Free-space optical distribution of local oscillator signals in aperture synthesis radio telescope arrays

Abstract

An alternative to individually phase-stabilised links for distribution of local oscillator (LO) signals in large arrays of radio telescopes is considered. An array is illuminated from an elevated optical source, intensity modulated at the LO frequency. LO phase feedback from the centre of the illuminated zone counteracts tower and atmospheric instabilities, locking a fixed phase at zone centre, and hence a template of constant phase contours around the zone centre point. Other LO detector planes are aligned to equiphase contours, providing a phase coherent LO to all telescopes aside from differential optical path effects. A local PLL at each site reduces the remaining noise from differential slant path variations.