JP2005084171A - Transparent directional screen capable of performing color display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a directional screen by which a color image can be observed while objects behind the screen is clearly observed with a hologram screen capable of preventing a color change caused depending on an observing position due to the use of a diffraction phenomenon which results in difference in diffraction angle between colors (wavelength), although the hologram screen is enabled to optionally set an extent (view extent) where a projection image can be seen while objects behind the screen can be seen through in a screen portion which is not projected. <P>SOLUTION: A hologram 11 on which a diffusing extent is recorded and which has no or a little wavelength selectivity is disposed on the observer side. A hologram 12 on which three primary colors are recorded at determined angles and which has wavelength selectivity is disposed on the back of the hologram which has no or a little wavelength selectivity. An angle for eliminating a diffraction angle difference caused by the wavelength of the hologram which has no or a little wavelength selectivity is recorded on the hologram which has wavelength selectivity. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention relates to a directional screen that diffuses light that forms a projected image only in a specific range.

The directional screen not only increases the light utilization efficiency but also limits the observation range, thus preventing peeping. In addition, different images can be displayed depending on the observation position by performing a plurality of projections. By utilizing this fact, different images (parallax images) corresponding to both eyes are projected on the directional screen, and the observation range corresponding to each eye is observed, so that a stereoscopic image can be observed without wearing glasses. it can.
Aiming for a more directional screen with a higher sense of presence, we set three specific objectives. The first is that the back of the screen can be seen through in the unprojected screen part, and the second is that the range (viewing zone) where the projected image can be seen is clearly divided and can be set arbitrarily by the recording method, three The color of the image seen by the eye does not change depending on the observation position. The reason for the first purpose is that if the unprojected screen portion is transparent and the back surface is seen through, the image is observed as if it is floating in the air, and the presence is increased. The reason for the second purpose is that if the viewing zone is not clearly divided, it is possible to look at a plurality of images at different positions, or the images may be seen twice or not at all. In particular, when performing stereoscopic display, the quality of the stereoscopic image is greatly involved. The reason for the third purpose is optimally the hologram screen that can fulfill the first and second purposes. However, because the hologram screen uses the diffraction phenomenon, the diffraction angle differs depending on the color (wavelength) and the observation position. Will change the color.

As a feature of the hologram screen, it has a feature that can fulfill the above two specific purposes. I will explain that.
Explain that the viewing area can be clearly defined and set arbitrarily. In the first place, the range (viewing zone) where the image of the screen can be observed is a region where all the light on the screen is collected. What is necessary is just to record with a hologram so that it may act like that with respect to such projection light. If light from a region (diffuser plate) that can diffuse light in all directions is converted into a real image by a lens, light can reach from any point from the lens at one point on the real image. In such a hologram screen on which object light is recorded, when the light for projecting the image is irradiated as reproduction illumination light, the image can be seen only in the real image portion of the diffusion plate. Since the reproduced light does not reach from other positions, the image cannot be seen.
Explain that the back is transparent. A hologram does not diffract all rays. Therefore, part of the light from the back surface is transmitted without being diffracted. As a result, the background on the back of the screen can be clearly presented. In other words, an image that can be seen floating in the space can be presented by seeing through the back. In an optical element using refraction, such as a lens, all the light from the back surface is affected and the magnification changes or looks blurry, and the back surface cannot be seen as it is. Further, when a directional screen is used for stereoscopic display, there is a possibility that fatigue during stereoscopic viewing can be reduced without being aware of the diffusing surface.

However, a problem when the hologram screen is used as a directional screen is a color due to a difference in observation position. As described above, since the hologram screen uses the diffraction phenomenon, the diffraction angle differs depending on the color (wavelength), and the color changes depending on the observation position. For example, when projecting obliquely from below, red light having a long wavelength and easily diffracted is observed only at a low position, and blue projection light having a short wavelength and difficult to diffract can be observed only at a high position.

