JP3271686B2 - Illumination device and illumination method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to illuminating an illuminated object using divergent light from a point light source or the like, in which a hologram is provided between the light source and the illuminated object to make the light intensity on the illuminated object uniform. The present invention relates to an illumination method and an illumination device that are capable of illuminating an illuminated object at a predetermined angle.

[0002]

2. Description of the Related Art Conventionally, when a liquid crystal panel is illuminated by a backlight system, as shown in FIG. 8, a fluorescent lamp 1 is provided with a transparent diffusion plate 2 having an uneven diffusion surface 2a formed on its surface by a light guide. And a method of illuminating the liquid crystal panel 3 with diffused light emitted from the transparent diffuser plate 2. However, in general, in a modulation element using liquid crystal,
When the angle of incidence of the incident light is inclined with respect to the liquid crystal surface, the rotation angle of the polarization plane slightly shifts. Therefore, when the liquid crystal panel 3 is illuminated with the diffused light as shown in FIG. There is a problem that the contrast of the image to be obtained is reduced.

In order to solve such a problem, the liquid crystal panel 3
It is desirable that the illumination light be incident on the liquid crystal surface at a constant angle (normally perpendicular to the liquid crystal surface) and in parallel. Therefore, as shown in FIG. 9, it is conceivable to combine a light source 4 that emits divergent light, such as a point light source, and a lens 5 so that a parallel light beam having a uniform wavefront is incident on the liquid crystal panel 3. However, combining the light source 4 and the lens 5 as shown in FIG. 9 increases the space of the entire lighting device, and is not practical.

FIG. 1 shows an illuminating device capable of causing illumination light to enter the liquid crystal panel 3 at a fixed angle.
As shown in FIG. 0, the light source 4 that emits divergent light and the transmission hologram 6 are combined, and the diffused light emitted from the light source 4 is transmitted and diffracted by the transmission hologram 6, so that the illumination light has a predetermined angle with respect to the liquid crystal panel 3. (Japanese Patent Laid-Open Publication No. Hei 4-303822) is known. According to such a device, it is possible to reduce the size of the lighting device to some extent.

[0005]

However, FIG.
In the illuminating device shown in (1), when the light source 4 and the hologram 6 are arranged close to each other in order to reduce the size of the illuminating device, the amount of incident light increases in a portion near the light source 4 on the hologram 6 surface. The amount of incident light is small at a portion distant from the light source 4, and unevenness in the amount of light occurs on the hologram 6 surface.
Therefore, it is not possible to illuminate the liquid crystal panel 3 with a uniform light amount, and the liquid crystal panel will have uneven brightness. FIG. 11 is a schematic diagram of such a state, in which the light source 4
The intensity of the light beam L emitted from is represented by the interval between lines indicating the light beam L. As described above, the light beam L is dense at a portion near the light source 4 on the hologram 6 surface, and conversely, the light beam L is sparse at a portion far from the light source 4.

Here, in order to reduce the unevenness in the amount of light,
It is conceivable that the diffraction efficiency in a portion near the light source and having a large amount of light on the surface of the hologram 6 is intentionally reduced, and the light amount in a portion close to the light source and a portion far from the light source are made equal.

However, lowering the diffraction efficiency is not preferable because energy of the light source is wasted. Further, when a light control film is provided on the back of the liquid crystal panel to regulate the incident angle of the light illuminating the liquid crystal panel 3, most of the light transmitted through the hologram part whose diffraction efficiency has been reduced is reduced by the light control film. Since it is absorbed by the film and converted into thermal energy, it raises the temperature of the liquid crystal panel and its surroundings, causing a misalignment of the liquid crystal. In order to prevent such an unnecessary rise in temperature, it is necessary to provide a cooling mechanism. However, the installation of the cooling mechanism is not preferable because the apparatus becomes complicated and the size becomes large.

An object of the present invention is to solve the above-mentioned problems of the prior art. In the case where a liquid crystal panel is illuminated by a backlight system, or when any other illuminated object is illuminated, the object to be illuminated can be provided. An object of the present invention is to enable illumination light to be incident at a predetermined angle, to make the amount of illumination light uniform without wasting energy of a light source, and to reduce the size of the illumination device.

[0009]

The present inventor uses a light source that emits divergent light such as a point light source, and controls the incident angle of illumination light using a hologram, and further controls the light amount distribution using a separate hologram. As a result, it has been found that the above object can be achieved, and the present invention has been completed.

That is, the present invention comprises a light source that emits divergent light, a first hologram that diffracts light from the light source, and a second hologram that further diffracts light diffracted by the first hologram. Consists of a hologram that equalizes the light intensity on the second hologram surface,
The second hologram is provided by a hologram that diffracts light in a predetermined direction.

