JP2002182201A - Video display unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thin video display unit which has a reflection type display part and provides a high quality image. SOLUTION: A diffraction grating is formed in a light guide plate arranged oppositely to the reflection type display pat. Illuminating light which is made incident from a light source part and advances the inside of the light guide plate is diffracted by the diffraction grating, and is guided to the display part. Settings are made in such a manner that light going to the light guide plate from the display part does not conversely follow the optical path of light going to the display part from the light guide plate. Thus, the light from the display part is not diffracted by the diffraction grating, and the light from the display part can be transmitted through the light guide plate.

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 which modulates illumination light with a displayed image to produce light representing the image. The present invention relates to an image display device provided with a light guide plate for guiding light to an image.

[0002]

2. Description of the Related Art In a portable information terminal device such as a mobile phone, a notebook personal computer, a PDA electronic organizer, etc., in order to provide an image with low power consumption, a reflection type display unit which reflects while modulating illumination light; 2. Description of the Related Art An image display device including a light source unit that supplies illumination light and a light guide plate that is disposed on a front surface of the display unit and guides illumination light from the light source unit to the display unit is employed. When the environment is bright, the environment light is used as the illumination light, and when the environment is dark, the illumination light is supplied from the light source unit, so that power consumption for providing an image can be suppressed.

The light guide plate of such an image display device has a matte surface or a prism array on the surface remote from the display unit, and transmits ambient light to the display unit, while entering a light source from the end. The illumination light from the unit is reflected by the matte surface or the prism array and guided to the display unit. Further, the light modulated and reflected by the display unit is transmitted and guided to the user's eyes.

[0004]

However, if the light guide plate has a matte surface, light from the display unit is scattered when passing through the light guide plate.
A decrease in contrast, uneven brightness and the like occur.

If the surface of the light guide plate is a prism array,
Although there is no light scattering, the prism pattern is visually recognized, or moire fringes are generated in the provided image due to the relationship between the prism pattern and the image on the display unit. In addition, a part of the light reflected by the prism array and traveling toward the display unit is reflected by the surface on the display unit side and reaches the user's eyes, causing flare and lowering the contrast. To avoid this,
It is necessary to perform an antireflection treatment on the surface on the display unit side. Moreover, since the prism array is exposed to the outside (user side), it is necessary to provide a protective film or the like in order to prevent scratches and dirt.

The present invention has been made in view of the above problems, and has as its object to provide an image display device having a reflective display unit and capable of providing high quality images. .

[0007]

In order to achieve the above object, according to the present invention, there is provided a reflection type display unit which displays an image and reflects given illumination light while modulating the image by the displayed image. A light source section for emitting illumination light to be given, and a light guide plate facing the display section, which emits the illumination light emitted from the light source section from an end portion, travels inside, emits from a surface close to the display section, and guides the light to the display section. In a video display device comprising:
The light guide plate is a diffractive optical element having a period equal to or less than the wavelength of the illumination light in a direction along the path of the incident illumination light, so that the illumination light is emitted from the surface near the display unit by diffraction.

The light guide plate emits the illumination light from the surface by causing a specific order of diffraction to occur in the illumination light traveling inside thereof to change the traveling direction. Here, the light guide plate may be a transmissive diffractive optical element that causes a specific order of diffraction in transmitted light, or a reflective diffractive optical element that causes a specific order of diffraction in reflected light. The part that functions as a diffractive optical element is a transmissive type,
It is provided on the side closer to the display section than the path of the illumination light, and in the case of the reflection type, it is provided on the side farther from the display section than the path of the illumination light.

When the light reflected by the display unit is incident on the light guide plate following the optical path of the illumination light from the light guide plate to the display unit in the opposite direction and is diffracted again, the light travels along the path in the light guide plate. You will go in the opposite direction. When such a situation occurs, light from the display unit does not pass through the light guide plate and an image cannot be provided, but this can be easily avoided. For example, the diffraction condition of the light guide plate may be set so that the illumination light does not enter the display unit vertically. Also, the diffraction conditions of the light guide plate are set so that the diffraction efficiency greatly differs depending on the polarization component, and the polarization component of the illumination light guided from the light guide plate to the display unit and the light representing the image contained in the light reflected by the display unit are set. The polarization components may be different. In this way, light representing an image can be transmitted through the light guide plate.

Since the light guide plate is a diffractive optical element, there is no scattering of light transmitted from the display unit. Also, since the period of the light guide plate as the diffractive optical element is extremely small,
The cycle is not visually recognized, and moire fringes do not occur. Therefore, a high-quality image can be provided.

