JP2003098598A - Illumination system for projector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an illumination system for a projector system which can enhance the availability of light and screen quality. SOLUTION: The illumination system comprises, a light source for emitting white light, a 1st lens array constituted of several lenses for splitting/condensing the light emitted from the light source, a 2nd lens array arranged near the focal point of the 1st lens array and constituted of lenses corresponding to each lens of the 1st lens array, and a polarized light conversion element for converting the light emitted from the white light source in a single polarization direction, and the incident and exit surfaces of each polarized light conversion element corresponding to each lens of the 2nd lens array are provided with specified curvature, and then, almost the whole light made incident on the polarized light conversion element at an incident angle different according to an incident wavelength is made nearly parallel to a main optical axis.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical system in a projection optical system projector, and more particularly to a design of a polarization conversion element that can be suitably used in a liquid crystal projector.

[0002]

2. Description of the Related Art Conventionally, in a liquid crystal projector for enlarging and projecting an image displayed on a liquid crystal display element, an illumination optical system for uniformly illuminating light from a white light source on a liquid crystal image display element by a lens array is used. A polarization conversion element that aligns the polarization direction of the illumination light according to the polarization characteristics of the liquid crystal display element is used for this illumination optical system, as proposed in Japanese Patent Laid-Open No. 8-304739.

In Japanese Unexamined Patent Publication No. 8-304739, a polarized illumination device having a high light utilization efficiency that is a combination of an integrator optical system and a polarization conversion optical system is constructed in a small size and compactly. Therefore, the polarized illumination device has random polarization directions. A first light source unit that emits light and a plurality of rectangular condenser lenses having a rectangular outer shape, collects light emitted from the light source, and forms a plurality of secondary light source images. The lens plate and the position where the plurality of secondary light source images are formed are placed in the vicinity of the lens plate, a condenser lens array, a polarization separation prism array, and λ.
It has a / 2 phase difference plate and a second lens plate having an exit side lens. The polarized light is separated at the stage when a minute secondary light source image is generated by the first lens plate that constitutes the integrator optical system. Therefore, it is possible to suppress the spatial expansion of the optical path due to the separation of the polarized light, so that it is possible to achieve the downsizing of the polarized illumination device, despite the provision of the polarization conversion optical system.

FIG. 5 shows the above-mentioned illumination optical system as a conventional example. When the two lens arrays 401 and 402 and the polarization conversion element 403 are combined, the polarized light can be separated in the vicinity of the second lens array 402.
It is separated into a P-polarized light component and an S-polarized light component at the light collecting position of 1.

Further, in Japanese Unexamined Patent Publication No. 10-333097, a light source device which emits a light beam having a uniform polarization direction,
In a projection device including a transmissive liquid crystal panel as an image display element arranged at a position where the light flux from the light source device is incident, and a projection lens that projects the light flux transmitted through the liquid crystal panel onto a screen, The device is
A light source with a random polarization state, a concave mirror that collects the light from the light source, a polarization conversion element that aligns the polarization direction of the light flux incident from the light source, and an intensity distribution of the light flux that is emitted from the polarization conversion element and has the same polarization direction. A uniformizing integrator is provided to prevent color unevenness that occurs in a projected image.

Further, in Japanese Patent Application Laid-Open No. 11-295658, a first multi-lens array having a lens eccentric only in one axial direction of a coordinate axis, and each of the lenses of the first multi-lens array is provided with the one axis. The second multi-lens array including the lenses capable of collecting the light refracted in the direction,
Incident angle correction is performed on the optical thin film that performs synthesis and polarization separation.

[0007]

By the way, the competition for screen brightness, which can be said as an eternal theme of liquid crystal projectors, is becoming more intense year by year. As one means for increasing the screen brightness, it is necessary to make an illumination optical system having a larger incident angle with respect to the panel irradiation area, that is, a smaller F number. Therefore, it is necessary to collect light having a larger incident angle on the polarization conversion element. However, on the separation surface of the polarization conversion element, the distribution of the spectral transmittance and the reflectance generally changes depending on the incident angle. Therefore, when the incident angle becomes large, the light emitted from the polarization conversion element changes, and the image of the panel or the like changes. There is a problem in that the display element is irradiated to cause color unevenness on the screen.