Further, the present invention uses a light source that emits divergent light, diffracts light emitted from the light source with a first hologram, and further diffracts light diffracted with the first hologram with a second hologram.
An illumination method for diffracting light with a hologram, wherein the first hologram makes the light intensity on the second hologram surface uniform, and the second hologram diffracts light in a predetermined direction. I do.

When illumination is performed using such an illumination device of the present invention or in accordance with the method of the present invention, the divergent light emitted from the light source is diffracted by the first hologram, whereby the second hologram is formed. The incident light is incident on the surface with a uniform light amount (that is, uniform light intensity), and the incident light is diffracted in a predetermined direction by the second hologram. It is possible to illuminate with a light quantity distribution.

The first hologram and the second hologram used in the illumination device or the illumination method of the present invention may be transmission holograms for transmitting and diffracting incident light, and reflection holograms for reflecting and diffracting incident light. May be. Whichever type of hologram is used, the first hologram can equalize the amount of light incident on the second hologram, and the second hologram can adjust the angle of light illuminating the object to be illuminated. .

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the drawings. In each of the drawings, the same reference numerals represent the same or equivalent components.

FIG. 1A is a schematic diagram of a case where the lighting device of the present invention is configured as a backlight of a liquid crystal panel 3. As shown in the figure, this illumination device includes a light source 4, a first hologram 7 of a transmission type that diffracts light from the light source 4, and a first hologram 7.
And a transmission type second hologram 8 that further diffracts the light transmitted and diffracted by the hologram 7. In the figure, the intensity of the light beam L emitted from the light source 4 is represented by the interval between the lines indicating the light beam L. FIG. 1B is an explanatory diagram of the pitch of the diffraction grating of the first hologram of the illumination device of FIG. 1A.

In this illumination device, it is preferable to use a light source 4 that emits diffused light with a size similar to a point light source or a point light source. Thus, the light transmitted through the second hologram 8 can be diffracted in a predetermined direction and can have a uniform light amount distribution. Examples of the light source 4 include a white light source having a relatively small diameter such as a tungsten lamp, a halogen lamp, and a krypton lamp, a chromatic light source such as a light emitting diode, a semiconductor laser, a solid-state laser, and a gas laser. Laser light source and the like can be used.

Further, in this illumination device, the first hologram 7 is used to eliminate illumination unevenness when the light transmitted and diffracted through the second hologram 8 illuminates the liquid crystal panel 3.
The second hologram 8 is provided to make the light amount distribution uniform on the surface. That is, when such an illumination device including a light source and a hologram is constituted by the light source 4 and the second hologram 8 without providing the first hologram 7, the conventional illumination device described with reference to FIG. As described above, on the surface of the second hologram 8, the amount of incident light increases in a portion close to the light source 4, and the amount of incident light decreases in a portion distant from the light source 4. Therefore, in this lighting device, in order to eliminate such light amount unevenness,
The light amount distribution is corrected by the first hologram 7. More specifically, for example, as shown in FIG. 1B, a diffraction grating of a portion of the first hologram 7 that transmits and diffracts light incident on a portion of the surface of the second hologram 8 far from the light source 4. 7a per pitch (Δdf /
df)

[0018]

## EQU1 ## The pitch of the diffraction grating 7b in the portion for transmitting and diffracting the light incident on the portion near the light source 4 on the surface of the second hologram 8 is more than [Δdf / df = | df + 1-df | / df]. Change per pitch (Δdn / dn)

[0019]

## EQU2 ## [.DELTA.dn / dn = | dn + 1-dn | / dn] is increased.

When the unevenness of the light quantity on the second hologram 8 is eliminated by adjusting the pitch of the diffraction grating of the first hologram 7, the light quantity on the second hologram 8 is more strictly controlled. Fig. 2
The iterative method of the flow shown in FIG. That is, first,
When the first hologram 7 does not exist, the light source 4
The complex amplitude distribution of the light emitted from the second hologram 8 is calculated by Fresnel transformation (step A). Next, assuming that the amplitude component of the obtained complex amplitude distribution on the surface of the second hologram 8 is constant (step B), the complex amplitude distribution on the first hologram 7 is obtained by performing inverse Fresnel transformation. (Step C). Then, the obtained amplitude component of the complex amplitude distribution on the first hologram 7 is replaced with the amplitude when the first hologram 7 is actually irradiated by the light source 4 (step D), and the Fresnel transform is performed again. To obtain a complex amplitude distribution on the second hologram 8 (step E). Then, if the obtained unevenness of the amplitude component of the complex amplitude distribution on the second hologram 8 surface is equal to or less than the desired level,
At this time, the diffraction grating of the first hologram 7 may be designed, and when the unevenness of the amplitude component exceeds the expected level, the steps B to B are repeated until the unevenness of the amplitude component becomes lower than the expected level. Repeat E.