Therefore, there are two possible methods for solving this problem. The first is to arrange holograms having wavelength selectivity in multiple recording or multiple layers. When determining the diffusion region, a complex grating corresponding to the diffusion range is recorded in the hologram. When reproducing with white light, a wavelength different from the design may be diffracted at a different angle, or the diffracted light may be diffracted by a grating for another wavelength. Therefore, scattering and noise increase and crosstalk occurs.
The other is a method in which micro-holograms having wavelength selectivity are arranged on a two-dimensional matrix, as known from Patent Document 1 (Japanese Patent Laid-Open No. 2002-148717). In this case, crosstalk does not occur. However, in this case, the size (resolution) of the pixel corresponding to the wavelength is determined by the size of the hologram array, and a high-definition image cannot be observed.

As known from Patent Document 2 (Japanese Patent Laid-Open No. 9-73133), a screen using a plurality of holograms having wavelength selectivity is considered. In this case, the aim is to increase the light efficiency, and the transparency of the screen cannot be obtained.
JP 2002-148717 A JP-A-9-73133

The present invention solves the problems of the directional screen device associated with the prior art described above. According to the present invention, the transparent screen has directivity capable of limiting the observation range, and the display can be arbitrarily limited and the display on the back of the screen can be observed as it is in the unprojected portion. In addition, there is no change in the color of the image that can be seen depending on the viewing position on the color expressible screen.
That is, an object of the present invention is to provide a directional screen capable of clearly observing the back of the screen and observing a color image.

In order to achieve the above object, the present invention
Claim 1 comprises a front hologram and a rear hologram,
The pre-hologram has the function of limiting the diffusion range with little or no wavelength selectivity, and is installed on the observation surface side.
The post hologram is a wavelength selective hologram that is recorded in multiple wavelengths at multiple wavelengths, and has a function of converting the diffraction angle to an angle that can eliminate the difference in diffraction angle due to the wavelength of the front hologram. It has the characteristic installed in.

Moreover, in Claim 2, it consists of a front hologram and a back hologram,
The pre-hologram has the function of limiting the diffusion range with little or no wavelength selectivity, and is installed on the observation surface side.
The post hologram is a set of a plurality of holograms each having different wavelength selectivity, and has a function of converting the hologram into an angle that can eliminate the difference in diffraction angle due to the wavelength of the front hologram. It has the characteristic of being installed in multiple layers.

Further, the third aspect of the present invention is the post-hologram corresponding to a plurality of different projection angles.

Further, according to a fourth aspect of the present invention, the front hologram is recorded by a surface relief hologram having a high light efficiency.

According to the first aspect of the present invention, it is possible to provide a directional screen capable of clearly observing the back of the screen and observing a color image.
According to the invention of claim 2, in addition to the effect of the invention of claim 1, the light efficiency of the front hologram can be increased and the light efficiency of the screen can be increased.
According to the invention of claim 3, in addition to the effect produced by the invention of claim 1 or claim 2, different parallaxes can be given in the vertical direction.
According to the invention of claim 4, in addition to the effects of the inventions of claims 1 to 3, it is possible to increase the optical efficiency of the post hologram and increase the optical efficiency of the screen.
According to the invention of claim 5, in addition to the effects of the inventions of claims 1 to 4, it is possible to realize a screen capable of providing parallax over the entire circumference using a rotary projection optical system.

The configuration of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing a schematic configuration of a directional screen according to the present invention. The directional screen includes a front hologram 11 and a rear hologram 12. The front hologram 11 is installed on the projection surface side, and the rear hologram 12 is installed on the observation surface side.
The front hologram 11 has an action of setting the viewing zone A by a recording method described later. This hologram is of a nature with little or no wavelength selectivity. When a color image (video) is projected onto a hologram screen that can determine the viewing zone A, the viewing zone A can be reproduced at the recording wavelength, but at different wavelengths, the viewing zone is created at different locations, and the color of the image changes depending on the observation position. End up. Therefore, the post hologram 12 has an action of converting to an angle that eliminates the pre hologram 11. The post hologram 12 is recorded using a hologram having wavelength selectivity so that light having a wavelength diffracted by the post hologram 11 overlaps the viewing zone set when diffracted by the front hologram 11. The post hologram 12 becomes a directional screen capable of observing a color image without changing its color by recording at least three primary colors by wavelength multiplexing.
Further, since the screen is constituted by the hologram optical element, the screen is transparent and the background can be seen through. That is, with such a configuration, it is possible to realize a directional screen in which the viewing zone can be freely set, the hue does not change in the viewing zone, and the background of the screen can be clearly seen.
The propagation of light from the projection light on this screen will be described with reference to FIG. The projection light is projected at an angle of θ2 from the position C so that it does not directly enter the eyes of the observer. This angle θ2 is designed from the observation position and the projection distance. In the post hologram 12, three holograms of RGB are recorded, and each hologram is a hologram having wavelength selectivity. Reproduction lights Rr, Gr, and Br having different angles for RGB are generated immediately after the front hologram 12. The diffracted lights Rr, Gr and Br of the front hologram enter the rear hologram 11 at respective diffraction angles. (Reproduced light comes out on the side of the observation surface, but in FIG. 1, each reconstructed light is drawn at the rear of the hologram so that the angle of diffraction can be seen schematically.) The projection light of the three wavelengths is diffracted at almost the same angle as the post hologram 11 since the diffraction is performed at the angle. For this reason, the viewing zone can be set at the same position, and no color change occurs within the viewing zone.

