Light source device and image display device

Abstract

To provide a small-sized light source device capable of illuminating an image display element evenly with high efficiency.SOLUTION: A light source device has a light source, and a light guide plate that propagates a light flux from the light source toward a specific direction. The light guide plate comprises separation means that divides the light flux from the light source into a plurality of light fluxes and emits the plurality of light fluxes from the light guide plate. The separation means is configured to increase transmittance for a predetermined wavelength contained in the light flux from the light source along the specific direction.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a light source device that uniformly illuminates an image display element or the like with a light beam from a light source, and to an image display device having the same. [Background technology]

[0002] Conventionally, a configuration has been disclosed in which a diffractive element is used to cause a light beam from a light source to propagate through a light guide plate by total reflection, and the light beam is split into a plurality of light beams to illuminate an image display element (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] US Patent Application Publication No. 2020 / 0292840 Summary of the Invention [Problem to be solved by the invention]

[0004] However, since the diffraction angle of a diffraction element changes depending on the wavelength, multiple light guide plates are required to uniformly illuminate the image display element with light beams of multiple wavelengths. Also, the performance of a diffraction element changes significantly with even a small change in its structure, making it difficult to mass-produce.

[0005] An object of the present invention is to provide a light source device which is small in size and capable of illuminating an image display element efficiently and uniformly. [Means for solving the problem]

[0006] A light source device according to one aspect of the present invention comprises a light source and a light guide plate that propagates a light beam from the light source in a specific direction, the light guide plate having a separation means that divides the light beam from the light source into a plurality of light beams and emits the plurality of light beams from the light guide plate, and the separation means is configured to increase the transmittance for a predetermined wavelength contained in the light beam from the light source along the specific direction. Effect of the Invention

[0007] According to the present invention, it is possible to provide a light source device which is small in size and capable of illuminating an image display element efficiently and uniformly. [Brief description of the drawings]

[0008] [Figure 1] 1 is a configuration diagram of a light source device according to a first embodiment. [Diagram 2] FIG. 2 is a configuration diagram of a light source according to the first embodiment. [Diagram 3] 4 is a diagram showing the transmittance and film thickness ratio of the first dielectric film in Example 1 for light of a predetermined wavelength. FIG. [Figure 4] FIG. 1 is a configuration diagram of an image display device according to a first embodiment. [Diagram 5] FIG. 11 is a configuration diagram of a light source device according to a second embodiment. [Figure 6] FIG. 11 is a configuration diagram of an image display device according to a third embodiment. [Figure 7] FIG. 11 is a configuration diagram of an image display device according to a fourth embodiment. [Figure 8] FIG. 13 is a configuration diagram of a light source device according to a fifth embodiment. [Figure 9] FIG. 13 is a diagram showing the transmittance and film thickness ratio of the first dielectric film of Example 5 for light of a predetermined wavelength. [Figure 10] FIG. 13 is a diagram showing another example of the film thickness ratio of the first dielectric film in Example 5. [Figure 11] FIG. 13 is a configuration diagram of a light source device according to a sixth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, the same reference numerals are used to refer to the same components, and duplicated descriptions will be omitted. EXAMPLES

[0010] 1 is a configuration diagram of a light source device 10 of this embodiment. The light source device 10 has a light source 11 and a light guide plate 12, and is applicable to an image display device.

[0011] The light source 11 emits collimated light obtained by collimating light from a laser light source using a collimator lens. The light source 11 may emit collimated light obtained by combining laser light of two or more colors. The light source 11 may also emit collimated light obtained by collimating light from a light source such as an LED or a mercury lamp. In this embodiment, collimated light obtained by combining laser light of 450 nm, 520 nm, and 635 nm is assumed.

[0012] Since light from a laser light source is emitted with a predetermined angular distribution, collimated light generally has an illuminance distribution in which the illuminance is high at the center and low at the periphery. In order to improve the uniformity of the illuminance of the illumination light, it is preferable that the collimated light emitted from the light source 11 has a uniform illuminance distribution.

