an optical projection device includes a laser engine , a first wave plate and a lens . the laser engine provides light . the first wave plate changes a light phase . the lens focuses light . a projecting method of an optical projection device includes providing a light including a first p polarized light , a first s polarized light , and a second s polarized light , and projecting light through a wave plate on a screen , wherein the wave plate moves in a direction perpendicular to light . a projecting method of an optical projection device includes providing light including a first p polarized light , a first s polarized light , and a second s polarized light , and projecting light through a wave plate on a screen , wherein the wave plate rotates around an axis parallel to a projecting direction of light .