US 6,185,047 B2 · Image projection system packaged to operate lying flat with a very low profile

Abstract

An image projection system implemented with a projector engine using a reflective light modulator, preferably a Digital Micromirror Device (DMD), operates lying flat with very low profile on a support table. The invention overcomes the disadvantage of previous DMD projectors that require either tilting all or part of the projection system 45 degrees relative to a support table top or packaging the projection system in a thick box that allows light to impinge on the DMD from above or below its light reflecting surface. This is accomplished with a prism assembly that sets up the correct illumination angles for the DMD and directs imaging (output) light along approximately the same vector as that of illumination (input) light incident to the prism assembly. The illumination light and imaging light do not propagate in a common plane within the prism assembly, but the vectors of the illumination light entering and the imaging light exiting the prism assembly are approximately the same. An alternative preferred embodiment of the prism assembly includes a light escape window through which illumination light reflected by the DMD in its off-state escapes from the prism assembly in a direction away from the projection lens. An implementation using a third prism optically fixed to an output prism or forming an integral part of an enlarged output prism is especially advantageous because it can provide a three-point mounting of the prism assembly to the floor of the interior of the projection system housing.

Claims18

Dependent claims

In an image display system that includes a light source from which a first light beam characterized by a first principal ray propagates in a first direction and a reflective light modulator which responds to a control signal to selectively change an optical property of incident light derived from the first light beam and thereby provide an information-carrying light beam for display on a display screen, the improvement comprising:

an angle-dependent beam separator comprised of multiple optical elements, the beam separator positioned to receive the first light beam and constructed so that an incident light beam derived from the first light beam propagates along a first travel path within the beam separator and strikes the reflective light modulator at an angle of incidence, the reflective light modulator responding to the control signal to selectively reflect the incident light beam at a controlled angle of reflection that differs from the angle of incidence of the incident light beam to provide an on-state reflected light beam that propagates along a second travel path within the beam separator and exits the beam separator to form a second light beam characterized by a second principal ray that propagates in a second direction, the optical elements having shapes and surface angles that cause the first and second travel paths and the first and second principal rays of the respective first and second light beams not to lie in a common plane.

An image display system, comprising:

a light source from which an illumination light beam propagates;
a reflective light modulator responsive to a control signal to selectively reflect incident light at controlled angles of reflection;
a prism assembly positioned between the light source and the reflective light modulator so that the illumination light beam enters and propagates through the prism assembly, strikes the reflector light modulator, and reenters the prism assembly as a reflected imaging light beam that propagates through and exits the prism assembly as an imaging light beam;
and
the prism assembly including first and second prism components separated by an angular discrimination region, the first prism component having an entrance surface on which the illumination light beam is incident at an angle defined by an illumination beam vector direction and the second prism component having an exit surface from which the imaging light beam propagates from the prism assembly at an angle defined by an imaging beam vector direction, and the first and second prism components having shapes and surface angles that cooperate to produce propagation of the imaging light beam so that the illumination and imaging beam vector directions are substantially the same.

2 more elements

Dependencies are inferred from the claim text.

Image projection system packaged to operate lying flat with a very low profile

Life of this patent

Image projection system packaged to operate lying flat with a very low profile

Life of this patent

Abstract

Claims18