[0013] 2 is a configuration diagram of the light source 11. The light source 11 includes a laser light source 21, a first deflection element 22, and a second deflection element 23. The first deflection element 22 deflects the radiation light having a predetermined angular distribution from the laser light source 21 to radiation light having a uniform angular distribution, and the second deflection element 23 collimates the radiation light. The deflection element is an optical element such as a metasurface, a diffraction element, or an aspheric collimator lens, and a configuration in which the first deflection element 22 and the second deflection element 23 are provided on both sides of one element may be used. Since a typical collimated light has a circular or elliptical distribution, it is preferable to shape the illuminance distribution of the collimated light having a rectangular distribution by using a deflection element.

[0014] The light guide plate 12 includes a first dielectric film (separation means) 12a, a second dielectric film (reflection means) 12b, a third dielectric film 12c, and a fourth dielectric film 12d.

[0015] The first dielectric film 12a has a property of reflecting a part of the light beam from the light source 11 and transmitting the other part. As a result, the first dielectric film 12a has a property of dividing the light beam from the light source 11 (light of a predetermined wavelength in the light guide plate 12) into multiple light beams and emitting the multiple light beams from the light guide plate 12. The first dielectric film 12a is configured such that the transmittance for a predetermined wavelength contained in the light beam from the light source 11 increases along the +x direction (a specific direction) in which the light beam from the light source 11 propagates through the light guide plate 12. The predetermined wavelength is the central wavelength of the light beam from the light source 11 or the wavelength at which the intensity is strongest.

[0016] In this embodiment, the first dielectric film 12a is a dielectric gradient film configured so that the transmittance increases along the +x direction. For example, the first dielectric film 12a is configured so that the transmittance Tx(x1) at a first position x1 of the first dielectric film 12a is 25%, and the transmittance Tx(x2) at a second position x2 different from the first position x1 in the +x direction is 75%. In addition, the transmittance Tx(x3) at a third position x3 (=(x2+x1) / 2) between the first position x1 and the second position x2 in the +x direction satisfies the following conditional formula (1).

[0017] 30≦Tx(x3)≦70 (1) In addition, when the film thicknesses of the first dielectric film 12a at the first position x1, the second position x2, and the third position x3 are U(x1), U(x2), and U(x3), respectively, the following conditional formula (2a) or (2b) is satisfied.

[0018] U(x1) <U(x3)<U(x2) (2a) U(x2) <U(x3)<U(x1) (2b) It is preferable that the thickness of the first dielectric film 12a continuously increases or decreases along the +x direction. If the film thickness is a gradient film that changes continuously, the dielectric film can be deposited in a single deposition process, and the production can be simplified.

[0019] 3(a) and 3(b) respectively show the transmittance and film thickness ratio of the first dielectric film 12a for light of a predetermined wavelength. In this embodiment, the predetermined wavelength is 520 nm. Wavelengths of 450 nm and 635 nm have similar characteristics. In FIG. 3(b), the film thickness at the center is normalized to 1. The first dielectric film 12a may be configured with minute regions so that the transmittance changes stepwise.

[0020] In this embodiment, the refractive index n of the light guide plate 12 is 1.52, the incident angle θ of the light in the light guide plate 12 is 21.6°, and the exit angle θa of the light exiting the light guide plate 12 is 34.0°. Also, a diffraction element, a hologram element, a metasurface, or the like may be used instead of the first dielectric film 12a.

[0021] The second dielectric film 12b is disposed opposite to the first dielectric film 12a and has a characteristic of reflecting light incident at a predetermined angle. In this embodiment, the second dielectric film 12b has a characteristic of reflecting light with an incident angle of 21.6° and transmitting light with an incident angle of 0°. The third dielectric film 12c has a characteristic of reflecting light with an incident angle of at least 21.6°. The second dielectric film 12b may be used as the third dielectric film 12c. The fourth dielectric film 12d is an anti-reflection film.

