JP2002100224A - Point-to-line light source converting light guide body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a point-to-line light source converting light guide body which can effectively convert a point light source to a line light source having an even brightness while realizing cost reduction and size reduction and which can be preferably used as a line light source for an end face of a light guide plate. SOLUTION: Light from point light sources 5a and 5b are introduced into a transparent rod-like body via both end faces 1c and 1d. A diffraction grating is provided on a side face 1b of a transparent rod-like body. The diffraction grating diffracts incident light I so that the light is emitted from another side face 1b. A grating part 3 and a non-grating part 4 comprise a unit width W and plural diffraction grating parts 3 are provided with certain spacing. The ratio between the width of the grating part and the width of the non-grating part within each unit width W is changed so that the brightness at the other side face 1b is high and uniform.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a point-to-line light source conversion light guide used for a backlight or front light of a liquid crystal, and more particularly to a surface light source for obtaining a high-intensity and uniform line light source from a point light source. The present invention relates to a point-to-line light source conversion light guide provided with a diffraction grating.

[0002]

2. Description of the Related Art Conventionally, as a light emitting device for obtaining a surface light source having uniform luminance, for example, a light emitting device as shown in FIG. 5 is known.
(Japanese Unexamined Patent Publication No. 7-11771). In this light emitting device, first and second light source units 35a and 35b each having a reflection mirror 32 on the rear surface on both sides in the housing 31 and a cold cathode tube 34 having a lens film 33 on the front surface are shown in FIG. Provided in a vertical direction, the rear end and the front end between the two light source units 35a and 35b are provided with a reflecting plate 36 and a reflecting sheet 37 having an inverted V-shaped cross section, a first prism array plate 38, and a first having a V-shaped cross section. A first lens film 40 having a V-shaped cross section, a transparent plate 41, a diffusion plate 42, and a second lens film 43 on the front surface of the second prism array plate 39, respectively. And a light emitting member 44 composed of Each of the prisms on the opposing surfaces of the first and second prism array plates 38 and 39 has a triangular cross section with apex angles of 90 ° and 120 °, respectively, and the former ridge line is parallel to the paper surface and the latter ridge line is the paper surface. And extend vertically.

In this light emitting device, the light source units 35a, 35
The light exiting from the lens 5b through the lens film 33 is reflected by the first prism array plate 38, and then becomes substantially parallel light through the second prism array plate 39, as shown by the arrow in the drawing. The light enters the light emitting member 44 via the first lens film 40, is dispersed in multiple directions while passing through each layer of the light emitting member, and is uniformly emitted from the entire surface of the second lens film 43. A bright surface light source is obtained.

[0004]

However, in the above-mentioned conventional light emitting device, although the first and second prism array plates 38 and 39 have a large number of prisms, one side thereof is, for example, 0.16.
mm, which is considerably larger than the wavelength of light, and since each prism individually reflects or totally reflects or refracts light in pure geometrical optics without cooperating, increase the brightness of the exit surface as a whole. In this case, there is a problem that irregular reflection occurs at a position corresponding to the valley of each prism and the amount of emitted light is reduced, resulting in an extremely bright and dark contrast on the surface of the second lens film 43 which is the exit surface. In addition, the above-mentioned conventional light emitting device,
A pair of light source units 35a and 35b including a reflection mirror 32, a lens film 33, and a cold cathode tube 34, two prism array plates 38 and 39, two lens films 40 and 43,
Since it is composed of a large number of members such as the transparent plate 41, the diffusion plate 42, and the reflection plate 36, a large amount of light is lost while passing through these optical media, and the amount of light generated by the linear light source cannot be converted to surface illumination with high efficiency. In addition, there is a problem that it is difficult to reduce the manufacturing cost and reduce the weight and thickness of the device. Here, if an attempt is made to use a light emitting diode or the like as a point light source in place of the cold cathode tube 34 as a line light source in order to reduce the size of the device, sufficient brightness due to the above-mentioned contrast between light and dark and light loss in the optical path will be caused. Cannot obtain a satisfactory uniform line light source.

