JP2819625B2 - Display device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a liquid crystal display device using a liquid crystal light valve.

[Prior Art] FIG. 10 is a configuration diagram showing an optical system of a conventional liquid crystal display device. Conventionally, the light emitted from the light source 1 is directly separated by the light separating means 29.
And is separated into three primary colors of red, green and blue by the light separating means 29, and the liquid crystal light valves 12R, 12G,
There has been known a liquid crystal display device in which light is modulated by 12B and synthesized by a light synthesizing unit 30, and then enlarged and projected on a front screen 17 by a projection lens 31. The liquid crystal light valves 12R, 12G, and 12B have polarizing plates 18 and 1 before and after, respectively.
9 and the light is polarized by the incident polarizer 18 to the P-polarized component or S
Polarized light components are selectively transmitted, and unnecessary polarized light components are incident-side polarizers
Absorbed by 18. The selectively transmitted polarized light component is selectively transmitted again by the output side polarizing plate 19 after passing through the liquid crystal light valves 12R, 12G, and 12B, thereby enabling image display.

[Problems to be Solved by the Invention] However, in the conventional technique, the emitted light from the light source 1 is taken into the light separating means 29, and unnecessary polarization components are absorbed by the incident side polarizing plates 18 of the liquid crystal light valves 12R, 12G, and 12B. However, since the desired polarization component is selectively transmitted, 50% of the light incident on the light separating means 29 is automatically lost, and the desired brightness cannot be obtained even with a high-intensity light source. Had. In addition, the temperature of the incident-side polarizing plate 18 significantly increases due to heat absorption, and the incident-side polarizing plate 18 that has absorbed the heat is provided immediately before the liquid crystal light valves 12R, 12G, and 12B as shown in FIG. Since heat conduction to 12G and 12B is also remarkable, in order to guarantee reliability under a wide range of environmental temperature conditions, a high-rotation type cooling fan 32 having a high cooling capacity is used as shown in FIG.
And 19, it is necessary to provide the liquid crystal light valves 12R, 12G, 12B in the immediate vicinity, and the high rotation type cooling fan 32 involves noise corresponding to the number of rotations. On the other hand, in order to satisfy the life and color characteristics of the light source 1, it is necessary to provide a cooling fan 33 in the immediate vicinity, and the synergy between the cooling fan 33 and the high-speed cooling fan 32 further increases the noise. It is not suitable as an AV-oriented liquid crystal display device.

The liquid crystal display device of the present invention solves the above problems, and aims at realizing a high-brightness image utilizing the luminous flux emitted from the light source to the maximum, and having high reliability under a wide range of environmental temperature conditions. Another object of the present invention is to provide a low-cost liquid crystal display device which is low noise and can be adapted to today's AV-oriented.

[Means for Solving the Problems] In order to solve the above problems, the present invention provides a display device including a light source, a light valve for modulating light, and a projection unit for projecting the light modulated by the light valve. And a polarization separation unit that separates light from the light source into light of a P polarization component and light of an S polarization component, and converts the light of one polarization component separated by the polarization separation unit into the other polarization light. A polarization direction conversion unit for converting the component light into a polarization direction, the polarization direction conversion unit comprising a polarization rotation element and a reflection unit, and being disposed on the light exit side of the polarization separation unit, The light of the one polarization component separated by the means passes through the polarization rotation element and is incident on the reflection means. After being reflected by the reflection means and passing through the polarization rotation element again, the other polarization component is emitted. The polarization direction of the light component light is converted, the light of the other polarization component separated by the polarization separation means, the light of the one polarization component whose polarization direction is converted by the polarization direction conversion means, The light is incident on the light valve.

[Operation] In the liquid crystal display device configured as described above, the light emitted from the light source is separated into a P-polarized light component and an S-polarized light component by a polarizing beam splitter, and a desired polarized light component is straightened or its path is changed by a reflecting means. The undesired polarized light component is converted into a desired polarized light component by passing through a polarization rotating element, and then its path is changed by a straight traveling or reflecting means and is incident on a light separating means. Therefore, all light incident on the polarizing beam splitter is incident on the liquid crystal light valve as desired light.

