Planar optical demultiplexer with chirped grating for WDM fibre systems

The theory presented allows the analysis of multimode planar multiplexers and demultiplexers using plane gratings of arbitrary grating constant and blaze angles. In a configuration with a plane chirped grating, the wavelength-selective device has to provide the correct phase matching of the divergent phase front of the input fibre. This refocuses the radiation onto the wavelength-dependent output fibre locations. Computations show an excellent device property for ideal chirp and blaze angles. Taking practical deviations into account, the diffraction behaviour of five different grating configurations have been calculated and optimised with regard to the blaze angle. A grating configuration consisting of four regions with constant angles leads to an intensity loss of only 0.72 dB compared to the ideal case.