The role of the front hologram 12 will be described.
As the front hologram 12, a hologram having wavelength selectivity is used. A hologram having a thick hologram thickness with respect to a grating interval, such as a (reflective) hologram in which diffracted light emerges on the incident light side, has high wavelength selectivity. Therefore, wavelength selectivity can be obtained even with a transmission hologram by increasing the thickness of the hologram with respect to the grating interval. If a hologram with wavelength selectivity is prepared corresponding to the three primary colors, a color image can be observed. In this method, multiple recording may be performed, or multiple recordings may be arranged separately.
Since the pre-hologram 12 serves only to convert the angle into an angle corresponding to the wavelength, the grating is simple. If there is wavelength selectivity when the incident angles are equal, no diffraction occurs at different wavelengths and crosstalk does not occur.

The design of the diffraction angle will be described.
In the hologram, part of the light is transmitted as it is. If the light from the projector is seen through as it is, it becomes light unrelated to the image and disturbs observation. If the light diffracted by the front hologram 12 is seen as it is, it will interfere with the observation of the image. Therefore, the projection light is projected at a turning angle, and the design is made so that the transmitted light does not directly enter the observer's eyes. Also, the diffraction by the front hologram is designed so that the light directly transmitted without being diffracted by the post hologram does not enter the eyes of the observer. For this purpose, the projection light is projected from the bottom to the top, diffracted greatly by the post hologram, and light transmitted through the post hologram as it is goes down. (Conversely, the projection light may be projected from the top to the bottom, and the diffracted light may be diffracted upward.)
That is, it is designed so that the diffracted light of the preceding hologram or the projected light that passes through the screen as it is escapes upward and downward at the assumed observation distance. In FIG. 1, the projection angle θ <b> 1 and the diffraction angle θ <b> 2 may be designed so that the light that is transmitted as it is does not enter the observation range. θ1 can be designed by the projection distance and the observation distance. At this time, θ2 is designed using the diffraction angle of the longest wavelength among the design wavelengths because light having a longer wavelength is more difficult to bend.

The directional screen will be described.
The directional screen 1 refers to a screen that diffuses light of the entire screen only in a specific range with reference to the projected optical axis. Figure 2 shows the concept of a directional screen. When an eye is placed in the viewing area A, which is a range diffused by the directional screen, the projected image can be observed, and when it is out of the viewing area A, the projected image cannot be observed.
By using the directional screen, it is possible to perform stereoscopic display by putting different images in the left and right eyes without the need for glasses. FIG. 3 is a diagram for explaining stereoscopic display using a directional screen. The left eye projector 4b and the right eye projector 4a project images corresponding to the left and right eyes, respectively. Then, an image for the right eye can be observed only in the viewing zone A, and similarly, an image for the left eye can be observed only in the viewing zone B. By doing so, a stereoscopic display device can be made using a clean screen.
At this time, if the back surface of the screen can be seen as it is, the presence of the screen hardly affects the stereoscopic vision. Therefore, it is possible to reduce a sense of incongruity when performing stereoscopic display.