Embodiment An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of an optical system according to an embodiment of the present invention. In FIG. 1, light emitted from a light source 1 is incident on a polarization beam splitter 2, and a P (S) polarization component is transmitted and an S (P) polarization component is reflected on a reflection surface of the polarization beam splitter 2. The P (S) -polarized light component transmitted through the polarization beam splitter 2 is transmitted through the λ / 4 plate 3 as a polarization rotating element, so that linearly polarized light is circularly polarized. After the propagation direction of the converted outgoing light beam is reversed, it is again linearly polarized by transmitting through the λ / 4 plate 3 again, and is orthogonal to the linearly polarized light before entering the λ / 4 plate 3 S (P ) The light is converted into a polarized light component and returns to the polarization beam splitter 2. The S (P) polarization component returned to the polarization beam splitter 2 is turned by 90 ° at the reflection surface of the polarization beam splitter 2, and
After the direction change is repeated by 6 and 7, the light becomes parallel to the optical axis of the light source 1 and enters the light separating means 8. On the other hand, the S (P) polarized light component first reflected by the reflecting surface of the polarizing beam splitter 2 is reflected by the reflection means 5 and 6 by reflecting the above-mentioned S (P) polarized light component and the reflection in a mirror state with respect to the optical axis of the light source 1 , 7 again, the light also becomes parallel to the optical axis of the light source 1 and enters the light separating means 8. S incident on both
As for the (P) polarized light component, blue light (light of about 500 nm or less) is reflected by the blue reflecting dichroic mirror 9 and other light (yellow light) is transmitted. The reflected blue light is redirected by the reflecting mirror 10 and the blue liquid crystal light valve 12b.
Incident on. The light transmitted through the blue reflecting dichroic mirror 9 is incident on the red transmitting dichroic mirror 11, reflects green light (light between about 500 nm to about 600 nm), and red light (light of about 600 nm or more) as other light. Through. The reflected green light enters the green liquid crystal light valve 12G, and the transmitted red light enters the red liquid crystal light valve 12R. Each incident color light is a liquid crystal light valve 12R, 12G, 12B
After light modulation corresponding to each color by the light combining means 13
, The blue light is transmitted through the blue transmission dichroic mirror 14 and then reflected by the red transmission dichroic mirror 15, the green light is reflected by the blue transmission dichroic mirror 14 and the red transmission dichroic mirror 15, and the red light is reflected by the reflection mirror.
After being reflected at 10, it passes through a red transmission dichroic mirror 15. The light synthesized as described above enters the projection lens 16 and is enlarged and projected on the screen 17 in front.

The liquid crystal light valves 12R, 12G, and 12B enable image display by receiving a selection of a polarization component in the polarizing plates 18 and 19 before and after the liquid crystal light valves. However, the polarizing plate 18 is used as an auxiliary polarizing plate of the polarizing beam splitter 2. This is unnecessary when the polarization degree of the polarization beam splitter 2 is close to 100%.

FIG. 2 shows the principle of the λ / 4 plate 3 described above, in which the angle θ formed between the linear polarization plane 22 of the incident light beam and the optical axis direction 21 of the crystal of the λ / 4 plate 3 is 45 °. FIG. 2 shows that linearly polarized incident light can be converted into circularly polarized light (or vice versa).

FIG. 3 shows another reference example in which the light from the light source 1 is monopolarized. In the light emitted from the light source 1, the P (S) polarized component is transmitted through the reflection surface of the polarizing beam splitter 2 and S (P) The polarization component is reflected. The transmitted P (S) polarized light component is rotated by 90 ° by passing through the λ / 2 plate 23, which is a front polarization rotating element, to become an S (P) polarized light component, and is incident on the light separating means 8. . On the other hand, the reflected S
(P) The polarization component has its course changed once in a direction parallel to the optical axis of the light source 1 by the reflection means 5 and again enters the light separation means 8. Therefore, in this case as well, it can be seen that all the light incident on the polarization beam splitter 2 becomes the S (P) polarization component. FIG. 4 shows the principle of the λ / 2 plate 23 at this time, and the angle θ between the linear polarization plane 22 of the incident light beam and the optical axis direction 21 of the crystal of the λ / 2 plate 23 is 45 °. If
P (S) because the plane of polarization of the incident linearly polarized light rotates 90 °
The polarization component is converted to an S (P) polarization component.