[0022] A light beam L11 from the light source 11 enters the light guide plate 12, propagates in the +x direction through the second dielectric film 12b and the third dielectric film 12c, enters the first dielectric film 12a, and is separated into a light beam L12a (about 25% of L11) and a light beam L13a (about 75% of L11). The light beam L13a is reflected by the second dielectric film 12b, enters the first dielectric film 12a, and is separated into a light beam L12b (about 25% of L11) and a light beam L13b (about 50% of L11). The light beam L13b is reflected by the second dielectric film 12b, enters the first dielectric film 12a, and is separated into a light beam L12c (about 25% of L11) and a light beam L13c (about 25% of L11). The light beam L13c is reflected by the second dielectric film 12b, enters the first dielectric film 12a, and is emitted as the light beam L12d (about 25% of L11). The light beam emitted from the light guide plate 12 is used as a light beam for illuminating an image display element (not shown) or the like.

[0023] 4 is a configuration diagram of the image display device of this embodiment. The image display device has a light source device 10, a digital mirror device 43, and a projection lens 44.

[0024] The digital mirror device 43 is an image display element in which pixels are composed of micromirrors, and images are generated by tilting each micromirror over time. In this embodiment, the deflection angle of the micromirrors is 17°, and the digital mirror device 43 emits light incident at an incident angle of 34° as ON light at an incident angle of 0°. The light beam emitted from the light guide plate 12 illuminates the digital mirror device 31 at an incident angle of 34.0°. The ON light reflected by the digital mirror device 43 is emitted as light beam L43 (L43a, L43b, L43c, L43d), passes through the first dielectric film 12a and the second dielectric film 12b at an incident angle of 0°, and illuminates the illuminated surface via the projection lens 34.

[0025] A preferred configuration of this embodiment will now be described.

[0026] It is preferable to diffuse the light flux L43 by disposing a diffusion plate between the digital mirror device 43 and the light guide plate 12, or between the projection lens 44 and the light guide plate 12. This is preferable because it makes it possible to obtain high resolution performance in accordance with the F-number of the projection lens 44.

[0027] When the number of regions of the first dielectric film 12a with different transmittance is n and the number of divisions of the light beam (the number of multiple light beams generated by dividing the light beam from the light source 11 by the first dielectric film 12a) is m, it is preferable to satisfy the following conditional formula (3).

[0028] n / m≧2.0 (3) In this embodiment, the number of regions n is ∞, and the number of divisions m is 4. If it is below the lower limit, the difference in transmittance becomes large, and the transmittance changes significantly when the position of the light beam incident on the vicinity of the boundary between the regions deviates slightly from the design value, which is not preferable because it significantly reduces the uniformity of the light beam illuminating the illuminated surface.

[0029] It is more preferable that the numerical range of conditional expression (3) be the numerical range of the following conditional expression (3a).

[0030] n / m≧4.0 (3a) It is further preferable that the numerical range of conditional expression (3) be the numerical range of the following conditional expression (3b).

[0031] n / m≧10.0 (3b) It is preferable that the light source device 10 of this embodiment satisfies the following conditional expression (4).

[0032] u / (d×sinθ)≦0.50 (4) Here, d (mm) is the thickness of the light guide plate 12 (the distance between the reflecting means and the separating means). u (mm) is the width of the smallest region among the regions with different characteristics of the first dielectric film 12a in the xz cross section. In this embodiment, the width u is infinitely close to 0. θ is the angle of incidence of the chief ray incident on the first dielectric film 12a.

[0033] If the upper limit value is exceeded, the difference in transmittance becomes large, and the transmittance changes significantly when the position of the light beam incident near the boundary of the area deviates slightly from the design value, which is undesirable as it significantly reduces the uniformity of the light beam illuminating the irradiated surface.

[0034] It is more preferable that the numerical range of conditional expression (4) be the numerical range of the following conditional expression (4a).

[0035] u / (d×sinθ)≦0.25 (4a) It is further preferable that the numerical range of conditional expression (4) be the numerical range of the following conditional expression (4b).

[0036] u / (d×sinθ)≦0.10 (4b) When the transmittance of the second dielectric film 12b for light incident at an angle θ (°) is T(θ) (%), it is preferable that the following conditional formula (5) be satisfied.

[0037] 0≦T(θ)≦20 (5) If the upper limit is exceeded, the light utilization efficiency of the light beam propagating through the light guide plate 12 decreases, which is undesirable.

