JP2003057652A - Picture display device, illuminator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a picture display device and an illuminator having a diffractive optical element which can obtain uniform illuminance over a wide region to incident light having a large wavelength band such as white light and can provide a high quality picture without lowering a contrast. SOLUTION: In the picture display device having a reflection type display part, a light transmission plate in which a diffraction grating is formed on one surface and a front light optical system including a light transmission plate, the diffraction conditions of a light transmission plate can be set so that diffraction efficiency is high to incident light and the diffraction efficiency is low to light from a reflection type display part by forming a first transparent layer having a refractive index different from that of a light transmission plate along the diffraction grating. That is, the lowering of the contrast is prevented. Illuminating light is efficiently transmitted to the reflection type display part, and a picture with high uniformity is provided over the whole area of a wavelength band.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image display device and an illuminating device having a light guide plate having a diffractive optical element for guiding illuminating light to a reflective display portion.

[0002]

2. Description of the Related Art In portable information terminals such as mobile phones and PDAs, in consideration of visibility and low power consumption, external light such as sunlight is used to illuminate in a bright place, and from a built-in light source in a dark place. In many cases, a reflection type display unit is used in which the light of (1) is guided to the surface of the display unit by a light guide plate for illumination.
As one form of a light guide plate which is an illumination member provided in such a reflective display unit, a diffractive optical element is provided on the surface opposite to the display unit so that ambient light is transmitted and guided to the display unit. , Having a structure in which illumination light from a light source portion incident from an end portion of the light guide plate is guided to a display portion by diffracting it by a diffractive optical element, and light modulated and reflected by the display portion is transmitted and guided to a user. There is something. For example, in Japanese Patent Application No. 2000-376169, as shown in FIG. 13 (a), the light guide plate 5b has a period equal to or shorter than the wavelength of the incident light in the direction along the path of the incident light which is indicated by the arrow 1b. However, there is proposed an image display device C in which a diffractive optical element having a saw-tooth shape whose cross-sectional shape is a right triangle (hereinafter, abbreviated as a right triangle blazed diffractive optical element). By using the right-angled triangular blazed diffractive optical element, the image light is not scattered, and deterioration of the image quality due to scattering such as blurring, deterioration of contrast, and uneven brightness can be avoided. Moreover, since the period of the diffraction grating is extremely small, the period is not visually recognized, and moire fringes do not occur in any image. Therefore, it is disclosed that a high-quality image can be provided in an image display device in which illumination light is modulated by a displayed image to produce image light.

[0003]

In the above conventional image display device C, the diffractive optical element for supplying the illumination light to the reflective display section 4b gradually reflects the incident light 1b while gradually diffusing it from the diffraction grating 15b. Since it is a structure that allows the light to pass through, the incident angle of the incident light 1b on the light guide plate becomes a problem in order to uniformly supply the illumination light over the entire area of the reflective display unit 4b. For example, as shown in FIG. 13B, when the incident light 1b is incident at an angle smaller than a predetermined incident angle, a region near the light source is illuminated brightly and a region far from the light source is darkened. Conversely, FIG.
When the incident light 1b is incident at an incident angle larger than a predetermined incident angle as in (c), the far area is illuminated brightly and the area near the light source becomes dark. That is, incident light 1
Depending on the incident angle of b, a bright and dark area is formed in the reflective display section, and the brightness of the illumination light is not uniform over the entire reflective display section. When illuminating the color display part, the illumination light of different wavelength bands is used. If the incident angle is different for each wavelength band of the incident light, the bright and dark depending on the incident angle for each wavelength band. Area is formed, and the hue of the illumination light is not uniform over the entire reflective display section. Therefore, in order to make the brightness and color of the illumination uniform over the entire reflective display portion, the incident angle of the incident light needs to be strictly adjusted over the entire wavelength band. However, the diffraction efficiency of the diffraction grating in the blazed diffractive optical element used in the above-described conventional image display device C exhibits characteristics depending on the wavelength of incident light, so that the diffractive optical element is not affected by white light or the like. When incident light having a wide wavelength width is incident at the same incident angle, the hue of the illumination light may not be uniform over the entire display portion depending on the wavelength band. Considering the case where white light including a wide wavelength range is incident on the right-angled triangular blazed diffractive optical element at the same incident angle, the component of light that deviates from the wavelength dependence of the blazed diffractive optical element is considered. Therefore, it is impossible to provide a high-quality image because the reduction of contrast due to unnecessary diffracted light that is reflected without being subjected to regular diffraction is significantly observed particularly in the short wavelength region. In addition to the image display device, the object and the imaging optical system are composed of a microscope or the like in which the distance between the object and the optical system is short due to the short focal length of the optical system, or a large number of imaging optical systems corresponding to minutely divided objects Although a thin illumination device is required even in the observation or imaging optical system of a scanner or the like having a small distance, it is possible to obtain high-quality illumination without unevenness over the entire subject due to the above-mentioned problems. No device was present. Therefore, the present invention has been made in view of the above circumstances, and an object thereof is to obtain uniform illuminance over a wide region even for incident light having a wide wavelength band such as white light. Another object of the present invention is to provide an image display device or an illumination device equipped with a diffractive optical element capable of providing a high-quality image without deterioration in contrast.