Accordingly, an object of the present invention is not to provide total reflection or refraction by a conventional prism utilizing the geometrical optical properties of light, but to use a diffraction grating which has not been used until now due to the difficulty of fine processing. By utilizing the diffraction phenomena based on the wave dynamics of a point light source, it is possible to convert a point light source into a line light source with uniform brightness at a much higher efficiency than before, while reducing costs and miniaturization. An object of the present invention is to provide a point-to-line light source conversion light guide suitable for use as a light source.

[0006]

To achieve the above object, a point-to-line light source conversion light guide for converting a point light source to a line light source according to the present invention comprises a transparent rod having a rectangular cross section. Light from a point light source enters from one side surface or at least one end surface of the body, and is diffracted onto one side surface or the other side surface of the rod-like body so that light incident from the point light source exits from the other side surface. A diffraction grating is provided, and at least one of the cross-sectional shape of the diffraction grating or the ratio of the grating portion width to the non-grating portion width in a unit width is changed so that the brightness on the other side surface is increased and uniformized. It is characterized by being hampered.

As shown in FIG. 1, when one side surface 1a of a light guide plate 1 made of a transparent rod is provided with diffraction gratings 2 (cut grooves) at an interval d, for example, the light guide plate 1 The light I from the point light source incident from one end face 1c toward the side face 1a of the
The incident light is diffracted toward b, and the following formula (1) is established between the incident light I and the diffracted light D, where i is the incident angle, θ is the diffraction angle, λ is the wavelength of light, and m is an integer. . (sini−sin θ) = ± m (λ / d) (1) D ₁ , D ₂ and D ₃ in the figure are diffractions when m in the above equation (1) is ₁ , ₂ , and ₃ , respectively. The direction of light is shown. Since the incident angle of the incident light I on the diffraction grating 2 on the side surface 1a is larger than the critical angle φ (for example, in the case of an acrylic light guide plate, φ = 42 °),
The first-order diffracted light D ₁ is a diffraction angle θ ₁ close to the incident angle i, the second-order diffracted light D ₂ is a diffraction angle θ ₂ narrower than θ ₁ , and the third-order diffracted light D ₃ is more than θ ₂ At a narrow diffraction angle θ ₃ , each of the side surfaces 1 a is subjected to reflection-type diffraction toward the other side surface 1 b. Since the angle of incidence of the first and second order diffracted lights on the other side 1b is larger than the critical angle φ, the first and second order diffracted lights D ₁ and D ₂ are
The light is totally reflected at b and guided further inside the light guide plate 1,
Since the higher-order diffracted lights D ₃ ,... Are refracted at an emission angle larger than the incident angle and go forward from the other side surface 1 b, the higher-order diffracted lights D ₃ ,. Is illuminated brightly, thereby obtaining a line light source.

The diffraction grating method of the present invention is essentially different from the conventional prism array plates 38, 39 (see FIG. 5) in which each prism totally reflects or refracts light individually without cooperation. The interval d is 1/100 of submicron to several tens of microns (0.1 to 10 μm) compared to 0.16 mm on one side of the above prism. Thus, light as a wave can be remarkably strongly diffracted, and the illuminated surface 1b with remarkably high brightness can be obtained. In addition, the light guide plate having such a diffraction grating,
For example, the engraved groove is machined on the inner surface or molded by a mold with a hologram electroformed film of a diffraction grating, or the engraved groove is directly machined or printed on the back surface of the light guide plate,
It can be made by attaching a film by printing or hologram.

In the point-to-line light source conversion light guide according to the first aspect of the present invention, the diffraction grating provided on one or the other side surface of the transparent bar having a rectangular cross section has a cross-sectional shape or a non-grating portion width in a unit width. At least one of the ratios of the widths of the portions is changed so that the brightness on the other side surface 1b is increased and uniformized. That is, the diffraction grating 2 of the point-line light source conversion light guide 1 is, for example, one end face 1 on the light source side.
As the distance from c increases, that is, as the amount of light reaching the light source decreases, for example, the cross-sectional shape changes from a sine wave to a saw-tooth shape, or the ratio of the grating portion width to the non-grating portion width in a unit width gradually increases. Therefore, the light from the light source is weakly diffracted on the one end face 1c side where the light quantity is large, and is strongly diffracted on the far side where the light quantity is small, so that the other side face 1b of the light guide is illuminated with very uniform luminance. . That is, the light from the point light source is converted into a high-intensity and uniform line light source by the point-to-line light source conversion light guide.