It is preferable that the light guide plate has a diffraction grating which is in contact with the path of the incident illumination light, and each of the diffraction gratings has an asymmetrical sectional shape. The diffraction grating is a part that functions as a diffractive optical element. The diffraction grating may be provided on the surface of the light guide plate or may be provided inside the light guide plate. By making the cross-sectional shape of the diffraction grating asymmetric, it becomes easy to cause diffraction of a specific order in the illumination light.

Here, when the diffraction grating of the light guide plate is located closer to the display than the path of the illumination light, and the height of the unevenness of the diffraction grating is determined corresponding to the distance from the center of the path of the illumination light, It is preferable that the highest point of the diffraction grating is farther from the end where the illumination light is incident than the center from the lowest point to the lowest point. That is, the light guide plate is a transmission type diffractive optical element, and the highest part of the diffraction grating is made closer to the lowest part on the downstream side of the path of the illumination light. In the case of the transmission type, the diffraction efficiency can be increased by bringing the highest part of the diffraction grating close to the lowest part on the downstream side of the path of the illumination light. In this configuration, since no diffraction grating is provided on the surface of the light guide plate far from the display unit, there is no need to particularly protect this surface.

[0013] When the diffraction grating of the light guide plate is located farther from the display than the path of the illumination light, and the height of the unevenness of the diffraction grating is determined corresponding to the distance from the center of the path of the illumination light, The configuration may be such that the highest part is closer to the end where the illumination light is incident than the center from the lowest part to the lowest part. That is, the light guide plate is a reflection type diffraction grating, and the highest part of the diffraction grating is made closer to the lowest part on the upstream side of the path of the illumination light. In the case of the reflection type, the diffraction efficiency can be increased by moving the highest part of the diffraction grating closer to the lowest part on the upstream side of the path of the illumination light.

[0014] The light source unit may emit a plurality of illumination lights having different wavelengths at different angles. By supplying a plurality of illumination lights having different wavelengths from the light source unit, a color image can be provided. Although the diffraction angle of light by a diffractive optical element changes depending on the wavelength even if the diffraction order is the same, the light source unit emits illumination light with different wavelengths at different angles so that the diffraction angles of illumination light with different wavelengths are the same. Can be. This makes it possible to cause illumination lights having different wavelengths to enter the display unit from the same direction, and to provide a high-quality color image without color shift.

An optical element for rotating the polarization direction of the light reflected by the display unit and entering the light guide plate by 90 ° from the polarization direction of the illumination light emitted from the light guide plate may be provided between the light guide plate and the display unit. Further, an optical element for changing an angle of the light reflected by the display unit and incident on the light guide plate with respect to the light guide plate from an angle of the illumination light emitted from the light guide plate with respect to the light guide plate is provided between the light guide plate and the display unit. You may.

In either configuration, it is easy to set the diffraction conditions of the light guide plate so that the diffraction efficiency with respect to the illumination light is high and the diffraction efficiency with respect to the light from the display unit is low, and the illumination light is efficiently displayed. And on the other hand, the light representing the image can be guided to the user's eyes with little diffraction.

Preferably, the light guide plate has a diffraction grating in contact with the path of the incident illumination light, and the difference in height of the unevenness of the diffraction grating increases as the distance from the end where the illumination light is incident increases. Further, the light guide plate has a diffraction grating in contact with the path of the incident illumination light, and the diffraction grating is divided into a plurality of spaced regions in a direction along the path of the illumination light, and is far from an end where the illumination light is incident. The configuration may be such that the width of the region of the diffraction grating is wider as the area becomes larger.

Since the amount of illumination light is diffracted while traveling in the light guide plate and the amount thereof is reduced, if the diffraction efficiency of the diffraction grating is set to be constant, the amount of illumination light guided to the display unit becomes non-uniform.
However, the diffraction efficiency of the diffraction grating can be increased by increasing the height difference between the irregularities, and can be adjusted by the width of the region. In either configuration, the diffraction efficiency of the diffraction grating is increased as the distance from the end where the illumination light is incident is increased, whereby the amount of illumination light guided to the display unit can be made uniform.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Some embodiments of the video display device according to the present invention will be described below with reference to the drawings and tables at the end of this section. FIG. 1 shows the configuration of the video display device 1 of the first embodiment, which is the basic configuration of the video display device of the present invention. The image display device 1 includes a display unit 20, a light source unit 3,
0, and a light guide plate 40.

The display section 20 is of a reflection type that displays an image, and reflects forward, while modulating the illumination light given from the front by the displayed image. In the present embodiment, the display unit 2
As 0, a reflective liquid crystal display (LCD) in which a liquid crystal layer 21 is sandwiched between a reflection plate 22 and a polarizing plate 23 is used.

