JP3646847B2 - Image display device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image display device. In particular, the present invention relates to an image display device that performs polarization conversion by spatially modulating light using a hologram optical element.
[0002]
[Prior art]
As a conventional image display device, there is a polarization illumination device described in Japanese Patent Laid-Open No. 8-304739. Hereinafter, a conventional image display apparatus will be described with reference to the drawings and descriptions described in this publication.
FIG. 4 is a schematic configuration diagram of a main part of a conventional polarization illumination device as viewed in plan.
The polarized illuminating device 1 of the present example is generally composed of a light source unit 2, a first lens plate 3, and a second lens plate 4 arranged along the system optical axis L. The light emitted from the light source unit 2 is condensed in the second lens plate 4 by the first lens plate 3, and in the process of passing through the second lens plate 4, the randomly polarized light has a polarization direction. The light is converted into a single type of polarized light and reaches the illumination area 5.
[0003]
The light source unit 2 is generally composed of a light source lamp 201 and a parabolic reflector 202. Random polarized light emitted from the light source lamp 201 is reflected in one direction by the parabolic reflector 202 and is incident on the first lens plate 3 as a substantially parallel light beam. Here, instead of the parabolic reflector 202, an elliptical reflector, a spherical reflector, or the like can be used. The light source optical axis R is inclined with respect to the system optical axis L by a certain angle.
[0004]
FIG. 5 shows the appearance of the first lens plate 3.
As shown in this figure, the first lens plate 3 has a configuration in which a plurality of minute rectangular condenser lenses 301 having a rectangular outline are arranged vertically and horizontally. The light incident on the first lens plate 3 forms the same number of condensing images as the number of the rectangular condenser lenses 301 in a plane perpendicular to the system optical axis L by the condensing action of the rectangular condenser lens 301. Since the plurality of condensed images are nothing but projection images of the light source lamp, they are hereinafter referred to as secondary light source images.
[0005]
Next, referring to FIG. 4 again, the second lens plate 4 of this example will be described.
The second lens plate 4 is a composite laminate including a condenser lens array 410, a polarization separation prism array 420, a λ / 2 phase difference plate 430, and an exit side lens 440. They are arranged in a plane perpendicular to the system optical axis L in the vicinity of the position where the next light source image is formed. The second lens plate 4 has a function as a second lens plate of the integrator optical system, a function as a polarization separation element, and a function as a polarization conversion element.
[0006]
The condensing lens array 410 has substantially the same configuration as the first lens plate 3. That is, a plurality of condensing lenses 411 having the same number as the rectangular condensing lenses 301 constituting the first lens plate 3 are arranged, and has an action of condensing light from the first lens plate 3. The condenser lens array 410 corresponds to the second lens plate of the integrator optical system.
[0007]
The condensing lens 411 constituting the condensing lens array 410 and the rectangular condensing lens 301 constituting the first lens plate 3 do not have to have exactly the same size and shape and lens characteristics. It is desirable to optimize each according to the characteristics of the light from the light source unit 2. However, it is ideal that the light incident on the polarization separation prism array 420 has the principal ray tilted parallel to the system optical axis L. From this point, the condensing lens 411 has the same lens characteristics as the rectangular condensing lens 301 constituting the first lens plate 3 or has a similar shape to the rectangular condensing lens 301. In many cases, they have the same lens characteristics.
[0008]
FIG. 6 shows the appearance of the polarization separation prism array 420.
As shown in this figure, the polarization separation prism array 420 includes a polarization beam splitter 421 made of a prismatic prism composite with a polarization separation film inside, and a prismatic prism composite with a reflection film inside. A pair consisting of the reflecting mirrors 422 is a basic structural unit, and a plurality of pairs are arranged in a plane (arranged in a plane on which a secondary light source image is formed). A pair of basic structural units are regularly arranged so as to correspond to the condenser lens 411 constituting the condenser lens array 410. Further, the lateral width Wp of one polarization beam splitter 421 and the lateral width Wm of one reflection mirror 422 are equal. Further, in this example, the values of Wp and Wm are set so as to be ½ of the lateral width of the condenser lens 411 constituting the condenser lens array 410, but the present invention is not limited to this.
[0009]
Here, the second lens plate 4 including the polarization separation prism array 420 is arranged so that the secondary light source image formed by the first lens plate 3 is positioned at the portion of the polarization beam splitter 421. For this purpose, the light source unit 2 is arranged such that the light source optical axis R forms a slight angle with respect to the system optical axis L.