According to a second aspect of the present invention, there is provided a point-to-line light source conversion light guide, wherein the light of the point light source enters from both end surfaces of the rod, and the diffraction grating is provided with a diffraction groove in a longitudinal direction on one side surface of the rod. A prism array is provided on the other side surface of the rod in a vertical or horizontal direction.

In the point-to-line light source conversion light guide according to the second aspect, the light of the point light source incident from both end faces of the rod is provided by a diffraction grating provided on one side surface of the rod in a vertical direction. The light is diffracted in the same manner as described in 1, and becomes a high-intensity and uniform line light source, and is emitted from the other side. At this time, low-order diffracted light to be emitted at a large emission angle is vertically transmitted to the other side. Alternatively, the light is converged to a small emission angle by a prism array provided in the lateral direction. Since the point light source is on both sides of the rod and the low-order diffracted light is converged by the prism array, the other side is illuminated with higher brightness and uniformity. Done.

According to a third aspect of the present invention, the point-to-line light source conversion light guide is formed of a transparent rod having a right-angled triangular cross section. Light from the point light source enters from a horizontal lower surface of the rod. On the vertical side surface, a diffraction grating that is incident from the point light source and diffracts the light totally reflected on the inclined surface of the rod-shaped body so as to emit from the vertical side surface is provided. At least one of the ratios of the grid width to the non-grid width is changed so that the luminance on the vertical side surface is increased and is made uniform.

According to a third aspect of the present invention, there is provided a light guide for converting light into a point-to-line light source. At least one of the width ratios is changed so that the brightness on the vertical side surface is increased and uniformized, and the light of the point light source incident from the horizontal lower surface of the rod-shaped body is inclined. , And is incident on the diffraction grating on the vertical side surface. As the incident light amount is reduced based on the incident light amount determined by the relative position with respect to the point light source, for example, the diffraction grating has a cross-sectional shape from a sine wave to a sawtooth shape, or a ratio of the grating portion width to the non-grating portion width in a unit width. Is changed, and the luminance is made uniform. Therefore, the light from the point light source is weakly diffracted at the portion where the amount of incident light on the diffraction grating is large, and is strongly diffracted at the portion where the amount of incident light is small, so that the vertical side surface of the light guide has very uniform brightness. Illuminated. That is, the above point-
The light from the point light source is converted into a high-intensity and uniform line light source by the line light source conversion light guide.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the illustrated embodiments. 2A and 2B are a perspective view and a plan view, respectively, showing one embodiment of the point-to-line light source conversion light guide according to claim 1 of the present invention. As shown in FIG. 2A, the point-to-line light source conversion light guide 1 is made of a transparent resin rod having a square cross section, and both end faces 1c and 1d of the rod.
The light I of the point light sources 5a and 5b (see FIG. 2B) is incident on the rod, and the light I incident on one side 1a of the rod is diffracted so as to be emitted from the other side 1b. A grid 2 is provided. Although the diffraction grating 2 is depicted in FIG. 2A as being provided at a constant grating interval d as in FIG. 1, actually, the non-grating in the unit width W shown in FIG. The ratio of the grid width to the width of the edge is equal to both end faces 1c,
The amount of diffracted light is set to increase as the amount of diffracted light increases as the amount of light reaching from 1d decreases. Here, the unit width W is the sum of one lattice portion width 3 and one non-lattice portion width 4, and is the width of a unit section. On the side surface 1a of the light guide plate 1 in FIG. 2B, 14 sections each having a unit width W schematically shown are provided,
The grid portion width is indicated by the thick line portion 3 of each section, and the non-grid portion width is indicated by the thin line portion 4 of each section. Therefore, it can be understood that the amount of diffracted light increases. Although the number of the sections is set to 14 for convenience of explanation, the number is actually much larger, for example, about 1000 in one example. Further, the cross-sectional shape and the grating interval d of the diffraction grating 2 are
It is set so that the ratio of higher-order diffracted light that contributes to the illumination of the side surface 1b to the total diffracted light with respect to the wavelength λ of the light source increases.