The light source section 30 emits illumination light L1 to be given to the display section 20. The display unit 2 as the light source unit 30
In the application where the user directly observes the image displayed on the display unit 0, a device that emits visible light is used. In the application where the image displayed on the display unit 20 is photographed, light in a wavelength range matching the element used for photography is used. For example, when photographing with an infrared CCD, a device that emits infrared light is used.

The light guide plate 40 is made of a material transparent to light emitted from the light source unit 30, and is disposed in front of the display unit 20 so as to face the display unit 20. The surface 40a of the light guide plate 40 closer to the display unit 20 and the display unit 20
The surfaces 40b farthest from the display unit 2 are parallel to each other.
It is also parallel to 0. The end surface 40c of the light guide plate 40 is inclined with respect to the surfaces 40a and 40b.
The light source unit 30 is disposed so as to face c.

The angle formed by the end face 40c and the surface 40b is set to 40 ° or more. This is because the illumination light emitted from the light source unit 30 is made substantially perpendicular to the end face 40c, the illumination light is efficiently guided into the light guide plate 40, and the introduced illumination light is totally reflected by the light guide plate 40. This is to make progress inside. Although the end face 40c and the surface 40b form an acute angle here, the end face 40c and the surface 40a may form an acute angle.

A diffraction grating 41 is provided on a surface 40a closer to the display section 20, so that the light guide plate 40 is a diffractive optical element. The diffraction grating 41 is of a transmission type, and causes −1st-order diffraction of illumination light traveling inside the light guide plate 40, and emits the diffracted light from the surface 40a.

The illumination light emitted from the surface 40a of the light guide plate 40 is incident on the display section 20 and transmitted through the polarizing plate 23 to be converted into linearly polarized light. The linearly polarized illumination light passes through the liquid crystal layer 21 and is reflected by the reflector 22, passes through the liquid crystal layer 21 again, and enters the polarizing plate 23. The liquid crystal layer 21 displays an image, and rotates the polarization direction of a part of the illumination light transmitted by the displayed image by 90 °. That is, the illumination light is modulated to include linearly polarized light whose polarization direction has not been rotated and linearly polarized light whose polarization direction has been rotated. Of the modulated light, the linearly polarized light whose polarization direction has been rotated is blocked by the polarizing plate 23, and only the linearly polarized light whose polarization direction has not been rotated passes through the polarizing plate 23. This linearly polarized light becomes image light L2 representing an image.

The image light re-enters the light guide plate 40 from the surface 40a, but the diffraction grating 41 is set so as not to cause diffraction of the image light, and transmits the image light. The image light transmitted through the diffraction grating 41 is emitted from the surface 40b, reaches the user's eye E, and provides an image to the user.

The setting of the diffraction grating 41 for causing the illumination light L1 to diffract and guide the illumination light L1 to the display unit 20 and transmitting the image light L2 to guide the eye L to the eye E will be described below. Tables 1 and 2 show the results of a simulation in which the diffraction efficiency was calculated with various settings of the shape of the diffraction grating and the angle of incidence of light rays on the diffraction grating.

Here, the diffraction grating has the shape shown in FIG.
In the table, “N blaze” is (a), “N4 level” is (b), “V blaze” is (c), “） blaze” is (d), and “2 level” is (e). ).
"N-blaze" and "@blaze" have a constant level of the inclined surface and a vertical step at the boundary between the highest part (part farthest from the incident light) and the lowest part (part closest to the incident light). It is an asymmetric blaze type. However, the directions of the inclined surfaces are opposite. In “N blaze”, the highest part is adjacent to the lowest part on the downstream side of the incident light, and in “И blaze”, the highest part is on the lowest part on the upstream side of the incident light. Adjacent.

The "V blaze" is a symmetric blaze type in which inclined planes in opposite directions are alternately arranged. “N4 level” is a multi-level binary type in which the inclined surface of “N blaze” is approximated by a 4-level horizontal plane. "Two levels" is a binary type having two levels of horizontal planes.

The period / wavelength is the ratio of the period Λ of the diffraction grating to the wavelength λ of light. The height / wavelength is the ratio of the height difference h between the highest part and the lowest part of the diffraction grating to the wavelength λ of light.
Regarding the direction of the light beam, “out” indicates the direction from the optical material on which the diffraction grating is formed to the air side, and “in” indicates the direction from the air side to the optical material. The incident angle is the angle θ between the normal to the diffraction grating and the incident light, and the emission angle is the angle θ ′ between the normal to the diffraction grating and the output light (diffraction light). The exit angle is that of transmitted light having a diffraction order of -1.

