The invention relates to a planar lightwave circuit including a two stage
optical filter for use in a bi-directional transceiver. A first stage
includes a non-dispersive optical filter, which enables light within in a
certain wavelength range, e.g. a signal channel from a laser source, to
be launched onto an input/output waveguide, while light within another
wavelength range, e.g. one or more detector channels, will be directed
from the input/output waveguide to a second stage. The second stage
includes a reflective diffraction grating with a higher resolution than
the first stage providing passbands 2 to 5 times thinner than the first
stage.