[0038] It is more preferable that the numerical range of conditional expression (5) be the numerical range of the following conditional expression (5a).

[0039] 0≦T(θ)≦15 (5a) It is further preferable that the numerical range of conditional expression (5) be the numerical range of the following conditional expression (5b).

[0040] 0≦T(θ)≦10 (5b) When the transmittance of the second dielectric film 12b for light incident at an angle of 0° is T(0) (%), it is preferable that the following conditional expression (6) be satisfied.

[0041] 80≦T(0)≦100 (6) If the value falls below the lower limit, the amount of ON light reflected by the digital mirror device 43 and guided to the projection lens 34 decreases, which is undesirable because it reduces the light utilization efficiency.

[0042] It is more preferable that the numerical range of conditional expression (6) be the numerical range of the following conditional expression (6a).

[0043] 90≦T(0)≦100 (6a) It is further preferable that the numerical range of conditional expression (6) be the numerical range of the following conditional expression (6b).

[0044] 95≦T(0)≦100 (6b) When the refractive index within the light guide plate 12 is n, the incident angle θ1 (°) of light incident on the first dielectric film 12a preferably satisfies the following conditional expression (7).

[0045] 10≦θ1≦Arcsin(1 / n) (7) If the value falls below the lower limit, it is undesirable because it becomes difficult to design a dielectric film that satisfies conditional expressions (3) and (4).If the value exceeds the upper limit, the angle of incidence of light incident on the first dielectric film 12a becomes larger than the critical angle, the light beam inside the light guide plate 12 is totally reflected by the light guide plate 12, and the split light beams cannot be extracted, which is undesirable.

[0046] It is more preferable that the numerical range of conditional expression (7) be the numerical range of the following conditional expression (7a).

[0047] 15≦θ1≦Arcsin(1 / n) (7a) It is further preferable that the numerical range of conditional expression (7) be the numerical range of the following conditional expression (7b).

[0048] 15≦θ1≦40 (7b) In order to design a dielectric film that satisfies conditional expressions (3) and (4), it is preferable to satisfy the following conditional expression (6), where the central wavelength of at least one spectrum of the light beam from the light source 11 is R (nm) and the half-width of the spectrum is W (nm).

[0049] 0.00 <W / R<0.03 (8) In this embodiment, the central wavelength R is 450 nm, 520 nm, or 635 nm, which are the main wavelengths of the laser light source. If the upper limit is exceeded, it becomes difficult to design a dielectric film that controls transmission and reflection depending on the angle as in conditional expressions (3) and (4) over a wide wavelength range, and this is not preferable because it reduces the light utilization efficiency.

[0050] It is more preferable that the numerical range of conditional expression (8) be the numerical range of the following conditional expression (8a).

[0051] 0.00 <W / R<0.02 (8a) It is further preferable that the numerical range of conditional expression (8) be the numerical range of the following conditional expression (8b).

[0052] 0.00 <W / R<0.15 (8b) It is necessary to increase the angle of the light beam propagating in the +x direction in order to thin the light guide plate 12. According to Snell's law, the smaller the refractive index is, the larger the angle of incidence on the first dielectric film 12a is with respect to the angle θa. Therefore, it is preferable that the refractive index n of the light guide plate 12 satisfies the following conditional expression (7).

[0053] 1.00≦n≦1.80 (9) It is more preferable that the numerical range of conditional expression (9) be the numerical range of the following conditional expression (9a).

[0054] 1.00≦n≦1.70 (9a) It is further preferable that the numerical range of conditional expression (9) be the numerical range of the following conditional expression (9b).

[0055] 1.00≦n≦1.60 (9b) EXAMPLES

[0056] 5 is a configuration diagram of a light source device 50 of this embodiment. The light source device 50 has a light source 51, a first optical member 52, and a second optical member 53. The first optical member 52 and the second optical member 53 form a light guide plate.

[0057] The first optical member 52 is a reflecting means and includes a first dielectric film 52a having an optical effect similar to that of the second dielectric film 12b in Example 1, and a second dielectric film 52b which is an anti-reflection film. The second optical member 53 includes a third dielectric film 53a which is a separating means, a fourth dielectric film 53b which is a reflecting film, and a fifth dielectric film 53c which is an anti-reflection film.

