The "piston errors" and aberrations of the mirror segments used in large telescopes, are typically measured with on-board optical instruments, usually a dispersed Hartman sensor (DHS) and/or dispersed fringe sensor (DFS). Calibrating and testing of the wavefront sensors are typically performed using custom-built fused silica phase plate arrays. The manufacture and assembly of each custom phase plate array is time-intensive and expensive. Proposed is a gradient index (GI) phase plate array (PPA), which integrates the corrections of the DHS, an intermediate smoothing phase plate, and the DFS. This reduces the number of phase plates required, from three to one, and allows for the PPA t be used in the pupil plane, allowing for more precise calibration. The monolithic construction of the innovation significantly reduces development time and cost.