JP4645088B2 - Light guide plate formed by blazed grating - Google Patents

Description

  The present invention relates to a light guide plate formed by a blazed grating, and more particularly to a light guide plate suitable for use in an illumination device such as a liquid crystal display device or a backlight of a display device.

  In general, a so-called backlight, which is an illumination light source used on the back surface of a transmissive liquid crystal panel, uses a light guide plate made of a transparent resin in order to uniformly guide light from the light source to the liquid crystal panel. As shown in the perspective view of FIG. 9, in an illumination device 14 in which a light source 12 that emits white light, for example, is disposed on this type of light guide plate 10, light incident on the light guide plate 10 from the end surface 11 of the light guide plate 10. Advances along the average light guide direction F in the light guide plate 10 while totally reflecting the flat portion of the light guide plate 10. Although FIG. 9 shows an example in which a linear light source is used as the light source 12, the shape of the light source 12 is not limited to a linear shape, and may be, for example, a dot shape. Prisms 16 are provided at various locations on the planar portion of the light guide plate 10, and light that hits the prisms 16 exits from the exit surface 13 of the light guide plate 10 according to the exit direction E indicated by the arrows in the drawing.

  As shown in the perspective view of FIG. 10, a transmissive liquid crystal panel 18 is disposed above the exit surface 13 of the light guide plate 10 of the illumination device 14, and an image is displayed by transmitting light emitted from the exit surface 13. A display device 24 is formed. As a known example of the light guide plate 10 in which the prism 16 is provided on the back surface as shown in FIG. 9 and FIG. As an example of an illuminating device that does not use a prism, there is a method of diffusing and emitting light by printing scattering dots on the bottom surface of the light guide plate 10.

  On the other hand, a diffraction grating is known as an optical element that efficiently guides light from the light source 12 in a desired direction. A typical configuration of a diffraction grating is an assembly of parallel lines (lattice lines) arranged at equal intervals. When the grating lines are expressed by shading, an amplitude type diffraction grating is obtained, and when expressed by an uneven shape, a phase type diffraction grating is obtained. .

  Generally, for visible light, a diffraction grating having a grating interval (pitch) of about 0.5 to 2 μm is used. As the phase type diffraction grating, a so-called binary grating having a rectangular or sinusoidal cross-sectional shape is known. However, the cross-section is assumed to have higher light utilization efficiency (diffraction efficiency) and strictly control the light emission direction. There is a blazed grating with a serrated shape.

When constructing a blazed grating, it is theoretically possible to determine the tilt angle so that the exit angle of the diffracted light determined according to the lattice spacing of the blazed grating and the exit angle of the reflected light from the gentle slope are the same. 100% diffraction efficiency can be obtained.
JP-A-5-264819 Japanese Patent No. 2865618

  However, such a conventional light guide plate has the following problems.

  That is, when the blazed grating is formed on the exit surface 13 of the light guide plate 10 or the opposed surface 15 of the exit surface 13, and the light guide plate 10 having the function of diffracting the light from the light source 12 and emitting it from the exit surface 13 is created, Due to the optical characteristics of the grating, light with little loss can be emitted from the emission surface 13. However, at the same time, due to the spectral action during diffraction, the emitted light appears to be iridescent or a specific color is observed. Therefore, the light guide plate using the diffraction grating is separately provided with a diffusion plate, or a layer having a diffusion function is integrally formed on the light guide plate, so that the color and light amount distribution of the obtained emitted light are made uniform. Is common.

  However, there is a problem in that the light utilization efficiency is lowered due to scattering of light other than the light from the exit surface by causing the light guide plate to have diffusibility, or absorption of light in the diffusion layer.

  The color of the emitted light obtained by the diffractive action of the blazed grating and the angle at which the light quantity is maximized also change depending on the wavelength of the light emitted from the light source 12. A white LED light source, a white CCFL (cold cathode tube) light source, or the like is used for the backlight of the small liquid crystal display device. The main wavelength, which is the peak wavelength of light emitted from the light source 12 that emits white light, is used. There are various values, that is, the color tone of light emitted from the light source.

