JPH1031111A - Polarizing splitter and projection display device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarizing splitter and a projection type display device which are inexpensive, improve polarizing splitting characteristics, get light and eliminate image nonuniformity. SOLUTION: Plural polarizing film boards forming optical thin films 2 on both the sides of a glass board 1, frames 3 for mounting these polarizing film boards and plural zigzag-shaped polarizing splitters arranged in the zigzag form while providing an air gap to the frames 3 so as to provide almost the angle of polarization to P polarized light made incident along an incident optical axis for these respective polarizing film boards are arranged while facing mutually. Then, any one of these plural zigzag-shaped polarizing splitters is arranged at least so that the positions of mountain parts and valley parts in their respective zigzag forms can be made different respect to the incident optical axis.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarization separation device that emits light that is close to linearly polarized light when random polarized light such as natural light enters.

[0002]

2. Description of the Related Art Conventionally, as an example of a device in which randomly polarized light is incident and polarized light close to linearly polarized light is output, Japanese Patent Application Laid-Open No. HEI-5-205 is disclosed.
An apparatus disclosed in JP-A-157915 is known. In this apparatus, a single layer of, for example, a titanium oxide (TiO ₂ ) thin film having a high refractive index is formed on both surfaces of a glass substrate, and incident light is simulated by a pseudo-Brewster angle. P-polarized light transmitted and reflected at an incident angle near the Brewster angle) and reflected S
This device separates polarized light. Although it is not as good as a polarization separation device using a glass prism in terms of characteristics, it is relatively easy to form a film on a plate substrate by vacuum evaporation, etc., so preliminary polarization separation of the projection device of the polarization optical system Used as a device. Furthermore, since the Brewster angle is around 70 degrees, a single polarization separation device is bent into a zigzag shape as a device that improves the point that a considerable space is required when the plate-shaped device is arranged at this incident angle, and this is further bent. There is known an example in which a plurality of sheets are stacked to improve the polarization separation efficiency. FIG. 8 shows the configuration of this device. This device is composed of two polarizing devices arranged in a zigzag manner in parallel.

A single layer film is formed on both surfaces of a glass plate substrate arranged in a zigzag shape.

[0004]

However, in the configuration of the conventional two-layered zigzag polarization separation device,
Since the peaks and valleys of the zigzag shape coincide with each other and overlap each other, the device is compact, but there is a problem that the contrast is reduced and image unevenness occurs. Further, as described above, the polarization separation device in which the surface of the plate substrate is coated with the film having a high refractive index is not satisfactory because the polarization separation characteristics are not good as compared with the polarization separation device of the prism.

An object of the present invention is to provide a polarization separation device and a projection display device which are inexpensive, have excellent polarization separation characteristics, are bright, and have no image unevenness.

[0006]

In order to solve the above-mentioned demands and problems, a polarizing beam splitter according to the present invention comprises a plurality of polarizing film substrates having optical thin films formed on both surfaces of a glass substrate, and the polarizing film substrate. And a pair of the polarizing film substrates arranged in a zigzag manner and provided with an air gap so that each of the polarizing film substrates has a substantially Brewster angle with respect to a light ray incident along an incident optical axis. Are arranged, and at least one set of the plurality of zigzag polarization separation devices is arranged such that the positions of the peaks and valleys of the respective zigzag shapes are different from each other with respect to the incident optical axis. It is characterized by the following.

According to a second aspect of the present invention, in addition to the first aspect, it is preferable that the polarizing film substrate has a multilayer film composed of two or more layers of a high refractive index material and a low refractive index material. Features. The polarized light separating device according to the present invention is a light source, a polarized light separating device for extracting a linearly polarized light component from light emitted from the light source, and a polarized light for separating the linearly polarized light component from the polarized light separating device into RGB three-color lights. 2. A polarization separation device comprising: a separation unit; a light valve that modulates each of the RGB light beams emitted from the polarization separation unit; and a projection lens that projects light emitted from the light valve onto a screen. 3. The projection display device according to any one of 2.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the polarizing device according to the present invention will be described. FIG. 1 shows the basic configuration of the polarization beam splitter of the present invention. A set of zigzag polarization splitters is formed by arranging a plurality of polarizing film substrates having polarizing films formed on both surfaces of a glass substrate so as to have a substantially Brewster angle with respect to the incident optical axis. The arrangement is such that the separation devices are displaced from each other by a displacement amount Δ with respect to the incident optical axis.

