PASSBAND FLATTENING IN AN ARRAYED WAVEGUIDE GRATING

An AWG having a passband flattening feature disposed between at least one of the input and output waveguides and an adjacent one of the first and second free space couplers in which the passband flattening feature comprises a non-adiabatic tapered waveguide which widens in width towards the respective free space coupler. The passband flattening feature merges smoothly with the or each input and output waveguide, and is shaped to minimize radiation losses and thus insertion loss of the device. In one embodiment, the passband flattening feature consists of an exponentially tapered waveguide followed by a phase shifting waveguide. In another embodiment the feature is a curvilinear waveguide having a shape defined by a perturbed cosine function.