The P-polarization diffraction efficiency is the ratio of the intensity of the polarized light component that becomes P-polarized light to the diffraction grating to the intensity before diffraction, and the S-polarized light diffraction efficiency is S-polarized light to the diffraction grating. This is the ratio of the intensity of the polarized light component after diffraction to the intensity before diffraction. These are reflected light and transmitted light having diffraction orders of −2, −1, and 0, respectively.

The values in Tables 1 and 2 are calculated based on the following general formula. n ′ · sin (θ ′) − n · sin (θ) = m · λ / Λ where n is the refractive index of the medium on the incident side, and n ′ is the refractive index of the medium on the outgoing side. Is air, and the refractive index is 1. The incident angle θ and the emission angle θ ′ are defined as positive in the counterclockwise direction and negative in the clockwise direction. m is the diffraction order, and defines diffraction in the counterclockwise direction as positive and diffraction in the clockwise direction as negative.

The diffraction grating 41 of the light guide plate 40 is set so that −1st-order transmitted light is emitted to illuminate the display unit 20 and 0-order reflected light travels inside the light guide plate 40. In order to realize this efficiently, it is preferable to concentrate the diffraction efficiency on the -1st order transmitted light and the 0th order reflected light.

The setting numbers 1 to 6 in Table 1 are obtained by examining the relationship between the ratio of the period of the diffraction grating to the wavelength of light and the diffraction efficiency. Looking at the S-polarization diffraction efficiency, the diffraction efficiency of the -1st-order transmitted light and the 0th-order reflected light is high in any setting where the period / wavelength is 1 or less. Therefore, the period Λ of the diffraction grating 41 may be set to be equal to or less than the wavelength λ of the illumination light emitted from the light source unit 30.

Setting numbers 7 to 10 in Table 1 are obtained by examining the relationship between the cross-sectional shape of the unevenness of the diffraction grating and the diffraction efficiency. S
Looking at the polarization diffraction efficiencies, "2 levels" and "V blaze"
The “N blaze” and “N4 level” have higher diffraction efficiency of the −1st order transmitted light than the “N blaze” and “N4 level”. Therefore, an asymmetrical diffraction grating is more preferable than a diffraction grating having a symmetrical cross section.

In the image display device 1, the diffraction grating 41 of the light guide plate 40 is set so as to satisfy these conditions. When the illumination light is perpendicularly incident on the display unit 20,
The image light from the display unit 20 enters the diffraction grating 41 by following the optical path of the illumination light in the reverse direction, is diffracted again, and proceeds inside the light guide plate 40 toward the end surface 40c. When such a situation occurs, it becomes impossible to provide an image. Therefore, the diffraction grating 41 is set so that the emission angle of the −1st-order transmitted light does not become 0 °.

It should be noted that the illumination light transmitted through the diffraction grating 41 is immediately emitted from the light guide plate 40.
Then, it is not necessary to perform the antireflection treatment on the surface 40a of the light guide plate 40. Although the surface 40b is exposed to the outside, the surface 40b does not need to be particularly protected because the diffraction grating 41 is not provided.

Hereinafter, a video display device according to another embodiment will be described. The video display device according to each embodiment is obtained by modifying or modifying the video display device 1, and components having the same or similar functions as the components of the video display device 1 are denoted by the same reference numerals, and overlapping descriptions are given. Is omitted.

FIG. 3 shows the configuration of the image display device 2 according to the second embodiment, and FIG. 4 shows the diffraction grating 41 thereof. The video display device 2 is similar to the video display device 1 of the first embodiment,
The diffraction grating 41 is provided on the surface 40a closer to the display unit 20 to be a transmission type.

As described above, it is preferable to make the cross section of the unevenness of the diffraction grating 41 asymmetrical. However, the setting numbers 11 and 12 in Table 1 examine the relationship between the direction of the blazed type inclined surface and the diffraction efficiency. It is a thing. Looking at the S-polarization diffraction efficiency, “N-blaze” has a high diffraction efficiency of -1st order transmitted light,
"@Blaze" has a high diffraction efficiency of -1st order reflected light. That is, a diffraction grating in which the highest part of the unevenness is closer to the lowest part on the downstream side of the illumination light is more suitable for the transmission type. Therefore, as shown in FIG. 4, in the present embodiment, the diffraction grating 41 is set to “N blaze”.
Is set to

As apparent from the comparison between the setting numbers 8 and 10, the diffraction efficiencies of "N4 level" and "N blaze" are substantially equal. Therefore, the diffraction grating 41 may be of an “N4 level” binary type as shown in FIG.

FIG. 6 shows the configuration of the video display device 3 according to the third embodiment, and FIG. 7 shows the diffraction grating 41 thereof. The image display device 3 has a diffraction grating 41 provided on a surface 40 b far from the display unit 20. The diffraction grating 41 is of a reflection type, and allows the −1st-order reflected light to enter the surface 40a at less than the critical angle and transmit the surface 40a. Further, the zero-order reflected light is incident on the surface 40a at a critical angle or more and totally reflected.

