Lighting system and projection type display unit using thereof

Details Lighting system and projection type display unit using thereof Lighting system and projection type display unit using thereof

2001-03-29

2003-06-10

Adams, Russell (Department: 2851)

Optics: image projectors

Reflector

C362S268000

Reexamination Certificate

active

06575580

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to an optical system for illumination (lighting system) for applying an illuminating light to a light bulb such as a liquid crystal or DMD (Digital Micromirror Device) and a projection type display unit using the same, and more particularly to an optical system for illumination (lighting system) for a projection type display unit that is excellent in the illumination uniformity, and has a high light utilization efficiency, and the projection type display unit using this optical system for illumination (lighting system).
In recent years, a projector device (projection type display unit) as an image display device of large screen has drawn a good deal of public attention.
A CRT projector device using a high definition and high luminance CRT of small size, a liquid crystal projector device using a liquid crystal panel, and a DMD projector device using a DMD (Digital Micromirror Device) have been manufactured.
Various products not only coping with the AV sources such as movies or TV programs, but also belonging to a category called a data projector for projecting the computer image, have extended rapidly the market. The remarkable improvements of performance including the enhanced brightness or contrast, higher resolution, and more uniform brightness of the projection screen, have been made.
Particularly, a projector device using a light bulb such as the liquid crystal or DMD is superior to a CRT projector device in the respect of capability of enhancing the brightness and resolution independently, and has been more applied to the projection television (rear projection type projector).
The conventional light bulb optical system for illumination (lighting system) typically relies on a Koehler illumination method of one kind in which a light bulb is arranged and illuminated in the optical path of a lens system in a conjugate relation between a light source and an exit pupil of a projection lens.
However, to improve the illumination uniformity in recent years, a fly-eye integrator method or a rod integrator method has been mostly employed, and an image forming performance at higher level and a more intricate constitution have been required for the optical system for illumination (lighting system).
FIG. 17
shows a conventional reflection type projector as disclosed in Japanese Patent No. 2939237.
In the figure, reference numeral
110
denotes alight source for generating and emitting a light; reference numeral
120
denotes a color wheel for selectively transmitting the light emitted from the light source
110
with the wavelength; reference numeral
130
denotes light mixing means (light mixing element) for diverging/converging or irregularly reflecting the light incident from the light source
110
into the uniform light; reference numeral
140
denotes a relay lens unit for converging the incident light into the parallel light; reference numeral
150
denotes a critical angle prism for reflecting the light reflected and incident again from image generating means
160
; and reference numeral
170
denotes a projection lens unit for enlarging and transmitting the incident light to be directed toward a screen.
As a specific example of the light mixing means
130
, a scrambler
135
is arranged in the figure.
Reference numerals
135
a
and
135
b
denote a plane of incidence and a plane of emergence for the scrambler
135
, respectively. At a point to which a light emitted from a lamp
111
of the light source
110
is converged, the plane of incidence
135
a
perpendicular to the optical path is arranged. This plane of incidence
135
a
, the plane of emergence
135
b
perpendicular to the optical path and four lateral faces form a rectangular parallelepiped.
An aspect ratio of the plane of emergence
135
b
results in a rectangle corresponding to that of an FLCD (Ferroelectric Liquid Crystal Display) constituting the image generating means
160
.
A nonuniform light from the light source
110
is mixed into the uniform light by the scrambler
135
, and emitted from the plane of emergence
135
b.
The relay (transmission) lens unit
140
is composed of a convergent lens
141
for diverging this uniform light, and a collimator lens
143
for converging the incident divergent light into the parallel light. This parallel light illuminates the FLCD
163
.
With this conventional constitution, a reflection type projector can be provided in which the critical angle prism
150
is employed to transform a proceeding path of light, without the use of a polarizing beam splitter, and the arrangement of optical axes for the optical system can be easily made without need of a long optical length.
The critical angle prism
150
is not described in detail here, but has a lot of problems with degrading the resolution of a projected image, easily causing an unnecessary ghost light, and increasing the costs owing to significant difficulties in the manufacture, except for an action of separating optically and physically the optical system for illumination and the optical system for projection.
In the case where the critical angle prism
150
is not employed, there is the high possibility of bringing about the problem with physical interference between the optical system for illumination and the optical system for projection.
In the conventional examples, an instance was disclosed in which a DMD was employed as the image generating means, but when the DMD is employed, the interference problem can not be mostly avoided.
The DMD acts to modulate an incident light flux on the basis of the image information by changing the tilt of a micromirror to select a reflecting direction of the incident light.
Hence, the incident angle of rays illuminating the DMD is limited, causing interference between the optical system for illumination and the optical system for projection.
FIG. 18
is a perspective view illustrating the constitution of two pixels of DMD.
In the figure, reference numerals
510
,
511
denote micromirrors, which are tilted by +10 degrees and −10 degrees from the normal of an element
500
, respectively.
For more details of the DMD, see Larry J. Hornbeck, “Digital Light Processing for High-Brightness, High-Resolution Applications.” SPIE Vol.3013, pp.27-40. The DMD will not be described in any detail.
In order to illuminate the DMD, the ray of light must be incident from a direction inclined at a certain angle from the normal of the DMD, as will be apparent from the operation of the micromirror.
The micromirror is tilted at an angle of ±10 degrees, and the rotational axis of the micromirror is directed at 45 degrees toward the square micromirror. Therefore, in the case where a reflected light is directed in a normal direction of the DMD, an illuminating light must be made incident from a direction inclined by 20 degrees from the normal and with an azimuth of 45 degrees.
FIG. 19
is a schematic view illustrating part of an optical system employing the DMD as image generating means, wherein the physical interference between the optical system for illumination and the optical system for projection is described in the case where the critical angle prism is not used.
In the figure, reference numeral
440
denotes a final lens of the optical system for illumination; reference numeral
441
denotes a lens-barrel of the final lens
440
; reference numeral
512
denotes a DMD; reference numeral
70
denotes an optical axis of illumination; reference numeral
71
denotes an optical axis of projection; reference numeral
80
denotes a projection lens; and reference sign &agr; denotes an admission angle of the ray of beam on the DMD
512
, or an angle made between the optical axis of illumination
70
and the normal of the DMD
512
.
The projection lens
80
is placed in the front of the DMD
512
, and is supposed to be a post diaphragm type in the figure.
In the case where the tilt of the micromirror for the DMD
512
is ±10 degrees, the incident angle of the ray of light onto the DMD
512
must be &agr;=20°, leading to the

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