Illumination – With polarizer
Reexamination Certificate
2001-12-19
2003-03-18
O'Shea, Sandra (Department: 2875)
Illumination
With polarizer
C362S359000, C362S551000, C362S583000, C349S062000, C385S048000
Reexamination Certificate
active
06533427
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application claims priority of Taiwan Patent Application No. 90212813, filed on Jul. 27, 2001.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an illuminating device, more particularly to an illuminating device that is adapted to provide a light output with a predetermined polarization state to a projection display, thereby achieving a higher light utilization rate.
2. Description of the Related Art
Light is a kind of electromagnetic wave that, in addition to having the characteristics of direction of travel, frequency, and phase, etc., also has a polarization. Light with a fixed direction of electric field oscillation and a direction of magnetic field oscillation is known as polarized light. Where the polarized light has an electric field direction parallel or perpendicular to an incident light ray, the same is referred to as P-polarized light or S-polarized light. As polarized light occurs only in a plane and can be interpreted by using mathematical models, it provides facility in use. Therefore, in a conventional projection display system, a light polarization state converter is often employed to convert the polarization state of light from one to the other for optimum utilization of light rays.
Referring to
FIGS. 1 and 2
, a conventional illuminating device
1
for a projection display system is shown to include a light source
11
, a light integrator
12
, a polarization state converter
2
and a lens unit
13
. The light source
11
includes a reflector
111
and a light bulb
112
. The reflector
111
is disposed to reflect the light rays emitted from the light bulb
112
toward the light integrator
12
for passage through the polarization state converter
2
and the lens unit
13
for subsequent projection on a display panel
14
. The polarization state converter
2
in the conventional illuminating device
1
includes a reflective seat
21
and a plurality of half-wavelength plates
22
. The reflective seat
21
has a light input side
211
, a light output side
212
, and a plurality of first and second plated films
213
,
214
alternately arranged and interposed between the light input side
211
and the light output side
212
. The light input side
211
faces the light integrator
12
, and is provided with a plurality of light shielding regions
215
that are vertically spaced apart from each other. The light output side
212
faces the display panel
14
. The first and second plated films
213
,
214
are disposed parallel to each other and to incline downwardly from the light input side
211
to the light output side
212
. The half-wavelength plates
22
are disposed on the light output side
212
facing the display panel
14
such that they are vertically spaced apart from each other. The half-wavelength plates
22
correspond in position and length to reflective portions of the first plated films
213
, respectively.
When S-polarized light is employed for displaying images in the conventional projection display system, light of both the P-polarization state and the S-polarization state from the light source
11
radiates toward the light integrator
12
and the polarization state converter
2
. When light of the P-polarization state reaches parts of the light input side
211
that are not shielded by the light shielding regions
215
, it will pass directly through the first plated films
213
and the half-wavelength plates
22
, and is converted into light of the S-polarization state for subsequent projection onto the display panel
14
. However, when light of the S-polarization state reaches the first plated films
213
, it will be reflected by the latter toward the second plated films
214
for further reflection so as to pass through parts of the light output side
212
that are not provided with the half-wavelength plates
22
for projection onto the display panel
14
. Accordingly, when P-polarized light is adopted for the conventional projection display system, the half-wavelength plates
22
will be disposed to correspond in position to reflective portions of the second plated films
214
so as to convert the S-polarized light radiated from the light source
11
. A further discussion thereon is dispensed with herein for the sake of brevity.
In the conventional illuminating device
1
, in order that the light to be projected onto the display panel
14
can have the same polarization state, about one-half of the area of the light input side
211
of the reflective seat
21
has to be provided with the light shielding regions
215
so that the light passing through the light input side
211
can be effectively converted for utilization. Although the construction of the aforesaid device
1
can ensure that the light outputted to the display panel
14
has the same polarization state, about 50% of the light emitted from the light source
11
is wasted. It is therefore evident that although the polarization state converter
2
is capable of providing light of the same polarization state, the light conversion efficiency is low, and the luminosity of the converted light is relatively poor.
SUMMARY OF THE INVENTION
Therefore, the main object of the present invention is to provide an illuminating device that is adapted to provide a light output with a predetermined polarization state to a projection display and that is capable of overcoming the aforesaid drawbacks of the prior art.
Accordingly, an illuminating device of the present invention is adapted to provide a light output to a projection display, and includes a light source, a light guiding pipe, a quarter-wavelength plate, a reflective polarizer, and a reflector. The light source generates output light that converges at a focal point. The light guiding pipe is aligned with the light source along an optical axis, and has a reflective surrounding wall surface that defines a passage. The passage has a light input end proximate to the light source, and a light output end distal from the light source. The focal point is coincident with a plane of the light input end such that the output light from the light source can enter into the passage via the light input end, can be guided by the surrounding wall surface toward the light output end, and can exit from the passage via the light output end. The quarter-wavelength plate and the reflective polarizer are disposed in sequence relative to the passage of the light guiding pipe such that the light that travels in a direction from the light input end to the light output end of the light guiding pipe passes through the quarter-wavelength plate before reaching the reflective polarizer. The reflective polarizer allows light of a first polarization state to pass therethrough, and reflects light of a second polarization state back into the passage of the light guiding pipe via the light output end. The reflector is mounted on the light guiding pipe at the light input end of the passage, and has an outer surface that faces the light source, an inner surface that faces the light output end of the passage, and a through-hole that extends through the outer and inner surfaces of the reflector and that is centered at the focal point to permit entry of the output light from the light source into the passage. The reflector reflects the light that travels in the light guiding pipe in a direction from the light output end to the light input end back to the light output end. The light of the second polarization state that was reflected by the reflective polarizer is converted into the light of the first polarization state when passing through the quarter-wavelength plate for a second time.
REFERENCES:
patent: 6236785 (2001-05-01), Parker et al.
patent: 2001/0048493 (2001-12-01), Swanson et al.
O'Shea Sandra
Prokia Technology Co., Ltd.
Trop Pruner & Hu P.C.
Tsidulko Mark
LandOfFree
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