A set of these zigzag polarized light separating devices is arranged in parallel with the incident optical axis, and at this time, the positions of the peaks and valleys of the front and rear polarized light separating devices are not aligned. At the peaks and valleys in the zigzag shape, the polarization splitting device is not continuous, and the ends of the glass pieces are exposed according to the inclination at the corresponding portions. Further, no thin film for polarization separation is formed in this portion, and uneven polarization separation is formed. Furthermore, there is no guarantee that the end of the plate member can come into contact with an adjacent plate member, and a space is formed due to a mounting error.
In the conventional example shown in FIG. 8, since the space portion overlaps the front and rear stages, a portion that is not polarization-separated is formed, and when used in a projection display device or the like, unevenness of the projected image occurs. Will be. In the embodiment of the present invention, in order to minimize the influence of this defect, the positions of the zigzag-shaped peaks or valleys at the front stage and the peaks or valleys at the rear stage are shifted from each other. This relative shift amount Δ is effective for image unevenness even if slightly shifted, and is at most within 1/2 pitch. The larger the amount of displacement, the thicker the polarizing device becomes in the thickness direction, so that the size of the device becomes large, which is disadvantageous for compactness. Since the part that is not polarization-separated in the zigzag-shaped valley or crest of the former stage is always incident on the part of the film formation that is polarization-separated in the latter stage,
At least once, the polarized light is separated and emitted from the polarized light separating apparatus of this embodiment. FIG. 2 shows a configuration in which a frame on which a plurality of polarization substrates are mounted and two zigzag polarization separation devices are arranged to face the frame. In the embodiment of the present invention, two zigzag polarizers are arranged. However, the number of polarizers is not limited to two. 3
It goes without saying that more than two zigzag polarizing devices may be used.

Next, the structure of the polarizing film of the polarizing device substrate will be described with reference to FIG. The structure of the polarizing substrate of the present invention is such that a multilayer film 3 composed of a high-refractive-index film nH and a low-refractive-index film nL is formed on at least one surface of the glass substrate 1 so that the Brewster angle is substantially equal to the incident light. It was arranged.
Details will be described later in Examples 1 to 3. In addition, the polarization separation characteristics of the polarizing film are obtained by forming several multilayer films on a glass substrate, measuring the spectral transmittance characteristics in a wavelength region of 400 nm to 650 nm, and determining the ratio of the P-polarized light transmittance to the S-polarized light transmittance ( Hereinafter, it will be referred to as an extinction ratio).

FIG. 6 shows the polarization separation characteristics of each embodiment.
Was. The vertical axis indicates the polarization separation ratio (P-polarized light / S-polarized light), and the horizontal axis indicates the wavelength.
400 to 700 nm was indicated. The figure shows a comparative example.
Also shows the polarization separation characteristics of the conventional polarization separation film configuration.
Was. The polarization separation film has a substrate thickness of 1 mm and a refractive index of 1.
One side of a 52 glass substrate 101 is made of TiO having a refractive index of 2.3.
_TwoA film thickness of 597 angstroms was formed. Also,
Polarization separation characteristics are ± 5 degrees around 77.2 degrees with respect to the optical axis
In the wavelength range of 40 to 70 nm at an incident angle of
It is obtained from the spectral transmittance measurement results. A few percent
Although the transmittance of S-polarized light is slightly reduced, polarization separation
It can be seen that the characteristics increase.

FIG. 7 shows a projection type display device using the polarization beam splitter of the present invention. Hereinafter, Embodiments 1 to 4 will be specifically described.

[0013]

FIG. 3 shows a first embodiment of the present invention. On one side of a glass substrate 1 having a refractive index of 1.52 and a thickness of 1 mm, MgF ₂ of a low refractive index layer nL (refractive index: 1.37) is provided on the first layer from the substrate side.
A TiO ₂ film having a high refractive index layer nH (refractive index: 2.3) was formed as a _second layer having a thickness of 597 Å, and the incident angle was set to 7
It is arranged to be inclined at 2.7 degrees. FIG. 5 shows ± 5 degrees of 67.5 degrees and 7 degrees centered on the incident angle of 77.2 degrees.
The spectral transmittance characteristics at 7.2 degrees are shown. The polarization separation characteristics are shown in FIG.

As compared with the conventional example, the transmittance of S-polarized light is reduced by about 10%, the transmittance of P-polarized light is slightly increased, and the polarization separation performance is improved.

