JP2002221605A - Fresnel lens, illumination device and display device which use the same, method for designing fresnel lens and designing device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a Fresnel lens with an easy designing method in which uniform illumination light quantity can be obtained without depending on the position from the optical axis of the Fresnel lens, and to provide a display device with high display quality which uses the above Fresnel lens. SOLUTION: In the Fresnel lens 7a, prisms 23 generating higher intensity of the exiting light selected from refractive prisms and reflective prisms are disposed according to the distance from the optical axis 24 of the Fresnel lens. The apex of the prism 23 is designed corresponding to the distance from the optical axis. The Fresnel lens 7a satisfying the desired display quality is disposed in the display device.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a Fresnel lens,
And a lighting device and a display device using the same.

[0002]

2. Description of the Related Art FIG. 14 shows a conventional Fresnel lens.
FIG. 14A is a plan view of the Fresnel lens 140, and FIG. 14B is a cross-sectional view of the Fresnel lens 140. The conventional Fresnel lens 140 is a flat lens in which the refracting surface 141 is not a continuous spherical surface but a refracting surface 141 inclined in a stepwise manner, and the prism of which the curvature of the lens is converted into a prism 143 and arranged on a plane. An array.

The prism 143 formed on the Fresnel lens 140 generally has an inclined surface, and has a function of refracting light on the inclined surface to bend the traveling direction of light. Fresnel lenses are flat lenses, and are generally formed of a transparent resin such as an acrylic resin or a polycarbonate resin, which has the advantage of making the lens thinner and lighter, and is widely used in lighting devices, display devices, and light receiving devices. I have.

An example used as a lighting device of a liquid crystal display device will be described with reference to FIG. In FIG. 15, a liquid crystal display device 150 includes a backlight 154 including a light source 151, a Fresnel lens 152, and a spherical mirror 153;
The liquid crystal display element 155 has a configuration in which a pair of polarizing plates 157 are disposed at both ends of the liquid crystal display element 155, and a light diffusion layer 156 is disposed on the viewer side. In the backlight 154, the light source 151 is disposed near the focal point of the Fresnel lens 152, and the light 158 from the light source 151
The illumination light 159 is refracted by the prism formed at 52 and emitted as substantially parallel illumination light 159. The spherical mirror 153 is disposed so as to face the Fresnel lens 152, and reflects light 158 from the light source 151 toward the Fresnel lens 152 to improve light use efficiency. The arrows in the drawings in the present invention indicate the traveling directions of light. The liquid crystal display element 155 receives substantially parallel illumination light 159 from the backlight 154, the transmittance thereof is controlled for each pixel, and the viewing angle dependency is improved by the light diffusion layer 156.

[0005] In addition, a configuration using a lens array sheet as a light diffusion layer has been reported.

On the other hand, a Total Internal Reflection lens
Japanese Patent Application Laid-Open No. 11-504124 discloses a technique (hereinafter referred to as a TIR lens) and an application example using the same. The TIR lens has a dome shape as a whole lens, and a prism is formed on the surface thereof. This TIR
Unlike a conventional Fresnel lens, a lens can emit illumination light with a uniform light amount and high parallelism without being restricted by the distance between the lens and the light source.

[0007]

However, conventional Fresnel lenses and TIR lenses have the following problems.

[0008] When a conventional illuminating device including a Fresnel lens is used for a liquid crystal display device, the amount of light passing through the Fresnel lens varies depending on the position of the Fresnel lens from the optical axis. This led to non-uniformity in the amount of illumination light, which greatly affected the display quality of the liquid crystal display device. The reason will be described with reference to FIGS. In FIG. 16, the light source 161 is arranged near the focal length f of the Fresnel lens. Under these conditions, the intensity of the outgoing light 164 passing through an arbitrary point of the Fresnel lens 162 was measured. The result is shown in FIG. The horizontal axis in FIG. 17 indicates the distance from the optical axis 163, and the vertical axis indicates the intensity of the emitted light.
The intensity when the intensity of the outgoing light in No. 3 is 1 is shown as a relative ratio. FIG. 17 shows the intensity of the outgoing light 164 at each position from the optical axis 163, and it can be seen that the intensity of the outgoing light 164 decreases as the distance from the optical axis 163 increases. This is because, when the light source 161 is arranged near the focal point of the Fresnel lens, almost no incident light needs to be refracted near the optical axis of the Fresnel lens, so that the incident angle of the light to the Fresnel lens is small and the transmittance is high. However, as the position becomes farther from the optical axis, the angle of incidence of the incident light on the Fresnel lens increases, the light reflected on the surface of the Fresnel lens increases, and the transmittance decreases. As described above, in the conventional Fresnel lens, the emitted light can be emitted substantially parallel to the optical axis 163 of the Fresnel lens, but the intensity of the emitted light decreases from the optical axis 163 toward the periphery. There was a problem.

Further, the conventional Fresnel lens is used as a backlight 1 of a liquid crystal display device 150 shown in FIG.
When used for No. 54, there were the following problems.

In this method, when light is incident on the liquid crystal display element 155, the incident light is concentrated in a direction in which display characteristics (brightness, contrast, color tone, etc.) are good (usually in the front direction), and the liquid crystal display element 155 After passing through, the light diffusion layer 156
Therefore, a technique of realizing excellent display characteristics over a wide viewing angle region by expanding the emission direction is used. In other words, the light illuminating the liquid crystal display element 155 includes a large amount of light in the viewing angle direction with poor display characteristics, or the intensity of the light illuminating the liquid crystal display element 155 in the front direction greatly varies depending on the location. In such a case, excellent display characteristics cannot be realized.

