Integrated optical comb filter for dispersion compensation with slanted grating lines

A novel architecture of an optical filter for pulse compression in dense wavelength-division multiplexing (DWDM) systems is presented. We propose a comb filter for dispersion compensation within a transmission channel. A pair of chirped gratings with slanted grating lines is used. The effect of filtering is not based on resonances as used in Bragg gratings, but it is achieved by interferences of parts of the optical wave. Furthermore, the filter concept enables an amplification to compensate transmission losses. The filter parameters are adjusted by different phase shiftings of the grating lines. Their geometrical dimensions are equal for all grating lines. It will be shown, how different grating lengths and phase shiftings between the grating lines contribute to the transmission characteristic of the filter. We will give design rules for the chirp to develop appropriate filter functions for positive or negative dispersion values up to 1500 ps/nm while the linearity of the group delay is restricted to 6.5%. The performance of the structure will be presented by a filter designed for a DWDM-system with a channel distance of 0.4 nm.