[0015]

Second Embodiment Although not shown, a second embodiment of the present invention will be described. This is an example in which a two-layer multilayer film configuration is used as in the first embodiment, but the film type is different. The first on one side of the glass substrate 1
A low-refractive-index layer nL (refractive index: 1.47) is formed as an SiO ₂ film having a thickness of 1200 Å, and a _second layer is further formed thereon.
As a layer, a TiO ₂ film of a high refractive index layer nH (refractive index: 2.3) was formed to a thickness of 597 Å. 72.
It is arranged to be inclined twice. The polarization separation characteristics are shown in FIG.

It can be understood that the transmittance of S-polarized light is slightly reduced by several percent as compared with the conventional example, and the transmittance of P-polarized light is slightly increased, and the polarization separation performance is improved.

[0017]

Third Embodiment FIG. 4 shows a third embodiment of the present invention. Example 1
A high refractive index layer nH (refractive index: 2...) Is formed on the first layer from the substrate side on one side of a glass substrate 1 having a refractive index of 1.52 and a thickness of 1 mm similar to that of the above.
3) The TiO ₂ film is 270 angstroms thick, the second
The layer has a low refractive index layer nL (refractive index: 1.37) of MgF ₂ film having a thickness of 200 Å, the third layer has a high refractive index layer nH of a TiO ₂ film having a thickness of 825 Å, and the fourth layer has a low refractive index. The MgF ₂ film of the layer nL is formed to a thickness of 1380 Å, the TiO ₂ film of the high refractive index layer nH is formed to a thickness of 600 Å in the fifth layer, and the polarizing beam splitter is arranged to be inclined at 72.2 degrees with respect to the optical axis. is there. FIG. 6 shows the polarization separation characteristics of this polarizing device. The extinction ratio is improved several times as compared with the conventional one. Although the transmittance of P-polarized light is slightly reduced, the transmittance of S-polarized light is reduced by nearly 20% as compared with the conventional example, and as a result, the polarization separation characteristics are improved.

As described above, according to the embodiment of the present invention,
A polarization separation characteristic several times better than that of the conventional example could be obtained. Thus, the examples shown in Examples 1 to 3 were examples in which two or more thin films were formed on at least one surface of one glass substrate. It has been found that these have remarkably excellent polarization separation ratios as compared with conventional polarizing devices having the same shape.
However, the arrangement of one polarizing film substrate is
A large space is required if the device is arranged at a large inclination of approximately 70 degrees so as to have a substantially Brewster angle. Forming a structure of polarized light separation device drawbacks with improved, as previously described in Figure 1 of the embodiment of the present invention, MgF ₂ film on both sides of the glass substrate from the substrate side, a TiO ₂ film thereon The polarizing device having the above configuration was cut in the length direction, and each member was arranged in a zigzag shape so that each member had a Brewster angle with respect to the optical axis. In addition, two zigzag polarization splitters are arranged in parallel, and the valleys and peaks of the two zigzag polarization splitters do not overlap. With this configuration, unevenness of an image projected on the screen is reduced, and a bright and compact polarizing device can be realized.

An embodiment in which the polarizing device of the present invention is used in a projection display device will be described below.

[0020]

Embodiment 4 FIG. 7 shows a fourth embodiment. This embodiment is a projection type display device using a polarization beam splitting device according to an embodiment of the present invention based on the polarizing film configurations of Embodiments 1 to 3. The white light emitted from the light source 71 is mostly reflected and discarded by the polarization splitting device 72 shown in the embodiment of the present invention through an ultraviolet and infrared cut filter (not shown), and only the P polarized light is transmitted and the three colors are transmitted. The light enters the separation optical system. First, only the B light is reflected by the B light reflecting dichroic mirror 73B, and is incident on a polarizing beam splitter (PBS) 74B. The R light transmitted through the dichroic mirror is reflected by the R light dichroic mirror 7.
At 3, only the R light is reflected and enters the PBS 74R.

Most of the P-polarized light (first polarized light) is transmitted by the polarization separating device 72 due to the polarization separation effect shown in the above embodiment, and the transmitted S-polarized light (second polarized light) is a few percent. In the projection device of this structure, the PBS 74
In B, 73R, and 74G, the first polarized light is the polarized light reflected by the polarization separating unit, and the second polarized light corresponds to the polarized light transmitted by the polarized light separating unit. Since most of the second polarized light is incident on each PBS in a form removed by the preceding polarizer, the second polarized light component in the light separated and reflected by the polarization splitting characteristics of each PBS is very small. , The excellent first polarized light is a light valve 75B, 75R,
The light is incident on 75G as readout light. Light valve 7
5B, a light valve 75R, and a light valve 75G are reflection-type light valves.
It has a function of reflecting and emitting polarized light as second modulated light that is projection light. The light emitted from each light valve is
Only the second modulated light that has entered and modulated S74B, 74R, and 74G passes through the polarization splitting unit, and is projected onto the screen by the projection lenses 76B, 76R, and 76G installed for each color.

