A thin film light modulator (50) for use in an electro- optic line printer (11). A light valve utilizes a thin electro- optic film (54) on a substrate (52) with the index of refraction of the film being higher than the substrate so that the light can be guided in it. A laser beam (48) is caused to be guided in the film, the beam expanding sideways so that a sheet of collimated light is provided. This light is guided beneath an array of electrodes (58), consisting of an extended set of individually addressed metal fingers. The light diffracted by the electrode set is reimaged onto the recording medium (14), with the zero order diffracted light blocked out, so that each electrode pair acts as a light modulator for one picture element on the output. Alternatively, the zero order is reimaged and the higher order diffraction components are blocked out. By applying each bit of a serial stream of data to the corresponding electrode, a line recording is achieved.