JP2000098119A - Diffraction-refraction type optical element and liquid crystal projector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the proportion of light emitting area of a liquid crystal panel by using an optical element having functions to diffract light beams emergent from filters and to make the diffracted light beams parallel again, although the liquid crystal panel transmits light only through the filter opening but not through the black strips. SOLUTION: Light beams of a color image emergent from the color filter parts of a liquid crystal panel equipped with black stripe parts 7 are diffracted with a diffraction grating 8 to make the black stripes invisible. The directions of the diffracted light beams are then made to coincide with the direction parallel to the incident light by refraction. The mixing of light beams emergent from adjacent filters is prevented and an unblurred image free from the shadows of the black stripes 7 is given.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for projecting an image on a liquid crystal panel, in which a black stripe portion, which is a light opaque portion, is also enlarged, so that a relatively thick black stripe is formed on the projected image. The present invention relates to an optical element which solves the drawback of visually obstructing by having a structure combining a diffraction grating surface and an optical refraction surface. Also,
The present invention relates to a liquid crystal projector in which such an optical element is incorporated to eliminate black stripe projection.

[0002]

2. Description of the Related Art There are two methods for enlarging a video image to make it easier to see: (1) using a large-sized CRT, and (2) using a CRT for each of the three primary colors with high luminance. There are a method of projecting an image on a rear projection screen, and (3) a method of projecting an image on a reflective screen by an illumination light source using a liquid crystal panel.

However, the method (1) has a drawback that the size that can be manufactured is limited and that the weight of the entire apparatus increases. In (2), the drawback that the screen becomes dark due to the enlargement is inevitable. In (3), since a light source for illumination can be used instead of a vacuum tube such as a cathode ray tube, the brightness is high, and therefore, there is an advantage that enlargement can be realized with a sufficient magnification for practical use, and there are many occasions of use.

However, the method (3) has a drawback that a black stripe existing between optical filters of each color of a liquid crystal panel is conspicuous. The black stripe of the liquid crystal panel is very thin in a display for a personal computer (a large one is about 30 cm in diagonal length even if it is large), and the intensity of light transmitted through the optical filter is sufficient. Therefore, the presence of the black stripe is relatively unnoticeable. However, when the screen of the liquid crystal panel is enlarged and projected, the black stripes gradually become thicker and the intensity of the light transmitted through the optical filter decreases as the magnification increases, so that the black stripes can be seen relatively well. And becomes quite annoying.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to keep the black stripe of a liquid crystal panel intact and to make the black stripe invisible when enlarged and projected.

[0006]

According to the present invention, a color image of a liquid crystal panel generated with a black stripe portion is diffracted using a diffraction grating to diffract light of each color filter portion. After the loss, the light emitted from the adjacent filter would be mixed as it is, but by returning the direction of the diffracted light to the direction parallel to the original light direction and aligning it, there is no black stripe and there is no blur Succeeded to give no picture.

The invention according to claim 1 is used in combination with a liquid crystal panel having a black stripe, and the incident light from the liquid crystal panel is increased by +1 at a position corresponding to the optical filter except for the black stripe on the side facing the liquid crystal panel. A transmissive diffraction grating having a function of diffracting light of the first and second order, and diffracting the light diffracted by the transmissive diffraction grating at a position where adjacent diffracted lights on the opposite side to the liquid crystal panel cross each other. A diffractive refraction type optical element having a refraction surface having a function of refracting outgoing light parallel to the incident light.

A second aspect of the present invention relates to the diffractive refraction optical element according to the first aspect, wherein the grating interval of the transmission type diffraction grating is determined according to the width of the corresponding black stripe portion. Things.

According to a third aspect of the present invention, in the second aspect, the grating interval の of the transmission type diffraction grating is such that the width of the corresponding black stripe portion is d, the wavelength of the incident light is λ, and the thickness of the diffractive optical element is And t is a diffraction refractive optical element characterized by being determined by the following “Equation 3”.