[0004]

In order to achieve the above object, the present invention comprises a reflective display section, a light guide plate having a diffraction grating formed on one surface, and a front light optical system including the light guide plate. In this image display device, the first transparent layer having a refractive index different from that of the light guide plate is formed along the diffraction grating, and the image display device is configured. With such a configuration, the diffraction condition of the light guide plate is set so that the diffraction efficiency for incident light is high and the diffraction efficiency for light from the reflective display unit is low.
That is, it is possible to prevent the contrast from being lowered, and it is possible to efficiently guide the illumination light to the reflective display unit, while providing an image with high uniformity over the entire wavelength band.

Further, the first transparent layer may be formed on the surface of the light guide plate which faces the reflective display portion. With such a configuration, the light guide plate can be configured as a transmissive diffractive optical element, which is a structure for guiding the -1st order transmitted light in the diffraction grating as the illumination light to the reflective display unit.

Further, the first transparent layer may be formed on the surface of the light guide plate opposite to the reflective display portion. With this configuration, it is possible to provide a structure that guides the −1st order reflected light in the diffraction grating as the illumination light for the reflective display unit.

A second transparent layer having a refractive index different from that of the light guide plate may be formed on the surface of the light guide plate on the side facing the reflective display portion. Since the second transparent layer is formed of a material having a refractive index lower than that of the light guide plate, it is possible to totally reflect incident light incident at an arbitrary angle less than the critical angle, and thus the reflective display unit. The illumination light can be efficiently supplied to the.

Further, the light guide plate may be closely attached to the reflective display section. With such a configuration, it is possible to reduce the thickness of the image display device as a whole.

Further, the light guide plate may form an optical member of the reflection type display section. By being configured in this way,
The overall thickness of the image display device can be reduced.

Further, a cylindrical lens array may be formed between the light guide plate and the reflection type display section. With this configuration, the diffracted light emitted at different diffraction angles for each wavelength band is converged in the same direction, and the incident angle of the diffracted light on the reflective display unit is made the same direction over the entire wavelength band. This makes it possible to provide high-quality images with little color shift over the entire wavelength band.

Further, it is desirable that the difference between the refractive index of the light guide plate and the refractive index of the first light guide plate is 0.05 or more and less than 0.3. With such a configuration, the ratio (S /
The N ratio) can be set to 0.02 or less, and an image with high contrast can be provided over the entire wavelength band.

Further, the shape of the diffractive optical element may be an asymmetric blazed shape with respect to the normal direction of the surface on which the diffraction grating is formed. With such a configuration, it is possible to cause diffraction of a specific order with respect to incident light, and it is possible to provide a high-quality image.

The width of the incident angle of the incident light may be constant over the entire wavelength band. With such a configuration, the above-described image forming apparatus can be configured without a method for injecting incident light at an incident angle different for each wavelength band or a new member.

