  We present a numerical and experimental study of the impact of phase errors
on the performance of large, high-resolution Arrayed Waveguide Gratings (AWG)
for applications in astronomy. We use a scalar diffraction model to study the
transmission spectrum of an AWG under random variations of the optical
waveguide lengths. We simulate phase error correction by numerically trimming
the lengths of the optical waveguides to the nearest integer multiple of the
central wavelength. The optical length error distribution of a
custom-fabricated silica AWG is measured using frequency-domain interferometry
and Monte-Carlo fitting of interferogram intensities. In the end, we give an
estimate for the phase-error limited size of a waveguide array manufactured
using state-of-the-art technology. We show that post-processing eliminates
phase errors as a performance limiting factor for astronomical spectroscopy in
the H-band.