[Number 3] ^{χ = 2λ (t 2 + d} 2/4) 1/2 / d

According to a fourth aspect of the present invention, there is provided a projection light source, a condensing optical system for condensing light emitted from the projection light source to illuminate a liquid crystal panel, and surrounded by a black stripe and a black stripe. A liquid crystal panel having an optical filter section for each of three primary colors for each pixel, receiving light from the condensing optical system, and emitting color image light corresponding to a video signal; And a projection optical system for projecting light from the screen onto a screen, and on the light exit side of the liquid crystal panel, has a diffractive refractive optical element, and the diffractive refractive optical element is At a position corresponding to the optical filter portion except the black stripe portion on the side facing the liquid crystal panel, a transmission type diffraction grating having a function of diffracting + 1st and -1st order incident light from the liquid crystal panel is provided,
The liquid crystal panel has a function of refracting light diffracted by the transmission type diffraction grating into outgoing light parallel to the incident light at a position where adjacent diffracted lights on the side opposite to the liquid crystal panel intersect. LCD projector.

A fifth aspect of the present invention relates to the liquid crystal projector according to the fourth aspect, wherein a grating interval of the transmission type diffraction grating is determined according to a width of a corresponding black stripe portion. .

According to a sixth aspect of the present invention, in the fifth aspect, the grating interval の of the transmission type diffraction grating is such that the width of the corresponding black stripe portion is d, the wavelength of the incident light is λ, and the thickness of the diffractive refractive optical element is Assuming that t, the present invention relates to a liquid crystal projector characterized by being determined by the following “Equation 4”.

[Number 4] ^{χ = 2λ (t 2 + d} 2/4) 1/2 / d

[0013]

FIG. 1 is a diagram conceptually showing the principle of a diffractive refractive optical element and a liquid crystal projector according to the present invention. Light emitted from a light source 1 for illumination is Thus, the light is condensed in a certain angle range, becomes parallel light, for example, and enters the liquid crystal panel 3. Alternatively, the light may be condensed by a Porola reflective mirror or the like to form parallel light. The liquid crystal panel 3 corresponds to blue (region B in the drawing), green (region G in the drawing), and red (region R in the drawing) minute filter regions and each minute filter region for each pixel. Electrodes are formed, and a voltage corresponding to a video signal is applied to each electrode, and the transmittance of light is controlled by the action of the liquid crystal. Therefore, when the light incident on the liquid crystal panel 3 is transmitted, the hue and the light intensity are determined for each of the fine filter regions, and a color image is given as a whole. The light emitted from the liquid crystal panel 3 is
Next, the light enters the diffractive refractive optical element 4 of the present invention. In a normal liquid crystal projector, this portion is not provided, and light is directly introduced from the liquid crystal panel to the next projection optical system 5. As will be described later, the diffractive refraction optical element 4 diffracts the light on the incident side to convert the parallel incident light into the direction of the angle θ determined by the diffraction grating and the −
It has a function of diffracting light in the direction of θ, and has a function of making light having the same directionality as incident light again, in this case, parallel light, by refraction on the output side. The light emitted from the diffractive refraction optical element 4 is adjusted to an appropriate angle by the projection optical system 5,
It is projected on a reflective screen or the like.

FIG. 2 is a conceptual diagram showing the function of the diffractive refractive optical element. 3f indicates a color filter of the liquid crystal panel 3, and 4 indicates a diffractive refractive optical element. The hatched portion 7 of the color filter 3f is a black stripe portion,
The portions of the color filter 3f with the letters B, G, and R, which do not transmit light, are blue, green, and red fine optical filter portions, respectively, which transmit light. The diffractive refraction optical element 4 has a diffraction grating section 8 on the surface on the liquid crystal panel side,
The position and size of the diffraction grating and the shape of the formed area correspond to the optical filter of the left liquid crystal panel.
The other surface of the diffractive refraction optical element has two pairs of refraction surfaces 9 and 10 having different angles at positions corresponding to the diffraction grating. However, the size and shape of the pair of refraction surfaces 9 and 10 are larger than the size of the optical filter unit, and include the half width of the black stripe around the optical filter unit. It corresponds to the pitch of the optical filter section. The light transmitted through each optical filter section is diffracted by the action of the diffraction grating 8, and among the arrows indicated by the dotted lines in the figure, the light traveling obliquely to the upper right is refracted by the refraction surface 9 and becomes parallel light to the right. The light traveling obliquely to the lower right is refracted by the refracting surface 10 and again becomes parallel light and exits to the right. Therefore, when the liquid crystal panel exits, the black stripe portion does not emit light, so there is a black portion, but the diffractive refraction optical element 4 makes the black portion invisible.