Further, in a lighting device comprising a light guide plate having a diffraction grating formed on one surface and a front light optical system including the light guide plate, a first transparent layer having a refractive index different from that of the light guide plate is provided. , And is formed along a diffraction grating as a lighting device. With this configuration, it is possible to set the diffraction conditions of the light guide plate so that the diffraction efficiency for incident light is high and the diffraction efficiency for light from the illuminated portion is low, and the illuminated portion is evenly distributed. It can be illuminated uniformly.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments and examples of the present invention will be described below with reference to the accompanying drawings to provide an understanding of the present invention. It should be noted that the following embodiments and examples are merely examples embodying the present invention and are not of the nature to limit the technical scope of the present invention. 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention, FIG. 2 is a ray tracing diagram of a transmission type diffractive optical element, and FIG. 3 is a ray tracing of a reflection type diffractive optical element. 4 and 5 are configuration diagrams of a thin image display device using a transmissive diffractive optical element, and FIG. 5 is a light guide plate using a transmissive diffractive optical element forming an optical member of a reflective display portion. 6 is a block diagram of an image display device, FIG. 6 is a block diagram of a thin image display device using a reflective diffractive optical element,
FIG. 7 is a configuration diagram of an image display device in which a light guide plate using a reflection type diffractive optical element forms an optical member of a reflection type display section,
8 is a configuration diagram in which a cylindrical lens array is applied to a transmissive diffractive optical element, FIG. 9 is a configuration diagram in which a cylindrical lens array is applied to a reflective diffractive optical element, and FIG.
Is a diagram showing the S / N ratio of a transmissive diffractive optical element, FIG. 11 is a diagram showing the S / N ratio of a reflective diffractive optical element, and FIG. 12 is an image formation using a conventional reflective diffractive optical element. FIG. 13 is a schematic configuration diagram of the device, and FIG. 13 is a schematic configuration diagram of an image display device using a conventional transmission type diffractive optical element.

First, an example of the overall configuration of the image display device A according to the embodiment of the present invention will be described with reference to FIG. The image display device A includes a reflective display section 4 and a first transparent layer 6 formed along a diffraction grating 15 formed on the surface of the light guide plate 5 facing the reflective display section 4. The light source unit 14 that supplies illumination light to the reflective display unit 4 is roughly configured to reflect the incident light 1 from the light source unit 14 incident from the end of the light guide plate 5 by diffracting it by the diffraction grating 15. It is an image display device that provides an image to the user by guiding it to the mold display unit 4, modulating it by the reflection display unit 4, and reflecting it. The liquid crystal layer 12 shown in FIG. 4 is used as the reflective display unit 4 in the present embodiment.
A reflection-type liquid crystal display in which the liquid crystal display is sandwiched between the diffuse reflection electrode 13 and the polarizing plate 8 is used.

As a constitutional example of the front light optical system for supplying the illumination light from the front of the reflection type display section 4, the light guide plate 5 is used.
Is used as a transmissive diffractive optical element (FIG. 1 or 2) and as a reflective diffractive optical element (FIG. 3). The difference between the two configurations will be described. When the diffraction grating 15 is arranged so as to face the reflective display section 4 as shown in FIG. 1 or 2, it becomes a transmissive diffractive optical element, which is emitted from the light source unit 14 and totally reflected inside the light guide plate 5. A structure in which the −1st-order diffraction is generated in the incident incident light 1 in the diffraction grating 15 and is transmitted through the first transparent layer 6 to be incident on the reflective display unit 4, and the transmitted diffracted light 2 is visually recognized as image light. Become. On the contrary, when the rear surface of the surface of the light guide plate 5 on which the diffraction grating 15 is formed faces the reflective display unit 4 as shown in FIG. 3, it becomes a reflective diffractive optical element.
Incident light 1 that travels through the light guide plate 5 while being totally reflected from the light source unit 14 causes -1st-order reflection in the diffraction grating 15 and is incident on the reflection type display section 4, and the reflected diffraction light 3
Will be visually recognized as image light. As an index for evaluating the quality of the image light, it is preferable to use the S / N ratio calculated by the ratio of the image light and the unnecessary diffracted light, but in the case of a transmission type diffractive optical element, the image light is the transmitted diffracted light. 2, the unnecessary diffracted light is the reflected diffracted light 3, and conversely, in the case of the reflection type diffractive optical element, the image light is the reflected diffracted light 3 and the unnecessary diffracted light is the transmitted diffracted light 2. Generally, if the contrast of the image light is 10 or more, it is considered that the S / N ratio is good.
The ratio is preferably 0.02 or less.

