Optical waveguide gratings

An optical waveguide grating suitable for operation in an optical transmission device, comprising:

• an array of laterally spaced grating waveguides each having an end extending from a free space region and another end terminating at a reflector surface;
• neighboring ones of said grating waveguides differing in optical path length from each other by a constant optical path length increment;
• each of said grating waveguides includes a single curved portion connected to said free space region by a straight portion, said curved portions having respective radii of curvature which decrease progressively from one grating waveguide to the next according to the sequential location of the grating waveguides commencing from a reference grating waveguide, wherein each said grating waveguide includes another straight portion extending tangentially to the curved portion of that grating waveguide and terminates at said reflector surface, and wherein the overall length of the optical waveguide grating array is less than the overall length of the free space region, both measured along the general direction of extent of said array of grating waveguides.

An optical waveguide grating, suitable for operation in an optical transmission device, comprising:

• an array of laterally spaced grating waveguides, said array having opposite peripheral grating waveguides on either side of a center region of said array, neighboring ones of said grating waveguides differing in length from each other by a constant optical path length increment such that the ratio of the difference in length between the longest and shortest grating waveguides to the length of the shortest grating waveguide exceeds one half;
• each grating waveguide including a curved portion having a radius of curvature differing from the radius of curvature of the curved portion of a neighboring waveguide, the radii of curvature progressively decreasing in an approximately parabolic manner as the numerical sequential location of a said curved portion increases from curved portions at the center region of the array to each of said peripheral grating waveguides,
• each said curved portion located between straight grating waveguide portions.