Further, as shown in FIG. 6, although the outgoing angle of the light reflected by the separation surface 503 of the polarization conversion element 502 in the conventional example does not change, the longer the optical path, the wider the light spreads, and the next. It caused a loss of light on the matching polarization splitting surface.

3 and 4, the distribution of the spectral reflectance and the spectral transmittance of the polarization splitting surface designed to split the light incident at an incident angle of 45 ° into two linearly polarized light components whose polarization directions are orthogonal to each other. Indicates. From the figure, for the S-polarized component, when the incident angle changes from 45 °, the reflectance increases and decreases on the long wavelength side, and P
It can be seen that the transmittance of the polarized component decreases on the short wavelength side and the intermediate wavelength.

Further, as an example of correcting the incident angle characteristic to the polarization conversion element as described above, Japanese Patent Application Laid-Open No. 10-33309.
7, JP-A-11-295658 and the like, which have been proposed from a viewpoint different from the present invention.

[0011]

In order to solve the above-mentioned problems, the illumination optical system of the projector according to the present invention comprises:
A first lens array including a light source that emits white light, a plurality of lenses for dividing and condensing light from the light source, a first lens array that is disposed near a focal point of the first lens array, and a first lens Each lens of the second lens array includes a second lens array including lenses corresponding to each lens of the array and a polarization conversion element that converts light from the white light source into a single polarization direction. The incident surface and the exit surface of each polarization conversion element corresponding to are parallel to the principal ray axis, and almost all the light incident on the polarization conversion element at different incident angles depending on the incident wavelength is It is characterized by

More preferably, the incident surface and the exit surface of the polarization conversion element have substantially the same specific curvature, and the directions of curvature of the incident surface and the exit surface of the polarization conversion element are the same or opposite. Characterize things.

[0013]

DETAILED DESCRIPTION OF THE INVENTION An embodiment of the present invention will be described with reference to FIGS. 2 is a layout view of a projector optical system in which the present invention is preferably used. FIG. 1 is a layout view of the optical system of FIG.
Of the second lens array 1 after passing through the lens array 102 of
FIG. 3 is an enlarged view of the polarization conversion element 104 that is focused near 03 and is disposed near the focusing position. The light from the white light source 101 is supplied to the second lens array 1 by each of the lenses of the first lens array 102 in order to make the light on the screen uniform.
Although the light is condensed in the vicinity of 03, it is important in the present invention that the incident surface and the emission surface of the polarization conversion element 104 in the vicinity of the condensed light have a specific curvature.

Using FIG. 1, 3 passing through one lens cell
This will be explained in detail with reference to the movements of the two light rays. The three rays A, B (principal rays) and C shown in FIG. 1 are refracted by the curvature 105 so that the incident angles of the rays A and C are almost parallel to the principal ray B. The polarization conversion element has a specific curvature surface that is incident on the polarization separation surface 106 inside the polarization conversion element at about 45 °. The polarization splitting surface 106 splits the light into P-polarized light and S-polarized light for the purpose of improving the light utilization efficiency. The curvature r that makes the rays parallel is shown by the following approximate expression. The ray angle (angle between A and B) incident on the polarization conversion element is θ, the distance height between A and B is h,
When the refractive index of the polarization conversion element is n, the following equation holds.

R = -h * (n-1) / θ By designing in this way, it is possible to eliminate (cancel) the difference in the incident angle depending on the incident position of the light beam on the lens array, so that the image is finally obtained. It is possible to eliminate or reduce the change in the spectral characteristics due to the light rays having different incident angles, which causes the color unevenness on the projected screen. From Figure 3, 45 degrees compared to 40 degrees and 50 degrees
It can be seen that in a red color with a spectral characteristic of 600 nm or more, a decrease in reflectance or a sharp drop is suppressed, and color unevenness due to the brightness of red can be reduced.

Furthermore, since high transmittance and reflectance characteristics at the polarization splitting surface can be maintained, it is possible to improve the light utilization efficiency. This can be read from FIG. 4 because the reflectance is not lowered in the entire visible light range of 400 to 700 nm where the spectral characteristics at 45 degrees are higher than those at 40 degrees and 50 degrees. Further, since the incident angle of each light beam can be set to about 45 °, the spread of the light beam in the polarization conversion element is eliminated, interference loss at the adjacent polarization separation surface is reduced, and further, in the polarization separation surface. It is possible to suppress the influence of uneven brightness on the display. In other words, since the spread of light rays can be suppressed as described above, it is possible to make it less susceptible to uneven coating on the polarization splitting surface.