The hologram screen will be described. A hologram has a feature that allows a recorded light wave to be reproduced as it is. FIG. 4 is a diagram for explaining a method of photographing a hologram screen. The light from the diffusing plate 60 is converted into a real image A1 by the lens 110. By installing a hologram dry plate between the lens 110 and the real image A1, hologram exposure can be performed by simultaneously irradiating the reference light R in which the light from the lens becomes the object light O. As for the object light O, all the light on the hologram dry plate 11 is collected at any point on the real image A1. FIG. 5 is a diagram for explaining the use of a hologram screen. When the projection light of the image is irradiated as the reproduction illumination light C on the dry plate 11 which has been subjected to necessary processing and becomes a hologram, the light diffused from the entire screen comes only to the real image portion A2 of the diffusion plate. So, the projected image can be seen in the viewing area (real image area of the diffuser), and since the regenerated light does not reach from other positions, it can act as a directional screen that cannot see the image. .

The wavelength selectivity of the hologram will be described. A hologram having a sufficiently thick hologram with respect to the grating provides wavelength selectivity. FIG. 6 is a diagram for explaining wavelength-selective hologram recording. This is a schematic diagram for recording a hologram on a hologram material that is sufficiently thicker than the lattice spacing to be recorded. Arrow O represents one wavelength of object light recorded on the hologram, and arrow R represents one wavelength of reference light. The intensity distribution is caused by the overlapping of the light waves. This is the hologram recording.
FIG. 7 is a diagram for explaining the reproduction of a hologram with wavelength selection. When the illumination light C1 is incident on the interference fringes at the same wavelength and the same angle as the reference light, it is diffracted by the recorded interference fringes and the same light as the object light is emitted. At this time, since the hologram is thick, diffracted light does not come out unless the angle of interference and strengthening is almost the same as the object light.
FIG. 8 is also a diagram for explaining the reproduction of a hologram with wavelength selection. Even if the wavelength is exactly the same, if the angle of the reproduction light C2 is different, it does not interfere with the interference fringes and no diffracted light is emitted. This is angle selectivity. Similarly, if the reproduction light C3 incident at the same angle has different wavelengths, interference does not occur and diffracted light does not appear.

However, even at different wavelengths, diffraction occurs even in a wavelength-selective hologram if it is incident at an angle that interferes with the grating. FIG. 9 is a diagram for explaining the reproduction of a wavelength-selective hologram using different wavelengths. Even with gratings recorded at different angles of different wavelengths, interference occurs and diffraction occurs when the angle exactly matches the interference fringes as in the reproduction light C4.
This is why crosstalk occurs when a wavelength-selective hologram screen is made of RGB colors and installed in multiple layers. The grid that sets the viewing zone is recorded by mixing various grids. For this reason, conditions occur at other wavelengths and diffraction occurs, and multiple observations do not make the observation range as designed.

If this is used, it is shown that even if the wavelength of the photosensitive material is not sensitive, recording can be performed with a simple grating. By calculating the grating of the desired wavelength and calculating the angle at the recording wavelength for that purpose, recording can be performed regardless of the desired hologram recording wavelength.

Next, the reproduction of a hologram with little or no wavelength selectivity will be described. 10 and 11 are diagrams for explaining a hologram with little or no wavelength selectivity. A hologram 11 with little or no wavelength selectivity has a thin hologram. For this reason, the hologram is diffracted and interferes in the air rather than in the hologram. Therefore, diffraction occurs when the phase difference between the gratings of the incident light and the phase difference between the gratings of the reproduction light are equal to the wavelength. That is, when the reproduction light C2 of another wavelength is incident at the same angle as shown in FIG. 11 on the hologram 11 diffracted by the reproduction light C1 of a certain wavelength as shown in FIG. 10, diffraction occurs at a different angle. When reproducing with white light mixed with various wavelengths, the diffraction angle is different for each wavelength, so it can be split into seven colors.

The relationship as shown in Equation 1 is established for the diffraction angle of a hologram having no or little wavelength selectivity.

