Abstract: An array of optical elements for processing a spatially dispersed optical beam including monitoring optical elements for determining the position of the optical beam in the array is disclosed. The monitoring optical elements have a width that varies in ay direction normal to the array axis, enabling the determination of the beam position across the monitoring elements in both x and y directions. The monitoring optical elements are preferably disposed in the end portions of the array for the beam tilt determination. The optical elements can be e.g. liquid crystal pixels or micro-mirrors.