Patent ID: 7200301

Claim:
A method of iteratively optimising a design function for a grating structure, the method comprising: (a) obtaining a first design function describing a refractive index variation defining a multi-channel grating structure in a waveguide material; (b) generating a second design function from the first design function, the second design function having a reduced maximum amplitude compared with the first design function; (c) determining a second response function associated with the second design function, the second response function describing a spectral response of the grating structure defined by the second grating function; (d) replacing selected parts of the second response function to create a third response function having predetermined spectral characteristics in a functional portion of the spectral domain; (e) determining a third design function associated with the third response function; and (f) repeating steps (b) to (e), wherein the third design function of the previous iteration is taken as the first design function of the current iteration, and wherein the iterative repetition continues until predetermined quality criteria are satisfied, the quality criteria comprising a reduction of a maximum refractive index variation in the waveguide material along the waveguide structure and the preservation of the predetermined spectral characteristics in the functional portion of the spectral domain.