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

We use a numerical simulation to investigate the effectiveness of pinhole s patial filters for optical/IR interferometers and to compare them with sing le-mode optical fibre spatial filters and interferometers without spatial f ilters. We show that fringe visibility measurements in interferometers cont aining spatial filters are much less affected by changing seeing conditions than equivalent measurements without spatial filters. This reduces visibil ity calibration uncertainties, and hence can reduce the need for frequent o bservations 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 giv e SNRs within 17 per cent of the values obtained with single-mode fibres fo r aperture diameters up to 3r(0). Given the simplicity of the use of pinhol e filters we suggest that it represents a competitive, if not optimal, tech nique for spatial filtering in many current and next generation interferome ters.