The setting of the light guide plate for guiding the incident light 1 to the reflection type display section 4 by causing the incident light 1 to be diffracted and supplying a high quality image to the user will be described below. Here, FIG. 10 shows a light guide plate 5 having a first transparent layer 6 formed thereon.
Is a transmissive diffractive optical element, and shows the results of calculating the S / N ratio for each wavelength band under various conditions when incident light having a wide wavelength width is incident. Table 1 shows the results. It is a diffraction grating condition. Further, FIG. 11 shows the calculation of the S / N ratio for each wavelength band when the light guide plate 5 formed with the first transparent layer 6 is used as a reflection type diffractive optical element and incident light having a wide wavelength width is incident. Table 2 shows the diffraction grating conditions used in the calculation.

The shape of the diffraction grating 15 formed on the light guide plate 5 is a blaze shape, the grating period is Λ, and the aspect ratio is 1. N1 is the refractive index of the light guide plate, n2 is the refractive index of the first transparent layer, and n1 and n
The difference of 2 is represented by Δn. For incident light, the wavelength length is λ, the angle between the incident light and the normal of the diffraction grating is θ, and the angle between the reflected diffracted light and the normal of the diffraction grating is θ ′. The horizontal axis wl / λ in FIGS. 10 and 11 represents the wavelength ratio between the wavelength for which the S / N ratio is calculated as shown in Table 3 and the wavelength used as the reference for setting the diffraction grating. In the above embodiment, the reference wavelength is 550 nm.

[0020]

[Table 1]

[0021]

[Table 2]

[0022]

[Table 3]

First, the setting of the light guide plate 5 when the light guide plate 5 according to the present invention is a transmissive diffractive optical element will be described with reference to FIG. When the difference Δn between the refractive index n1 of the light guide plate 5 and the refractive index n2 of the first transparent layer 6 is 0.2 (thick line), the wavelength ratio (wl / λ) is 0.775 to 0. 8
65 and 0.955 to 1.18, that is, the wavelength λ of the incident light 1 is 425 nm to 475 nm and 525 nm to 6
Under the condition of 50 nm, the S / N ratio is 0.02 or less, so that it is possible to provide an image with high contrast over a wide wavelength band. On the other hand, under conditions where wl / λ other than the above wavelength ratio is 0.865 to 0.955, that is, the wavelength λ of the incident light is 480 nm to 520 nm, the S / N ratio sharply increases and an image with low contrast is obtained. Here, the condition for making the illumination on the reflective display unit 4 white illumination with high color purity is that the S / N ratio is desirably 0.02 or less over the entire wavelength range of the white illumination. However, at least the pure color wavelength of blue, which is the three primary colors of light, is 430 nm (w
1 / λ = 0.775), green pure color wavelength 550 nm (wl
/Λ=1.0), red pure color wavelength 650 nm (wl / λ =
The S / N ratio in each wavelength range of 1.18) may be 0.02 or less. That is, if the contrast of the illumination light incident on the reflective display unit 4 in the pure color wavelength range that constitutes the three primary colors of light can be increased, white illumination with high color purity can be obtained. . Therefore, Δn is 0.
In the case of 2, a wavelength range capable of displaying a high-contrast image (425 nm to 475 nm and 525 nm to 650 n
Since m) includes the pure color wavelength regions of the three primary colors of the light, white illumination with high color purity can be obtained. Also,
Since a wavelength band other than the wavelength bands of the three primary colors of light and causing a decrease in contrast is unnecessary, a filter for cutting the wavelength band is added to the light source unit 14.
Alternatively, by making the light source itself of the light source unit 14 not include the wavelength band in advance, it is possible to obtain a display device having higher color purity. Also, Δn is 0.05, 0.
Also in the cases of 1 and 0.3, the S / N ratio in the pure color wavelength range of the three primary colors of light is approximately 0.
When it is 02 or less, it is possible to increase the contrast of the illumination light incident on the reflection type display unit 4 in the pure color wavelength range that constitutes the three primary colors of light, and obtain white illumination with high color purity. be able to.