With reference to FIGS. 3A and 3B, description will be made in more detail on the dimensions of each part of the diffractive refraction type optical element 4 for making the black stripe part invisible and the like. First, the diffraction grating 8
Will be described. As shown in FIG. 3, the light exiting from the filter B (meaning the blue filter portion) and diffracted in the lower right direction by the diffraction grating 8, and the light exiting from the filter G (meaning the green filter portion) and traveling in the upper right direction by the diffraction grating 8. If the light diffracted into the right direction just hits the right surface of the diffractive refractive optical element 4 at a position corresponding to the center of the black stripe, the shadow due to the black stripe is eliminated. The diffraction angle θ at this time is as follows, where t is the thickness of the diffractive refraction optical element, and d is the width of the black stripe (upward direction in FIG. 3).

Tan θ = (d / 2) / t = d / 2t, and θ in the expression 5 is an angle at which the diffraction grating diffracts light. Θ determined in this way is determined by the grating interval χ of the diffraction grating. When the incident wavelength is λ, from the Bragg equation,

６ sin θ = λ From Equation 5, sin θ = d / (4t ²
+ D ² ) ^1/2 , substituting this into “Equation 6” gives

Equation 7] ^{χ = 2λ (t 2 + d} 2/4) 1/2 / d , and the in accordance with the "Number 7", blue, green, or red color difference of a wavelength λ of the optical filter portion of the color The grating spacing of the corresponding diffraction grating will be changed. The width of the area where the diffraction grating is formed may be theoretically the same as the width d of the optical filter of each color. However, when the alignment is performed with the optical filter of the liquid crystal panel, the light incident due to a shift is generated. If there is a portion where is not diffracted, the effect of eliminating the black stripe is impaired. Therefore, it may be manufactured to be slightly wider than the width of the optical filter portion.

Next, the specifications of the refraction surface on the exit side of the diffractive refraction optical element 4 will be described. As shown in FIG. 3, the two refraction surfaces 9 and 10 are located at positions corresponding to the respective optical filter units of the liquid crystal panel 3, and centered on the optical axis of each optical filter unit.
The cross section has a mountain-shaped cross-sectional shape formed symmetrically.
The angle of the refraction surface corresponding to each slope of the mountain with respect to the vertical direction of the diffractive refraction optical element 4 is ξ, the refractive index of the material of the diffractive refraction type optical element 4 is n, and the angle of diffraction by the diffraction grating is θ. Then, as shown in FIG. 4, since the refracting surface is inclined with respect to the diffractive refraction optical element 4, the angle of incidence of the diffracted light on the refracting surface is not θ, but ξ−θ. Since the angle of outgoing light perpendicular to the element 4 is ξ with respect to the normal to the refraction surface, applying Snell's equation for refraction between different media gives

## EQU8 ## n × sin ({−θ) = 1 × sin}. Here, the refractive index n of the material is a constant determined by the material, and the diffraction angle θ is determined by the specifications of the filter of the liquid crystal panel and the thickness t of the diffractive refraction type optical element 4. ξ is required.

In the above description, it is not specified whether the diffraction is performed in the vertical direction of the screen or in the horizontal direction. In any case, since it is an explanation of eliminating only the black stripe in one direction, when the black stripe exists only in one of the vertical direction and the horizontal direction, the above-described diffractive refraction type optical element is used. If it does, it will be enough. For example, when there is a black stripe only in the vertical direction, diffraction is performed only in the horizontal direction,
The refracting surface may correspond to it. When the black stripes are in two directions, the up-down direction and the left-right direction, the above-described diffractive refraction type optical elements can be formed in two types for the left-right direction and the up-down direction, and used in an overlapping manner. In some cases, the pitch and thickness of the stripes may be different between the horizontal and vertical directions. In this case, two types of diffractive refraction optical elements with different diffraction angles θ and refraction surface angles ξ are manufactured. To use.