Therefore, in the conventional backlight 154, since the intensity of the emitted light in the front direction is very uneven, excellent display characteristics cannot be realized. Since the uniform irradiation intensity is limited to a limited small area near the optical axis, the number of backlights to be arranged increases, and as a result,
This will increase the size of the liquid crystal display device.

On the other hand, the TIR lens disclosed in Japanese Unexamined Patent Publication No. Hei 11-504124 has a large number of parameters required for designing, so that it is difficult to design the lens. In addition to the shape of the prism, a dome-shaped curve where the prisms are arranged,
In addition, it is necessary to comprehensively design the shape of the surface on which the prism is not formed, and the lens design requires a great deal of labor and labor.

Further, since the TIR lens has a dome-shaped overall shape and a prism formed thereon,
It was also difficult to form a prism with high accuracy.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has as its object to provide, in particular, a Fresnel lens suitably used as a lighting device of a liquid crystal display device, and a lighting device having such a Fresnel lens. A device and a display device are provided.

[0015]

According to a Fresnel lens of the present invention, the Fresnel lens includes a plurality of prisms, and the plurality of prisms include an inclined surface inclined with respect to an optical axis of the Fresnel lens. The focal length of the Fresnel lens is f, and the distance from the optical axis at any position is x
When at least some regions satisfying x <f,
A refraction prism having a refraction function is formed on the inclined surface, and a reflection prism having a reflection function on the inclined surface is formed in at least a part of the region satisfying x> f. Thereby, the above object can be achieved.

Further, in the Fresnel lens, at an arbitrary position where the distance from the optical axis is x, the larger of the outgoing light intensity of the refracting prism and the outgoing light intensity of the reflecting prism is exhibited. A prism is arranged. Thereby, the above object can be achieved.

Further, the plurality of prisms are formed only on one surface of the Fresnel lens, and the vertex angle θ ₁ of the reflecting prism at the arbitrary position satisfies (Equation 1). Thereby, the above object can be achieved.

Further, the plurality of prisms are formed only on one surface of the Fresnel lens, and the apex angle θ ₂ of the refractive prism at an arbitrary position satisfies (Equation 2).
Thereby, the above object can be achieved.

The plurality of prisms may further include:
The Fresnel lens has a surface substantially parallel to the optical axis. Thereby, the above object can be achieved.

Further, the Fresnel lens, a light source, and a reflector for reflecting light from the light source are arranged in this order, and the prism of the Fresnel lens is arranged on a surface facing the light source. Thereby, the above object can be achieved.

Further, a display device is constituted by a light receiving type display element including at least a light modulation layer and the illumination device. Thereby, the above object can be achieved.

In the display device, the light modulation layer is a liquid crystal layer, and a light diffusion layer for diffusing light emitted from the liquid crystal layer is provided on the viewer side of the liquid crystal layer. Thereby, the above object can be achieved.

Further, the Fresnel lens is made of acrylic resin, in any position distance of x ₂ from the optical axis, the refractive prism is formed, also, the distance from the optical axis in x ₁ At an arbitrary position, when the reflection prism is formed, distances x ₁ and x ₂ from the optical axis are 0 ≦ x ₂ ≦ 0.5f and 0.5f ≦ x ₁ ≦ 1.1f, respectively. Meet the range. Thereby, the above object can be achieved.

Moreover, the Fresnel lens is made of polycarbonate resin, in any position distance of x ₂ from the optical axis, the refractive prism is formed, also, the distance from the optical axis is x ₁ When the reflecting prism is formed at an arbitrary position, distances x ₁ and x ₂ from the optical axis are formed.
Are respectively 0 ≦ x ₂ ≦ 0.55f and 0.55f ≦ x ₁ ≦
Satisfies the range of 1.1f. Thereby, the above object can be achieved.

In a Fresnel lens having a plurality of prisms, the plurality of prisms may have an inclined surface inclined with respect to the optical axis of the Fresnel lens. Determined by the first condition setting step of setting the refractive index n and the focal length f, the second condition setting step of obtaining the apex angle θ ₂ of the refractive prism from the relational expression of (Equation 2), and the second condition setting step A third condition setting step for obtaining the intensity of the emitted light based on the obtained refraction prism, a fourth condition setting step for obtaining the vertex angle θ ₁ of the reflection prism from the relational expression of (Equation 1), and the fourth condition setting step A fifth condition setting step of obtaining the output light intensity using the reflection prism determined by the step (a), and the output light intensity calculated in the third condition setting step and the fifth condition setting step.
A comparing step of comparing the emitted light intensity calculated in the condition setting step, and a setting step of arranging the prism exhibiting the larger emitted light intensity in the comparing step at a position where the distance from the optical axis is x. In. Thereby, the above object can be achieved.

