Illumination optical system, illumination unit and image projection apparatus employing the same

Abstract

An illumination optical system, an illumination unit, and an image projection apparatus employing the same are provided. The illumination optical system includes a light source irradiating a diverging light, a reflection optical system condensing the diverging light from the light source, and a lens optical system projecting the light condensed by the reflection optical system. The reflection optical system is comprised of an aspherical concave mirror. The lens optical system comprises a condensing lens having a positive refractive power in a central part and a refractive power of the condensing lens being decreased toward a circumferential part. Optical efficiency may be improved even when a light-emitting surface of the light source is relatively large and the light source cannot be regarded as a point light source.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings, in which:

FIG. 1 is a schematic view of an image projection apparatus using an illumination optical system according to an exemplary embodiment of the present invention;

FIGS. 2A and 2B respectively illustrate light beams showing a schematic construction of the illumination optical system illustrated in FIG. 1;

FIG. 3 is a plan view illustrating an example of a light source used in the illumination optical system illustrated in FIG. 1;

FIG. 4 is a graph illustrating an example of a light beam emission angle distribution from the illumination optical system including on-axis light and off-axis light in the illumination optical system illustrated in FIG. 1;

FIGS. 5A and 5B respectively illustrate light beams showing a schematic construction of the illumination optical system illustrated in FIG. 1;

FIG. 6 is a graph illustrating an example of a light beam emission angle distribution from the illumination optical system including on-axis light and off-axis light in the illumination optical system illustrated in FIG. 5;

FIG. 7 illustrates a schematic construction of an image projection apparatus using an illumination optical system according to another exemplary embodiment of the present invention; and

FIG. 8 illustrates a schematic construction of an image projection apparatus using an illumination optical system according to another exemplary embodiment of the present invention.

Claims

1. An illumination optical system, comprising: a light source for irradiating a diverging light;a reflection optical system for condensing the diverging light from the light source; anda lens optical system for projecting the light condensed by the reflection optical system, wherein the reflection optical system is comprised of an aspherical concave mirror, and the lens optical system comprises a condensing lens having a positive refractive power in a central part and a refractive power of the condensing lens being decreased toward a circumferential part.

2. The illumination optical system of claim 1, wherein the concave mirror of the reflection optical system comprises a rotationally symmetrical aspherical concave reflective surface.

3. The illumination optical system of claim 2, wherein the concave reflective surface of the concave mirror has a refractive power increasing from the central part to the circumferential part.

4. The illumination optical system of claim 1, wherein the concave mirror is disposed at a distance in which on-axis light reflected from the circumferential part in a diameter direction of the concave mirror becomes substantially parallel light.

5. The illumination optical system of claim 1, wherein the condensing lens is a bilateral apsherical lens.

6. The illumination optical system of claim 5, wherein the condensing lens has a first surface that is a side surface of the concave mirror, is formed as a concave surface in the central part and is formed as a convex surface in the circumferential part; anda second surface that is a rear surface of the side surface of the concave mirror, is formed as a convex surface having a smaller curvature than the concave surface of the first surface in the central part and is formed as a concave surface having the shape of the convex surface of the first surface in the circumferential part.

7. The illumination optical system of claim 1, wherein the light source is not a point light source.

8. The illumination optical system of claim 1, wherein the light source is a surface light source having a finite size with respect to an effective diameter of the reflection optical system.

9. The illumination optical system of claim 1, wherein the light source is constituted by arranging a plurality of light-emitting elements.

10. The illumination optical system of claim 9, wherein the light-emitting elements are red (R), green (G), and blue (B) of monochrome light-emitting elements

11. The illumination optical system of claim 9, wherein the monochrome light-emitting elements disposed on the circumferential part of a light-emitting surface of the light source are disposed so that the respective monochrome colors are circulated.

12. The illumination optical system of claim 9, wherein the monochrome light-emitting elements disposed on the central part of a light-emitting surface of the light source are disposed so that the respective monochrome colors are bilaterally symmetrical or rotationally symmetrical with one another.

13. An illumination unit having a plurality of illumination optical systems, wherein each illumination optical system comprises: a light source for irradiating a diverging light;a reflection optical system for condensing the diverging light from the light source; anda lens optical system for projecting the light condensed by the reflection optical system, wherein the reflection optical system is comprised of an aspherical concave mirror, and the lens optical system comprises a condensing lens having a positive refractive power in a central part and a refractive power of the condensing lens being decreased toward a circumferential part.

14. The illumination unit of claim 13, wherein the concave mirror of the reflection optical system comprises a rotationally symmetrical aspherical concave reflective surface.

15. The illumination unit of claim 13, wherein the light source is a surface light source having a finite size with respect to an effective diameter of the reflection optical system.

16. An image projection apparatus in which an illumination optical system is employed as a projection light source, wherein the illumination optical system comprises: a light source for irradiating a diverging light;a reflection optical system for condensing the diverging light from the light source; anda lens optical system for projecting the light condensed by the reflection optical system, wherein the reflection optical system is comprised of an aspherical concave mirror, and the lens optical system comprises a condensing lens having a positive refractive power in a central part and a refractive power of the condensing lens being decreased toward a circumferential part.

17. The image projection apparatus of claim 16, wherein the concave mirror of the reflection optical system comprises a rotationally symmetrical aspherical concave reflective surface.

18. The image projection apparatus of claim 16, wherein the light source is a surface light source having a finite size with respect to an effective diameter of the reflection optical system.

19. An image projection apparatus in which an illumination unit having a plurality of illumination optical systems is employed as a projection light source, wherein each illumination optical system comprises: a light source for irradiating a diverging light;a reflection optical system for condensing the diverging light from the light source; anda lens optical system for projecting the light condensed by the reflection optical system, wherein the reflection optical system is comprised of an aspherical concave mirror, and the lens optical system comprises a condensing lens having a positive refractive power in a central part and a refractive power of the condensing lens being decreased toward a circumferential part.

20. The image projection apparatus of claim 19, wherein the concave mirror of the reflection optical system comprises a rotationally symmetrical aspherical concave reflective surface.

21. The image projection apparatus of claim 20, wherein the light source is a surface light source having a finite size with respect to an effective diameter of the reflection optical system.