As described above, since the undesired polarized light component hardly enters the light separating means 8, the temperature rise of the liquid crystal light valves 12R, 12G, and 12B is minimized, and even if environmental temperature conditions are taken into consideration, the liquid crystal light valve 12R is not affected. , 12G, and 12B dedicated cooling fans are not required, and cooling as a device is achieved by the light source 1 as shown in FIG.
It is sufficient to use a single cooling fan 20 for simultaneously cooling the liquid crystal light valves 12R, 12G, 12B and the polarizing plates 18, 19.

FIG. 5 shows a reference example in which a glass plate 26 is used as the polarization beam splitter 2 in FIG. 3, and FIG. 6 shows an embodiment in which a glass plate 26 is used as the polarization beam splitter 2 in FIG. As described above, the polarizing beam splitter 2 generally has a cube shape in which the slopes of a pair of right-angle prisms are bonded to each other as described above. In this case, a polarization degree of about 98% can be achieved, so that the polarizing plate 18 becomes unnecessary. Will be expensive. The principle of the polarization beam splitter shown in FIGS. 5 and 6 is realized at low cost, and its principle will be described with reference to FIG. In FIG. 7, when the refractive index of the glass plate 26 is n, the incident angle of light is ζ, and the glass plate 26 is provided in a relation of ζ = tan ⁻¹ n, the P-polarized component 27 becomes 10
0% is transmitted and about 15% of the S-polarized component 28 is reflected. (In this case, ζ is the Brewster's angle.) Therefore, when a plurality of glass plates 26 are stacked in parallel to form a structure as shown in FIGS. 5 and 6, ideally the P-polarized light component 27 finally becomes 100% is transmitted, and the S-polarized component 28 is reflected 100%. In the actual measurement, when the number of glass plates 26 is plotted on the horizontal axis and the degree of polarization is plotted on the vertical axis, the relationship shown in FIG. 8 is obtained.
A degree of polarization of 80% can be achieved. As described above, by setting eight to ten glass plates 26 in parallel so that the incident angle of the superposed light becomes the Brewster angle, the degree of polarization is about 80.
%, The absorption of the S-polarized light component by the incident-side polarizing plate 18 in FIG. 1 is less than 30%, and the temperature rise of the polarizing plate 18 can be minimized. Therefore, even if the polarizing plate 18 is provided immediately before the liquid crystal light valves 12R, 12G, and 12B, the influence of the temperature rise of the polarizing plate 18 on the liquid crystal light valves 12R, 12G, and 12B is extremely small, and the environmental temperature condition is also taken into consideration. Even if it is inserted, a cooling fan dedicated to the liquid crystal light valves 12R, 12G, 12B becomes unnecessary, and cooling as a device is performed by the light source 1, the liquid crystal light valves 12R, 12G, 12B, the polarizing plates 18, 19 as shown in FIG. It is sufficient to use the cooling fan 20 that cools the air at the same time. In FIGS. 5 and 6, the relationship among the light source, the polarization beam splitter, the polarization rotation element, the reflection means, and the light separation means is exactly the same as that described above with reference to FIGS.

FIG. 9 is a reference example in which a convex lens 24 and a concave lens 25 are provided in combination in front of the light separating means 8 in FIG. 3, and the cross-sectional area of light incident on the light separating means 8 can be reduced by this configuration. Therefore, a combination of a larger light source and a smaller light separating means becomes possible, and the above configuration is more effective for brightness. This is shown in FIG.
The same is true in the case of FIG. 6 and FIG.

