Roughly described, arrayed waveguide grating apparatus includes one or
more input and/or output waveguides which are shaped and oriented such
that optical energy communicated with the waveguide array is, within a
distance of no more than 1 mm into the mouth of the waveguide, directed
substantially in-line with the optical centerline of the waveguide. In
one embodiment, the waveguides are shaped and oriented such that the
optical energy enters or exits the waveguide substantially-line with the
optical centerline of each waveguide. In another embodiment the
waveguides are shaped and oriented such that optical energy is, at the
mouth of each waveguide, directed off-axis, and the waveguide includes
mode conversion means such that optical energy is directed substantially
in-line with the optical centerline within a distance of no more than 1
mm into the mouth of the waveguide. The mode conversion means may, for
example, include a non-adiabatic lateral optical centerline shift.