  For example, when a white LED light source has a peak at a blue wavelength and a yellow wavelength, that is, when there are two main wavelength values, light of both wavelengths must be emitted in a balanced manner from the emission surface 13. White light with ideal chromaticity cannot be obtained. When the white LED light source has peaks at red, blue, and green wavelengths, that is, when there are three main wavelength values, it is necessary to emit light of the three main wavelengths from the emission surface 13 in a well-balanced manner. . However, with a light guide plate using a diffraction grating, it is difficult to adjust the chromaticity of the emitted light because the light is split by diffraction and the emission angle and the quantity of emitted light change according to the wavelength of the light.

  The present invention has been made in view of such circumstances, and by using a blazed grating, the light use efficiency is high and the chromaticity of the emitted light is strictly controlled, so that a desired color can be obtained. It is an object of the present invention to provide a light guide plate capable of obtaining emitted light having a degree.

  In order to achieve the above object, the present invention takes the following measures.

That is, in the invention of claim 1, a blazed grating is formed in each cell arranged in a matrix or a band, and the light emitted from the light source is diffracted in a predetermined direction by the blazed grating. In the light guide plate that emits the emitted light from the light exit surface, at least one of the cells, a gentle slope that forms a blazed grating, and a light exit surface on which the blazed grating is disposed or a surface opposite to the light exit surface A blazed grating having an inclination angle different from that of other cells is formed , and each cell is formed by a set of blazed gratings having the same inclination angle, and the length of each cell is 300 μm (300 × 10 6). ⁻⁶ m) or less, and there are types of inclination angles corresponding to the number of dominant wavelengths of light emitted from the light source .

Therefore, in the light guide plate of the invention of claim 1, by taking the above-described means, the light quantity of the emitted light emitted from the emission surface can be controlled for each wavelength, and the emitted light having a desired chromaticity. Can be obtained. In particular, by changing the tilt angle of the blazed grating for each cell and independently determining the peak wavelength, emission angle, and amount of emitted light for each cell, design and manufacturing can be facilitated. Become.
In addition, by taking the above measures, it is possible to adjust the tilt angle of the blazed grating in accordance with the peak wavelength of the light emitted from the light source. It is possible to adjust chromaticity.

According to a second aspect of the present invention, in the light guide plate of the first aspect of the present invention, the inclination angle of the blazed grating on the downstream side in the lattice vector direction in the cell is equal to or greater than the inclination angle of the blazed grating on the upstream side in the cell. the inclination angle of the blazed grating on the downstream side of a or in the cell, the tilt angle or less is cell blazed grating on the upstream side of the cell is at least one exists.

Therefore, in the light guide plate of the invention of claim 2 , by taking the above-described means, light of a wide range of wavelengths can be emitted uniformly and continuously from each cell. That is, it becomes possible to emit light having a substantially uniform chromaticity over a wide range.

According to a third aspect of the present invention, in the light guide plate of the first or second aspect of the present invention, at least one cell having a plurality of blazed lattice intervals is present.

Therefore, in the light guide plate of the invention of claim 3 , by taking the above-mentioned means, light incident on the blazed grating from various directions can be diffracted and emitted, and thus any light on the emission surface can be emitted. In this direction, it is possible to obtain light with higher brightness and adjusted chromaticity.

According to a fourth aspect of the present invention, in the light guide plate of the first or second aspect of the present invention, among the cells formed by the blazed gratings arranged at a single lattice interval, the lattice interval is another cell. There is at least one cell different from the lattice spacing.

Therefore, in the light guide plate of the invention of claim 4 , by taking the above-mentioned means, the light incident on the blazed grating from various directions can be diffracted and emitted, and any light on the emission surface can be emitted. In this direction, it is possible to obtain light with higher brightness and adjusted chromaticity.