[0058] A light beam from a light source 51 enters a light guide plate composed of a first optical member 52 and a second optical member 53, and is divided and emitted from the light guide plate in the same principle as in Example 1. In this example, the incident angle θ of the light in the light guide plate is 34.0°, and the emission angle θa of the light emitted from the light guide plate is 34.0°. EXAMPLES

[0059] 6 is a configuration diagram of the image display device of this embodiment. The image display device has a light source device 60 equipped with a light source 61 and a light guide plate 62, a phase plate 63, a reflective liquid crystal panel 64 as an image display element, a polarizing plate 65, and a projection lens 66.

[0060] The light guide plate 62 includes a first diffraction element 62a and a second diffraction element 62b. The second diffraction element 62b has a characteristic that the transmittance increases continuously along the +x direction, and is different from the dielectric film of the first embodiment in that the transmitted light is deflected by diffraction. A light beam of a predetermined polarization from the light source 61 is deflected by the first diffraction element 62a, propagates in the +x direction in the light guide plate 62 by total reflection, and is split into a plurality of deflected light beams by the second diffraction element 62b and emitted. The light beam emitted from the light guide plate 62 illuminates the reflective liquid crystal panel 64 via the phase plate 63. The light (ON light) whose polarization is modulated by the reflective liquid crystal panel 64 passes through the polarizing plate 65, and the light (OFF light) that is not modulated is absorbed by the polarizing plate 65.

[0061] The second diffraction element 62b may be composed of minute regions and have a characteristic of increasing the transmittance stepwise along the +x direction. In this embodiment, the incident angle θ of the light in the light guide plate 62 is 50.0°, and the exit angle θa of the light exiting the light guide plate 62 is 0.0°. Also, a hologram element, a metasurface, or the like may be used instead of the diffraction element. EXAMPLES

[0062] FIG. 7 is a configuration diagram of the image display device of this embodiment. The image display device includes a light source device 70 including a light source 71 and a light guide plate 72, a first polarizing plate 73, a transmissive liquid crystal panel 74 as an image display element, a second polarizing plate 75, and a projection lens 76. The light guide plate 72 includes a first diffraction element 72a and a second diffraction element 72b. A light beam of a predetermined polarized light from the light source 71 is deflected by the first diffraction element 72a, propagates in the +x direction in the light guide plate 72 by total reflection, and is split into a plurality of light beams deflected by the second diffraction element 72b and emitted. The light beam emitted from the light guide plate 72 illuminates a transmissive liquid crystal panel 74 via the first polarizing plate 73. The light (ON light) whose polarization has been modulated by the transmissive liquid crystal panel 74 passes through the second polarizing plate 75, and the light (OFF light) that has not been modulated is absorbed by the second polarizing plate 75. EXAMPLES

[0063] 8 is a configuration diagram of a light source device 80 of this embodiment. The light source device 80 has a light source 81 and a light guide plate 82. The light guide plate 82 has a first dielectric film 82a which is a separating means, a second dielectric film 82b which is a reflecting means, and a third dielectric film 82c which is an anti-reflection film.

[0064] 9(a) and 9(b) respectively show the transmittance and film thickness ratio of the first dielectric film 82a for light of a predetermined wavelength. In FIG. 9(b), the film thickness at the center is normalized to 1. The first dielectric film 82a is a gradient film having a characteristic that the reflectance is about 100% at position E and the transmittance is about 100% at position F. The first dielectric film 82a is configured so that the film thickness increases along the +x direction, but may be configured so that the film thickness decreases along the +x direction. The first dielectric film 82a may be configured to have a film thickness shown in FIG. 10. EXAMPLES

[0065] 11 is a configuration diagram of a light source device of this embodiment. The light source device has a light source 101, a first light guide 102, a first deflection means 103, a second light guide plate 104, and a second deflection means 105.

