INSTITUTE OF APPLIED PHYSICS - Broadband metallic polarizers

Broadband metallic polarizers

Wire grid polarizers are of great interest for many applications such as in the field of microscopy, spectroscopy, or imaging systems. They consist of a parallel arrangement of conductive (metallic) wires on a transparent substrate. The optical function is given by the transmission of TM-polarized light and the suppression of TE-polarized light. Wire grid polarizers are characterized by the transmission of TM-polarized light and the extinction ratio, which is defined by the ratio of TM- and TE-polarized light. Since the operation wavelength of optical systems is decreasing to the UV spectral range, optical components for typical application wavelengths like 365 nm, 325 nm, 266 nm, or 193 nm are required. The decreasing of the operation wavelength demands sophisticated fabrication technologies to reduce the grating period or new grating materials.

For the fabrication of wire grid polarizers, a multi-step double patterning process based on electron beam lithography was used to fabricate UV polarizers with a period of 100 nm and a vertical aspect ratio of about 5:1. Different grating materials were used to enable a broadband optical function from the infrared down to a target wavelength of 250 or 193 nm. Here, iridium was used as grating material as a corrosion resistant alternative to the commonly used aluminum for applications down to 250 nm and tungsten to provide functionality in the DUV spectral range at 193 nm.

 Chiral loop wire metamaterials_ Weber
SEM image of an iridium wire grid polarizer fabricated by double patterning and spectral measured extinction ratio of an iridium and tungsten wire grid polarizer.

[1] T. Weber, T. Käsebier, E.-B. Kley, A. Tünnermann, Broadband iridium wire grid
     polarizer for UV applications, Optics Letters 36, 445-447 (2011).

[2] T. Weber, T. Käsebier, A. Szeghalmi, M. Knez, E.-B. Kley, A. Tünnermann,
     Iridium wire grid polarizer fabricated using atomic layer deposition,
     Nanoscale Research Letters 6, 558 (2011).

[3] T. Weber, T. Käsebeier, M. Helgert, E.-B. Kley, A. Tünnermann,
     Tungsten wire grid polarizer for applications in the DUV spectral
     range, Applied Optics 51, 3224-3227 (2012).