Next, the setting of the light guide plate 5 when the light guide plate 5 according to the present invention is a reflection type diffractive optical element will be described with reference to FIG. When the difference Δn between the refractive index n1 of the light guide plate 5 and the refractive index n2 of the first transparent layer 6 is 0.2 (thick line), the wavelength ratio (wl / λ) is 0.775 to 0. 8
90 and 0.990 to 1.18, that is, the wavelength λ of the incident light 1 is 425 nm to 490 nm and 545 nm to 65.
Under the condition of 0 nm, the S / N ratio is 0.02 or less, so that it is possible to provide an image with high contrast in these wavelength bands. On the other hand, wl other than the above wavelength ratio
Under the condition that / λ is 0.890 to 0.990, that is, the wavelength λ of the incident light is 495 nm to 540 nm, the S / N ratio exceeds 0.02, and the image has low contrast. Therefore, in the case of the reflective type as well as the transmissive type, since the pure color wavelength range of the above three primary colors of light is included in the wavelength range capable of displaying an image with high contrast, it is possible to obtain white illumination with high color purity. I know that I can do it. Also in this case, as in the case of the transmissive type, a wavelength band (495 nm to 540 nm) other than the wavelength bands of the three primary colors that causes a decrease in contrast
Is unnecessary, an image display device with higher color purity can be obtained by adding a filter for cutting the wavelength band to the light source unit 14 or by configuring the light source of the light source unit 14 not to include the wavelength band in advance. Can be obtained.

In the present invention, the diffraction grating 1 of the light guide plate 5
Since the first transparent layer 6 is formed on the surface on which 5 is formed, the transmissive light guide plate 5 is adhered to the reflective liquid crystal display B with the first transparent layer 6 as a boundary layer. Can be configured as. This case will be described with reference to FIG.
In the conventional embodiment shown in FIG. 13A, the scratches and stains on the diffraction grating 15b are prevented by providing a space between the light guide plate 5 and the reflective display section 4. Here, in the light guide plate 5 according to the present embodiment, the first transparent layer 6 is formed on the surface on which the diffraction grating 15 is formed as the boundary layer of the close contact, so that the first transparent layer 6 is formed by the diffraction grating. It can be regarded as having a function as a protective layer for preventing scratches, damages, etc. of 15. Further, as shown in FIG. 4, the light guide plate 5 can be closely attached to the reflective liquid crystal display B, and
The image display device A can be made thin.

In another embodiment of the present invention, as shown in FIG. 6, the first transparent layer 6 is formed along the surface of the light guide plate 5 on which the diffraction grating 15 is formed, and the diffraction grating 15 is formed.
The second transparent layer 7 is formed on the surface opposite to the surface on which is formed. In this configuration, the reflective light guide plate 5 can be configured to be in close contact with the reflective liquid crystal display B with the second transparent layer 7 as a boundary layer. In the embodiment shown in FIG. 6, the reflective light guide plate 5 is used as described above. In the conventional image display device using the reflection type light guide plate shown in FIG. 12, since the diffraction grating 15 is exposed to the user side, by providing the protection plate 16, the diffraction grating 15 is provided.
Prevents scratches and dirt. In addition, the diffraction grating 15 of the light guide plate 5 is provided with a space provided between the light guide plate 5 and the reflective display unit 4.
The area adjacent to the surface opposite to the surface on which the
By making the air layer constantly lower than the refractive index n1 of the above, the incident light 1 entering the light guide plate 5 at a critical angle or less is totally reflected. On the other hand, in the reflection-type light guide plate 5 according to the present embodiment shown in FIG. 6, the first transparent layer 6 is formed along the surface of the light guide plate 5 on which the diffraction grating 15 is formed. Similar to the case of the mold, the first transparent layer 6 has a function as a protective layer of the diffraction grating 15. Further, in this light guide plate 5, a second transparent layer 7 is formed on the surface opposite to the surface on which the diffraction grating 15 is formed.
The refractive index n3 of the light guide plate 5 is set to be lower than the refractive index n1 of the light guide plate 5, so that the refractive index n of the light guide plate 5 is adjacent to the rear surface side of the surface on which the diffraction grating 15 is formed.
It is possible to make the value lower than 1 constantly, and it is possible to totally reflect the incident light 1 as in the conventional device shown in FIG. Further, the light guide plate 5 can be formed in close contact with the reflective liquid crystal display B with the second transparent layer 7 capable of forming a thin film as a boundary layer without an air layer interposed therebetween. It can also be made thinner.