[0066] The first light guide plate 102 includes a first dielectric film 102a as a separation means, a second dielectric film 102b as a reflection means, a third dielectric film 102c as a reflection film, and a fourth dielectric film 102d as an anti-reflection film. The second light guide plate 104 includes a fifth dielectric film 104a as a separation means, a sixth dielectric film 104b as a reflection means, and a seventh dielectric film 104c as an anti-reflection film. The light beam L101 from the light source 101 is deflected by the first deflection means 103 and enters the second light guide plate 104. The light beam L101 that enters the second light guide plate 104 is split by the second light guide plate 104, deflected by the second deflection means 105, and emitted as light beam L102 (L102a, L102b, L102c, L102d). The light beam L102 enters the first light guide plate 102, and is emitted as a light beam L103, which is used as a light beam for illuminating an image display element (not shown) or the like.

[0067] The disclosure of this embodiment includes the following configuration. (Configuration 1) a light guide plate that propagates a light beam from the light source in a specific direction; the light guide plate includes a separation means for dividing a light beam from the light source into a plurality of light beams and emitting the plurality of light beams from the light guide plate; A light source device characterized in that the separation means is configured so that transmittance for a predetermined wavelength contained in the light beam from the light source increases along the specific direction. (Configuration 2) 2. The light source device according to claim 1, wherein the transmittance increases continuously or stepwise along the specific direction. (Configuration 3) 3. The light source device according to configuration 1 or 2, wherein the predetermined wavelength is a central wavelength of a light beam from the light source, or a wavelength at which the intensity is strongest. (Configuration 4) When the number of the regions with different transmittance of the separation means is n and the number of the plurality of light beams is m, n / m≧2.0 4. The light source device according to any one of configurations 1 to 3, wherein the following condition is satisfied: (Configuration 5) When the thickness of the light guide plate is d, the width of the smallest region among the regions of the separation means with different transmittance is u, and the angle of incidence of the chief ray incident on the separation means is θ, u / (d×sinθ)≦0.50 5. The light source device according to any one of configurations 1 to 4, wherein the following condition is satisfied: (Configuration 6) the isolating means is a dielectric film, 6. The light source device according to any one of configurations 1 to 5, wherein an incident angle of the light beam from the light source incident on the separation means is smaller than a critical angle. (Configuration 7) the light guide plate is provided opposite the separation means and includes a reflection means for reflecting a light beam from the light source; When the transmittance of the reflecting means with respect to the light beam from the light source incident on the reflecting means at an incident angle θ(°) is T(θ), 0≦T(θ)≦20 7. The light source device according to any one of configurations 1 to 6, wherein the following condition is satisfied: (Configuration 8) The light guide plate is provided so as to face the separation means, and includes a reflection means for reflecting the light beam from the light source. When the transmittance of the reflection means with respect to the light beam from the light source incident at an incident angle of 0 (°) on the reflection means is T(0), 80 ≦ T(0) ≦ 100 The light source device according to any one of Configurations 1 to 7, characterized by satisfying the conditional expression. (Configuration 9) When the central wavelength of at least one spectrum of the light beam from the light source is R and the half-value width of the spectrum is W, 0.00 < W / R < 0.03 The light source device according to any one of Configurations 1 to 8, characterized by satisfying the conditional expression. (Configuration 10) The separation means is a dielectric inclined film configured such that the transmittance increases along the specific direction, and the light source device according to any one of Configurations 1 to 9. (Configuration 11) The separation means is configured such that the transmittance at the first position is 25% and the transmittance at the second position different from the first position in the specific direction is 75%, and the light source device according to Configuration 10. (Configuration 12) When the transmittance at the third position intermediate between the first position and the second position in the specific direction is Tx, 30 ≦ Tx ≦ 70 The light source device according to Configuration 11, characterized by satisfying the conditional expression. (Configuration 13) When the film thickness at the first position of the inclined film is U(x1), the film thickness at the second position different from the first position in the specific direction is U(x2), and the film thickness at the third position intermediate between the first position and the second position in the specific direction is U(x3), U(x1) < U(x3) < U(x2) or U(x2) < U(x3) < U(x1) 13. The light source device according to any one of configurations 10 to 12, wherein the following condition is satisfied: (Configuration 14) the light guide plate is provided opposite the separation means and includes a reflection means for reflecting a light beam from the light source; 14. The light source device according to any one of configurations 1 to 13, wherein the separating means reflects a part of the light beam from the light source and transmits the other part. (Configuration 15) A light source device according to any one of configurations 1 to 14; and an image display element illuminated by the light beam emitted from the light guide plate.

