We study a nematic dispersion formed in a UV-polymerized matrix with a low content of a liquid crystal component. The dispersions contains sub-micrometer liquid crystal droplets obtained in a two-step process: (a) phase separation during a fast cooling process (b) stabilization of droplets size by photo-polymerization caused by a low power UV exposure. The dispersion is homogeneous, highly transparent and shows little light scattering at wavelength 633 nm. We demonstrate that it can be used as an electrically-controlled birefringent slab with a relatively low driving voltage and a short response time. For example, application of the electric field 6 V/mu m changes phase retardation by pi/4 with the characteristic response time of several milliseconds.