In a Fresnel lens having a plurality of prisms, the plurality of prisms has an inclined surface inclined with respect to the optical axis of the Fresnel lens. Condition input means for setting a refractive index n and a focal length f;
The prism apex angle calculating means for obtaining the apex angle θ ₂ of the refractive prism from the relational expression of (Equation 2) and the apex angle θ ₁ of the reflecting prism from the relational expression of (Equation 1), and the prism apex angle calculating means. Simulation means for obtaining the output light intensity based on the refractive prism and the reflection prism having the apex angle, and evaluation means for determining whether or not the output light intensity calculated by the simulation means satisfies a desired display quality. Have. Thereby, the above object can be achieved.

The operation of the present invention will be described below.

The Fresnel lens of the present invention has a prism composed of an inclined surface that is inclined with respect to the optical axis, and the direction in which light travels is changed by this inclined surface to form a prism-formed surface. The light exits from the exit surface facing the. From the optical axis of the Fresnel lens toward the periphery, at least a part of the area smaller than the focal length has a refractive prism having a refracting action, and at least a part of the area larger than the focal length has a reflecting action. A reflecting prism is formed. By arranging either the refraction prism or the reflection prism optimally according to the distance from the optical axis in this way, a Fresnel lens having a diameter larger than the focal length is formed, and evenly over the entire Fresnel lens. Light can be emitted. Further, since the prism is formed of an inclined surface and a parallel surface, a region for emitting light substantially parallel to the optical axis increases,
Light can be used efficiently. The apex angle of each prism is designed with respect to the distance from the optical axis of the Fresnel lens, and since the refraction prism or the reflection prism is arranged, the light can be uniformly emitted and efficiently emitted. .

The illuminating device of the present invention comprises the above-mentioned Fresnel lens, and the prism is arranged on the surface of the Fresnel lens facing the light source and the opposing light source. And the light exits from the above-mentioned exit surface, thereby uniformly irradiating the object to be irradiated.
Since the display device of the present invention includes the above-described lighting device, it is possible to provide a display with uniform luminance characteristics. In particular, by using a diffusion layer and a liquid crystal display element together,
Light with high uniformity can be made incident in the direction in which the display characteristics of the liquid crystal display element are excellent, and furthermore, the region can be enlarged by the diffusion layer, and a liquid crystal display device having excellent display characteristics can be realized. .

Further, when the Fresnel lens is an acrylic resin, 0 ≦ x ₂ ≦ 0.5f, 0.5f ≦ x ₁ ≦ 1.1
When f is a polycardnate resin, 0 ≦ x ₂ ≦
By satisfying 0.55f and 0.55f ≦ x ₁ ≦ 1.1f, display characteristics with excellent uniformity can be realized.

In the Fresnel lens design method and Fresnel lens design apparatus of the present invention, when designing a Fresnel lens, only the prism which is the most dominant function of the Fresnel lens is set as a parameter, and these are simply set. Since it is composed only of calculations, the Fresnel lens can be designed with relatively little effort.

[0032]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the Fresnel lens of the present invention,
Embodiments of a lighting device, a display device, a light receiving device, and a zoom strobe using the same will be described with reference to the drawings. In the following embodiments, embodiments of a Fresnel lens and a liquid crystal display device using the same will be described, but the present invention is not limited thereto. In the drawings used in the description of the following embodiments, the same members are denoted by the same reference numerals. (Embodiment 1) A cross-sectional view of a transmission type liquid crystal display device 1 of Embodiment 1 is shown in FIG.

The liquid crystal display device 1 has a transmissive liquid crystal panel 6 and an illuminating device (backlight) 10 on the opposite side of the viewer.

The transmission type liquid crystal panel 6 is a transmission type liquid crystal panel manufactured by a known method. Generally, the light diffusion layer 2, the polarizing plate 3, the transmission type liquid crystal cell 4, and the transmission type liquid crystal panel 4 are arranged in this order from the observer side. It has a polarizing plate 5. The transmission type liquid crystal cell 4
A liquid crystal layer and an electrode (not shown) for applying a voltage to the liquid crystal layer are provided between a pair of substrates (not shown). Here, 90
A liquid crystal display element having a degree of twist was used. The backlight 10 includes, in order from the liquid crystal panel 6, a Fresnel lens 7a,
It comprises a linear light source 8 and a reflector 9 and is arranged on the opposite side of the viewer so as to irradiate the liquid crystal panel 6.
The refraction prism and the reflection prism of each Fresnel lens 7 a are formed linearly in a direction parallel to the linear light source 8. That is, prisms having the same size and apical angles are arranged linearly in parallel with the linear light source 8. FIG. 2A is a schematic view of the configuration of the Fresnel lens 7a. 2A and 2B, the direction d is a direction parallel to the linear light source 8, and the prism 23 of the Fresnel lens 7a is formed parallel to the direction d. The prism 23
Is different depending on the distance from the optical axis 24. Then, the back light unit 1 is obtained from the Fresnel lens 7a, one linear light source 8 and a part of the reflector 9.
3 are configured. Further, the backlight 10 is configured by arranging a plurality of the backlight units. Here, a specific configuration of the prism of the funnel lens 7a will be described below.

As shown in FIG. 2B, the prism forming the Fresnel lens has a parallel surface 2 substantially parallel to the optical axis.
1 and an inclined surface 22 inclined with respect to the optical axis.
The prism 23 may be constituted only by the inclined surface, but in terms of efficient use of light, the prism 2 is formed by the parallel surface and the inclined surface.
It is more desirable to configure 3. The reason will be described with reference to FIGS. 3A and 3B.