As described in the second embodiment, a diffraction grating in which the highest part of the unevenness is closer to the lowest part on the upstream side of the illumination light is more suitable for the reflection type. Therefore, in the present embodiment, as shown in FIG. 7, the diffraction grating 41 is set to “И blaze”. Although not shown in the table, even if the inclined plane of “４１ Blaze” is approximated by a 4-level horizontal plane, substantially the same diffraction efficiency can be obtained. May be a binary type.

It is desirable to provide an antireflection film on the surface 40a in order to prevent the light reflected on the surface 40a from becoming a flare. Further, in order to protect the diffraction grating 41, it is desirable to provide a protective film on the surface 40b.

FIG. 8 shows the light guide plate 40 of the video display device 4 according to the fourth embodiment. The diffraction grating 41 has a surface 4 closer to the display unit 20 as in the image display device 2 of the second embodiment.
0a. However, the diffraction grating 41 of the image display device 4 is set such that the difference in height of the unevenness increases as the distance from the end surface 40c into which the illumination light from the light source unit 30 is guided (h ″ <h ′). Is the light guide plate 40
In consideration of the amount of illumination light that decreases as the light travels through the inside, the diffraction efficiency increases as the distance from the end face 40c increases, and the amount of illumination light guided to the display unit 20 becomes uniform.

The setting numbers 13 to 24 in Table 1 are obtained by examining the relationship between the height difference of the unevenness of the diffraction grating and the diffraction efficiency. Looking at the S-polarization diffraction efficiency, the greater the height difference between the irregularities,
The diffraction efficiency of the -1st order transmitted light is high, and conversely, the diffraction efficiency of the 0th order reflected light is low. Therefore, the end face 40c
By increasing the difference in height of the unevenness in a portion farther from the camera, the amount of illumination light guided to the display unit 20 can be made uniform. In the image display device 4, the height difference between the unevenness of the diffraction grating 41 and the product of the amount of the S-polarized light component included in the illumination light and the diffraction efficiency of the −1st-order transmitted light is constant over the entire diffraction grating 41. Has been established.

FIG. 9 shows the light guide plate 40 of the video display device 5 according to the fifth embodiment. The diffraction grating 41 of the image display device 5 according to the present embodiment is also provided on the surface 40 a closer to the display unit 20. In the image display device 5, the diffraction grating 41 is divided into a plurality of spaced regions, the portions between the regions are flattened, and the portions between the regions do not have diffractive ability. In addition, the width of the region is increased as the position is farther from the end face 40c through which light is guided from the light source unit 30. This too
This is to make the amount of illumination light guided to the display unit 20 uniform.

It is to be noted that the difference in height of the unevenness of the diffraction grating 41 is increased as the distance from the end face 40c increases, and
The amount of illumination light guided to the display unit 20 can be made uniform by combining the width of the region with the distance from the end face 40c. These methods for making the amount of illumination light guided to the display unit 20 uniform can also be applied to a case where the diffraction grating 41 is of a reflection type as in the image display device 2 of the second embodiment.

FIG. 10 shows the illumination unit 30 and the light guide plate 40 of the video display device 6 of the sixth embodiment. The image display device 6 of the present embodiment provides a color image. The light source unit 30 supplies white light having a wavelength over the entire visible region. Display unit 20
Each of the pixels is provided with a color filter that selectively transmits any of blue (B) light, green (G) light, and red (R) light. If you provide color video,
In order to prevent color misregistration, light having different wavelengths is
At the same angle. Also, in order to correctly represent colors, it is necessary to make the amounts of light having different wavelengths the same.

The setting numbers 25 to 28 in Table 2 are obtained by examining the relationship between the change in the wavelength of light and the diffraction efficiency, and the relationship between the change in the wavelength of light and the incident angle necessary to obtain the same emission angle. It is. Here, the calculated wavelength / wavelength is a ratio of a wavelength at which diffraction efficiency is calculated with respect to a wavelength (for example, 550 nm) used as a reference for setting a diffraction grating. As the wavelength becomes longer, the incident angle required to make the emission angle constant becomes larger, and the diffraction efficiency of the -1st order transmitted light of the S-polarized light decreases.

Therefore, the light source unit 30 of the image display device 6
Is provided with a diffraction grating 31 for diffracting emitted white light at different angles according to the wavelength, and a filter 32 having a different transmittance depending on the wavelength. The diffraction grating 31 is set such that the longer the wavelength of the light, the larger the incident angle with respect to the surfaces 40 a and 40 b of the light guide plate 40.
The emission angle of the primary transmitted light is equal from R light to B light. Also,
The transmittance of the filter 32 is higher as the wavelength is longer, and the amount of the primary transmission light by the diffraction grating 41 is also equal from R light to B light. With such a setting of the light source unit 30, the image display device 6 can provide a high-quality color image.