[0068] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications and changes are possible within the scope of the gist of the present invention. [Explanation of symbols]

[0069] 11 Light source 12 Light guide plate 12a First dielectric film (separation means) 100 Light source device

Claims

1. Light source and It has a light guide plate that propagates the light beam from the light source in a specific direction, The light guide plate includes a separation means for dividing the light beam from the light source into a plurality of light beams and emitting the plurality of light beams from the light guide plate. The separation means is configured such that the transmittance for a predetermined wavelength included in the light beam from the light source increases along the specific direction, When the number of regions with different transmittances in the separation means is n, and the number of the plurality of luminous beams is m, n / m ≥ 2.0 A light source device characterized by satisfying the following conditional expression.

2. The light source device according to claim 1, characterized in that the transmittance increases continuously or stepwise along the specific direction.

3. The light source device according to claim 1 or 2, characterized in that the predetermined wavelength is the central wavelength of the light beam from the light source, or the wavelength at which the intensity is strongest.

4. When the thickness of the light guide plate is d, the width of the smallest region among the regions of the separation means with different transmittances is u, and the incident angle of the principal light rays incident on the separation means is θ, u / (d×sinθ)≦0.50 The light source device according to claim 1 or 2, characterized in that it satisfies the following conditional expression.

5. The separation means is a dielectric film, The light source device according to claim 1 or 2, characterized in that the angle of incidence of the light beam from the light source incident on the separation means is smaller than the critical angle.

6. The light guide plate is provided opposite the separating means and includes a reflecting means for reflecting the light beam from the light source. When T(θ) is the transmittance of the reflecting means with respect to the light beam from the light source incident on the reflecting means at an incident angle θ(°), 0 ≤ T(θ) ≤ 20 The light source device according to claim 1 or 2, characterized in that it satisfies the following conditional expression.

7. The light guide plate is provided opposite the separating means and includes a reflecting means for reflecting the light beam from the light source. When the transmittance of the reflecting means with respect to the light beam from the light source incident on the reflecting means at an incident angle of 0 (°) is T (0), 80 ≤ T(0) ≤ 100 The light source device according to claim 1 or 2, characterized in that it satisfies the following conditional expression.

8. When R is the central wavelength of at least one spectrum of the luminous beam from the light source, and W is the full width at half maximum of the spectrum, 0.00<W / R<0.03 The light source device according to claim 1 or 2, characterized in that it satisfies the following conditional expression.

9. The light source device according to claim 1 or 2, characterized in that the separation means is a gradient film of dielectric material configured to increase in transmittance along the specific direction.

10. The light source device according to claim 9, characterized in that the separation means is configured such that the transmittance at the first position is 25%, and the transmittance at the second position, which is different from the first position in the specific direction, is 75%.

11. When the transmittance at a third position midway between the first and second positions in the aforementioned specific direction is Tx, 30 ≤ Tx ≤ 70 The light source device according to claim 10, characterized in that it satisfies the following condition.

12. When the film thickness at a first position of the gradient film is U(x1), the film thickness at a second position different from the first position in the specific direction is U(x2), and the film thickness at a third position intermediate between the first and second positions in the specific direction is U(x3), U(x1)<U(x3)<U(x2) or U(x2)<U(x3)<U(x1) The light source device according to claim 9, characterized in that it satisfies the following conditional expression.

13. The light guide plate is provided opposite the separating means and includes a reflecting means for reflecting the light beam from the light source. The light source device according to claim 1 or 2, characterized in that the separation means reflects a portion of the light beam from the light source and transmits the other portion.

14. A light source device according to claim 1 or 2, An image display device characterized by having an image display element that is illuminated by a light beam emitted from the light guide plate.

Images