FIG. 3 is an enlarged view of the prism 33 of the refractive prism in the Fresnel lens.
FIG. 4 is a schematic diagram showing a state in which the traveling direction of light changes after passing through the optical path. FIG. 3A shows a case where the refraction prism is formed of a parallel surface 21 and an inclined surface 22, and FIG.
(B) shows that the refraction prism is composed of the inclined surface 22 and the inclined surface 22a.
It shows the case where it is formed by. The light incident on the inclined surface 22 is refracted and emitted light 31 substantially parallel to the optical axis.
Becomes The outgoing light 31 is an outgoing light that realizes excellent display characteristics. On the other hand, the light incident on the parallel surface 21 or the inclined surface 22a is refracted, and becomes the outgoing light 32 oblique to the optical axis. The outgoing light 32 is likely to be surface-reflected when entering the object to be irradiated (a liquid crystal display element in this embodiment). Alternatively, the light is incident in a direction with poor display characteristics. Further, the hatched portion L in FIGS. 3A and 3B
1 indicates the area of the inclined surface 22. Also, the shaded portion L
2 indicates the area of the parallel plane 21 or the inclined plane 22a. The amount of light incident on each surface increases as the area of the corresponding surface increases. That is, the shaded portion L1
When the area of the light-emitting device is made as large as possible, more outgoing light 31 substantially parallel to the optical axis is emitted. Therefore, FIG. 3A and FIG.
3B, the ratio of the hatched portion L1 to the hatched portion L2 is larger in FIG. 3A, and the light use efficiency is improved. Therefore, it is desirable that the refraction prism be formed of a parallel surface and an inclined surface.

FIG. 4 is an enlarged view of the prism 43 of the reflection prism in the Fresnel lens.
FIG. 4 is a schematic diagram showing a state in which the traveling direction of light changes after passing through the optical path. FIG. 4A shows a case where the reflecting prism is formed by a parallel surface 21 and an inclined surface 22.
(B), the reflecting prism is composed of the inclined surface 22 and the inclined surface 22b.
It shows the case where it is formed by.

When the light incident on the parallel surface 21 or the inclined surface 22b is refracted and further reflected on the inclined surface 22, the emitted light 41 becomes substantially parallel to the optical axis. The outgoing light 41 is an outgoing light that realizes excellent display characteristics. On the other hand, when the light incident on the parallel surface 21 or the inclined surface 22b undergoes only a refraction function, the light is emitted in a direction oblique to the optical axis. The outgoing light 42 is incident on a body to be irradiated (which is a liquid crystal display element in this embodiment) in a direction in which the surface is easily reflected or a direction in which display characteristics are not good. Further, the hatched portion L3 in FIG. 4A and FIG.
The area of the inclined surface 22 is shown. The hatched portion L4 is
The area of the parallel surface 21 or the inclined surface 22b is shown.
The amount of light incident on each surface increases as the area of the corresponding surface increases. That is, it is better to increase the area of the hatched portion L3 as much as possible.
1 is emitted more. Thus, comparing FIG. 4A and FIG. 4B, FIG. 4A shows that the ratio of the oblique line portion L3 to the oblique line portion L4 is larger and the light use efficiency is improved. Therefore, it is desirable that the refraction prism be formed of a parallel surface and an inclined surface.

As described above, when both the refracting prism and the reflecting prism are formed from a plane parallel to the optical axis and an inclined plane, excellent display characteristics can be obtained. The parallel plane may be inclined by about 2 ° with respect to the optical axis.

Next, in FIG. 2B, the linear light source 8 was arranged near the focal length f of the Fresnel lens, and the intensity of the emitted light 14 was measured at an arbitrary position. 5 and 6 show the results.
Shown in 5 and 6, the horizontal axis is the optical axis 24 of the measurement point.
The vertical axis represents the intensity of the emitted light 14 at the optical axis 24 and the intensity of the emitted light 14 at an arbitrary position as a relative ratio. FIG. 5 shows the case where the material of the Fresnel lens is an acrylic resin (refractive index 1.49), and FIG. 6 shows the case where the material is a polycarbonate resin (refractive index 1.59).
The vertex angles θ1 and θ2 of the reflecting prism and the refracting prism were designed by the above-described equations (Equation 1) and (Equation 2), and the results are shown in Table 1. Table 1
(A) shows the case where the Fresnel lens is made of an acrylic resin, and Table 1 (b) shows the case where the Fresnel lens is made of a polycarbonate resin.

[0041]

[Table 1]

In FIGS. 5 and 6, the intensity of the outgoing light refracted by the refraction prism is large near the optical axis, but the intensity of the outgoing light generally decreases as the distance from the optical axis increases. On the other hand, the intensity of the emitted light refracted and reflected by the reflection prism is small near the optical axis, but generally, the intensity of the emitted light tends to increase as the distance from the optical axis increases.
Therefore, from the optical axis toward the Fresnel lens periphery, at least a part of the region smaller than the focal length has a refractive prism having a refraction effect, and at least a part of the region larger than the focal length has a reflection function. By forming a reflecting prism having the same, it is possible to suppress a remarkable decrease in the intensity of the emitted light and to obtain a substantially uniform intensity of the emitted light.