The diffraction grating 31 of the light source unit 30 is of a two-level binary type, and has a high diffraction efficiency for S-polarized light. Therefore, the light amount loss due to the provision of the diffraction grating 31 is small. Since the period of the diffraction grating 41 of the light guide plate 40 is equal to or less than the wavelength of the illumination light, the diffraction grating 31 of the light source unit 30 is not used.
It is desirable that the period of the illumination light be equal to or less than the wavelength of the illumination light.

Looking at the S-polarization diffraction efficiencies of setting numbers 25 to 28, the diffraction efficiency of the -1st order reflected light is low regardless of the wavelength. This means that flare does not occur even if the surface 40a provided with the diffraction grating 41 is not subjected to the antireflection treatment. Further, looking at the S-polarization diffraction efficiencies of setting numbers 13 to 24 in Table 1, the diffraction efficiency of the −1st-order reflected light decreases as the aspect ratio of the diffraction grating (the ratio of the height difference of the unevenness to the period) increases. . It is understood that when the aspect ratio is 0.9 or more, generation of flare can be almost surely prevented.

FIG. 11 shows the illumination unit 30 and the light guide plate 40 of the video display device 7 of the seventh embodiment. The image display device 7 also provides a color image. The light source unit 30 includes three light emitting diodes (LEDs) 33 that emit R light, G light, and B light, respectively.
R, 33G, and 33B. LED33R, 33
The directions of G and 33B are different from each other, so that the emission angle of the primary transmission light by the diffraction grating 41 of the light guide plate 40 is changed to R light, G light
Light and B light are made equal. LED33R, 3
By changing the currents applied to the 3G and 33B or by changing the on / off duty ratios of the LEDs 33R, 33G and 33B, the R led to the display unit 20 is increased.
The amounts of light, G light and B light are made equal.

The image light from the display section 20 is S-polarized light with respect to the diffraction grating 41. In order to efficiently guide this light to the user's eyes, it is necessary to increase the diffraction efficiency of the zero-order transmitted light.

The setting numbers 29 to 32 in Table 2 are the setting numbers 2
In this figure, the diffraction efficiency when the −1st-order transmitted light is specularly reflected by the display unit 20 and re-enters the diffraction grating 41 at the settings of 5-28 is examined. Looking at the S-polarization diffraction efficiency, the diffraction efficiency of the zero-order transmitted light is 1 in the setting numbers 30 to 32. This means that it is not necessary to provide an antireflection film on the surface 40a on which the diffraction grating 41 is provided.

In the setting No. 29, the diffraction efficiency of the 0th-order transmitted light is 0.9, and the diffraction efficiency of the -1st-order transmitted light is 0.9.
08. At first glance, it seems as if the −1st-order transmitted light travels in a different direction from the 0th-order transmitted light and becomes a flare. However, the emission angle of this primary transmission light is -4.
5 °, which exceeds the critical angle of the surface 40b.
Since the light is totally reflected at 0b, there is no flare and the quality of the image is not degraded.

The setting numbers 33 to 36 in Table 2 are displayed on the display unit 20.
FIG. 9 shows the diffraction efficiency when image light is vertically incident on the diffraction grating 41. In the setting numbers 33 and 34, the diffraction efficiency of the -1st order transmitted light is further higher than in the setting number 29, but in this case also, the outgoing angle exceeds the critical angle of the surface 40b, so that no flare occurs.

FIG. 12 shows the configuration of the video display device 8 according to the eighth embodiment. In the image display device 8, the prism array 50 is arranged between the light guide plate 40 having the diffraction grating 41 on the surface 40 a and the display unit 20, and the angle of the image light incident on the light guide plate 40 is emitted from the light guide plate 40. The angle is changed from the angle of the illumination light. Setting numbers 29, 33, 3
Even when the diffraction efficiency of the 0th-order transmitted light becomes low as it is as in No. 4, it is possible to increase the diffraction efficiency by changing the angle in this way.

FIG. 13 shows the configuration of the video display device 9 according to the ninth embodiment. The image display device 9 is provided between the display unit 20 and the light guide plate 40 having the diffraction grating 41 on the surface 40 a.
The wave plate 60 is arranged to rotate the polarization direction of the image light by 90 ° from the polarization direction of the illumination light. Looking at the P-polarization diffraction efficiencies of setting numbers 29 to 36 in Table 2,
The diffraction efficiency of the polarized zero-order transmitted light is high at any incident angle. The image light can be efficiently guided to the user's eyes regardless of the incident angle by rotating the polarization direction by 90 ° by the quarter-wave plate 60 and making the image light P-polarized with respect to the diffraction grating 41. I understand.