According to such an iterative method, the uniformity of the amplitude on the second hologram 8, that is, the uniformity of the light amount can be achieved in consideration of the unevenness of the light amount depending on the light source 4. Lighting can be obtained.

FIG. 1 shows an on-axis hologram in which the optical axis does not change before and after the diffraction as the first hologram 7, but the optical axis changes before and after the diffraction as the first hologram 7. Off-axis holograms may be used. Also in this case, as in the case of the first hologram 7, similarly to the above, the change amount per pitch of the pitch of the diffraction grating of the portion that diffracts the light incident on the portion of the surface of the second hologram 8 far from the light source 4 ( Δdf / df)

[0023]

## EQU3 ## As compared with [.DELTA.df / df = | df + 1-df | / df], per unit pitch of the diffraction grating pitch of a portion transmitting light incident on a portion near the light source 4 on the second hologram 8 surface. (Δdn / dn)

[0024]

## EQU4 ## The one having a large value of .DELTA.dn / dn = | dn + 1-dn | / dn may be provided.

In FIG. 1, the first hologram 7 is arranged perpendicular to the optical axis of the light source 4. However, in the present invention, the inclination of the first hologram 7 with respect to the optical axis of the light source 4 is not particularly limited.

Therefore, the first hologram 7 may be constituted as an on-axis hologram arranged so as to be parallel to the optical axis of the light source 4 as shown in FIG. 3, for example. As shown in FIG. 4, the first hologram 7 may be configured as an off-axis hologram arranged so as to be parallel to the optical axis of the light source 4.

The method for producing the first hologram 7 is as follows.
A diffraction grating is patterned on an electron beam resist using an electron beam lithography apparatus, and the formed pattern is hot-pressed on a transparent plate (for example, a polycarbonate plate or an acrylic plate) using a known pattern duplication stamper. Or
The resin may be formed by pressing and irradiating a radiation-curable resin that is cured by radiation such as ultraviolet rays and electron beams. Also,
The first hologram 7 may be manufactured by a laser beam drawing apparatus, a photograph reduction method, a two-beam interference method using a laser, or the like. Further, once the first hologram 7 is manufactured, the hologram may be copied in a large amount by an embossing method, an etching method, or the like. In the present invention, a hologram copied in this manner can also be used.

As described above, in the illustrated apparatus of the present invention, a transmission hologram is provided as the first hologram 7, but a reflection hologram may be used.

Further, the first hologram 7 is described in which the unevenness of the light amount on the second hologram 8 is eliminated by adjusting the pitch of the diffraction grating.
In the present invention, the present invention is not limited to this. For example, a diffuser hologram or the like can be used as the first hologram 7.

Next, the second hologram 8 of the illumination device of FIG. 1 will be described. The second hologram 8 transmits and diffracts the light from the first hologram 7 in a direction perpendicular to the surface of the liquid crystal panel 3 and into a parallel light flux.

The second hologram 8 can be manufactured by a two-beam interference method as shown in FIG. That is, first,
The interference fringes of the reproduced light L1 of the first hologram 7 produced as described above and the light L2 having a uniform intensity and a uniform wavefront are recorded on the photosensitive material 9 as a hologram. For this purpose, for example, as shown in the figure, light emitted from a laser light source 10 is split by a half mirror 11 and one of them is used by a lens 12 as a light source for a reproduction light L1 of the first hologram 7. Then, the other light may be collimated by a lens 13 having a large diameter into parallel light, and this may be used as light L2.

Here, as the photosensitive material 9, for example, a silver salt photosensitive resin, a photoresist or the like can be used.

Next, the exposed photosensitive material 9 is developed according to a conventional method. Thereby, the second hologram 8 can be obtained.

The second hologram 8 may be manufactured by using an electron beam drawing apparatus, a laser beam drawing apparatus, or the like, instead of using the two-beam interference method. Similarly to the first hologram 7, the second hologram 8 may be produced once, copied in large quantities by an embossing method, an etching method, or the like, and the duplicated hologram may be used.

The second hologram 8 is not limited to a transmission hologram but may be a reflection hologram.

As described above, in the illustrated illuminating device, the lighting device is preferably used as a backlight of a liquid crystal panel.
The light transmitted and diffracted through the second hologram 8 is transmitted to the liquid crystal panel 3
Although the light beam is made to be a parallel light beam which is vertically incident on the illumination device, the illumination device of the present invention is not limited to this. If necessary, the light transmitted and diffracted through the second hologram may be converted into a parallel light flux in an arbitrary predetermined direction, or may be converted into divergent light or convergent light.

