This disclosure is directed to thermally controlled optical systems. In one aspect, an optical system includes a sub-wavelength grating having a planar geometry and a grating pattern associated with a particular shape of, and direction in which, a wavefront emerges from the grating, when the grating is illuminated by a beam of light. The system includes at least one heating element separately connected to a current source. The current source to inject a current into each heating element to heat a corresponding region of the grating and produce a desired change in the shape of, and/or direction in which, the wavefront emerges from the grating.