Light source apparatus and image display apparatus

Abstract

The invention relates to a light source apparatus and an image display apparatus. The light source apparatus includes a light source and a light guide plate configured to propagate a light beam from the light source in a specific direction. The light guide plate includes a beam splitter configured to split a light beam from the light source into a plurality of light beams and emit the plurality of light beams from the light guide plate. The beam splitter is configured such that a transmittance for a predetermined wavelength included in a light beam from the light source increases along the specific direction. A predetermined inequality is satisfied.

Description

Technical Field

[0001] One aspect of the embodiment relates to a light source apparatus configured to uniformly illuminate an image display element or the like with a light beam from a light source, and an image display apparatus having the light source apparatus. Background Art

[0002] Conventionally, a configuration has been disclosed that uses a diffraction element to propagate a light beam from a light source by total reflection within a light guide plate, splits the light beam into multiple light beams, and illuminates an image display element (see U.S. Patent Application Publication No. 2020 / 0292840).

[0003] However, the diffraction angle of the diffraction element varies according to the wavelength, so in order to uniformly illuminate the image display element with light beams of multiple wavelengths, multiple light guide plates are required. In addition, the mass production rate of the diffraction element is low because its performance varies significantly due to slight structural changes. Summary of the invention

[0004] The light source device includes a light source and a light guide plate, the light guide plate being configured to propagate a light beam from the light source in a specific direction. The light guide plate includes a beam splitter, the beam splitter being configured to split the light beam from the light source into a plurality of light beams and emit the plurality of light beams from the light guide plate. The beam splitter is configured so that the transmittance for a predetermined wavelength included in the light beam from the light source increases along the specific direction. The following inequality is satisfied:

[0005] 2.0≤n / m

[0006] Where n is the number of regions of the beam splitter with different transmittance, and m is the number of beams.

[0007] Further features of various embodiments of the present disclosure will become apparent from the following description of the embodiments with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 This is a diagram showing the structure of the light source device according to Example 1.

[0009] Figure 2 This is a diagram showing the composition of the light source according to Example 1.

[0010] Figure 3A and Figure 3B The graph illustrates the transmittance and film thickness ratio of the first dielectric film according to Example 1 with respect to light of a predetermined wavelength.

[0011] Figure 4 This is a diagram showing the structure of an image display device according to Example 1.

[0012] Figure 5This is a diagram showing the structure of the light source device according to Example 2.

[0013] Figure 6 This is a diagram showing the configuration of an image display device according to Example 3.

[0014] Figure 7 This is a diagram showing the structure of an image display device according to Example 4.

[0015] Figure 8 This is a diagram showing the structure of the light source device according to Example 5.

[0016] Fig. 9A and Fig. 9B The graph illustrates the transmittance and film thickness ratio of the first dielectric film according to Example 5 with respect to light of a predetermined wavelength.

[0017] Fig.10 Another example of the film thickness ratio of the first dielectric film according to Example 5 is illustrated.

[0018] Fig.11 This is a diagram showing the structure of the light source device according to Example 6. DETAILED DESCRIPTION

[0019] Now, with reference to the accompanying drawings, embodiments according to the present disclosure will be described in detail. Corresponding elements in various figures are denoted by the same reference numerals, and repeated descriptions thereof will be omitted.

[0020] Example 1

[0021] Figure 1 1 is a diagram showing a configuration of a light source device 10 according to this example. The light source device 10 includes a light source 11 and a light guide plate 12, and can be applied to an image display device.

[0022] The light source 11 emits collimated light obtained by collimating light from a laser light source with a collimating lens. The light source 11 may emit collimated light as a combination of laser light of two or more colors. The light source 11 may emit collimated light obtained by collimating light from a light source such as an LED and a mercury lamp. This example assumes collimated light as a combination of laser beams having wavelengths of 450 nm, 520 nm, and 635 nm.

[0023] Since the light from the laser light source is emitted at a predetermined angle distribution, the collimated light generally has an illumination distribution with high central illumination and low peripheral illumination. In order to improve the illumination uniformity of the irradiated light, the collimated light emitted from the light source 11 may have a uniform illumination distribution.

[0024] Figure 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 converts the outgoing light having a predetermined angle distribution from the laser light source 21 into a deflected outgoing light having a uniform angle distribution, and the second deflection element 23 collimates the deflected outgoing light. The deflection element is an optical element such as a metasurface, a diffraction element, or an aspheric collimating lens, and may have a configuration in which the first deflection element 22 and the second deflection element 23 are arranged on both sides of a single element. Since collimated light generally has a circular or elliptical distribution, the illumination distribution of the collimated light may be shaped into a rectangular distribution using a deflection element.

