IMAGING ERRORS IN ARRAYED WAVEGUIDE GRATINGS

A detailed assessment of imaging errors in arrayed waveguide gratings (AWG) is presented, focussing on possible design related imaging errors as well as on typical imaging errors mediated by the fabrication process. From a design point of view, special interest is drawn to the effect of coupling within the array of grating waveguides and to the impact of the paraxial approximation for the star couplers which is commonly used in the design of AWGs. Both become important design issues affecting the performance of AWG devices when moving to high numbers of narrowly spaced channels. For the technology related imaging errors we focus on one side on the impact of almost uncorrelated phase errors at high spatial frequencies. They can typically be attributed to fluctuations in the index profile and waveguide dimensions in the grating region. On the other side correlated long range phase errors are treated which occur in the grating region as well as within the star couplers and which are typical for stress induced index changes in silica-on-silicon waveguides. It is shown that only modelling tools which include all types of the above imaging effects can provide reliable boundary conditions for a comprehensive design of high end AWG concerning spectral shape and chromatic dispersion.