In this embodiment, the lattice 3 and the non-grid 4
Are provided on the left and right sides of each unit width W, but they are alternately provided in one unit width so that the unit width can obtain the ratio of the lattice width to the specific non-grid width. Is also good.
Also, the ratio of the grid width to the non-grid width need not be gradually increased as approaching the central portion as shown in FIG. 2B, but may be any value as long as high and uniform brightness can be obtained on the other side surface 1b. Can be changed to In this embodiment, the diffraction grating 2 is formed at the same time as the light guide using a mold having a grating interval d of several μm and a machined groove on the inner surface. d is 0.1 to 10μ
m, it can also be formed by in-mold molding in which a hologram film of a diffraction grating is inserted, machining of a groove on the back surface of the light guide plate, printing on the back surface of the light guide plate, or pasting the diffraction grating film by a hologram.

The point-to-line light source conversion light guide 1 configured as described above converts a point light source to a line light source as follows. Point light sources 5a on both sides,
The light from 5b is incident on the side surface 1a via both end surfaces 1c and 1d, and hits the diffraction grating provided on the grating portion 3 within each unit width W of the side surface 1a. The diffracted light is diffracted by the cooperation of the mirror surface between the grooves, and the higher-order diffracted light is shown in FIG.
Is emitted from the other side 1b, as shown by arrows in (B) to the outside, the low-order diffracted light is totally reflected into the interior on the other side surface 1b toward the direction of the arrow D ₁ of the Figure 1.

The diffraction grating has one side described in the conventional example of FIG.
Compared to the conventional prism array, which is about 0.16 mm and totally reflects light individually and geometrically, a large number of grooved grooves cooperate with each other in the order of 1/100, synergistically, and act as a wave in a specific direction. Since the light is diffracted intensively, diffracted light of much higher intensity than in the conventional example can be obtained. In addition, the cross-sectional shape and the grating interval d of the diffraction grating are set so that the ratio of higher-order diffracted light that contributes to the illumination of the other side surface 1b in the total diffracted light increases, and the non- The ratio of the width of the grating portion 3 to the width of the grating portion 4 is set so as to gradually increase from the end surfaces 1c and 1d toward the center. Therefore, the light from the point light sources 5a and 5b can be efficiently used for illuminating the other side surface 1b by diffraction, and the decrease in the amount of light accompanying the separation from the point light source can be compensated for by increasing the density of the diffraction grating. Is illuminated with a very high and uniform brightness. That is, the light from the point light sources 5a and 5b is converted by the point-to-line light source conversion light guide 1 into a line light source having high and uniform luminance. In addition, double brightness can be obtained as compared with a case where a point light source is provided on only one side.

The point-to-line light source conversion light guide of the present invention including the above-described embodiment is a front light light guide plate (Japanese Patent Application No. 2000-27) using a diffraction grating recently applied by the applicant.
No. 8456) as a line light source, it provides a surface light source with high and uniform brightness while reducing the manufacturing cost and reducing the weight and thickness of the front light unit and hence the liquid crystal display illuminated thereby. be able to. It is also possible to increase the intensity of the diffracted light by changing the cross-sectional shape of the diffraction grating from a sine wave to a sawtooth shape without increasing the ratio of the grating portion width to the non-grating portion width in the unit width W of the diffraction grating. Can be.

In the point-to-line light source conversion light guide 1 shown in FIG. 2, a prism array (not shown) may be provided in the vertical direction on the other side surface 1b. In this prism array, an isosceles triangle having an acute vertex angle is continuously arranged along the side surface 1b in FIG. 2B, and the ridge line of the prism array is in a direction perpendicular to the plane of FIG. 2B. That is, it extends in the vertical direction. The low-order diffracted light diffracted by the diffraction grating on one side 1a is incident on the other side 1b at such a large incident angle as to be totally reflected as described above, but the prism array is provided on the other side 1b. In this case, the light beam incident at the large incident angle is caught by the prism array and emitted forward so as to converge in the normal direction. Therefore, according to this point-to-line light source conversion light guide, the other side surface 1b emits light with higher luminance and more uniformly, so that a more efficient conversion from a point light source to a line light source can be performed. In addition, the prism array can be provided so that the ridge line extends in the horizontal (horizontal) direction, so that the same operation and effect can be obtained.

