Numerical simulations of pinhole and single-mode fibre spatial filters for optical interferometers

We use a numerical simulation to investigate the effectiveness of pinhole spatial filters for optical/IR interferometers and to compare them with single-mode optical fibre spatial filters and interferometers without spatial filters. We show that fringe visibility measurements in interferometers containing spatial filters are much less affected by changing seeing conditions than equivalent measurements without spatial filters. This reduces visibility calibration uncertainties, and hence can reduce the need for frequent observations of separate astronomical sources for calibration of visibility measurements. We also show that spatial filters can increase the signal-to-noise ratios (SNRs) of visibility measurements and that pinhole filters give SNRs within 17 per cent of the values obtained with single-mode fibres for aperture diameters up to 3 r ₀. Given the simplicity of the use of pinhole filters we suggest that it represents a competitive, if not optimal, technique for spatial filtering in many current and next generation interferometers.