In particular, in order to sufficiently exhibit the display function as a liquid crystal display device, the intensity of the emitted light needs to be 0.5 (au) or more. Therefore, the arrangement area of the refraction prism and the reflection prism is determined so that the output light intensity becomes 0.5 (au) or more. First, the acrylic resin Fresnel lens shown in FIG. 5 will be described. It is around 0.5f that the light intensity emitted by the refracting prism and the light intensity emitted by the reflecting prism are about the same, and at that boundary, the light intensity emitted by the refractive prism and the light intensity emitted by the reflecting prism are The intensity is reversed. Therefore, in the Fresnel lens made of acrylic resin shown in FIG. 5, the refractive prism is arranged in a region where the distance from the optical axis is 0 or more and 0.5f or less, and at that time, corresponding to the position from each optical axis, The apex angle of the refracting prism is formed in a range from 90 ° to 64 °. In addition, a reflecting prism is arranged in an area of 0.5f or more and 1.1f or less, and a vertex angle of the reflecting prism is formed in a range of 27 ° or more and 32 ° or less corresponding to a position from each optical axis. I do. By doing so, the Fresnel lens made of acrylic resin can form a lens having a distance of 1.1f from the optical axis, that is, a lens width of 2.2f. Thus, uniform outgoing light can be obtained in a wider range. Further, as the lighting device, the lighting device in which the light source and the Fresnel lens of this embodiment are combined has a uniform outgoing light intensity and a short focal length when compared with the same irradiation area. Thinning is possible.

Next, the polycarbonate resin Fresnel lens shown in FIG. 6 will be described. It is around 0.55f that the light intensity emitted by the refracting prism and the light intensity emitted by the reflecting prism are approximately the same, and at that boundary, the light intensity emitted by the refractive prism and the light intensity emitted by the reflecting prism are equal to each other. The intensity is reversed. Therefore, in the polycarbonate resin shown in FIG. 6, the refraction prism is arranged in a region where the distance from the optical axis is 0 or more and 0.55f or less, and at that time, corresponding to the position from each optical axis,
The apex angle of the refracting prism is formed in a range from 90 ° to 56 °. Further, a reflecting prism is arranged in an area of 0.55f or more and 1.1f or less, and at this time, the apex angle of the reflecting prism is formed in a range of 28 ° or more and 33 ° or less corresponding to a position from each optical axis. This makes it possible to obtain an emitted light intensity that can function as a liquid crystal display device. Note that the same effect as when the Fresnel lens is made of acrylic resin is obtained. The diagonal using the above-mentioned acrylic resin Fresnel lens is 20 (inc
h) is specifically described below with reference to FIG. As the light source 8, a cold cathode tube was used, and as the Fresnel lens 7a, an acrylic resin Fresnel lens having a focal length of 17.3 (mm) was used. Fresnel lens 7a
In FIG. 5, the refraction prism is formed in a region where the distance from the optical axis is 0 or more and 0.5f or less, that is, in a region from the optical axis to 8.65 (mm). 6, the distance from the optical axis is 0.5f to 1.1f, that is, the distance from the optical axis is 8.65 (mm) to 19 (m).
A reflecting prism is formed in the area of m). Therefore,
A desired emission light intensity of 0.5 (au) or more can be realized in a range of 38 (mm) corresponding to a lens width of 2.2 f. In the case of a 20 (inch) liquid crystal display device, it is necessary to arrange eight backlight units 13. On the other hand, in the case of the conventional Fresnel lens, in the case of the same focal length, as shown in FIG. 17, in order to obtain a desired emission light intensity of 0.5 (au) or more, only the region whose distance from the optical axis is 0.55 f is used. It becomes a Fresnel lens that cannot be done. That is, a prism is formed in a region where the distance from the optical axis is 9.51 (mm), and the lens width is 19 (mm). Therefore, the lens width of the Fresnel lens of the present embodiment is 38
(Mm), the lens width of the conventional Fresnel lens is 19 (mm), and when the focal length is the same, uniform outgoing light can be obtained in twice as large a range. In other words, when irradiating the same area, the distance between the Fresnel lens and the light source according to the present embodiment can be reduced to 以下 or less as compared with the conventional distance between the Fresnel lens and the light source. In the case where the lens and the Fresnel lens are combined, it is possible to reduce the thickness of the lighting device.

FIG. 7 shows viewing angle characteristics of the liquid crystal display device shown in FIG. In FIG. 7, the horizontal axis represents the angle in the observation direction (viewing angle) when the angle in the front direction is set to 0, and the vertical axis represents the contrast. According to FIG. 7, the way of changing the contrast is symmetrical in the positive direction and the negative direction, and the viewing angle range where the contrast is 100 or more is −35 ° to + 35 ° in the related art.
On the other hand, in the present embodiment, it can be seen that the range with good contrast is expanded to -42 ° to + 42 °. That is, the liquid crystal display device of the present embodiment can obtain a display quality with good contrast over a wide range.

Although the illumination device described in the embodiment of the present invention uses a linear light source as a light source, a point light source such as an LED may be used. In that case, the Fresnel lens
The point light source has a structure arranged concentrically with respect to the optical axis.

In the embodiment of the present invention, a lenticular lens film is used as the light diffusion layer. However, an optical film adapted to desired optical characteristics, a scattering film mixed with scattering particles inside, or the like may be arranged. Good.

In the embodiment of the present invention, the liquid crystal is described as the light modulating layer, but any material that modulates light may be used.