FIG. 3 is a perspective view showing another embodiment of the point-to-line light source conversion light guide according to the first aspect. The point-to-line light source conversion light guide 11 includes point light sources 5a,
This embodiment differs from the embodiment shown in FIG. 2 in that 5b is replaced behind one side surface 11a to make four, and the diffraction grating on one side surface 11a is of a transmission type. The relief shapes of the reflection type and transmission type diffraction gratings can be obtained by performing calculations using a computer to cause desired diffraction based on the theoretical equations of diffraction derived from Maxwell's equation. In this case, the reflectance can be changed. The ratio of the grid width to the non-grid width in each unit width W of the side surface 1a is expressed by the unit width W for the four point light sources 5.
Are gradually increased as the amount of light received from the point light source, which is determined by the relative position of the light source, decreases.

According to this embodiment, the light from the point light source 5 is weakly diffracted at the unit width portion of the side surface 11a where the amount of received light is large and strongly diffracted at the unit width portion where the amount of received light is small. Is illuminated with very uniform brightness, so point light sources 5,
, Can be converted into a high-intensity and uniform line light source. The other side surface 11b of this embodiment can be provided with a prism array in the vertical or horizontal direction in the same manner as described above, thereby making it possible to perform more efficient conversion from a point light source to a line light source. it can.

FIG. 4 is a perspective view showing an embodiment of the point-to-line light source conversion light guide according to the third aspect. The point-to-line light source conversion light guide 21 is formed of a transparent rod having a right-angled triangular cross section. Light from the three point light sources 5 is incident from a horizontal lower surface 21a of the rod, and the rod-shaped light is converted to a light. The incident light from the point light source 5 is incident on the vertical side surface 21c, and the inclined surface 21b
There is provided a transmission type diffraction grating for diffracting the light totally reflected by the light source so as to exit from the vertical side surface 21c. This diffraction grating is also illustrated in a simplified manner as in the embodiment of FIG. 3, but the ratio of the grating portion width to the non-grating portion width in each unit width W of the side surface 21c is different for each unit for the three point light sources 5. As the amount of light received from the point light source, which is determined by the relative position of the width W, decreases, the amount is compensated for.

In this embodiment, the point at which light from the point light source 5 enters the rod-shaped body and then enters the front diffraction grating after being totally reflected is that light from the point light source 5 in FIG. Differs from the embodiment in which a grid is entered. However, since the diffraction gratings are of the same transmission type, the diffraction action itself does not differ at all. Therefore, also in this embodiment, the light from the point light sources 5, 5,... Can be converted into a high-intensity and uniform line light source, and the front light source has no space at the back of the point-line light source conversion light guide. It can be suitably incorporated in a light guide device such as a light unit.

[0024]

As is apparent from the above description, the point-to-line light source conversion light guide according to claim 1 of the present invention has a rectangular cross section on which light from the point light source enters from one side surface or at least one end surface. A diffraction grating that diffracts incident light and emits it from the other side surface is provided on one or the other side surface of the transparent rod-shaped body having a cross-sectional shape or a non-grating portion width in a unit width. Since at least one of the ratios is changed so that the brightness on the other side is increased and made uniform, the lack of light amount far from the point light source is compensated by the increase in the density of the diffraction grating, and the directivity is high. By emitting high-intensity diffracted light, a high-intensity and uniform line light source can be obtained on the other side, and can be conveniently applied to a light guide device such as a front light unit while reducing the size, weight, and manufacturing cost. thing It can be.