According to a fifth aspect of the present invention, in the light guide plate according to the first or second aspect of the present invention, the lattice intervals of the cells formed by the blazed gratings arranged at a single lattice interval are all equal.

Therefore, in the light guide plate of the invention of claim 5 , by taking the above-described means, there is a problem of non-uniformity in optical characteristics due to a difference in processing accuracy of the blazed grating caused by different grating intervals, It is possible to avoid or reduce the problem that moiré occurs non-uniformly between the fine pattern of the optical film such as the diffusion plate, polarizing plate, and color filter and the blazed grating.

  As described above, the light guide plate of the present invention is formed using a blazed grating, so that the light use efficiency is high and the chromaticity of the emitted light can be strictly controlled.

  Note that a light guide plate in which diffraction gratings having different shapes are arranged in the same light guide plate is also disclosed in Patent Document 2, but the invention of Patent Document 2 improves the brightness and uniformity of emitted light. It is aimed at achieving the desired chromaticity as in the present invention. When the exit light is obtained by using a diffraction grating as in the invention of Patent Document 2, coloring due to the spectrum by the diffraction grating is inevitable, but the light guide plate of the present invention avoids this coloring while white diffracted light. Can be injected.

  According to the present invention, it is possible to realize a light guide plate that has high light utilization efficiency and can strictly control the chromaticity of emitted light, and can obtain emitted light having a desired chromaticity. Can do.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  In addition, the code | symbol in the figure used for description of each following form attaches | subjects and shows the same code | symbol about the same part as FIG. 9 thru | or FIG.

  First, the optical action when coherent monochromatic light such as a laser beam is incident on the blazed grating and the diffracted light is emitted will be described with reference to FIG. 1 showing an elevational section of the blazed grating.

The blazed grating 30 is composed of a gentle slope 41 and a steep slope 42 as shown in FIG. The sum of the lengths of the bottom surfaces of one gentle slope 41 and one steep slope 42 is the lattice spacing (pitch) d, and the reciprocal of the lattice spacing d is the spatial frequency. For example, when monochromatic incident light 44 having a wavelength λ is incident on such a blazed grating 30 at an angle α with respect to the normal direction with respect to the bottom surface, a relational expression between the grating interval d and the emission angle β and wavelength λ of the m-th order diffracted light.
md = λ / (sin α−sin β) (1)
Therefore, the exit angle β of the diffracted light 47 is uniquely determined. Here, in the blazed grating 30, by setting the inclination angle θ of the gentle slope 41 so that the exit angle β of the diffracted light 47 and the exit angle of the regular reflected light of the incident light 44 coincide, In addition, it is possible to obtain an emitted light having a high diffraction efficiency. By changing the grating interval d, the angle of the diffracted light 47 when coherent light such as a laser beam is incident is changed.

  Optical characteristics when white light enters the blazed grating 30 will be described with reference to FIG. When white light 48 is incident on the blazed grating 30 from the normal direction to the bottom surface, each wavelength depends on the incident angle of the white light 48, the light of each wavelength constituting the white light, and the grating interval d of the blazed grating 30. The emission angle of the diffracted light is uniquely determined, and is emitted after being dispersed.

  As shown in FIG. 2, the light 49a having a long wavelength (for example, red) emits a large diffraction angle and the light 49b having a short wavelength (for example, blue) emits a small diffraction angle. Further, when white light is incident from an angle different from that in FIG. 2, the diffracted diffracted light is emitted at an angle different from that in FIG. 2 based on the above equation (1).