The Fresnel lens according to the embodiment of the present invention is not limited to the acrylic resin or polycarbonate described above, but may be another transparent resin. The method of manufacturing the Fresnel lens includes compression molding, injection molding, and hot press molding. In addition to molding by, for example, a method of separately forming a prism with a cured resin on a transparent flat plate, a method of bonding a prism sheet having a prism formed on a transparent flat plate, and the like, and in this case, the prism is formed The refractive index n is determined by the material. The Fresnel lens manufactured as described above can be mass-produced at low cost.

The reflector 9 is a plane in the present embodiment. However, as shown in FIG. 8A, the reflector 9a has a structure in which a planar reflector is arranged so as to cover the light source.
The reflector 9b may have a structure in which a curved reflector covers the light source as shown in FIG.

The illumination device of the present invention can be used as a single illumination device, and the object to be illuminated is not limited to a display device, but can be used as an illumination device for uniformly illuminating a printed display medium. May be used.

Next, a method and an apparatus for designing a Fresnel lens used in the embodiment of the present invention will be described with reference to FIGS. The design device 90 of FIG. 9 includes a condition input unit 91 for inputting the refractive index and the focal length of the Fresnel lens.
And a prism vertex angle design unit 92 that calculates the vertex angle of the prism corresponding to the distance from the optical axis based on (Equation 1) and (Equation 2) described above, and simulates the intensity of light emitted from the prism. The simulation unit 93 includes a simulation processing unit 93, an evaluation unit 94 that evaluates the characteristics of the Fresnel lens derived by the simulation, and a parameter storage unit 95 that stores design conditions that satisfy the evaluation criteria. If the evaluation criteria are not satisfied, design conditions such as a refractive index and a focal length are changed and input, and the simulation is repeated. For the members 91 to 95, for example, an arithmetic unit such as a CPU
This is realized by executing a program stored in a storage unit such as an OM or a RAM.

Next, in the design device 90, the condition input unit 91 executes step 1 (hereinafter abbreviated as S1) shown in FIG. In S1, conditions necessary for design are input to the condition input unit 91 based on a user's instruction or the like. Here, the refractive index and the focal length of the prism are input as conditions necessary for the design. In the above S1,
When the conditions are input, S2 and S3 are executed in the prism vertex angle calculator 92, and the vertex angle θ2 corresponding to the distance from the optical axis and the vertex angle of the reflective prism corresponding to the distance from the optical axis. The vertex angle of the angle θ1 is calculated, and each refractive prism and reflective prism are designed. After that, in the simulation processing section 93, S4 and S5 are executed, and the intensities of the light emitted from the refraction prism and the reflection prism are obtained by simulation. After that, in the evaluation unit 94, S4 and S5 are executed to evaluate whether or not the simulated intensity of the light emitted from the refraction prism and the reflection prism satisfies a desired display quality. Thereafter, S6 is executed, and if the desired display quality is satisfied,
The refraction prism and the reflection prism are arranged in a range satisfying the display quality, and the data from S1 to S6 is stored in the parameter storage unit 95. The configuration is such that data can be freely extracted from the parameter storage unit 95 of the design device 90. On the other hand, if the evaluation unit 94 does not satisfy the desired display quality, the process returns to S1 to set the conditions again, and S1 to S6
Repeat until

In the design device 90, when the intensity of the outgoing light on the optical axis is 1, the intensity of the outgoing light corresponding to each distance from the optical axis toward the peripheral portion is 0.5 (au) or more. Since the arrangement range of the refraction prism and the reflection prism is determined as described above, the design device 90 can easily design the shape of the Fresnel lens to obtain a desired display quality without requiring a complicated operation.

Embodiment 2 In Embodiment 2, a light receiving device using a Fresnel lens will be described with reference to FIG.
In the drawings used in the description of the second embodiment, the same components are denoted by the same reference numerals.

In FIG. 11, the light receiving device 110 includes a light receiving element 116, a Fresnel lens 7b having a concentric prism, an infrared cut filter 114, and a light diffusing plate 1.
13 is housed in the case 115. The Fresnel lens 7b has a prism 2 on the surface facing the light receiving element 116.
3 are formed. Note that the present embodiment is different from the first embodiment in that prisms having the same size and apical angles are Fresnel lenses arranged concentrically around the optical axis, and details of the prisms are the same as those in the first embodiment. It is. Light receiving element 116 in light receiving device of the present invention
Is disposed near the focal point of the Fresnel lens 7b,
The light incident from the outside and passing through the light diffusion plate 113 and the infrared cut filter 114 has its traveling direction bent by a prism formed on the Fresnel lens 7b, and is collected on the light receiving element 116.

The light receiving device of the present embodiment can receive a wider range of light with the same focal length than the conventional light receiving device, so that the amount of light that can be received can be increased. In other words, the distance between the light receiving element and the Fresnel lens is not limited, and the thickness of the conventional light receiving device can be reduced when the light collecting range is the same.

(Embodiment 3) FIG. 12 shows a three-dimensional view of a zoom strobe in Embodiment 3. The principle of the zoom strobe will be described with reference to FIG. FIGS. 13A, 13B, and 13C show changes in the state of the emitted light depending on the relationship between the distance from the light source to the Fresnel lens and the focal length from the Fresnel lens. FIG. Light source 1
34 is disposed at a position smaller than the focal length f of the Fresnel lens, and the direction of the emitted light 131 is a direction parallel to the optical axis or a direction different therefrom, and illuminates a wide range. FIG. 13B shows a case where the light source 134 is disposed near the focal length f, and the direction of the emitted light 132 is parallel to the optical axis, and uniformly illuminates the same range as the diameter of the Fresnel lens. You can do it. FIG.
(C) is a case where the light source 134 is arranged at a position larger than the focal length f of the Fresnel lens, and the direction of the emitted light 133 is in a direction parallel to the optical axis or in a direction different from that, and Can be illuminated.

