Patent ID: 7492988

Claim:
A planar lightwave circuit comprising: an input MMI (multi-mode interferometric) slab comprising one or more input ports; an output MMI slab comprising one or more output ports; a plurality of grating waveguides embedded in a cladding material, the cladding material having a refractive index of less than 2.5, the plurality of grating waveguides having an index contrast of less than 5 percent relative to the cladding material, the plurality of grating waveguides configured to photonicly connect the input MMI slab to the output MMI slab, each grating waveguide of the plurality of grating waveguides having a unique path length; and wherein each grating waveguide of the plurality of grating waveguides comprises a plurality of straight segments interconnected with a plurality of reflective bends, each reflective bend comprising: an input segment, an output segment disposed at a bending angle of less than 70 degrees relative to the input segment, and a single air trench forming a TIR (total internal reflective) surface on a portion of the input segment and the output segment, the TIR surface configured to reflect at least 80 percent of lightwave energy provided by the input segment to the output segment.