Next, in the image display device according to the present invention, the components of the reflection type display section 4 and the first transparent layer 6 are provided.
It is also possible to promote the reduction in thickness of the entire device by combining the above. As shown in FIG. 13A, the conventional reflective display unit 4b needs a transparent material substrate 10 represented by a glass substrate on its surface as a protective layer. On the other hand, in the first embodiment of the present invention shown in FIG.
The first transparent layer 6 is formed on the surface facing to. As described above, since the first transparent layer 6 itself can serve as a protective layer, it can be integrated with the transparent material substrate 10 or can also be used as a common material. The first transparent layer 6 shown in FIG. 5 has a structure that doubles as a transparent material substrate 10 as a constituent element of the reflective display unit 4. In this case, the transparent material substrate 10 is omitted as compared with the case where the transparent material substrate 10 and the first transparent layer 6 are bonded together with the polarizing plate 8 and the retardation plate 9 as the boundary layers as shown in FIG. Minutes,
It is easily understood that the thickness can be significantly reduced.
The polarizing plate 8 and the retardation plate 9 may be formed between the reflective display unit 4 and the light guide plate 5, or may be formed on the surface side of the light guide plate 5 as shown in FIG. . Here, 11 is a color filter, 12 is a liquid crystal layer, and 13 is a diffuse reflection electrode.

The same applies to the reflection type light guide plate 5. 6 and 7 are explanatory views of the reflection-type light guide plate 5. In this case, the transparent material substrate 10 and the light guide plate 5 are in a relationship of being combined or integrated with each other. That is,
When the light guide plate 5 is also used as the transparent material substrate 10 as shown in FIG. 7, compared with the case where the light guide plate 5 and the transparent material substrate 10 are closely joined as separate members as shown in FIG. Since the transparent material substrate 10 is omitted, it is excellent in thinning. The places where the polarizing plate 8 and the retardation plate 9 are provided are the same as those shown in FIGS. 4 and 5.

Finally, referring to FIGS. 8 and 9, the light guide plate 5
A configuration in which a cylindrical lens array is formed between the reflection type display unit 4 and the reflection type display unit 4 will be described. Since the diffraction angle of the diffracted light diffracted by the diffraction grating has wavelength dependence as described above, the transmitted diffracted light 2 diffracted by the diffraction grating 15 is emitted at different diffraction angles for each wavelength band. Therefore, there is a problem that the illumination position on the reflective display unit 4 is deviated for each wavelength for the same light beam. Therefore, by forming the cylindrical lens arrays S1 and S2 as shown in FIGS. 8 and 9 between the light guide plate 5 and the reflective display unit 4, the incident light to the reflective display unit 4 is converged in the same direction. This makes it possible to provide high-quality images with little color shift over the entire wavelength band. Of course, as shown in FIGS. 8 and 9, the first transparent layer 6 or the second transparent layer 7 may be formed in a cylindrical lens array, or a new member formed with the cylindrical lens array may be formed in each transparent layer. It may be configured to be attached to.

