JP2003090916A - Wavelength plate and projection display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wavelength plate usable in a wide wavelength band and showing excellent durability even when used for a projection display device. SOLUTION: The wavelength plate 1 has a grating part 4 with two kinds of media A (2) and B (3), with mutually different wavelength dispersion of refractive indexes, alternately arranged in stripes with a period shorter than the wavelength of the light and the media are selected in such a way that the refractive index of the medium A is larger than that of the medium B and further the wavelength dispersion of the refractive index of the medium A is smaller than that of the medium B.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wave plate and a projection display device, and more particularly to the structure of a structural birefringent wave plate.

[0002]

2. Description of the Related Art In recent years, the development of information equipment has been remarkable, and the demand for thin, high-resolution, low-power-consumption display devices has been increasing, and research and development have been advanced. Among them, the liquid crystal display device is expected to be a display device that can electrically control the alignment of liquid crystal molecules to change the optical characteristics and can meet the above needs, and also developed a liquid crystal display device with a large screen. Has been done. As one form of such a liquid crystal display device, a projection display device is known in which an image emitted from a video source including an optical system using a liquid crystal panel is enlarged and projected on a screen through a projection lens. This type of projection type display device uses a liquid crystal panel as a light modulating means. However, when a TN (Twisted Nematic) type liquid crystal panel is used, this liquid crystal panel uses only polarized light in one direction in principle. Therefore, the polarization conversion means is provided for the purpose of aligning the indefinitely polarized light beam emitted from the light source into the unidirectional polarized light before entering the liquid crystal panel. For the polarization conversion means, for example, a half wave plate is used.

The wave plate is also called a retardation plate and is composed of a member having birefringence. When the difference in refractive index due to birefringence is Δn and the thickness is d, the product Δnd of these is called retardation (R). When the wavelength of light is λ,
A half-wave plate that satisfies R = λ / 2 can be used as a polarization conversion element. As a method of obtaining birefringence, for example, (1) a method of producing birefringence in a film by stretching a polymer film,
(2) A method of polymerizing a polymer precursor originally having a refractive index anisotropy to form a film, (3) a method of forming a high-density relief structure on the surface to cause structural birefringence (special Kakai No. 62-170902) and the like have been proposed.

[0004]

Generally, the wave plate functions as a wave plate only for light of a certain specific wavelength (monochromatic light). For example, when a light flux containing light of different wavelengths is incident on one wavelength plate, such as white light source light of a projection display device, a desired polarization conversion action is obtained for light of one wavelength. However, a sufficient polarization conversion action cannot be obtained for light of other wavelengths.
As a result, there have been problems that the utilization efficiency of light of other wavelengths is reduced, a bright image cannot be obtained as a projection display device, and the color reproduction range (color balance) is narrowed.
Under these circumstances, there has been a demand for a plate that functions as a wave plate in a certain wide wavelength range as well as a specific wavelength range.

In order to function as a wave plate having desired characteristics in a wide wavelength band, for example, if it is a half wave plate, it is necessary to always satisfy the relation of R = λ / 2 even if the wavelength changes. Therefore, when the wavelength becomes longer, the retardation value must be increased accordingly. However, the wavelength dependence (wavelength dispersion) of the refractive index of a general dielectric material is that the refractive index becomes smaller as the wavelength becomes longer in the wavelength band of visible light.
The conventional wave plate has a characteristic that the retardation value becomes smaller or hardly changes as the wavelength becomes longer.

On the other hand, in recent years, a broadband retardation film having an inverse dispersion property has been proposed ("Wide-Band R").
etardation Films with Reverse Wavelength Dispersio
n ", A.Uchiyama et al., Proceedings of the seventh i
nternational display workshops (IDW), p.407-410, 20
00). This film has reverse dispersibility, that is, the retardation value increases as the wavelength becomes longer, and satisfies the above requirements. However, this film is made of an organic material, and in a projection type display device using a light source of high brightness, the film has a considerably high temperature, which causes a problem in durability.

The present invention has been made in order to solve the above problems and can be used in a wide wavelength band, and exhibits excellent durability even when used in a projection type display device or the like. An object is to provide a wave plate.

[0008]

In order to achieve the above object, the wavelength plate of the present invention has a different wavelength dispersion of refractive index.
There is a grating portion in which different kinds of media are alternately arranged in a stripe shape with a period shorter than the wavelength of light, and one of the two kinds of media has a refractive index higher than that of the other medium. It is characterized in that it is large and the wavelength dispersion of the refractive index of the one medium is smaller than the wavelength dispersion of the refractive index of the other medium.

