Characterisation of phase-shifts in gratings fabricated by over-dithering and simple displacement

Several different gratings utilizing phase-shifts in their designs are fabricated and characterised: a uniform grating with a single phase shift in the centre, a sinc-profile grating (with intrinsic phase shifts at the zeros), and a stretched cosine apodised grating with multiple and arbitrary phase shifts. The gratings are fabricated by either over-dithering the phase mask or a simple displacement of the phase-mask. The gratings are then characterised by measuring their spectral and group delay characteristics and using a grating reconstruction algorithm to determine the apodisation and phase profiles of the grating. The relative susceptibility of the different fabrication methods to errors is discussed along with the role of grating reconstruction in characterisation of gratings. (C) 2003 Elsevier Inc. All rights reserved.