Apparatus for filtering an optical input signal includes a coupler and
an arrayed waveguide grating connected to the coupler having a phase shifting region.
The phase shifting region is a back wall of a free space region of the arrayed
waveguide grating with concentric image and reflector surfaces. Radial waveguides
between the surfaces are divided into alternating regions of wider and thinner
sets of waveguides. A corresponding change in optical length alters the phase of
the input signal which forces an output signal of a desired wavelength to appear
at a desired port of the filter.