In order to obtain the birefringence required for the wave plate, the present inventor applies a structural birefringent element to the wave plate, which has recently been proposed as an application example to a diffraction grating or a polarizer. Thought. "Structural birefringence" means polarization components parallel to a stripe (TE wave) and polarization perpendicular to a stripe when two types of media having different refractive indexes are alternately arranged in a stripe shape with a cycle shorter than the wavelength of light. It means that the refractive index that the light effectively senses differs from the component (TM wave), and a birefringence action occurs.

For example, as shown in FIGS. 2 and 3, let us consider an element in which a lattice portion in which two kinds of media A and B having different refractive indexes are alternately arranged is formed on a substrate. The effective refractive index for the polarized light component parallel to the stripe and the effective refractive index for the polarized light component perpendicular to the stripe are different, and the effective refractive index for the polarized light component parallel to the stripe is n _TE , and the effective refractive index for the polarized light component perpendicular to the stripe is n. _{Let TM} be expressed as the following equations (1) and (2), respectively.

[0011]

[Equation 1] However, in the formulas (1) and (2), a and b are the widths of the media A and B, respectively, and n ₁ and n ₂ are the refractive indices of the media A and B, respectively.

Here, the refractive indices of the media A and B and FIGS.
FIG. 6 shows the relationship of Δn (Δn = n _TE −n _TM ) of the structural birefringent element shown in FIG. In FIG. 6, the horizontal axis represents the refractive index of the medium B, the vertical axis represents Δn, and the legend represents the refractive index of the medium A. The shape of the curve in FIG. 6 changes depending on the ratio of the widths a and b of the media A and B, but this is an example when a = b.
From equations (1) and (2), when n ₁ = n ₂ , n _TE = n _TM, and therefore Δn = 0. That is, when the refractive indexes of the media A and B are equal, the curve passes through the point of Δn = 0 and draws a curve such that Δn increases as the refractive index difference between the media A and B increases.

In FIG. 6, for example, the refractive index of the medium A is 1
Focusing on the curve of, the curve has an upward slope in the area shown in FIG. 6 (in the following description, an upward slope is a positive slope and a downward slope is a negative slope). . If the refractive index of the medium A does not change at all even if the wavelength of light changes, that is, if the wavelength dispersion of the refractive index of the medium A is 0, the slope of this curve itself does not change. On the other hand, when the wavelength of light becomes longer, the refractive index of the medium B becomes smaller, that is, assuming that the medium B has wavelength dispersion of the refractive index, the wavelength of light becomes longer at normal wavelength dispersion. The medium B on the curve with a positive slope
Direction where the refractive index of becomes smaller (left side of the horizontal axis in the figure)
Therefore, Δn becomes smaller. If the thicknesses d of the media A and B are constant, the vertical axis in FIG. 6 can be regarded as the retardation value, so the retardation value R becomes small. That is, in this case, the retardation value R becomes smaller as the wavelength of light becomes longer, so that it is not possible to achieve the purpose of realizing a wave plate having desired characteristics regardless of the change in wavelength, as in the conventional wave plate.

Next, focusing on a curve in which the refractive index of the medium A is 2.5, for example, this curve has a negative slope in the region shown in FIG. As in the above case, assuming that the wavelength dispersion of the refractive index of the medium A is 0, the slope of this curve itself does not change. Assuming that the medium B has wavelength dispersion of normal refractive index, when the wavelength of light becomes longer, the refractive index of the medium B becomes smaller on the curve of the negative slope (left side of the horizontal axis in the figure). Direction), Δn becomes large and the retardation value R becomes large. That is, in this case, contrary to the above case, the retardation value R increases as the wavelength of light becomes longer, so that a wavelength plate having desired characteristics can be realized even if the wavelength changes.

In summary, by using the region of the negative slope of each curve in FIG. 6, the retardation value R becomes larger as the wavelength of light becomes longer, and the wave plate aimed at by the present invention can be obtained. In other words, the negative gradient region of the curve in FIG. 6 is a region in which the medium A has a higher refractive index than the medium B. Therefore, by selecting a combination of the media A and B in which the refractive index of the medium A is larger than that of the medium B, it is possible to obtain a wave plate having desired characteristics in a wide wavelength band.