  For example, when the main light source has three main peak wavelengths of 633 nm (red), 520 nm (green), and 442 nm (blue), and the grating interval d of the blazed grating 30 is 1 μm, the exit surface of the light guide plate 10 In order to emit light of those wavelengths in a direction perpendicular to 13, the incident angle α of incident light is about 39 degrees, about 31 degrees, and about 26 degrees from Equation (1). At that time, as a condition for maximizing the amount of diffracted light in the direction perpendicular to the exit surface 13, the inclination angle θ of the blazed grating 30 is about 19.5 degrees, about 15.5 degrees, It will be about 13 degrees.

  Here, by changing the inclination angle θ of any of these three types of blazed gratings 30, the amount of light emitted from the blazed gratings 30 in the direction perpendicular to the emission surface 13 can be adjusted.

  In the above example, the tilt angle θ of the blazed grating 30 that emits light having a wavelength of 633 nm perpendicular to the exit surface 13 is about 19.5 degrees. By changing the tilt angle θ, the vertical direction As a result, the chromaticity of the light perceived in the vertical direction is slightly shifted to blue or green.

  Thus, by adjusting the inclination angle θ of each blazed grating 30, the amount of emitted light can be adjusted for each wavelength, and the chromaticity can be set to a desired value. Here, in general, a white light source serving as incident light does not have a constant light amount at each wavelength, and there are variations in peak values, and light having wavelengths around the peak wavelength is emitted in different amounts for each light source. In addition, brightness recognition is different due to the difference in wavelength even with the same amount of light due to the human's specific visual sensitivity characteristics. It is preferable to determine the chromaticity of the emitted light in consideration of such a phenomenon.

  When realizing such a function in the light guide plate 10, it is necessary to consider the refractive index of the light guide plate 10. For example, the wavelength of light propagating in a medium having a refractive index n needs to be 1 / n times the wavelength propagating in the air (refractive index 1.0).

(First embodiment)
Based on the above-described principle, the light guide plate according to the first embodiment of the present invention will be described below.

  That is, in the light guide plate according to the present embodiment, a blazed grating is formed in each cell arranged in a matrix or a band, and the light emitted from the light source is diffracted in a predetermined direction by the blazed grating. In the light guide plate that emits the diffracted light from the exit surface, at least one of the cells, a gentle slope that forms a blazed grating, and the exit surface on which the blazed grating is disposed or a surface facing the exit surface A blazed grating having an inclination angle different from that of other cells is formed. In this embodiment, blazed gratings are arranged at a single lattice interval in any cell, and the lattice intervals in each cell are all equal. Further, the types of tilt angles exist corresponding to the number of main wavelengths of light emitted from the light source.

  FIG. 3A is an example of a top view of such a light guide plate 10 viewed from the exit surface 13 side, and FIG. 3B is a standing view along the AA cross section shown in FIG. It is sectional drawing.

That is, as shown in FIG. 3A, the light guide plate 10 has blazed gratings 51, 50 having different inclination angles θ ₁ , θ ₀ , θ ₂ for the cells 61, 60, 62 divided in a matrix. , 52 are arranged. In any of the cells 61, 60, 62, the blazed gratings 51, 50, 52 are arranged with the same grating interval d. The cells are periodically arranged in the order of the cells 60, 62, 61 along the X direction, and are arranged periodically in the order of the cells 62, 61, 60 along the Y direction. A band-shaped cell distribution in which the number of rows or columns of the matrix is 1 is also included in the light guide plate according to the present embodiment.

  The light source 12 that emits white light such as a white LED light source disposed on the one end surface 11 side of the light guide plate 10 generally emits light of two or three types of specific wavelengths, and the light of those wavelengths is mixed. The color is white or close to white. For example, three types of peak wavelengths of 633 nm (red), 520 nm (green), and 442 nm (blue), that is, light sources having three types of main wavelengths, two types of peak wavelengths of 442 nm (blue) and 580 nm (yellow), That is, a light source that has two types of main wavelengths and expresses white color by mixing them is common. As such a light source, there is a white CCFL (cold cathode tube) light source in addition to a white LED light source. Therefore, as the light source 12, not only a white LED light source but also a white CCFL (cold cathode tube) light source may be used.