図12は波長選択性のない若しくは少ないホログラムの生成を説明する図である。数1は傾きφで波長λcの再生光C1が格子間隔ｄのホログラムに入射したとの回折角θを表している。格子間隔ｄ離れた光との光路差が波長と同じ長さになると回折した光が干渉しその方向に光を強めあう。その角度θは入射側の位相差と回折した後の位相差により求まり数1が導ける。（光エレクトロニクス151ページ参照（大越孝雄著、コロナ社、昭和57出版））

FIG. 12 is a diagram for explaining the generation of a hologram with little or no wavelength selectivity. Formula 1 represents the diffraction angle θ when the reproduction light C1 having the inclination φ and the wavelength λc is incident on the hologram having the grating interval d. When the optical path difference from the light separated from the grating distance d becomes the same length as the wavelength, the diffracted light interferes and intensifies the light in that direction. The angle θ is obtained from the phase difference on the incident side and the phase difference after diffraction, and the number 1 can be derived. (See page 151 of Optoelectronics (written by Takao Ohkoshi, Corona, Showa 57))

光エレクトロニクス32ページ（大越孝雄著、コロナ社、昭和57出版）にあるように物体光の入射角θo、参照光の入射角θｒ波長λｗで記録されるホログラムの格子間隔ｄは数2によって求められる。これは角度の違う参照光と物体光の位相がホログラム平面上のそろった点が格子となるために導ける。数2を数1に代入することで数3が得られる。

As shown on page 32 of optoelectronics (Takao Ohkoshi, Corona, Showa 57 publication), the grating interval d of the hologram recorded with the incident angle θo of the object light and the incident angle θr wavelength λw of the reference light can be obtained by Equation 2. . This can be derived because the point where the phase of the reference beam and the object beam at different angles is aligned on the hologram plane is a grating. Substituting Equation 2 into Equation 1 yields Equation 3.

この式より入射角に対する各波長の回折角θを計算することができる。この式より、波長の長い赤はよく曲がり、波長の短い青はあまり曲がらないということがわかる。
記録した波長でなくとも物体光の角度θoと同じ角度で回折する投影光の入射角度φは数3を変形することによって数4と書き直せる。この入射角度φで前置ホログラムを照明すれば視域を設計位置に重ねることができる。

From this equation, the diffraction angle θ of each wavelength with respect to the incident angle can be calculated. From this equation, it can be seen that red with a long wavelength bends well and blue with a short wavelength does not bend very much.
Even if it is not the recorded wavelength, the incident angle φ of the projection light diffracted at the same angle as the object light angle θo can be rewritten as Equation 4 by transforming Equation 3. If the front hologram is illuminated at this incident angle φ, the viewing zone can be overlapped with the design position.

視域がスクリーンサイズに対して小さい場合、若しくは観察距離が十分遠いときには視域の中心とスクリーンの中心を結んだ線分とスクリーン面の角度をθoとして1つに代表できる。このとき、視域に対する角度はスクリーン上のどの点でもほぼ等しいと考えられる。
例えば、参照光の入射角度θｒが30°で視域の角度θoがほぼ0度だとする。そのとき、記録波長が青色の488nmであるとする。このとき0度に回折するのは488nmだけとなってしまう。前置ホログラムによって他の色（例えば赤633nm、緑532nm）の再生照明角θ、を再生されて出てきて欲しい角度φ（=0度）とすれば赤色（633nm）なら40°と、緑色（532nm）なら33°と計算できる。この角度で回折する前置ホログラムを設置すればよい。（青色は30度のままでよいので30の角度で回折する前置ホログラムがあればよい）

When the viewing area is small with respect to the screen size, or when the observation distance is sufficiently long, the angle between the line segment connecting the center of the viewing area and the center of the screen and the screen surface can be represented as θo. At this time, the angle with respect to the viewing zone is considered to be almost equal at any point on the screen.
For example, it is assumed that the incident angle θr of the reference light is 30 ° and the viewing angle θo is approximately 0 degrees. At this time, it is assumed that the recording wavelength is blue, 488 nm. At this time, only 488 nm is diffracted at 0 degree. If the reproduction illumination angle θ of other colors (for example, red 633 nm, green 532 nm) is reproduced by the front hologram and the desired angle φ (= 0 degree) is output, red (633 nm) is 40 °, green ( 532nm) can be calculated as 33 °. A pre-hologram that diffracts at this angle may be installed. (The blue color can be kept at 30 degrees, so a front hologram that diffracts at an angle of 30 is sufficient.)