However, as a premise of the above description, the medium A
The wavelength dispersion of the refractive index of the medium B is 0, and the wavelength dispersion of the refractive index of the medium B is a finite value. Here, when the wavelength dispersion of the refractive index of the medium A increases, the gradient of the curve of FIG. 6 tends to become gentle. For example, assuming that the wavelength dispersion of the refractive index of the medium A has a very large value, the curve of FIG. The negative slope of is small enough. At this time, if the wavelength dispersion of the refractive index of the medium B is smaller than the wavelength dispersion of the refractive index of the medium A,
The degree to which the gradient of the curve in FIG. 6 becomes smaller than the degree to which the refractive index of the medium B moves on the curve becomes smaller, and Δn becomes larger when the wavelength of light becomes longer. There will be no. Therefore, in order for the retardation value R to increase as the wavelength of light increases, it is a necessary condition that the wavelength dispersion of the refractive index of the medium A is smaller than the wavelength dispersion of the refractive index of the medium B.

As described above, it is desirable that the wavelength dispersion of the refractive index of the medium A is 0 or a sufficiently small value.
Further, in the case of having the characteristic that the refractive index increases as the wavelength becomes longer, that is, the so-called reverse dispersion, the slope of the curve in FIG. Can be achieved. Summarizing the wavelength dispersion, the medium A may have any characteristics of "0", "normal dispersion", and "inverse dispersion", and the medium B needs to have "normal dispersion". In any combination, the condition that "the wavelength dispersion of the refractive index of the medium A is smaller than that of the medium B" must always be satisfied.

Under the above conditions, the wave plate of the present invention is a grating in which two types of media (mediums A and B) having different wavelength dispersions of refractive index are alternately arranged in a stripe shape at a cycle shorter than the wavelength of light. If the refractive index of the medium A is larger than that of the medium B and the wavelength dispersion of the refractive index of the medium A is smaller than that of the medium B, Retardation value R as the wavelength of light becomes longer
Can be realized, and a wave plate that can obtain desired characteristics in a wide wavelength band can be realized. Regarding the condition that the refractive index of the medium A is larger than the refractive index of the medium B, this relationship must always be satisfied even if the wavelength of light changes and the refractive index of each medium changes. In addition, since an inorganic material can be selected as a medium that satisfies the above conditions,
The heat resistance can be improved as compared with the conventional wave plate using an organic film.

At least one of the one medium and the other medium may have birefringence. In the above description, the effective refractive indices n _TE and n _TM for each polarization component of the incident light are based on the equations (1) and (2), but this is the refractive index n ₁ and n ₂ for the media A and B. It is assumed that the material has a so-called refractive index isotropic property, which is uniquely determined by. However, at least one of the media A and B may have birefringence, and in that case, the refractive indices n ₁ and n _{2 in} the formulas (1) and (2) are the refractive indices n with respect to ordinary light. _o , only replaced by the refractive index n _e for extraordinary light. According to this configuration, even if the refractive index of the medium decreases as the wavelength increases, the retardation value increases if the difference between the ordinary light refractive index and the extraordinary light refractive index increases. Even an isotropic material can have birefringence by being stretched, so that various materials can be selected. This makes it possible to improve light resistance, moisture resistance, heat resistance and the like.

The projection type display device of the present invention comprises a light source, a light modulation means for modulating the light from the light source, and a projection means for projecting the light modulated by the light modulation means. In addition, the wave plate of the present invention is provided. According to this configuration, a desired polarization characteristic can be obtained in a wide wavelength band, and since the wavelength plate having excellent heat resistance is provided, a bright display screen and a highly reliable projection display device can be realized.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a perspective view showing a wave plate of the present embodiment, FIG. 2 is a plan view of the same, and FIG. 3 is A- of FIG.
Sectional drawing which follows the A'line, FIG. 4 is process sectional drawing which shows the manufacturing process of the same wavelength plate one by one. In each of the following drawings, in order to make each layer and each member recognizable in the drawing, the scale is different for each layer and each member.

In the wave plate of this embodiment, as shown in FIG. 1, two kinds of mediums A (2) (one medium) and medium B (3) (the other medium) having different refractive indexes are alternately arranged. The lattice portions 4 arranged in stripes are formed on the transparent substrate 5. Of the two types of media, the refractive index of the medium A (2) is larger than that of the medium B (3), and the wavelength dispersion of the refractive index of the medium A (2) is the refractive index of the medium B (3). Each medium is selected to be smaller than the wavelength dispersion of.