  As described above, the wavelength distribution of the light from the light source 12 is not uniform over the entire visible light region, and has two or three types of main wavelengths, so that only light having these main wavelengths is emitted in an arbitrary direction. Thus, by determining the inclination angle θ of the blazed grating, it is possible to obtain emission light with sufficiently high brightness and chromaticity adjusted. Hereinafter, a case where light having three main wavelengths of 633 nm (red), 520 nm (green), and 442 nm (blue) is emitted from the light source 12 will be described as an example.

  The light having the three main wavelengths (red (R), green (G), and blue (B)) emitted from the light source 12 to the light guide plate 10 is repeatedly totally reflected as shown in FIG. In the process of propagating in the light guide plate 10 in the direction of the average light guide direction F, when reaching the blazed gratings 51, 50, 52, it is diffracted there and emitted from the exit surface 13.

The blazed gratings 51, 50, and 52 having three kinds of inclination angles θ ₁ , θ ₀ , and θ ₂ in accordance with the types of main wavelengths are arranged and formed in different cells 61, 60, and 62, respectively. The blazed gratings 51, 50, 52 have a function of efficiently emitting red (R), green (G), and blue (B) light in the direction perpendicular to the emission surface 13. That is, the types of inclination angles θ (three types of θ ₁ , θ ₀ , and θ ₂ ) exist corresponding to the number of main wavelengths of light emitted from the light source 12 (three types of R, G, and B). ing.

Here, in consideration of the wavelength distribution of the light source 12, the inclination angles θ ₁ , θ ₀ , θ ₂ of the blazed gratings 51, 50, 52 in the cells 61, 60, 62 are changed as necessary, and the exit surface 13 is changed. It is possible to control the chromaticity in the vertical direction.

As described above, the light guide plate 10 is divided into three types of matrix cells 61, 60, 62 in accordance with the type of the main wavelength of the light emitted from the light source 12, and each cell 61, 60, 62 is divided. By determining the inclination angles θ ₁ , θ ₀ , and θ ₂ of the blazed gratings 51, 50, and 52, design, manufacturing, ray tracing simulation, and the like can be performed efficiently. The same applies to cells arranged in a strip shape in an arbitrary direction instead of a matrix.

  Each cell 61, 60, 62 may be regularly arranged on a two-dimensional plane as shown in FIG. 3A, or may be arranged by another law. The sizes of the cells 61, 60, and 62 may not be uniform. For example, the cell 61 that emits a red wavelength having a low specific visibility in an arbitrary direction may have a larger area.

  When the light guide plate 10 according to the present embodiment is used as a backlight member for a liquid crystal device, the size of each cell 61, 60, 62 occurs between a pixel of the liquid crystal panel and a cell of the light guide plate. In order to suppress moire, it is desirable that the area is the same as or smaller than each pixel of the liquid crystal panel. Even when the light guide plate 10 according to the present embodiment is used for other purposes, the light emitted from the cells 61, 60, 62 can be reduced by making the size smaller than the resolution of the human eye, for example, 300 μm or less. It can be avoided that colors are perceived independently.

(Second Embodiment)
The light guide plate according to the second embodiment of the present invention will be described below. Since the light guide plate according to the present embodiment is a modification of the light guide plate according to the first embodiment, the same parts as those in the first embodiment are denoted by the same reference numerals. Only the differences will be described.

  That is, the light guide plate according to the present embodiment is the same as the light guide plate according to the first embodiment, in particular, the inclination angle θ of the blazed grating on the downstream side in the lattice vector direction is the inclination of the blazed grating on the upstream side. The light guide plate includes at least one cell having an angle θ that is equal to or greater than the angle θ or a tilt angle θ of the blazed grating on the downstream side is equal to or less than the tilt angle θ of the blazed grating on the upstream side.