[0010]
Referring to FIGS. 4 and 6, random polarized light incident on the polarization separation prism array 420 is separated into two types of polarized light of P-polarized light and S-polarized light having different polarization directions by the polarization beam splitter 421. Is done. P-polarized light passes through the polarization beam splitter 421 without changing the traveling direction. On the other hand, the S-polarized light is reflected by the polarization separation film 423 of the polarization beam splitter 421, changes the traveling direction by about 90 degrees, and is reflected by the reflecting surface 424 of the adjacent reflecting mirror 422 (a pair of reflecting mirrors). Is finally output from the polarization separation prism array 420 at an angle substantially parallel to the P-polarized light.
[0011]
A λ / 2 phase difference plate 430 in which λ / 2 phase difference films 431 are regularly arranged is installed on the output surface of the polarization separation prism array 420. That is, the λ / 2 retardation film 431 is disposed only on the exit surface portion of the polarization beam splitter 421 that constitutes the polarization separation prism array 420, and the λ / 2 retardation film 431 is disposed on the exit surface portion of the reflection mirror 422. Not. Accordingly, the P-polarized light emitted from the polarization beam splitter 421 undergoes a rotating action of the polarization plane when passing through the λ / 2 retardation film 431 and is converted into S-polarized light. On the other hand, since the S-polarized light emitted from the reflection mirror 422 does not pass through the λ / 2 retardation film 431, it does not receive any rotation of the polarization plane and passes through the λ / 2 retardation plate 430 as it is. To do.
To summarize the above, random polarized light is converted into one type of polarized light (in this case, S-polarized light) by the polarization separation prism array 420 and the λ / 2 phase difference plate 430.
[0012]
In this way, the light flux aligned with the S-polarized light is guided to the illumination area 5 by the exit side lens 440 and is superimposed and coupled on the illumination area 5. In other words, the image surface cut out by the first lens plate 3 is superimposed on the illumination area 5 by the second lens plate 4. At the same time, randomly polarized light is spatially separated into two types of polarized light having different polarization directions by the polarization separation prism array 420 on the way, and one type of polarized light passes through the λ / 2 phase difference plate 430. It is converted into light and almost all the light reaches the illumination area 5. For this reason, the illumination area 5 is illuminated almost uniformly with almost one type of polarized light.
[0013]
FIG. 7 shows an example of a projection display device in which the polarization illumination device 1 shown in FIG. 4 is incorporated.
As shown in FIG. 7, the polarization illumination device 1 of the projection display device 3400 of this example includes a light source unit 2 that emits randomly polarized light in the position direction, and the randomly polarized light emitted from the light source unit 2. After being guided to a predetermined position of the second lens plate 4 in a state of being condensed by the first lens plate 3, two kinds of polarized light are polarized by the polarization separation prism array 420 in the second lens plate 4. Separated into light. Of the separated polarized light, P-polarized light is converted to S-polarized light by the λ / 2 phase difference plate 430.
[0014]
The luminous flux emitted from the polarized illumination device 100 first transmits red light and reflects blue light and green light in the blue-green reflective dichroic mirror 3401. The red light is reflected by the reflection mirror 3402 and reaches the first liquid crystal light valve 3403. On the other hand, of the blue light and the green light, the green light is reflected by the green reflecting dichroic mirror 3404 and reaches the second liquid crystal light valve 3405.
[0015]
Here, since the blue light has the longest optical path length among the respective color lights, the light guide composed of a relay lens system including the incident side lens 3406, the relay lens 3408, and the emission side lens 3410 with respect to the blue light. Means 3450 are provided. That is, after the blue light passes through the green reflecting dichroic mirror 3404, it first passes through the incident side lens 3406 and the reflecting mirror 3407, is guided to the relay lens 3408, is focused on the relay lens 3408, and then is reflected by the reflecting mirror 3409. The light is guided to the exit side lens 3410 and then reaches the third liquid crystal light valve 3411. Here, the first to third liquid crystal bulbs 3403, 3405, and 3411 modulate the respective color lights and include the video information corresponding to each color, and then the modulated color lights are supplied to the dichroic prism 3413 (color synthesis means). Incident. In the dichroic prism 3413, a red reflective dielectric multilayer film and a blue reflective dielectric multilayer film are formed in a cross shape, and the respective modulated light beams are combined. The combined light beam passes through the projection lens 3414 (projection unit) and forms an image on the screen 3415.
