  Arrayed waveguide gratings (AWGs) are key optical components of various new
applications in telecommunication, astrology, medical imaging, and
spectroscopy. It is a very powerful integrated light dispersion technology with
significant flexibility for tailoring its performance to the individual system
needs of each application. There are several examples of custom AWG designs in
the literature aiming for improved system performance. In this review, we will
provide an overview of the available methods for improving the bandwidth,
spectral resolution, and transmission function shape of AWGs. The working
principle as well as the advantages and disadvantages of each method will be
discussed.