FIG. 14 shows the configuration of the video display device 10 according to the tenth embodiment. The video display device 10 includes a display unit 2
The zero polarizing plate 23 is replaced with a mere glass plate 23a, and a polarizing plate 70 is arranged on the surface 40b side of the light guide plate 40. In this configuration, the light guide plate 40 is
Is incident on the light, the S-polarized light as the image light and the unnecessary P-polarized light are included, and the unnecessary P-polarized light is removed by the polarizing plate 70.

In this configuration, it is possible to control the display unit 20 so that the light whose polarization direction is rotated by 90 ° becomes image light representing an image. In that case, the polarizing plate 70 is set to transmit the P-polarized light to the diffraction grating 41. Further, in this case, even when the emission angle of the illumination light is set to 0 ° and the image light follows the optical path of the illumination light in reverse, the image light can be guided to the user's eyes.

FIG. 15 shows a light guide plate 40 of an image display device 11 according to the eleventh embodiment. The light guide plate 40 is formed by joining two materials 42 and 43, and an interface between the materials 42 and 43 is a diffraction grating 41. Refractive index n of material 42 and material 4
3 have different refractive indices n ′. Illumination light from the light source unit 30 is incident on only one material 42. In this configuration, since the refractive index n ′ of the material 43 on the emission side is also a variable parameter,
The diffraction conditions of the diffraction grating 41 can be set flexibly. In order to prevent the reflected light from becoming flare, it is desirable to provide an anti-reflection film on the surface 40a of the material 43 on the emission side.

The video display devices 1 to 11 of the above embodiments
Is suitable as a video providing means for a portable terminal information device because it can provide high quality video while being thin and consumes less power. Further, it can be used for a projector. Here, the diffraction grating 41
Is constant, but the diffraction grating 41 may have a plurality of periods to guide the illumination light to the display unit 20 at different angles.

[0065]

[Table 1]

[0066]

[Table 2]

[0067]

According to the image display apparatus of the present invention in which the light guide plate is a diffractive optical element, light is not scattered, and deterioration in image quality due to scattering such as blur, reduced contrast, and uneven brightness can be avoided. . Further, since the cycle as the diffractive optical element is extremely small, the cycle is not visually recognized, and no moiré fringes are generated even when any image is displayed. Therefore, a high-quality image can be provided.

In a configuration in which a diffraction grating is provided on the light guide plate and the cross-sectional shape of the unevenness of the diffraction grating is made asymmetric, the light guide plate can be easily formed as a diffractive optical element, and the illumination light is guided to the display section. It is also easy to cause diffraction of a particular order.

The light guide plate is formed as a transmissive diffractive optical element by positioning the diffraction grating closer to the display section than the path of the illumination light.
In a configuration in which the highest part of the diffraction grating is farther from the end where the illumination light is incident than the center from the lowest part to the lowest part, the amount of the illumination light guided to the display unit can be increased to provide a bright image. . Further, it is not necessary to particularly protect the surface of the light guide plate far from the display unit. Furthermore, if a diffraction grating is provided on the surface closer to the display unit, the occurrence of flare can be prevented without performing antireflection treatment on the surface.

The diffraction grating is positioned farther from the display than the path of the illumination light, and the light guide plate is a reflection type diffractive optical element. The highest part of the diffraction grating is more illuminating light than the center from the lowest part to the lowest part. Even in a configuration close to the end where light is incident, the amount of illumination light guided to the display unit can be increased, and a bright image can be provided.

In a configuration in which the light source unit emits a plurality of illumination lights having different wavelengths at different angles, it is possible to provide a high quality color image without color shift.

An optical element for rotating the polarization direction by 90 °,
In the configuration in which an optical element that changes the angle of light with respect to the light guide plate is provided between the light guide plate and the display unit, the illumination light is efficiently guided to the display unit, and the light representing the image is hardly diffracted to the user's eyes. I can guide you.

A structure in which a diffraction grating is provided on the light guide plate and the difference in height of the unevenness of the diffraction grating is increased as the distance from the end where the illumination light is incident, or the diffraction grating is divided into a plurality of spaced regions to provide illumination light In the configuration in which the width of the region of the diffraction grating is increased as the distance from the end where light is incident, the amount of illumination light guided to the display unit can be made uniform, and an image with uniform brightness can be provided.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically illustrating a configuration of a video display device according to a first embodiment.

FIG. 2 is a diagram showing a shape, a period, a height difference, an incident angle, and an outgoing angle of a diffraction grating.

