Abstract: A compact wavefront sensor includes an array of microlenses supported above a microchip. The microchip includes an array of gratings and photodetectors, which correspond to a particular microlens. Light incident on a grating will be diffracted back towards the array of microlenses, where it is focussed onto a corresponding photodetector. The photodetector receives light from gratings adjacent thereto, and detects a resulting interference therebetween. The detected interference is then used to reconstruct the wavefront. The detected interference can also be used to correct wavefronts by controlling a modulating element reflecting the wavefront.