Superimposed phase gratings in planar optical waveguides for wavelength demultiplexing applications

A theoretical analysis of superimposed phase gratings in planar optical waveguides for wavelength demultiplexing applications is developed. Using coupled-mode theory, it is shown that the coupling between the gratings affects diffraction characteristics for output beams of close angular or wavelength separation. Nevertheless, taking into account the coupling effects and adjusting critical parameters, high-performance devices are found to be achievable in carefully designed structures. The authors predict that wavelength demultiplexers having efficiencies larger than 95%, angular and wavelength separation smaller than 0.2 degrees and 20 AA, respectively, and crosstalk attenuation lower than -40 dB are possible.<>