processing capabilities implementation of automated wafer handling is thus limited by small production volumes rather than by process compatibility there are a variety of different structures that may be used for the diffraction gratings in one embodiment the gratings are produced using a binary optics technique illustrated in fig5 this technique forms initial trenches at the pitch of the final grating and progressively introduces additional features as may be understood more clearly with reference to the drawing an initially flat substrate may be formed into a two level structure 404 by etching trenches 428 at the grating pitch this process is repeated at half the pitch as indicated with structure 408 trenches 428 at half the pitch are formed by using lithographic techniques and are etched to a depth half that of the initial trenches this produces a four level structure 412 having profile 432 the process is repeated again at a quarter of the pitch as indicated with structure 416 trenches 436 at a quarter the pitch are formed by using lithographic techniques and are etched to a depth a quarter that of the initial trenches this produces an eight level structure 420 having profile 440 the result of this type of processing produces a diffraction grating structure having the same initial pitch as the first structure 404 but having a total depth that is the sum of the depths of the.