[0030]

[Embodiment] In the above-mentioned embodiment, the image display device is constructed by using the illuminating device including the light guide plate according to the present invention, but the present invention is applicable to the illuminating device used for other purposes. You can For example, a subject such as a microscope having a short distance between the subject and the photographing or imaging optical system due to a short focal length of the photographing or imaging optical system, or a large number of imaging optical systems corresponding to minutely divided subjects In a scanner or the like having a short imaging optical system distance, by providing the illuminating device according to the present invention between the object and the photographing or imaging optical system, it is possible to improve the high image quality over the entire object as in the case of applying to the image display device. It is possible to provide quality illumination light.

[0031]

As described above, according to the present invention,
An image display device including a reflective display unit, a light guide plate having a diffraction grating formed on one surface thereof, and a front light optical system including the light guide plate, wherein a first transparent layer having a refractive index different from that of the light guide plate. Is formed along the diffraction grating as an image display device. With this configuration, the diffraction efficiency for incident light is high,
It is possible to set the diffraction condition of the light guide plate so that the diffraction efficiency for the light from the reflective display unit is lowered, that is, it is possible to prevent the contrast from being lowered, and the illumination light is efficiently guided to the reflective display unit. Thus, an image with high uniformity can be provided over the entire wavelength band.

Further, the first transparent layer may be formed on the surface of the light guide plate on the side facing the reflective display portion. With such a configuration, the light guide plate can be configured as a transmissive diffractive optical element, which is a structure for guiding the -1st order transmitted light in the diffraction grating as the illumination light to the reflective display unit.

Further, the first transparent layer may be formed on the surface of the light guide plate opposite to the reflective display portion. Such a configuration can provide a structure that guides the −1st order reflected light in the diffraction grating as the illumination light for the reflective display unit.

Further, a second transparent layer having a refractive index different from that of the light guide plate may be formed on the surface of the light guide plate facing the reflective display portion. Since the second transparent layer is formed of a material having a refractive index lower than that of the light guide plate, it is possible to totally reflect incident light incident at an arbitrary angle less than the critical angle, and thus the reflective display unit. The illumination light can be efficiently supplied to the.

Further, the light guide plate may be closely attached to the reflection type display section. With this configuration, it is possible to reduce the thickness of the image display device as a whole.

Further, the light guide plate may form an optical member of the reflection type display section. With this configuration, it is possible to reduce the thickness of the image display device as a whole.

Further, a cylindrical lens array may be formed between the light guide plate and the reflection type display section. With this configuration, the diffracted light emitted at different diffraction angles for each wavelength band should be converged in the same direction, and the incident angle of the diffracted light to the reflective display section should be the same direction over the entire wavelength band. It is possible to provide high quality images with little color shift over the entire wavelength band.

Further, it is desirable that the difference between the refractive index of the light guide plate and the refractive index of the first light guide plate is 0.05 or more and less than 0.3. With this configuration, it is possible to set the ratio (S / N ratio) of image light and unnecessary diffracted light, which is an index of contrast, to 0.02 or less, and an image with high contrast over the entire wavelength band. Can be provided.

Further, the shape of the diffractive optical element may be an asymmetric blazed shape with respect to the normal direction of the surface on which the diffraction grating is formed. With this configuration, it is possible to generate a specific order of diffraction for incident light,
A high quality image can be provided.

The width of the incident angle of the incident light may be constant over the entire wavelength band. With this configuration, it is possible to configure the above-described image forming apparatus without a method for making incident light incident at a different incident angle for each wavelength band or a new member.

Further, in an illuminating device comprising a light guide plate having a diffraction grating formed on one surface and a front light optical system including the light guide plate, the first transparent layer having a refractive index different from that of the light guide plate is provided. , And is formed along a diffraction grating as a lighting device. With this configuration, it is possible to set the diffraction condition of the light guide plate so that the diffraction efficiency with respect to the incident light is high and the diffraction efficiency with respect to the light from the illuminated portion is low, and the illuminated portion is evenly distributed. Can be illuminated like.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus.

FIG. 2 is a ray tracing diagram of a transmissive diffractive optical element.

FIG. 3 is a ray tracing diagram of a reflective diffractive optical element.