As shown in FIG. 2, medium A (2) and medium B
The pitch P of (3) is a value smaller than the wavelength of incident light, and is set to, for example, about 100 to 150 nm.
Although it is convenient in manufacturing, it is more preferable to set the wavelength to about 1/10 of the wavelength of incident light. Regarding the thickness d of the medium A (2) and the medium B (3), for example, if the desired wave plate is a half wave plate, R = Δnd = λ / 2 at the wavelength of the light used.
In the case of a ¼ wavelength plate, the thickness d may be set to satisfy R = Δnd = λ / 4 at the wavelength of the light used.

In this embodiment, GFK70 (trade name, manufactured by Sumita Glass Co., Ltd.), which is a kind of glass material, is used as the material of the medium A (2). Further, the translucent substrate 5 and the medium B (3) are integrally configured, and LLF8 (trade name, manufactured by Sumita Glass Co., Ltd.), which is a kind of glass material, is used as the material thereof. Regarding the physical properties of each glass material, the refractive index of GFK70 is 1.56907, the Abbe number is 71.3, the refractive index of LLF8 is 1.53256, and the Abbe number is 46.0. The "Abbe number" is an amount that defines the property relating to wavelength dispersion of light in a transparent medium such as glass, is the reciprocal of the dispersive power, and is also called the reverse dispersive power. The larger the value, the smaller the chromatic dispersion, and the smaller the value, the larger the chromatic dispersion. Therefore, in the above case, the wavelength dispersion of the refractive index of GFK70 (medium A) is L
This is smaller than the wavelength dispersion of the refractive index of LF8 (medium B).

When the wave plate 1 having the above-mentioned structure is manufactured, as shown in FIG. 4A, the LL which is the material of the medium B (3).
The substrate 5 of F8 is prepared, and the photoresist 6 is applied as shown in FIG. Next, the photoresist 6 is exposed to light, but since a fine pattern in which the pitch of the medium A and the medium B is smaller than the wavelength of light is formed, normal exposure using a photomask is impossible. As shown in c), two-beam interference exposure using laser light is performed. Next, development is performed to obtain a resist pattern 7 as shown in FIG. Then, as shown in FIG. 4E, the substrate 5 is etched using the resist pattern 7 as a mask to form a large number of grooves on the surface of the substrate. After that, FIG.
As shown in (f), GFK70, which is the material of the medium A (2), is embedded in the groove by performing glass pressing. The wave plate 1 of the present embodiment is completed through the above steps. In addition, the shape of FIG.
Unlike the one shown in FIG. 3 and FIG.
Although the medium A (2) consisting of 0 is located over the entire surface, the medium A (2) in this portion does not necessarily have to be removed.

In the wave plate 1 of the present embodiment, the refractive index of the medium A (2) is the refractive index of the medium B (3) as described in the principle in the section "Means for solving the problem". Is smaller than the wavelength dispersion of the refractive index of the medium B (3) and is smaller than the wavelength dispersion of the refractive index of the medium B (3). The provision of the pitch grating portion 4 makes it possible to obtain a characteristic that the retardation value R increases as the wavelength of light becomes longer, and it is possible to realize a wave plate that can obtain desired characteristics in a wide wavelength band. Also, the medium A (2) and the medium B
Since an inorganic material such as glass can be selected as the material of (3), it is possible to improve heat resistance as compared with a conventional wave plate using an organic film, and a projection display device having a light source of high brightness. It can be suitably used for the above.

FIG. 5 shows the wave plate of the above embodiment, especially 1
It is a schematic block diagram which shows an example of the projection type display device provided with the / 2 wavelength plate. In the figure, reference numeral 11 is a light source, 12 is an integrator, 13 is a polarization conversion element, 14 and 15 are half-wave plates, 16 and 17 are dichroic mirrors, 18, 19 and
20 is a reflection mirror, 21 and 22 are relay lenses, 23,
Reference numerals 24 and 25 denote liquid crystal light valves (light modulation means), 26 a composite prism, and 27 a projection lens (projection means).

The light source 11 is a lamp 28 such as a metal halide.
And a reflector 29 that reflects the light of the lamp. Since the light emitted from the light source 11 has an illuminance distribution,
In order to make the illuminance uniform, an integrator 12 including, for example, two fly-eye lenses 30a and 30b is arranged at the subsequent stage of the light source 11. This projection type display device 10 uses a TN type liquid crystal panel as a light modulating means and uses only one direction of polarized light for display. Therefore, the indefinite polarized light flux emitted from the light source 11 is not incident on the liquid crystal panel. For the purpose of aligning this light flux with polarized light in one direction, the polarization conversion element 13
Is provided. Here, the polarization conversion element 13 has one
A half wave plate 14 is used.