  FIG. 4A is an elevational sectional view showing an example of the light guide plate according to the present embodiment. Note that the X direction shown in the figure coincides with the lattice vector direction. Here, the blazed gratings 51, 50, 52 arranged in the cells 61, 60, 62 have the inclination angle θ of the blazed grating on the downstream side in the lattice vector direction equal to or larger than the inclination angle θ of the blazed grating on the upstream side. It is said. The lattice spacing d is the same for all the cells 61, 60, 62. FIG. 4B is an enlarged view typically showing the cell 61 in order to show this state.

That is, the cell 61 is formed by sequentially arranging three blazed gratings 51 (# 1), 51 (# 2), and 51 (# 3) from the upstream side in the lattice vector direction. Furthermore, the inclination angles θ ₁₁ , θ ₁₂ , θ ₁₃ of the blazed gratings 51 (# 1), 51 (# 2), 51 (# 3) increase in this order (θ ₁₁ <θ ₁₂ <θ _13). ).

FIG. 4C shows another example of the present embodiment, and is an enlarged view representatively showing the cell 61 similarly. That is, in this case, the inclination angles θ ₁₁ , θ ₁₂ , θ ₁₃ of the blazed gratings 51 (# 1), 51 (# 2), 51 (# 3) become smaller in this order (θ ₁₁ > θ ₁₂ > Θ ₁₃ ).

As shown in FIGS. 4B and 4C, the inclination angles θ of the blazed gratings 51 arranged in the same cell 61 do not have to be different from each other. For example, FIG. 5A and FIG. As shown in FIG. 5B, blazed gratings 51 having the same inclination angle may be adjacent to each other. This also makes the inclination angle θ of the blazed grating on the downstream side in the lattice vector direction equal to or larger than the inclination angle θ of the blazed grating on the upstream side (θ ₁₁ <θ ₁₂ = θ ₁₂ <θ ₁₃ = θ ₁₃ = θ ₁₃ <θ ₁₄ = θ ₁₄ <θ ₁₅ ), or the inclination angle θ of the blazed grating on the downstream side is equal to or less than the inclination angle θ of the blazed grating on the upstream side (θ ₁₁ = θ ₁₁ = θ ₁₁ > θ _{12 = θ 12 = θ 12>} θ 13 = θ 13 = can be theta _13).

  Next, the operation of the light guide plate according to the present embodiment configured as described above will be described.

  As described above, the light source 12 such as a white LED light source or a white CCFL light source emits not only light of a specific wavelength but also light of a wavelength around the peak wavelength. FIG. 6 shows an example of the wavelength distribution of the light emitted from the light source 12. The light source 12 shown in the example of FIG. 6 has peaks at three wavelengths (red (R), green (G), and blue (B)), but also emits light having wavelengths around each peak wavelength, It is distributed so that the base spreads around the peak wavelength. Moreover, the way of spreading is usually different.

Thus, in order to emit incident light having a certain wavelength distribution spread from the exit surface 13 in any direction, the tilt angle θ of the blazed grating is not constant along the grating vector direction. It is convenient to change as shown in. In particular, it is preferable to continuously arrange blazed gratings having different inclination angles θ around a blazed grating having an inclination angle θ corresponding to a peak wavelength in each cell 61, 60, 62. In this case, since the optimum inclination angle θ differs depending on the wavelength of the incident light, the same cells 61, 60, 62 can be optimally emitted based on the light quantity distribution characteristics for each wavelength of the incident light. Are determined (θ _{11 to} θ _{13 in} the case of FIGS. 4B, 4C, and 5B, and θ _{11 to} θ _{15 in} the case of FIG. 5A).

In particular, the same angle of inclination in accordance with, as shown in FIG. 5 (a), blazed grating 51 having a tilt angle theta ₁₃ corresponding to the peak wavelength (# 4 to # 6) Many (3) constitutes, the amount of light is reduced Reducing the number of blazed gratings having θ (two blazed gratings each having an inclination angle θ ₁₂ and an inclination angle θ ₁₄ , one blazed grating having an inclination angle θ ₁₁ and an inclination angle θ ₁₅ each), and even better emission Light can be obtained.

