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A stack of polarization gratings each having a grating pitch, the stack having a first end and a second end and, the polarization grating stack including N stages wherein one or more of the N stages in the stack comprise a first set of gratings which direct an incident beam through angles lying substantially in a first plane and one or more of the N stages in the stack comprise a second set of gratings which direct an incident beam through angles lying substantially in a second, different, plane lying at an angle relative to the first plane and wherein each of the N stages provide one of a plurality of deflection angles and wherein the N stages are arranged such that a stage having the smallest deflection angle is nearest the first end of the stack and a stage having the largest deflection angle is nearest the second end of the stack and wherein the deflection angles of the gratings in each set are chosen such that the grating pitch of each grating is at least one of: substantially twice the grating pitch of another member of the set; or substantially one-half the grating pitch of another member of the set.