US Patent 7409123 Grating having reduced mode dispersion

An optical device includes an echelle grating and input waveguide arranged such that the echelle grating receives an input signal that exits from a port of the input waveguide. The echelle grating is configured to reflect the input signal such that when the input signal has a plurality of channels, the input signal separates into output signals that each includes a different one of the channels. The device also includes a plurality of output waveguides that each includes a port positioned to receive one of the output signals. The output waveguides include central waveguides. The central waveguides are the three centermost output waveguides when the total number of output waveguides is odd and the two centermost output waveguides when the total number of output waveguides is even. The central waveguides are positioned such that the grating axis passes through the port associated with one of the central waveguides or passes between the ports associated with the central waveguides.