If two types (= 2) of the diffractive optical elements are used, there is a loss of light and there is a disadvantage in view of the brightness of the screen. If you want to make the black stripe invisible in any of the up and down directions, make two types of diffraction grating grooves perpendicular to the diffraction grating surface, and use one diffraction grating surface to transmit light in the horizontal direction and up and down. It is preferable to use a diffraction grating that diffracts in two directions. As for the refracting surfaces, each of the two refracting surfaces corresponding to the one optical filter section described above is further divided into four as shown in FIG. , 13, and 14 as one set and correspond to one optical filter unit. Reference numeral 15 denotes an optical axis.
However, since the production of the mold becomes complicated, the diffractive refraction optical element is formed with only a refraction surface having a function of aligning light diffracted in one direction, for example, in the left-right direction, in the other direction, and in other directions, For example, a separate refraction sheet having a function of aligning the light diffracted in the vertical direction in parallel may be manufactured and used repeatedly.

The formation of the diffraction grating and the refraction surface on both sides of one sheet is based on the light transmittance.
The production efficiency by hot press etc. is good, but it is also possible to form it in separate sheets,
And parallel light by refraction of diffracted light in the vertical direction and parallel light by refraction of diffracted light in the left and right direction are all separate sheets, and each of up to four sheets has its own role. It can also be done.

[0020]

EXAMPLE A diffractive / refractive optical element (element thickness 1 mm, refractive index 1.5) for a liquid crystal panel having a black stripe width of 100 μm and a filter opening width of 100 μm was produced as follows. (Preparation of Diffraction Grating Surface Type) A glass dry plate coated with a photoresist (Microposit 1350, manufactured by Shipley Co., Ltd.) was prepared, and a mask having only a blue portion of a liquid crystal color filter opened was brought into close contact. An argon laser having a wavelength of 488 nm is used as a light source, and the optical path is divided into two by a half mirror. Then, an interference fringe is exposed on a photoresist on a glass dry plate at an interference angle of 3.1 ° so that a grid interval becomes 9 μm. did. Subsequently, a mask having an opening only in the green portion of the color filter for liquid crystal was brought into close contact with the mask, and interference fringes were exposed at an interference angle of 2.5 ° so that the lattice spacing became 11 μm. Lastly, a mask having an opening only in the red portion of the color filter for liquid crystal is brought into close contact with the mask, and an interference angle of 2.2 ° is set so that the lattice spacing is 13 μm.
Exposed the interference fringes. After three exposures, development was performed with a predetermined developing solution (Microposit Developer, manufactured by Shipley Co., Ltd.), and diffraction gratings having different grating intervals were formed in portions corresponding to each of the blue, green, and red colors. Then, a prototype of the diffraction grating surface of the diffraction refractive optical element of the present invention was obtained, and subsequently, a stamper of the diffraction grating surface was manufactured by nickel plating.

(Preparation of Refraction Surface Type) On a stainless steel plate having a thickness of 10 mm, the angles corresponding to B (blue), G (green), and R (red) of the color filters are 9 ° and 7, respectively. V-shaped grooves of 5 ° and 6.6 ° are formed by a cutting machine so that the pitch of the grooves is 200 μm (= the sum of the width of the black stripe and the width of the filter opening). A surface stamper was made. (Production of Diffractive Refraction Type Optical Element) On both sides of a polycarbonate sheet (1 mm thick) having no birefringence, the above-described stamper of the diffraction grating surface and the stamper of the diffraction grating surface are aligned and set. And heated to 200 ° C.
Heat embossing was performed at a pressure of 0 atm to obtain a diffractive refractive optical element of the present invention.

[0022]

According to the first aspect of the present invention, by combining the liquid crystal panel with the liquid crystal panel, the light of each filter is once diffracted and then parallelized again. The light exits only from the black stripe portion and no light exits from the black stripe portion, but the ratio of the area from which light exits can be increased.

According to the second aspect of the present invention, since the lattice interval is determined according to the width of the black stripe, light can be emitted from the entire surface of the diffractive refractive optical element including the portion corresponding to the black stripe.