A description will be given of a shift in the viewing zone due to a difference in wavelength due to a hologram having no or little wavelength selectivity. FIG. 13 is a diagram for explaining a change in color depending on the observation position of the hologram screen using a hologram with little or no wavelength selectivity. As described above, the diffraction angle varies depending on the wavelength, and the viewing zone recorded on the hologram screen can be varied depending on the wavelength. The viewing zone where the red component of the image projected from C1 onto the hologram screen 11 can be seen is the Ri region. Similarly, the viewing zone in which the green component can be observed is Gi, and the viewing zone in which the blue component can be seen is Bi. At this time, the projected wavelengths are continuously present, so that a continuous viewing zone is formed, but only three primary colors are schematically shown in the figure. In this way, only the red component can be seen in the portion of Ri that protrudes upward, and only the blue component can be seen in the portion of Bi that protrudes downward. In the hologram screen created by the hologram having no wavelength selectivity, the color changes depending on the observation position. At this time, diffraction occurs even at wavelengths other than RGB, and each real image can be continuously formed. As a result, a wavelength that cannot be observed is born depending on the observation position, and the color changes.

A description will be given of selecting only a representative wavelength by a hologram having wavelength selectivity. Normally, RGB light output from a projector is output at a wavelength having a width. Therefore, even in a region where the color does not change in the viewing area designed for each single RGB wavelength (the part where RGB overlaps in Fig. 13), wavelengths shorter than blue or longer than red do not overlap. It can be a cause of change. By selecting only the design wavelength by the post hologram, it is possible to suppress the color change at the observation position.

The position where this hologram forms an image will be described. The position of the real image of the diffuser that becomes the viewing zone differs depending on the wavelength. Although it is possible to analyze the hologram fringes by Equation 3, it is difficult, so it is possible to calculate where the object to be reproduced is imaged according to the position of the recorded object, the position of the reference light, and the position of the reproduction light. The hologram imaging position is a position determined by Equation 5 to Equation 7, as shown on 100 pages of holography (written by Junpei Uchiuchi, Hankabo, 1997). λc is a reproduction illumination wavelength, λw is a writing wavelength, R is a distance from the hologram, x is a horizontal position, and y is a vertical position. The subscript O represents object light, R represents reference light, I represents reproduced light, and C represents illumination light for reproduction.

FIG. 14 is a diagram for explaining that the color change is eliminated by separating the illumination according to the wavelength. By separating the wavelength and changing the position of the reproduction illumination light as shown in Equations 5 to 7, the position of the viewing zone can be almost overlapped. As a result, it is possible to reduce the color change due to the observation position and crosstalk when a plurality of viewing zones are arranged.
Regenerative lighting is used at a projection angle to avoid transmitted light directly entering the eye. Therefore, it is projected. Therefore, when recording on the hologram screen, the reference light and the object light are recorded corresponding to the turning projection. Therefore, the angle in the vertical direction is mainly recorded in the hologram, and the color change also occurs in that direction. Therefore, the color change can be eliminated by changing the vertical angle. (Number 1 which is the condition of the angle in the vertical direction corresponds to number 7)

Further, it is conceivable that the reproduction position of the diffusing surface real image by the hologram differs depending on the reproduction wavelength only by adjusting the angle, which may cause crosstalk. (This may not affect much, but the effect varies depending on the size of the screen and the viewing zone.) The illumination projection light (projection light diffracted from the post hologram) at the time of reproducing the front hologram is Since it can design for every wavelength, it can design for every wavelength so that the diffused surface real image position to reproduce | regenerate may be united. The projection light diffracted from the post hologram can be designed so that the real image position of the diffusion surface of Formula 5 is matched. Two examples of the method for adjusting the imaging position of the diffusing surface real image will be described.
The first is a method in which the reference light of the front hologram is converged and converged from the hologram at a position equidistant from the viewing zone and recorded. When the object light distance Ro (real image distance of the recorded diffuse scattering surface) of the front hologram is equal to the convergence distance Rr of the reference light to be recorded, the right side of Equation 5 is zero, and the imaging position at the time of reproduction is the recording wavelength. No longer depend on it. At this time, in order to make the imaging positions of the front holograms equal at the respective wavelengths, the convergence distances Rc of the illumination projection lights of the respective wavelengths may be made equal. Therefore, in this case, the post hologram is recorded so that the light waves to be reproduced of the respective wavelengths converge at the equidistant position and the solution position of Formula 7 that eliminates the vertical shift caused by the tilt projection.
The second is a method in which the reference light of the front hologram is recorded as parallel light, and the imaging position of the viewing zone is adjusted by changing the divergence (convergence) position of the post hologram according to the wavelength. The divergence position of the reference light becomes infinity and can be ignored in Equation 5. By doing so, Equation 5 can be transformed and Equation 8 can be derived so that the real image positions of the diffused surfaces recorded on the hologram are equal. That is, this equation is obtained from Equation 5 from the condition of Ri = Ro and Rr = ∞. When the value is negative, it is sufficient to use light that converges Rc on the observation surface side.