As described above, the polarization separation device 72 is provided for each PBS.
This has the effect of increasing the degree of polarization of light incident on the light valve in advance, so that the degree of polarization of light that is polarized and separated by each PBS and incident on the light valve increases. As a result, it is possible to obtain a projection image with good image unevenness and contrast.
If the degree of polarization of the light incident on each light valve is poor, even if the light valve is ideally in a black state, it will not be possible to form a projected image in a black state, causing a decrease in contrast or image unevenness. Become.

Although the present embodiment has shown an example in which a reflection type light valve is used, it is needless to say that the present invention can be applied to a projection type using a transmission type light valve, that is, a transmission type liquid crystal panel. That is, three transmission panels are arranged for each of the R, G, and B colors, and are devices that project the modulated transmission light from these panels with the projection lens. At this time, the modulated transmitted light of each color transmitted through each panel is subjected to color synthesis by a color synthesis optical system including a dichroic prism and the like, and is projected on a screen by a single projection lens. The liquid crystal panel for each color is sandwiched on both sides by a polarizing plate forming a cross Nicol to constitute a light valve. Also in the case of the projection type display device of the present invention, the polarization separation device of the above-described embodiment of the invention is disposed immediately before the three-color separation optical system. The direction of the arrangement is a direction in which the polarized light transmitted by the polarizing plate on the front surface of the liquid crystal panel is mainly emitted by the polarized light separating device. With such a configuration, polarized light absorbed by the polarizing plate on the front surface of the liquid crystal panel can be discarded in advance, so that a light source having a large power can be used. If there is no polarization separation device, polarized light other than the polarized light transmitted through the polarizing plate in front of the panel will be absorbed by the polarizing plate.If the light source power is large, the polarizing plate itself will melt due to the heat absorbed, or the polarizing plate The reason is that the function as is lost.

In the case of this projection device, a very bright projection image can be obtained because a high output is possible as a light source.

[0025]

According to the present invention, a polarization device having a higher polarization separation function than the conventional polarization separation device can be provided. If this device is used as a projection device, a projection device having higher contrast and less image unevenness than a conventional device can be provided, and a projection device with a bright projected image can be provided.

[Brief description of the drawings]

FIG. 1 is a basic configuration diagram of a polarization beam splitter of the present invention.

FIG. 2 is a conceptual configuration diagram of a polarization beam splitter of the present invention.

FIG. 3 is a configuration diagram of a polarizing film shown in Embodiment 1 of the present invention.

FIG. 4 is a configuration diagram of a polarizing film according to a third embodiment of the present invention.

FIG. 5 shows a spectral transmittance characteristic of the polarization beam splitter of the present invention in a visible wavelength region.

FIG. 6 is a polarization separation characteristic diagram in the visible wavelength region of the polarizing films shown in Examples 1 to 3 of the present invention.

FIG. 7 is a configuration diagram of a projection display device using the polarization separation device of the present invention.

FIG. 8 is a diagram showing a conventional polarization separation device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Glass substrate 2 Multilayer film for polarization separation 3 Frame of polarization separation device 72 Polarization separation device

Claims (3)

[Claims] 1. A plurality of polarizing film substrates having optical thin films formed on both surfaces of a glass substrate, a frame on which the polarizing film substrates are mounted, and each of the polarizing film substrates for P-polarized light incident along an incident optical axis. A plurality of zigzag polarization splitters arranged in a zigzag manner with an air gap in the frame so as to have a substantially Brewster angle with respect to each other, and at least one of the plurality of zigzag polarization splitters is arranged. The set is arranged so that the positions of the peaks and valleys of the respective zigzag shapes with respect to the incident optical axis are different from each other. 2. The polarization separation device according to claim 1, wherein the polarizing film substrate has a multilayer film composed of two or more layers of a high refractive index material and a low refractive index material. 3. A light source, a polarization separation device for extracting a linearly polarized light component from light emitted from the light source, a polarization separation device for separating the linearly polarized light component from the polarization separation device into RGB three-color lights, and the polarization separation device. 3. A light separating device comprising: a light valve for modulating each of the RGB light beams emitted from the means; and a projection lens for projecting the light emitted from the light valve onto a screen. Projection display device.