Polarizing metal stripe gratings for a micro-optical polarimeter

Several applications in science and industry require a precise measurement of the polarization of the incident light, e.g. the online characterization of textil e-fiber birefringency in spinning machines. A promising concept to realize these polarimeters is based on structured polarizers that consist of three polarizing metal stripe gratings, whose spatial orientations are tilted against each other with an angle of 60deg. With such an approach the state of polarization can be determined with a very small device without any moving parts. Here we report on the fabrication of a micro optical polarimeter based on three polarizing metal s tripe gratings with a grating period of 300nm and a size of 0.3 mm x 0.3 mm each. To achieve the necessary high aspect ratio we combined electron-beam direct wr iting with dry etching and metal coating under oblique incidence. The measured p olarization contrast of the fabricated micropolarizers is more than 300:1 over a large spectral range (wavelength between 450nm and 1000nm), moreover they have a contrast of even more than 1000:1 if light with a wavelength between 500nm and 600nm is used. Thus, they are well suited for microsensors to detect birefringency.