[0025] The light guide plate 12 includes a first dielectric film (beam splitter, separator, or divider) 12 a , a second dielectric film 12 b (reflector), a third dielectric film 12 c , and a fourth dielectric film 12 d .

[0026] The first dielectric film 12a has a property of reflecting a part of the light beam from the light source 11 and transmitting another part. Thus, the first dielectric film 12a has a property of splitting (separating or dividing) the light beam from the light source 11 (light having a predetermined wavelength in the light guide plate 12) into a plurality of light beams and emitting the plurality of light beams from the light guide plate 12. The first dielectric film 12a is configured so that the transmittance for a predetermined wavelength included in the light beam from the light source 11 increases along the +x direction (specific direction) which is the direction in which the light beam from the light source 11 propagates within the light guide plate 12. The predetermined wavelength is the central wavelength of the light beam from the light source 11 or the wavelength with the strongest intensity.

[0027] In this example, 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 the first position x1 of the first dielectric film 12a is 25%, and the transmittance Tx(x2) at the second position x2 different from the first position x1 in the +x direction is 75%. The transmittance Tx(x3) at the third position x3 (=(x2+x1) / 2) which is the middle of the first position x1 and the second position x2 in the +x direction can satisfy the following inequality (1).

[0028] 30 ≤ Tx(x3) ≤ 70 (1)

[0029] The following inequality (2a) or (2b) can be satisfied:

[0030] U(x1) <U(x3)<U(x2)(2a)

[0031] U(x2) <U(x3)<U(x1)(2b)

[0032] Wherein U(x1), U(x2), and U(x3) are the film thicknesses of the first dielectric film 12a at the first position x1, the second position x2, and the third position x3, respectively.

[0033] The thickness of the first dielectric film 12a may continuously increase or decrease along the +x direction. In the case where the film thickness is a gradient film in which the film thickness continuously changes, the dielectric film may be deposited in a single deposition process, so that the film may be easily manufactured.

[0034] Figure 3A and Figure 3B The transmittance and the film thickness ratio of the first dielectric film 12a for light having a predetermined wavelength are illustrated respectively. In this example, the predetermined wavelength is 520nm. Wavelengths of 450nm and 635nm have similar characteristics. Figure 3B , the film thickness at the center is normalized to 1. The first dielectric film 12a may include a minute region so that the transmittance changes stepwise.

[0035] In this example, the refractive index n of the light guide plate 12 is 1.52, the incident angle θ of light in the light guide plate 12 is 21.6°, and the exit angle θa of light emitted from the light guide plate 12 is 34.0°. Instead of the first dielectric film 12a, a diffraction element, a hologram element, a metasurface, etc. may be used.

[0036] The second dielectric film 12b is arranged to face the first dielectric film 12a, and has a characteristic of reflecting light incident near a predetermined angle. In this example, 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 can be used as the third dielectric film 12c. The fourth dielectric film 12d is an anti-reflection film.

[0037] The light beam L11 from the light source 11 enters the light guide plate 12, propagates in the +x direction via the second dielectric film 12b and the third dielectric film 12c, enters the first dielectric film 12a, and is split into the light beam L12a (about 25% of L11) and the 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 split into the light beam L12b (about 25% of L11) and the 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 split into the light beam L12c (about 25% of L11) and the 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 irradiating an image display element or the like not shown.

[0038] Figure 4 4 is a block diagram of an image display device according to this embodiment. The image display device includes a light source device 10, a digital mirror device 43 and a projection lens 44.

[0039] The digital mirror device 43 is an image display element whose pixels include tiny mirrors and generates an image by temporally tilting each tiny mirror. In this example, the tiny mirrors have a deflection angle of 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 irradiates the digital mirror device 43 at an incident angle of 34.0°. The ON light reflected by the digital mirror device 43 is emitted as a light beam L43 (L43a, L43b, L43c, L43d), and the light beam L43 is transmitted through the first dielectric film 12a and the second dielectric film 12b at an incident angle of 0°, and irradiates the irradiated surface via the projection lens 44.

[0040] An example configuration according to this example will now be described.

[0041] The diffusion plate may be disposed between the digital mirror device 43 and the light guide plate 12 or between the projection lens 44 and the light guide plate 12 to diffuse the light beam L43. Thus, high-resolution performance may be obtained according to the F number of the projection lens 44.

[0042] The following inequality (3) can be satisfied:

[0043] 2.0 ≤ n / m (3)

[0044] wherein n is the number of regions of the first dielectric film 12a having different transmittances, and m is the number of splits (separations or divisions) of light beams (the number of light beams generated by splitting the light beam from the light source 11 by the first dielectric film 12a).