The zoom strobe 120 shown in FIG. 12 achieves a desired illumination condition by changing the distance between the light source and the Fresnel lens. In FIG. 12, the zoom strobe 120 is the light source 12
1, a Fresnel lens 7 having a prism formed on a surface facing the light source 121, and a reflector 123 disposed on the side opposite to the Fresnel lens 7 with the light source 121 interposed therebetween. The reflector 123 reflects the light from the light source 121 toward the Fresnel lens 7 to improve the light use efficiency. Further, a movable device 124 for changing the distance of the Fresnel lens 7 from the light source 121 in the optical axis direction is provided. The movable device 124 changes the distance between the light source 121 and the Fresnel lens 7 in the optical axis direction. This changes the parallelism of the light emitted from the Fresnel lens 7, and thus controls the illumination range as described above. it can. In addition, a range larger than the diameter of the Fresnel lens can be uniformly illuminated, so that the zoom strobe can be made thinner and the light use efficiency can be improved.

The zoom strobe of the present embodiment not only controls the illumination range but also arranges a light source near the focal length f to uniformly illuminate the same range as the diameter of the Fresnel lens. A wider area can be uniformly illuminated. In other words, when irradiating the same range as a conventional zoom strobe using a Fresnel lens having the same focal length, the distance from the light source to the Fresnel lens can be shortened, so that a thinner zoom strobe than before can be provided.

[0061]

According to the present invention, a refracting prism having a parallel surface substantially parallel to the optical axis and an inclined surface, and refracting light incident on the inclined surface, and reflecting light incident on the inclined surface. When the reflection prism is mixed, the optical performance by the action of the reflection prism is added to the optical performance of the Fresnel lens by the conventional refraction prism, and the thickness can be reduced. Since the display device using the Fresnel lens of the present invention has higher light use efficiency than the conventional one, high display quality can be obtained and the display device can be made thin. Further, a Fresnel lens whose design method is simple can be provided.

Similarly, as an application using the Fresnel lens of the present invention, an illuminating device, a zoom strobe, and a light receiving device which can be reduced in thickness are provided.

[Brief description of the drawings]

FIG. 1 is a transmission type liquid crystal display device according to a first embodiment of the present invention.
1 is a sectional view of FIG.

FIG. 2A is a perspective view of a Fresnel lens according to a first embodiment of the present invention, and FIG. 2B is a cross-sectional view illustrating emitted light at a position from an optical axis toward a peripheral portion.

FIG. 3A shows a case where the refraction prism is formed from a slope and a parallel surface, and FIG. 3B shows a case where the refraction prism is formed only by a slope.

FIG. 4 (a) shows a case where the reflecting prism is formed from an inclined surface and a parallel surface, and FIG. 4 (b) shows a case where the reflecting prism is formed only from the inclined surface.

FIG. 5 is a graph showing the intensity of emitted light with respect to the distance from the optical axis in the refractive prism and the reflective prism when the material of the prism of the Fresnel lens is acrylic resin (refractive index: 1.49).

FIG. 6 is a graph showing the intensity of emitted light with respect to the distance from the optical axis in the refractive prism and the reflective prism when the material of the prism of the Fresnel lens is a polycarbonate resin refractive index (1.59).

FIG. 7 is a diagram showing a change in contrast depending on the viewing angle of the transmissive liquid crystal display device 1 according to the first embodiment of the present invention and a conventional transmissive liquid crystal display device.

8A and 8B are application examples of the reflector according to the first embodiment of the present invention.

FIG. 9 is a design flowchart of the design device 90 according to the first embodiment of the present invention.

FIG. 10 is a simulation flowchart of the first embodiment according to the present invention.

FIG. 11 is a sectional view of a light receiving device according to a second embodiment of the present invention.

FIG. 12 is a schematic diagram of a zoom strobe according to a third embodiment of the present invention.

FIG. 13 is an explanatory diagram illustrating a relationship between a distance from a light source to a Fresnel lens and a focal length in a zoom strobe according to a third embodiment of the present invention.

FIG. 14A is a plan view of a conventional Fresnel lens,
(B) is a sectional view of a conventional Fresnel lens.

FIG. 15 is a sectional view of a conventional transmission type liquid crystal display device.

FIG. 16 is a schematic diagram for explaining outgoing light depending on a distance from an optical axis to a peripheral portion in a cross-sectional view of a conventional Fresnel lens.