According to a second aspect of the present invention, there is provided a point-to-line light source conversion light guide, wherein the light of the point light source is incident from both end faces of the rod, and the diffraction grating is provided on one side surface of the rod in a vertical direction. Vertical or horizontal prism array on the other side of the rod
Since the (ridge line) is provided, the prism array converges a low-order diffracted light that is to be emitted at a large exit angle to a small exit angle in addition to the above-described function and effect of claim 1, so that the other side surface is A more efficient conversion to a linear light source can be performed with higher luminance and uniform illumination.

According to a third aspect of the present invention, there is provided a point-to-line light source conversion light guide, wherein a transparent rod-like body having a right-angled triangular cross section on which light from the point light source enters from a horizontal lower surface is formed by a slope. A diffraction grating for diffracting the totally reflected incident light and emitting the diffracted light from a vertical side surface, wherein at least one of the sectional shape of the diffraction grating or the ratio of the grating portion width to the non-grating portion width in a unit width is set to the other side surface; Is increased so as to be uniform, so that the shortage of the light amount far from the point light source is compensated by the increase in the density of the diffraction grating, and by the emission of the diffracted light having strong directivity, the vertical A high-intensity and uniform line light source can be obtained on the side surface, and it can be conveniently applied to a light guide device such as a front light unit while reducing the size and weight and reducing the manufacturing cost.

[Brief description of the drawings]

FIG. 1 is a schematic view showing the principle of light diffraction by a diffraction grating provided on a side surface of a point-to-line light source conversion light guide.

FIG. 2 is a perspective view and a plan view showing an embodiment of a point-to-line light source conversion light guide according to claim 1 of the present invention.

FIG. 3 is a perspective view showing another embodiment of the point-to-line light source conversion light guide according to claim 1 of the present invention.

FIG. 4 is a perspective view showing an embodiment of a point-to-line light source conversion light guide according to claim 3 of the present invention.

FIG. 5 is a cross-sectional view showing a conventional light emitting device.

[Explanation of symbols]

 1,11,21 Point-to-line light source conversion light guide 1a, 11a One side 1b, 11b The other side 1c, 11c One end 1d, 11d The other end 2 Diffraction grating W Unit width 3 Grating portion 4 Non-grating portion 5, 5a, 5b Point light source 21a Horizontal lower surface 21b Slope 21c Vertical side light from I point light source

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (reference) // F21S 2/00 F21Y 101: 02 G02F 1/13357 F21S 1/00 D F21Y 101: 02 G02F 1/1335 530 F term (reference) 2H038 AA54 BA01 2H049 AA07 AA13 AA25 AA31 AA43 AA55 AA65 AA66 CA05 CA08 CA09 CA15 2H091 FA19Z FA21Z FA23Z FA29Z FA41Z FD03 LA12 LA18

Claims (3)

[Claims] 1. A point-to-line light source conversion light guide for converting a point light source to a line light source, wherein the point-to-line light source conversion light guide comprises a transparent rod having a rectangular cross section. And a diffraction grating that diffracts the light incident from the point light source on one side or the other side of the rod-shaped body so that the light is emitted from the other side. At least one of the cross-sectional shape of the diffraction grating or the ratio of the grating portion width to the non-grating portion width in the unit width is changed so that the brightness on the other side surface is increased and uniformized. A point-to-line light source conversion light guide. 2. The point-to-line light source conversion light guide according to claim 1, wherein the light of the point light source is incident from both end faces of the rod, and the diffraction grating is vertically arranged on one side surface of the rod. A point-to-line light source conversion light guide, wherein a diffraction groove is provided, and a prism array is provided in the vertical or horizontal direction on the other side surface of the rod-shaped body. 3. A point-to-line light source conversion light guide for converting a point light source to a line light source, wherein the point-to-line light source conversion light guide comprises a transparent rod having a right-angled triangular cross section. While the light of the point light source is incident from the horizontal lower surface, the light incident from the point light source on the vertical side surface of the rod is diffracted so that the light totally reflected on the inclined surface of the rod is emitted from the vertical side surface. A diffraction grating is provided, and at least one of the cross-sectional shape of the diffraction grating or the ratio of the grating portion width to the non-grating portion width in a unit width is changed so that the luminance on the vertical side surface is increased and uniformized. A point-to-line light source conversion light guide, comprising: a light source;