Patent ID: 8052284

Claim:
A projector with reduced size and higher contrast, comprising: a light system with a first optical axis for emitting a first light; a digital micro-mirror device (DMD) comprising a plurality of micro mirrors rotatable to a first angle or a second angle; a prism assembly comprising: a medium layer having a reference refractive index; a first prism locating at a first side of the medium layer and having a prism refractive index, the prism refractive index being larger than the reference refractive index, the first light entering the first prism and being totally reflected internally as a second light to the DMD; and a second prism locating at a second side of the medium layer and having the prism refractive index; and a lens assembly with a second optical axis, as the micro mirrors of the DMD rotating to the first angle, the micro mirrors of the DMD reflecting the second light into the lens assembly through the first prism, the medium layer, and the second prism in sequence; wherein as the micro mirrors of the DMD rotate to the second angle, the second light is reflected from the micro mirrors of the DMD to the prism assembly and emits out of the prism assembly in a direction away from the second optical axis after two-time internally total reflection in the prism assembly.