The red light / green light reflecting dichroic mirror 16 transmits the blue light L _B of the light flux emitted from the polarization conversion element 13 and also transmits the red light L _R and the green light L _G.
And reflect. The transmitted blue light L _B is reflected by the reflection mirror 18.
It is reflected by and enters the liquid crystal light valve 23 for blue light. On the other hand, of the colored light reflected by the dichroic mirror 16, the green light L _G is reflected by the dichroic mirror 17 for reflecting green light, and the liquid crystal light valve 24 for green light is used.
Incident on. On the other hand, the red light L _R passes through the dichroic mirror 17, passes through the relay lens 21, the reflection mirror 19, the relay lens 22, and the reflection mirror 20, and enters the liquid crystal light valve 25 for red light.

The three color lights modulated by the liquid crystal light valves 23, 24 and 25 enter the combining prism 26. The synthetic prism 26 is composed of a cross dichroic prism, and four right-angle prisms are attached to each other, and a dielectric multilayer film that reflects the red light L _R and a dielectric multilayer film that reflects the blue light L _B are cross-shaped on the inner surface thereof. Is formed in. For green light L _G , red light L _R and blue light L
_Since the polarized light which is orthogonal to _B is transmitted through these dielectric multilayer films, the liquid crystal light valve for green light 2
1 to rotate the polarization direction by 90 ° before entering 4
A half wave plate 15 is arranged.

The three color lights are combined by the dielectric multilayer film of the combining prism 26 to form light representing a color image. The combined light is a projection lens 2 which is a projection optical system.
An image projected and enlarged on a screen (not shown) is displayed by 7.

The wave plate used in the conventional projection type display device is designed so as to obtain desired characteristics in light (color light) of a certain specific wavelength. For example, the wave plate is designed for green light having the highest intensity. It was. Therefore, the red light and the blue light are not able to obtain the desired polarization conversion, resulting in light loss, and as a result, there are drawbacks such as dark display and poor color balance. On the other hand, in the case of the projection display apparatus 10 according to the present embodiment, a bright and well-balanced image can be obtained by providing the 1/2 wavelength plates 14 and 15 that can obtain desired polarization characteristics in a wide wavelength band. You can Further, by using the wave plate having excellent heat resistance, it is possible to realize a highly reliable projection display device.

The technical scope of the present invention is not limited to the above-mentioned embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, the specific description of the materials, pitches, etc. of the media A and B in the wave plate of the above-described embodiment can be changed as appropriate. Further, in the above embodiment, the materials A and B are made of a material having a refractive index isotropic, but at least one of them may be made of a material having a refractive index anisotropy. In that case, since the range of material selection is widened, heat resistance and light resistance can be improved.

[0034]

As described above in detail, according to the present invention, it is possible to realize a wavelength plate having desired characteristics in a wide wavelength band and excellent in durability. Further, by using this wave plate, it is possible to realize a projection type display device having excellent display quality and high reliability.

[Brief description of drawings]

FIG. 1 is a perspective view showing a wave plate according to an embodiment of the present invention.

FIG. 2 is a plan view of the same.

FIG. 3 is a cross-sectional view taken along the line A-A ′ in FIG.

FIG. 4 is a process cross-sectional view showing the steps of manufacturing the wave plate in the same order.

FIG. 5 is a schematic configuration diagram of the projection type display device of the embodiment of the present invention including the wavelength plate.

FIG. 6 is a diagram for explaining the principle of the present invention,
6 is a graph showing the relationship between the refractive index of two types of media and Δn of a structural birefringent element.

[Explanation of symbols]

1 Wave plate 2 medium A 3 Medium B 4 lattice 5 Translucent substrate 10 Projection display device 14,15 1/2 wave plate 23, 24, 25 Liquid crystal light valve (light modulator) 27 Projection lens (projection means)

Claims (3)

[Claims] 1. A grating portion, in which two kinds of media having different wavelength dispersions of refractive indices are alternately arranged in a stripe shape with a period shorter than the wavelength of light, and one of the two kinds of media is provided. The refractive index of the medium is larger than that of the other medium,
A wavelength plate, wherein the wavelength dispersion of the refractive index of the one medium is smaller than the wavelength dispersion of the refractive index of the other medium. 2. The wave plate according to claim 1, wherein at least one of the one medium and the other medium has birefringence. 3. A projection type display device comprising a light source, a light modulating means for modulating the light from the light source, and a projecting means for projecting the light modulated by the light modulating means. Alternatively, the projection type display device is provided with the wave plate described in 2.