Next, the light rays reflected by the polarization splitting surface 106 are returned to the light ray angle of the incident state by the curvature 107 of the exit surface of the polarization conversion element and are emitted. Further, the light ray transmitted through the polarization splitting surface 106 is returned to the light ray angle of the incident state by the curvature 107 of the exit surface of the polarization conversion element, and is emitted.
At this time, by making the curvatures 105 and 107 of the entrance surface and the exit surface approximately the same, the outgoing light beam maintains the angle of the incoming light beam, and then the first and second condenser lenses 109,
Due to the lens action of 110, light rays as designed can reach the liquid crystal panel 112.

In the case of FIG. 1, the curvatures of the entrance and exit surfaces are 10
Reference numerals 5 and 107 are concave lenses having a negative curvature and have the same curvature direction. However, when another ray design is performed, an optical design in which the convex lens having a positive curvature enters and the concave lens emits light has the opposite curvature direction. However, it goes without saying that the present invention is applicable.

The light reflected by the polarization splitting surface 106 is the wave plate 1
08, the light transmitted through the polarization splitting surface is rotationally combined in the same polarization direction, and the first and second condenser lenses 10
By using 9, 110, the color separation means 111, the liquid crystal panel 112, and the projection lens 113, a bright image with no color unevenness can be obtained on the screen 114.

[0020]

As described above, according to the present invention,
Since the input / output surface of the polarization conversion element has a curvature, it is possible to suppress the loss of light use efficiency and color unevenness on the screen, and as a result, it is possible to improve the brightness and quality at the time of screen projection.

[Brief description of drawings]

FIG. 1 is an optical design diagram of a polarization conversion element according to the present invention.

FIG. 2 is a schematic diagram of a polarization conversion optical system of the projection type projector of the present invention.

FIG. 3 is a distribution diagram of the spectral reflectance of the polarization splitting surface in the vicinity of an incident angle of 45 °.

FIG. 4 is a distribution diagram of a spectral transmittance of a polarization splitting surface in the vicinity of an incident angle of 45 °.

FIG. 5 is a configuration diagram of a conventional illumination optical system.

6 is a schematic diagram of polarization conversion performed in the polarization conversion element shown in FIG.

[Explanation of symbols]

101 white light source 102 first lens array 103 Second lens array 104 Polarization conversion element 105 Incident curvature surface of polarization conversion element 106 polarized light separation plane 107 exit curvature surface of polarization conversion element 108 Wave plate 109 First condenser lens 110 Second condenser lens 111 color separation means 112 LCD panel 113 Projection lens 114 screen 401 First lens array 402 Second lens array 403 Polarization conversion element 404 First condenser lens 501 Second lens array 502 Polarization conversion element 503 Polarization separation plane 504 Wave plate

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G02F 1/1335 G02F 1/1335 510 510 1/13357 1/13357 G03B 21/00 G03B 21/00 E H04N 5 / 74 H04N 5/74 A F-term (reference) 2H049 BA05 BA07 BB62 BC22 2H088 EA14 EA15 HA13 HA17 HA20 HA25 HA28 MA06 2H091 FA05X FA05Z FA10Z FA11Z FA29Z FA41Z FD06 LA30 MA07 2H099 AA12 BA09 CA02 CA08 DA05 5C058 AA06 AB03 AB06 BA05 BA23 EA02 EA11 EA26 EA51

Claims (3)

[Claims] 1. A first lens array composed of a light source that emits white light, a plurality of lenses for dividing and condensing light from the light source, and a first lens array that is disposed near a focal point of the first lens array. , A second lens array composed of lenses corresponding to the respective lenses of the first lens array, and a polarization conversion element for converting light from the white light source into a single polarization direction are arranged. Each polarization conversion element corresponding to each lens of the lens array has an entrance surface and an exit surface with a specific curvature, and almost all the light incident on the polarization conversion element at an incident angle different depending on the incident wavelength is converted into a chief ray. An illumination optical system for a projector, which is substantially parallel to the axis. 2. The illumination optical system for a projector according to claim 1, wherein the incident surface and the exit surface of the polarization conversion element have substantially the same specific curvature. 3. The illumination optical system for a projector according to claim 1, wherein the incident surface and the exit surface of the polarization conversion element have the same or opposite curvature directions.