An optical device capable of emitting polarized light includes a light emitting means, two multi-layer optical films disposed above and below the light emitting means and two metal layers. The two metal layers cover the two multi-layer optical layers from the upper and lower sides respectively. Each of the two multi-layer optical films includes at least two films made from materials of different refractive indexes that are stacked in a staggered manner. The optical film formed by the multi-layer optical films and metal layers provides greater reflectance to S-polarized light (TE) and higher absorption to P-polarized light. Light generated by the light emitting means emits diagonally to the optical films and is reflected several times thereof to form S-polarized light (TE) to emit sideward.