The above is the conventional apparatus disclosed in JP-A-8-304739.
[0016]
[Problems to be solved by the invention]
Since the conventional polarization illumination device is configured as described above, it is necessary to tilt the light beam with respect to the optical axis. Further, when performing polarization conversion, a microlens array is required, and there is a drawback that the structure becomes complicated.
[0017]
The present invention has been made to solve the above problems, and it is not necessary to incline the light beam from the light source with respect to the optical axis, and to obtain an image display device that does not require a microlens array. Objective.
[0018]
[Means for Solving the Problems]
The image display apparatus according to the present invention has the following elements.
(A) a light source that outputs light;
(B) A hologram optical element that inputs light from the light source and changes the traveling direction of the light,
(C) a polarization conversion optical system that inputs light output from the hologram optical element and performs polarization conversion;
(D) An image display optical system that displays an image using the light output from the polarization conversion optical system.
[0019]
The hologram optical element is a computer generated hologram that receives light of wavelength λ, modulates light of wavelength λ with frequency f _i , changes the traveling direction of the input light to directions of λf _i and −λf _i , and outputs it. It is characterized by being.
[0020]
The polarization conversion optical system is
A condenser lens that inputs and collects light from the hologram optical element;
A polarization beam splitter array that is arranged at a position where light from the condenser lens is collected and separates linearly polarized light of either P wave or S wave;
A reflection mirror array that reflects one linearly polarized light of the P wave and the S wave separated by the polarization beam splitter array;
And a λ / 2 plate array for converting the light reflected by the reflecting mirror array into the other linearly polarized light.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Embodiment 1 FIG.
FIG. 1 is a principle diagram of the present invention.
The image display apparatus according to the present invention includes a light source 40, a hologram optical element 50, a polarization conversion optical system 60, and an image display optical system 70. The polarization conversion optical system 60 includes a condensing lens 61, a polarization beam splitter array 62, a reflection mirror array 63, and a λ / 2 plate array 64. The image display optical system 70 includes an exit lens 71 and a liquid crystal panel 72. Since the configuration of the polarization conversion optical system 60 is the same as that shown in the conventional example, a detailed description is not given here.
[0022]
Next, the hologram optical element 50 will be described.
FIG. 2 is a diagram for explaining the principle of the hologram.
The hologram is originally a dry plate on which interference fringes (amplitude and phase) of two lights are recorded. Here, a computer generated hologram (computer generated hologram) on which a calculated digital pattern is recorded will be considered. When a laser beam having a wavelength λ is incident on a phase plate modulated at a frequency f _i , the laser beam is divided in directions of angles λf _i and −λf _i . A computer generated hologram is a kind of diffractive optical element, which can be considered as a phase plate that gives a periodic optical path difference to the wavefront of incident laser light and applies spatial modulation in the direction in which the light is desired to propagate. If modulation is performed simultaneously with a large number of frequencies f1, f2, f3,... According to the principle of superposition, it is possible to divide in the direction of each frequency. Here, if the hologram optical element 50, the condensing lens 61 (focal length is F), and the polarization beam splitter array 62 are arranged in the arrangement as shown in FIG. 3, Fλf from the optical axis on the polarization beam splitter array 62. _The focal point can be shifted to positions _i and −Fλf _i apart.
[0023]
In the design of a holographic optical element (HOE), the Fourier transform spectrum of the HOE pattern is designed by a computer so that it has a sharp peak at a frequency corresponding to a position where an image is to be placed. For example, as a HOE, a surface relief type transmission phase hologram (kinoform) that directly etches synthetic quartz to give a multi-stage phase difference is employed. The HOE pattern is composed of 256 × 256 to 1024 × 1024 pixels with a pixel size of 1 to 2 μm as a unit.
In the actual calculation, an error function (evaluation function) that first gives a random phase to each pixel and can determine that the Fourier transform spectrum is approaching the target value when it has a high peak at the required frequency. And the convergence calculation is performed so as to minimize the error function by sequentially changing the phase of each pixel.
[0024]
Next, a multi-zone homogenizer possessed by the hologram will be described.
