module 14 refracts the light ray toward the digital micromirror device dmd 15 as the light ray is refracted by digital micromirror device dmd 15 and image is formed the prism module 14 again refracts it toward the projection lens set 16 then an image is focused and formed on an external projection surface 91 to locate the above mentioned elements precisely the optical engine 10 of the invention is specifically devised as shown in fig2 and 3 the optical engine 10 further includes a base 17 and an upper lid 18 the base 17 and the upper lid 18 is made of plastic materials manufacture with injection molding technique upon the base 17 there are a right cover 171 and a lower lid 172 inside the right cover 171 a first space 173 is formed to the contain digital micromirror device dmd 15 and in the lower lid 172 a v shaped lower concave base 174 and a below prism shading piece 175 connected in adjacent to right cover 171 are formed also there is a lower concave groove 176 located between v shaped lower concave base 174 and below prism shading piece 175 upper lid 18 provides connection for lower lid.