FIG. 17 is a graph showing the intensity of emitted light with respect to a distance from an optical axis to a peripheral portion in a conventional Fresnel lens.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 transmission liquid crystal display device 2 light diffusion layer 3 polarizing plate 4 transmission liquid crystal cell 5 polarizing plate 6 transmission liquid crystal panel 7 Fresnel lens 8 linear light source 9 reflector 10 backlight 13 backlight unit 14 outgoing light 21 prism parallel Surface 22 Inclined surface of prism 23 Prism 31 Outgoing light 32 Outgoing light 33 Refracting prism 80, 81 Reflector 91 Design condition input unit 92 Prism vertex angle calculation unit 93 Simulation processing unit 94 Evaluation unit 95 Parameter storage unit 110 Light receiving device 113 Light diffusing plate 114 Infrared cut filter 115 Case 116 Light receiving element 120 Zoom strobe 121 Light source 123 Reflector 124 Moving device 131, 132, 133 Emitted light 134 Light source 140 Conventional Fresnel lens 141 Refracted surface 142 Concentric circle 143 Prism 15 Conventional transmission type liquid crystal display device 151 a light source 152 conventional Fresnel lens 153 reflector 154 backlight 155 liquid crystal display device 156 the light diffusion layer 157 light 159 illumination light 161 source from the polarizer 158 light source 162 a Fresnel lens 163 optical axis 164 light emitted

Claims (12)

[Claims] 1. A Fresnel lens having a plurality of prisms, wherein the plurality of prisms has an inclined surface inclined with respect to an optical axis of the Fresnel lens, and the focal length of the Fresnel lens is f, and an arbitrary position. When the distance from the optical axis at x is x, a refraction prism having a refraction function on the inclined surface is formed in at least a part of the area satisfying x <f, and is formed in at least a part of the area satisfying x> f. Is
A Fresnel lens, wherein a reflection prism having a reflection function is formed on the inclined surface. 2. A prism which presents a larger one of the intensity of light emitted from the refracting prism and the intensity of light emitted from the reflecting prism at an arbitrary position when the distance from the optical axis is x. The Fresnel lens according to claim 1, wherein the Fresnel lens is arranged. 3. The method according to claim 1, wherein the plurality of prisms are formed only on one surface of the Fresnel lens, and a vertex angle θ ₁ of the reflecting prism at an arbitrary position satisfies (Equation 1). 4. The Fresnel lens according to 2 or 3. (Equation 1) 4. The method according to claim 1, wherein the plurality of prisms are formed only on one surface of the Fresnel lens, and the apex angle θ ₂ of the refractive prism at an arbitrary position satisfies (Equation 2). 4. The Fresnel lens according to any one of items 2 and 3. (Equation 2) 5. The Fresnel according to claim 1, wherein the plurality of prisms further include a surface substantially parallel to an optical axis of the Fresnel lens. lens. 6. The Fresnel lens according to claim 1, a light source, and a reflector that reflects light from the light source, and a prism of the Fresnel lens faces the light source. A lighting device characterized by being arranged in a lighting device. 7. A display device comprising: a light-receiving display element including at least a light modulation layer; and the lighting device according to claim 6. 8. The display device according to claim 7, wherein the light modulation layer is a liquid crystal layer, and a light diffusion layer for diffusing light emitted from the liquid crystal layer is provided on a viewer side of the liquid crystal layer. 9. becomes the Fresnel lens is an acrylic resin, a position distance of x ₂ from the optical axis, the refractive prisms formed is formed, also, the distance from the optical axis is x ₁ When the reflective prism is formed at the position, distances x ₁ and x ₂ from the optical axis are in the ranges of 0 ≦ x ₂ ≦ 0.5f and 0.5f ≦ x ₁ ≦ 1.1f, respectively. 9. The display device according to claim 7, wherein the display device is satisfied. Wherein said Fresnel lens is made of polycarbonate resin, a position distance is x ₂ from the optical axis, is formed the refraction prism, also, the distance from the optical axis any is x ₁ In the position, when the reflecting prism is formed, the distances x ₁ and x ₂ from the optical axis satisfy the ranges of 0 ≦ x ₂ ≦ 0.55f and 0.55f ≦ x ₁ ≦ 1.1f, respectively. The display device according to any one of claims 7 to 8, wherein: 11. A Fresnel lens comprising a plurality of prisms, wherein each of the plurality of prisms has an inclined surface inclined with respect to an optical axis of the Fresnel lens. A first condition setting step for setting the refractive index n of the lens and the focal length f; a second condition setting step for obtaining the apex angle θ ₂ of the refractive prism from the relational expression of (Equation 2);
A third condition setting step for obtaining the output light intensity based on the refraction prism determined in the condition setting step, and a fourth angle obtaining the apex angle θ ₁ of the reflection prism from the relational expression of (Equation 1)
A condition setting step, a fifth condition setting step of obtaining an output light intensity using the reflection prism determined in the fourth condition setting step, and an output light intensity calculated in the third condition setting step and the fifth A comparing step of comparing the outgoing light intensities calculated in the condition setting step of 5, and a setting step of disposing the prism exhibiting the larger outgoing light intensity in the comparing step at a position where the distance from the optical axis is x. A method for designing a Fresnel lens, comprising: 12. The Fresnel lens designing apparatus according to claim 1, wherein the Fresnel lens includes a plurality of prisms, and the plurality of prisms includes an inclined surface inclined with respect to an optical axis of the Fresnel lens. The condition input means for setting the refractive index n of the lens and the focal length f, and the apex angle θ ₂ of the refracting prism from the relational expression of (Equation 2) are expressed by (Expression 1)
A prism apex angle calculating means for calculating the apex angle θ ₁ of the reflecting prism from the relational expression; A Fresnel lens design device, comprising: means for evaluating whether the intensity of the emitted light calculated by the simulation means satisfies a desired display quality.