A tunable interferometer for creating gratings of variable periodicity in an
optical
waveguide is disclosed. The interferometer includes a beam splitter for producing
first and second write beams from an input beam. First and second reflectors receive
the first and second write beams, respectively, from the beam splitter and direct
the first and second write beams to intersect at a fixed location. The angle of
intersection of the first and second write beams is a function of impingement locations
of the first and second write beams on the first and second reflectors. The impingement
locations of the first and second write beams on the first and second. reflectors
may be varied to vary the angle of intersection at the fixed location.