FIG. 4 is a configuration diagram of a thin image display device using a transmission type diffractive optical element.

FIG. 5 is a configuration diagram of an image display device in which a light guide plate using a transmissive diffractive optical element forms an optical member of a reflective display section.

FIG. 6 is a configuration diagram of a thin image display device using a reflective diffractive optical element.

FIG. 7 is a configuration diagram of an image display device in which a light guide plate using a reflective diffractive optical element forms an optical member of a reflective display section.

FIG. 8 is a configuration diagram in which a cylindrical lens array is applied to a transmissive diffractive optical element.

FIG. 9 is a configuration diagram in which a cylindrical lens array is applied to a reflective diffractive optical element.

FIG. 10 is a diagram showing an S / N ratio of a transmissive diffractive optical element.

FIG. 11 is a diagram showing the S / N ratio of a reflective diffractive optical element.

FIG. 12 is a schematic configuration diagram of an image forming apparatus using a conventional reflective diffractive optical element.

FIG. 13 is a schematic configuration diagram of an image display device using a conventional transmission type diffractive optical element.

[Explanation of symbols]

A ... Image display device B ... Reflective liquid crystal display C ... Conventional image display device 1 ... Incident light 1b ... Incident light (conventional image display device) 2 ... Transmitted diffracted light 2b ... Transmitted diffracted light (conventional image display device) 3 ... Reflected diffracted light 4 ... Reflective display 4b ... Reflective display unit (conventional image display device) 5 ... Light guide plate 5b ... Light guide plate (conventional image display device) 6 ... First transparent layer 7 ... second transparent layer 8 ... Polarizing plate 9 ... Retardation plate 10 ... Transparent material substrate 11 ... Color filter 12 ... Liquid crystal layer 13 ... Diffuse reflection electrode 14 ... Light source unit 14b ... Light source unit (conventional image display device) 15 ... Diffraction grating 15b ... Diffraction grating (conventional image display device) 16 ... Protection plate

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G02B 6/00 331 G02B 6/00 331 G09F 9/00 313 G09F 9/00 313 336 336B // F21Y 103: 00 F21Y 103: 00 F term (reference) 2H038 AA55 BA06 2H049 AA03 AA50 AA60 AA63 2H091 FA14Z FA19X FA29X FA41X FD03 FD06 FD07 LA18 5G435 AA02 AA03 BB16 DD09 DD14 EE22 FF02 FF08 GG03 LL0606

Claims (11)

[Claims] 1. An image display device comprising: a reflective display unit; a light guide plate having a diffraction grating formed on one surface; and a front light optical system including the light guide plate. An image display device, wherein a first transparent layer having a different rate is formed along the diffraction grating. 2. The first transparent layer is formed on the surface of the light guide plate on the side facing the reflection type display section.
The image display device according to. 3. The image display device according to claim 1, wherein the first transparent layer is formed on a surface of the light guide plate opposite to the reflective display section. 4. The image display device according to claim 3, wherein a second transparent layer having a refractive index different from that of the light guide plate is formed on a surface of the light guide plate facing the reflective display section. 5. The image display device according to claim 2, wherein the light guide plate is in close contact with the reflective display section. 6. The image display device according to claim 2, wherein the light guide plate forms an optical member of the reflective display section. 7. Between the light guide plate and the reflective display section,
7. The image display device according to claim 1, wherein a cylindrical lens array is formed. 8. The image display according to claim 1, wherein a difference between the refractive index of the light guide plate and the refractive index of the first light guide plate is 0.05 or more and less than 0.3. apparatus. 9. The image display device according to claim 1, wherein the diffractive optical element has an asymmetric blazed shape with respect to a direction normal to a surface on which the diffraction grating is formed. 10. The image display device according to claim 1, wherein the width of the incident angle of the incident light is constant over the entire wavelength band. 11. A lighting device comprising: a light guide plate having a diffraction grating formed on one surface thereof; and a front light optical system including the light guide plate, wherein a first transparent material having a refractive index different from that of the light guide plate. An illumination device, wherein a layer is formed along the diffraction grating.