[0045] In this example, the number of regions n is ∞, and the number of split beams m is 4. In the case where the value becomes lower than the lower limit of inequality (3), the transmittance step difference increases, and if the incident beam position near the region boundary deviates slightly from the design value, the transmittance changes significantly, so the uniformity of the beam irradiating the irradiated surface is significantly reduced.

[0046] Inequality (3) can be replaced by the following inequality (3a):

[0047] 4.0≤n / m(3a)

[0048] Inequality (3) can be replaced by the following inequality (3b):

[0049] 10.0≤n / m(3b)

[0050] The following inequality (4) can be satisfied:

[0051] u / (d×sinθ) ≤ 0.50 (4)

[0052] Wherein d (mm) is the thickness of the light guide plate 12 (the distance between the reflector and the beam splitter), u (mm) is the width of the smallest area among the areas with different characteristics of the first dielectric film 12a in the xz cross section (although the width u is extremely close to 0 in this case), and θ is the incident angle of the main light entering the first dielectric film 12a.

[0053] When the value becomes higher than the upper limit of inequality (4), the transmittance step difference increases, and if the incident beam position near the region boundary deviates slightly from the design value, the transmittance changes significantly, so the uniformity of the beam irradiating the illuminated surface is significantly reduced.

[0054] Inequality (4) can be replaced by the following inequality (4a):

[0055] u / (d×sinθ)≤0.25(4a)

[0056] Inequality (4) can be replaced by the following inequality (4b):

[0057] u / (d×sinθ)≤0.10(4b)

[0058] The following inequality (5) can be satisfied:

[0059] 0 ≤ T (θ) ≤ 20 (5)

[0060] Here, T(θ)(%) is the transmittance of the second dielectric film 12 b with respect to light incident at an angle θ(°).

[0061] In the case where the value becomes higher than the upper limit of the inequality (5), the light utilization efficiency of the light beam propagating through the light guide plate 12 decreases.

[0062] Inequality (5) can be replaced by the following inequality (5a):

[0063] 0≤T(θ)≤15(5a)

[0064] Inequality (5) can be replaced by the following inequality (5b):

[0065] 0≤T(θ)≤10(5b)

[0066] The following inequality (6) can be satisfied:

[0067] 80 ≤ T (0) ≤ 100 (6)

[0068] Here, T(0) (%) is the transmittance of the second dielectric film 12b with respect to light incident at an angle of 0°.

[0069] In the case where the value becomes lower than the lower limit of the inequality (6), the amount of ON light reflected by the digital mirror device 43 and guided to the projection lens 44 decreases, so that the light utilization efficiency decreases.

[0070] Inequality (6) can be replaced by the following inequality (6a):

[0071] 90≤T(0)≤100(6a)

[0072] Inequality (6) can be replaced by the following inequality (6b):

[0073] 95≤T(0)≤100(6b)

[0074] The following inequality (7) can be satisfied:

[0075] 10 ≤ θ1 ≤ Arcsin(1 / n) (7)

[0076] Wherein n is the refractive index within the light guide plate 12, and θ1 (°) is the incident angle of light incident on the first dielectric film 12a.

[0077] When the value becomes lower than the lower limit of inequality (7), it becomes difficult to design a dielectric film that satisfies inequalities (3) and (4). When the value becomes higher than the upper limit of inequality (7), the incident angle of light entering the first dielectric film 12a becomes larger than the critical angle, and the light beam in the light guide plate 12 is totally reflected by the light guide plate 12, so that the split light beam cannot be extracted.

[0078] Inequality (7) can be replaced by the following inequality (7a):

[0079] 15≤θ1≤Arcsin(1 / n)(7a)

[0080] Inequality (7) can be replaced by the following inequality (7b):

[0081] 15≤θ1≤40(7b)

[0082] In order to design a dielectric film that satisfies inequalities (3) and (4), the following inequality (8) can be satisfied:

[0083] 0.00 < W / R < 0.03 (8)

[0084] Wherein R (nm) is the central wavelength of at least one spectrum of the light beam from the light source 11, and W (nm) is the half maximum full width of the spectrum.

[0085] In this example, the central wavelength R is 450 nm, 520 nm, and 635 nm, which are the main wavelengths of the laser light source. When the value becomes higher than the upper limit of inequality (8), it becomes difficult to design a dielectric film that controls transmission and reflection in a wide wavelength range depending on the angle as shown in inequalities (3) and (4), thereby reducing light utilization efficiency.