[Effects of the Invention] As described above, the display device of the present invention includes a light source,
A display device comprising: a light valve that modulates light; and a projection unit that projects light modulated by the light valve, wherein the light from the light source is separated into light of a P-polarized component and light of an S-polarized component. And a polarization direction conversion unit that converts light of one of the polarization components separated by the polarization separation unit into a polarization direction of light of the other polarization component. The one polarization component light, which comprises a polarization rotation element and a reflection means, is disposed on the light emission side of the polarization separation means, and is separated by the polarization separation means, passes through the polarization rotation element and passes through the reflection means. After being reflected by the reflection means, passes through the polarization rotation element again, thereby being converted into the polarization direction of the light of the other polarization component, and separated by the polarization separation means. The light of the polarized light component and the light of the one polarized light component whose polarization direction has been converted by the polarization direction converting means are incident on the light valve, so that the light flux emitted from the light source is maximized. Brightness display can be realized.

In addition, the above configuration can minimize the temperature rise of the polarizing plate and the liquid crystal light valve, thereby ensuring reliability under a wide range of environmental temperature conditions, and cooling the light source and the liquid crystal light valve with a common cooling fan. It is possible to realize a liquid crystal display device that can be adapted to today's AV orientation with noise.

Furthermore, when a plurality of glass plates are provided in parallel as the polarizing beam splitter so that the incident angle becomes the Brewster angle, a low-cost liquid crystal display device can be realized while satisfying the above-mentioned effects.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an optical system of a liquid crystal display device of the present invention, FIG. 2 is a principle diagram of a λ / 4 plate used in the present invention, and FIG. 3 is a reference example relating to a polarizing means of the present invention. FIG. 4 is a diagram showing the principle of a λ / 2 plate used in a reference example of the present invention, FIG. 5 is a diagram showing the configuration of another reference example of the present invention, and FIG. FIG. 7 is a diagram showing the principle of the polarizing beam splitter of the present invention, and FIG. 8 is a diagram showing the number of glass plates and the degree of polarization of the polarizing beam splitter of the present invention. FIG. 9 is a configuration diagram of another reference example relating to the polarizing means of the present invention, and FIG. 10 is a configuration diagram of an optical system of a conventional liquid crystal display device. DESCRIPTION OF SYMBOLS 1 ... Light source 2 ... Polarization beam splitter 3 ... λ / 4 plate (polarization rotation element) 4, 5, 6, 7 ... Reflecting means 8 ... Light separating means 12 ... Liquid crystal light valve 13 ... Photosynthesis means 16 Projection lens 17 Screen 18, 19 Polarizing plate 20 Cooling fan 21 Crystal optical axis direction 22 Linear polarization plane of incident light 23 λ / 2 plate (polarization rotating element) 24 Convex lens 25 Concave lens 26 Glass plate 27 P-polarized component 28 S-polarized component

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G02F 1/13-1/141 G02B 27/18 G03B 21/00 G09F 9/00-9/30

Claims (3)

(57) [Claims] 1. A display device comprising: a light source; a light valve for modulating light; and projection means for projecting the light modulated by the light valve, wherein the light from the light source is converted to a P-polarized component light. Polarized light separating means for separating light of the S polarized light component into light of the S polarized light component; and polarization direction converting means for converting the light of the one polarized light component separated by the polarized light separating means into the polarization direction of the light of the other polarized light component. The polarization direction conversion unit includes a polarization rotation element and a reflection unit, and is disposed on the light emission side of the polarization separation unit. The light of the one polarization component separated by the polarization separation unit is the polarization rotation unit. After passing through the element, the light is incident on the reflection means, is reflected by the reflection means, and then passes through the polarization rotation element again to be converted into the polarization direction of the light of the other polarization component. The display device, wherein the light of the other polarization component separated more and the light of the one polarization component whose polarization direction has been converted by the polarization direction conversion means are incident on the light valve. . 2. The apparatus according to claim 1, wherein said polarization direction changing means is arranged close to said polarization separation means.
The display device according to the above. 3. The display device according to claim 1, wherein said reflecting means is a flat reflecting means.