The characteristics of the homogenizer using a hologram are that a conventional general prism or kaleidoscope type homogenizer forms a uniform irradiation area in one place, whereas it is necessary for several necessary zones (zones). It is possible to irradiate a homogenized beam at the same time. The irradiation area can be adjusted to the arrangement of the polarization beam splitter array 62 and can have an arbitrary shape. For example, as can be seen in the example shown in FIG. 1, when there are openings (positions of polarization beam splitters) through which light is transmitted in nine regions, beam spots can be divided into nine regions. it can. By doing so, it is possible to improve the light transmittance at the opening compared to irradiating the entire region. The irradiation method that makes the most of this feature is to perform beam irradiation in accordance with the pattern of openings as shown in FIG. Moreover, there is a possibility that the intensity distribution of the focused spot may vary if only one divided beam is irradiated to one opening. Therefore, several beams are superimposed on each opening to homogenize the intensity distribution. Can be achieved.
In this way, a technique for irradiating a beam having a uniform intensity distribution and a uniform intensity distribution in a large number of regions simultaneously is called a multi-zone homogenizer.
[0025]
The light beam emitted from the light source 40 is preferably a parallel light beam. Since the hologram optical element 50 converts the traveling direction to a predetermined angle with respect to the traveling direction of the incident light, the higher the parallelism of the light beam incident from the light source 40, the more desirable.
[0026]
As described above, in this embodiment, the parallel optical beam from the light source 40 is spatially modulated using the hologram optical element 50 designed by a computer based on the principle of the hologram, that is, the traveling direction of the light is changed. In other words, the light is guided to the polarization beam splitter array 62 prepared as the polarization conversion optical system 60. The light converted into linearly polarized light by the polarization conversion optical system 60 is irradiated from the exit lens 71 to the liquid crystal panel 72. When irradiating the liquid crystal panel 72 from the exit lens 71, the exit light from the exit lens 71 is superimposed on the liquid crystal panel 72, so that the luminance distribution can be made flat and uniform. An image emitted from the liquid crystal panel 72 is output by a conventionally known configuration.
The polarization conversion optical system is not limited to that shown in FIG. 1, and other configurations may be used.
[0027]
【The invention's effect】
As described above, according to the present invention, by adopting a hologram, a conventionally required microlens array can be eliminated, and the optical system can be simplified.
[0028]
Further, according to the present invention, it is not necessary to incline the optical axis of the light beam as in the prior art, so that the arrangement and adjustment of the optical system can be simplified.
[0029]
Further, according to the present invention, the luminance distribution can be made uniform by using the hologram.
[Brief description of the drawings]
FIG. 1 is a principle diagram of the present invention.
FIG. 2 is a diagram showing the principle of a hologram of the present invention.
FIG. 3 is a diagram showing the principle of a hologram projection system according to the present invention.
FIG. 4 is a diagram showing a conventional polarized illumination apparatus.
FIG. 5 is a diagram showing a conventional microlens array.
FIG. 6 is a diagram showing a conventional polarization conversion optical system.
FIG. 7 is a diagram showing a conventional projection display device.
[Explanation of symbols]
40 light source, 50 hologram optical element, 60 polarization conversion optical system, 61 condensing lens, 62 polarization beam splitter array, 63 reflection mirror array, 64λ / 2 plate array, 70 image display optical system, 71 exit lens, 72 liquid crystal panel.

Claims (3)

An image display device having the following elements: (a) a light source that outputs light;
(B) A hologram optical element that inputs light from the light source and changes the traveling direction of the light,
(C) a polarization conversion optical system that inputs light output from the hologram optical element and performs polarization conversion;
(D) An image display optical system that displays an image using the light output from the polarization conversion optical system. The hologram optical element is a computer generated hologram that receives light of wavelength λ, modulates light of wavelength λ with frequency f _i , changes the traveling direction of the input light to directions of λf _i and −λf _i , and outputs it. The image display apparatus according to claim 1, wherein the image display apparatus is provided. The polarization conversion optical system is
A condenser lens that inputs and collects light from the hologram optical element;
A polarization beam splitter array that is arranged at a position where light from the condenser lens is collected and separates linearly polarized light of either P wave or S wave;
A reflection mirror array that reflects one linearly polarized light of the P wave and the S wave separated by the polarization beam splitter array;
3. The image display device according to claim 2, further comprising a λ / 2 plate array for converting light reflected by the reflection mirror array into the other linearly polarized light.

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