FIG. 3 is a cross-sectional view schematically illustrating a configuration of a video display device according to a second embodiment.

FIG. 4 is a sectional view schematically showing the shape of a diffraction grating provided on a light guide plate of the image display device according to the second embodiment.

FIG. 5 is a sectional view schematically showing another shape of the diffraction grating provided on the light guide plate of the image display device according to the second embodiment.

FIG. 6 is a sectional view schematically showing the configuration of a video display device according to a third embodiment.

FIG. 7 is a sectional view schematically showing the shape of a diffraction grating provided on a light guide plate of the image display device according to the third embodiment.

FIG. 8 is a sectional view schematically showing a configuration of a light guide plate of an image display device according to a fourth embodiment.

FIG. 9 is a cross-sectional view schematically illustrating a configuration of a light guide plate of an image display device according to a fifth embodiment.

FIG. 10 is a sectional view schematically showing a configuration of a light source unit and a light guide plate of an image display device according to a sixth embodiment.

FIG. 11 is a sectional view schematically showing a configuration of a light source unit and a light guide plate of an image display device according to a seventh embodiment.

FIG. 12 is a sectional view schematically showing the configuration of an image display device according to an eighth embodiment.

FIG. 13 is a sectional view schematically showing the configuration of a video display device according to a ninth embodiment.

FIG. 14 is a sectional view schematically showing the configuration of a video display device according to a tenth embodiment.

FIG. 15 is a sectional view schematically showing a configuration of a light guide plate of the image display device according to the eleventh embodiment.

DESCRIPTION OF SYMBOLS 1 to 11 Image display device 20 Display unit (liquid crystal display) 21 Liquid crystal layer 22 Reflector 23 Polarizer 23a Glass plate 30 Light source unit 31 Diffraction grating 32 Filter 33R, 33G, 33B Light emitting diode 40 Light guide plate 40a , 40b Light guide plate surface 41 Diffraction grating 42, 43 Light guide plate material 50 Prism array 60 1/4 wavelength plate 70 Polarizing plate

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Claims (9)

[Claims] A display unit that displays an image and reflects illumination light to be applied while modulating the image by the displayed image; a light source unit that emits illumination light to be applied to the display unit; A light guide plate for causing the illumination light emitted from the light source unit to enter from an end portion, to travel through the interior, to emit from a surface close to the display unit, and to guide the light to the display unit. A diffractive optical element having a period equal to or less than the wavelength of the illumination light in a direction along the path of the image display device, wherein the illumination light is emitted from a surface near the display unit by diffraction. 2. The image display apparatus according to claim 1, wherein the light guide plate has a diffraction grating in contact with the path of the incident illumination light, and each of the diffraction gratings has an asymmetric cross-sectional shape. 3. The method according to claim 1, wherein the diffraction grating of the light guide plate is located closer to the display than the path of the illumination light, and the height of the unevenness of the diffraction grating is determined in accordance with the distance from the center of the path of the illumination light. 3. The grating according to claim 2, wherein the highest point of the grating is farther from the end where the illumination light is incident than the center from the lowest point to the lowest point.
3. The video display device according to 1. 4. When the diffraction grating of the light guide plate is positioned farther from the display than the path of the illumination light, and the height of the unevenness of the diffraction grating is determined in accordance with the distance from the center of the path of the illumination light, diffraction is performed. 3. The grating according to claim 2, wherein the highest point of the grating is closer to the end where the illumination light is incident than the center from the lowest point to the lowest point.
3. The video display device according to 1. 5. The image display device according to claim 1, wherein the light source unit emits a plurality of illumination lights having different wavelengths at different angles. 6. An optical element between the light guide plate and the display unit for rotating the polarization direction of light reflected by the display unit and entering the light guide plate by 90 ° from the polarization direction of illumination light emitted from the light guide plate. The video display device according to claim 1, wherein: 7. An optical element for changing an angle of light reflected by the display unit and incident on the light guide plate with respect to the light guide plate from an angle of illumination light emitted from the light guide plate with respect to the light guide plate, between the light guide plate and the display unit. The video display device according to claim 1, further comprising: 8. The light guide plate according to claim 1, wherein the light guide plate has a diffraction grating in contact with the path of the incident illumination light, and the difference in height of the unevenness of the diffraction grating increases as the distance from the end where the illumination light is incident increases. The image display device according to the above. 9. A light guide plate having a diffraction grating in contact with the path of the incident illumination light, wherein the diffraction grating is divided into a plurality of separated regions in a direction along the path of the illumination light, and an end on which the illumination light is incident. 2. The image display device according to claim 1, wherein the farther from the part, the wider the area of the diffraction grating.