：
T. Siefke;C. B. Rojas Hurtado;J. Dickmann;M. Heusinger;S. Kroker
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作者：
T. Siefke;C. B. Rojas Hurtado;J. Dickmann;M. Heusinger;S. Kroker
控制光的偏振在许多应用中至关重要，例如光谱学、椭圆偏振测量、光刻或工业视觉。线栅偏振器是一种大纵横比的零级光栅，可以实现偏振控制。这些元件根据入射光的偏振方向提供各向异性透射率。WGP的高吸引力源于其大的自由孔径，同时非常薄。此外，这些元件可以很容易地集成到其他纳米光学器件中。最近，这种元素被成功地开发用于深紫外光谱范围。然而，在较短的波长下，结构的粗糙度的影响对可行的光学性能造成了严重的限制。为了解决这个问题，我们数值模拟了线边缘粗糙度对WPG偏振特性的影响。因此，我们通过Thorsos方法生成粗糙光栅线的边缘位置数据，并通过时域有限差分法计算得到的光学响应。用此方法研究了标准偏差、相关长度、Hurst指数和波长等因素的影响。我们发现，标准偏差为2.5 nm和5.0 nm的偏振对比度分别减少了3和7倍。极化对比度显示了最小的中间相关长度，而几乎没有观察到的赫斯特指数的影响。这是由几种机制来解释的粗糙度的空间频率和入射光的频率之间的不同比率。我们的理论研究结果与实验结果，我们检索与测量粗糙度参数的制造元件。
Controlling the polarization of light is crucial in numerous applications such as spectroscopy, ellipsometry, photo lithography or industrial vision. Polarization control can be realized by wire grid polarizers (WGPs), which are large aspect ratio, zero order gratings. These elements provide an anisotropic transmittance depending on the polarization direction of the incident light. WGPs’ high attractiveness originates from their large free aperture, while simultaneously being extremely thin. Furthermore, these elements can be easily integrated into other nano-optical devices. Recently, such elements were successfully developed for applications down to the deep ultra violet spectral range. However, at shorter wavelengths the influence of roughness of the structures poses a severe limitation on the feasible optical performance. To tackle this problem, we numerically simulated the impact of line edge roughness on the polarization properties of WPGs. Therefore, we generated edge position data of rough grating lines by means of the Thorsos method and calculated the resulting optical response by finite difference time domain method. With this procedure the influence of standard deviation, correlation length, Hurst exponents and wavelength was investigated. We find that for standard deviations of 2.5 nm and 5.0 nm the polarization contrast is reduced by a factor of 3 and 7, respectively. The polarization contrast shows a minimum for intermediate correlation lengths, while virtually no impact of the Hurst exponent is observed. This is explained by several mechanisms occurring for different ratios between the spatial frequency of the roughness and the frequency of incident light. Our theoretical findings correlate well with experimental results we retrieved with measured roughness parameters of fabricated elements.