Here, in order to adjust the chromaticity of emitted light by changing the inclination angle theta ₁₃ of blazed grating (FIGS. 5 (a) in the case blazed grating 51 (# 4 to # 6)) corresponding to the peak wavelength, it Accordingly, the inclination angle of the blazed grating corresponding to other wavelengths (in the case of FIG. 5A, the blazed grating 51 (# 1 to # 3, # 7 to # 9)) may be changed.

  By providing the blazed grating in this way, it is possible to obtain emitted light having a close chromaticity not only in a specific direction (for example, a direction perpendicular to the emission surface) but also in a direction in the vicinity thereof. Thus, it is possible to obtain emitted light having a substantially uniform color.

(Third embodiment)
A light guide plate according to the third embodiment of the present invention will be described below. Since the light guide plate according to the present embodiment is also a modification of the light guide plate according to the first embodiment, the same parts as those in the first embodiment are denoted by the same reference numerals. Only the differences will be described.

  That is, the light guide plate according to the present embodiment is the light guide plate according to the first embodiment, in particular, a light guide plate in which at least one cell having a plurality of blazed lattice intervals exists.

This will be described with reference to FIG. FIG. 7 shows an example of a vertical sectional shape of a certain cell included in the light guide plate according to the present embodiment. The cell comprises two blazed grating 70 composed by placing two blazed gratings 71 in series, the arrangement interval d ₀ of blazed grating 70 is different from the arrangement interval d ₁ of blazed grating 71 (d ₀ ≠ d ₁ ). Note that the inclination angle theta ₀ blazed grating 70, even the same as the inclination angle theta ₁ of the blazed grating 71, may be different. As described above, at least one cell having a plurality of lattice intervals d of the blazed lattice is provided.

  In a light guide plate using a blazed grating, incident light is dispersed as described above, and diffracted light is emitted at different angles depending on the wavelength. The exit angle of the diffracted light is determined by the incident angle of the incident light and the grating interval d of the blazed grating. Therefore, in order to obtain light with higher brightness and adjusted chromaticity in any direction on the exit surface 13, it is desirable to change the lattice spacing d of the blazed grating depending on the location, for example, as shown in FIG.

  Usually, the light from the light source 12 is emitted in a wide range to some extent, so that it also enters the blazed grating formed on the light guide plate 10 at various angles. Therefore, since light having each wavelength component is incident from various angles, it is preferable to optimize the grating interval d in consideration of the peak wavelength and incident angle of the light incident on the blazed grating.

  Furthermore, since the incident angle of the light that repeatedly reaches the total reflection also changes between the blazed grating located near the light source 12 in the light guide plate 10 and the blazed grating located away from the light source 12, the grating spacing d is also changed depending on the position. It is good to optimize. This will be described with reference to FIG.

FIGS. 8A and 8B show examples of the cross-sectional shapes of two cells included in the light guide plate according to the present embodiment. Cell shown in FIG. 8 (a) is made by placing the three blazed grating 70 at an arrangement interval d _0, the cell shown in FIG. 8 (b), by placing three blazed grating 71 at arrangement intervals d ₁ Become. The arrangement interval d ₀ and the arrangement interval d ₁ are different (d ₀ ≠ d ₁ ). Note that the inclination angle theta ₀ blazed grating 70, even the same as the inclination angle theta ₁ of the blazed grating 71, may be different. Thus, in the light guide plate according to the present embodiment, the lattice spacing of each cell formed by blazed gratings arranged at a single lattice spacing is the lattice spacing of other cells as necessary. At least one cell different from the above is provided.

  Therefore, the light guide plate according to the present embodiment makes it possible to obtain light with higher brightness and chromaticity adjusted in any direction on the exit surface 13.

