Optical systems for projection displays

• US 6,461,000 B1
• Filed: 03/20/2000
• Issued: 10/08/2002
• Est. Priority Date: 06/29/1999
• Status: Expired due to Term

• Current Assignee: Regents of The University of Minnesota (University of Minnesota)
• Original Assignee: US Precision Lens, Inc. (3M Company)
• Inventors: Magarill, Simon
• Primary Examiner(s): Dowling, William
• Application Number:
  US09/528,630
• Time in Patent Office: 932 Days
• Field of Search: 353/81, 353/98, 353/99, 353/31, 353/33, 353/34, 353/37, 348/771, 348/742, 348/743, 345/31, 359/831, 359/833
• US Class Current: 353/81
• CPC Class Codes: G02B 26/0875 by means of one or more refracting elements
• CPC Class Codes: G02B 26/0883 the refracting element being a prism
• CPC Class Codes: G03B 21/005 Projectors using an electronic spatial light modulator but not peculiar thereto
• CPC Class Codes: G03B 21/2066 Reflectors in illumination beam in projection beam G03B21/28
• CPC Class Codes: H04N 5/7458 the modulator being an array of deformable mirrors, e.g. digital micromirror device [DMD]
• CPC Class Codes: H04N 9/3141 Constructional details thereof details not peculiar to the presence of an electronic spatial light modulator G03B21/14

Abstract

A prism (13) for use in a projection system which employs a digital light panel (35) is provided. The prism includes first (19) and second (21) spaced part surfaces which are oriented such that: (a) light from a light source (33) will pass through the spaced apart surfaces to the digital light panel; (b) light from “on” pixels will undergo total internal reflection at the second surface (21) and be directed into the acceptance angle of a projection lens (39); and (c) light from “off” pixels which reflects from the second surface will be directed away from the lens'"'"' acceptance angle.

Claims

1. In an image projection system comprising:

(a) a light source which provides illuminating light;

(b) a plurality of selectively adjustable reflecting elements which are arranged in a common plane, said elements being adjustable between at least a first position and a second position;

(c) a lens having a principal plane which is parallel to said common plane; and

(d) a prism positioned between said lens and said plurality of reflecting elements;

the improvement wherein;

(A) the lens has an acceptance angle;

(B) the prism comprises first and second spaced apart surfaces that are oriented relative to the light source, the plurality of reflecting elements, and the lens such that;

(i) light from the light source passes through the first and second spaced apart surfaces to the plurality of reflecting elements, and

(ii) light reflected from reflecting elements in the first position (a) passes through a first reflected-light transmitting side of the prism, (b) is reflected at the second spaced apart surface in directions which are within the lens'"'"' acceptance angle, and (c) passes through a second reflected-light transmitting side of the prism;

(C) the system has an image side optical axis which is;

(i) perpendicular to the common plane; and

(ii) undergoes a change in direction at the second spaced apart surface;

(D) the principal plane is parallel to the common plane when translated along the image side optical axis and reflected from the second spaced apart surface; and

(E) the first and second reflected-light transmitting sides of the prism have an internal angle of intersection that is acute.

2. The image projection system of claim 1 wherein:

(i) light reflected from some reflecting elements in the second position is reflected at the second spaced apart surface in directions which are not within the lens'"'"' acceptance angle; and

(ii) light reflected from other reflecting elements in the second position passes through the second spaced apart surface.

3. In an image projection system comprising:

(a) a light source which provides illuminating light;

(b) a plurality of selectively adjustable reflecting elements which are arranged in a common plane, said elements being adjustable between at least a first position and a second position;

(c) a lens having a principal plane which is parallel to said common plane; and

(d) a prism positioned between said lens and said plurality of reflecting elements;

the improvement wherein;

(A) the lens has an acceptance angle;

(B) the prism comprises first and second spaced apart surfaces that are oriented relative to the light source, the plurality of reflecting elements, and the lens such that;

(i) light from the light source passes through the first and second spaced apart surfaces to the plurality of reflecting elements, and

(ii) light reflected from reflecting elements in the first position is reflected at the second spaced apart surface in directions which are within the lens'"'"' acceptance angle;

(C) the system has an image side optical axis which is;

(i) perpendicular to the common plane; and

(ii) undergoes a change in direction at the second spaced apart surface;

(D) the principal plane is parallel to the common plane when translated along the image side optical axis and reflected from the second spaced apart surface;

(E) the first spaced apart surface is associated with a first component of the prism through which light from the light source passes but light reflected from the reflecting elements in the first position does not pass;

(F) the second spaced apart surface is associated with a second component of the prism through which both light from the light source and light reflected from the reflecting elements in the first position passes; and

(G) the first component has a lower optical quality than the second component.

4. In an image projection system comprising:

(a) a light source which provides illuminating light;

(b) a plurality of selectively adjustable reflecting elements which are arranged in a common plane, said elements being adjustable between at least a first position and a second position;

(c) a lens having a principal plane which is parallel to said common plane; and

(d) a prism positioned between said lens and said plurality of reflecting elements;

the improvement wherein;

(A) the lens has an acceptance angle;

(B) the prism comprises first and second spaced apart surfaces that are oriented relative to the light source, the plurality of reflecting elements, and the lens such that;

(i) light from the light source passes through the first and second spaced apart surfaces to the plurality of reflecting elements, and

(ii) light reflected from reflecting elements in the first position is reflected at the second spaced apart surface in directions which are within the lens'"'"' acceptance angle;

(C) the system has an image side optical axis which is;

(i) perpendicular to the common plane; and

(ii) undergoes a change in direction at the second spaced apart surface;

(D) the principal plane is parallel to the common plane when translated along the image side optical axis and reflected from the second spaced apart surface;

(E) light reflected from some reflecting elements in the second position is reflected at the second spaced apart surface in directions which are not within the lens'"'"' acceptance angle;

(F) light reflected from other reflecting elements in the second position passes through the second spaced apart surface;

(G) the first spaced apart surface is associated with a first component of the prism through which light from the light source passes but light reflected from the reflecting elements in the first position does not pass;

(H) the second spaced apart surface is associated with a second component of the prism through which both light from the light source and light reflected from the reflecting elements in the first position passes; and

(I) the first component has a lower optical quality than the second component.