An optical system having a spatial light modulator (SLM), in which each pixel has an optical cavity and is adapted to: (i) change the intensity of a reflected beam by changing the size of the cavity and (ii) change the phase of the reflected beam by changing the position of the cavity with respect to a reference plane. In one embodiment, the optical system has optics configured to image the apertures of an optical input mask onto the pixels of the SLM and to form an optical spot array by imaging the light reflected by the pixels onto a plane orthogonal to the plane of the mask. Each aperture can be configured to have a transmission pattern to spatially modulate the light imaged onto the corresponding pixel, thereby enabling control of the spatial mode at the corresponding spot in the optical spot array.