このとき、後置ホログラムを回折する光波の発散（収束）位置は数8より求められる距離で煽り投影による垂直方向のずれを解消する数7の解の位置に収束するように記録する。
このように後置ホログラムを照明する前置ホログラムで回折した光を最適化することによって、ほぼ各波長の視域が重なり設計どおりの視域と視域間のクロストークを削減することができる。

At this time, the divergence (convergence) position of the light wave diffracting the post hologram is recorded so as to converge to the position of the solution of Expression 7 that eliminates the vertical shift due to the turning projection at the distance obtained from Expression 8.
Thus, by optimizing the light diffracted by the front hologram that illuminates the post hologram, the viewing zones of the respective wavelengths are almost overlapped, and crosstalk between the viewing zones as designed can be reduced.

There are two types of pre-holograms: multiple recording at each wavelength on a wavelength-selective hologram and a method of stacking holograms recorded at each wavelength in multiple layers. FIG. 15 is a diagram for explaining the reproduction of a multilayered wavelength selective hologram. The diffraction efficiency of one layer can be increased by using multiple layers.
FIG. 16 is a diagram for explaining reproduction of a wavelength-selective hologram that has been multiplexed and recorded. Multiplexing simplifies recording and reduces the thickness of the hologram support.

Further, the present invention is not limited to a full-color image, and can also be considered as a monochrome image. It can also be implemented as a screen capable of selectively observing only a single wavelength by selecting the wavelength with a post hologram. By doing so, it is possible to increase the contrast of the light transmitted from behind the transparent screen and make it easier to see.

As a variation of the first embodiment, a reflective screen can be considered. By using a reflection hologram as a post hologram, it can be used as a reflection directional screen. Originally, a reflection hologram has a wavelength selectivity with a narrow lattice interval with respect to the thickness of the hologram. However, since the light projected onto the post hologram passes through the front hologram, there is a possibility that crosstalk occurs due to the light diffracted by the front hologram. FIG. 17 is a diagram for explaining the reproduction of a wavelength-selective reflection hologram recorded in a multiplexed manner. Corresponding to the front hologram, each wavelength of RGB is reflected at the same position as the rear hologram, and diverging light of each wavelength is applied from the position of Rc, Gc, Bc, and the light from C which is the projection position is used as reference light Multiple reflection holograms are recorded. Then, when projected from the recorded hologram front C, RGB is reproduced from different positions, the RGB viewing areas of the front hologram are bulky, and a reflective directional screen with no color change is obtained.
In addition, there is a method in which the front hologram is first recorded in order to reduce the crosstalk of the front hologram, and is recorded in the same manner as when the rear hologram is used as a screen. By recording in this way, the light diffracted by the front hologram also becomes the reference light. By doing so, even the light diffracted by the front hologram at the time of reproduction is diffracted in a predetermined direction, leading to reduction of crosstalk.
Further, a method of multilayering hologram recording is also conceivable.

In holograms with wavelength selectivity, the angle and the diffracted wavelength are related, and if the vertical projection angle, which is the main diffraction angle, changes, it will not function as designed. On the other hand, the deviation of the angle in the horizontal direction does not greatly affect. Therefore, in the horizontal direction, the projection angle can be changed and used as a stereoscopic display system as described in FIG.
However, it is also possible to add parallax by shifting in the vertical direction. A plurality of front holograms may be prepared corresponding to the vertical direction. For holograms that do not meet the conditions, the efficiency is not reduced because it is only transmitted. A method of multiple recording is also conceivable in consideration of the convenience of the screen.