According to the third aspect of the present invention, the grating interval χ of the diffraction grating is determined by the width d of the corresponding black stripe of the liquid crystal panel, the wavelength λ of the incident light, and the thickness t of the optical element. Even if the thickness of the element changes, there is an advantage that the lattice spacing is determined by calculation.

According to the fourth aspect of the present invention, the black stripe on the projected image, which cannot be solved by the conventional liquid crystal projector, can be made thin.

According to the fifth aspect of the present invention, the black stripe on the projected image is eliminated.

According to the sixth aspect of the present invention, the grating interval χ of the diffraction grating is determined by the width d of the corresponding black stripe of the liquid crystal panel, the wavelength λ of the incident light, and the thickness t of the optical element. Even if the thickness of the element changes, the grid spacing is determined by calculation, so even if there is a change in the specifications of the liquid crystal panel, the specifications of the optical element can be changed by calculation and the data on the projected image can be configured, Black stripes can be eliminated.

[Brief description of the drawings]

FIG. 1 is a diagram showing the concept of the present invention.

FIG. 2 is a diagram showing the principle of the present invention.

FIG. 3 is a diagram showing a cross section of a diffractive refractive optical element according to the present invention.

FIG. 4 is a diagram showing a refraction surface of the diffractive refraction optical element of the present invention.

FIG. 5 is a diagram showing another embodiment of the refraction surface.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Light source 2 Condensing lens 3 Liquid crystal panel 4 Diffractive refraction type optical element 5 Projection lens 7 Black stripe 8 Diffraction grating 9, 11-14 Refraction surface 15 Optical axis

Claims (6)

[Claims] 1. A liquid crystal panel having a black stripe is used in combination with a position corresponding to an optical filter except a black stripe on the side facing the liquid crystal panel.
A transmissive diffraction grating having a function of diffracting + 1st and -1st order incident light from the liquid crystal panel. The transmissive diffraction grating is located at a position where adjacent diffracted lights on the opposite side to the liquid crystal panel intersect. A diffractive refraction optical element having a refraction surface having a function of refracting light diffracted by a diffraction grating into outgoing light parallel to the incident light. 2. The diffractive refractive optical element according to claim 1, wherein a grating interval of the transmission type diffraction grating is determined according to a width of a corresponding black stripe portion. 3. The grating interval １ of the transmission type diffraction grating is represented by the following “Equation 1”, where d is the width of the corresponding black stripe portion, λ is the wavelength of incident light, and t is the thickness of the diffractive optical element. The diffractive refraction optical element according to claim 2, characterized by: [Number 1] ^{χ = 2λ (t 2 + d} 2/4) 1/2 / d 4. A light source for projection, a light-collecting optical system for condensing light emitted from the light source for projection and illuminating a liquid crystal panel, and a black stripe surrounded by black stripes, A liquid crystal panel for receiving light from the optical system for condensing light and outputting color image light corresponding to a video signal; and a screen for filtering light from the liquid crystal panel. A projection optical system for projecting the light onto the liquid crystal panel, and a diffractive refractive optical element on the light exit side of the liquid crystal panel, wherein the diffractive refractive optical element is directed toward the liquid crystal panel. A transmission type diffraction grating having a function of diffracting + 1st and -1st order incident light from the liquid crystal panel at a position corresponding to the optical filter section excluding the black stripe section, and opposite to the liquid crystal panel. Side adjacent A liquid crystal projector having a function of refracting light diffracted by the transmission type diffraction grating into outgoing light parallel to the incident light at a position where the diffracted lights intersect. 5. The liquid crystal projector according to claim 4, wherein a grating interval of the transmission type diffraction grating is determined according to a width of a corresponding black stripe portion. 6. The grating interval の of the transmission type diffraction grating is given by the following “Equation 2”, where d is the width of the corresponding black stripe portion, λ is the light wavelength of the company, and t is the thickness of the diffractive refractive optical element. 6. The liquid crystal projector according to claim 5, wherein the liquid crystal projector is determined. [Number 2] ^{χ = 2λ (t 2 + d} 2/4) 1/2 / d