  The best mode for carrying out the present invention has been described above with reference to the accompanying drawings, but the present invention is not limited to such a configuration. Within the scope of the invented technical idea of the scope of claims, a person skilled in the art can conceive of various changes and modifications. The technical scope of the present invention is also applicable to these changes and modifications. It is understood that it belongs to.

  For example, as an example of the above embodiment, a blazed grating is formed on the opposing surface 15 of the exit surface 13 of the light guide plate and functions as a reflective diffraction grating. However, a blazed grating is formed on the exit surface 13 and transmitted. The same effect can be realized as a type of diffraction grating.

The elevation sectional view of a blazed grating for explaining optical action of monochromatic light which entered a blazed grating. FIG. 3 is an elevational sectional view of a blazed grating for explaining optical characteristics when white light is incident on the blazed grating. The top view and elevation sectional view which show an example of the light-guide plate which concerns on the 1st Embodiment of this invention. FIG. 6 is an elevational sectional view showing an example of a light guide plate according to a second embodiment of the present invention. FIG. 3 is an elevational sectional view showing a detailed example of a blazed grating disposed in the same cell. The figure which shows an example of the wavelength distribution of the emitted light from a white light source. The elevation sectional view showing an example of a certain cell contained in the light guide plate concerning a 3rd embodiment of the present invention. FIG. 4 is an elevational sectional view showing an example of a cell formed by a blazed grating having different grating intervals. The perspective view of the illuminating device of the prior art in which the light-guide plate was used. The perspective view of the display apparatus of the prior art in which the light-guide plate was used.

Explanation of symbols

  E: Ejection direction, F: Average light guide direction, d: Lattice spacing, α: Incident angle, β: Ejection angle, θ ... Inclination angle, 10 ... Light guide plate, 11 ... End face, 12 ... Light source, 13 ... Emission face, DESCRIPTION OF SYMBOLS 14 ... Illuminating device, 15 ... Opposite surface, 16 ... Prism, 18 ... Transmission type liquid crystal panel, 24 ... Display apparatus, 30 ... Blaze grating, 41 ... Slight slope, 42 ... Steep slope, 44 ... Incident light, 47 ... Diffracted light, 48 ... incident light, 49 ... light, 50, 51, 52 ... blazed grating, 60, 61, 62 ... cell, 70, 71 ... blazed grating

Claims (5)

A blazed grating is formed in each of the cells arranged in a matrix or band, and the light emitted from the light source is folded in a predetermined direction by the blazed grating, and the diffracted light is reflected on the light exit surface. In the light guide plate emitted from
At least one of the cells has an inclination angle formed between a gentle slope that forms the blazed grating and the light emitting surface on which the blazed grating is disposed or a surface facing the light emitting surface of another cell. A blazed grating different from that is formed, and each cell is formed by a set of the blazed gratings having the same inclination angle, and the length of each cell is 300 μm (300 × 10 ⁻⁶ m) or less. And the type of the tilt angle exists corresponding to the number of main wavelengths of light emitted from the light source . The light guide plate according to claim 1,
Blazed the tilt angle of said blazed grating, the blazed grating tilt angle or more in either of upstream side in the cell, or on the downstream side in the cell located downstream of the grating vector direction in the cell A light guide plate in which at least one cell having a grating inclination angle equal to or less than an inclination angle of a blazed grating on the upstream side in the cell exists. The light guide plate according to claim 1 or 2 ,
A light guide plate having at least one cell having a plurality of lattice intervals of the blazed lattice. The light guide plate according to claim 1 or 2 ,
A light guide plate in which at least one cell in which the lattice interval is different from the lattice interval of other cells among the cells formed by blazed lattices arranged at a single lattice interval. The light guide plate according to claim 1 or 2 ,
A light guide plate in which the lattice intervals of the cells formed by blazed lattices arranged at single lattice intervals are all equal.

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