For example, when the illumination device of the present invention is used for an OHP projector, the light diffracted by the second hologram 8 may be converged as shown in FIG. In the illumination device of FIG. 6 as well, similarly to the illumination device shown in FIG. 1, the first hologram 7 corrects the light amount distribution of the light emitted from the light source 4 and converts the light having the corrected light amount distribution to the first light. The hologram 8 is made to enter the hologram 8. And the second
The hologram 8 changes the direction of the light incident on the second hologram 8 so that the light converges in the imaging lens 14. The light whose direction has been changed by the second hologram 8 passes through the OHP document 15 and enters the imaging lens 14. Next, this light is reflected by the mirror 16, and the original 15 is placed on the screen 17 by the effect of the imaging lens 14.
Is formed.

The image on the screen 17 obtained in this manner is a bright image with no unevenness.

The configuration similar to that of the illumination device shown in FIG. 6 can be used for an optical system of an imaging system such as a slide projector.

On the other hand, when the illuminating device of the present invention is used for illuminating a hologram, as shown in FIG. 7, the light transmitted and diffracted by the second hologram 8 is transmitted to the hologram 18 to be illuminated. The light may be incident as a parallel light beam having a predetermined incident angle. Thus, by using the illuminating device of the present invention as the hologram illuminating device, a reproduced image 19 of the hologram can be obtained with uniform brightness. Further, the size of the lighting device can be reduced.

Although FIG. 7 shows the case where the illumination device of the present invention is used as a transmission type hologram illumination device, the illumination device of the present invention is also used as a reflection type hologram illumination device. be able to.

[0042]

According to the present invention, when the liquid crystal panel is illuminated by the backlight system, the illumination light is made incident on the illuminated object at a predetermined angle, and the energy of the light source is not wasted. In addition, it is possible to make the amount of illumination light uniform and to further reduce the size of the illumination device.

[Brief description of the drawings]

FIG. 1 is a schematic diagram (FIG. 1A) of an illumination device of the present invention and an explanatory diagram (FIG. 1B) of a pitch of a diffraction grating of a first hologram.

FIG. 2 is a flowchart of a method for determining a pitch of a diffraction grating of a first hologram.

FIG. 3 is a schematic view of another embodiment of the lighting device of the present invention.

FIG. 4 is a schematic view of another embodiment of the lighting device of the present invention.

FIG. 5 is an explanatory diagram of a method for producing a second hologram.

FIG. 6 is a schematic view of another embodiment of the lighting device of the present invention.

FIG. 7 is a schematic view of another embodiment of the lighting device of the present invention.

FIG. 8 is a schematic diagram of a backlight of a conventional liquid crystal panel.

FIG. 9 is a schematic view of another embodiment of the backlight of the conventional liquid crystal panel.

FIG. 10 is a schematic diagram of another embodiment of the backlight of the conventional liquid crystal panel.

FIG. 11 is an explanatory diagram of a light quantity distribution of a backlight of a conventional liquid crystal panel.

[Explanation of symbols]

 Reference Signs List 3 liquid crystal panel 4 light source 5 lens 6 hologram 7 first hologram 8 second hologram 9 photosensitive material 10 laser light source

Claims (8)

(57) [Claims] 1. A light source that emits divergent light, a first hologram that diffracts light from the light source, and a second hologram that further diffracts light diffracted by the first hologram. An illumination device comprising a hologram for equalizing light intensity on a second hologram surface, wherein the second hologram comprises a hologram for diffracting light in a predetermined direction. 2. The lighting device according to claim 1, wherein the light source is a point light source. 3. The second hologram surface has a variation in pitch per pitch of a diffraction grating constituting the first hologram, compared with a portion of the second hologram surface that diffracts light incident on a portion far from the light source. The lighting device according to claim 1, wherein a portion that diffracts light incident on a portion close to the light source is large. 4. A second hologram is provided on the back surface of the liquid crystal panel to illuminate the liquid crystal panel by a backlight system, and light diffracted from the second hologram becomes a parallel light beam, and is provided at a predetermined angle on the back surface of the liquid crystal panel. The illumination device according to any one of claims 1 to 3, wherein the light is incident on the illumination device. 5. A light source that emits divergent light, wherein the light emitted from the light source is diffracted by a first hologram, and
An illumination method for diffracting light diffracted by the first hologram further by the second hologram.
An illumination method characterized in that the light intensity on the hologram surface is made uniform and light is diffracted in a predetermined direction by the second hologram. 6. The lighting method according to claim 5, wherein a point light source is used as the light source. 7. As a first hologram, a change amount of a pitch of a diffraction grating constituting the hologram per pitch is:
7. The illumination according to claim 5, wherein a portion of the second hologram surface that diffracts light incident on a portion of the second hologram surface that is closer to the light source is larger than a portion of the second hologram surface that diffracts light of the portion closer to the light source. Method. 8. The liquid crystal panel according to claim 5, wherein the second hologram is provided on the back surface of the liquid crystal panel, and the light diffracted by the second hologram is converted into a parallel light beam and incident on the back surface of the liquid crystal panel at a predetermined angle. The lighting method according to 1.