  The surface relief grating can record holograms by refraction and diffraction of the medium surface. Therefore, the wavelength selectivity is small depending on the depth of the relief, and the diffraction efficiency can be increased. Therefore, a directional screen with high light efficiency can be realized by using the surface relief grating for the post hologram.

  Different directivities can be recorded depending on the screen position. In a display hologram, called a holographic stereogram, the visible image can be changed depending on the observation position by changing the recording position and recording a two-dimensional image. Using this method, a rotationally symmetric screen can be created, and the directivity can be changed depending on the projection position. By doing so, it is possible to realize a video display device that can observe different images at different locations without rotating the screen if the projection light is rotated. Further, by arranging the viewing area without interruption, the amount of information can be controlled and an image can be displayed all around.

The figure explaining the outline of the directional screen of this invention Diagram explaining directional screen The figure explaining the three-dimensional display using a directional screen The figure explaining the imaging method of a hologram screen Diagram explaining use of hologram screen The figure explaining the recording of the hologram with wavelength selectivity The figure explaining reproduction of a hologram with wavelength selectivity The figure explaining reproduction of a hologram with wavelength selectivity A diagram for explaining the reproduction of a wavelength-selective hologram at different wavelengths The figure explaining the reproduction of a hologram with little or no wavelength selectivity The figure explaining the reproduction of a hologram with little or no wavelength selectivity The figure explaining the reproduction of a hologram with little or no wavelength selectivity The figure explaining the color change by the observation position of a hologram screen The figure explaining eliminating the color change by separating the illumination according to the wavelength Diagram illustrating the reproduction of a multilayered wavelength selective hologram The figure explaining reproduction | regeneration of the hologram with wavelength selectivity which carried out multiple recording A diagram for explaining the reproduction of a wavelength-selective reflection hologram recorded in a multiplexed manner

Explanation of symbols

1 Directional screen
11 Pre-hologram
12 Post hologram
110 lenses
4 projector groups
41a, 41b Light source
42a, 42b spatial modulator
43a, 43b projection lens
60 Diffuser
A, B, A2 viewing zone
A1 Real image of diffuser
O Object light
R Reference beam
C, C1, C2, C3, C4 Reproduction illumination light (divergence position)
Gi Green light viewing zone
Ri Red light viewing area
Bi Blue light viewing area
Gc Green light illumination projection light divergence position
Rc Red light illumination projection light divergence position
Bc Blue light illumination projection light divergence position
Gr Green light reference light of pre-hologram
Rr Reference light of red light in front hologram
Br Blue reference light of the front hologram

Claims (5)

It consists of a pre-hologram and a post-hologram, and the pre-hologram is installed on the observation surface side with the function of limiting the diffusion range with little or no wavelength selectivity, and the post-hologram is recorded in multiple wavelengths at multiple wavelengths. A directional screen with the characteristic that it is installed on the back side of the front hologram with each recorded wavelength having the function of converting the diffraction angle to the angle that can eliminate the difference in diffraction angle due to the wavelength of the front hologram. It consists of a pre-hologram and a post-hologram, and the pre-hologram is installed on the observation surface side with the function of limiting the diffusion range with little or no wavelength selectivity, and each post-hologram has different wavelength selectivity. A directional screen with the characteristic that it is installed in multiple layers on the back side of the pre-hologram, which has the function of converting the diffraction hologram to an angle that can eliminate the difference in diffraction angle due to the wavelength of the pre-hologram in a set of multiple holograms . The directional screen according to claim 1, further comprising a post hologram corresponding to a plurality of different projection angles. The directional screen according to claim 1, wherein the front hologram is recorded by a surface relief hologram having high light efficiency. Claims having a directivity characteristic that varies depending on the position by forming any one of a cylinder, a cone, a hemisphere, and other rotationally symmetric surfaces formed around the axis of symmetry, and changing the position to multiplex-record the hologram. 5. The directional screen according to any one of 1 to 4.

Images