Abstract
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.
