16 May 2017 Miniature optical components for a small inline polarimeter
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Abstract
We present two novel components for a small polarimeter: A laser light source and a polarization measuring element. The polarimeter is designed for the use in experimental biogas fermenters, where the optical activity information is needed as an input for the process control loop. For this purpose reproducible measurements over several days and a very small sample volume are necessary. The laser light source provides the collimated and linearly polarized light which passes the sample chamber towards the polarization detector. The beam diameter is smaller than 1 mm over the whole length of 10 cm in order to prevent reflections from the chamber walls. The micro lasers are surface emitting laser diodes (VCSELs) that are mounted on a metalized glass / polymer micro optics in a wafer based process flow. This makes it possible to reduce the size of the polarized light source down to 1.40 x 0.64 x 0.70 mm3. The polarization angle detector consists of a beam polarizing splitter cube with a splitting ratio of better than 10000:1. At both exits a monolithic pair of photodiodes is mounted directly. The sum of the two signals is a measure for the parallel or perpendicular polarized part of the light, respectively. The double diodes are tilted by 90° within the plane, in order to create a four-quadrant detector that is suited to analyze the beam position. This additional position measurement is used for detection of adverse illumination.
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J. Freitag, A. T. Winzer, M. Schädel, T. Frank, R. Müller, K. Neckermann, "Miniature optical components for a small inline polarimeter", Proc. SPIE 10231, Optical Sensors 2017, 102312D (16 May 2017); doi: 10.1117/12.2267137; https://doi.org/10.1117/12.2267137
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