  One promising application of photonics to astronomical instrumentation is the
miniaturization of near-infrared (NIR) spectrometers for large ground- and
space-based astronomical telescopes. Here we present new results from our
effort to fabricate arrayed waveguide grating (AWG) spectrometers for
astronomical applications entirely in-house. Our latest devices have a peak
overall throughput of ~23%, a spectral resolving power
(${\lambda}/{\delta}{\lambda}$) of ~1300, and cover the entire H band
(1450-1650 nm) for Transverse Electric (TE) polarization. These AWGs use a
silica-on-silicon platform with a very thin layer of Si3N4 as the core of the
waveguides. They have a free spectral range of ~10 nm at a wavelength of ~1600
nm and a contrast ratio or crosstalk of about 2% (-17 dB). Various practical
aspects of implementing AWGs as astronomical spectrographs are discussed,
including the coupling of the light between the fibers and AWGs,
high-temperature annealing to improve the throughput of the devices at ~1500
nm, cleaving at the output focal plane of the AWG to provide continuous
wavelength coverage, and a novel algorithm to make the devices polarization
insensitive over a broad band. These milestones will guide the development of
the next generation of AWGs with wider free spectral range and higher resolving
power and throughput.