[0086] Inequality (8) can be replaced by the following inequality (8a):

[0087] 0.00 <W / R<0.02(8a)

[0088] Inequality (8) can be replaced by the following inequality (8b):

[0089] 0.00 <W / R<0.15(8b)

[0090] In order to reduce the thickness of the light guide plate 12, the angle of the light beam propagating in the +x direction should be increased. According to Snell's law, the smaller the refractive index relative to the angle θa, the larger the incident angle on the first dielectric film 12a. Therefore, the following inequality (9) can be satisfied:

[0091] 1.00 ≤ n ≤ 1.80 (9)

[0092] Here, n is the refractive index of the light guide plate 12 .

[0093] Inequality (9) can be replaced by the following inequality (9a):

[0094] 1.00≤n≤1.70(9a)

[0095] Inequality (9) can be replaced by the following inequality (9b):

[0096] 1.00≤n≤1.60(9b)

[0097] Example 2

[0098] Figure 5 2 is a diagram showing the structure of a light source device 50 according to this example. The light source device 50 includes 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 constitute a light guide plate.

[0099] The first optical member 52 is a reflector and includes a first dielectric film 52a having the same optical effect as the second dielectric film 12b according to Example 1, and a second dielectric film 52b as an antireflection film. The second optical member 53 includes a third dielectric film 53a as a beam splitter, a fourth dielectric film 53b as a reflective film, and a fifth dielectric film 53c as an antireflection film.

[0100] The light beam from the light source 51 enters the light guide plate including the first optical member 52 and the second optical member 53, is split according to the same principle as in Example 1, and is emitted from the light guide plate. In this example, the incident angle θ of the light on the light guide plate is 34.0°, and the exit angle θa of the light emitted from the light guide plate is 34.0°.

[0101] Example 3

[0102] Figure 6 6, a phase plate (wave plate) 63, a reflective liquid crystal panel 64 as an image display element, a polarizing plate 65, and a projection lens 66. The light source device 60 includes a light source 61 and a light guide plate 62.

[0103] 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 according to Example 1 in that the transmitted light is deflected by diffraction. A predetermined polarized light beam 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, is deflected and split into a plurality of light beams by the second diffraction element 62b, and is emitted. The light beam emitted from the light guide plate 62 irradiates 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 is transmitted through the polarizing plate 65, and the light (OFF light) whose polarization is not modulated is absorbed by the polarizing plate 65.

[0104] The second diffraction element 62b may include a micro region and has a characteristic of increasing the transmittance in a stepwise manner along the +x direction. In this example, the incident angle θ of the light in the light guide plate 62 is 50.0°, and the exit angle θa of the light emitted from the light guide plate 62 is 0.0°. Instead of the diffraction element, a holographic element, a metasurface, etc. may be used.

[0105] Example 4

[0106] Figure 77 is a diagram of the structure of the image display device according to this example. The image display device includes a light source device 70, 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 source device 70 includes a light source 71 and a light guide plate 72. The light guide plate 72 includes a first diffraction element 72a and a second diffraction element 72b. The predetermined polarized light beam from the light source 71 is deflected by the first diffraction element 72a, propagates in the +x direction by total reflection in the light guide plate 72, is deflected and split into a plurality of light beams by the second diffraction element 72b, and is emitted. The light beam emitted from the light guide plate 72 irradiates the transmissive liquid crystal panel 74 via the first polarizing plate 73. The light (ON light) whose polarization is modulated by the transmissive liquid crystal panel 74 is transmitted through the second polarizing plate 75, and the unmodulated light (OFF light) is absorbed by the second polarizing plate 75.

[0107] Example 5

[0108] Figure 8 8 is a diagram showing a configuration of a light source device 80 according to this example. The light source device 80 includes a light source 81 and a light guide plate 82. The light guide plate 82 includes a first dielectric film 82a as a beam splitter, a second dielectric film 82b as a reflector, and a third dielectric film 82c as an antireflection film.

[0109] Fig. 9A and Fig. 9B The transmittance and the film thickness ratio of the first dielectric film 82a for light of a predetermined wavelength are respectively illustrated. Fig. 9B , the film thickness at the center is normalized to 1. The first dielectric film 82a is a gradient film having a characteristic that the reflectivity at position E is about 100% and the transmittance at position F is about 100%. The first dielectric film 82a is configured so that the thickness increases along the +x direction, but the thickness may decrease along the +x direction. In addition, the first dielectric film 82a may be configured to have Fig.10 The film thickness is shown in the diagram.

