Patent ID: 7352931

Claim:
A method for manufacturing a multi-channel optical grating in a photosensitive medium, each channel of said multi-channel grating having an individual spectral response, said method comprising the steps of: a) for each channel, individually designing an index profile of a sub-grating providing the corresponding individual spectral response, each of said index profiles comprising an individual apodization profile and an individual phase profile of the corresponding sub-grating; b) determining a target index profile Δn struct (z) of the multi-channel grating based on a combination of the index profiles of said sub-gratings such that: Δ ⁢ ⁢ n struct ⁡ ( z ) = Δ ⁢ ⁢ n offset + ∑ k ⁢ Δ ⁢ ⁢ n k ⁡ ( z ) ⁢ ⅇ ⅈ ⁡ ( θ k ⁡ ( z ) + ϕ k ) where z is an optical axis of said multi-channel grating, k is an indicia representing said sub-gratings, Δn k (z) and θ k (z) are respectively the individual apodization and phase profiles of each sub-grating, φ k is a relative phases between the sub-gratings and Δn offset is an index offset selected to make the target index profile strictly positive, said target index profile defining a target spectral response of said optical grating; c) determining a modified index profile having a smooth apodization profile and providing said target spectral response at least within a spectral region of interest; d) encoding a phase mask according to said modified index profile; and e) photoinducing said multi-channel grating in the photosensitive medium using said phase mask.