An optical device for filtering an optical signal is described. The optical filtering
device comprises an optical input receiving the optical signal; an elongated waveguide
connected to the input and having a modified transverse dimension to create a series
of partially reflective segments having predetermined effective indices of refraction
(neff) with a distribution within the waveguide to provide the filtering
of the optical signal, wherein the segments are designed for single mode operation
and wherein a reflected filtered output optical signal is generated, wherein the
transverse dimension varies within a narrow range over which a transverse size
of the mode remains close to its minimum value; an optical output connected to
the waveguide for providing the filtered optical signal.