[0110] Example 6

[0111] Fig.11 1 is a diagram showing the structure of a light source device according to this example. The light source device includes a light source 101 , a first light guide plate 102 , a first deflector 103 , a second light guide plate 104 and a second deflector 105 .

[0112] The first light guide plate 102 includes a first dielectric film 102a as a beam splitter, a second dielectric film 102b as a reflector, a third dielectric film 102c as a reflective film, and a fourth dielectric film 102d as an anti-reflective film. The second light guide plate 104 includes a fifth dielectric film 104a as a beam splitter, a sixth dielectric film 104b as a reflector, and a seventh dielectric film 104c as an anti-reflective film. The light beam L101 from the light source 101 is deflected by the first deflector 103 and enters the second light guide plate 104. The light beam L101 incident on the second light guide plate 104 is split by the second light guide plate 104, deflected by the second deflector 105, and emitted as a light beam L102 (L102a, L102b, L102c, L102d). The light beam L102 enters the first light guide plate 102, exits as a light beam L103, and serves as a light beam for illuminating an image display element or the like not shown.

[0113] Although the disclosure describes example embodiments, it is to be understood that some embodiments are not limited to the disclosed embodiments.The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

[0114] Each example can provide a light source device having a reduced size and capable of illuminating an image display element efficiently and uniformly.

Claims

1. A light source device, comprising: A light source; And A light guide plate configured to propagate a light beam from the light source in a specific direction, Characterized in that the light guide plate includes a beam splitter configured to split the light beam from the light source into a plurality of light beams and emit the plurality of light beams from the light guide plate, Wherein the beam splitter is configured such that the transmittance for a predetermined wavelength included in the light beam from the light source increases along the specific direction, and Where the following inequality is satisfied: 2.0 ≤ n / m Where n is the number of regions of the beam splitter having different transmittances, and m is the number of light beams.

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, characterized in that: The predetermined wavelength is the central wavelength or the wavelength with the highest intensity of the light beam from the light source.

4. The light source device according to claim 1, characterized in that: The following inequality is satisfied: u / (d×sinθ) ≤ 0.50 Where d is the thickness of the light guide plate, u is the width of the smallest region among the regions of the beam splitter having different transmittances, and θ is the incident angle of the principal ray incident on the beam splitter.

5. The light source device according to claim 1, characterized in that: The beam splitter includes a dielectric film, and the incident angle of the light beam from the light source entering the beam splitter is less than the critical angle.

6. The light source device according to claim 1, characterized in that: The light guide plate is arranged facing the beam splitter and includes a reflector configured to reflect the light beam from the light source, Where the following inequality is satisfied: 0 ≤ T(θ) ≤ 20 Where T(θ) is the transmittance of the reflector for the light beam from the light source entering the reflector at an incident angle θ (°).

7. The light source device according to claim 1, characterized in that: The light guide plate is arranged facing the beam splitter and includes a reflector configured to reflect the light beam from the light source, Where the following inequality is satisfied: 80≤T(0)≤100 Where T(0) is the transmittance of the reflector for the light beam from the light source entering the reflector at an incident angle of 0 (°).

8. The light source device according to claim 1, characterized in that: The following inequality is satisfied: 0.00 < W / R < 0.03 Where R is the central wavelength of at least one spectrum of the light beam from the light source, and W is the full width at half maximum of the spectrum.

9. The light source device according to claim 1, characterized in that: The beam splitter is a dielectric film configured such that the transmittance increases along the specific direction, Where the thickness of the dielectric film varies along the specific direction.

10. The light source device according to claim 9, characterized in that: The beam splitter includes a dielectric gradient film having a transmittance of 25% at a first position and a transmittance of 75% at a second position different from the first position in the specific direction.

11. The light source device according to claim 10, characterized in that: The following inequality is satisfied: 30 ≤ Tx ≤ 70 Where Tx is the transmittance of the beam splitter at a third position that is the middle of the first position and the second position in the specific direction.

12. The light source device according to claim 9, characterized in that: The following inequality is satisfied: U(x1) < U(x3) < U(x2) or U(x2) < U(x3) < U(x1) Where U(x1) is the thickness of the dielectric gradient film at the first position, U(x2) is the film thickness at a second position different from the first position in the specific direction, and U(x3) is the film thickness at a third position that is the middle of the first position and the second position in the specific direction.

13. The light source device according to any one of claims 1 to 12, characterized in that: The light guide plate is disposed to face the beam splitter and includes a reflector configured to reflect the light beam from the light source, The beam splitter reflects a portion of the light beam from the light source and transmits another portion of the light beam.

14. An image display device, comprising: The light source device according to any one of claims 1 to 13; as well as An image display element illuminated by the light source device.

Images