We propose a new planar device for reading light supply on a spatial light modulator. The new device, reading light supplier (RLS), consisting of a fiber plate and a redirector was found to be a suitable device for stacked optical computing systems. A fiber plate has a normal light propagation mode and a spreading light propagation mode, both of which are efficiently utilized in a RLS. The redirector placed on a surface of the fiber plate redirects the propagation direction of light in the fiber plate. Elementary experiments were carried out with RLSs, and we can successfully read out 2-dimensional images.