Polarization Effects and Their Minimization in an Infrared Single-mode Fibre-optic Double-fourier Stellar Interferometer

Abstract

In astronomical double-Fourier interferometry, stretching a single-mode fibre to generate optical path length modulation is an attractive alternative solution to the more classical bulk delay line. However, such an operation is not free from side effects, one of them being the perturbation of the radiation state of polarization by the waveguide. We present both theoretical and experimental investigations of the polarization behaviour of single-mode fibres in a double-Fourier interferometer. Changes in the state of polarization can be induced by asymmetries in the fibre parameters, and macrobending, twisting, etc., but the main cause of perturbation is the stretch of the fibre which is wrapped onto a piezoelectric tube driven by a high voltage. Not only are these fibre-stretch-induced polarization effects chromatic, but also they depend on the stretching state. The general consequences of the polarization perturbations for double-Fourier interferometric imaging are to distort the source's reconstructed spe...